Ratiometric fluorescence sensing of metal-organic frameworks: Tactics and perspectives

Coordination Chemistry Reviews 404 (2020) 213113

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Review

Ratiometric fluorescence sensing of metal-organic frameworks: Tactics and perspectives Li Chen a, Donghao Liu a, Jun Peng b, Qiuzheng Du a,⇑, Hua He a,c,d,* a

Department of Analytical Chemistry, China Pharmaceutical University, Nanjing 211198, China The Key Laboratory for Medical Tissue Engineering, College of Medical Engineering, Jining Medical University, Jining 272067, China c Key Laboratory of Drug Quality Control and Pharmacovigilance, Ministry of Education, China Pharmaceutical University, Nanjing 211198, China d Key Laboratory of Biomedical Functional Materials, China Pharmaceutical University, Nanjing 211198, China b

a r t i c l e

i n f o

Article history: Received 22 August 2019 Accepted 31 October 2019

Keywords: Metal-organic frameworks Dual-emission Ratiometric fluorescence sensor Design tactics

a b s t r a c t Metal-organic frameworks (MOFs) are an important class of inorganic-organic hybrid crystals with applications in various fields. In last ten years, MOFs-based fluorescence sensing has gained much attention. MOFs can exhibit luminescence by metal nodes, ligands and the inserted or absorbed guests, which offer an excellent fluorescence response in analyzing. However, MOFs-based monochromatic fluorescence probes are limited by concentration, the effect of ambient and excitation light intensity, resulting in low detection accuracy. To overcome this defect, MOFs-based ratiometric fluorescence (RF) sensors have been proposed and rapidly developed. This review focuses on the design tactics of MOFs-based RF sensing and describes the detection mechanism of different RF sensors. Based on different strategies of synthesis, the MOFs-based RF sensors are categorized into three classes: MOFs’ intrinsic dual-emission, singleemissive MOFs with a chromophore and non-emissive MOFs with two chromophores. In each categorization, the design approaches and relative merits were discussed separately. Finally, the applications of MOFs-based RF sensors are summarized and prospected. Ó 2019 Elsevier B.V. All rights reserved.

Contents 1. 2.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Luminescence mechanism of MOFs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Luminescence mechanism of MOFs based composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abbreviations: MOFs, Metal-organic frameworks; RF, ratiometric fluorescence; S0, ground states; S1, first excited singlet state; S2, second excited singlet state; T1, first three-line state; LMCT, ligand-to-metal charge transfer; MLCT, metal-to-ligand charge transfer; MC, Metal-centered; Ln-MOFs, lanthanide MOFs; HMOFs, heterometalorganic frameworks; 5-bop, 5-boronoisophthalic acid; H2OBA, 4,40 -oxybis(benzoate) acid; LOD, limit of detection; LC, Ligand centered; LLCT, ligand-to-ligand charge transfer; ILCT, intra-ligand charge transfer; PL, Photoluminescence; LMOFs, luminescent MOFs; bpy, 2,20 -bipyridine; H2BDC-NH2, 2-aminoterephthalic acid; ATZ, 5-amino-1-Htetrazolate; BTB, 1,3,5-tris (4-carboxyphenyl)-benzene; DET, Dexter energy transfer; FRET, fluorescence resonance energy transfer; tpt, 2,4,6-tri(4-pyridyl)-1,3,5-triazine; H2TZB, 4-(1H-tetrazol-5yl)benzoic acid; DMF, N,N-dimethylformamide; Rh6G, rhodamine 6G; TNP, 2,4,6-trinitrophenol; H4-BODSDC, benzophenone-3,3-disulfonyl-4,4dicarboxylic acid; AnC, 9-anthracenecarboxylic acid; HPTS, 8-hydroxy-1,3,6-pyrenetrisulfonicacid trisodium salt; hfa, hexafluoro acetylacetonato; BPDC, 2,20 -bipyridine-5,50 dicarboxylate; FA, formaldehyde; PAP, p-aminophenol; DA, dopamine; DBA, 3,5-dicarboxybenzeneboronic acid; H3BTC, 1,3,5-benzenetricarboxylate; H2DHT, 2,5dihydroxyterephthalic acid; ESIPT, excited-state intramolecular proton-transfer; SA, salicylaldehyde; HDBB, (4,40 -(hydrazine-1,2-diylidene bis (methanylylidene)) bis (3-hydroxybenzoic acid)); R-BF-CQDs, red fluorescent carbon quantum dots; ACQ, aggregation-caused quenching; SG7, 8-hydroxypyrene-1,3,6-trisulfonate; FS, fluorescein; TCA, trichloroacetic acid; TC, Tetracycline; DMASM, 4-[p-(dimethylamine)styryl]-1-methylpyridinium; NPs, nanoparticles; QDS, quantum dots; CDs, carbon dots; AuNPs, gold nanoparticles; AgNCs, silver nanoclusters; BSA, bovine serum albumin; CTAB, cetyltrimethylammonium bromide; BSA-AuNPs, BSA-capped AuNPs; DPA, 2,6pyridinedicarboxylic acid; AMP, adenosine 50 -monophosphate; AgNCs, silver nanoclusters; CS, core-shell; PVP, polyvinylpyrrolidone; 6-MP, 6-mercaptopurine; CQDs, carbon quantum dots; GQDs, graphene quantum dots; GO, graphene oxide sheets; BTEX, benzene homologues; FLQY, fluorescence quantum yield; TDA, diaminotoluene; MNPs, Fe3O4 magnetic nanoparticles; MSNs, mesoporous silica nanoparticles; FITC, fluorescein isothiocyanate; AF, 5-aminofluorescein; H2BPDA, biphenyl-3,5-dicarboxylic acid; Acf, acriflavine; PAHs, Polycyclic Aromatic Hydrocarbons; NMOFs, nanoscale MOFs; H4EDDA, tetracarboxylate acid; MIPs, molecularly imprinted polymers. 1-hydrox ypyrene@Co/Tb-dipicolinic acid (1-OHP@Co/Tb-DPA MOF); Sr, relative sensitivity. ⇑ Corresponding authors at: Department of Analytical Chemistry, China Pharmaceutical University, Nanjing 211198, China (H. He). E-mail addresses: [email protected] (Q. Du), [email protected] (H. He). https://doi.org/10.1016/j.ccr.2019.213113 0010-8545/Ó 2019 Elsevier B.V. All rights reserved.

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2.3. Detecting mechanism of MOFs-based RF sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 MOFs’ intrinsic dual-emission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1. Bimetallic-based MOFs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2. Ligands-based MOFs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.3. Target analyst induced ratio fluorescence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Single-emissive MOFs with fluorescent monomers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.1. Dyes@MOFs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.2. Nanoparticles@MOFs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.2.1. Noble metal NPs@MOFs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.2.2. QDS@MOFs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.2.3. CDs@MOFs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Non-emissive MOFs with encapsulated chromophores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 6.1. Temperature sensing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 6.2. Ions sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 6.3. Biomarkers sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 6.4. pH sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 6.5. Other sening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Conclusion and outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Declaration of Competing Interest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

1. Introduction Metal-organic frameworks (MOFs) are crystal hybrids assembled from inorganic metal ions and suitable organic ligands (Fig. 1). The transition metal ions with an unfilled d orbital are often selected as the metal center to accept the lone pair of electrons of the ligands [1]. The ligand contains at least one multidentate functional group such as the carboxyl group for multicoordinating with metal ions. Different metal ions and plenty of organic ligands through coordination bonds could create multidimensional network frame materials with multi-functional properties [2], such as rich spatial structure, light, electricity and magnetic properties. These characteristics allow MOFs to be applicable in adsorption [3] and separations [4], catalysis [5], sensing [6], nonlinear optics and light-harvesting [7]. Particularly, as fluorescent sensing material, the luminescent MOFs (LMOFs) have gained much attention due to their adjustability and diversity for sensing [8,9]. In the last ten years, fluorescence-based sensors characterized with various merits (e.g. high sensitivity, simple operation and short response time) have received more and more attention in monitoring [10,11]. Moreover, there are numerous reports focus on MOFs-based fluorescence sensor particularly in indirect fluorescence detection because MOFs possess clear merits as follows: i) MOFs are easily synthesized through one-pot methods [12]; ii) MOFs can enhance the sensitivity of detection with high surface areas; iii) MOFs can achieve specific recognition with exceptional selectivity through specific functional sites [13,14]; iv) MOFs

display excellent recyclability with flexible porosity [15]. Most importantly, the nonfluorescent substance can be detected by adding a second or a third substance to have indirect fluorescent properties [16], thus it greatly expands the types of analytes. However, during fluorescence intensity measurement, the effects of concentration, environment and excitation light intensity result in low accuracy of detection for the MOFs-based monochromatic fluorescence sensors. To ameliorate this drawback, another fluorescence signal is introduced to construct a MOFs-based ratiometric fluorescence (RF) sensor. The emission intensities at two wavelengths is independent of the above interfering factors, thus, the RF sensors can eliminate these shortcomings of single fluorescence sensing by self-calibration of dual-emission and achieve accurate detection [17]. For example, Zhang [18] reported a MOFs-based RF sensor applied in sensing H2S. It is the ratio signal that helps to exclude the interference, resulting in a lower limit of detection (LOD, 5.45 lM), which is comparable to some other formerly MOFs-based fluorescent sensors for H2S. Accordingly, MOFsbased sensors show greater selectivity and sensitivity by contrast with fluorescent sensors without the amplifying effect of MOFs, and the dual-emission sensors produce a more accurate result as compared with MOFs-based single signal. Because the intensity of the dual-emission can be used as an internal standard and exhibiting self-reference characteristics, thus effectively avoiding interference from environmental factors. For the above advantages, MOFs-based RF sensing has achieved rapid development in recent years. Hence, there are some featured review articles on the pro-

Fig. 1. Scheme for the preparation of a MOF, different metals are mixed with linkers.

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Fig. 2. The basic photophysical processes; S: singlet, T: triplet states; intersystem crossing is a nonradiative process and accompanied by a forbidden change in the spin state [26].

up-to-date information and insights into the fundamental aspects of MOFs-based RF sensing.

2. Mechanism

Fig. 3. Manifestations of probable emission modes in MOFs. Metal nodes, green spheres; Organic linkers, yellow cylinders; Guest in MOFs, red sphere.

gress and achievements of RF sensing [19–23]. However, rarely have comprehensive reviews are about MOFs-based RF sensing [24]. According to the development process of MOFs-based RF sensing, we focus on the detection mechanism and the design strategies (Fig. 13) and their applications in the last ten years (Fig. 27). Finally, the prospects and optimization of MOFs-based RF sensors are discussed and prospected through comparative analysis of various design ideas. This review intends to provide

Luminescence is defined as the ‘‘spontaneous emission of radiation from an electronically or vibrationally excited species” [25]. Principal mechanism of molecular luminescence is the absorption of a photon to raise an electron from the ground state (S0) to an excited state. The excited state includes the first excited singlet state (S1) and second excited singlet state (S2), both of which are unstable states. The fluorescence originates from electron return from the S1 or S2 to S0. Moreover, the first singlet state could turn into the first three-line state (T1) through the intersystem crossing, which is a non-radiative transition process resulting from electron spin reversal, and phosphorescence is produced by the electron return from T1 to S0 (Fig. 2). However, as the mechanism of the MOFs-based RF sensing in this review, three questions need to be answered: i) How do MOFs emit fluorescence; ii) How could MOFs-based composites with fluorescence; iii) How is a ratio fluorescence sensor constructed for target detection.

Fig. 4. Mechanism of LMCT and LMCT.

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Fig. 5. Antenna effect for lanthanide luminescence [26].

Fig. 6. Schematic diagram of Eu-MOF 1 with the antenna effect. [‘‘a”: absorption; ‘‘f” : fluorescence; ‘‘p”: phosphorescence; ‘‘l”: luminescence. ISC: intersystem crossing; ET: energy transfer; S: singlet; and T: triplet.] [32].

2.1. Luminescence mechanism of MOFs MOFs allow for sensible choice of metal ions and suitable ligands of various functionalities. They are easy to introduce fluorescent functions through metal ions, ligands or guest molecules due to the covalent bonding between ligands and metals. Simultaneously, ligand-metal intermetallic charge transfer increases its fluorescence function. Thus, MOFs provide an ideal platform for the progress of solid luminescent materials [27]. There are diverse emitting mechanisms for tunable dual-emission MOFs, including metal-centered (MC) emission (e.g. ligand-to-metal charge transfer (LMCT)), ligands-centered (LC) emission (e.g. metal-to-ligand charge transfer (MLCT)), guests introduced emission and so on [28,29] (Fig. 3). LMCT and MLCT are mainly associated with relative height of the lowest excited state energy levels in MOFs. If the energy of the lowest excited state level of the organic ligand is lower than that of the metal ions, then the charge will transfer from the metal ions to the organic ligands to emit light, i.e. the process of LMCT. Conversely, the charge will transfer from the ligands to the metal ions, i.e. the process of MLCT (Fig. 4). MC is often found in lanthanide MOFs (Ln-MOFs) or transition lanthanide heterometal-organic frameworks (HMOFs). Whether in Ln-MOFs or HMOFs, the luminescence of lanthanide ions needed to be sensitized by the organic ligands owing to the Laporte forbidden f-f transitions [30]. Ligands with free carboxyl groups can coordinate with lanthanide ions, resulting in the energy transfer from the ligand to the lanthanide ions, and this is vividly named as ‘‘antenna effect” [31] (Fig. 5). In fact, the essence of the above ‘‘antenna effect” is the LMCT, e.g. an Eu-MOF [32] is composed of Eu (III) and ligand 5-boronoisophthalic acid (5-bop), in which the emission of Eu3+ is sensitized by the ligand 5-bop through the LMCT, also called the ‘‘antenna effect” (Fig. 6). The organic ligand 4,4’-oxybis (benzoate) acid (H2OBA) is an exceptional antenna ligand to Tb3+ and Eu3+ ions. In a Ln-MOF formed in H2OBA and mixed lanthanide

metal ions (Eu3+ and Tb3+) [33], the emission of H2OBA is well matched with the excitation energy of Eu3+ and Tb3+, leading to high energy transfer from the OBA2 to the lanthanide ions and forming the dual-emission peaks for the both Eu3+ and Tb3+. The sensitized lanthanide metal emits its characteristic peak through the energy transfer. The typical emission peaks at 590, 614, 650 and 701 nm are attributed to the 5D0 ? 7FJ (J = 1–4) transitions of Eu3+ and the peaks of 488, 545, 587 and 619 nm are attributed to the 5D4 ? 7FJ (J = 6–3) transitions of Tb3+ [34]. LC emission is based on the emission of the ligands used in the assembly of MOFs, mostly relying on the charge transfer, i.e. MLCT, LLCT and the intra-ligand charge transfer (ILCT). Firstly, MLCT is an excited state generally occurring in complexes [35] with oxidizable d6, d8 and d10 electronic configurations and p-receptor ligands [26]. Absorption of visible light by these complexes creates a single excited state 1MLCT that can efficiently transit to a triplet state 3MLCT through intersystem crossing [36]. The fluorescence emission appeared after the electron return from 1MLCT to ground states (S0), while phosphorescence emission emerged after the electron return from 3MLCT state to S0. The MLCT luminescence of MOFs is the process of energy transfer from metal ions to ligands after the metal ions illuminated by light, resulting in the metal excited states changing into the ligand excited states, and then return to S0 to emit the fluorescence. The stronger the reducibility of metal ions, the stronger the oxidizability of the ligands, and the more likely MLCT occurs. Ru2+ and its derivatives are known to the prototypical MLCT complex, and these compounds usually take the form of heterometallic MOFs. For example, [Ru(bpy)3](PF6)2 (bpy = 2,20 -bipyridine) shows two MLCT emissions at 434 nm and 471 nm [37]. Secondly, the p-electrons in an organic ligand with an aromatic moiety or an extended p-system have significantly contributions in luminescence, which can be classified as LLCT and LC or ILCT [38]. For the former, LLCT mainly derived from MOFs constructed with different ligands. Two Zn-MOFs (Ⅰ and II) based on mixed-ligands [39] were synthesized at room temperature. Photoluminescence (PL) measurements of Ⅰ and II showed ligandbased emissions owing to LLCT (p* ? n) transitions. For the latter, LC or ILCT often occurs when MOFs contains only one ligand, e.g. upon excitation at 355 nm, H2BDC-NH2 (2-aminoterephthalic acid) displays an emission peak at 566 nm owing to the ligand-based p* to p transitions [40]. In the MOF Eu3+@UiO-66-(COOH)2, the ratio fluorescence was based on the LC emission and Eu3+ emission [18] (Fig. 7). However, in most cases, LLCT and ILCT appeared in a system. Zhang [27] designed a Zn-MOF containing two ligands, 5-amino-1-H-tetrazolate (ATZ) and 1,3,5-tris(4-carboxyphenyl)-b enzene (BTB), both of them are classic p conjugated organic luminophores. As a small multidentate co-ligand, ATZ can bring the luminophores close together, enabling electronic interactions (e.g. the cascade p-p* interactions) and causing the LLCT and ILCT (Fig. 8). Actually, the luminescent properties of MOFs are not only controlled by the metal clusters or ligands, it can also be adjusted by guest molecules and the interactions among them [41].

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Fig. 7. Schematic diagram of fluorescence detection mechanism [18].

Fig. 8. The Dexter energy transfer (DET) mechanism in a dual-emissive system [27].

2.2. Luminescence mechanism of MOFs based composites

Fig. 9. Scheme of FRET, the spectral overlap (shadow part) of the donor emission profile (yellow line) and the absorption spectrum of an acceptor (green line).

MOFs can be integrated with different molecules as to form a variety of composites. Among them, the luminescent composites are formed by encapsulating or absorbing chromophores such as dyes, quantum dots and luminescent nanomaterials into or on the surface of MOFs. The luminescence of MOFs composites can be divided into two aspects: mutual independence and mutual influence. In first case, the fluorescence of each of the MOF and its encapsulated materials does not interfere with each other. The fluorescence intensity is unchanged after the formation of the composite. In the second case, the luminescence mechanism of MOFs-based composites is mainly the fluorescence resonance energy transfer (FRET) among encapsulants and MOFs. When the emission band of the donor overlaps with absorption band of the acceptor, the excitation of the donor can induce fluorescence of the acceptor while the fluorescence intensity of the donor is attenuated, then the FRET occurs (Fig. 9). The FRET between MOFs and guests can be regulated through tuning the guests’ species or their concentrations [42]. Most importantly, the energy donor must be close enough to the energy receptor, so as to enhance the probability of energy transfer.

In Chen’s research [43], MOF was served as a crystalline container to encapsulate the dye rhodamine 6G (Rh6G). The obtained dyes@MOFs composite features a weak ligand emission and a strong Rh6G emission, indicating the presence of an efficient FRET form MOF to dye [44,45]. Without limitation of dyes, quantum dots (QDs) were used to harvest photons. The photon-generated excitons in the QDs are then transferred to the MOFs through FRET, in order to enhance light harvesting. For instance, CdSe as the fluorescence donor was bound to the surface of F-MOF [46] formed the CdSe@F-MOF composite, which was able to harvest photons through FRET. Across the experimental data, a high quantum efficiency of up to 84% through energy transfer was realized by tuning the size of the QDs. In fact, the intensity of the MOFs-based composites can be tuned by the characteristics of the chromophores for increasing the spectral overlap between the donor emission and MOF absorption. For non-emissive MOFs, the luminescence mechanism of MOFs composites can be independent of MOFs, but relying on the illuminating mechanism of the illuminator itself. The two emissions are coming from two luminescent monomers in

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MOFs. Similarly, the two luminescent monomers can be mutual independence and mutual influence. Although the luminescence mechanism is not affected by MOFs, the sensing ability of the two illuminants enclosed in the MOFs to be measured is much stronger than the simple superposition outside the MOFs. This is because the adsorption of MOFs facilitates the concentration and aggregation of the analyte, thereby increasing the detection signal. 2.3. Detecting mechanism of MOFs-based RF sensors

Fig. 10. Fluorescence spectra of MOF-QD in the presence of different concentrations of 6-MP (from 0 to 60 lM) [60].

Fig. 11. Fluorescence spectra of the CDs@Eu-MOFs upon the addition of Cr (VI) at different concentration [59].

