Metal-organic framework-based nanocomposites for sensing applications – A review

Journal Pre-proofs Review Metal-organic framework-based nanocomposites for sensing applications - A Review Ali Amini, Sima Kazemi, Vahid Safarifard PII: DOI: Reference:

S0277-5387(19)30705-3 https://doi.org/10.1016/j.poly.2019.114260 POLY 114260

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Polyhedron

Received Date: Revised Date: Accepted Date:

27 August 2019 14 November 2019 4 December 2019

Please cite this article as: A. Amini, S. Kazemi, V. Safarifard, Metal-organic framework-based nanocomposites for sensing applications - A Review, Polyhedron (2019), doi: https://doi.org/10.1016/j.poly.2019.114260

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Metal-organic framework-based nanocomposites for sensing applications - A Review Ali Amini, # Sima Kazemi,# Vahid Safarifard Department of Chemistry, Iran University of Science and Technology, Tehran 16846-13114, Iran. Email: [email protected]; Fax: +98 21 73021415; Tel: +98 21 73228327 #

A.A. and S.K. contributed equally to this work.

Abstract: Metal-organic frameworks (MOFs) are a kind of porous material in which metal ions or clusters are linked by organic ligands. Their excellent properties including large surface area, tunable pore dimension, and structure, possessing active sites, high thermal and chemical stability lead to various applications containing catalysis, gas storage, drug delivery, absorption, and sensing for different molecules. Making composites with modification of MOF could transform them into the best candidate for the detection of different items such as biomolecules, cations, anions, gas molecules, and organic compound and so on. In this review, we will consider the constructed MOF-based composites and their performance in electrochemical and luminescent_based detection performances. Keywords: Sensing; Composites; Metal-organic frameworks

Contents 1.

Introduction ........................................................................................................................................... 2

2. Photoluminescence-based method ............................................................................................................ 4 2.1.

Lanthanide-based frameworks ...................................................................................................... 4

2.2.

Non-lanthanide-based frameworks ............................................................................................... 7

3.

Electrochemical-based method ........................................................................................................... 11

4.

Gas sensing ......................................................................................................................................... 25

5.

SERS Sensing ..................................................................................................................................... 27

6.

Refractive index sensor ....................................................................................................................... 28

7.

Conclusion and Future Outlook .......................................................................................................... 29 Acknowledgements ................................................................................................................................. 30 Abbreviation ........................................................................................................................................... 32 References ............................................................................................................................................... 35 1

1. Introduction Current procedures for sensing mainly rely on the chromatography [1] including gas chromatography_mass spectrometry, liquid chromatography_tandem mass spectrometry, and high-performance liquid chromatography, fluorometry [2], colorimetry [3], enzymatic biosensors [4] and electrochemical method [5]. Drawbacks related to these evaluation techniques include complicated sample processing, expensive equipment, considerable time-cost, and toxic chemicals. Expansion of an accurate, simple, time-saving and inexpensive method for the determination of different kinds of analytes, therefore, is urgently required. Metal-organic frameworks (MOFs) which are constructed by the self-assembly process of metal cations or metal clusters and pliable organic ligands [6] have been received considerable attention in the last decade [7] due to possessing large surface areas, high porosity, tunable structural and robust thermal stability [6, 8]. These features make MOFs promising nominee for different applications containing [9, 10] and separations, heterogeneous catalysis[11, 12], drug delivery[13-16] and adsorption of various materials [17-22]. Furthermore, MOFs have been also employed to be one of the leading nominees for chemical sensing[23-26] in environmental and industrial applications[27], and different MOFs have been synthesized as detecting platforms for special analytes such as anions, cations, gases, organic small molecules, explosives, temperature, humidity and pH, based on the eximious sorption kinetics, reversibility, and guest-induced changes in their structure and/or characteristics [28-33]. Optical MOFs are in the center of attention due to their aromatic sub-units. As aromatic linkers exhibit luminescent emission[34], a large number of MOFs have been found to be photoluminescent. The other type of MOF sensors as according to the luminescence changes of lanthanide ions (Ln3+) based on the intense photoluminescence characterization [35, 36]. For example, lanthanide MOFs are found to be the best choice for preparing new fluorescent sensor due to the abundant 4f−4f transitions of the lanthanide centers and the well-defined porosity of the frameworks [37-39]. In this regard, Ln-doped MOF composites provide a new class of fluorescent sensor for detecting cations, anions, organic small molecules[40], gases, humidity, 2

temperature, and pH [41]. As another kind of MOF-based sensor, designing of new electrochemical sensors/ biosensors with desirable analytical and electrochemical features can be obtained by modifying the electrode surface with various hybrid materials (e.g. functionalized graphene, preanodized/mediator-modified carbon substrates, and Au-based nanomaterials) to exploit for ordinary environmental sensing or biosensing systems[42]. As the huge vacant volume of MOFs limits its conductivity, choosing suitable materials to combine with the frameworks could overcome this restriction[43]. Consequently, different MOF composite-based platforms have been developed to overcome this challenge and act as effective electrochemical sensors for environmental and biochemical targets [42]. On the other hand, noble-metal nanoparticles (NPs) (such as Au, Ag, Pd, and Pt) based on their excellent physicochemical properties can be anticipated in sensing, imaging, cancer therapy, optical data storage, and catalysis. But their high surface energy leads to aggregation limiting the mentioned performances. So scholar combines them with MOFs to overcome this obstacle through various strategy. The result composites could act as an excellent sensor for recognition of various molecules [44]. In this review, we try to sum up the sensing properties of MOF nanocomposites[45] reported for photoelectrochemical sensing (Table 1). We shortly examine the design and the functionalization of MOFs with many molecules via post-synthesis/dopant modifications[46] and entrapping [35]. The functional materials used for synthesizing MOF nanocomposites for photoelectrochemical detection are different and include metal/metal oxide nanoparticles, carbon-based materials (reduced graphene oxide (rGO), graphene oxide (GO)), quantum dots (QDs), enzymes, and heteropoly acids [42]. Moreover, this review paper also considers different benefits of the above functional materials applied for the preparation of MOF nanocomposites. MOF nanocomposites have been used for sensing of various important analytes like heavy metal ions, anions, aromatic hydrocarbons, toxic phenolic compounds, and temperature. We anticipate that the information in this review relating to the preparation and applications of MOF nanocomposites as photoelectrochemical sensors should help the research groups expand and establish more advanced MOF-based sensing approaches.

