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Recyclable Eu3+ functionalized Hf-MOF fluorescent probe for urinary metabolites of some organophosphorus pesticides
Journal Pre-proof 3+ Recyclable Eu functionalized Hf-MOF fluorescent probe for urinary metabolites of some organophosphorus pesticides Bing-Hui Wang, Xiao Lian, Bing Yan PII:
S0039-9140(20)30147-8
DOI:
https://doi.org/10.1016/j.talanta.2020.120856
Reference:
TAL 120856
To appear in:
Talanta
Received Date: 28 December 2019 Revised Date:
18 February 2020
Accepted Date: 19 February 2020
3+ Please cite this article as: B.-H. Wang, X. Lian, B. Yan, Recyclable Eu functionalized Hf-MOF fluorescent probe for urinary metabolites of some organophosphorus pesticides, Talanta (2020), doi: https://doi.org/10.1016/j.talanta.2020.120856. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.
CRediT author statement Bing-Hui Wang: Data curation, Writing- Original draft preparation. Bing-Hui Wang: Visualization, Investigation. Xiao Lian: Validation, Reviewing and Editing. Bing Yan: Conceptualization, Methodology, Supervision.
Novel luminescence probe Eu3+ functionalized Hf-MOF Eu3+@1 have been prepared to effectively sense PNP and PNMC(the metabolites of some common OPs pesticides) in human urine, without the interference of urinary constituents.
Recyclable Eu3+ functionalized Hf-MOF fluorescent probe for urinary metabolites of some organophosphorus pesticides
Bing-Hui Wanga, Xiao Liana, and Bing Yana,b* a
School of Chemical Science and Engineering, Tongji University, Siping Road 1239, Shanghai 200092, China.
b
School of Materials Science and Engineering, Liaocheng University, Liaocheng 252059, China
* Corresponding author: Email address: [email protected] (Bing Yan)
Abstract A luminescent metal-organic framework Eu3+ functionalized Hf-MOF (Eu3+@1) is designed through post-synthesis modification (PSM) and utilized as a probe for detecting p-nitrophenol (PNP,
the
urinary
metabolite
of
parathion,
methyl-parathion
and
EPN)
and
3-methyl-4-nitrophenol (PNMC, the urinary metabolite of fenitrothion). The apparent quenching effect in urine is observed from the Eu3+@1 with the addition of organophosphorus metabolites. The fluorescent probe has several appealing merits, such as high selectivity, excellent sensitivity (0.36 µg mL-1 for PNP, 0.41 µg mL-1 for PNMC), fast response time (less than 1 min) and easy preparation. Linear correlation between the fluorescence intensity of Eu3+@1 and the concentration of PNP and PNMC are from 0.005–0.15 mg mL-1 and 0.005– 0.30 mg mL-1, respectively. Furthermore, this fluorescent material also demonstrated the possibility for recycling. It is a prominent candidate for potential application in personalized monitoring the internal dose of human exposure to some organophosphorus pesticides. Keywords: 4-nitrophenol; 3-methyl-4-nitrophenol; Metal-organic frameworks; Metabolites; Fluorescence sensing; Photofunctional hybrid material.
1. Introduction For nearly five decades, organophosphorus (OPs) compounds are significantly applied in the agriculture industry around the world, especially as pesticides [1]. Estimates from Center for Disease Control and Prevention (CDC), about 60 million pounds of OPs pesticides are applied to 38 million acres of U.S. agricultural crops every year [2]. Wide use of OPs causes serious consequence. Apart from insect, OPs are also highly toxic to human. Previous researches have proved that there is a link between OPs compounds exposure and delayed polyneuropathy(Parkinson's disease) [3], muscle weakness [4], immunotoxicity [5], endocrine disruption [6], cancer incidence [7] and paralysis [8]. World Health Organization (WHO) declares that approximately 1 million accidental and 2 million suicidal poisonings related to OPs pesticides occur annually [9]. Parathion (O, O-diethyl-O-p-nitrophenyl phosphorothioate), methyl-parathion (O, O-dimethyl O-p-nitrophenyl phosphorothioate), ENP (O-ethyl O-4-nitrophenyl phenylphosphonothioate) are representative organophosphorus (OPs) insecticides which can inhibit acetylcholinesterase, leading to an accumulation of acetylcholine at nerve endings like others [10-12]. Among the carcinogen list assessed by International Agency for Research on Cancer (IARC), parathion is classified as Group 2B (possibly carcinogenic to humans) [13]. Methyl parathion is a class Ia (extremely toxic) insecticide evaluated by WHO and also classified as Toxicity Category I (most toxic) insecticide from the United States Environmental Protection Agency (U.S. EPA) [14]. EPN is an endocrine-disrupting chemical with estrogenic and antiandrogenic activity confirmed by the previous research [15]. All of the poisonous insecticides can result in the urinary excretion of p-nitrophenol (PNP) after metabolized by the liver and kidney. Fenitrothion (O,O-dimethylO-4-nitro-m-tolyl phosphorothioate) is overused in the field of agriculture for crop protection [16]. However, the toxicosis of the pesticides is usually life threatening and even fatal for human [17]. 3-Methyl-4-nitrophenol (PNMC) is the specific metabolite of it
[18]. Based on the fact that the four OPs are rapidly metabolized in humans, it is not practical to determinate the original OPs in urine/blood if we want to make an accurate assessment of individual exposure [19-21]. Instead, exposure metabolites always associate with physiological or pathophysiological process, so it is more effective to evaluate the OPs intoxication level in human [22-23]. At present, monitoring the metabolites of exposure is the most frequently used approach for the detection of exposure chemicals [24-25]. To date, many efforts have been made to determine PNP or PNMC in urine, such as spectrophotometric measurements [26], liquid chromatography-mass spectrometry (LC-MS) [17], gas chromatography–mass spectrometry (GC–MS) [27-28], and high performance liquid chromatography (HPLC) [29-30]. Although these methods have high selectivity and excellent sensitivity, they have some limitations unavoidably, including expensive equipment, toxic reagents, complicated and time-consuming procedures and the requirement of professionals. As a result, it is significant to explore a new method which is simple, environmentally friendly and own immediate feedback. Lanthanide metal–organic frameworks (Ln-MOFs) is a special kind of luminescent MOFs which have been extensively studied in recent years [31-32]. Most Ln-MOFs materials are relatively simple to prepare. It possesses unique luminescence properties, like large Stokes shifts, relatively long luminescence lifetimes and characteristically sharp line emissions, deriving from 4f–4f transitions via “antenna effect’’ [33-35]. It is worth noting that the emission of Ln-MOFs is quite sensitive to their structural characteristics, coordination environment of lanthanide ions and interactions with analytes, making it possibility to be applied in the sensing field [36]. So far, Ln-MOFs have exhibited detection abilities for inorganic ions [37-38], organic small molecules [39-40], nitro explosives [41-42], vapors [43-44] and so on. In this study, we prepare a Eu3+ functionalized Hf-MOF (UIO-67-bpydc) fluorescent probe