To date, there are mainly three fluorescence detection sorts: fluorescence enhancement (‘‘turn-on”) [47,48], fluorescence quenching (‘‘turn-off”) [49,50] and RF detection [51,52]. The luminescent sensing method of ‘‘turn-on” detection is based on a new emission peak evolving from a previously dark background [53-55]. Conversely, ‘‘turn-off” is based on luminescence quenching resulting from the interaction between the analyte and the fluorophore, causing the energy transfer from the fluorophore to analyte. However, both of ‘‘turn-on” and ‘‘turn-off” detection are affected by the sensors’ concentration, the environmental conditions and divergence in optical components between instruments [56]. By contrast, RF sensors can break the above limitations and provide accurate detection through self-calibration with two emissive bands [57,58]. From the representation of present experimental results, the RF detection mechanism can be summarized as follows: 1) two emissions with ‘‘turn-on” and ‘‘turn-off”, one emission increased while another decreased (Fig. 10); 2) two emissions with ‘‘turn-on” or ‘‘turn-off”, one emission changed (increased or decreased) while another kept intensity (Fig. 11) [59]; 3) the same change of the two emissions, both increased or decreased in varying degrees (Fig. 12) [42]. In case of ‘‘turn-on” and ‘‘turn-off”, Zhang [61] developed a temperature-dependent probe Tb0.93Eu0.07BODSDC (H4-BODSDC = benzophenone-3,3’-disulfonyl-4,4’-dicarboxylic acid) showing an increasing Eu (III) emission and a decreasing Tb (III) emission as temperature increases. In case of ‘‘turn-on” or ‘‘turn-off”, EuPS@AnC/ZIF-8 [62] was developed as a RF sensor to detect 1O2. The emission of 9-anthracenecarboxylic acid (AnC) served as a response signal while the emission of Eu3+ was a reference signal for providing self-calibration to avoid environmental effects. In case of the same change of the two emissions at different degrees, a Zn-based MOF [42] was combined with dye 8-hydroxy-1,3,6-pyr enetrisulfonicacid trisodium salt (HPTS) forming a RF sensor for the detection of 2,4,6-trinitrophenol (TNP). The emission intensities of both Zn-MOF and HPTS decreased with increasing TNP, and the emission intensities of HPTS (reduced to 57% of the initial intensity) is quenched more intense than the Zn-based MOF emission (decreases to 42%). With the above diverse combinations of fluorescence intensity change, many RF sensors are developed for all kinds of applications. According to previous work, the tactics of ratio sensing caused by dual-emission MOFs could be summarized as the following parts: 1) Synthesis of self-illuminating MOFs based on MC and LC or introducing a specific target to bridge the two emissions. 2) Combine single-emissive MOFs with a chromophore such as QDs and dyes. 3) Encapsulating two chromophores into the frameworks of non-emissive MOFs (Fig. 13). 3. MOFs’ intrinsic dual-emission

Fig. 12. Fluorescence spectra of Eu-MOF upon exposure to different concentrations of F [42].

MOFs with intrinsic dual-emission are mainly synthesized by three routes, one is using mixed lanthanide metal ions to form double emitting, namely, the bimetallic MOFs. The other is a combination of two luminescent ligands and for the last, the target analyst can also be the key to emitting dual fluorescence, it can work as a bridge, causing the energy transfer between the metal center

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Fig. 13. MOFs-based ratiometric fluorescence probes synthesized by different design schemes. MC: metal-center emission, LC: ligand-centered emission.

Fig. 14. Energy transfer processes of the Eu3+ and Tb3+ coordination polymer (EnT: energy transfer, BEnT: energy back transfer, Em: emission) [70].

and ligands. In some cases, the RF sensors can also be composed of a single lanthanide and luminescent ligand [63–65]. 3.1. Bimetallic-based MOFs Bimetallic MOFs are typically based on lanthanide metal ions such as Ln-MOFs or HMOFs. They can generate strong PL emission arising from f-f or f-d energy transfer when exposed to UV light, and the PL emission can be adjusted by appropriate adjacent chromophores [66]. Eu3+ and Tb3+ are widely applicated among various lanthanide ions because of the large stokes shift and relative long lifetimes [67,68]. The emission wave lengths of the mixed LnMOFs can be tuned by adjusting the Eu3+/Tb3+ ratios. In Chen’s research [33], the results show that the ratio fluorescence can occur when the content of Eu reaches the range of 5% to 30% in the two lanthanide metal elements. Besides, the emission of Eu3+ in mixed Ln-MOFs can be sensitized by Tb3+ [69]. In another Tbbased MOF [70], the Tb3+ was sensitized by the ligand, and Eu3+ was then sensitized by the Tb3+ (Fig. 14). Thus, bimetallic LnMOFs with dual-emission upon one excitation can construct a RF sensor with cheap and easy-to-use material [71]. Ln-MOFs have been served as colorimetric RF sensors for application in sensing temperature, small organic molecules (e.g. formaldehyde) and toxic cationic or anionic pollutants [72]. Significant examples for RF sensing with bimetallic-based MOFs are luminescence ther-

mometers [70,73] (see details in 6.1). For the HMOFs, it contains mixed metal ions that can link with each other through the organic ligand, intervention on one of the metal ions could impact another metal ion, so as to adjust the properties of the whole HMOFs. The introduction of heterometals can both expand the structural diversity and enhance catalytic, luminescent or other properties of MOFs [74,75]. For example, a HMOF (Eu/Pt-MOFs) based on ligand of 2,20 -bipyridine-5,50 -dicarboxylate (H2BPDC) have been fabricated as a RF sensor towards carbonate ions. The ligand H2BPDC produced a broad LC emission and the emission of Eu3+, making the straight, quick and reliable detection of carbonate ions for real application possible [76]. Unfortunately, since chemical and physical characteristic which stem from d and f electrons are totally disparate, it is harder to synthesize HMOFs than homometallic MOFs. Hence, Ln-MOFs are more popular than HMOFs in the field of MOFs-based RF detection. The lanthanide metals are often used as the center node whether in Ln-MOFs or HMOFs. Besides, lanthanide metals can also be used for modification and mixing with other non-lanthanide metals. For instance, a Ag (I)-Eu (III) modified MOF [77] was employed as a RF sensor for recognizing formaldehyde (FA). Although the emission of Eu3+ and organic ligands are the two centers, the fluorescence properties are ruled by the coordinated Ag+ on account of its ability to change the electronic structure and energy transfer process. It deserves to be mentioned that the application in biology, specifically in metabolite determination, the lanthanide functionalized MOFs have made considerable research progress [78,79]. In Qin’s group, a sensor based on Tb3+ functionalized MOF [80] shows the strong emission of Tb3+ was utilized for paminophenol (PAP) sensing. Being a luminescent sensor, it can quickly track down the aniline metabolite PAP in less than five minutes, and the MOF can be recycled simply by washing with deionized water. For this reason, the MOFs-based sensors are often employed as a portable and economical material. As it shown in the above examples, the bimetallic MOFs-based RF detection is widely applicated. However, the intrinsic dual-emissive MOFs with mixed or functionalized lanthanide metal ions are rarer than MOFs simultaneously incorporate different ligands. This might be attributed to Kasha’s rule, which allow only the lowest excited state to emit [81]. In the mixed ligand MOFs, the spectral properties of

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Fig. 15. Schematic diagram of the synthetic process of the Eu-MOF detection system [89].

the two ligands are quite different to provide the energy resolution of two emissions, non-radiative relaxation customarily occurs from the higher energy chromophore to the lower one, which is consistent with Kasha’s rule [37]. Therefore, it is a highly desired target to search MOFs that have a tunable functional organic ligand to achieve dual-emission [82–84]. 3.2. Ligands-based MOFs Organic ligands in MOFs are often used to link metal ions or metal clusters to form stable and porous frameworks. The designability and tunability of MOFs are precisely come from these organic ligands [85–87], the luminescence of MOFs can be easily

regulated by functionalizing the ligands. Common modifications of nonfluorescent ligands to produce fluorescence are hydroxylation, carboxylation and amination, e.g., a luminescent hydroxyl functionalized MOF [88] was synthesized for sensing Fe3+. The hydroxyl functional group can offer its lone pair of electrons and lead to the electron transfer with Fe3+, resulting in fluorescence quenching of LC emission while enhancement of a new emission, which allows RF sensing of Fe3+. Additionally, there are also specific modifications for specific recognition. In our group’s work [89], a boric acid-modified Eu-MOF was synthesized for specific recognition of dopamine (DA), which exhibited dual-emission from the 3,5-dicarboxybenzeneboronic acid (DBA) and Eu3+ (Fig. 15). The boric acid group served as a specific receptor of DA could bound

Fig. 16. a, b) Calculated and experimentally observed dual emissions of Zn-MOF taken in water (a) and DMF (b). c) Pictorial representation of the proton transfer occurs from the enol form of the Zn-MOF that exhibits ESIPT phenomena [92].

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Fig. 17. Two typical tautomeric forms of the linker and its two-fluorescence state in MOF [93].

to DA through covalent effect, leading to an enhanced ligand emission with a weakened Eu3+ emission and further realizing the detection of DA. For the ligand-based luminescence MOFs, a tunable functional organic ligand can achieve specific recognition. Generally, MOFs are constructed with only one kind of ligand, but this does not affect the fabrication of RF probes because a ligand can simultaneously excite two emissions with the antenna effect. Such as 1,3,5benzenetricarboxylate (H3BTC) can efficiently sensitize the Tb3+ and Eu3+ ions at evaluated temperature, causing a dual-emission (545 nm and 614 nm) with one excitation, which was utilized for the synthesis of the thermostable and thermosensitive mixed LnMOF Eu0.37Tb0.63-BTC [90]. In fact, this cannot be classified as the ligand-based MOFs because the dual-emission was from Tb3+ and Eu3+ rather than the H3BTC. In ligand-based MOFs, the single ligand can emit two fluorescent bands such as 2,5-dihydroxyterephthalic acid (H2DHT). As an excited-state intramolecular proton-transfer (ESIPT) chromophore in protic solvent, H2DHT often shows dualemission from both the initial excited form (a keto or enol) and the proton-transferred tautomer [91]. This feature is also preserved in the MOF, Biswajit [92] reported that a Zn-MOF based on ligand H2DHT has the ability to exhibit dual-emission in water (Fig. 16). Moreover, Zhang and co-workers [93] constructed a fluorescent ligand by combining benzothiadiazole (BTD) as a fluorophore and tautomeric QD as a response site, which can exhibit a RF response for sensing amine in two tautomeric form (Fig. 17). The single ligand based dual-emission is the simplest way to construct MOFs-based RF sensor. However, it is difficult to meet the demand simply by revision of a single ligand, and the reports about it are rare. The introduction of mixed ligands in MOFs provides more possibilities, and the sensor is more designable. Compared to single ligand, MOFs with mixed-ligands have achieved a new level of rational design and construction, including the synergetic coordination of different ligands with metals [94]. The mixed-ligands system containing two or more organic bridging ligands has been widely adopted to generate new Co2+/ Cu2+ MOFs [95,96], e.g., Wang [97] synthesized a series of novel MOF (AHU-TW) by employing fluorescent mixed ligands of Vshape dicarboxylate ligands and 2,6-di(1H-imidazol-1-yl)pyridine to detect TNP with the single fluorescence response. As for the RF sensing by mixed-ligands based MOFs, the polycarboxylate ligands and the neutral N-donor organic ligands are the most efficient collocation to construct those MOFs. For example, the ligand mixture ATZ and BTB based MOF ZnATZ-BTB [27] was used to monitor cryogenic temperatures (30–130 K). The dual-emission is from the Dexter energy transfer (DET) process between mixed organic lumiphores, an emission around 510 nm is dependent on the cryogenic

temperatures. Although the RF sensor provides a new insight into measuring cryogenic temperature, the researches based on mixedligands MOFs are limited by the species of the multidentate ligands and the special targets that can simultaneously excite two ligands or promote the generation of energy transfer between the mixedligands. In a word, the ligand-based MOFs can select different ligands for different analytes to achieve good selectivity. Generally, the two ligands in MOFs should have structural similarities, and the geometry, functional side groups, acid strength and rigidity of the linkers need to be considered [98]. However, ligands with similar structures often produce close emissions, thus the ligands demand a special design to achieve ratio detection, but it might not yet be predictable considering the current state of research, there is still much room for improvement. This is why the mixed-ligands MOFs sounds reasonable but are not common. In order to foster strengths and avoid weaknesses, a more ingenious method of achieving RF sensing by guest induced fluorescence has been developed, which retains better selectivity while being easier to implement.

3.3. Target analyst induced ratio fluorescence The selective binding of analytes can activate an intense emission of the originally low-emitting or non-emitting MOFs, namely the guest induced emissions. To further improve selectivity, an analyte-dependent RF sensing method is developed in which the analyte can be a switch that turns on dual-emission. A lot of examples can exemplify this conclusion, a novel fluorescent sensor UiO66-NH2-SA [40] (SA = salicylaldehyde) for detection of Al3+ was shaped. Al3+ can coordinate with the nitrogen and oxygen atoms. It is proposed that upon increasing the concentration of Al3+, there are more Al3+ ions coordinated with the ligand in UiO-66-NH2-SA, resulting in the different effects on the energy transfer from the ligand to Al3+. At last, a new LMCT creates another emission in UiO-66-NH2-SA-Al3+. Besides, Lin [99] synthesized a RF sensor for the determination of Zn2+. The distinction is that upon the addition of Zn2+, some carboxylic groups on the surface of Tb-HDBB-CPNs were binding to Zn2+, facilitating the formation Zn-Tb-HDBBCPNs with dual-emission (Fig. 18). What’s more, a blue zirconium MOF [100] with red fluorescent carbon quantum dots (R-BF-CQDs) was developed for detecting Cu2+ (Fig. 19). The target analyte Cu2+ can react with the carboxyl group of the MOF and the amino group of the carbon quantum dot, causing the energy transfer from the MOF to the carbon quantum dot. In the above three cases, the metal cation both reacts with the carboxylate group, resulting in FRET to produce a second fluorescence. Such an ingenious way to

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Fig. 18. (A) Fluorescence emission spectra of 0.035 mg mL1 Tb-HDBB-CPNs in the absence (curve a) and presence of 0.15 mM Zn2+ (curve b). (B) Schematic representation of the cation exchange process of Tb-HDBB-CPNs with Zn2+ [99].

Fig. 19. Scheme of the complexation of UiO-66-(COOH)2 and R-BF-CQDs with Cu2+ as the bridging unit [100].

Fig. 20. The design tactic of dyes@MOFs composite. To overcome the ACQ effect, two methods were offered: one is that dissolving the molecules in an appropriate solvent could induce emission in pyrene; another is encapsulating the molecule to diminish the aggregation of pyrene [42].

construct the RF sensor can be developed as a specific ion detection, such as Al (III), Cu (II) and Zn (II). In a word, the above three routes provide a luminous MOF, but it is difficult to obtain MOFs with high fluorescence quantum yield (FLQY) through the utilization of the intrinsic emission of MOFs or the generated fluorescence from the weak metal-ligand charge

transfer in MOFs [101]. Therefore, it is required to introduce other fluorophores with high luminescence quantum yield such as organic dyes and quantum dots into MOFs [102]. This is an important alterative way to synthesize ideal LMOFs for chemical sensing with a higher sensitivity. Besides, if fluorophores species of wider emission wavelengths can be encapsulated into the MOFs to form

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fluorophores@MOFs composite, then the range of the detection substance can be expanded [6,103–105]. 4. Single-emissive MOFs with fluorescent monomers As a class of porous materials, MOFs provide a special platform to stabilize functional species, causing the specific behavior within the defined pores. Actually, through the leading of quantities of fluorophores (e.g. QDs and fluorescent dyes) into their pores, various sorts of MOFs-based composites have been brought about as novel functional materials for optical devices and gas storage [106–110]. 4.1. Dyes@MOFs Dyes are diffusely applied as colorants, photographic sensitizers, markers and fluorescent sensors [6,111], but dyes has been faced with the problem of aggregation-caused quenching (ACQ). The chromophores of dyes showed high FLQYs in dilute solutions but nonfluorescent in the colloidal or solid state [112,113]. Pyrene, as a synthetic raw material for dyes is prone to the ACQ effect [114]. Such as 8-hydroxypyrene-1,3,6-trisulfonate (SG7), the derivative of pyrene, was nonfluorescent in solid state. Apart from this, the fluorescent dye Rh6G molecule also has no emission in the solid state owing to the aggregation effect. Fortunately, MOFs have been explored to emit fluorescence or phosphorescence by integrating emissive modules into the frameworks, which can overcome the ACQ effect of the luminescent material in a solid state (Fig. 20). Zhang’s group have successfully synthesized a water stable MOF FIR-53 [115] to realize dichromate trapping. SG7@FIR-53 showed the outstanding exciter emission of SG7 ions owing to the spatial confinement and partition effect [116]. It precisely demonstrated that immobilization of organic dyes into the pores of MOFs can reduce ACQ. The incorporation of dye allows the composite exhibits the emission of both ligand and dye to form a dual-emission sensor [41,43]. Hence, plenty of pioneering work has reported the dyes@MOFs based RF sensors for temperature sensing [58] and probing small molecules. In Zhao’s work [117], the dye (fluorescent brightener KS-N) doped in UiO-66 was utilized as a reference for probing Tetracycline (TC). The new point is that as a reference signal, it grafted the lanthanide Eu3+ on the surface of UiO-66 as a reaction signal, achieving the detection limit of 17.9 nM. Moreover, the dye-

Fig. 21. Schematic diagram of dual-emitting ZJU-88  perylene composite (EnT: energy transfer, Em: emission) [58].

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based fluorescence was often increased [118] or decreased [119] due to the FRET between the dyes and MOFs. Zhao [44] constructed a dual-emissive composite DMASM@ZJU-21, which was used as a ratiometric thermometric sensor with a tunable temperature range from 20 to 80 °C. In this composite, 4-[p-(dimethylamine)styryl]1-methylpyridinium (DMASM) was sensitized by organic ligand. The emission intensity of the ligand from ZJU-21 significantly increased while that of the dye slightly decreased as the raising of the temperature. It can be explained by the process of energy back-transfer, where energy is transferred from DMASM to the ligand via the FRET. Another composite perylene@ZJU-88 [58] was also synthesized for temperature sensing. Similarly, the luminescence intensity of perylene decreased while the strengthen in emission of ZJU-21 with a raising temperature due to the energy transfer from perylene to ZJU-21 (Fig. 21). Both of the two instances referred FRET was from dye to MOFs, correspondingly, the energy transfer from MOFs to dye are also existed. In Wang’s research [120], when the dye fluorescein (FS) was enclosed into the Zn-based MOF, a sensor for trichloroacetic acid (TCA) was shaped. It exhibits a weak emission of MOF and a strong emission peak of TCA, which means the existence of an efficient MOF-to-dye energy-transfer process. In summary, dyes can be straightly sensitized by organic ligands through FRET [121]. The FRET between dyes and MOFs can be readily tuned by controlling the concentration of the dye [44]. However, the nonuniform distribution of the dye in MOFs brings about differences in the energy transfer between the MOFs and dyes [122]. To improve the uniformity of encapsulated materials in MOFs’ cavity, researchers focused on the size of the composites, thus it is inevitable to mention the nanomaterials.

4.2. Nanoparticles@MOFs Nanomaterial fluorescent sensors, especially based on MOFs are attracting special attention owing to their strong encapsulation capabilities, adjustable pore sizes and large specific surface area. Correspondingly, MOFs are expanded by encapsulating nanoparticles (NPs) such as noble metal NPs [123] and QDs within MOFs, forming NPs@MOFs nanocomposites [124]. Those composites have elicited great attention because they provide MOFs and certain sorts of NPs with PL properties, flexible porosity, and higher surface area [125]. As shells, MOFs could protect NPs from aggregation and enhance the chemical activity and stability [126]. Hence, NPs@MOFs are broadly applied in fields of gas storage [127], molecular separation [128], catalysis [129,130], chemical sensing [131] and drug delivery [132]. The NPs@MOFs can also work as

Fig. 22. Schematic for the construction of AgNCs/metal-organic shell composite and the mechanism for ratiometric sensing of phosphate [140].