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2. Photoluminescence-based method 2.1. Lanthanide-based frameworks

Lanthanide coordination compounds have been used for temperature sensing since 2004, because of the luminescence properties of lanthanide ions [47]. In order to achieve this class of lanthanide compounds for temperature sensing, they need to be dispersed and stabilized in polymeric networks, such as MOFs [48]. Moreover, to make solid-state luminescence thermometers with high sensitivity, the MOF⊃luminescent guest species composite strategy is very attractive. In order to exploit of luminescent characteristics of lanthanide ions and a luminescent guest species as a stable self-calibrated temperature sensors, Cui and coworkers put organic dye perylene into the pores of biocompatible isostructural lanthanide-based MOFs with low toxicity, namely ZJU88 ([Eu2(QPTCA)(NO3)2(DMF)4]·(CH3CH2OH)3) (H4QPTCA = 1,1′:4′,1′′:4′′,1′′′-quaterphenyl3,3′′′,5,5′′′- tetracarboxylic acid) through making a mixture of Eu(NO3)3·6H2O and H4QPTCA in the DMF/ H2O/ CH3CH2OH heating at 80 °C for 2 days, then as-synthesized NOF was immersed in the perylene solution to replace with DMF, and made use of the dual-emitting from lanthanide ions and organic dyes within the ZJU-88⊃perylene composite for physiological temperature sensing (Figure 1a)[49]. The perylene dye molecules were included in the 1D channels of ZJU-88 which is about 8 × 12 Å2, realized by the single-crystal X-ray diffraction results (Figure 1b). Based on XRD patterns, perylene was embedded into the pores of MOF and the composite has an identical structure to the as-prepared MOF (Figure 1c). Since the relative luminescence intensity of the dyes to Eu3+ changes with various dye content in pores, perylene uniformly encapsulated in the channels of ZJU-88 as free individual molecules, as a result, the formation of aggregate or excimer in the materials was prevented. As expected, the obtained composite exhibited a red-emitting of Eu3+ at 615 nm and an appended blue-emitting around 473 nm of perylene dyes together having a linear correlation with the physiological temperature in the range of 20 to 80 °C. With increasing the temperature from 20 to 80 °C, the luminescence intensity at 473 nm of perylene dye in ZJU-88⊃perylene substantially declined because of the thermal activation of nonradiative-decay pathways, but on the other hand, the intensity of the 5D0 → 7F2 transition of Eu3+ at 615 nm would be improved (Figure 1d). In comparison with the composite, the emission intensity of isolated dye also decreased with temperature increasing, but in less 4

percentage (14.8% vs. 32.3% for ZJU-88⊃perylene). So the perylene in ZJU-88⊃perylene composite is more sensitive to temperature than in the solution. The authors thought that the energy transfer from dye molecules to Eu3+ ions is answerable for the luminescence reduction of perylene and the enhancement in the emission of Eu3+ in ZJU-88⊃perylene, confirming by the lifetime measurements. Calculations showed that the quantum yield of ZJU-88⊃perylene with 0.10% of dye content is identical to 13.12%, therefore they claimed that this composite can act as a perfect nominee for temperature luminescent sensors. Furthermore, preliminarily investigation exhibited that the composite has very low toxicology and very good stability under simulated physiological conditions, establishing its potential for biological applications.

Figure 1 (a) Dual-emitting ZJU-88⊃perylene composite. (b) Crystal structure of ZJU-88. (c) PXRD patterns of ZJU88 and ZJU-88⊃perylene. (d) Emission spectra of ZJU-88⊃perylene recorded. Adapted from Ref. [49].

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As the sensing of hydrogen sulfide (H2S) is a worldwide challenging issue, Zhang and coworkers proposed a post-synthetic modification of UiO-66-(COOH)2 by Eu3+ and Cu2+ ions, Eu3+/Cu2+@UiO-66-(COOH)2 (Figure 2) [37]. Eu3+/Cu2+@UiO-66-(COOH)2 were obtained through The obtained modified MOF exhibited the characteristic Eu3+ emissions and the wide ligand-centered (LC) emission concurrently. H2S has an intense affinity to bind with calcium ions, so enhance the fluorescence of Eu3+ and quench the wide LC emission. Therefore, authors could say their sensor is greatly sensitive toward H2S over other environmentally and biologically relevant species (F-, Cl-, Br-, I-, HCOO-, CH3COO-, NO2-, SiO32-, NO3-, HPO42-, PO43-, P3O93-, S2O32-, SO42-, HCO3-, N3-, HNO, NO, GSH, Hcy and Cys) under physiological conditions. Although HNO and the thiol-including amino acids (GSH, Hcy, and Cys) affected the fluorescence intensity of Eu3+/Cu2+@UiO-66-(COOH)2, had no bearing on sulfide sensing. They claim that this probe has the practical potential for detecting H2S in important biological samples quickly (within 30 s).

Figure 2 Schematic recognition of the fluorescence recognition mechanism. Adapted from Ref. [37].

Polycyclic aromatic hydrocarbons (PAHs) are a band of chemical carcinogens threatening human health, and 1-Hydroxypyrene (1-HP) is a detectable metabolite of PAHs in urine that is an important way of assaying PAHs from all exposure routes. An anionic three-dimensional MOF, namely JXNU-4 with (Me2NH2)2[Zn6(μ4-O)(ad)4(BPDC)4] formula, occupied by the extra framework dimethylammonium cations was synthesized by using Zn(NO3)2·6H2O, adenine and 4,4′-biphenyldicarboxylic acid in DMF/H2O at 120 °C for 3 days. Then the parent compound was soaked in aqueous solutions of chloride salts of Eu3+ to act as a host for Eu3+ cations by 6

uncoordinated carboxylate oxygen atoms in cages through a cation exchange process to detect 1Hydroxypyrene which is a biomarker of polycyclic aromatic hydrocarbons (PAHs) carcinogens [41]. The Eu3+@JXNU-4 composite displayed excellent Eu3+ luminescence and good fluorescence stability in aqueous solution up to 360 °C within the pH range of 4.0–8.0. Based on XPS data, the Eu‒O coordination bonds were formed between the incorporated Eu3+ ions and the free carboxylate oxygen of the BPDC2− ligands in Eu3+@JXNU-4. Parent JXNU-4 exhibited a photoluminescent emission centered at 427 nm with a shoulder at 474 nm upon excitation at 318 nm but Eu3+@JXNU-4 had a strong and characteristic emission spectrum of the Eu3+ ion upon excitation at 329 nm with the luminescence quantum yield of JXNU-4 and Eu3+@JXNU-4 identical to 15.4% and 39.7%, respectively. So, the Eu3+ luminescence is effectively sensitized by the organic ligands. In general, there was no luminescent emission band arising from the JXNU-4 (400–500 nm) in the emission spectrum of Eu3+@JXNU-4 composite, therefore the framework emission in Eu3+@JXNU-4 was suppressed by the energy transfer from ligand to Eu3+ ions. As the chief compounds of human urine are H2O, creatinine, creatine, urea, uric acid, K+, Na+, NH4+, Cl−, and glucose, the selectivity of the composite toward 1-HP was examined. The results showed that the creatinine, creatine, urea, KCl, NH4Cl, glucose, and uric acid had no observable influence on the luminescence intensity under equal conditions, while the 1-HP indicated an excellent decline (85.6%) in the luminescence intensity of the composite. Meanwhile, more studies proved that the emission intensity of Eu3+ progressively reduced with a gradual enlarging in the concentration of 1-HP. Thus, the authors claimed that this composite material could act as a selective and sensitive platform for detecting 1-HP with a 0.86 μg/L detection limit. According to the PXRD patterns of before and after threating with 1-HP, there was no observable change in the pattern indicating that the framework remains perfect with the addition of 1-HP, thus the luminescence quenching should occur through a direct interaction between the 1-HP and the emission centers of Eu3+. 2.2. Non-lanthanide-based frameworks