by the hydrothermal approach for the detection of PNP and PNMC in human urine (Fig. 1). On the one hand, the ligand with bipyridyl moieties can effectively sensitize the emission of Eu3+ through the ligand-to-metal energy transfer (LMET) process to emit sharp and characteristic luminescence. On the other hand, according the previous study, the UV-absorption of the ligand has large overlap with the PNP and PNMC, suggesting the possibility of competitive absorption between ligand and metabolites. Hence, we assume that the efficiency of LMET process will be decreased by the competitive absorption, leading to the luminescence quenching and thus detecting the existence of metabolites. Moreover, the method is further applied in human urine. Satisfactory outcomes have been obtained, including superior water/pH toleration, high selectivity, excellent sensitivity and fast response time and great recyclability. (Figure 1 insert here) 2. Experimental section 2.1. Materials and reagents Lanthanide nitrates EuCl3·6H2O were prepared by dissolving the corresponding oxide compounds quantitatively in concentrated nitric acid followed by evaporation and recrystallization. Urine was collected from student volunteers from the Institute of Chemical Science and Engineering. (Informed consent statement: informed consent was obtained from all subjects.) All the other materials were commercially available reagents of analytical grade. Deionized water was used throughout the experiments. 2.2. Experimental equipment Powder X-ray diffraction patterns (PXRD) patterns were recorded with a Bruker D8 diffractometer under CuKa radiation and the data were collected within the 2θ in range of 5-40 °. Fourier transform infrared (FTIR) spectra were measured within KBr slices from 4000 to
400
cm-1
using
a
Nicolet
IS10
infrared
spectrum
radiometer.
Nitrogen
adsorption/desorption isotherms were measured at a liquid nitrogen temperature using a TRISTAR 3020 analyzer. X-ray photoelectron spectroscopy (XPS) was performed on a RBD upgraded PHI-5000C ESCA system (Perkin Elmer) with MgKa radiation (h υ = 1253.6 eV). Energy-dispersive X-ray analysis (EDX) were conducted on a Hitachi S-4800 field emission scanning electron microscope operating at 15 kV. Transmission electron microscopy (TEM, JEM-2100) was used to characterize the morphology of the sample. UV–vis absorption spectra were measured with an Agilent spectrophotometer. Excitation spectra, emission spectra of the samples were performed on an Edinburgh FLS920 phosphorimeter with a 450 W xenon lamp as excitation source. 2.3. Synthesis of Hf-MOF 1 Hf-MOF 1 was synthesized according to the reported method [45]. HfCl4 (96.1 mg, 0.3 mmol), H2bpydc (73.2 mg, 0.3 mmol), 4 mL N,N-dimethylformamide (DMF) and 1 mL formic acid were added to a 25 mL Teflon-lined stainless steel reactor. Then, the reactor was sealed and heated to 150 °C for 24 h. The resultant white powder was cooled to room temperature, filtered and washed several times with DMF. To remove the unreacted ligand, the product was washed with DMF at 70 °C for 24 h. After washed by chloroform for 3 times and dried in an oven with 150 °C for 24 h, target product 1 was synthesized eventually. 2.4. Synthesis of Eu3+@1 Eu3+@1 was synthesized according to the reported method [46]. Eu3+@1 was prepared by dispersing 1(100 mg) into the methanol solution of EuCl3·6H2O (30 mL, 5 mmol). The solution was stirred for 12 h at 60 °C. After separation by centrifugation and washing three times with ethanol for removal of residual Eu3+, the resulting white powder was dried at 80 °C for 12 h. 2.5. Luminescent sensing experiment For the detection of PNP and PNMC, the Eu3+ @1 was dispersed into distilled water to
form an aqueous suspension (1 mg mL-1), followed by adding the metabolites to the solution. To investigate the selectivity and sensitivity of Eu3+ @1, experiments were tested under unitive condition except different aqueous suspension (10 mM) present in human urine, including creatinine (Cre), creatine, urea, uric acid (UA), glucose (Glu), NaCl, NH4Cl, KCl and Na2SO4.
3. Results and discussion 3.1. Physical characterization of 1 and Eu3+ @1 The precursor Hf-MOF (UIO-67(Hf)-bpydc, 1) is synthesized by hydrothermal method, after blending HfCl4 and ligand H2bpydc in the solvent containing DMF and formic acid [45]. As shown in Fig. S1, the three-dimensional MOF comprises a hexagonal-close-packed (hcp) array of Hf12O8 (OH)14 clusters linked with bpydc2− ligands. Particularly, the accessible sites of the bipyridyl moieties in the framework show the potential of post-synthetic modification (PSM), which make it possible to prepare a new material with better luminescence. Powder x-ray diffraction (PXRD) shows that the diffraction peaks of the as-synthesized 1 matches well with the simulated, verifying the successful synthesis of 1 with a pure phase (Fig. 2a). N2 adsorption measurement reveals that the Brunauer-Emmett-Teller (BET) surface area of the MOF is 504.13 m2 g−1 (Fig. S2), demonstrating that the MOF is adequately porous to offer a space in lattice for lanthanide cations. Hence, we introduce Eu3+ into the channels of 1 to prepare Eu3+@1 hybrid by immersing the samples in methanol solution of EuCl3·6H2O. The material retains its crystallinity and morphology after introducing Eu3+, proved by PXRD patterns in Fig. 2a. However, compared with 1, the BET surface of Eu3+@1 displays a big drop, with only 129.14 m2 g−1 (Fig. S2). The phenomenon is ascribed to the residence of the coordinated Eu3+ in the cavities of 1. X-ray photoelectron spectroscopy (XPS) spectra are recorded to determine the chemical states of Eu3+ in Eu3+@1 (Fig. 2b). The peaks of Eu 3d5/2