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RF probes, the sensors of multicolor luminescent speciesfunctionalized nanoparticles such as the noble metal nanoparticles, QDS and carbon dots (CDs) have received considerable attention due to their elevated photostability, good water dispersibility and enrich and separation capacity to analyte [133,134]. 4.2.1. Noble metal NPs@MOFs In the recent decade, one of the most adopted nanomaterials in MOFs is the noble metal nanoparticles including gold nanoparticles (AuNPs) and silver nanoclusters (AgNCs). The AuNPs are regarded only as supporting materials of the core-shell composites, but with the modification of end-capper, they could emit fluorescence as other fluorophores [135]. For example, BSA-capped AuNPs (BSA = bovine serum albumin) exhibited two emissions at 405 nm and 635 nm, which could respectively respond to 2,6pyridinedicarboxylic acid (DPA) and Hg2+. Cai [136] synthesized a MOFs-based RF probe by encapsulating BSA-capped AuNPs into Tb-AMP-MOF (AMP = adenosine 50 -monophosphate) for the detection of DPA and Hg2+. DPA could deeply coordinate with Tb3+ to replace water from the Tb3+ center. The presence of DPA enhanced the emission of Tb-AMP-MOF whereas the emission of BSA-capped AuNPs at 405 nm kept constant. Besides, the emission of BSAcapped AuNPs at 635 nm was quenched with the addition of Hg2+ while the emission of Tb-AMP-MOF was maintained. Finally, the RF probe achieved a detection limit as low as 17.4 nM of DPA and 20.9 nM of Hg2+, which strongly proved the excellent merits of the combination of AuNPs and MOFs. Silver nanoclusters (AgNCs) are promising in sensing and bioimaging on account of their good optical properties [137], low toxicity, and small size [138,139]. However, they have similar irreversible aggregation phenomenon with the dyes. The high surface energy restricts their further applications [140] while shells with MOFs could ameliorate thermodynamic stability with minimized agglomeration [141-143]. In 2015, Yan [140] developed a RF sensor with the fabrication of AgNCs and metal-organic shell composite for discerning phosphate. The dual-emission originated from a strong fluorescence at 720 nm and a weak fluorescence at 510 nm due to the process of FRET. However, the fluorescence intensity at 510 nm was enhanced while at 720 nm was weakened upon the presence of phosphate (Fig. 22). Because the high affinity between phosphate and Zn2+ ion broke the original FRET, achieving the RF sensing of phosphate. In 2018 Wang’s group [144], the AgNCs wrapped in BSA were encapsulated into ZIF-8 by the protein-mediated biomineralization process for the evaluation of Cu2+ ions. Compared to the research in 2015, AgNCs-BSA have improved photostability and storage stability. Furthermore, AgNCs-BSA@ZIF-8 was coated onto the hydrophobic arraying slides with a microdot array-based fluorometric method, ensuring the high-throughput analysis of Cu2+ in some complex media, such as the recognition of Cu2+ in blood. This indicates that AgNCsBSA@ZIF-8 can be diffusely applied in fields of food safety, clinical test and environmental monitoring. Although without the emission of MOF, as a single response senor, it still inspired that the capped NPs can improve the NPs’ stability in MOFs. In general, the combination of the noble metal NPs and MOFs is a mutually beneficial method and apart from this, QDs with a highly fluorescence perform are another kind of nanomaterials that are usually combined with MOFs. Furthermore, the most common QDs in MOFs are divided into metal semiconductor QDs and carbon QDs. 4.2.2. QDS@MOFs Quantum dots (QDs) are nanoscale semiconductors, which can emit a specific frequency of light upon a certain electric field or light pressure and vary with the size of such semiconductors. In contrast of ordinary organic fluorophores, the QDs own clear merits of broad absorption spectra, high FLQY, good photostability and

long fluorescence lifetime [145-148]. Hence, QDs have gradually taken place of the ordinary fluorophores with broad applications in microarrays, fluorescence imaging, immunoassays [149]. However, the fluorescence of QDs is affected by the trapped surface states that can lead directly to QDs fluorescence quenching [150,151]. Nowadays, the core-shell structure seems to be one of the most promising to increase the FLQY [152]. MOFs can be a good shell for their porosity and stable framework. Therefore, the integration of QDs with MOFs brings new opportunities in sensing [153], photocatalysis [154] and energy [46]. Methods for preparing QDs@MOFs composites include: 1) fixing functional or nanoscale objects in a MOF, known as ‘‘ships in ships” and ‘‘bottles around ships” methods (Fig. 23 a, b); 2) photochemical deposition of semiconductor NPs onto the surface of the skeleton [152] (Fig. 23 c, d). In 2012, Lu [155] reported the incorporation of CdTe within ZIF8 to introduce PL properties in MOFs. In contrast to the nucleation of MOF crystals induced by NPs, this study employed a strategy of simultaneous synthesis and encapsulation, the NPs were continuously adsorbed onto the surface of the ZIF-8 during the growing of the ZIF-8. Additionally, an amphiphilic and non-ionic polymer polyvinylpyrrolidone (PVP) was added into ZIF-8 to stabilize various nanoparticles. Generally, the pre-synthesized nanoparticles are stabilized with certain surfactants, capping agents or even ions. In fact, all of these are used to control the spatial distribution of NPs in ZIF-8 crystals. In view of this research, another paper based on the incorporation of QDs with porphyrin-based MOFs [46] to enhance light harvesting was published in 2013. The core-shell composite was constructed of MOFs with CdSe/ZnS, showing an enhancement of light harvesting via energy transfer from the QDs to the MOFs. It was this energy transfer that increased MOFs-based fluorescence and decreased QDs-based fluorescence, forming a ratio fluorescence RF probe. The above two researchers chose ZIF-8 as the shell and Cd-QDs as the core, because the QDs can bind on the ZIF-8 due to amine-Zn coordination. Even so, this is not limited to ZIF-8, NH2-MIL-53 (Al) [60] was assigned to combine with 3-mercaptopropionic acid-capped CdTe and a new RF sensor for discerning 6-mercaptopurine (6-MP) was fabricated. The emission intensity of NH2-MIL-53 (Al) reduced and the fluorescence intensity of the QDs increased with the increasing concentration of 6-MP. Different with the above FRET mechanism, the change of the dual-emission was attributed to the strong inner filter effects [156] between 6-MP and NH2-MIL-53 (Al) and the complexation of incompletely bound cadmium ions on the QDs surface by the thiol group of 6-MP [157]. Finally, this RF senor achieved a much lower detection LOD of 0.15 lM when compared with some other measurements such as Fe-MIL-88-NH2 MOF luminescent method [158]. However, QDs are often extracted from a mixture of lead, cadmium and silicon, and these QDs are generally toxic and have a great environmental hazard. Accordingly, as the lowtoxic quantum dots, carbon quantum dots are developed and used in combination with MOFs for the development of a RF sensor. 4.2.3. CDs@MOFs Carbon dots (CDs) are carbon particles with a fluorescent property of less than 20 nm in size, and have a single or multiple layers of graphite structure. They are generally spherical and are classified into amorphous and crystalline forms, wherein the crystalline form less than 10 nm in size is carbon quantum dots (CQDs) and the single layer of graphite structure is the graphene quantum dots (GQDs). CQDs have obvious advantages than QDs in negligible cytotoxicity and easy synthesis [159]. As promising emerging fluorescent labels, those carbon nanoparticles have wide application in cellular imaging, bioimaging [160] and sensing [161]. For the GQDs, as graphene sheets with lateral sizes under 100 nm and radial thicknesses of less than 10 nm [162], it has photocatalytic and photodetector properties compared to graphene

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Fig. 23. Methods used to prepare MOFs@QDs composites. (a) Ship in bottle; (b) bottle around ship; (c) photochemical deposition; and (d) direct surface functionalization [152].

oxide sheets (GO) due to their illustrious quantum confinement and edge effects [163,164]. Nevertheless, stabilizing GQDs in the porous MOFs still remains a challenge because the complicated process and consumption of time during the polymerization. Biswal [165] reported a strategy to encapsulate luminescent GQDs in ZIF-8 for photoluminescence tuning. The emission of the GQD@ZIF-8 composite with a red shift remained after three months under normal laboratory conditions. It is proved that GQDs can be encapsulated in MOF in a long-term with great stability in a simple method, opening up a platform for the application of the GQDs@MOFs. The hybrid N-GQDs/Eu3+@Mg-MOF [166] was synthesized for decoding benzene homologues (BTEX). Interestingly,

with different excitation, there were two kinds of ratio fluorescence. The composite exhibited the characteristic emission bands of N-GQDs and Eu3+ upon excitation in 394 nm while another emission based on Mg-MOF and Eu3+ was excited at 349 nm. Although both of them were used in BTEX sensing, the former can distinguish BTEX better, indicating that N-GQDs have significant superiority in selectivity of RF sensing. CQDs or CDs can emit intense light when illuminated such as metal QDs, the difference is that CQDs are low-toxic and environmentally friendly [167]. CQDs offer numerous advantages compared with organic dyes and other phosphors, including their photobleaching stability, high fluorescence intensity, tunable func-

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Fig. 24. Synthetic route for CDs@Eu-DPA MOFs and the mechanism for Cu2+ detection based on the CDs@Eu-DPA MOFs [168].

tionalities at the surface and low toxicity [101]. Inspired by the strong adsorption capacity of MOFs and the above advantages on highly fluorescent CQDs, the composite CQDs@MOFs was utilized for the construction of a RF sensor to selectively accumulate target analytes and increase the sensitivity of the measurement. A RF sensor CDs@Eu-DPA [168] was fabricated by encapsulating CDs into the Eu-DPA MOF for recognizing Cu2+. The ratio fluorescence comes from the CDs and the Eu-DPA, Eu3+ was sensitized by DPA and Cu2+ could replace Eu3+ to coordinate with DPA. The emission of Eu-DPA MOFs decreased while the emission of CDs kept constant upon the addition of Cu2+ (Fig. 24). The last results showed a LOD of 26.3 nM with great sensitivity, stability and selectivity. With the same metal ion (Eu3+) and different ligands, another Eu-MOFs [169] was composited with N,S-CDs for the detection of water. The capped N,S-CDs were aggregated and confined in the pores of the Eu-MOFs, showing a very weak PL signal while the fluorescence of Eu-MOFs was quenched in water after the capped N,SCDs were released thus realized the RF detection of water. The highlights of this research are the nitrogen and sulfur co-doped CDs, most obtained CDs have a relatively low FLQY (less than 50%) compared with the ordinary semiconductor QDs. The N,SCDs show very high FLQY (73%) and excitation independent emission, resulting from the synergy effect of the adulterated nitrogen and sulfur atoms [170]. In addition to the heteroatomization of carbon quantum dots, other modifications can also bring an enhancement of the fluorescence intensity. For example, ethanediamine modified CDs were encapsulated into luminescent Eu-MOF and the hybrid material CDs@Eu-MOF [171] exhibited high selectivity and sensitivity (the LOD was 0.36 mM) towards doxycycline. Nevertheless, the strong emission of CDs sometimes could cover the emission of MOFs. In the RF sensor of Eu3+/CDs@MIL-53-COOH,

the emission of MIL-53-COOH was covered by the strong emission of CDs. Then, the lanthanide ion Eu3+ was encapsulated into MIL53, forming a RF sensor to successfully recognize diaminotoluene (TDA) [31]. Actually, this research definitively illustrates that without the fluorescence of the MOFs, a RF probe can still be shaped with more than one chromophore. 5. Non-emissive MOFs with encapsulated chromophores Apart from the MOFs-based luminescence, there are reports of luminescence from fluorophores introduced into the nonemissive MOFs or bound to the surface through post-synthetic modification [172]. The non-emissive MOFs can act as a container [173] with the encapsulation of mixed chromophores to form a RF sensor likewise. For example, a MOFs-based RF sensor was prepared by encapsulating yellow emitting and blue emitting CDs into the ZIF-8, achieving the detection of glutathione with a LOD of 0.90 nM in fruit samples [174]. QDs/CDs@ZIF-8 [175] was synthesized by encapsulating QDs and CDs into ZIF-8 (Fig. 25) for application in detecting Cu2+ ions and reached a LOD of 1.53 nM. Except for ZIF-8, Qin and Yan [31] have been synthesized a RF sensor Eu3+/C-dots@MIL-53 with a LOD of 6.8 mg/mL by encapsulating the luminescent CDs and Eu3+ into the MOF to yield the composites with dual-emission. All of the three examples exhibit good selectivity and sensitivity of the non-emissive MOF formed RF sensors. However, as containers, MOFs are often limited by the size of the pores, only the properly sized material can be successfully blocked. For molecules with smaller pore sizes, a common solution is to bond small molecules with the Fe3O4 magnetic nanoparticles (MNPs) and mesoporous silica nanoparticles (MSNs) for successful encapsulation in the MOF. For example, since the chromophores

Fig. 25. Schematic diagram of the process for sensing Cu2+ based on the fluorescent QDs/CDs@ZIF-8 composite [175].

L. Chen et al. / Coordination Chemistry Reviews 404 (2020) 213113

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Fig. 26. Synthetic route to AF-MSN-QD@ZIF-8 with the enzyme immobilization and ratiometric fluorescence strategy based on AF-MSN-QD-ChOx@ZIF-8 for cholesterol detection [178].

as a carrier for fluorophores, several NPs have been successfully encapsulated in it, demonstrating its potential as a host matrix [179,180]. ZIF-8 is sought after by many researchers not only because it is stable and easy to synthesize but also has good adsorption properties and amplifies fluorescent signals. As we know, most detections are performed in a water matrix, and ZIF8 is stable in water while many other MOFs are moisture sensitive [177]. More rarely, ZIF-8 could deliver a nucleic acid probe based on DNA enzyme to living cells. As a nanocarrier, it protects nucleic acid probes from nuclease degradation, enhances probe cellular uptake, and promotes probe escape from endosomes [181], which broaden the development prospects of nonfluorescent MOFs in biological field. 6. Applications Fig. 27. The composites of dual-emissive MOFs and their applications in recent years. The bold font represents recently hot applications that referred in the article.

fluorescein isothiocyanate (FITC) and Eu3+ are too small to be encapsulated by the skeleton, Wang [176] prepared a nanoprobe by encapsulating FITC and Eu3+ complex-functionalized Fe3O4 into ZIF-8 for ratiometric detection of Cu2+. It happens that there is a similar case, a MOFs-based nanoprobe for enhanced HClO sensing [177] was prepared by encapsulating MNPs and dual-emissive RhB modified CDs in ZIF-8. The Fe3O4 here was not only used for the successful encapsulation of RhB modified carbon dots but for the better separation. In those examples, we found that MNPs possess a good bonus attribute as a carrier, the magnetic property enables the nanocomposite with separation ability to reduce the matrix effect and augment the remaining luminescence signal for detection, which is specially vital for larger volumes of the liquid phase [102]. MSNs are often exploited as a carrier of fluorescent small molecule. In Wang’s research [178], the core–shell nanocomposite AFMSN-QD@ZIF-8 (AF = 5-aminofluorescein) was prepared for detection of cholesterol. The AF-MSN-QDs was a sandwich structure with AF inside MSNs and QDs on the surface (Fig. 26). ZIF-8 was in the role of protector while MSNs were a carrier of chromophore for the formation of a RF probe. Evidently, ZIF-8 is widely exploited

MOFs-based RF sensors can be successfully created for chemical and biological sensing through the various design options mentioned above. Based on nearly ten years of literature, studies have shown that MOFs-based RF sensors can be used for sensing temperature, ions, biomarkers, pH, gas, water [102] and volatile

Fig. 28. (a) Energy transfer process between Tb3+ and Eu3+. (b) Luminescence images of [Tb,Eu(hfa)3(dpbp)]n (Tb/Eu = 10) at 100, 200 and 300 K [190].

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organic compounds (VOCs) [182], in which temperature, ion, biomarkers sensing and pH are four hot research topics of those applications (Fig. 27). 6.1. Temperature sensing As the former Section 3.1 referred, it is the mixed Ln-MOFs especially those TbxEuy-MOFs with dual-emission that are mostly designed for temperature sensing [183]. The fluorescence intensity ratio of Tb3+ and Eu3+ is linearly correlated with temperature in a certain range [184,185], which is attributed to the energy transfer between the two light-emitting metal ions. For example, Tb0.8Eu0.2BPDA [186] (H2BPDA = biphenyl-3,5-dicarboxylic acid) exhibits a good linear relationship in the range of 303–328 K. Since the first research in 2003 on (p(DDA-Eu(TTA)3Phen)) [187] as a potential RF thermometer less than a decade, extensive varieties have been reported. Eu0.0069Tb0.9931DMBDC [188] exhibits a sensing range from 10 to 300 K, Tb0.95Eu0.05cpna [189] and Tb0.95Eu0.05bpydc [189] with the change from 25 K to 300 K upon heating, Eu0.37Tb0.63-BTC [90] are in the high temperature range of 313– 473 K under the UV excitation in 296 nm etc. Both of those LnMOFs-based temperature sensors are relying on the dualemission of Tb3+ and Eu3+. The fluorescence of the Tb3+ quenched while that of the Eu3+ enhanced with the temperature due to the energy transfer from Tb3+ to Eu3+, and the energy transfer efficiency depends on Tb/Eu ratios. Besides, the changes can be easily observed by naked eyes due to the vivid color changes. For example, Eu(hfa)3(dpbp)]n [190] own a sensing range of 100–450 K when Tb/Eu = 10, which shows a bright green color at 100 K and changed to red upon 300 K (Fig. 28). Moreover, those mixed LnMOFs own self-calibration of luminescence intensity and could be more accurate and specific. In 2019, Eu0.036Tb0.964BPTC [34] showed good linear responses from 220 K to 310 K, and the maximum relative sensitivity (Sr) was 9.42% K1, which is quite with those of the most excellent Ln-MOFs thermometers reported. From 2003 to 2019, the obtained mixture Ln-MOFs realized RF temperature sensing based on the distinguished characteristic emission of lanthanides. Moreover, the color of the composite

change from green to red upon temperature rising, thus it can be visualized. On the whole, with further research, the higher sensitivity together with the robustness of Ln-MOFs are achieved. However, scarcity of rare earth metals restricted extensive applications of any kind. The temperature sensing is based on the FRET, while luminophores capable of energy transfer are not confined to lanthanides [191]. For instance, thermosensitive luminescent dye acriflavine (Acf) shows temperature-sensitive emission [192] and it is the thermo-sensitivity of dyes that cause the luminescence intensity of MOFs-based composites own a linear respond to the surrounding temperature. In Cai’s research [193], Acf was chosen as the fluorophore to integrate with MOF Zn-BTCA. The spectral overlap between Zn-BTCA and Acf dictated the emission of dye is photosensitized by MOF through energy transfer from MOF to Acf. Particularly, Acf showed little sensitivity to temperature from 80 to 260 K, yet it began to response when the temperature exceeded 280 K whereas the emission intensity of Zn-BTCA continuously decreased from 80 to 380 K. This process proves the emission intensity of dyes can be used as an internal reference or an indicator, rendering Acf@Zn-BTCA a self-calibrating temperature sensor. Eventually, Acf@Zn-BTCA showed higher Sr values (5.001% K1) in the range of 260–380 K with the color change from cyan to green in comparation with some other mixed LMOFs [73,194-197]. The results demonstrated that it was the thermosensitive luminescent that helped the MOFs based RF sensors get expansion with higher sensitivity. 6.2. Ions sensing Among a great diversity research about MOFs-based RF sensing of ions, the detection of anions most are focused on CO2– 3 [76], HClO [198-200], phosphate [140,201,202] and peroxynitrite [203] etc., and cations are mainly focused on the detection of metal ions such as Cr6+ [204],Cu2+ [175,205], Hg2+ [206,207], Fe3+ [88], Eu3+ [208] and Al3+ [40,209] etc. With the intensity fluorescence of the RF sensor enhanced or decreased, the determination of different ions is easily accomplished with good selectivity and a low detection limit.

Fig. 29. Diagram of Eu-MOF in fluoride ions sensing and fluorescence spectra of Eu-MOF upon the addition of fluoride. Inset illustrate the color change at different concentration of fluoride [32].

L. Chen et al. / Coordination Chemistry Reviews 404 (2020) 213113

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Fig. 30. Sensing Mechanism of the NMOF Probe [198].

In case of anion, a MOFs-based RF sensor (Eu-MOF) [32] for selectivity detection of F was synthesized with Eu3+ ions and the ligand 5-bop due to the high affinity of boric group toward fluoride. The emission of 5-bop was enhanced accompanying with the decreased emission of Eu3+ (Fig. 29), which could respectively attribute to the strong covalent interaction between fluoride and boron and the disrupted pp–p conjugation of 5-bop decreased the intersystem crossing efficiency. Besides, only fluoride showed the striking fluorescence change while a negligible change was observed from the other ions under the same conditions. At last, the sensor was applied sensing F in river and underground water and the obtained recovery was from 95.2% to 114.5%, which illustrates the high accuracy of the Eu-MOF. Besides, with the innerreference, MOFs-based RF sensors also possess high sensitivity due to self-calibration. Sun [76] constructed a HMOF (Eu/PtMOFs) for RF sensing carbonate ions (CO2– 3 ) and achieved a low detection limit of 0.021 mM. Liu [199] designed nanoscale RF sensor (AuNPs-BSA@Tb/GMP) for the detection of superoxide anion. Compared with other superoxide anion sensors [210–213], AuNPs-BSA@Tb/GMP exhibits a lower LOD (4.7 nM) and wider linear range (14 nM-10 lM). Ingeniously, Ding [198] designed a NMOF-based RF probe for both sensing peroxynitrite (ONOO) and hypochlorite (ClO). The emission peak of NMOF decreased with an increase of the peak at 410 nm upon the presence of ONOO. On the contrary, the emission of NMOF was enhanced while the emission at 410 nm was kept stable with the increase of ClO concentration (Fig. 30). Eventually, the AuNPs-BSA@Tb/ GMP shows a low LOD of ONOO and ClO of 0.05 mM and 1 mM respectively. In case of cation, a few LMOFs have been reported for sensing the potent carcinogenic Cr (VI) anions [214–217]. However, with the presenting indistinguishable co-quenching effect of Fe3+, none of them can realize independent selective sensing. Jin [204] prepared RhB@NZIF-90 to selectively sense Cr (VI) anions 2 (CrO2 4 and Cr2O7 ) with highly sensitivity and selectivity. To rule out interference from other cations, the NZIF-90 based RF sensor

was completed with the doping of RhB, MOF based emission (357 nm) was quenched through electrostatic interaction while RhB (556 nm) keep constant. It is the dual-emission of I357/I556 show negligible changes with the addition of other ions, and then get to a low detection limits of CrO2 (0.16 ppm) and Cr2O2 4 7 (0.38 ppm) among the reported fluorescent MOFs-based probes for Cr (VI). 6.3. Biomarkers sensing Biomarker refers to a biochemical indicator that can label changes or possible changes in the structure, function, cell and subcellular structure or function of a system, which can be applicated in disease diagnosis. Currently on the application of biomark-

Fig. 31. Schematic diagram of the preparation of the ZnO/Eu nanostructure and the sensing mechanism for DPA [228].