3. Mercury(II) ions are known as a dangerous pollutant item due to its harmfulness to both human health and the environment [50]. Consequently, different efforts have been made by researchers to find useful methods for the sensing of Hg2+ [51]. The construction of a duplex building between various metals and nucleic acids has proven to be an adequate strategy for

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metal-ion detection [52]. Interestingly, Hg2+ ions have a high affinity for thymine-thymine (T–T) base pairs instead of other metal ions, and thymine-Hg2+-thymine (T-Hg2+-T) base pairs sandwich complexes can form via binding Hg2+ ions to T-T mismatched base pairs in oligonucleotides [53]. In 2016, Wu and coworkers utilized the MOF/DNA hybrid system as a biosensing platform to detect Hg2+, sensitively and selectively [6]. They proposed a new fluorescence-based hybrid to sense Hg2+ using UiO-66-NH2 modifying with T-rich singlestranded DNA (ssDNA) labeled with a fluorophore (FAM) at its 3ʹ end as the probe (P). This selection was based on the fact that the π electron-rich ligands could adsorb ssDNA through π-π stacking interactions, so quenching the labeled fluorophores, which improve MOFs performance. The schematic concept of the fluorescent sensing template as illustrated in Figure 3. The detection of Hg2+ was monitored by the fluorescence intensity. Researchers

claim that the fluorescence recovery was related to the helical structure generation by the Hg2+ ion from ssDNA inhibiting the ssDNA from binding to UiO-66-NH2. Free P exhibits strong fluorescence at 518 nm under excitation at 480 nm. Before contacting with Hg2+, P would bind to UiO-66-NH2 by π–π stacking and hydrogen-bonding interactions between the DNA nucleotide bases and the aromatic ligand of amino functionalized UiO-66-NH2, thus the FAM fluorescence is quenched as a result of the photoinduced energy transfer (PET). Figure 4 illustrates the fluorescence emission spectra of P under different conditions in Tris-

HCl buffer (pH 7.4). When UiO-66-NH2 does not exist, the free P exhibits intense fluorescence emission upon exciting at 480 nm (curve a), while the addition of UiO-66-NH2 leads to a striking decline of the emission peak (curve d). As the fluorescence quenching efficiency (QE) is about 75%, UiO-66-NH2 can interact with P resulting in quenching the fluorescence emitting from FAM effectively. In curve c, upon the addition of Hg2+ cations, a significant enhancement of the fluorescence emission intensity of the P/UiO-66-NH2 was observed. In contrast, the fluorescence of P is almost not affected by Hg2+ without UiO-66NH2 (curve b). Therefore, the fluorescent detection of Hg2+ is on the basis of the fluorescence intensity changes. In the presence of Hg2+ cations, T–Hg2+–T structures were formed, then the structural alteration could get P from UiO-66-NH2 and regenerate the dye fluorescence. Meanwhile, the fluorescence intensity was enhanced via increasing the mercury cation concentration. Authors observed a linear relationship among the fluorescence intensity and mercury ions concentration in the range of 0.1-10.0 µm with 17.6 nm value of detection limit 8

that is lower than the amount that the World Health Organization (WHO) defined. Moreover, they assessed the selectivity of this system for a suspension of metal ions containing Ca2+, Cd2+, Co2+, Cu2+, Fe2+, Fe3+, Mg2+, Mn2+, Ni2+, and Pb2+, those were showed only a slight response, so it can be said that this composite acts as a selective detection platform.

Figure 3 Schematic concept of the fluorescent sensing for DNA/UiO-66-NH2 hybrid system. Adapted from Ref. [6].

Figure 4 Fluorescence emission spectra of P under different conditions (λ ex=480 nm): a) P; b) P+Hg2+ ; c) P+UiO66-NH2+Hg2+ ; and d) P+UiO-66- NH2 . In all measurements the concentrations were P=100 nm, UiO-66-NH2=0.15 μgμL -1 , and Hg2+ =10.0 μM.[6].

To devise a fluorescent sensing platform for phosphate (Pi) pollution, Zhao et al. combined MOFs with ZnO quantum dots (QDs) capped by (3-aminopropyl) trimethoxysilane (APTMS– 9

ZnO QDs) through electrostatic attraction among negatively charged frameworks and positively charged QDs, which resulted in the quenching ZnO QDs fluorescence because of the electrontransfer processes (Figure5) [54]. The synthesis of APTMS-capped ZnO QDs was performed through a two-step procedure, in the first step, KOH and ethanol were dropwise added to Zn(OAc)2 ethanol solution. Then, the ZnO QDs were precipitated by the addition of ethyl acetate. In the second step, the ZnO QDs were capped with APTMS by adding APTMS ethanol solution to the as_prepared ZnO QDs solution dispersed in ethanol. The product was obtained by ultracentrifugation. After diffusion of Pi ions into the resultant system, the fluorescence of ZnO QDs was turn on again with depending on concentrations of Pi ions. Based on SEM and XRD results, Pi cut the attraction between MOFs and QDs and destroyed the MOFs structure, thus the quenching effect would be prevented. Resulted from the time-resolved fluorescence spectra of the QDs and the obtained complex, the fluorescence lifetime of the QDs lessened after interacted with MOFs. The comparative fluorescence intensity and the concentrations of Pi in the range from 0.5 to 12 µM occurred a linear relationship with the detection limit identical to 53 nM (S/N = 3). Moreover, in order to assay the selectivity of this platform, several anions, such as SO42−, SO32−, Cl−, NO3−, C2O42−, ClO3−, I− , as well as generic metal ions containing Cr3+, Mg2+, Fe3+, Cu2+, Al3+, Ca2+, Zn2+, Ag+, and amino acids like leucine (Leu), histidine (His), arginine (Arg), glutamate (Glu), serine (Ser), cysteine (Cys), ascorbic acid (AA), alanine (Ala) were selected to check their interfering effect on Pi detection, indicating that the anions had no clear influence but the others slightly affected on Pi determination. Thus researches believed that the present platform senses Pi ions selectively as a result of the special interactions between framework and Pi ions. For evaluation of the platform’s practical applications, authors investigated the detection of Pi in tap water via standard addition method, concluding the recoveries of spiked samples were in the range of 95% to 104% with relative standard deviation (RSD) of about 2%. So this method could be useful for Pi detection in water samples.

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Figure 5 Schematic illustration of Pi recognition according to the interactions between the ZnO QDs, MOFs, and Pi. Adapted from Ref. [54].