and 3d3/2 appear at 1131.9 eV and 1161.8 eV in Eu3+@1, respectively, and the peak at 134.4 eV corresponds to the 4d of Eu, indicating the successful encapsulation of Eu3+ into the MOF. Whereas, the Eu 3d peaks of Eu3+@1 show a lower binding energy compared to EuCl3 (Fig. S3). It could be attributed to the coordination of Eu-N bonds between to Eu3+ and the free N,N-chelating sites [47, 48]. As shown in the Fourier transform infrared (FTIR) spectra (Fig. S4), 1 and Eu3+@1 exhibit similar results. The peaks at around 1590 cm-1 and 1415 cm-1 are consistent with the absorption of the bipyridyl and carboxylic group, respectively. Energy dispersive analysis of X-rays (EDX) analysis confirms that the Eu3+ is incorporated with the compound 1 again (Fig. S5 and Table S1). The TEM images of Eu@1 (Figure S6) show a lamellar structure with nanoscale dimensions, which is correspond with reported hcp MOFs based materials [45, 46]. (Figure 2 insert here) 3.2. Luminescence properties of 1 and Eu3+ @1 The emission spectrum of the ligand H2bpydc displays a broad band from 400 to 650 nm with a maximum at 558 nm under the UV irradiation of 377 nm, attributed to the π → π* electron transition of the organic linkers (Fig. S7a). The hybrid 1 shows a strong emission band at 524 nm when excited at 365 nm (Fig. S7b). The blue shifting between ligand and compound 1 is ascribed to the coordination of H2bpydc to Hf4+ cations [46]. After post-synthetic functionalized by Eu3+, Eu3+@1 exhibits five Eu3+ emission peaks at 579(5D0 → 7F0), 592(5D0 → 7F1), 613(5D0 → 7F2), 650(5D0 → 7F3) and 701 nm(5D0 → 7F4) upon excitation at 332 nm, leading to a bright red light which can be easily distinguished by naked eye (Fig. 3a). The typical electric dipole transition 5D0 → 7F2 transition is very sensitive to the local symmetry of Eu3+. At the same time, the parity-allowed magnetic dipole transition 5D0 → 7F1 is independent of the ions’ surroundings. The high ratio of I(5D0 →7F2)/I(5D0 → 7F1) (about 5.7) confirms that Eu3+ is located in a low symmetry chemical environment [49-50].
Whereas, the luminescence spectrum of Eu3+@1 displays little evidence of the ligand-centered emission from 400 to 650 nm. It can be attributed to the effective energy transfer from the H2bpydc ligand to the Eu3+ ions (Fig. 3b). As shown in Fig. S8, the Commission internationale de l’Eclairage (CIE) chromaticity diagram of Eu3+@1 is located at (0.6611, 0.3196), corresponding to the luminescence spectrum and the photo under the irradiation of UV-light. (Figure 3 insert here) 3.3. Stability investigation of Eu3+@1 Urinalysis tests can reflect the physical parameters of the individual. P-nitrophenol (PNP, the urinary metabolite of parathion, methyl-parathion and EPN) and 3-methyl-4-nitrophenol (PNMC, the urinary metabolite of fenitrothion) are the typical urinary metabolite of the corresponding organophosphorus (OPs) pesticides. It is realistic to monitor the level of PNP and PNMC in urine for the detection of OPs pesticides exposure and intoxication of human beings. As water is the major component of urine, water-stability of Eu3+@1 probe is first studied. According the previous study [46], the probe Eu3+@1 with nanoscale dimensions can be uniformly dispersed in the water. To monitor the structure variations of Eu3+@1 before and after immersed in aqueous solution for 48 h, we record the related PXRD patterns and emission spectra in Fig. S9. As the figures show, both of the crystalline structure and luminescence of Eu3+@1 have hardly change, suggesting the good water-stability of the hybrid. In addition, pH-independent stability is another crucial factor to estimate the property of urinary probe, while the pH value of real human urine ranges from 4.6 to 8.0. Fig. S10 presents that the compound crystallinity and luminescence of Eu3+@1 stay the same even though dipping in diverse pH aqueous solutions. Moreover, as shown in Fig. S11, the luminescence spectra of the probe have hardly changed although the temperature varies from 15 °C to 30 °C. The excellent water-stability, pH-independent stability and temperature
stability of Eu3+@1 lay the foundation for the detection of the metabolites in urine. 3.4. Sensing for PNP and PNMC Besides water, there are other molecules and ions existing in urine, which may disturb the detection result, containing glucose (Glu), uric acid (UA), creatinine (Cre), creatine, urea, KCl, NaCl, NH4Cl and Na2SO4. To study the effect of the urinary constituents to the luminescence probe, we conduct a series of controlled experiments. Certain amount of Eu3+@1 (3 mg) is added to the nine urine constituents, PNP and PNMC aqueous solutions (0.01 M) under the same conditions (temperature, pressure, excitation and response time). The luminescence spectra in Fig. 4a illustrate that the participations of these urinary components only cause negligible changes in the luminescence compared to the Eu3+@1 aqueous solution with the excitation at 332nm. On the contrary, with the addition of PNP and PNMC, a prominent decrease in the luminescence of Eu3+ can be easily observed by the naked eye, leading to the luminescence transforms from bright red to almost vanishing under a UV lamp (Fig. 4b). The histogram, made by mirroring the characteristic emission peak (613 nm) of Eu3+@1 with the existence of different constituents, visually proves the high selectivity of Eu3+@1. The response time is very short. According to the Fig. S12, the luminescence of Eu3+@1 is dramatically reduced with the immersion of PNMC and PNP for 30 s. After 1 min, the luminescence decrease reaches a constant. (Figure 4 insert here) Further, to explore whether the existence of the coexisting urinary substances will influence the luminescence detection process of Eu3+@1 to PNP and PNMC, we conduct a series of competition experiments under the same excitation (332 nm). As shown in the luminescence intensity histogram (Fig. 5), the quenching effect of Eu3+@1 is not affected by the coexisting components. It only happens when the metabolite PNMC or PNP is added to the solution, whether there exist other urine chemicals or not. These results indicate Eu3+@1 have the