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Table 1 Comparative study of the lanthanide ion-functionalized fluorescent sensors with different materials for sensing bacillus anthracis [228]. Material

LOD

Time

Ref

A supramolecular monolayer Bio-metal–organic frameworks Silver nanoparticles Carbon nanotubes Fluorescein isothiocyanate dye-doped silica nanoparticles Graphene quantum dots PAN nanoparticles A PES film ZnO QDs

25 nM 34 nM 10 nM 1 lM 0.2 nM

10 min 20 s 10 min 3s 30 s

[231] [226] [232] [233] [234]

50 pM 50 pM 0.5 nM 3 nM

7.7 s 20 s 50 s 8s

[235] [236] [237] [228]

ers for MOFs-based RF sensors, there are metabolites such as diaminotoluene [31], 1-hydroxypyrene (a detectable metabolite of chemical carcinogens polycyclic aromatic hydrocarbons (PAHs) [218,219]), cancer biomarkers [220] and anti-cancer drug 6-MP [60]. However, among the various detection species, researchers are obsessed with the anthrax biomarker DPA [221,222], which occupies a large proportion in application of MOFs-based RF probe in biomarker detection. In 2007, Rieter [223] firstly reported a RF sensor based on NMOF 30 -Tb-EDTM. It was prepared by Eu-doped composite (30 ) and functionalized the silica surface with a silylated Tb-EDTA monoamide derivative. By complexing to DPA, Tb3+ ions [224] and molecular Tb composites [225] have been used as sensitive luminescence sensors for anthrax and other bacterial spores. In this research, the Tb luminescence was a ‘‘turn-on” signal after the addition of DPA. 3’-Tb-EDTM only gave an emission of Eu because the TbEDTM moiety is virtually non-emissive, whereas the emission of Tb became markedly visible due to the DPA-to-Tb3+ energy transfer after the addition of DPA. The Tb luminescence signal was for DPA recognition and the emission of Eu from the NMOF acts as noninterfering internal calibration. In the following years, with the expansion of the types of MOFs, the detection of DPA is further optimized. In 2016, a RF sensor [226] based on luminescent bioMOF was formed by exchanging both Tb3+ and Eu3+ cations into anionic bio-MOF-1 [227] for rapid (within 20 s) recognize of DPA. Upon the addition of DPA, DPA-to-Tb3+ energy transfer was progressively enhanced along with the energy transfer from Tb3+ to Eu3+ was remarkably weakened. Although it is the same detection mechanism as NMOF 3’-Tb-EDTM, the LOD of Tb/Eu@bio-MOF-1 for DPA was much lower than 3’-Tb-EDTM. However, MOFsbased RF sensors in response time and detection limit are not the best in sensing DPA. For example, a sensor based on Eu3+ chelated ZnO (Eu-QDs) [228] has been made for RF sensing DPA with dualemission of the Eu3+ and ZnO QDs (Fig. 31), realizing a much lower LOD of 3 nM and a faster response in 8 s. In comparison with the bio-MOF-1, both of them showed a great selectivity for DPA over other aromatic ligands, amino acids and common cellular ions. Compared with other developed optical detection method for Bacillus anthracis, the LOD and response time of the Eu-QDsbased method are quite competitive (table 1). Although, Eu-QDs is better than bio-MOF-1 in sensitivity, the MOFs-based RF sensors still have significant advantages, e.g. the structure of the MOFs can be precisely designed and tuned to meet specific needs. For example, bio-MOF-1 can work equally well in human serum whereas the Eu-QDs are generally toxic and have a great environmental hazard. More importantly, the infectious dose of the bacillus anthracis spores for human being is 60 lM, hence all researches could make sense as long as the concentration was less than 60 lM. In 2018, Li [229] synthesized a RF sensing probe with MOF Eu-BTC and rhodamine-derived RB@Eu-BTC with LOD value of 3.4 lM. With the same probe, Lin and Fang [230] achieved detection limit at

3.2 mM. Both of those MOFs-based RF sensors have unique advantages over traditional DPA optical sensing systems due to their dual sensing skills and the possibility of naked eye recognition.

6.4. pH sensing pH is a crucial factor in a broad scope of applications including biomedical and environmental. The MOFs-based RF sensors have inherent advantages in luminescence sensing with a more accurate analysis [238], a number of researches of the MOFs-based pH sensors are gradually reported in monitoring small pH changes in the last 5 years. For example, a MOFs-based composite 1-hydroxypyre ne@Co/Tb-dipicolinic acid (1-OHP@Co/Tb-DPA MOF) [239] was prepared as a RF pH sensor, which exhibited a rapid response (30 s) and a broad pH range of 0.3–7.8. Actually, the early implementations about the MOFs-based RF sensors in detection of pH were proposed by Rocha and Yan. Rocha [240] reported a Eu3+ based MOF (ITQMOF-3-Eu) that showed linear pH-dependence in the range of 5.0 to 7.5. The two types 5D0-7F0 emissions of the two Eu3+ in ITQMOF-3-Eu are Eu1 at 580.7 nm and Eu2 at 579.0 nm under the excitation on 350 nm. Eu2-based emission was enhanced whereas the emission intensity of Eu1 remained unchanged with an increase of the pH value from 5.0 to 7.5. Yan [241] described a RF pH sensor in the range from 5.0 to 7.2 based on MOF-253. MOF-253 can emit two Eu3+ characteristic emissions (614 nm) of Eu1 and Eu2 under different excitation at 330 nm and at 375 nm, respectively. Thus, there are two peaks in the excitation spectra of MOF-253 under the emission of 614 nm. The excitation peak intensity of Eu1 (kex = 330 nm) keep constant while Eu2based excitation peak (kex = 375 nm) was quenched with a decrease of the pH value. Finally, MOF-253 successfully achieved pH sensing in the range of 5.0–7.2 without external calibration. However, neither of them expressed good reusability, which limits their application in real environments. To ameliorate this situation, Wang [242] synthesized a MOF Cd-EDDA with ethylene glycol ether bridging tetracarboxylate (H4EDDA), which possess a binding site for binding hydrogen or hydroxyl ions through hydrogenbonding interactions. This interaction could tune the dualemission in charge transition, causing an enhancement in chargetransfer-based emission intensity and a decline in the ligandbased emission. The results found the MOF with excellent chemical

Fig. 32. The fitted curve and pH-Dependent emission spectra of Eu0.034Tb0.966NMOF in the pH ranging from 3.00 to 7.00 [246].

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stability displayed a RF response to pH in the range of 2.0–11.5. Especially, the sensor could be repeatedly used and this is the first example of recyclable MOFs-based RF sensor for pH. Moreover, most pH sensors need to be applied in biological environments and living cells, and MOFs-based RF sensors are no exception. He and co-workers [243] reported the first example of nanoscale MOFs (NMOFs) for real time intracellular pH sensing in live cells. A pH sensitizer FITC [244] was covalently conjugated to a UiONMOF to afford the F-UiO NMOF. Hydronium ions could diffuse rapidly and freely through the open channels of NMOFs, provided a fast sensor response at pH = 5.0–7.0, and the standard deviations of pH were below 0.2 pH unit in this pH range. More than this, in this study the F-UiO NMOF exhibited desired structural stability, fluorescence efficiency and efficient cellular uptake, thus it was a reliable and accurate sensor for real-time intracellular pH sensing. In comparison with the sensor NMOF in living cells, Cd-EDDA have a wider range of pH sensing but was weaker in biocompatibility, which may limit the application. The NMOF was bridged by the ligand amino-TPDC, which has certain biological toxicity. Taking both the detection range and biocompatibility [245] into consideration, in the following year, Xia [246] constructed a biocompatible Eu/Tb-mixed NMOF with ligands of fumarate and oxalate. To the best of our knowledge, fumaric acid and oxalic acid are environmentally friendly with low toxicity than common ligand of MOFs, such as benzene or biphenyl. This NMOF exhibited significant pHdependent ‘‘antenna” emission from Tb3+ (545 nm) and Eu3+ (618 nm), which was blocked gradually by hydrogen/hydroxyl ions. Hence, as the pH decreases, the emissions of Eu3+ and Tb3+ were quenched, but the decreasing rate of Eu3+ is more drastic than Tb3+ (Fig. 32), thus it can act as a self-referenced pH sensor with the pH range from 3 to 7.

6.5. Other sening Apart from the four hot applications, MOFs-based RF sensors can also be applied in gas, VOCs, humidity sensing. In gas sensing, the closely health-related H2S, O2 [247–249] and SO2 [250] etc. are common analytes. Taking advantage of the superior affinity of H2S for Cu2+ ions, Zhang [18] and Zheng [251] et al. designed two MOFs-based RF sensors (Eu3+/Cu2+@UiO-66-(COOH)2 and Tb3+@Cu-MOF respectively) for sensing H2S. Tb3+@Cu-MOF showed a LC emission and a characteristic emission of Tb3+ ions. However, Cu2+ tends to weaken the antenna efficiency of the ligands to Tb3+, causing a weak emission of Tb3+.Thus the fluorescence of Tb3+ was increased and the LC emission was decreased after the combination of H2S and Cu2+ (Fig. 33). The same for Eu3+/Cu2+@UiO-66(COOH)2, Cu2+ can interrupt the FRET from ligand to Eu3+ while H2S have priority to combine with Cu2+ and then the fluorescence of Eu3+ was enhanced and the broad LC emission was quenched. Finally, the LOD of Eu3+/Cu2+@UiO-66-(COOH)2

Table 2 Comparative study of the detection limit and response time of MOFs-based fluorescent probes for H2S [18]. Material

LOD (mM)

Time (min)

Ref

UiO-66@NO2 UiO-66@N3 IRMOF-3 (–N3) Ce-UiO-66-N3 Ce-UiO-66-NO2 Eu3+/Cu2+@UiO-66-(COOH)2

188 118 28.3 12.2 34.84 5.45

7.7 3 <2 12.7 12.7 <0.5

[257] [258] [259] [260] [260] [18]

was better than some other previously reported MOFs-based fluorescent probes for H2S (table 2). As for VOCs sensing, poisonous and harmful substances such as xylene, phenol, benzyl alcohol, and FA are most common VOCs. Zheng [252] developed a dyes@MOFs sensor for sensing different VOCs. The composite exhibits the emission both of ligand and dye, and they are clearly enhanced and/or quenched by different VOCs, e.g., both of the fluorescence of dye and MOF are quenched upon the addition of nitrobenzene. In comparation with traditional MOFs-based sensors [253–256], the internal reference strategy has obvious advantages in sensitivity. For example, Hao and co-workers [77] achieved a high sensitivity (51 ppb) for FA sensing by utilizing a dual-emissive Ag (I)-Eu (III) @MOFs sensor. At last, for the water sensing, water is a contaminant for dry products and the content of water in organic solvents should be strictly controlled. Dong [169] synthesized a nanohybrids Eu-MOFs/N,S-CDs with red light emission (623 nm) of EuMOFs and blue light emission (420 nm) of N,S-CDs. The red-light emission can be quenched own to the effect of O–H oscillators in water while the blue light was enhanced due to the release of N, S-CDs (Fig. 34), thus, the light intensity ratio (I420/I623) linearly increases with increasing water content. The last LOD was 0.03% whereas the water response range of the sensors was limited no more than 30%, which means this RF sensor has great potential to practical application. Yin and co-workers [16] prepared a guest-encapsulation MOF (Ru@MIL-NH2) by a simple one-pot method for RF sensing H2O. The dual-emission originates from the MIL-NH2 (465 nm) and Ru(bpy)2+ 3 (615 nm), the emission at 465 nm was enhanced whereas the emission around 615 nm kept stable with the presence of water (Fig. 35). Compared with the EuMOFs/N,S-CDs, Ru@MIL-NH2 reached a lower LOD of 0.02%. Both of the above two researches’ results show advantages of RF sensing that the dual-emission changes lead to clear changes in color and then it was easily identified by naked eye. In general, as for those application around MOFs-based RF sensing, the obvious merits in comparation with single emission sensors can be concluded as follows: i) the self-calibrating ability helps to get rid of the interference from the probe concentration and environment; ii) a highly selectivity and sensitivity due to another signal; iii) the dual-emission changes lead to clear changes in color, which can be identified by naked eye.

Fig. 33. Diagram of the composite Tb3+@Cu-MOF for the detection of H2S [251].

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Fig. 34. Synthesis of Eu-MOFs/N,S-CDs and detection of H2O content in organic solvents [169].

Fig. 35. Diagram of Ru@MIL-NH2 in water sensing and emission spectra of Ru@MIL-NH2 in pure water [16].

Table 3 Conclusion of numerous MOFs-based RF sensors. RF Sensors

MOF

Chromophores

Excitation

Emission 1

Emission 2

Application

Ref

Ru@MIL-NH2 Eu3+/Cu2+@UiO-66-(COOH)2

ON ON

300 nm 305 nm

465 nm" 393 nm?

615 nm? 615 nm"

H2O H2S

[16] [18]

Eu3+@In1 Eu3+@JXNU-4 [Zn(TIPA)(NO3)2(H2O)] 5H2O DBI-PEG-NH2-Fe3O4@Zr-MOFs-RBITC(RB-PCN) CdSe@F-MOF ZnS@DA-MOF CdTe@NH2-MIL-53 (Al) CDs@Eu-DPA CQDs@UiO-66-(COOH)2 CDs@Eu-MOF RhB@NZIF-90 N,S-CDs@Eu-MOFs En-CDs@Eu-MOF AgNCs@MOF OPD/H2O2@NH2-MIL-101 N-GQDs/Eu3+@Mg-MOF

ON ON ON ON ON

Ru(bpy)2+ 3 Eu3+ Cu2+ Eu3+ Eu3+ HPTS Fe3O4 CdSe

315 nm 329 nm 340 nm 520 nm 400 nm

[208] [218] [42] [263] [46]

ZnS CDs CQDs CDs RhB N,S-CDs En-CDs AgNCs OPD/H2O2 N-GQDs

335 nm 275 nm 370 nm 390 nm 373 nm 365 nm 365 nm 430 nm 410 nm 394 nm

617 nm" 616 nm; 575 nm; 641 nm 680 nm" 680 nm" 528 nm" 615 nm; 470 nm; 616 nm? 556 nm? 623 nm; 616 nm" 730 nm; 556 nm; 618 nm;

Eu3+ 1-HP RDX pH light harvesting

ON ON ON ON ON ON ON ON ON ON

408 nm; 502 nm" 375–450 nm; 575 nm 550 nm; 620 nm; 425 nm; 425 nm? 610 nm" 467 nm; 357 nm; 420 nm" 436 nm; 510 nm" 456 nm" 430 nm"

6-MP Cu2+ Cu2+ Cr (VI) Cr (VI) H2O MnO 4 phosphate pyrophosphate BTEX

[60] [168] [100] [59] [204] [169] [171] [140] [202] [166]

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L. Chen et al. / Coordination Chemistry Reviews 404 (2020) 213113 Table 3 (continued) RF Sensors

MOF

Rhodamine B@TMU-4 Rho@Zn-MOF R6H@Eu-BTC RB@Eu-BTC BSA-AuNPs@Tb-AMP RB@Eu-BTC BSA-AuNPs@Tb-AMP Rh6G@MOF PB@UiO-66-NH2 perylene@ZJU-88 Acf@ZnBTCA RhB@CZJ-3 FS@Zn-MOF DMASM@ZJU-21 N,S-CDs@Eu-MOFs AuNPs/GO@MOF [Tb0.9Eu0.1(OBA)2](Hatz)(H2O)1.5}n Eu/Pt-MOFs Cd-EDDA Eu-MOF 1 Cd-EDDA Eu0.034Tb0.966-NMOF Eu@SiNRs ITQMOF-3-Eu {[(CH3)2NH2][Zn(BTB)2/3(ATZ)]H2ODMF}n Eu0.37Tb0.63-BTC Tb0.8Eu0.2BPDA Eu0.0069Tb0.9931DMBDC [Tb-Eu(hfa)3(dpbp)]n Eu0.036Tb0.964BPTC {(H3O)[Tb0.93Eu0.07(BODSDC)(H2O)2]n Eu-OHBDC Eu-MOFs (Me2NH2)[Eu2L2(NO3)2(l3-OH)(H2O)]2H2O2DMA Eu/Tb-MOF PDA-Eu@ZIF-8 EuPS@AnC/ZIF-8

ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON ON OFF OFF

RhB-CDs-Fe3O4@ZIF-8

OFF

Eu-Fe3O4-FITC@ZIF-8

OFF

AF-MSN-QD@ZIF-8

OFF

QDs/CDs@ZIF-8

OFF

Eu3+/CDs@MIL-53

OFF

Tb/ Eu@bio-MOF-1

OFF

Eu-TTA@MOF-253

OFF

BYCDs@ZIF-8 Dye@Eu3+/UiO-66

OFF OFF

Chromophores Eu3+ RhB Rho R6H RB AuNPs RB AuNPs Rh6G phloxine B (PB) Perylene Acriflavine RhB fluorescein (FS) DMASM N,S-CDs AuNP@GO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO Eu (III) EuPS AnC RhB CDs Eu-Fe3O4 FITC AF-MSNs CdTe CdTe CDs Eu3+ C-dots Tb Eu Eu1/Eu2–TTA BYCDs Dye Eu3+

Excitation

Emission 1

Emission 2

Application

Ref

338 nm 310 nm 284 nm 289 nm 276 nm 285 nm 276 nm 320 nm 330 nm 388 nm 340 nm 340 nm 367 nm 366 nm 365 nm 485 nm 316 nm 340 nm 310 nm 275 nm 310 nm 340 nm 405 nm 350 nm 330 nm 296 nm 323 nm 488 nm 380 nm 322 nm 368 nm 318 nm 275 nm 335 nm 300 nm 284 nm 350 nm

462 nm; 416 nm; 556 nm" 553 nm " 405 nm? 555 nm" 545 nm? 373 nm; 430 nm? 473 nm; 410 nm; 595 nm" 427 nm; 492 nm" 420 nm" 516 nm; 545 nm" 560 nm; 350 nm; 366 nm 410 nm 545 nm" 470 nm; 579 nm" 377 nm" 542 nm; 544 nm; 545 nm; 543 nm; 545 nm 544 nm; 375 nm" 313 nm" 362 nm" 545 nm;; 613 nm; 410 nm;

588 nm; 583 nm; 616 nm; 616 nm? 545 nm" 616 nm; 635 nm; 570 nm? 560 nm; 615 nm" 505 nm" 420 nm; 522 nm" 604 nm; 623 nm; 704 nm? 618 nm? 614 nm" 410 nm" 625 nm 350 nm 618 nm"" 620 nm? 580 nm? 510 nm; 614 nm" 614 nm" 613 nm" 613 nm" 614 nm 616 nm" 427 nm; 615 nm; 620 nm? 613 nm; 613 nm" 615 nm?

NA nitrobenzene DPA DPA DPA DPA Hg2+ TNP CTAB Temperature Temperature VOCs TCA Temperature H2O p53 gene CH3OH CO2– 3 Hg2+  F pH pH (3–7) pH pH Temperature Temperature Temperature Temperature Temperature Temperature 1-HP Fe3+ dopamine Al3+ H2O ClO/SCN Oxygen

[264] [252] [221] [229] [136] [230] [136] [43] [119] [58] [193] [6] [120] [44] [169] [220] [33] [76] [206] [32] [242] [246] [245] [240] [27] [90] [186] [188] [190] [34] [61] [88] [89] [209] [102] [265] [62]

355 nm

415 nm?

580 nm;

HClO

[177]

330 nm

515 nm?

616 nm;

Cu2+

[176]

440 nm

520 nm"

618 nm;

cholesterol

[178]

2+

[175]

370 nm

430 nm?

620 nm;

Cu

350 nm

450 nm?

616 nm;

TDA

[31]

290 nm

545 nm"

615 nm?

DPA

[226]

330 375 365 365

616 nm

616 nm

pH

[241]

440 nm" 430 nm?

565 nm; 617 nm"

Glutathione TC

[174] [117]

nm? nm; nm nm

Note: ‘‘ON” represents the MOFs with emissions while ‘‘OFF” represents the non-emission MOFs.