4. Electrochemical-based method Hydroquinone (HQ) and catechol (CT) are some types of dihydroxybenzene isomers (DBIs) of toxic phenolic compounds which spread in the environment as a result of cosmetics, dye, pesticides, and pharmaceutical industries activities. Li et al. prepared composites from graphene (GN) and HKUST-1 to sense these pollutant agents [43]. HKUST-1 was synthesized using Cu(NO3)2·6H2O and H3BTC (BTC = 1,3,5-benzenetricarboxylicacid) in water/ethanol at 150 °C for 24 h. Also, graphite oxide was first synthesized with graphite using a modified Hummers method. After that, the Cu-MOF and graphene oxide was ultrasonically dispersed and then, dropped on the cleaned electrode surface and dried under room temperature. The electrochemical properties of analytes on different modified electrodes were studied by CV at pH 7.0. As can be seen in Figure , in the bare glassy electrode (GCE), the oxidation peak current of HQ was only 49 μA, which rapidly increased in the presence of the GN or Cu-MOF on GCE. With introducing Cu-MOF-GN composite on the GCE, the oxidation peak current of HQ reached to a maximum of 11

98 μA. So because of the large surface area and good adsorption properties of the Cu-MOF and the excellent conductivity and stability of GN, Cu-MOF-GN composite exhibited perfect performance in the detection of HQ. The authors believe that GN improves the electron transfer rate. On the other hand, it could increase the stability of the electrodes up to two months with a response current of 95% of the first current. Further experiments showed that this composite could also act in real samples effectively.

Figure 6 CVs of 1.0 × 10−4 M of HQ (A), 1.0 × 10−4 M CT (B) and a mixture of 1.0 × 10−4 M HQ and 1.0 × 10−4 M CT (C) at the various modified electrodes on the basis of GCE, GN/GCE, Cu-MOF/GCE and Cu-MOF-GN/GCE in 0.1 M (pH 7.0) phosphate buffer solution at inspect rate: 100 mV/s. Adapted from Ref. [43].

In a similar work to recognize dihydroxybenzene isomers (DBIs) of phenolic compounds, Deng and coworkers prepared UiO-66/mesoporous carbon (MC) composite via the hydrothermal method for the first time with adding MC in the well-dispersed mixture of ZrCl4 and BDC in DMF/acetic acid [55]. The sensor was prepared as mentioned above. Figure illustrates the construction and detection strategy of the prepared sensor at pH equal to 6.0 as the optimum pH value. The bare GCE demonstrated a great semicircle part at high frequency but after the modification process with UiO-66 on the electrode, the semicircle diameter for EIS declined. They observed that when the mass proportion of UiO-66 and MC was 1:2, the peak currents and peak-to-peak separations of DBIs become a maximum value. The semicircle of MC/GCE and UiO-66/MC/GCE is not clear thus the electron transfer capability of UiO-66 is developed immensely after modifying MC. Based on these results, the authors conclude that UiO-66/M becomes a competitive designee for different electrochemical performances. Further experiments on UiO-66/MC stability by cyclic voltammetry showed that the modified electrode exhibits the identical peak current as of the initial one after 50 cycles and this material can be stored for 15 days with an ignorable decrease of performance. Moreover, the selectivity of the prepared 12

electrode was discussed in the presence of K+, Na+, Mg2+, Zn2+, Cu2+, Al3+, Fe3+, Cl-, NO3- and SO42- in 10-fold excess, which had no effect on HQ, CT and RS detection signals at the modified electrode. Meanwhile, the determination ability of the electrode in the real sample was satisfactory.

Figure 7 Schematic representation of the construction and recognition technique of the sensor. Adapted from Ref. [55].

In 2016, a composite sensor containing loaded Cu nanoparticles into ZIF-8 (Cu-in-ZIF-8) was reported to sense glucose in alkaline media for clinical diagnosis of diabetes due to high sensitivity and more active sites. Encapsulation of Cu NPs by ZIF-8 prevent them to dissolve or agglomerate during the electrocatalytic process [56]. On the other hand, more investigation showed that in comparison with Cu-in-ZIF-8, Cu NPs loaded on the surface of ZIF-8 (Cu-onZIF-8) exhibit less stability and performance. The resultant composite was additionally modified on screen-printed carbon electrodes (SPCE). As shown in Figure , during two steps Cu oxidized to CuOOH with oxidizing CuIII state. In the alkaline medium, the glucose is deprotonated and made enediol isomer. CuOOH oxidizes enediol into gluconolactone, and at the end, this molecule hydrolyzes into gluconic acid. Regeneration test showed that after 35 times of detection, Cu-in-ZIF-8 preserves its sensitivity equal to 90.7%. The authors believe that this significant stability of the composite is attributed to the special steric location of Cu NPs. In order to check the practical detection of this material, three obvious rat serum were selected, which the result of data with a commercial glucometer. They observed that the glucose

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concentration achieved from the Cu-in-ZIF-8 sensor is an invalid contract with the glucometer, indicating the reliability for real sample detection.

Figure 8 Schematic representation of glucose oxidized on Cu-in-ZIF-8 modified SPCE. Adapted from Ref. [56].

In order to detect tryptophan (Trp), MIL-101(Fe) with the exterior modified by silver nanoparticles (AgNPs) was put on the surface of a glassy carbon electrode (AgNPs/MIL101/GCE) (Figure ) [7]. FeCl3•6H2O and H2BDC were dissolved in DMF was heated at 110 ̊C for 20 h. then, the obtained MOF was suspended in water and TA solution was injected into the mixture under stirring. Adding AgNO3 gradually led to AgNPs/MIL-101(Fe). The sensor was prepared as mentioned before. The combination of the great specific surface area of MOF and high electrical conductivity of silver nanoparticles makes AgNPs/MIL-101 an excellent sensor for this purpose with 0.14 μM (S/N=3) detection limit in optimum pH = 2.4. The AgNPs/MIL101/GCE increased the electron transfer between the electrode and the solution leading to a more sensitive current response in the oxidation of Trp under the selected experimental conditions. As 14

CV plots described, the charge transfer resistance (Rct) value of MIL-101/GCE is less than that of bare GCE. Moreover, an apparent decrease in Rct is observed in AgNPs/MIL-101/GCE, due to the good electrical conductivity of silver nanoparticles, so AgNPs were attached to the MOF successfully. As shown in the CVs, no peak is observed in the absence of Trp for all electrodes, while with introducing of Trp, one stable oxidation peak occurred in every electrode. Results showed that the current responses were aroused from Trp, meanwhile, electrocatalytic activity towards Trp of AgNPs/MIL-101/GCE was greatly improved. Researchers believe that this enhanced electrochemical response is attributed to the following three factors: (1) the ligands and Trp contain a conjugated π-electron system, thus π-π stacking between MOF and tryptophan could be formed, therefore an increase of the interaction on the surface of AgNPs/MIL-101/GCE and MIL-101/GCE versus GCE occurs, (2) metallic silver NPs own remarkable electrical conductivity, which could accelerate the electron transfer between the electrode and species in solution, and (3) noble metallic NPs create high electromagnetic field, and the electromagnetic field from AgNPs would promote the accumulation of the tryptophan molecules at the surface of MIL-101, which possessed great surface area. As the possible interference materials for Trp determination at the electrode are serine, threonine, lysine, histidine, valine, arginine, proline and leucine in BR (pH 2.4), the effect of them was examined too. The DPVs certified that all the changes of the peak currents are less than 15% relative to tryptophan, so the AgNPs/MIL101/GCE can be selected as a selective Trp sensor in the presence of most of the general interferents.