potentially to be a highly selective probe for PNP and PNMC in the background of other urine ingredients. (Figure 5 insert here) Besides selectivity, the sensitivity of the probe Eu3+@1 to PNP and PNMC is also very important. Thus, we prepare a batch of Eu3+@1 suspensions with diverse concentrations of PNP and PNMC in real urine. The experiments are repeated three times, and the results are presented as the average value of the data. Error bar has been also displayed in the inset of Figure 6. As displayed in the figure, under 332 nm excitation, the luminescent emission intensity of Eu3+@1 gradually decrease with the increasing concentration of metabolites. For PNP, the emission peaks gradually flatten and almost disappear at about 0.15 mg mL-1. There is a preeminent linear relationship between the concentrations of PNP and the emission intensity (613 nm) in a large concentration range. The linear correlation can be fitted into the equation I= -10.017-11.217 log CPNP(R = 0.991, linear range: 0.005–0.15 mg mL-1). The LOD is calculated to be 0.36 µg mL-1, which is lower than the threshold limit value of 0.5 µg mL-1 [51]. Further details on the calculations is provided in the supporting information. The relative standard deviation (RSD) of three repeated determination is calculated from 0.74% to 3.78%. As for PNMC, The value of curve is calculated as I= -5.417-9.234 log CPNMC (R = 0.995, linear range: 0.005–0.3 mg mL-1). The LOD is calculated to be 0.41µg mL-1. The RSD is calculated from 1.35% to 4.18%. The results demonstrate that the fabricated probe Eu3+@1 possess excellent sensitivity to the metabolites of OPs pesticides. Comparing with previously reported methods in Table S2, Eu3+@1 probe has a wider linear detection range without the cumbersome operational process. The LOD is also very low which can satisfy daily monitoring needs. (Figure 6 insert here) All of the facts have testified that the Eu3+@1 is an outstanding probe for PNP and PNMC
detection in urine. Moreover, in practice, recoverability of a probe plays a crucial role in its applications. Hence, the recovery experiment is investigated. As shown in Fig. 7, the luminescence intensity of Eu3+@1 is almost recovered to its initial state via centrifugation and washing with deionized water. After three recycles performed by metabolites addition (PAP, 0.1 mg mL-1; PNMC, 0.2 mg mL-1) and ultrasonic washing, the luminescence of the recycled treated probe is similar to the initial hybrid. The result reveals that the probe Eu3+@1 could be reused for PNP and PNMC detection. Furthermore, the detection process also suggests the weak interaction between the metabolites and the probe Eu3+@1. The luminescence of the probe is closely linked to the presence or absence of the PNP and PNMC and the removal of metabolites can be realized by ultrasonic washing. (Figure 7 insert here) 3.5. Sensing mechanism Moreover, we explore the detection mechanism of the probe. Generally, the possible mechanism of quenching effect on the luminescence of lanthanide MOF can be divided into three ways: (1) the collapse of the crystal MOF material; (2) the interaction with the lanthanide ions; (3) the interaction with the ligands. From Fig. S13, the PXRD patterns of Eu3+@1 with PNP, PNMC or other constituents of urine are coincident with the original patterns, suggesting that the basic structure of the MOF is well-remained. For another, there are no available functional group, like β-diketone moieties, in PNP or PNMC to coordinate with Eu3+. Thus, to investigate the quenching effect to PNP and PNMC, we study the related UV-vis spectra as shown in Fig. S14. It is obviously illustrated that the absorption peak of the MOF framework (ligands) in Eu3+@1 nearly overlaps with the adsorption of PNP and PNMC. In fact, the efficiency of the luminescence in lanthanide MOF depends on the degree of the energy transfer. If the guest molecule competes source energy with the ligand, the energy transfer efficiency from ligand to lanthanide will decrease and the luminescence will reduce
accordingly [52]. Summing up the above, competitive absorption between ligands of Eu3+@1 and metabolites is the most practical mechanism.
4. Conclusion In summary, the paper reports a luminescent metal-organic framework Eu3+ functionalized Hf-MOF (Eu3+@1) material to detecting p-nitrophenol (PNP, the urinary metabolite of parathion, methyl-parathion and EPN) and 3-methyl-4-nitrophenol (PNMC, the urinary metabolite of fenitrothion). The as-prepared Eu3+@1 not only possesses the excellent water-stability and pH-independent tolerance but also have high sensitivity without the interference of urinary constituents and fast response time(less than 1min). According to the linear relationship between the increasing concentrations of metabolites and the emission intensity in real urine, the probe can achieve effective detection from 0.005–0.15 mg mL-1 (for PNP) and 0.005–0.30 mg mL-1 (for PNMC). The detection limit is also very low with 0.36 µg mL-1 for PNP and 0.41 µg mL-1 for PNMC which can satisfy daily monitoring needs. Moreover, the probe Eu3+@1 shows the good recyclability as well, which is a crucial advantage in the practical applications. Given the above, the probe possesses the potential to serve as a powerful detection tool to help human judge intoxication degree of the OPs pesticides.
CRediT author statement Bing-Hui Wang: Data curation, Writing- Original draft preparation. Bing-Hui Wang: Visualization, Investigation.
Xiao Lian: Validation, Reviewing and Editing. Bing
Yan: Conceptualization, Methodology, Supervision.
Acknowledgment
This work was supported by the National Natural Science Foundation of China (21571142, 21971194), and Developing Science Funds of Tongji University.
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Figure legends Fig. 1 Schematic illustration of the fabricated Eu3+ @1 as a fluorescence probe for PNP and PNMC. Fig. 2 (a) PXRD patterns of simulated 1, as-synthesized 1 and Eu3+ @1 samples; (b) XPS spectra of compound 1 and Eu3+ @1. Fig. 3 (a) Excitation and emission spectra of Eu3+ @1. The inset shows the corresponding photo with the irradiation of a UV lamp; (b) Schematic representation of energy transfer process from ligand to Eu3+ in Eu3+@1. S, singlet; T, triplet; ET, energy transfer; J, J = 0-4. Fig. 4 The luminescence spectra (a) and relative intensities (b) of Eu3+ @1 at 613 nm (5D0 → 7
F2) when dispersed in diverse aqueous solutions (λex = 332nm). Inset: the corresponding
photograph under UV-light irradiation. Fig. 5 Comparison of the relative luminescence intensity of Eu3+ @1 (613 nm) toward coexisting urinary substances in the presence and absence of PNP and PNMC (λex = 332 nm). Fig. 6 Fluorescence spectra of Eu3+@1 in the presence of different concentrations of PNP (a)
and PNMC (b) in real urine (λex = 332 nm), inset: the plot of luminescence intensity versus logarithm of the concentrations of the PNP and PNMC. Fig. 7 The generation cycles of sample of Eu3+@1 used in detecting PNP (a), PNMC (b).