7. Conclusion and outlook In conclusion, MOFs-based RF sensors can be shaped with luminescent MOFs based on mixed lanthanide/ligands or encapsulate a fluorophore and non-emissive MOFs with two fluorophores. Most importantly, a single emission can become dual-emission after adding a characteristic analyst that can interact with MOFs or guests causing FRET. Researches mentioned in this article on RF detection through different methods can be categorized into dual-emission MOFs with or without fluorophores and they are concluded in Table 3. Among them, single emissive MOF with a fluorophore is the most commonly used tactic for researchers. Because MOFs’ intrinsic dual-emission is limited by the available

lanthanide luminescence emission of the mixed-lanthanide and the detection range of the mixed-ligands. Following the addition of fluorescence guests, the analytes coverage was expanded with a higher luminescence quantum yield. What’s more, in terms of synthesis, a fluorophore-based composite is easier than two fluorophores. Taking all factors above into consideration, it’s easy to find that single-emissive MOFs with a fluorophore is the most used in the above four design tactics. Although, RF sensors based on dual-emission of MOFs are more reliable and accurate than those based on a single emission intensity, the majority of related reports are limited to the detection of analytes using single emission. This illustrates it still has great potentials for making further progress: (1) More stable: many of these MOFs based composites lack long

22

L. Chen et al. / Coordination Chemistry Reviews 404 (2020) 213113

term stability [165],e.g., the capping agent was referred more than once in Section 4.2 because it has been demonstrated [155] a controlled encapsulation strategy by introducing surfactant-capped nanostructures into MOFs can improve the stability. Consequently, the NPs@MOFs can be stable longer by different capped NPs, and there still exist explore room for other guests to stable in the MOFs. (2) Higher selectivity: molecular imprinting can be added into RF sensing for further increased selectivity. The same with MOFs, molecularly imprinted polymers (MIPs) also have specific and selective pores in a three-dimensional polymer network [261], which bring about various unique properties of MIPs and the best known is their tailorability for practically any target analyte. The great thing is that MIPs have broadly applicated in sensing and the MIP/MOF sensors on conductive substrates, showing high sensitivity and great selectivity in complex matrices [261]. The same will apply to MOFs-based RF sensors, but it’s still a new emerging research field, there are only a few reports about MOFs-based sensors including a molecularly imprinted structure, the developing room is large. (3) Wider application: the test range can be extended by developing the type of luminescent ligand with doped metal ion or increasing the type of guests. It is worth mentioning that the luminescent fluorophores are not limited in dyes and QDs or NPs, the luminous MOF as a fluorophore [262] can also be wrapped into non/single-emissive MOFs to construct a new RF probe, which may open a new platform for the MOFs-based dualemission sensing. Moreover, most samples in RF detection are liquid or in water matrix, thus it is necessary to make the watersoluble MOFs modified with the fluorescence and to expand the range of analytes, and new MOFs that can achieve solid/gas fluorescence recognition are need to exploit. In view of the above advances, we do believe the MOFs based ratiometric fluorescence probes will have a better development in chemical sensing and biosensing. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements This work was financially supported by the Independent Innovation Fund Project of Agricultural Science and Technology of Jiangsu Province in 2017 (NoCX (17) 1003); Guizhou Provincial Science and Technology Department Joint Fund Project (Qian Kehe LH word [2016] No. 7076). References [1] M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter, M. O’Keeffe, O.M. Yaghi, Systematic design of pore size and functionality in isoreticular MOFs and their application in methane storage, Science 295 (2002) 469–472, https:// doi.org/10.1126/science.1067208. [2] A. Tabacaru, C. Pettinari, S. Galli, Coordination polymers and metal-organic frameworks built up with poly(tetrazolate) ligands, Coord. Chem. Rev. 372 (2018) 1–30, https://doi.org/10.1016/j.ccr.2018.05.024. [3] V. Colombo, C. Montoro, A. Maspero, G. Palmisano, N. Masciocchi, S. Galli, E. Barea, J.A.R. Navarro, Tuning the adsorption properties of isoreticular pyrazolate-based metal-organic frameworks through ligand modification, J. Am. Chem. Soc. 134 (2012) 12830–12843, https://doi.org/ 10.1021/ja305267m. [4] J. Peng, H. Tian, Q. Du, X. Hui, H. He, A regenerable sorbent composed of a zeolite imidazolate framework (ZIF-8), Fe3O4 and graphene oxide for enrichment of atorvastatin and simvastatin prior to their determination by HPLC, Microchim. Acta 185 (2018), https://doi.org/10.1007/s00604-0182697-6. [5] Y.-B. Huang, J. Liang, X.-S. Wang, R. Cao, Multifunctional metal-organic framework catalysts: synergistic catalysis and tandem reactions, Chem. Soc. Rev. 46 (2017) 126–157, https://doi.org/10.1039/c6cs00250a.

[6] M.-J. Dong, M. Zhao, S. Ou, C. Zou, C.-D. Wu, A luminescent Dye@MOF platform: emission fingerprint relationships of volatile organic molecules, Angew. Chem.-Int. Edit. 53 (2014) 1575–1579, https://doi.org/10.1002/ anie.201307331. [7] L.R. Mingabudinova, V.V. Vinogradov, V.A. Milichko, E. Hey-Hawkins, A.V. Vinogradov, Metal-organic frameworks as competitive materials for nonlinear optics, Chem. Soc. Rev. 45 (2016) 5408–5431, https://doi.org/10.1039/ c6cs00395h. [8] B. Wang, X.L. Lv, D.W. Feng, L.H. Xie, J. Zhang, M. Li, Y.B. Xie, J.R. Li, H.C. Zhou, Highly stable Zr(IV)-based metal-organic frameworks for the detection and removal of antibiotics and organic explosives in water, J. Am. Chem. Soc. 138 (2016) 6204–6216, https://doi.org/10.1021/jacs.6b01663. [9] B. Wang, P.L. Wang, L.H. Xie, R.B. Lin, J. Lv, J.R. Li, B.L. Chen, A stable zirconium based metal-organic framework for specific recognition of representative polychlorinated dibenzo-p-dioxin molecules, Nat. Commun. 10 (2019) 8, https://doi.org/10.1038/s41467-019-11912-4. [10] A.C. Sedgwick, L. Wu, H.-H. Han, S.D. Bull, X.-P. He, T.D. James, J.L. Sessler, B.Z. Tang, H. Tian, J. Yoon, Excited-state intramolecular proton-transfer (ESIPT) based fluorescence sensors and imaging agents, Chem. Soc. Rev. 47 (2018) 8842–8880, https://doi.org/10.1039/c8cs00185e. [11] X. Liu, D. Huang, C. Lai, G. Zeng, L. Qin, H. Wang, H. Yi, B. Li, S. Liu, M. Zhang, R. Deng, Y. Fu, L. Li, W. Xue, S. Chen, Recent advances in covalent organic frameworks (COFs) as a smart sensing material, Chem. Soc. Rev. (2019), https://doi.org/10.1039/c9cs00299e. [12] X.J. Kong, T. He, Y.Z. Zhang, X.Q. Wu, S.N. Wang, M.M. Xu, G.R. Si, J.R. Li, Constructing new metal-organic frameworks with complicated ligands from ‘‘One-Pot” in situ reactions, Chem. Sci. 10 (2019) 3949–3955, https://doi.org/ 10.1039/c9sc00178f. [13] Q. Yang, B. Wang, Y. Chen, Y.B. Xie, J.R. Li, An anionic In(III)-based metalorganic framework with Lewis basic sites for the selective adsorption and separation of organic cationic dyes, Chin. Chem. Lett. 30 (2019) 234–238, https://doi.org/10.1016/j.cclet.2018.03.023. [14] B. Wang, Q. Yang, C. Guo, Y.X. Sun, L.H. Xie, J.R. Li, Stable Zr(IV)-based metalorganic frameworks with predesigned functionalized ligands for highly selective detection of Fe(III) ions in water, ACS Appl. Mater. Interfaces 9 (2017) 10286–10295, https://doi.org/10.1021/acsami.7b00918. [15] D. Feng, T.-F. Liu, J. Su, M. Bosch, Z. Wei, W. Wan, D. Yuan, Y.-P. Chen, X. Wang, K. Wang, X. Lian, Z.-Y. Gu, J. Park, X. Zou, H.-C. Zhou, Stable metal-organic frameworks containing single-molecule traps for enzyme encapsulation, Nat. Commun. 6 (2015), https://doi.org/10.1038/ncomms6979. [16] H.-Q. Yin, J.-C. Yang, X.-B. Yin, Ratiometric fluorescence sensing and real-time detection of water in organic solvents with one-pot synthesis of Ru@MIL-101 (Al)-NH2, Anal. Chem. 89 (2017) 13434–13440, https://doi.org/10.1021/acs. analchem.7b03723. [17] A. Bigdeli, F. Ghasemi, S. Abbasi-Moayed, M. Shahrajabian, N. Fahimi-Kashani, S. Jafarinejad, M.A.F. Nejad, M.R. Hormozi-Nezhad, Ratiometric fluorescent nanoprobes for visual detection: Design principles and recent advances – a review, Anal. Chim. Acta 1079 (2019) 30–58, https://doi.org/10.1016/j. aca.2019.06.035. [18] X. Zhang, Q. Hu, T. Xia, J. Zhang, Y. Yang, Y. Cui, B. Chen, G. Qian, Turn-on and ratiometric luminescent sensing of hydrogen sulfide based on metal-organic frameworks, ACS Appl. Mater. Interfaces 8 (2016) 32259–32265, https://doi. org/10.1021/acsami.6b12118. [19] R. Gui, H. Jin, X. Bu, Y. Fu, Z. Wang, Q. Liu, Recent advances in dual-emission ratiometric fluorescence probes for chemo/biosensing and bioimaging of biomarkers, Coord. Chem. Rev. 383 (2019) 82–103, https://doi.org/10.1016/j. ccr.2019.01.004. [20] M.H. Lee, J.S. Kim, J.L. Sessler, Small molecule-based ratiometric fluorescence probes for cations, anions, and biomolecules, Chem. Soc. Rev. 44 (2015) 4185–4191, https://doi.org/10.1039/c4cs00280f. [21] P. Wu, X. Hou, J.-J. Xu, H.-Y. Chen, Ratiometric fluorescence, electrochemiluminescence, and photoelectrochemical chemo/biosensing based on semiconductor quantum dots, Nanoscale. 8 (2016) 8427–8442, https://doi.org/10.1039/c6nr01912a. [22] R. Zhang, F. Yan, Y. Huang, D. Kong, Q. Ye, J. Xu, L. Chen, Rhodamine-based ratiometric fluorescent probes based on excitation energy transfer mechanisms: construction and applications in ratiometric sensing, RSC Adv. 6 (2016) 50732–50760, https://doi.org/10.1039/c6ra06956h. [23] X. Huang, J. Song, B.C. Yung, X. Huang, Y. Xiong, X. Chen, Ratiometric optical nanoprobes enable accurate molecular detection and imaging, Chem. Soc. Rev. 47 (2018) 2873–2920, https://doi.org/10.1039/c7cs00612h. [24] S. Wu, H. Min, W. Shi, P. Cheng, Multicenter metal-organic framework-based ratiometric fluorescent sensors e1805871–e1805871 Adv. Mater. (Deerfield Beach, Fla.) (2019), https://doi.org/10.1002/adma.201805871. [25] J.W. Verhoeven, Glossary of terms used in photochemistry, Pure Appl. Chem. 68 (1996) 2223–2286, https://doi.org/10.1351/pac199668122223. [26] J. Heine, K. Mueller-Buschbaum, Engineering metal-based luminescence in coordination polymers and metal-organic frameworks, Chem. Soc. Rev. 42 (2013) 9232–9242, https://doi.org/10.1039/c3cs60232j. [27] H. Zhang, C. Lin, T. Sheng, S. Hu, C. Zhuo, R. Fu, Y. Wen, H. Li, S. Su, X. Wu, A luminescent metal-organic framework thermometer with intrinsic dual emission from organic lumophores, Chem.-Eur. J. 22 (2016) 4460–4468, https://doi.org/10.1002/chem.201504432. [28] M.S. Wang, S.P. Guo, Y. Li, L.Z. Cai, J.P. Zou, G. Xu, W.W. Zhou, F.K. Zheng, G.C. Guo, A direct white-light-emitting metal-organic framework with tunable

L. Chen et al. / Coordination Chemistry Reviews 404 (2020) 213113

[29]

[30] [31]

[32]

[33]

[34]

[35]

[36]

[37]

[38]

[39]

[40]

[41]

[42]

[43]

[44]

[45]

[46]

[47]

[48]

[49]

[50]

[51]

yellow-to-white photoluminescence by variation of excitation light, J. Am. Chem. Soc. 131 (2009) 13572–13573, https://doi.org/10.1021/ja903947b. L. Li, S. Zhang, L. Han, Z. Sun, J. Luo, M. Hong, A non-centrosymmetric dualemissive metal-organic framework with distinct nonlinear optical and tunable photoluminescence properties, Cryst. Growth Des. 13 (2013) 106– 110, https://doi.org/10.1021/cg301243e. J.C.G. Bunzli, Benefiting from the unique properties of lanthanide ions, Accounts Chem. Res. 39 (2006) 53–61, https://doi.org/10.1021/ar0400894. S.-J. Qin, B. Yan, Dual-emissive ratiometric fluorescent probe based on Eu3+/Cdots@MOF hybrids for the biomarker diaminotoluene sensing, Sens. Actuator B-Chem. 272 (2018) 510–517, https://doi.org/10.1016/j.snb.2018.06.018. Z.-R. Yang, M.-M. Wang, X.-S. Wang, X.-B. Yin, Boric-acid-functional lanthanide metal organic frameworks for selective ratiometric fluorescence detection of fluoride ions, Anal. Chem. 89 (2017) 1930–1936, https://doi.org/ 10.1021/acs.analchem.6b04421. D.-M. Chen, C.-X. Sun, Y. Peng, N.-N. Zhang, H.-H. Si, C.-S. Liu, M. Du, Ratiometric fluorescence sensing and colorimetric decoding methanol by a bimetallic lanthanide-organic framework, Sens. Actuator B-Chem. 265 (2018) 104–109, https://doi.org/10.1016/j.snb.2018.03.028. Y. Pan, H.-Q. Su, E.-L. Zhou, H.-Z. Yin, K.-Z. Shao, Z.-M. Su, A stable mixed lanthanide metal-organic framework for highly sensitive thermometry, Dalton Trans. 48 (2019) 3723–3729, https://doi.org/10.1039/c9dt00217k. Y. Li, Z. Wang, T. Xia, H. Ju, K. Zhang, R. Long, Q. Xu, C. Wang, L. Song, J. Zhu, J. Jiang, Y. Xiong, Implementing metal-to-ligand charge transfer in organic semiconductor for improved visible-near-infrared Photocatalysis, Adv. Mater. 28 (2016) 6959–6965, https://doi.org/10.1002/adma.201601960. S.M. Barrett, C. Wang, W. Lin, Oxygen sensing via phosphorescence quenching of doped metal-organic frameworks, J. Mater. Chem. 22 (2012) 10329–10334, https://doi.org/10.1039/c2jm15549d. R. Sen, S. Koner, A. Bhattacharjee, J. Kusz, Y. Miyashita, K.-I. Okamoto, Entrapment of [Ru(bpy)3]2+ in the anionic metal–organic framework: Novel photoluminescence behavior exhibiting dual emission at room temperature, Dalton Trans. 40 (2011) 6952–6960, https://doi.org/10.1039/c0dt01647k. Z. Hu, B.J. Deibert, J. Li, Luminescent metal-organic frameworks for chemical sensing and explosive detection, Chem. Soc. Rev. 43 (2014) 5815–5840, https://doi.org/10.1039/c4cs00010b. C.M. Nagaraja, B. Ugale, Self-assembled coordination polymers of Zn(II): Syntheses, structural diversity, luminescence properties and base catalysis, Polyhedron 155 (2018) 433–440, https://doi.org/10.1016/j.poly.2018.09.002. S.-Y. Zhu, B. Yan, A novel covalent post-synthetically modified MOF hybrid as a sensitive and selective fluorescent probe for Al3+ detection in aqueous media, Dalton Trans. 47 (2018) 1674–1681, https://doi.org/10.1039/ c7dt04266c. J. Yu, Y. Cui, H. Xu, Y. Yang, Z. Wang, B. Chen, G. Qian, Confinement of pyridinium hemicyanine dye within an anionic metal-organic framework for two-photon-pumped lasing, Nat. Commun. 4 (2013) 2719, https://doi.org/ 10.1038/ncomms3719. H.-R. Fu, L.-B. Yan, N.-T. Wu, L.-F. Ma, S.-Q. Zang, Dual-emission MOFdye sensor for ratiometric fluorescence recognition of RDX and detection of a broad class of nitro-compounds, J. Mater. Chem. A 6 (2018) 9183–9191, https://doi.org/10.1039/c8ta02857e. D.-M. Chen, N.-N. Zhang, C.-S. Liu, M. Du, Dual-emitting dye@MOF composite as a self-calibrating sensor for 2,4,6-trinitrophenol, ACS Appl. Mater. Interfaces 9 (2017) 24671–24677, https://doi.org/10.1021/acsami.7b07901. D. Zhao, D. Yue, K. Jiang, Y. Cui, Q. Zhang, Y. Yang, G. Qian, Ratiometric dualemitting MOFdye thermometers with a tunable operating range and sensitivity, J. Mater. Chem. C 5 (2017) 1607–1613, https://doi.org/10.1039/ c6tc05203g. X. Sun, Y. Liu, G. Shaw, A. Carrier, S. Dey, J. Zhao, Y. Lei, Fundamental study of electrospun pyrene-polyethersulfone nanofibers using mixed solvents for sensitive and selective explosives detection in aqueous solution, ACS Appl. Mater. Interfaces. 7 (2015) 13189–13197, https://doi.org/10.1021/ acsami.5b03655. S. Jin, H.-J. Son, O.K. Farha, G.P. Wiederrecht, J.T. Hupp, Energy transfer from quantum dots to metal-organic frameworks for enhanced light harvesting, J. Am. Chem. Soc. 135 (2013) 955–958, https://doi.org/10.1021/ja3097114. Y. Zhao, G. Zhang, Z. Liu, C. Guo, C. Peng, M. Pei, P. Li, Benzimidazo [2,1-a]benz [de]isoquinoline-7-one-12-carboxylic acid based fluorescent sensors for pH and Fe3+, J. Photochem. Photobiol. A-Chem. 314 (2016) 52–59, https://doi.org/ 10.1016/j.jphotochem.2015.08.003. X. Wu, Q. Niu, T. Li, A novel urea-based ‘‘turn-on” fluorescent sensor for detection of Fe3+/F- ions with high selectivity and sensitivity, Sens. Actuator B-Chem. 222 (2016) 714–720, https://doi.org/10.1016/j.snb.2015.08.097. S. Joshi, S. Kumari, R. Bhattacharjee, A. Sarmah, R. Sakhuja, D.D. Pant, Experimental and theoretical study: Determination of dipole moment of synthesized coumarin-triazole derivatives and application as turn off fluorescence sensor: High sensitivity for iron(III) ions, Sens. Actuator BChem. 220 (2015) 1266–1278, https://doi.org/10.1016/j.snb.2015.07.053. S. Bhattacharyya, A. Chakraborty, K. Jayaramulu, A. Hazra, T.K. Maji, A bimodal anionic MOF: turn-off sensing of CuII and specific sensitization of EuIII, Chem. Commun. 50 (2014) 13567–13570, https://doi.org/10.1039/ c4cc05991c. L. Wang, G. Fang, D. Cao, A novel phenol-based BODIPY chemosensor for selective detection Fe3+ with colorimetric and fluorometric dual-mode, Sens. Actuator B-Chem. 207 (2015) 849–857, https://doi.org/10.1016/j. snb.2014.10.110.