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Figure 9 Schematic Preparation of AgNPs/MIL-101(Fe) modified electrode. Adapted from Ref. [7].

Based on the importance of sensing of cocaine in clinical diagnostics, Su and others began to synthesize 2D Zr-MOF nanosheets combined with Au nanoclusters (NCs) (AuNCs@521-MOF) and examined its efficiency as an electrochemical aptasensor for detecting cocaine (Figure ) [57]. The excellent electrochemical activity of Au NCs and high special surface area of the 2D nanosheets, as well as the exceptional chemical and thermal stability, encouraged authors to use this framework. Due to electrochemical data, the AuNCs@521-MOF-based aptasensor exhibited better detection efficiency for cocaine compared with the pristine 521-MOF. The LOD parameter was calculated at nearly 0.44 pg·mL−1. Moreover, the coexisting species containing AA, ATP, IgG, UA, BSA, and lysozyme were investigated to prove the selectivity of the sensing platform, which demonstrates the proposed aptasensor shows weak responses to other interferences in comparison with cocaine. Furthermore, the stability and reusability of the sensor were considered. They claimed that the constructed aptasensor could be stored at 4 °C for 15 days with only a 1.7% change in the Rct response relative to the initial test, suggesting the acceptable stability of the material. Meanwhile, it could detect the analyte during seven runs of

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regeneration. They think that the sensing process is related to the attachment of the cocaine onto the AuNCs@521-MOF via strong π−π stacking and covalent bonding interactions.

Figure 10 Schematic of the fabrication of electrochemical biosensor, namely AuNCs@Zr-MOF-based, nanosheets for detection of cocaine, containing (i) the preparation of the 2D AuNCs@Zr-MOF nanosheets, (ii) the immobilization of the aptamer strands, and (iii) the detection of cocaine. Adapted from Ref. [57].

Based on Zhang et al. works, a hydrothermal synthesis of hybrid material [polyoxometalate based-MOF (POMOF)/rGO)] integrating POMOF, [Mo5P2O23] [Cu(phen)(H2O)]3 (Cu3Mo5P2), and reduced graphene oxide (rGO) has been proposed through adding reduced graphene oxide aqueous suspension into phosphomolybdic acid hydrate, CuCl2•2H2O, concentrated H3PO4, and 1,10-phenanthroline water solution to recognize dopamine electrochemically (Figure )[58]. They reported that the promoted electron transfer, available active sites, open channels, and aromatic planes in the hybrid material provided a wider linear detection range from 1 × 10 −6 to 2×10−4 M with the lower detection limit of 80.4 × 10−9 M(S/N = 3) and sensitivity of 0.373 mA × 10−3 M−1 cm−2 during 100 reusability cycles with 21% of performance reduction. In cyclic voltammetry 17

(CV) experiments, DA exhibited a pair of redox peaks related to oxidation (≈ 0.3V vs Ag/AgCl) of DA to dopamine quinone (DAQ) and reduction of DAQ to DA. After modified by POMOF, DA showed a considerable increase in the oxidative current because of the activity of the POMOF, which provided multiple metal sites and permanent porosity. Moreover, MOFs are able to increase the electrode/electrolyte contact and substantially stabilize the POM clusters. In order to inhibit the participation of protons in the electrode reaction, pH 7.0 (0.1 m PBS solution) solution was selected for the subsequent analytical experiments. The sensing performance relied on dopamine oxidation processes, so differential pulse voltammetry (DPV) technique was applied to examine the response of the POMOF/rGO/GCE electrode to DA in pH 7.0. As in the extracellular fluid of the central nervous system and serum exist other species which interferes with DA detection such as ascorbic acid (AA), uric acid (UA), and glucose, researchers added them into the analyte solution indicating that the electrode was insensitive to those interfering species. This result is probably related to the π–π interactions of DA molecules with graphene or 1,10-phenanthroline groups of the POMOF.

Figure 11 Schematic representation of the producing and detecting of DA in POMOFs/rGO. Adapted from Ref. [58].

In another study, a new hybrid nanocomposite made from copper terephthalate MOF-graphene oxide (Cu(tpa)-GO) with extraordinary dispersibility and stability in aqueous solution was produced through the cooperative of π-π stacking interaction, hydrogen bonding and Cu-O 18

coordination in order to recognizing of acetaminophen (ACOP) and dopamine (DA) (Figure ) [59]. In order to fabricate the Cu(tpa)-GO nanocomposite, doubly distilled water containing Cu(NO3)2・3H2O was mixed with TPA in DMF/ethanol, then the obtained blue powder was added to aqueous GO under stirring followed by sonication. For inspect the sensing application of the Cu(tpa)-EGR/GCE electrode toward ACOP and DA, CVs plot was drawn in potential range from 0 to +0.8 V. Two pairs of small and asymmetric redox peaks according to the electron transfers of ACOP (at the higher potential range) and DA (at the lower potential range) appeared. By applying the electro-reduced electrode (Cu(tpa)-EGR/GCE), the redox peaks of ACOP and DA increased dramatically reversibly. Moreover, the electrochemical behavior of the prepared electrode in PBS in the absence of ACOP and DA was examined, showing that no redox peak existed under the equal potential range. So the authors claim that the Cu(tpa)-EGR had especially electrocatalysis toward ACOP and DA. For correlation, the electrochemistry of the drugs at EGR/GCE was also studied. Additionally, the common inorganic ions like K+, Na+, NH4+, Ca2+, Cl−, SO42− and PO43− in 100-fold excess and biological interferents including hydroquinone, glucose, tyrosine, ascorbic acid, and L-cysteine had no influence on the peak currents of drugs. Furthermore, the fabricated sensor had a huge ability in the recognition of ACOP and DA in serum and urine samples.

19

Figure 12 Representation for the sonication-assisted preparation of Cu(tpa)-GO, and its performance in the simultaneous determination of ACOP and DA. Adapted from Ref. [59].

In another work, a new core-shell heterostructure of CuxO nanoparticles@ZIF-8 (CuxO NPs@ZIF-8) was produced via pyrolysis of a nanocrystalline Cu-based MOF [HKUST-1, i.e., Cu3(BTC)2 (BTC = 1,3,5-benzene-tricarboxylate)]@ZIF-8 (Figure ), with the various thermal stability of the two MOFs to recognize H2O2 as the molecular model electrocatalytically [60]. Researchers explained the reason of their choices as (1) the ZIF-8 shell protects CuxO NPs from aggregation and migration in calcination process; (2) the ZIF-8 provides narrow penetration channels to transit the small molecules; (3) the great surface area and innate porosity of ZIF-8 are useful for reactants quickly to arrive at the surface of CuxO NPs; and (4) the CuxO NPs are able to keep their catalytic activity and high dispersion inside the host materials during the catalytic process. During adding the H2O2 to a 0.10 M NaOH solution, they observed a clear increase of oxidation current with increasing H2O2 concentration confirming that the ZIF-8 shell had no effect on the H2O2 diffusion. The reaction mechanism may be in this way: first, Cu+ (i.e., Cu2O)

20

was oxidized to Cu2+ (i.e., Cu(OH)2, CuO), after that to Cu3+ (i.e., CuOOH) by an electrochemical approach in alkaline media. Subsequently, H2O2 was oxidized via Cu3+ (i.e., CuOOH), and Cu2+ was reproduced. But bare GCE, CuxO NPs @ZIF-8-1/GCE, ZIF-8/GCE, and CuxO NPs@ZIF-8/GCE were followed with this order: CuxO NPs@ZIF-8/GCE > CuxO NPs@ZIF-8-1/GCE > ZIF-8/GCE > bare GCE as a result of the large surface area, the catalytic activity and the quantity of encapsulated CuxO NPs. Additionally, the obtained sensor was not affected by the interferes of uric acid (UA), DA, amino acid, ascorbic acid (AA), etc. The outcome sensing data were achieved for eight repetitive measurements without any clear performance reduction. Moreover, they reported an extended linear detection range (from 1.5 to 21442 μM) and a low detection limit (0.15 μM).