Fig. 1
Fig. 2
Fig. 3
Fig. 4
Relative Intensity (a.u.)
origin PNMC PNP
H2O
NaCl NH4Cl
UA KCl
Urea
Cr
Glu
e
4
tin ea
SO Na 2
Cre
Fig. 5
Fig. 6
Fig. 7
Highlights
High sensitivity to detect even trace amount PNP and PNMC in urine
A turn-off fluorescence probe triggered by PNP and PNMC in urine
A novel microporous Hf-MOF functionalized with Eu3+ through the post-synthetic loading
Declaration of interests ☒ 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. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
S0039-9140(20)30147-8
DOI:
https://doi.org/10.1016/j.talanta.2020.120856
Reference:
TAL 120856
To appear in:
Talanta
Received Date: 28 December 2019 Revised Date:
18 February 2020
Accepted Date: 19 February 2020
3+ Please cite this article as: B.-H. Wang, X. Lian, B. Yan, Recyclable Eu functionalized Hf-MOF fluorescent probe for urinary metabolites of some organophosphorus pesticides, Talanta (2020), doi: https://doi.org/10.1016/j.talanta.2020.120856. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.
CRediT author statement Bing-Hui Wang: Data curation, Writing- Original draft preparation. Bing-Hui Wang: Visualization, Investigation. Xiao Lian: Validation, Reviewing and Editing. Bing Yan: Conceptualization, Methodology, Supervision.
Novel luminescence probe Eu3+ functionalized Hf-MOF Eu3+@1 have been prepared to effectively sense PNP and PNMC(the metabolites of some common OPs pesticides) in human urine, without the interference of urinary constituents.
Recyclable Eu3+ functionalized Hf-MOF fluorescent probe for urinary metabolites of some organophosphorus pesticides
Bing-Hui Wanga, Xiao Liana, and Bing Yana,b* a
School of Chemical Science and Engineering, Tongji University, Siping Road 1239, Shanghai 200092, China.
b
School of Materials Science and Engineering, Liaocheng University, Liaocheng 252059, China
* Corresponding author: Email address: [email protected] (Bing Yan)
Abstract A luminescent metal-organic framework Eu3+ functionalized Hf-MOF (Eu3+@1) is designed through post-synthesis modification (PSM) and utilized as a probe for detecting p-nitrophenol (PNP,
the
urinary
metabolite
of
parathion,
methyl-parathion
and
EPN)
and
3-methyl-4-nitrophenol (PNMC, the urinary metabolite of fenitrothion). The apparent quenching effect in urine is observed from the Eu3+@1 with the addition of organophosphorus metabolites. The fluorescent probe has several appealing merits, such as high selectivity, excellent sensitivity (0.36 µg mL-1 for PNP, 0.41 µg mL-1 for PNMC), fast response time (less than 1 min) and easy preparation. Linear correlation between the fluorescence intensity of Eu3+@1 and the concentration of PNP and PNMC are from 0.005–0.15 mg mL-1 and 0.005– 0.30 mg mL-1, respectively. Furthermore, this fluorescent material also demonstrated the possibility for recycling. It is a prominent candidate for potential application in personalized monitoring the internal dose of human exposure to some organophosphorus pesticides. Keywords: 4-nitrophenol; 3-methyl-4-nitrophenol; Metal-organic frameworks; Metabolites; Fluorescence sensing; Photofunctional hybrid material.
1. Introduction For nearly five decades, organophosphorus (OPs) compounds are significantly applied in the agriculture industry around the world, especially as pesticides [1]. Estimates from Center for Disease Control and Prevention (CDC), about 60 million pounds of OPs pesticides are applied to 38 million acres of U.S. agricultural crops every year [2]. Wide use of OPs causes serious consequence. Apart from insect, OPs are also highly toxic to human. Previous researches have proved that there is a link between OPs compounds exposure and delayed polyneuropathy(Parkinson's disease) [3], muscle weakness [4], immunotoxicity [5], endocrine disruption [6], cancer incidence [7] and paralysis [8]. World Health Organization (WHO) declares that approximately 1 million accidental and 2 million suicidal poisonings related to OPs pesticides occur annually [9]. Parathion (O, O-diethyl-O-p-nitrophenyl phosphorothioate), methyl-parathion (O, O-dimethyl O-p-nitrophenyl phosphorothioate), ENP (O-ethyl O-4-nitrophenyl phenylphosphonothioate) are representative organophosphorus (OPs) insecticides which can inhibit acetylcholinesterase, leading to an accumulation of acetylcholine at nerve endings like others [10-12]. Among the carcinogen list assessed by International Agency for Research on Cancer (IARC), parathion is classified as Group 2B (possibly carcinogenic to humans) [13]. Methyl parathion is a class Ia (extremely toxic) insecticide evaluated by WHO and also classified as Toxicity Category I (most toxic) insecticide from the United States Environmental Protection Agency (U.S. EPA) [14]. EPN is an endocrine-disrupting chemical with estrogenic and antiandrogenic activity confirmed by the previous research [15]. All of the poisonous insecticides can result in the urinary excretion of p-nitrophenol (PNP) after metabolized by the liver and kidney. Fenitrothion (O,O-dimethylO-4-nitro-m-tolyl phosphorothioate) is overused in the field of agriculture for crop protection [16]. However, the toxicosis of the pesticides is usually life threatening and even fatal for human [17]. 3-Methyl-4-nitrophenol (PNMC) is the specific metabolite of it
[18]. Based on the fact that the four OPs are rapidly metabolized in humans, it is not practical to determinate the original OPs in urine/blood if we want to make an accurate assessment of individual exposure [19-21]. Instead, exposure metabolites always associate with physiological or pathophysiological process, so it is more effective to evaluate the OPs intoxication level in human [22-23]. At present, monitoring the metabolites of exposure is the most frequently used approach for the detection of exposure chemicals [24-25]. To date, many efforts have been made to determine PNP or PNMC in urine, such as spectrophotometric measurements [26], liquid chromatography-mass spectrometry (LC-MS) [17], gas chromatography–mass spectrometry (GC–MS) [27-28], and high performance liquid chromatography (HPLC) [29-30]. Although these methods have high selectivity and excellent sensitivity, they have some limitations unavoidably, including expensive equipment, toxic reagents, complicated and time-consuming procedures and the requirement of professionals. As a result, it is significant to explore a new method which is simple, environmentally friendly and own immediate feedback. Lanthanide metal–organic frameworks (Ln-MOFs) is a special kind of luminescent MOFs which have been extensively studied in recent years [31-32]. Most Ln-MOFs materials are relatively simple to prepare. It possesses unique luminescence properties, like large Stokes shifts, relatively long luminescence lifetimes and characteristically sharp line emissions, deriving from 4f–4f transitions via “antenna effect’’ [33-35]. It is worth noting that the emission of Ln-MOFs is quite sensitive to their structural characteristics, coordination environment of lanthanide ions and interactions with analytes, making it possibility to be applied in the sensing field [36]. So far, Ln-MOFs have exhibited detection abilities for inorganic ions [37-38], organic small molecules [39-40], nitro explosives [41-42], vapors [43-44] and so on. In this study, we prepare a Eu3+ functionalized Hf-MOF (UIO-67-bpydc) fluorescent probe
by the hydrothermal approach for the detection of PNP and PNMC in human urine (Fig. 1). On the one hand, the ligand with bipyridyl moieties can effectively sensitize the emission of Eu3+ through the ligand-to-metal energy transfer (LMET) process to emit sharp and characteristic luminescence. On the other hand, according the previous study, the UV-absorption of the ligand has large overlap with the PNP and PNMC, suggesting the possibility of competitive absorption between ligand and metabolites. Hence, we assume that the efficiency of LMET process will be decreased by the competitive absorption, leading to the luminescence quenching and thus detecting the existence of metabolites. Moreover, the method is further applied in human urine. Satisfactory outcomes have been obtained, including superior water/pH toleration, high selectivity, excellent sensitivity and fast response time and great recyclability. (Figure 1 insert here) 2. Experimental section 2.1. Materials and reagents Lanthanide nitrates EuCl3·6H2O were prepared by dissolving the corresponding oxide compounds quantitatively in concentrated nitric acid followed by evaporation and recrystallization. Urine was collected from student volunteers from the Institute of Chemical Science and Engineering. (Informed consent statement: informed consent was obtained from all subjects.) All the other materials were commercially available reagents of analytical grade. Deionized water was used throughout the experiments. 2.2. Experimental equipment Powder X-ray diffraction patterns (PXRD) patterns were recorded with a Bruker D8 diffractometer under CuKa radiation and the data were collected within the 2θ in range of 5-40 °. Fourier transform infrared (FTIR) spectra were measured within KBr slices from 4000 to
400
cm-1
using
a
Nicolet
IS10
infrared
spectrum
radiometer.