23

[52] J.-C. Qin, Z.-Y. Yang, G.-Q. Wang, A novel ratiometric fluorescent probe for detection of Fe3+ by rhodamine-quinoline conjugate, J. Photochem. Photobiol. A-Chem. 310 (2015) 122–127, https://doi.org/10.1016/j. jphotochem.2015.05.010. [53] N.B. Shustova, A.F. Cozzolino, M. Dinca, Conformational locking by design: relating strain energy with luminescence and stability in rigid metal-organic frameworks, J. Am. Chem. Soc. 134 (2012) 19596–19599, https://doi.org/ 10.1021/ja3103154. [54] H. Xu, X. Rao, J. Gao, J. Yu, Z. Wang, Z. Dou, Y. Cui, Y. Yang, B. Chen, G. Qian, A luminescent nanoscale metal-organic framework with controllable morphologies for spore detection, Chem. Commun. 48 (2012) 7377–7379, https://doi.org/10.1039/c2cc32346j. [55] Y. Li, S. Zhang, D. Song, a luminescent metal-organic framework as a turn-on sensor for DMF vapor, Angew. Chem.-Int. Edit. 52 (2013) 710–713, https:// doi.org/10.1002/anie.201207610. [56] E.M. Nolan, S.J. Lippard, Tools and tactics for the optical detection of mercuric ion, Chem. Rev. 108 (2008) 3443–3480, https://doi.org/10.1021/cr068000q. [57] X.-Y. Xu, B. Yan, Fabrication and application of a ratiometric and colorimetric fluorescent probe for Hg2+ based on dual-emissive metal-organic framework hybrids with carbon dots and Eu3+, J. Mater. Chem. C 4 (2016) 1543–1549, https://doi.org/10.1039/c5tc04002g. [58] Y. Cui, R. Song, J. Yu, M. Liu, Z. Wang, C. Wu, Y. Yang, Z. Wang, B. Chen, G. Qian, Dual-emitting MOFDye composite for ratiometric temperature sensing, Adv. Mater. 27 (2015) 1420–1425, https://doi.org/10.1002/adma.201404700. [59] Y. Wang, J. He, M. Zheng, M. Qin, W. Wei, Dual-emission of Eu based metalorganic frameworks hybrids with carbon dots for ratiometric fluorescent detection of Cr(VI), Talanta 191 (2019) 519–525, https://doi.org/10.1016/ j.talanta.2018.08.078. [60] M. Jin, Z.-L. Mou, R.-L. Zhang, S.-S. Liang, Z.-Q. Zhang, An efficient ratiometric fluorescence sensor based on metal-organic frameworks and quantum dots for highly selective detection of 6-mercaptopurine, Biosens. Bioelectron. 91 (2017) 162–168, https://doi.org/10.1016/j.bios.2016.12.022. [61] W. Zhang, X. Wang, Y. Wu, Z. Qi, R. Yang, Lanthanide-benzophenone-3,3’disulfonyl-4,4’-dicarboxylate frameworks: temperature and 1-hydroxypyren luminescence sensing and proton conduction, Inorg. Chem. 57 (2018) 3883– 3892, https://doi.org/10.1021/acs.inorgchem.8b00865. [62] J. Gao, C. Wang, H. Tan, Dual-emissive polystyrene@zeolitic imidazolate framework-8 composite for ratiometric detection of singlet oxygen, J. Mat. Chem. B. 5 (2017) 9175–9182, https://doi.org/10.1039/c7tb02684f. [63] Y. Cue, F. Chen, X.-B. Yin, A ratiometric fluorescence platform based on boricacid-functional Eu-MOF for sensitive detection of H2O2 and glucose, Biosens. Bioelectron. 135 (2019) 208–215, https://doi.org/10.1016/j.bios.2019.04.008. [64] L. Li, J. Cheng, Z. Liu, L. Song, Y. You, X. Zhou, W. Huang, Ratiometric luminescent sensor of picric acid based on the dual-emission mixedlanthanide coordination polymer, ACS Appl. Mater. Interfaces 10 (2018) 44109–44115, https://doi.org/10.1021/acsami.8b13719. [65] W. Liu, X. Dai, Y. Wang, L. Song, L. Zhang, D. Zhang, J. Xie, L. Chen, D. Juan, J. Wang, Z. Chai, S. Wang, Ratiometric monitoring of thorium contamination in natural water using a dual-emission luminescent europium organic framework, Environ. Sci. Technol. 53 (2019) 332–341, https://doi.org/ 10.1021/acs.est.8b04728. [66] J. Rocha, L.D. Carlos, F.A. Almeida Paz, D. Ananias, Luminescent multifunctional lanthanides-based metal-organic frameworks, Chem. Soc. Rev. 40 (2011) 926–940, https://doi.org/10.1039/c0cs00130a. [67] S. Petoud, S.M. Cohen, J.C.G. Bunzli, K.N. Raymond, Stable lanthanide luminescence agents highly emissive in aqueous solution: Multidentate 2hydroxyisophthalamide complexes of SM3+, Eu3+, Tb3+, Dy3+, J. Am. Chem. Soc. 125 (2003) 13324–13325, https://doi.org/10.1021/ja0379363. [68] M.H.V. Werts, R.T.F. Jukes, J.W. Verhoeven, The emission spectrum and the radiative lifetime of Eu3+ in luminescent lanthanide complexes, PCCP 4 (2002) 1542–1548, https://doi.org/10.1039/b107770h. [69] J. Zhou, H. Li, H. Zhang, H. Li, W. Shi, P. Cheng, A bimetallic lanthanide metalorganic material as a self-calibrating color-gradient luminescent sensor, Adv. Mater. 27 (2015) 7072–7077, https://doi.org/10.1002/adma.201502760. [70] K. Miyata, Y. Konno, T. Nakanishi, A. Kobayashi, M. Kato, K. Fushimi, Y. Hasegawa, Chameleon luminophore for sensing temperatures: control of metal-to-metal and energy back transfer in lanthanide coordination polymers, Angew. Chem.-Int. Edit. 52 (2013) 6413–6416, https://doi.org/ 10.1002/anie.201301448. [71] B. Li, W. Wang, Z. Hong, E.-S.M. El-Sayed, D. Yuan, Ratiometric fluorescence detection of trace water in an organic solvent based on bimetallic lanthanide metal-organic frameworks, Chem. Commun. 55 (2019) 6926–6929, https:// doi.org/10.1039/c9cc02324k. [72] X. Feng, R. Li, L. Wang, S.W. Ng, G. Qin, L. Ma, A series of homonuclear lanthanide coordination polymers based on a fluorescent conjugated ligand: syntheses, luminescence and sensor for pollutant chromate anion, CrystEngComm 17 (2015) 7878–7887, https://doi.org/10.1039/c5ce01454a. [73] A. Cadiau, C.D.S. Brites, P.M.F.J. Costa, R.A.S. Ferreira, J. Rocha, L.D. Carlos, Ratiometric nanothermometer based on an emissive ln3+-organic framework, ACS Nano 7 (2013) 7213–7218, https://doi.org/10.1021/nn402608w. [74] D.-B. Dang, B. An, Y. Bai, G.-S. Zheng, J.-Y. Niu, Three-dimensional homochiral manganese-lanthanide frameworks based on chiral camphorates with multicoordination modes, Chem. Commun. 49 (2013) 2243–2245, https://doi.org/ 10.1039/c3cc37680j. [75] Y. Yang, Y. Zhang, C.J. Sun, X. Li, W. Zhang, X. Ma, Y. Ren, X. Zhang, Heterobimetallic metal-organic framework as a precursor to prepare a

24

[76]

[77]

[78]

[79]

[80]

[81]

[82] [83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

[92]

[93]

[94]

[95]

[96]

[97]

[98]

L. Chen et al. / Coordination Chemistry Reviews 404 (2020) 213113 nickel/nanoporous carbon composite catalyst for 4-nitrophenol reduction, ChemCatChem 6 (2014) 3084–3090, https://doi.org/10.1002/cctc.201402607. N.-N. Sun, B. Yan, Rapid and facile ratiometric detection of CO23 based on heterobimetallic metal-organic frameworks (Eu/Pt-MOFs), Dyes Pigment. 142 (2017) 1–7, https://doi.org/10.1016/j.dyepig.2017.03.014. J.-N. Hao, B. Yan, A dual-emitting 4d–4f nanocrystalline metal-organic framework as a self-calibrating luminescent sensor for indoor formaldehyde pollution, Nanoscale 8 (2016) 12047–12053, https://doi.org/ 10.1039/c6nr02446g. N.-N. Sun, B. Yan, A fluorescent probe based on a Tb3+/Cu2+ co-functionalized MOF for urinary sarcosine detection, Analyst. 143 (2018) 2349–2355, https:// doi.org/10.1039/c8an00425k. S. Wu, Y. Lin, J. Liu, W. Shi, G. Yang, P. Cheng, Rapid detection of the biomarkers for carcinoid tumors by a water stable luminescent lanthanide metal-organic framework sensor, Adv. Funct. Mater. 28 (2018) 1707169, https://doi.org/10.1002/adfm.201707169. S.-J. Qin, B. Yan, The point-of-care colorimetric detection of the biomarker of phenylamine in the human urine based on Tb3+ functionalized metal-organic framework, Anal. Chim. Acta 1012 (2018) 82–89, https://doi.org/10.1016/j. aca.2018.01.041. S.-Z. Zhan, M. Li, X.-P. Zhou, J.-H. Wang, J.-R. Yang, D. Li, When Cu4I4 cubane meets Cu3(pyrazolate)3 triangle: dynamic interplay between two classical luminophores functioning in a reversibly thermochromic coordination polymer, Chem. Commun. 47 (2011) 12441–12443, https://doi.org/10.1039/ c1cc14303d. R. Custelcean, Anions in crystal engineering, Chem. Soc. Rev. 39 (2010) 3675– 3685, https://doi.org/10.1039/b926221k. W.L. Leong, J.J. Vittal, One-dimensional coordination polymers: complexity and diversity in structures, properties, and applications, Chem. Rev. 111 (2011) 688–764, https://doi.org/10.1021/cr100160e. S.-Y. Liao, W. Gu, L.-Y. Yang, T.-H. Li, J.-L. Tian, L. Wang, M. Zhang, X. Liu, Series of novel 3D heterometallic frameworks based on the Co(II) coordination chains and Ln(III) coordination layers, Cryst. Growth Des. 12 (2012) 3927– 3936, https://doi.org/10.1021/cg300326e. E.A. Dolgopolova, A.M. Rice, C.R. Martin, N.B. Shustova, Photochemistry and photophysics of MOFs: steps towards MOF-based sensing enhancements, Chem. Soc. Rev. 47 (2018) 4710–4728, https://doi.org/10.1039/c7cs00861a. C.E. Housecroft, 4,2’:6’,4‘‘-Terpyridines: diverging and diverse building blocks in coordination polymers and metallomacrocycles, Dalton Trans. 43 (2014) 6594–6604, https://doi.org/10.1039/c4dt00074a. Y.-L. Wei, Y. Li, Y.-Q. Chen, Y. Dong, J.-J. Yao, X.-Y. Han, Y.-B. Dong, Pd(II)NHDC-functionalized UiO-67 Type MOF for catalyzing heck cross-coupling and intermolecular benzyne-benzyne-alkene insertion reactions, Inorg. Chem. 57 (2018) 4379–4386, https://doi.org/10.1021/acs. inorgchem.7b03271. H. Xu, Y. Dong, Y. Wu, W. Ren, T. Zhao, S. Wang, J. Gao, An -OH group functionalized MOF for ratiometric Fe3+ sensing, J. Solid State Chem. 258 (2018) 441–446, https://doi.org/10.1016/j.jssc.2017.11.013. Q. Du, P. Wu, P. Dramou, R. Chen, H. He, One-step fabrication of a boric acidfunctionalized lanthanide metal-organic framework as a ratiometric fluorescence sensor for the selective recognition of dopamine, New J. Chem. 43 (2019) 1291–1298, https://doi.org/10.1039/c8nj05318a. H. Wang, D. Zhao, Y. Cui, Y. Yang, G. Qian, A Eu/Tb-mixed MOF for luminescent high-temperature sensing, J. Solid State Chem. 246 (2017) 341–345, https://doi.org/10.1016/j.jssc.2016.12.003. J.E. Kwon, S.Y. Park, Advanced organic optoelectronic materials: harnessing excited-state intramolecular proton transfer (ESIPT) process, Adv. Mater. 23 (2011) 3615–3642, https://doi.org/10.1002/adma.201102046. B. Bhattacharya, A. Halder, L. Paul, S. Chakrabarti, D. Ghoshal, Eye-catching dual-fluorescent dynamic metal-organic framework senses traces of water: experimental findings and theoretical correlation, Chem.-Eur. J. 22 (2016) 14998–15005, https://doi.org/10.1002/chem.201602322. W.-Q. Zhang, Q.-Y. Li, J.-Y. Cheng, K. Cheng, X. Yang, Y. Li, X. Zhao, X.-J. Wang, Ratiometric luminescent detection of organic amines due to the induced lactam-lactim tautomerization of organic linker in a metal-organic framework, ACS Appl. Mater. Interfaces 9 (2017) 31352–31356, https://doi. org/10.1021/acsami.7b11125. Z. Shi, L. Li, Y. Xiao, Y. Wang, K. Sun, H. Wang, L. Liu, Synthesis of mixed-ligand Cu-MOFs and their adsorption of malachite green, RSC Adv. 7 (2017) 30904– 30910, https://doi.org/10.1039/c7ra04820c. J.-S. Hu, X.-Q. Yao, M.-D. Zhang, L. Qin, Y.-Z. Li, Z.-J. Guo, H.-G. Zheng, Z.-L. Xue, Syntheses, structures, and characteristics of four new metal-organic frameworks based on flexible tetrapyridines and aromatic polycarboxylate acids, Cryst. Growth Des. 12 (2012) 3426–3435, https://doi.org/10.1021/ cg201362x. Y. Gong, T. Wu, P.G. Jiang, J.H. Lin, Y.X. Yang, Octamolybdate-based metalorganic framework with unsaturated coordinated metal center as electrocatalyst for generating hydrogen from water, Inorg. Chem. 52 (2013) 777–784, https://doi.org/10.1021/ic3018858. D. Wang, Z. Hu, S. Xu, D. Li, Q. Zhang, W. Ma, H. Zhou, J. Wu, Y. Tian, Fluorescent metal-organic frameworks based on mixed organic ligands: new candidates for highly sensitive detection of TNP, Dalton Trans. 48 (2019) 1900–1905, https://doi.org/10.1039/c8dt03811b. J. Bitzer, W. Kleist, Synthetic strategies and structural arrangements of isoreticular mixed-component metal-organic frameworks, Chem.-Eur. J. 25 (2019) 1866–1882, https://doi.org/10.1002/chem.201803887.

[99] N. Lin, Q. Zhang, X. Xia, M. Liang, S. Zhang, L. Zheng, Q. Cao, Z. Ding, A highly zinc-selective ratiometric fluorescent probe based on AIE luminogen functionalized coordination polymer nanoparticles, RSC Adv. 7 (2017) 21446–21451, https://doi.org/10.1039/c6ra28551a. [100] J.-X. Wu, B. Yan, Visible detection of copper ions using a fluorescent probe based on red carbon dots and zirconium metal-organic frameworks, Dalton Trans. 46 (2017) 15080–15086, https://doi.org/10.1039/c7dt03393a. [101] X. Lin, G. Gao, L. Zheng, Y. Chi, G. Chen, Encapsulation of strongly fluorescent carbon quantum dots in metal- organic frameworks for enhancing chemical sensing, Anal. Chem. 86 (2014) 1223–1228, https://doi.org/10.1021/ ac403536a. [102] T. Wehner, M.T. Seuffert, J.R. Sorg, M. Schneider, K. Mandel, G. Sextl, K. Mueller-Buschbaum, Composite materials combining multiple luminescent MOFs and superparamagnetic microparticles for ratiometric water detection, J. Mater. Chem. C 5 (2017) 10133–10142, https://doi.org/10.1039/ c7tc03312e. [103] Q.L. Zhu, Q. Xu, Metal-organic framework composites, Chem. Soc. Rev. 43 (2014) 5468–5512, https://doi.org/10.1039/c3cs60472a. [104] J. Yu, Y. Cui, C. Wu, Y. Yang, Z. Wang, M. O’Keeffe, B. Chen, G. Qian, Secondorder nonlinear optical activity induced by ordered dipolar chromophores confined in the pores of an anionic metal-organic framework, Angew. Chem.-Int. Edit. 51 (2012) 10542–10545, https://doi.org/10.1002/ anie.201204160. [105] Z. Dou, J. Yu, Y. Cui, Y. Yang, Z. Wang, D. Yang, G. Qian, Luminescent metalorganic framework films as highly sensitive and fast-response oxygen sensors, J. Am. Chem. Soc. 136 (2014) 5527–5530, https://doi.org/ 10.1021/ja411224j. [106] B. Chen, Porous metal-organic framework materials for gas storage and separation, Abstracts Papers Am. Chem. Soc. 253 (2017). [107] M. Eddaoudi, D. Alezi, Y. Belmabkhout, Made-to-order metal-organic frameworks for gas capture and storage, Abstracts Papers Am. Chem. Soc. 253 (2017). [108] O. Farha, Metal-organic frameworks (MOFs): Design, preparation and gas storage, Abstracts Papers Am. Chem. Soc. 254 (2017). [109] Z.-G. Gu, A. Pfriem, S. Hamsch, H. Breitwieser, J. Wohlgemuth, L. Heinke, H. Gliemann, C. Woell, Transparent films of metal-organic frameworks for optical applications, Microporous Mesoporous Mat. 211 (2015) 82–87, https://doi.org/10.1016/j.micromeso.2015.02.048. [110] C. Wang, K.E. deKrafft, W. Lin, Pt nanoparticles@photoactive metal-organic frameworks: efficient hydrogen evolution via synergistic photoexcitation and electron injection, J. Am. Chem. Soc. 134 (2012) 7211–7214, https://doi.org/ 10.1021/ja300539p. [111] H.-N. Wang, F.-H. Liu, X.-L. Wang, K.-Z. Shao, Z.-M. Su, Three neutral metalorganic frameworks with micro- and meso-pores for adsorption and separation of dyes, J. Mater. Chem. A 1 (2013) 13060–13063, https://doi. org/10.1039/c3ta13242k. [112] K. Mizusawa, Y. Takaoka, I. Hamachi, Specific cell surface protein imaging by extended self-assembling fluorescent turn-on nanoprobes, J. Am. Chem. Soc. 134 (2012) 13386–13395, https://doi.org/10.1021/ja304239g. [113] K. Mizusawa, Y. Ishida, Y. Takaoka, M. Miyagawa, S. Tsukiji, I. Hamachi, Disassembly-driven turn-on fluorescent nanoprobes for selective protein detection, J. Am. Chem. Soc. 132 (2010) 7291–7293, https://doi.org/ 10.1021/ja101879g. [114] T.M. Figueira-Duarte, K. Muellen, Pyrene-based materials for organic electronics, Chem. Rev. 111 (2011) 7260–7314, https://doi.org/10.1021/ cr100428a. [115] H.R. Fu, Z.X. Xu, J. Zhang, Water-stable metal-organic frameworks for fast and high dichromate trapping via single-crystal-to-single-crystal ion exchange, Chem. Mat. 27 (2015) 205–210, https://doi.org/10.1021/cm503767r. [116] H.-R. Fu, X.-X. Wu, L.-F. Ma, F. Wang, J. Zhang, Dual-emission SG7@MOF sensor via SC-SC transformation: enhancing the formation of excimer emission and the range and sensitivity of detection, ACS Appl. Mater. Interfaces 10 (2018) 18012–18020, https://doi.org/10.1021/acsami.8b05614. [117] L. Jia, S. Guo, J. Xu, X. Chen, T. Zhu, T. Zhao, A ratiometric fluorescent nanoprobe for rapid and specific detection of tetracycline residues based on a dyedoped functionalized nanoscaled metal-organic framework, Nanomaterials (Basel, Switzerland) 9 (2019), https://doi.org/10.3390/nano9070976. [118] Z. Ding, C. Wang, S. Wang, L. Wu, X. Zhang, Light-harvesting metal-organic framework nanoprobes for ratiometric fluorescence energy transfer-based determination of pH values and temperature, Microchim. Acta 186 (2019), https://doi.org/10.1007/s00604-019-3608-1. [119] Z. Sun, Y. Ling, S.G. Liu, Y.Z. Yang, X.H. Wang, Y.Z. Fan, N.B. Li, H.Q. Luo, Metalorganic framework as a chemosensor based on luminescence properties for monitoring cetyltrimethylammonium bromide and its application in smartphones, Inorg. Chem. 58 (2019) 8388–8395, https://doi.org/10.1021/ acs.inorgchem.9b00470. [120] B.H. Wang, B. Yan, A dye@MOF crystalline probe serving as a platform for ratiometric sensing of trichloroacetic acid (TCA), a carcinogen metabolite in human urine, CrystEngComm 21 (2019) 4637–4643, https://doi.org/10.1039/ c9ce00924h. [121] A.R. Clapp, I.L. Medintz, J.M. Mauro, B.R. Fisher, M.G. Bawendi, H. Mattoussi, Fluorescence resonance energy transfer between quantum dot donors and dye-labeled protein acceptors, J. Am. Chem. Soc. 126 (2004) 301–310, https:// doi.org/10.1021/ja037088b. [122] D. Yan, Y. Tang, H. Lin, D. Wang, Tunable two-color luminescence and hostguest energy transfer of fluorescent chromophores encapsulated in metal-

L. Chen et al. / Coordination Chemistry Reviews 404 (2020) 213113

[123]

[124]

[125]

[126]

[127]

[128]

[129]

[130]

[131]

[132]

[133]

[134]

[135]

[136]

[137]

[138]

[139]

[140]

[141]

[142]

[143]

[144]