Figure 13 Schematic concept of the preparation of CuxO NPs@ZIF-8. Adapted from Ref. [60].

In another work to recognize the Cd2+ metal ion, a conductive electrochemical sensor, namely UiO-66-NH2@PANI, was synthesized during polymerizing the conductive polyaniline (PANI) polymer around the UiO-66-NH2 via using aniline as monomer due to good stability and the presence of amine group [61]. They used cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) to assess the characteristics of various modified electrodes [bare glassy carbon electrode (GCE), UiO-66-NH2/GCE and UiO-66-NH2@PANI/GCE]. Based on obtained curves, the CV response of UiO-66-NH2@PANI modified GCE exhibited the biggest current signal, demonstrating that the cooperation of UiO-66-NH2 and PANI accelerates the 21

electron transfer and improves the electrochemical sensitivity. In comparison with bare GCE (Rct=246 Ω), electron-transfer resistance of UiO-66-NH2/GCE decreased to 160 Ω, shows that the bare GCE was coated by UiO-66-NH2 efficiently. On the other hand, a reduction of Rct was observed after the growth of PANI on the exterior surface of the MOF (76 Ω), demonstrating the electron conduction of this polymer that can promote the electron transfer between the solution and electrode surface at optimum pH 5.0. The selection of this pH was as a result of preventing the protonation of the amino group in pH<5 and precipitation of cadmium ions as Cd(OH)2 in alkaline pH. In order to enhance the electrochemical determination sensitivity, the effects of accumulation potential and time on the oxidation peak current of Cd(II) were assessed indicating that when accumulation potential changed from -1.6 to -1.2 V the oxidation peak current of Cd(II) increased, and then slowly decreased from -1.2 to -0.6 V, thus the best value was -1.2 V for further experiments. On the other hand, with improving the accumulation time, cadmium accumulates at the UiO-66 NH2@PANI/GCE surface would increase, but the oxidation peak current almost kept a constant when the accumulation time is longer than 120 s, suggesting that the value of cadmium at the UiO-66-NH2@PANI electrode surface saturated. The oxidation peak currents are relative to the concentration of Cd(II) in a broader range of 0.5 to 600 μg L−1 with the detection limit as low as 0.3 μg L−1 (S/N = 3) in at least 10 cycles with 95.1% of the first current response. The R.S.D. of 4.5% was achieved showing the reliability of the fabrication procedure. Furthermore, they observed that the UiO-66- NH2@PANI modified GCE was very reliable and sensitive sufficient for sensing of Cd(II) in real environmental and biological samples due to the chelation mechanism between metal cations and amine groups. Moreover, they reported that no obvious changes were found in sensing performance in the presence of coexisting ions, so they claim that this material acts as a selective and sensitive sensor for determining the Cd ions. Recently, a novel nanoporous carbon and cobalt oxide-based composite (NPC–Co3O4) was proposed by direct thermal treatment of a single precursor source ZIF-67 to sense glucose electrochemically[62]. The NPC was synthesized from ZIF-67 as described previously[63]. A schematic representation of the preparation of NPC–Co3O4 composite for high-performance supercapacitor and electrochemical detection of glucose is shown in Figure14. As can be seen in Figure 15a, b, all the CV loops had a rectangular shape without redox transitions, demonstrating the good capacitive behavior. The integrated CV area of the composite was higher than that of 22

the NPC, exhibiting its charge storage efficiency. The enhanced-capacitance of the composite was based on the synergetic effect of NPC and Co3O4. Results show that the proposal composite has higher capacitance (885 F g-1) compared to that of pure Co3O4 (517 F g-1) and NPC (201 F g1

). The significant improvement in specific capacitance of NPC–Co3O4 composite is according to

the synergistic effect of small size and redox activity of the Co3O4 nanoparticles combined with a high surface area and electronic conductivity of the NPC. The NPC–Co3O4 composite consequently provided a higher available electrochemically reaction surface area for exploiting the full advantages of Co3O4 pseudocapacitance and NPC double-layer capacitance. Moreover, the decoration of Co3O4 nanoparticles onto the NPC surface led to electrochemical active sites, resulting in facilitating ion transport in the electrode and ultimately improving the capacitance. The selectivity of the NPC–Co3O4/GCE was examined by successive addition of 1.0 mM glucose and 1.0 mM interfering species including ascorbic acid (AA), uric acid (UA), dopamine (DA), and other carbohydrates [galactose (Gal), mannose (Man), and lactose (Lac)] resulting in no significant interference in the determination of glucose at the tested concentrations (Figure16a,b). The stability, reproducibility, and shelf life of the NPC–Co3O4/GCE were tested as can be seen in fig 6b. Only a 3.5% decline was appeared in the peak current, even after 100 cycles, illustrating the good stability of the electrode. The applicability of the proposed sensor in real samples was also evaluated validating the sensor as an excellent tool for the recognition of glucose in blood serum samples with high selectivity and sensitivity.

23

Figure 14.Schematic diagram of the fabrication of NPC–Co3O4 composite for glucose sensor and supercapacitor applications.[62].

Figure 15. (a) The CV curves illustrated from the NPC and NPC–Co3O4 composite at a scan rate of 0.1 V s-1, (b) the CVs of the composite at diverse scan rates.[62].

24

Figure 16. (a) Interference test of the NPC–Co3O4/GCE was documented in 0.1 M KOH, (b) CVs of the NPC– Co3O4/GCE for 100 various cycles in the existence of 1.0 mM glucose at a scan rate of 0.1 V s–1 ( The TEM image of the composite after 100 cycles was attached).[62].