Nitrogen
adsorption/desorption isotherms were measured at a liquid nitrogen temperature using a TRISTAR 3020 analyzer. X-ray photoelectron spectroscopy (XPS) was performed on a RBD upgraded PHI-5000C ESCA system (Perkin Elmer) with MgKa radiation (h υ = 1253.6 eV). Energy-dispersive X-ray analysis (EDX) were conducted on a Hitachi S-4800 field emission scanning electron microscope operating at 15 kV. Transmission electron microscopy (TEM, JEM-2100) was used to characterize the morphology of the sample. UV–vis absorption spectra were measured with an Agilent spectrophotometer. Excitation spectra, emission spectra of the samples were performed on an Edinburgh FLS920 phosphorimeter with a 450 W xenon lamp as excitation source. 2.3. Synthesis of Hf-MOF 1 Hf-MOF 1 was synthesized according to the reported method [45]. HfCl4 (96.1 mg, 0.3 mmol), H2bpydc (73.2 mg, 0.3 mmol), 4 mL N,N-dimethylformamide (DMF) and 1 mL formic acid were added to a 25 mL Teflon-lined stainless steel reactor. Then, the reactor was sealed and heated to 150 °C for 24 h. The resultant white powder was cooled to room temperature, filtered and washed several times with DMF. To remove the unreacted ligand, the product was washed with DMF at 70 °C for 24 h. After washed by chloroform for 3 times and dried in an oven with 150 °C for 24 h, target product 1 was synthesized eventually. 2.4. Synthesis of Eu3+@1 Eu3+@1 was synthesized according to the reported method [46]. Eu3+@1 was prepared by dispersing 1(100 mg) into the methanol solution of EuCl3·6H2O (30 mL, 5 mmol). The solution was stirred for 12 h at 60 °C. After separation by centrifugation and washing three times with ethanol for removal of residual Eu3+, the resulting white powder was dried at 80 °C for 12 h. 2.5. Luminescent sensing experiment For the detection of PNP and PNMC, the Eu3+ @1 was dispersed into distilled water to
form an aqueous suspension (1 mg mL-1), followed by adding the metabolites to the solution. To investigate the selectivity and sensitivity of Eu3+ @1, experiments were tested under unitive condition except different aqueous suspension (10 mM) present in human urine, including creatinine (Cre), creatine, urea, uric acid (UA), glucose (Glu), NaCl, NH4Cl, KCl and Na2SO4.
3. Results and discussion 3.1. Physical characterization of 1 and Eu3+ @1 The precursor Hf-MOF (UIO-67(Hf)-bpydc, 1) is synthesized by hydrothermal method, after blending HfCl4 and ligand H2bpydc in the solvent containing DMF and formic acid [45]. As shown in Fig. S1, the three-dimensional MOF comprises a hexagonal-close-packed (hcp) array of Hf12O8 (OH)14 clusters linked with bpydc2− ligands. Particularly, the accessible sites of the bipyridyl moieties in the framework show the potential of post-synthetic modification (PSM), which make it possible to prepare a new material with better luminescence. Powder x-ray diffraction (PXRD) shows that the diffraction peaks of the as-synthesized 1 matches well with the simulated, verifying the successful synthesis of 1 with a pure phase (Fig. 2a). N2 adsorption measurement reveals that the Brunauer-Emmett-Teller (BET) surface area of the MOF is 504.13 m2 g−1 (Fig. S2), demonstrating that the MOF is adequately porous to offer a space in lattice for lanthanide cations. Hence, we introduce Eu3+ into the channels of 1 to prepare Eu3+@1 hybrid by immersing the samples in methanol solution of EuCl3·6H2O. The material retains its crystallinity and morphology after introducing Eu3+, proved by PXRD patterns in Fig. 2a. However, compared with 1, the BET surface of Eu3+@1 displays a big drop, with only 129.14 m2 g−1 (Fig. S2). The phenomenon is ascribed to the residence of the coordinated Eu3+ in the cavities of 1. X-ray photoelectron spectroscopy (XPS) spectra are recorded to determine the chemical states of Eu3+ in Eu3+@1 (Fig. 2b). The peaks of Eu 3d5/2
and 3d3/2 appear at 1131.9 eV and 1161.8 eV in Eu3+@1, respectively, and the peak at 134.4 eV corresponds to the 4d of Eu, indicating the successful encapsulation of Eu3+ into the MOF. Whereas, the Eu 3d peaks of Eu3+@1 show a lower binding energy compared to EuCl3 (Fig. S3). It could be attributed to the coordination of Eu-N bonds between to Eu3+ and the free N,N-chelating sites [47, 48]. As shown in the Fourier transform infrared (FTIR) spectra (Fig. S4), 1 and Eu3+@1 exhibit similar results. The peaks at around 1590 cm-1 and 1415 cm-1 are consistent with the absorption of the bipyridyl and carboxylic group, respectively. Energy dispersive analysis of X-rays (EDX) analysis confirms that the Eu3+ is incorporated with the compound 1 again (Fig. S5 and Table S1). The TEM images of Eu@1 (Figure S6) show a lamellar structure with nanoscale dimensions, which is correspond with reported hcp MOFs based materials [45, 46]. (Figure 2 insert here) 3.2. Luminescence properties of 1 and Eu3+ @1 The emission spectrum of the ligand H2bpydc displays a broad band from 400 to 650 nm with a maximum at 558 nm under the UV irradiation of 377 nm, attributed to the π → π* electron transition of the organic linkers (Fig. S7a). The hybrid 1 shows a strong emission band at 524 nm when excited at 365 nm (Fig. S7b). The blue shifting between ligand and compound 1 is ascribed to the coordination of H2bpydc to Hf4+ cations [46]. After post-synthetic functionalized by Eu3+, Eu3+@1 exhibits five Eu3+ emission peaks at 579(5D0 → 7F0), 592(5D0 → 7F1), 613(5D0 → 7F2), 650(5D0 → 7F3) and 701 nm(5D0 → 7F4) upon excitation at 332 nm, leading to a bright red light which can be easily distinguished by naked eye (Fig. 3a). The typical electric dipole transition 5D0 → 7F2 transition is very sensitive to the local symmetry of Eu3+. At the same time, the parity-allowed magnetic dipole transition 5D0 → 7F1 is independent of the ions’ surroundings. The high ratio of I(5D0 →7F2)/I(5D0 → 7F1) (about 5.7) confirms that Eu3+ is located in a low symmetry chemical environment [49-50].