[145]

organic frameworks, Sci. Rep. 4 (2014) 4337, https://doi.org/10.1038/ srep04337. D. Esken, S. Turner, C. Wiktor, S.B. Kalidindi, G. Van Tendeloo, R.A. Fischer, GaN@ZIF-8: selective formation of gallium nitride quantum dots inside a zinc methylimidazolate framework, J. Am. Chem. Soc. 133 (2011) 16370–16373, https://doi.org/10.1021/ja207077u. L. Chen, R. Luque, Y. Li, Controllable design of tunable nanostructures inside metal-organic frameworks, Chem. Soc. Rev. 46 (2017) 4614–4630, https:// doi.org/10.1039/c6cs00537c. K. Wang, N. Li, J. Zhang, Z. Zhang, F. Dang, Size-selective QD@MOF core-shell nanocomposites for the highly sensitive monitoring of oxidase activities, Biosens. Bioelectron. 87 (2017) 339–344, https://doi.org/10.1016/j. bios.2016.08.026. M. Jahan, Q. Bao, K.P. Loh, Electrocatalytically active graphene-porphyrin MOF composite for oxygen reduction reaction, J. Am. Chem. Soc. 134 (2012) 6707–6713, https://doi.org/10.1021/ja211433h. D. Alezi, Y. Belmabkhout, M. Suyetin, P.M. Bhatt, L.J. Weselinski, V. Solovyeva, K. Adil, I. Spanopoulos, P.N. Trikalitis, A.-H. Emwas, M. Eddaoudi, MOF crystal chemistry paving the way to gas storage needs: aluminum-based soc-MOF for CH4, O2, and CO2 storage, J. Am. Chem. Soc. 137 (2015) 13308–13318, https://doi.org/10.1021/jacs.5b07053. A. Ibrahim, Y.S. Lin, Pervaporation separation of organic mixtures by MOF-5 membranes, Ind. Eng. Chem. Res. 55 (2016) 8652–8658, https://doi.org/ 10.1021/acs.iecr.6b01965. K. Shen, X. Chen, J. Chen, Y. Li, Development of MOF-derived carbon-based nanomaterials for efficient catalysis, ACS Catal. 6 (2016) 5887–5903, https:// doi.org/10.1021/acscatal.6b01222. C.P. Xu, R.Q. Fang, R. Luque, L.Y. Chen, Y.W. Li, Functional metal-organic frameworks for catalytic applications, Coord. Chem. Rev. 388 (2019) 268– 292, https://doi.org/10.1016/j.ccr.2019.03.005. J.-J. Liu, Y.-B. Shan, C.-R. Fan, M.-J. Lin, C.-C. Huang, W.-X. Dai, Encapsulating naphthalene in an electron-deficient MOF to enhance fluorescence for organic amines sensing, Inorg. Chem. 55 (2016) 3680–3684, https://doi.org/ 10.1021/acs.inorgchem.6b00252. M.H. Teplerisky, M. Fantham, P. Li, T.C. Wang, J.P. Mehta, L.J. Young, P.Z. Moghadam, J.T. Hupp, O.K. Farha, C.F. Kaminski, D. Fairen-Jimenez, Temperature treatment of highly porous zirconium-containing metalorganic frameworks extends drug delivery release, J. Am. Chem. Soc. 139 (2017) 7522–7532, https://doi.org/10.1021/jacs.7b01451. J. Liu, J. Liu, W. Liu, H. Zhang, Z. Yang, B. Wang, F. Chen, H. Chen, Tripleemitting dumbbell fluorescent nanoprobe for multicolor detection and imaging applications, Inorg. Chem. 54 (2015) 7725–7734, https://doi.org/ 10.1021/acs.inorgchem.5b00610. A. Zhu, Q. Qu, X. Shao, B. Kong, Y. Tian, Carbon-dot-based dual-emission nanohybrid produces a ratiometric fluorescent sensor for in vivo imaging of cellular copper ions, Angew. Chem.-Int. Edit. 51 (2012) 7185–7189, https:// doi.org/10.1002/anie.201109089. J. Shi, C. Chan, Y. Pang, W. Ye, F. Tian, J. Lyu, Y. Zhang, M. Yang, A fluorescence resonance energy transfer (FRET) biosensor based on graphene quantum dots (GQDs) and gold nanoparticles (AuNPs) for the detection of mecA gene sequence of Staphylococcus aureus, Biosens. Bioelectron. 67 (2015) 595–600, https://doi.org/10.1016/j.bios.2014.09.059. K. Cai, M. Zeng, F. Liu, N. Liu, Z. Huang, Y. Song, L. Wang, BSA-AuNPs@Tb-AMP metal-organic frameworks for ratiometric fluorescence detection of DPA and Hg2+, Luminescence 32 (2017) 1277–1282, https://doi.org/10.1002/bio.3321. R. Jin, Atomically precise metal nanoclusters: stable sizes and optical properties, Nanoscale 7 (2015) 1549–1565, https://doi.org/10.1039/ c4nr05794e. Z. Luo, K. Zheng, J. Xie, Engineering ultrasmall water-soluble gold and silver nanoclusters for biomedical applications, Chem. Commun. 50 (2014) 5143– 5155, https://doi.org/10.1039/c3cc47512c. S. Choi, R.M. Dickson, J. Yu, Developing luminescent silver nanodots for biological applications, Chem. Soc. Rev. 41 (2012) 1867–1891, https://doi. org/10.1039/c1cs15226b. C. Dai, C.-X. Yang, X.-P. Yan, Ratiometric fluorescent detection of phosphate in aqueous solution based on near infrared fluorescent silver nanoclusters/ metal-organic shell composite, Anal. Chem. 87 (2015) 11455–11459, https:// doi.org/10.1021/acs.analchem.5b03086. H. Khajavi, H.A. Stil, H.P.C.E. Kuipers, J. Gascon, F. Kapteijn, Shape and transition state selective hydrogenations using egg-shell Pt-MIL-101(Cr) catalyst, ACS Catal. 3 (2013) 2617–2626, https://doi.org/10.1021/ cs400681s. C. Hou, G. Zhao, Y. Ji, Z. Niu, D. Wang, Y. Li, Hydroformylation of alkenes over rhodium supported on the metal-organic framework ZIF-8, Nano Res. 7 (2014) 1364–1369, https://doi.org/10.1007/s12274-014-0501-4. J. Yang, F. Zhang, H. Lu, X. Hong, H. Jiang, Y. Wu, Y. Li, Hollow Zn/Co ZIF particles derived from core-shell ZIF-67@ZIF-8 as selective catalyst for the semi-hydrogenation of acetylene, Angew. Chem.-Int. Edit. 54 (2015) 10889– 10893, https://doi.org/10.1002/anie.201504242. C. Fan, X. Lv, F. Liu, L. Feng, M. Liu, Y. Cai, H. Liu, J. Wang, Y. Yang, H. Wang, Silver nanoclusters encapsulated into metal-organic frameworks with enhanced fluorescence and specific ion accumulation toward the microdot array-based fluorimetric analysis of copper in blood, ACS Sens. 3 (2018) 441– 450, https://doi.org/10.1021/acssensors.7b00874. J. Zhou, Y. Yang, C.-Y. Zhang, Toward biocompatible semiconductor quantum dots: from biosynthesis and bioconjugation to biomedical application, Chem.

[146]

[147]

[148]

[149]

[150]

[151]

[152]

[153]

[154]

[155]

[156]

[157]

[158]

[159]

[160]

[161]

[162]

[163]

[164]

[165]

[166]

[167]

[168]

25

Rev. 115 (2015) 11669–11717, https://doi.org/10.1021/acs. chemrev.5b00049. G. Xu, S. Zeng, B. Zhang, M.T. Swihart, K.-T. Yong, P.N. Prasad, New generation cadmium-free quantum dots for biophotonics and nanomedicine, Chem. Rev. 116 (2016) 12234–12327, https://doi.org/10.1021/acs.chemrev.6b00290. Z. Su, H. Shen, H. Wang, J. Wang, J. Li, G.U. Nienhaus, L. Shang, G. Wei, Motifdesigned peptide nanofibers decorated with graphene quantum dots for simultaneous targeting and imaging of tumor cells, Adv. Funct. Mater. 25 (2015) 5472–5478, https://doi.org/10.1002/adfm.201502506. L. Jing, S.V. Kershaw, Y. Li, X. Huang, Y. Li, A.L. Rogach, M. Gao, Aqueous based semiconductor nanocrystals, Chem. Rev. 116 (2016) 10623–10730, https:// doi.org/10.1021/acs.chemrev.6b00041. L. Cui, C.-C. Li, B. Tang, C.-Y. Zhang, Advances in the integration of quantum dots with various nanomaterials for biomedical and environmental applications, Analyst. 143 (2018) 2469–2478, https://doi.org/10.1039/ c8an00222c. H.X. Fu, A. Zunger, InP quantum dots: electronic structure, surface effects, and the redshifted emission, Phys. Rev. B. 56 (1997) 1496–1508, https://doi. org/10.1103/PhysRevB.56.1496. D.V. Talapin, A.L. Rogach, A. Kornowski, M. Haase, H. Weller, Highly luminescent monodisperse CdSe and CdSe/ZnS nanocrystals synthesized in a hexadecylamine-trioctylphosphine oxide-trioctylphospine mixture, Nano Lett. 1 (2001) 207–211, https://doi.org/10.1021/nl0155126. J. Aguilera-Sigalat, D. Bradshaw, Synthesis and applications of metal-organic framework-quantum dot (QD@MOF) composites, Coord. Chem. Rev. 307 (2016) 267–291, https://doi.org/10.1016/j.ccr.2015.08.004. Z. Long, J. Jia, S. Wang, L. Kou, X. Hou, M.J. Sepaniak, Visual enantioselective probe based on metal organic framework incorporating quantum dots, Microchem. J. 110 (2013) 764–769, https://doi.org/10.1016/j. microc.2013.08.013. S. Saha, G. Das, J. Thote, R. Banerjee, Photocatalytic metal-organic framework from CdS quantum dot incubated luminescent metallohydrogel, J. Am. Chem. Soc. 136 (2014) 14845–14851, https://doi.org/10.1021/ja509019k. G. Lu, S. Li, Z. Guo, O.K. Farha, B.G. Hauser, X. Qi, Y. Wang, X. Wang, S. Han, X. Liu, J.S. DuChene, H. Zhang, Q. Zhang, X. Chen, J. Ma, S.C.J. Loo, W.D. Wei, Y. Yang, J.T. Hupp, F. Huo, Imparting functionality to a metal-organic framework material by controlled nanoparticle encapsulation, Nat. Chem. 4 (2012) 310– 316, https://doi.org/10.1038/nchem.1272. J. Li, X. Li, X. Shi, X. He, W. Wei, N. Ma, H. Chen, Highly sensitive detection of caspase-3 activities via a nonconjugated gold nanoparticle-quantum dot pair mediated by an inner-filter effect, ACS Appl. Mater. Interfaces 5 (2013) 9798– 9802, https://doi.org/10.1021/am4029735. C. Frigerio, V. Abreu, J.L.M. Santos, Evaluation of acetylcysteine promoting effect on CdTe nanocrystals photoluminescence by using a multipumping flow system, Talanta 96 (2012) 55–61, https://doi.org/10.1016/ j.talanta.2012.02.002. Z. Sun, Y. Liu, Y. Li, Selective recognition of 6-mercaptopurine based on luminescent metal-organic frameworks Fe-MIL-88NH2, Spectroc. Acta Pt. AMolec. Biomolec. Spectr. 139 (2015) 296–301, https://doi.org/10.1016/j. saa.2014.12.009. P. Zuo, X. Lu, Z. Sun, Y. Guo, H. He, A review on syntheses, properties, characterization and bioanalytical applications of fluorescent carbon dots, Microchim. Acta 183 (2016) 519–542, https://doi.org/10.1007/s00604-0151705-3. S.N. Baker, G.A. Baker, Luminescent carbon nanodots: emergent nanolights, Angew. Chem.-Int. Edit. 49 (2010) 6726–6744, https://doi.org/10.1002/ anie.200906623. S. Li, D. Xiao, D. Liu, H. He, Calcium-doped fluorescent carbon nanoparticles: Spontaneous thermal synthesis, pH-sensitive fluorescence off-on, and mechanism, Sens. Actuator B-Chem. 266 (2018) 594–602, https://doi.org/ 10.1016/j.snb.2018.02.142. P. Zhang, X. Zhao, Y. Ji, Z. Ouyang, X. Wen, J. Li, Z. Su, G. Wei, Electrospinning graphene quantum dots into a nanofibrous membrane for dual-purpose fluorescent and electrochemical biosensors, J. Mat. Chem. B. 3 (2015) 2487– 2496, https://doi.org/10.1039/c4tb02092h. J. Shen, Y. Zhu, X. Yang, C. Li, Graphene quantum dots: emergent nanolights for bioimaging, sensors, catalysis and photovoltaic devices, Chem. Commun. 48 (2012) 3686–3699, https://doi.org/10.1039/c2cc00110a. Y. Song, K. Qu, C. Zhao, J. Ren, X. Qu, Graphene oxide: intrinsic peroxidase catalytic activity and its application to glucose detection, Adv. Mater. 22 (2010) 2206–2210, https://doi.org/10.1002/adma.200903783. B.P. Biswal, D.B. Shinde, V.K. Pillai, R. Banerjee, Stabilization of graphene quantum dots (GQDs) by encapsulation inside zeolitic imidazolate framework nanocrystals for photoluminescence tuning, Nanoscale 5 (2013) 10556–10561, https://doi.org/10.1039/c3nr03511e. H. Weng, B. Yan, N-GQDs and Eu3+ co-encapsulated anionic MOFs: twodimensional luminescent platform for decoding benzene homologues, Dalton Trans. 45 (2016) 8795–8801, https://doi.org/10.1039/c6dt00994h. M.L. Desai, S. Jha, H. Basu, R.K. Singhal, P.K. Sharma, S.K. Kailasa, Microwaveassisted synthesis of water-soluble Eu3+ hybrid carbon dots with enhanced fluorescence for the sensing of Hg2+ ions and imaging of fungal cells, New J. Chem. 42 (2018) 6125–6133, https://doi.org/10.1039/c7nj04835a. J. Hao, F. Liu, N. Liu, M. Zeng, Y. Song, L. Wang, Ratiometric fluorescent detection of Cu2+ with carbon dots chelated Eu-based metal-organic frameworks, Sens. Actuator B-Chem. 245 (2017) 641–647, https://doi.org/ 10.1016/j.snb.2017.02.029.

26

L. Chen et al. / Coordination Chemistry Reviews 404 (2020) 213113

[169] Y. Dong, J. Cai, Q. Fang, X. You, Y. Chi, Dual-emission of lanthanide metalorganic frameworks encapsulating carbon-based dots for ratiometric detection of water in organic solvents, Anal. Chem. 88 (2016) 1748–1752, https://doi.org/10.1021/acs.analchem.5b03974. [170] Y. Dong, H. Pang, H.B. Yang, C. Guo, J. Shao, Y. Chi, C.M. Li, T. Yu, Carbon-based dots co-doped with nitrogen and sulfur for high quantum yield and excitation-independent emission, Angew. Chem.-Int. Edit. 52 (2013) 7800– 7804, https://doi.org/10.1002/anie.201301114. [171] X. Fu, R. Lv, J. Su, H. Li, B. Yang, W. Gu, X. Liu, A dual-emission nano-rod MOF equipped with carbon dots for visual detection of doxycycline and sensitive sensing of MnO-4, RSC Adv. 8 (2018) 4766–4772, https://doi.org/10.1039/ c7ra12252g. [172] Y. Zhang, S. Yuan, G. Day, X. Wang, X. Yang, H.-C. Zhou, Luminescent sensors based on metal-organic frameworks, Coord. Chem. Rev. 354 (2018) 28–45, https://doi.org/10.1016/j.ccr.2017.06.007. [173] H. Furukawa, K.E. Cordova, M. O’Keeffe, O.M. Yaghi, The chemistry and applications of metal-organic frameworks, Science 341 (2013) 974–987, https://doi.org/10.1126/science.1230444. [174] R. Jalili, A. Khataee, M.R. Rashidi, R. Luque, Dual-colored carbon dot encapsulated metal-organic framework for ratiometric detection of glutathione, Sensors Actuators B-Chem. 297 (2019) 8, https://doi.org/ 10.1016/j.snb.2019.126775. [175] Y. Ma, G. Xu, F. Wei, Y. Cen, Y. Ma, Y. Song, X. Xu, M. Shi, S. Muhammad, Q. Hu, A dual-emissive fluorescent sensor fabricated by encapsulating quantum dots and carbon dots into metal-organic frameworks for the ratiometric detection of Cu2+ in tap water, J. Mater. Chem. C 5 (2017) 8566–8571, https:// doi.org/10.1039/c7tc01970j. [176] J. Wang, H. Chen, F. Ru, Z. Zhang, X. Mao, D. Shan, J. Chen, X. Lu, Encapsulation of dual-emitting fluorescent magnetic nanoprobe in metal-organic frameworks for ultrasensitive ratiometric detection of Cu2+, Chem.-Eur. J. 24 (2018) 3499–3505, https://doi.org/10.1002/chem.201704557. [177] Y. Ma, G. Xu, F. Wei, Y. Cen, X. Xu, M. Shi, X. Cheng, Y. Chai, M. Sohail, Q. Hu, One-pot synthesis of a magnetic, ratiometric fluorescent nanoprobe by encapsulating Fe3O4 magnetic nanoparticles and dual-emissive rhodamine B modified carbon dots in metal-organic framework for enhanced HClO sensing, ACS Appl. Mater. Interfaces 10 (2018) 20801–20805, https://doi. org/10.1021/acsami.8b05643. [178] K. Wang, H. Ren, N. Li, X. Tan, F. Dang, Ratiometric fluorescence sensor based on cholesterol oxidase-functionalized mesoporous silica nanoparticle@ZIF-8 core-shell nanocomposites for detection of cholesterol, Talanta 188 (2018) 708–713, https://doi.org/10.1016/j.talanta.2018.06.019. [179] L. Xu, G. Fang, J. Liu, M. Pan, R. Wang, S. Wang, One-pot synthesis of nanoscale carbon dots-embedded metal-organic frameworks at room temperature for enhanced chemical sensing, J. Mater. Chem. A 4 (2016) 15880–15887, https://doi.org/10.1039/c6ta06403e. [180] Y. Huang, Y. Zhang, X. Chen, D. Wu, Z. Yi, R. Cao, Bimetallic alloy nanocrystals encapsulated in ZIF-8 for synergistic catalysis of ethylene oxidative degradation, Chem. Commun. 50 (2014) 10115–10117, https://doi.org/ 10.1039/c4cc04479g. [181] J.-T. Yi, T.-T. Chen, J. Huo, X. Chu, Nanoscale zeolitic imidazolate framework-8 for ratiometric fluorescence imaging of MicroRNA in living cells, Anal. Chem. 89 (2017) 12351–12359, https://doi.org/10.1021/acs.analchem.7b03369. [182] C. Li, J. Huang, H. Zhu, L. Liu, Y. Feng, G. Hu, X. Yu, Dual-emitting fluorescence of Eu/Zr-MOF for ratiometric sensing formaldehyde, Sens. Actuator B-Chem. 253 (2017) 275–282, https://doi.org/10.1016/j.snb.2017.06.064. [183] P. Farger, C. Leuvrey, M. Gallart, P. Gilliot, G. Rogez, J. Rocha, D. Ananias, P. Rabu, E. Delahaye, Magnetic and luminescent coordination networks based on imidazolium salts and lanthanides for sensitive ratiometric thermometry, Beilstein J. Nanotechnol. 9 (2018) 2775–2787, https://doi.org/10.3762/ bjnano.9.259. [184] Y. Cui, F. Zhu, B. Chen, G. Qian, Metal-organic frameworks for luminescence thermometry, Chem. Commun. 51 (2015) 7420–7431, https://doi.org/ 10.1039/c5cc00718f. [185] Y. Cui, W. Zou, R. Song, J. Yu, W. Zhang, Y. Yang, G. Qian, A ratiometric and colorimetric luminescent thermometer over a wide temperature range based on a lanthanide coordination polymer, Chem. Commun. 50 (2014) 719–721, https://doi.org/10.1039/c3cc47225f. [186] D. Zhao, X. Rao, J. Yu, Y. Cui, Y. Yang, G. Qian, Design and synthesis of an MOF thermometer with high sensitivity in the physiological temperature range, Inorg. Chem. 54 (2015) 11193–11199, https://doi.org/10.1021/acs. inorgchem.5b01623. [187] M. Mitsuishi, S. Kikuchi, T. Miyashita, Y. Amao, Characterization of an ultrathin polymer optode and its application to temperature sensors based on luminescent europium complexes, J. Mater. Chem. 13 (2003) 2875–2879, https://doi.org/10.1039/b307309b. [188] Y. Cui, H. Xu, Y. Yue, Z. Guo, J. Yu, Z. Chen, J. Gao, Y. Yang, G. Qian, B. Chen, A luminescent mixed-lanthanide metal-organic framework thermometer, J. Am. Chem. Soc. 134 (2012) 3979–3982, https://doi.org/10.1021/ja2108036. [189] D. Zhao, D. Yue, K. Jiang, L. Zhang, C. Li, G. Qian, Isostructural Tb3+/Eu3+ Codoped metal organic framework based on pyridine-containing dicarboxylate ligands for ratiometric luminescence temperature sensing, Inorg. Chem. 58 (2019) 2637–2644, https://doi.org/10.1021/acs.inorgchem.8b03225. [190] Y. Hirai, T. Nakanishi, K. Miyata, K. Fushimi, Y. Hasegawa, Thermo-sensitive luminescent materials composed of Tb(III) and Eu(III) complexes, Mater. Lett. 130 (2014) 91–93, https://doi.org/10.1016/j.matlet.2014.05.074.