5. Gas sensing Detection of analytes in the gas phase is a serious issue in the fields of environmental, security, health, food, and industrial processes. In this regard, Sachdeva and coworkers proposed a composite including a well-known MOF, NH2-MIL-53(Al), in a polymeric matrix, namely Matrimid, to sense methanol as primary analyte [64]. With increasing the quantity of MOF in the final composite, the response of the material would be enhanced toward methanol and the maximum response was obtained in the presence of 40% of loaded MOF. So it can compete with the commercially available methanol sensors (having a measurement range within 0−10 000 ppm). The observed decrease in the response at a higher wt % of the MOF could be as a result of a transition from polymer-limited adsorption to MOF-limited adsorption. In order to assessment of selectivity and sensitivity, authors put the MOF-modified sensor devices in exposure to water, methanol, ethanol, and 2-propanol. Based on the results, the equilibrium response decreased to 50% saturation response (τ0.5) with increasing of the analyte molecular size (water, methanol, ethanol, and 2-propanol). So diffusion of ethanol and 2-propanol through Matrimid polymer composite were performed gradually. Then they focused on water and methanol sensing. Results 25

showed that the Matrimid-based sensor exhibited a higher response toward methanol than to water. On the other hand, pure MOF has a more intense response toward water than methanol. This is because of the hydrophilic nature of the MOF compared to the polymer. In summary, there is no competition between water and methanol, and both analytes behave as if the other constituent is not present, but according to the temperature dependence of the sensor devices, an Arrhenius-type behavior with stronger methanol adsorption than water adsorption was observed, confirming a greater affinity toward methanol. In 2017, Tae Koo and coworkers prepared PdO@ZnOSnO2 nanotubes (NTs) by using Pd loaded ZIF-8 (Pd@ZIF-8) templates via the electrospinning technique followed by rapid ramping rateassisted calcination (Figure ) to detect of acetone, a biomarker for diabetes that is enlarged to more than 1.8 ppm in exhaled breath of patients in comparison with normal people (900 ppb) [65]. The detection limit of the sensor toward acetone was calculated to be 10 ppb (with Rair/Rgas = 1.31) by linear approximation. Moreover, the selectivity of PdO@ZnO-SnO2 NTs was assessed toward other biomarker gases including hydrogen sulfide (H2S), toluene (C7H8), carbon monoxide (CO), pentane (C5H12), and ammonia (NH3), exhibiting high response to acetone (Rair/Rgas = 5.06) in contrast with other gases (Rair/Rgas <2.35). Authors believe that this sensitivity and selectivity give arise as a result of the creation of n-n (ZnO-SnO2) heterojunction and the electronic sensitization effect of PdO. It can be concluded that the PdO@ZnO catalysts on hollow SnO2 NTs efficiently enhanced the acetone sensing properties.

Figure 17 Schematic concept of synthetic process and acetone sensing mechanism of PdO@ZnO-SnO2 NTs. Adapted from Ref. [65].

26

Since free noble-metal NPs are unstable because of having high surface energies and tend to aggregate and fuse, introducing them into organic or inorganic matrix could develop their stability and functionalities. consequently, He and coworkers synthesized a core-shell Au@MOF-5 (Zn4O(BDC)3, BDC=1,4- benzenedicarboxylate) NPs through adding Au NPs to a mixed solution congaing precursors of 521-MOF following by magnetically stirring for three days at 50 °C, with both uniform shape and tunable size with Au NP core and MOF-5 shell with the thickness of (3.2±0.5) nm to sense CO2 in gas mixtures selectively [44]. The thickness of the shell is a key factor in the sensing process because the thick shells cause the difficult diffusion of CO2 into the interface of the Au NP cores. While the diffusion into the interface of free Au nanoparticle cores is easy, selective CO2 detection has not occurred. On the other hand, pure MOF-5 spheres did not contain a Raman signature because of absence of the amplification effect of Au NPs.

6. SERS Sensing In 2016, to detect a biomarker namely N-terminal pro-brain natriuretic peptide (NT-proBNP), He et al. combined the amino-functionalized IRMOF-3 with Au tetrapods (AuTPs) and toluidine blue (TB) as Surface-enhanced Raman spectroscopy (SERS) tags in a SERS-based sandwich immunosensor (Figure 4) [19]. Synthesis of IRMOF-3 was followed as dissolving PVP in DMF/ethanol, then a DMF solution containing NH2-H2BDC and Zn(NO3)2 was added to the above solution to heat at 120 ̊C for 16 h. Moreover, Au nanoparticles functionalized CoFe2O4 magnetic nanospheres (CoFe2O4@AuNPs) were produced to assemble the main antibody. The final composite, IRMOF-3@AuTPs@TB, could exhibit a strong SERS signal to sense NTproBNP via sandwiched antibody-antigen interactions with the detection limit of 0.75 g mL-1. The Raman peaks of IRMOF-3 and IRMOF-3@AuTPs are very weak, but after introducing TB, the peak was detected clearly. So it can be concluded that TB can act as a SERS molecular beacon. Then, CoFe2O4@AuNPs and IRMOF-3@AuTPs@TB were used to fix primary antibodies and second anti-NT-proBNP. When IRMOF-3@AuTPs@TB@Ab2 was conjugated with CoFe2O4@AuNPs@Ab1 with antigen-antibody immunoreaction, an obvious Raman signal has appeared. Authors think that this occurrence is related to enhancing TB signal by IRMOF3@AuTPs, furthermore, the CoFe2O4@AuNPs enhance the signal of TB through the magnetic field. So the obtained immunosensor exhibited a favorable sensitivity during fifteen different 27

spots constantly. Meanwhile, the sensor was applied in the presence of human alphafetoprotein (AFP), carcinoembryonic antigen (CEA), glucose (GLU), human serum albumin (HSA) and immunoglobulin G (IgG) in the equal conditions, demonstrating no clear change of the peak intensity. Moreover, the authors found that it could have the potential to be applied in clinical applications.

Figure 4 Schematic concept of the SERS-based immunosensor for the detection of NT-proBNP. Adapted from Ref. [19].

7. Refractive index sensor Fabricating composites via many functional materials, like polymers, and colloidal crystals create a modern approach to sense ions, biomolecules, and volatile molecules[8]. Colloidal crystals are a band of sub-micrometer-sized silica or polymer microspheres, arranging to reflect the specific wavelength of light based on the reflective index in the crystals. They were examined by sensing application, because of their stop band sensitivity relative to changes in the refractive index and/or lattice spacing which made from loading various materials such as solvents into the pores inside the crystal. HKUST-1, a constantly microporous MOF with the 28

empirical formula [Cu3(BTC)2] (BTC = 1, 3, 5-benzenetricarboxylicacid), for its good structure and perfect properties was selected to add into stable silica, making MOF-silica colloidal crystal (MOF-SCC) composites. The colloidal crystal thin film was assembled from monodisperse silica microspheres via vertical deposition and summarily sintered at 600 °C to enhance its mechanical stability and also to remove micropores in the silica microspheres. Moreover, silanization and oxidation were carried out to modify the surface of microspheres with carboxylic acid groups, and after preparing the purpose template, HKUST-1 grew on the crystal. As can be seen in Figure 5a,

b, the stopband of the MOF-SCC red shifts by up to ≈ 16 nm during irradiation to carbon

disulfide (CS2), which is occurred at the highest vapor concentrations. The MOF-SCC response to analyte vapors is hasty (seconds) and reversible. Based on stop-band peak shifts, the authors estimated potential detection limits of 2.6 ppm for water, 0.5 ppm for CS2, and 0.3 ppm for ethanol. They claim that these values are validated by quartz crystal microgravimetry measurements.