Whereas, the luminescence spectrum of Eu3+@1 displays little evidence of the ligand-centered emission from 400 to 650 nm. It can be attributed to the effective energy transfer from the H2bpydc ligand to the Eu3+ ions (Fig. 3b). As shown in Fig. S8, the Commission internationale de l’Eclairage (CIE) chromaticity diagram of Eu3+@1 is located at (0.6611, 0.3196), corresponding to the luminescence spectrum and the photo under the irradiation of UV-light. (Figure 3 insert here) 3.3. Stability investigation of Eu3+@1 Urinalysis tests can reflect the physical parameters of the individual. P-nitrophenol (PNP, the urinary metabolite of parathion, methyl-parathion and EPN) and 3-methyl-4-nitrophenol (PNMC, the urinary metabolite of fenitrothion) are the typical urinary metabolite of the corresponding organophosphorus (OPs) pesticides. It is realistic to monitor the level of PNP and PNMC in urine for the detection of OPs pesticides exposure and intoxication of human beings. As water is the major component of urine, water-stability of Eu3+@1 probe is first studied. According the previous study [46], the probe Eu3+@1 with nanoscale dimensions can be uniformly dispersed in the water. To monitor the structure variations of Eu3+@1 before and after immersed in aqueous solution for 48 h, we record the related PXRD patterns and emission spectra in Fig. S9. As the figures show, both of the crystalline structure and luminescence of Eu3+@1 have hardly change, suggesting the good water-stability of the hybrid. In addition, pH-independent stability is another crucial factor to estimate the property of urinary probe, while the pH value of real human urine ranges from 4.6 to 8.0. Fig. S10 presents that the compound crystallinity and luminescence of Eu3+@1 stay the same even though dipping in diverse pH aqueous solutions. Moreover, as shown in Fig. S11, the luminescence spectra of the probe have hardly changed although the temperature varies from 15 °C to 30 °C. The excellent water-stability, pH-independent stability and temperature
stability of Eu3+@1 lay the foundation for the detection of the metabolites in urine. 3.4. Sensing for PNP and PNMC Besides water, there are other molecules and ions existing in urine, which may disturb the detection result, containing glucose (Glu), uric acid (UA), creatinine (Cre), creatine, urea, KCl, NaCl, NH4Cl and Na2SO4. To study the effect of the urinary constituents to the luminescence probe, we conduct a series of controlled experiments. Certain amount of Eu3+@1 (3 mg) is added to the nine urine constituents, PNP and PNMC aqueous solutions (0.01 M) under the same conditions (temperature, pressure, excitation and response time). The luminescence spectra in Fig. 4a illustrate that the participations of these urinary components only cause negligible changes in the luminescence compared to the Eu3+@1 aqueous solution with the excitation at 332nm. On the contrary, with the addition of PNP and PNMC, a prominent decrease in the luminescence of Eu3+ can be easily observed by the naked eye, leading to the luminescence transforms from bright red to almost vanishing under a UV lamp (Fig. 4b). The histogram, made by mirroring the characteristic emission peak (613 nm) of Eu3+@1 with the existence of different constituents, visually proves the high selectivity of Eu3+@1. The response time is very short. According to the Fig. S12, the luminescence of Eu3+@1 is dramatically reduced with the immersion of PNMC and PNP for 30 s. After 1 min, the luminescence decrease reaches a constant. (Figure 4 insert here) Further, to explore whether the existence of the coexisting urinary substances will influence the luminescence detection process of Eu3+@1 to PNP and PNMC, we conduct a series of competition experiments under the same excitation (332 nm). As shown in the luminescence intensity histogram (Fig. 5), the quenching effect of Eu3+@1 is not affected by the coexisting components. It only happens when the metabolite PNMC or PNP is added to the solution, whether there exist other urine chemicals or not. These results indicate Eu3+@1 have the
potentially to be a highly selective probe for PNP and PNMC in the background of other urine ingredients. (Figure 5 insert here) Besides selectivity, the sensitivity of the probe Eu3+@1 to PNP and PNMC is also very important. Thus, we prepare a batch of Eu3+@1 suspensions with diverse concentrations of PNP and PNMC in real urine. The experiments are repeated three times, and the results are presented as the average value of the data. Error bar has been also displayed in the inset of Figure 6. As displayed in the figure, under 332 nm excitation, the luminescent emission intensity of Eu3+@1 gradually decrease with the increasing concentration of metabolites. For PNP, the emission peaks gradually flatten and almost disappear at about 0.15 mg mL-1. There is a preeminent linear relationship between the concentrations of PNP and the emission intensity (613 nm) in a large concentration range. The linear correlation can be fitted into the equation I= -10.017-11.217 log CPNP(R = 0.991, linear range: 0.005–0.15 mg mL-1). The LOD is calculated to be 0.36 µg mL-1, which is lower than the threshold limit value of 0.5 µg mL-1 [51]. Further details on the calculations is provided in the supporting information. The relative standard deviation (RSD) of three repeated determination is calculated from 0.74% to 3.78%. As for PNMC, The value of curve is calculated as I= -5.417-9.234 log CPNMC (R = 0.995, linear range: 0.005–0.3 mg mL-1). The LOD is calculated to be 0.41µg mL-1. The RSD is calculated from 1.35% to 4.18%. The results demonstrate that the fabricated probe Eu3+@1 possess excellent sensitivity to the metabolites of OPs pesticides. Comparing with previously reported methods in Table S2, Eu3+@1 probe has a wider linear detection range without the cumbersome operational process. The LOD is also very low which can satisfy daily monitoring needs. (Figure 6 insert here) All of the facts have testified that the Eu3+@1 is an outstanding probe for PNP and PNMC