[191] Q. Xiao, Y. Li, F. Li, M. Zhang, Z. Zhang, H. Lin, Rational design of a thermalresponsive-polymer-switchable FRET system for enhancing the temperature sensitivity of upconversion nanophosphors, Nanoscale 6 (2014) 10179–10186, https://doi.org/10.1039/c4nr02497d. [192] J.C. Fister, D. Rank, J.M. Harris, Delayed fluorescence optical thermometry, Anal. Chem. 67 (1995) 4269–4275, https://doi.org/10.1021/ac00119a011. [193] H. Cai, W. Lu, C. Yang, M. Zhang, M. Li, C.-M. Che, D. Li, Tandem forster resonance energy transfer induced luminescent ratiometric thermometry in dye-encapsulated biological metal-organic frameworks, Adv. Opt. Mater. 7 (2019) 1801149, https://doi.org/10.1002/adom.201801149. [194] X. Rao, T. Song, J. Gao, Y. Cui, Y. Yang, C. Wu, B. Chen, G. Qian, A highly sensitive mixed lanthanide metal-organic framework self-calibrated luminescent thermometer, J. Am. Chem. Soc. 135 (2013) 15559–15564, https://doi.org/10.1021/ja407219k. [195] Y.-H. Han, C.-B. Tian, Q.-H. Li, S.-W. Du, Highly chemical and thermally stable luminescent EuxTb1-x MOF materials for broad-range pH and temperature sensors, J. Mater. Chem. C 2 (2014) 8065–8070, https://doi.org/10.1039/ c4tc01336k. [196] Y. Wei, R. Sa, Q. Li, K. Wu, Highly stable and sensitive LnMOF ratiometric thermometers constructed with mixed ligands, Dalton Trans. 44 (2015) 3067–3074, https://doi.org/10.1039/c4dt03421j. [197] R.F. D’Vries, S. Alvarez-Garcia, N. Snejko, L.E. Bausa, E. Gutierrez-Puebla, A. de Andres, M.A. Monge, Multimetal rare earth MOFs for lighting and thermometry: tailoring color and optimal temperature range through enhanced disulfobenzoic triplet phosphorescence, J. Mater. Chem. C 1 (2013) 6316–6324, https://doi.org/10.1039/c3tc30858h. [198] Z. Ding, C. Wang, G. Feng, X. Zhang, Energy-transfer metal-organic nanoprobe for ratiometric sensing with dual response to peroxynitrite and hypochlorite, ACS Omega 3 (2018) 9400–9406, https://doi.org/10.1021/ acsomega.8b01489. [199] N. Liu, J. Hao, K. Cai, M. Zeng, Z. Huang, L. Chen, B. Peng, P. Li, L. Wang, Y. Song, Ratiometric fluorescence detection of superoxide anion based on AuNPsBSA@Tb/GMP nanoscale coordination polymers, Luminescence 33 (2018) 119–124, https://doi.org/10.1002/bio.3380. [200] K. Cai, M. Zeng, L. Wang, Y. Song, L. Chen, Ratiometric fluorescent detection of ClO- based on dual-emission F1-Rubpy@Nanoscale metal-organic frameworks, Chemistryselect 4 (2019) 2649–2655, https://doi.org/10.1002/ slct.201803414. [201] N. Gao, J. Huang, L. Wang, J. Feng, P. Huang, F. Wu, Ratiometric fluorescence detection of phosphate in human serum with a metal-organic frameworksbased nanocomposite and its immobilized agarose hydrogels, Appl. Surf. Sci. 459 (2018) 686–692, https://doi.org/10.1016/j.apsusc.2018.08.092. [202] S.Q. Li, X. Hu, Q.M. Chen, X.D. Zhang, H.X. Chai, Y.M. Huang, Introducing bifunctional metal-organic frameworks to the construction of a novel ratiometric fluorescence sensor for screening acid phosphatase activity, Biosens. Bioelectron. 137 (2019) 133–139, https://doi.org/10.1016/j. bios.2019.05.010. [203] Z. Ding, J. Tan, G. Feng, Z. Yuan, C. Wu, X. Zhang, Nanoscale metal-organic frameworks coated with poly(vinyl alcohol) for ratiometric peroxynitrite sensing through FRET, Chem. Sci. 8 (2017) 5101–5106, https://doi.org/ 10.1039/c7sc01077j. [204] H.-G. Jin, W. Zong, L. Yuan, X.-B. Zhang, Nanoscale zeolitic imidazole framework-90: selective, sensitive and dual-excitation ratiometric fluorescent detection of hazardous Cr(VI) anions in aqueous media, New J. Chem. 42 (2018) 12549–12556, https://doi.org/10.1039/c8nj02047g. [205] Y. Zhang, B. Yan, A ratiometric fluorescent sensor with dual response of Fe3+/ Cu2+ based on europium post-modified sulfone-metal-organic frameworks and its logical application, Talanta 197 (2019) 291–298, https://doi.org/ 10.1016/j.talanta.2019.01.037. [206] P. Wu, Y. Liu, Y. Liu, J. Wang, Y. Li, W. Liu, J. Wang, Cadmium-based metalorganic framework as a highly selective and sensitive ratiometric luminescent sensor for mercury(II), Inorg. Chem. 54 (2015) 11046–11048, https://doi.org/10.1021/acs.inorgchem.5b01758. [207] X.-J. Wu, F. Kong, C.-Q. Zhao, S.-N. Ding, Ratiometric fluorescent nanosensors for ultra-sensitive detection of mercury ions based on AuNCs/MOFs, Analyst. 144 (2019) 2523–2530, https://doi.org/10.1039/c8an02414f. [208] X. Du, R. Fan, L. Qiang, P. Wang, Y. Song, K. Xing, X. Zheng, Y. Yang, Encapsulation and sensitization of Ln3+ within Indium metal-organic frameworks for ratiometric eu3+ sensing and linear dependence of whitelight emission, Cryst. Growth Des. 17 (2017) 2746–2756, https://doi.org/ 10.1021/acs.cgd.7b00219. [209] X. Zhou, J. Cheng, L. Li, Q. Chen, Y. You, H. Xiao, W. Huang, A europium(III) metal-organic framework as ratiometric turn-on luminescent sensor for Al3+ ions, Sci. China-Mater. 61 (2018) 752–757, https://doi.org/10.1007/s40843017-9186-3. [210] X. Wang, M. Han, J. Bao, W. Tu, Z. Dai, A superoxide anion biosensor based on direct electron transfer of superoxide dismutase on sodium alginate sol-gel film and its application to monitoring of living cells, Anal. Chim. Acta 717 (2012) 61–66, https://doi.org/10.1016/j.aca.2011.12.045. [211] J. Tang, X. Zhu, X. Niu, T. Liu, H. Zhao, M. Lan, Anamperometric superoxide anion radicalbiosensor based on SOD/PtPd-PDARGO modified electrode, Talanta 137 (2015) 18–24, https://doi.org/10.1016/j.talanta.2015.01.009. [212] M. Zhuang, C. Ding, A. Zhu, Y. Tian, Ratiometric fluorescence probe for monitoring hydroxyl radical in live cells based on gold nanoclusters, Anal. Chem. 86 (2014) 1829–1836, https://doi.org/10.1021/ac403810g.

L. Chen et al. / Coordination Chemistry Reviews 404 (2020) 213113 [213] X. Gao, C. Ding, A. Zhu, Y. Tian, Carbon-dot-based ratiometric fluorescent probe for imaging and biosensing of superoxide anion in live cells, Anal. Chem. 86 (2014) 7071–7078, https://doi.org/10.1021/ ac501499y. [214] Z.-Q. Yao, G.-Y. Li, J. Xu, T.-L. Hu, X.-H. Bu, A water-stable luminescent Zn-II metal-organic framework as chemosensor for high-efficiency detection of Cr2VI-Anions (Cr2O27 and CrO4 ) in aqueous solution, Chem.-Eur. J. 24 (2018) 3192–3198, https://doi.org/10.1002/chem.201705328. [215] B. Parmar, Y. Rachuri, K.K. Bisht, R. Laiya, E. Suresh, Mechanochemical and conventional synthesis of Zn(II)/Cd(II) luminescent coordination polymers: dual sensing probe for selective detection of chromate anions and TNP in aqueous phase, Inorg. Chem. 56 (2017) 2627–2638, https://doi.org/10.1021/ acs.inorgchem.6b02810. [216] W. Liu, X. Huang, C. Xu, C. Chen, L. Yang, W. Dou, W. Chen, H. Yang, W. Liu, A multi-responsive regenerable europium-organic framework luminescent sensor for Fe3+CrVI anions, and picric acid, Chem.-Eur. J. 22 (2016) 18769– 18776, https://doi.org/10.1002/chem.201603607. [217] S. Chen, Z. Shi, L. Qin, H. Jia, H. Zheng, Two new luminescent Cd(II)-metalorganic frameworks as bifunctional chemosensors for detection of cations 2Fe3+, anions CrO24 , and Cr2O7 in aqueous solution, Cryst. Growth Des. 17 (2017) 67–72, https://doi.org/10.1021/acs.cgd.6b01197. [218] R. He, Y.-L. Wang, H.-F. Ma, H.-G. Yin, Q.-Y. Liu, Eu3+-functionalized metalorganic framework composite as ratiometric fluorescent sensor for highly selective detecting urinary 1-hydroxypyrene, Dyes Pigment. 151 (2018) 342– 347, https://doi.org/10.1016/j.dyepig.2018.01.018. [219] W. Zhang, X. Wang, Y. Wu, Z. Qi, R. Yang, Preparation and characterization of organic-norganic hybrid macrocyclic compounds: cyclic ladder-like polyphenylsilsesquioxanes, Inorg. Chem. 57 (2018) 3883–3892, https://doi. org/10.1021/acs.inorgchem.7b03264. [220] X. Huang, Z. He, D. Guo, Y. Liu, J. Song, B.C. Yung, L. Lin, G. Yu, J.-J. Zhu, Y. Xiong, X. Chen, Three-in-one nanohybrids as synergistic nanoquenchers to enhance no-wash fluorescence biosensors for ratiometric detection of cancer biomarkers, Theranostics 8 (2018) 3461–3473, https://doi.org/10.7150/ thno.25179. [221] K. Shi, Z. Yang, L. Dong, B. Yu, Dual channel detection for anthrax biomarker dipicolinic acid: The combination of an emission turn on probe and luminescent metal-organic frameworks, Sens. Actuator B-Chem. 266 (2018) 263–269, https://doi.org/10.1016/j.snb.2018.03.128. [222] K. Luan, R. Meng, C. Shan, J. Cao, J. Jia, W. Liu, Y. Tang, Terbium functionalized micelle nanoprobe for ratiometric fluorescence detection of anthrax spore biomarker, Anal. Chem. 90 (2018) 3600–3607, https://doi.org/10.1021/acs. analchem.8b00050. [223] W.J. Rieter, K.M.L. Taylor, W. Lin, Surface modification and functionalization of nanoscale metal-organic frameworks for controlled release and luminescence sensing, J. Am. Chem. Soc. 129 (2007) 9852–9853, https:// doi.org/10.1021/ja073506r. [224] P.M. Pellegrino, N.F. Fell, D.L. Rosen, J.B. Gillespie, Bacterial endospore detection using terbium dipicolinate photoluminescence in the presence of chemical and biological materials, Anal. Chem. 70 (1998) 1755–1760, https:// doi.org/10.1021/ac971232s. [225] M.L. Cable, J.P. Kirby, K. Sorasaenee, H.B. Gray, A. Ponce, Bacterial spore detection by [Tb3+(macrocycle)(dipicolinate)] luminescence, J. Am. Chem. Soc. 129 (2007) 1474–1475, https://doi.org/10.1021/ja061831t. [226] Y. Zhang, B. Li, H. Ma, L. Zhang, Y. Zheng, Rapid and facile ratiometric detection of an anthrax biomarker by regulating energy transfer process in bio-metal-organic framework, Biosens. Bioelectron. 85 (2016) 287–293, https://doi.org/10.1016/j.bios.2016.05.020. [227] J. An, S.J. Geib, N.L. Rosi, Cation-triggered drug release from a porous zincadeninate metal-organic framework, J. Am. Chem. Soc. 131 (2009) 8376– 8377, https://doi.org/10.1021/ja902972w. [228] R. Zhou, Q. Zhao, K.-K. Liu, Y.-J. Lu, L. Dong, C.-X. Shan, Europium-decorated ZnO quantum dots as a fluorescent sensor for the detection of an anthrax biomarker, J. Mater. Chem.C. 5 (2017) 1685–1691, https://doi.org/10.1039/ c6tc05108a. [229] J. Li, Y. Wu, C. Yang, R. Zhu, K. Zhao, For the optical detection of anthrax biomarker using a luminescent rare earth-organic framework modified by rhodamine molecules: Synthesis, characterization and two sensing channels, Spectroc. Acta Pt. A-Molec. Biomolec. Spectr. 203 (2018) 397–403, https:// doi.org/10.1016/j.saa.2018.06.005. [230] C. Lin, Z. Fang, Modifying luminescent metal-organic frameworks with rhodamine dye: Aiming at the optical sensing of anthrax biomarker dipicolinic acid, Inorg. Chim. Acta 477 (2018) 51–58, https://doi.org/ 10.1016/j.ica.2018.02.032. [231] M.D. Yilmaz, S.-H. Hsu, D.N. Reinhoudt, A.H. Velders, J. Huskens, Ratiometric fluorescent detection of an anthrax biomarker at molecular printboards, Angew. Chem.-Int. Ed. 49 (2010) 5938–5941, https://doi.org/10.1002/ anie.201000540. [232] H.L. Tan, Q. Li, C.J. Ma, Y.H. Song, F.G. Xu, S.H. Chen, L. Wang, Lanthanidefunctionalized silver nanoparticles for detection of an anthrax biomarker and test paper fabrication, J. Nanopart. Res. 16 (2013) 11, https://doi.org/10.1007/ s11051-013-2151-y. [233] C. Tan, Q. Wang, C.C. Zhang, Optical and electrochemical responses of an anthrax biomarker based on single-walled carbon nanotubes covalently loaded with terbium complexes, Chem. Commun. 47 (2011) 12521–12523, https://doi.org/10.1039/c1cc15857k.

27

[234] K. Ai, B. Zhang, L. Lu, Europium-based fluorescence nanoparticle sensor for rapid and ultrasensitive detection of an anthrax biomarker, Angew. Chem.Int. Ed. 48 (2009) 304–308, https://doi.org/10.1002/anie.200804231. [235] J. Ryu, E. Lee, K. Lee, J. Jang, A graphene quantum dots based fluorescent sensor for anthrax biomarker detection and its size dependence, J. Mater. Chem. B 3 (2015) 4865–4870, https://doi.org/10.1039/c5tb00585j. [236] W.-K. Oh, Y.S. Jeong, J. Song, J. Jang, Fluorescent europium-modified polymer nanoparticles for rapid and sensitive anthrax sensors, Biosens. Bioelectron. 29 (2011) 172–177, https://doi.org/10.1016/j.bios.2011.08.013. [237] I. Lee, W.-K. Oh, J. Jang, Screen-printed fluorescent sensors for rapid and sensitive anthrax biomarker detection, J. Hazard. Mater. 252 (2013) 186–191, https://doi.org/10.1016/j.jhazmat.2013.03.003. [238] J. Fan, M. Hu, P. Zhan, X. Peng, Energy transfer cassettes based on organic fluorophores: construction and applications in ratiometric sensing, Chem. Soc. Rev. 42 (2013) 29–43, https://doi.org/10.1039/c2cs35273g. [239] L. Yu, Q.T. Zheng, D. Wu, Y.X. Xiao, Bimetal-organic framework nanocomposite based point-of-care visual ratiometric fluorescence pH microsensor for strong acidity, Sensors Actuators B-Chem. 294 (2019) 199– 205, https://doi.org/10.1016/j.snb.2019.05.037. [240] B.V. Harbuzaru, A. Corma, F. Rey, J.L. Jorda, D. Ananias, L.D. Carlos, J. Rocha, A miniaturized linear pH sensor based on a highly photoluminescent selfassembled europium(III) metal-organic framework, Angew. Chem.-Int. Edit. 48 (2009) 6476–6479, https://doi.org/10.1002/anie.200902045. [241] Y. Lu, B. Yan, A ratiometric fluorescent pH sensor based on nanoscale metalorganic frameworks (MOFs) modified by europium(III) complexes, Chem. Commun. 50 (2014) 13323–13326, https://doi.org/10.1039/c4cc05508j. [242] J. Wang, Y. Li, M. Jiang, Y. Liu, L. Zhang, P. Wu, A highly chemically stable metal-organic framework as a luminescent probe for the regenerable ratiometric sensing of pH, Chem.-Eur. J. 22 (2016) 13023–13027, https:// doi.org/10.1002/chem.201602974. [243] C. He, K. Lu, W. Lin, Nanoscale metal-organic frameworks for real-time intracellular ph sensing in live cells, J. Am. Chem. Soc. 136 (2014) 12253– 12256, https://doi.org/10.1021/ja507333c. [244] E. Lanz, M. Gregor, J. Slavík, A.J.J.O.F. Kotyk, Use of FITC as a fluorescent probe for intracellular pH Measurement, J. Fluoresc. 7 (1997) 317–319, https://doi. org/10.1023/a:1022586127784. [245] B. Chu, B. Song, X. Ji, Y. Su, H. Wang, Y. He, Fluorescent silicon nanorods-based ratiometric sensors for long term and real-time measurements of intracellular pH in live cells, Anal. Chem. 89 (2017) 12152–12159, https:// doi.org/10.1021/acs.analchem.7b02791. [246] T. Xia, F. Zhu, K. Jiang, Y. Cui, Y. Yang, G. Qian, A luminescent ratiometric pH sensor based on a nanoscale and biocompatible Eu/Tb-mixed MOF, Dalton Trans. 46 (2017) 7549–7555, https://doi.org/10.1039/c7dt01604b. [247] X.-Y. Xu, B. Yan, Nanoscale LnMOF-functionalized nonwoven fibers protected by a polydimethylsiloxane coating layer as a highly sensitive ratiometric oxygen sensor, J. Mater. Chem. C 4 (2016) 8514–8521, https://doi.org/ 10.1039/c6tc02569b. [248] R. Xu, Y. Wang, X. Duan, K. Lu, D. Micheroni, A. Hu, W. Lin, Nanoscale metalorganic frameworks for ratiometric oxygen sensing in live cells, J. Am. Chem. Soc. 138 (2016) 2158–2161, https://doi.org/10.1021/jacs.5b13458. [249] J.-W. Ye, J.-M. Lin, Z.-W. Mo, C.-T. He, H.-L. Zhou, J.-P. Zhang, X.-M. Chen, Mixed-lanthanide porous coordination polymers showing range tunableratiometric luminescence for O2 sensing, Inorg. Chem. 56 (2017) 4238–4243, https://doi.org/10.1021/acs.inorgchem.7b00252. [250] M. Wang, L. Guo, D. Cao, Amino-functionalized luminescent metal-organic framework test paper for rapid and selective sensing of SO2 gas and its derivatives by luminescence turn-on effect, Anal. Chem. 90 (2018) 3608– 3614, https://doi.org/10.1021/acs.analchem.8b00146. [251] X. Zheng, R. Fan, Y. Song, A. Wang, K. Xing, X. Du, P. Wang, Y. Yang, A highly sensitive turn-on ratiometric luminescent probe based on postsynthetic modification of Tb3+@Cu-MOF for H2S detection, J. Mater. Chem. C 5 (2017) 9943–9951, https://doi.org/10.1039/c7tc02430d. [252] J.-P. Zheng, S. Ou, M. Zhao, C.-D. Wu, A highly sensitive luminescent dye@mof composite for probing different volatile organic compounds, Chempluschem 81 (2016) 758–763, https://doi.org/10.1002/cplu.201600057. [253] N. Zhang, S. Ruan, F. Qu, Y. Yin, X. Li, S. Wen, S. Adimi, J. Yin, Metal-organic framework-derived Co3O4/CoFe2O4 double-shelled nanocubes for selective detection of sub-ppm-level formaldehyde, Sensors Actuators B-Chem. 298 (2019), https://doi.org/10.1016/j.snb.2019.126887. [254] K. Vellingiri, A. Deep, K.-H. Kim, D.W. Boukhvalov, P. Kumar, Q. Yao, The sensitive detection of formaldehyde in aqueous media using zirconiumbased metal organic frameworks, Sensors Actuators B-Chem. 241 (2017) 938–948, https://doi.org/10.1016/j.snb.2016.11.017. [255] W. Zhou, Y.-P. Wu, X. Wang, X.-Q. Qiao, D.-F. Hou, J. Zhao, D.-S. Li, In-MOFsderived microsphere In2O3 for highly sensitive detecting formaldehyde vapor, Inorg. Chem. Commun. 85 (2017) 100–104, https://doi.org/10.1016/j. inoche.2017.07.013. [256] S. Nandi, E. Sharma, V. Trivedi, S. Biswas, Metal-organic framework showing selective and sensitive detection of exogenous and endogenous formaldehyde, Inorg. Chem. 57 (2018) 15149–15157, https://doi.org/ 10.1021/acs.inorgchem.8b02411. [257] S.S. Nagarkar, A.V. Desai, S.K. Ghosh, A nitro-functionalized metal-organic framework as a reaction-based fluorescence turn-on probe for rapid and selective H2S detection, Chem.-a Eur. J. 21 (2015) 9994–9997, https://doi.org/ 10.1002/chem.201501043.

28

L. Chen et al. / Coordination Chemistry Reviews 404 (2020) 213113

[258] S.S. Nagarkar, T. Saha, A.V. Desai, P. Talukdar, S.K. Ghosh, Metal-organic framework based highly selective fluorescence turn-on probe for hydrogen sulphide, Sci. Rep. 4 (2014), https://doi.org/10.1038/srep07053. [259] X. Zhang, J. Zhang, Q. Hu, Y. Cui, Y. Yang, G. Qian, Postsynthetic modification of metal-organic framework for hydrogen sulfide detection, Appl. Surf. Sci. 355 (2015) 814–819, https://doi.org/10.1016/j.apsusc. 2015.07.166. [260] A. Buragohain, S. Biswas, Cerium-based azide- and nitro-functionalized UiO66 frameworks as turn-on fluorescent probes for the sensing of hydrogen sulphide, CrystEngComm 18 (2016) 4374–4381, https://doi.org/10.1039/ c6ce00032k. [261] Z. Guo, A. Florea, M. Jiang, Y. Mei, W. Zhang, A. Zhang, R. Sa˘ndulescu, N. Jaffrezic-Renault, Molecularly imprinted polymer/metal organic framework based chemical sensors, Coatings 6 (2016) 42, https://doi.org/10.3390/ coatings6040042.

[262] J. Chen, H. Chen, T. Wang, J. Li, J. Wang, X. Lu, Copper ion fluorescent probe based on Zr-MOFs composite material, Anal. Chem. 91 (2019) 4331–4336, https://doi.org/10.1021/acs.analchem.8b03924. [263] H. Chen, J. Wang, D. Shan, J. Chen, S. Zhang, X. Lu, Dual-emitting fluorescent metal-organic framework nanocomposites as a broad-range pH sensor for fluorescence imaging, Anal. Chem. 90 (2018) 7056–7063, https://doi.org/ 10.1021/acs.analchem.8b01455. [264] M. Bagheri, M.Y. Masoomi, A. Morsali, Highly sensitive and selective ratiometric fluorescent metal-organic framework sensor to nitroaniline in presence of nitroaromatic compounds and VOCs, Sens. Actuator B-Chem. 243 (2017) 353–360, https://doi.org/10.1016/j.snb.2016.11.144. [265] C. Li, J. Hai, S. Li, B. Wang, Z. Yang, Luminescent magnetic nanoparticles encapsulated in MOFs for highly selective and sensitive detection of ClO-/ SCN- and anti-counterfeiting, Nanoscale. 10 (2018) 8667–8676, https://doi. org/10.1039/c8nr01487f.