Figure 5 a) Near-IR extinction spectra of the MOF-silica colloidal crystal thin film and the unmodified one before and after exposure to 10 000 ppm CS2. b) Responses of MOF-silica colloidal crystal thin film to a series of CS2 vapors of various concentrations versus time. Adapted from Ref.[8] .

8. Conclusion and Future Outlook As a new kind of crystalline molecular material, MOFs have excellent chemical and physical properties, such as tailorable pore sizes, great special surface area, and tunable structure. Due to the excellent properties, MOFs are found to have broad applications in different fields (e.g., gas storage, separation, catalysis, biomedical imaging, and sensing). However, MOFs still has some 29

disadvantages, such as poor mechanical strength, low stability, and single function, which limit their application. Therefore, the combination of MOF and functional materials can result in new MOF composites that are surpassing the performance of original components. MOF nanocomposites have the functions of selective adsorption and separation, catalysis, magnetism, and luminescence, which make the composite broadly applied in various kinds of sensors, such as electrochemical sensors, optical sensors, and others. In this review, we discussed some kinds of MOF-based composites in the sensing process. The synergetic effect of both components of the nanocomposite (e.g., the MOFs and metal/metal oxide NPs/rGO/GO/QDs/enzymes) should lead to a betterment in the photoelectrochemical detection of various analytes. As has been observed in many works, these MOF-nanocomposites can improve the sensing properties for detecting a broad range of species including heavy metal ions, anions, aromatic hydrocarbons, toxic phenolic compounds, and temperature. In future studies, using diverse functionalized MOFs could improve the recognition performance in composite-based sensors. Furthermore, joining various NPs with many other advantages could lead to significant efficiency in the sensing area.

Acknowledgments Support of this investigation by Iran University of Science and Technology, Iran National Science Foundation: INSF and Iran’s National Elites Foundation is gratefully acknowledged.

Table 1. Selected examples of MOFs nanocomposites for sensing applications. MOF

Composite

Method/Analyte

Ref

ZJU-88

perylene

Luminescent/ perylene

[48]

2+

UiO-66-NH2

ssDNA

Luminescent / Hg

[51]

JXNU-4

Eu3+

Luminescence/ 1-

[49]

Hydroxypyrene (1-HP) MOF-5

APTMS–ZnO QDs

Luminescence/ phosphate

[54]

(Pi) HKUST-1

silica colloidal crystal

Refractive index sensor / carbon disulfide (CS2)

30

[8]

UiO-66-(COOH)2

Eu3+/Cu2+ ions

Luminescence / hydrogen

[37]

sulfide (H2S) HKUST-1

carbon

Electrochemical/

[43]

Hydroquinone (HQ) and catechol (CT) UiO-66

ZIF-8

mesoporous carbon

Electrochemical/

(MC)

dihydroxybenzene isomers

Cu nanoparticles

Electrochemical/ glucose

[55]

[56]

in alkaline media MIL-101(Fe)

silver nanoparticles

Electrochemical/

[7]

(AgNPs)

tryptophan (Trp)

Zr-MOF

Au NCs

Electrochemical/ cocaine

[57]

[Mo5P2O23]

reduced graphene oxide

Electrochemical/

[58]

[Cu(phen)(H2O)]3

(rGO)

dopamine

graphene oxide

Electrochemical/

(Cu3Mo5P2) copper terephthalate MOF

acetaminophen (ACOP)

Cu(tpa)

and dopamine (DA)

[59]

ZIF-8

(CuxO NPs@ZIF-8)

Electrochemical/ H2O2

[60]

UiO-66-NH2

PANI

Electrochemical/ Cd2+

[61]

ZIF-67

NPC–Co3O4

Electrochemical/glucose [63]

NH2-MIL-53(Al)

(polymeric matrix)

Gas sensing/ Methanol

[64]

Matrimid ZIF-8

PdO@ZnOSnO2

Gas sensing /acetone

[65]

MOF-5

Au NP

Gas sensing / CO2

[44]

IRMOF-3

Au tetrapods (AuTPs)

SERS sensing /N-terminal

[19]

pro-brain natriuretic peptide (NT-proBNP)

31

Abbreviation 1-HP

1-Hydroxypyrene

AA ACOP

Ascorbic acid Acetaminophen

AFP

Alphafetoprotein

AgNPs

Silver nanoparticles

Ala

Alanine

APTMS

(3-aminopropyl) trimethoxysilane

Arg

Arginine

AuTPs

Au tetrapods

BDC

1,4- benzenedicarboxylate

BTC

1,3,5-benzene-tricarboxylate

C5H12

Pentane

C7H8

Toluene

CEA

Carcinoembryonic antigen

CO

Carbon monoxide

CS2

Carbon disulfide

CT

Catechol

Cu(tpa)-GO

Copper terephthalate graphene oxide

CV

Cyclic voltammetry

Cys

Cysteine 32

DA

Dopamine

DAQ

Dopamine quinone

DBIs

Dihydroxybenzene isomers

DBIs

Dihydroxybenzene isomers

DPV

Differential pulse voltammetry

EIS

Electrochemical impedance spectroscopy

FAM

Fluorophore

GCE

Glassy carbon electrode

Glu

Glutamate

GLU

Glucose

GN H2S

Graphene Hydrogen sulfide

H4QPTCA

(1,1′:4′,1′′:4′′,1′′′-quaterphenyl-3,3′′′,5,5′′′tetracarboxylic acid)

His

Histidine

HKUST-1

[Cu3(BTC)2]

HQ HSA

Hydroquinone Human serum albumin

IgG

Immunoglobulin G

JXNU-4

(Me2NH2)2[Zn6(μ4-O)(ad)4(BPDC)4]

LC

Ligand-centered

Leu

Leucine

MC

Mesoporous carbon

MC

Mesoporous carbon

MIL

Material sofistitute Lavoisier

MOFs

Metal-organic frameworks

MOF-SCC

MOF-silica colloidal crystal

33

NCs

Nanoclusters

NH3

Ammonia

NPs

Nanoparticles

NPs NT-proBNP

Nanoparticles N-terminal pro-brain natriuretic peptide

PAHs

Polycyclic aromatic hydrocarbons

PANI

Polymerizing the conductive polyaniline

PET

Photoinduced energy transfer

PET

Photoinduced energy transfer

Pi

Phosphate

POMOF

Polyoxometalate based-MOF

QDs

Quantum dots

rGO

Reduced graphene oxide

RSD

Relative standard deviation

Ser

Serine

SERS

Surface-enhanced Raman spectroscopy

SPCE ssDNA

Screen-printed carbon electrodes Single-stranded DNA

TB

Toluidine blue

T-Hg2+-T

Thymine-Hg2+-Thymine

Trp

Tryptophan

T–T

Thymine-Thymine

UA

Uric acid

WHO

World Health Organization

ZIF

Zeolitic imidazolate framework

ZJU-88

([Eu2(QPTCA)(NO3)2(DMF)4]·(CH3CH2OH)3)

NPC

Nanoporous carbon

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Making composites with modification of MOF transforms them to the best candidate for detection of different items

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