detection in urine. Moreover, in practice, recoverability of a probe plays a crucial role in its applications. Hence, the recovery experiment is investigated. As shown in Fig. 7, the luminescence intensity of Eu3+@1 is almost recovered to its initial state via centrifugation and washing with deionized water. After three recycles performed by metabolites addition (PAP, 0.1 mg mL-1; PNMC, 0.2 mg mL-1) and ultrasonic washing, the luminescence of the recycled treated probe is similar to the initial hybrid. The result reveals that the probe Eu3+@1 could be reused for PNP and PNMC detection. Furthermore, the detection process also suggests the weak interaction between the metabolites and the probe Eu3+@1. The luminescence of the probe is closely linked to the presence or absence of the PNP and PNMC and the removal of metabolites can be realized by ultrasonic washing. (Figure 7 insert here) 3.5. Sensing mechanism Moreover, we explore the detection mechanism of the probe. Generally, the possible mechanism of quenching effect on the luminescence of lanthanide MOF can be divided into three ways: (1) the collapse of the crystal MOF material; (2) the interaction with the lanthanide ions; (3) the interaction with the ligands. From Fig. S13, the PXRD patterns of Eu3+@1 with PNP, PNMC or other constituents of urine are coincident with the original patterns, suggesting that the basic structure of the MOF is well-remained. For another, there are no available functional group, like β-diketone moieties, in PNP or PNMC to coordinate with Eu3+. Thus, to investigate the quenching effect to PNP and PNMC, we study the related UV-vis spectra as shown in Fig. S14. It is obviously illustrated that the absorption peak of the MOF framework (ligands) in Eu3+@1 nearly overlaps with the adsorption of PNP and PNMC. In fact, the efficiency of the luminescence in lanthanide MOF depends on the degree of the energy transfer. If the guest molecule competes source energy with the ligand, the energy transfer efficiency from ligand to lanthanide will decrease and the luminescence will reduce
accordingly [52]. Summing up the above, competitive absorption between ligands of Eu3+@1 and metabolites is the most practical mechanism.
4. Conclusion In summary, the paper reports a luminescent metal-organic framework Eu3+ functionalized Hf-MOF (Eu3+@1) material to detecting p-nitrophenol (PNP, the urinary metabolite of parathion, methyl-parathion and EPN) and 3-methyl-4-nitrophenol (PNMC, the urinary metabolite of fenitrothion). The as-prepared Eu3+@1 not only possesses the excellent water-stability and pH-independent tolerance but also have high sensitivity without the interference of urinary constituents and fast response time(less than 1min). According to the linear relationship between the increasing concentrations of metabolites and the emission intensity in real urine, the probe can achieve effective detection from 0.005–0.15 mg mL-1 (for PNP) and 0.005–0.30 mg mL-1 (for PNMC). The detection limit is also very low with 0.36 µg mL-1 for PNP and 0.41 µg mL-1 for PNMC which can satisfy daily monitoring needs. Moreover, the probe Eu3+@1 shows the good recyclability as well, which is a crucial advantage in the practical applications. Given the above, the probe possesses the potential to serve as a powerful detection tool to help human judge intoxication degree of the OPs pesticides.
CRediT author statement Bing-Hui Wang: Data curation, Writing- Original draft preparation. Bing-Hui Wang: Visualization, Investigation.
Xiao Lian: Validation, Reviewing and Editing. Bing
Yan: Conceptualization, Methodology, Supervision.
Acknowledgment
This work was supported by the National Natural Science Foundation of China (21571142, 21971194), and Developing Science Funds of Tongji University.
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Figure legends Fig. 1 Schematic illustration of the fabricated Eu3+ @1 as a fluorescence probe for PNP and PNMC. Fig. 2 (a) PXRD patterns of simulated 1, as-synthesized 1 and Eu3+ @1 samples; (b) XPS spectra of compound 1 and Eu3+ @1. Fig. 3 (a) Excitation and emission spectra of Eu3+ @1. The inset shows the corresponding photo with the irradiation of a UV lamp; (b) Schematic representation of energy transfer process from ligand to Eu3+ in Eu3+@1. S, singlet; T, triplet; ET, energy transfer; J, J = 0-4. Fig. 4 The luminescence spectra (a) and relative intensities (b) of Eu3+ @1 at 613 nm (5D0 → 7
F2) when dispersed in diverse aqueous solutions (λex = 332nm). Inset: the corresponding
photograph under UV-light irradiation. Fig. 5 Comparison of the relative luminescence intensity of Eu3+ @1 (613 nm) toward coexisting urinary substances in the presence and absence of PNP and PNMC (λex = 332 nm). Fig. 6 Fluorescence spectra of Eu3+@1 in the presence of different concentrations of PNP (a)
and PNMC (b) in real urine (λex = 332 nm), inset: the plot of luminescence intensity versus logarithm of the concentrations of the PNP and PNMC. Fig. 7 The generation cycles of sample of Eu3+@1 used in detecting PNP (a), PNMC (b).
Fig. 1
Fig. 2
Fig. 3
Fig. 4
Relative Intensity (a.u.)
origin PNMC PNP
H2O
NaCl NH4Cl
UA KCl
Urea
Cr
Glu
e
4
tin ea
SO Na 2
Cre
Fig. 5
Fig. 6
Fig. 7
Highlights
High sensitivity to detect even trace amount PNP and PNMC in urine
A turn-off fluorescence probe triggered by PNP and PNMC in urine
A novel microporous Hf-MOF functionalized with Eu3+ through the post-synthetic loading
Declaration of interests ☒ 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. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: