Preparation and application of ratiometric fluorescence sensor based on dye-encapsulated Zn-MOF

Abstract

The present invention discloses a preparation method of a ratio fluorescence sensor based on dye-encapsulated Zn-MOF, and a ratio fluorescence sensor (RhB@Zn-MOF) is constructed by encapsulating RhB into a Zn-MOF framework using a one-pot method for ratio fluorescence detection of DQ. In the presence of DQ, the fluorescence intensity of Zn-MOF gradually increases, and the fluorescence intensity of RhB gradually decreases, forming an "on-off" ratio fluorescence sensor. The sensor has self-calibration capability, avoids interference from the external environment, effectively improves the precision and accuracy of the sensor, and is applied to the detection of DQ in actual samples, with a detection limit as low as 10.5 nM. Based on the above advantages, we believe that the ratio fluorescence sensor (RhB@Zn-MOF) will have broader application prospects in the field of food safety.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal organic framework material preparation, and relates to the preparation of a Zn-MOF material, and specifically to the preparation of a ratio fluorescence sensor based on dye encapsulated Zn-MOF and its high-sensitivity detection application of diquat in tap water and apple samples. Background Art

[0002] Food safety is closely related to human health. Over the past few decades, consumers' preference for organic food has shown a significant growth trend, but its safe consumption has also attracted widespread attention. Pesticides can widely promote crop yield and quality, but their excessive content or improper use will lead to excessive pesticide residues, thus affecting the quality of organic food, and then affecting human health and life safety. Countries around the world have made clear regulations on the minimum residue of pesticides in crops and foods. Eating food with excessive pesticide residues will cause many chronic and acute problems to the human body. Therefore, it is particularly important to control pesticide residues in food. How to quickly monitor on-site and prevent in advance has obviously become the most critical issue. In the past and now, researchers often use gas chromatography-mass spectrometry (GC-MS / MS) and high-performance liquid chromatography-mass spectrometry (LC-MS / MS) methods to quantitatively analyze pesticide residues in food. This method has high accuracy and effectiveness, but it usually requires cumbersome sample preparation steps and long analysis time, and it cannot accurately obtain real-time information on food quality. Therefore, it is necessary to develop a convenient and fast detection technology for on-site real-time monitoring to achieve food safety.

[0003] Fluorescent sensors based on MOFs have been widely developed for monitoring pesticide residues in food due to their unique physical and chemical properties. MOFs are porous organic framework materials assembled by metal ions or metal clusters. Due to their large specific surface area and adjustable pore size, they are widely used in various fields such as fluorescence sensing, energy storage, gas adsorption separation and photoelectrocatalysis. By carefully selecting organic ligands and metal ions / clusters, MOFs with variable shapes and easily adjustable pores / channels can be easily obtained. The pores / channels of these MOFs can provide a large number of recognition sites, increase the host-guest interaction with the analyte, and thus improve the accuracy of the fluorescent sensor. The obtained MOFs based on a single luminescent center are often difficult to avoid the errors caused by the experimental instruments and environment, while ratio fluorescence sensing can provide more reliable data and higher detection accuracy by calibrating the fluorescence signal by itself. Therefore, the development of ratio fluorescence sensors based on multiple luminescent centers of MOFs has become a current trend. Fluorescent dyes have become an important luminescent component combined with MOFs because of their cheap availability and high luminescence quantum yield. In addition. Introducing dyes into the framework of MOFs can not only effectively avoid the quenching caused by dye aggregation, but also greatly adjust the fluorescence signal and performance of the composite material. For example, Zheng et al. embedded RhB into UiO-(OH)2 through a simple solvothermal method and constructed a MOF for Al in water. 3+ The open-type ratiometric fluorescence sensor (UiO-(OH)2@RhB) was prepared. Wang et al. prepared dual-emission fluorescence sensors (RhB@1-0.4) for putrescine, aromatic diamines and nitrophenol by introducing RhB into the framework of Mn-MOF. Although MOFs materials with dual emission properties based on dye encapsulation have been widely studied, the powder state of MOFs materials is still not suitable for rapid and real-time detection on site. Therefore, it is necessary to construct a sensing platform based on MOFs materials to improve its practicality and convenience. Among various types of point-of-care (POCT) biosensors, paper-based sensors stand out due to their convenient operation, low cost and biodegradability. The MOFs material is dispersed in a solution and then dropped on a cellulose filter paper to achieve the deposition of MOFs. This method combined with a smartphone system can realize intelligent colorimetric and visual sensing of analytes.

[0004] Diquat (DQ) is a bipyridyl quaternary ammonium herbicide, which is often used as a plant seed desiccant and crop wilt-inducing agent. DQ may enter water bodies through water flow, thereby affecting aquatic ecosystems. The United States Environmental Protection Agency (USEPA) stipulates that the maximum residue level (MRL) of DQ in drinking water is 20 μg / L. The European Union (EU) does not clearly stipulate this content, but continues to use a maximum residue value of 0.1 μg / L. Studies have found that low doses of DQ may pose certain risks to human health, including potential carcinogenic risks. In addition, DQ may leave residues in crops. Although my country has stipulated that the MRL of DQ in apples is 0.1 mg / kg, long-term intake of these residues may have an impact on human health. Therefore, these hazards caused by DQ have attracted widespread attention. Our strategy is to achieve rapid detection and prevention of DQ through the above scheme.

[0005] Based on the above assumptions, we encapsulated rhodamine B (RhB) into the skeleton of Zn-MOF to prepare a ratiometric fluorescence sensor (RhB@Zn-MOF). Relying on the dual emission characteristics of RhB@Zn-MOF, DQ in tap water and apple samples was detected to achieve real-time rapid detection on site. Summary of the invention

[0006] The present invention aims to provide a method for preparing a ratio fluorescence sensor based on dye-encapsulated Zn-MOF, encapsulating RhB into the skeleton of Zn-MOF to prepare a ratio fluorescence sensor (RhB@Zn-MOF). RhB@Zn-MOF exhibits dual emission characteristics, has ratio fluorescence response and low detection limit for DQ detection, and can be applied to the detection of DQ in tap water and apple samples.

[0007] 1. Preparation of Zn-MOF and RhB@Zn-MOF

[0008] Zn-MOF: 4,4',4''-[1,3,5]triazine-2,4,6-triyl-tribenzoic acid (H3TATB), 1,4-bis((1H-imidazole-1-yl)methyl)benzene (bimb) and ZnCl2 were dissolved in a mixed solvent of ethanol and water, mixed evenly by ultrasonication, kept at 85~100℃ for 48~96h, cooled to room temperature at a rate of 8~12℃ / h, washed and dried.

[0009] The molar ratio of 4,4',4''-[1,3,5]triazine-2,4,6-triyl-tribenzoic acid to 1,4-bis((1H-imidazol-1-yl)methyl)benzene is 1:1; the molar ratio of 4,4',4''-[1,3,5]triazine-2,4,6-triyl-tribenzoic acid to ZnCl2 is 1:1.5.

[0010] RhB@Zn-MOF: Rhodamine B (RhB), 4,4',4''-[1,3,5]triazine-2,4,6-triyl-tribenzoic acid (H3TATB), 1,4-bis((1H-imidazole-1-yl)methyl)benzene (bimb) and ZnCl2 were dissolved in a mixed solvent of ethanol and water, mixed evenly by ultrasonication, kept warm at 85~100℃ for 48~96h, cooled to room temperature at a rate of 8~12℃ / h, washed and dried.

[0011] The molar ratio of rhodamine B to 4,4',4''-[1,3,5]triazine-2,4,6-triyl-tribenzoic acid is 1:1~5:1, preferably 2.5:1. The molar ratio of 4,4',4''-[1,3,5]triazine-2,4,6-triyl-tribenzoic acid to 1,4-bis((1H-imidazol-1-yl)methyl)benzene is 0.3:1~3:1, preferably 1:1. The molar ratio of 4,4',4''-[1,3,5]triazine-2,4,6-triyl-tribenzoic acid to ZnCl2 is 0.3:3~3:0.3, preferably 1:1.5.

[0012] The volume ratio of ethanol to water in the mixed solvent is 1:1~2:1.

[0013] 2. Characterization of Zn-MOF and RhB@Zn-MOF

[0014] First, single crystal X-ray diffraction of Zn-MOF was performed. The crystallographic data are shown in Table 1 and the structure is shown in Figure 1 .

[0015] Table 1 Crystal data and structure refinement of Zn-MOF

[0016]

[0017] Single crystal X-ray diffraction data show that Zn-MOF (CCDC: 2340856) is a three-dimensional framework. Pī The space group is triclinic crystal. Figure 1As shown in the figure, the asymmetric structural unit of Zn-MOF contains 1 Zn(Ⅱ) center, 1 partially deprotonated HTATB ligand, 1 bimb ligand and 1 lattice water molecule, in which the Zn atom is tetracoordinated with 2 oxygen atoms in 2 H3TATB ligands and 2 nitrogen atoms in 2 bimb ligands to form a distorted tetrahedral geometry. The Zn atom is linked by 2 H3TATB ligands and 2 bimb ligands to form a large window with a size of about 13.955 × 14.593 Å. Each layer is stacked together through the π-π interaction between the triazine ring and the benzene ring, and between the benzene rings to form a stable 2D supramolecular bilayer, and the distances between the layers are 3.613Å, 3.554Å and 7.373Å, respectively. Further, the benzene rings and triazine rings, and the benzene rings are stacked together through the strong π-π interaction between the layers to form a 3D supramolecular grid.

[0018] In order to verify the crystal phase of Zn-MOF and RhB@Zn-MOF, PXRD analysis and FT-IR spectroscopy analysis were performed. Figure 2a As shown in Figure 2, the PXRD pattern of RhB@Zn-MOF is consistent with that of Zn-MOF, indicating that the introduction of RhB did not destroy the skeleton of Zn-MOF and the crystal phase was intact. Figure 2b As shown in the figure, the characteristic peak positions of Zn-MOF and RhB@Zn-MOF are consistent, indicating that RhB is well encapsulated in the skeleton of Zn-MOF.

[0019] The thermal stability of Zn-MOF and RhB@Zn-MOF was studied by thermogravimetric experiments. Figure 3a As shown in the figure, Zn-MOF has a small weight loss before 362℃, indicating that it has good thermal stability, which lays a stable foundation for RhB encapsulation. After encapsulation, the thermal stability of RhB@Zn-MOF is slightly weakened, but at 326℃, it can also show that it has good stability ( Figure 3b ).

[0020] The morphologies of Zn-MOF and RhB@Zn-MOF were studied by scanning electron microscopy. Figure 4 a-4d shows the SEM image of Zn-MOF, which is a parallelepiped morphology with a size of about 3 μm. The morphology of the synthesized RhB@Zn-MOF is slightly different from that of Zn-MOF. The EDS image shows the uniform distribution of the four elements C, N, O, and Zn, indicating the successful synthesis of the composite material RhB@Zn-MOF ( Figure 4 e-4i).

[0021] The surface elemental composition and chemical state of Zn-MOF and RhB@Zn-MOF were investigated by XPS. Figure 5aThe XPS total spectra of Zn-MOF and RhB@Zn-MOF are shown in Figure 2. The peaks of RhB@Zn-MOF are located at 1021.08 eV, 286.08 eV, 401.08 eV, and 531.08 eV, which are attributed to Zn 2p, C 1s, N 1s, and O 1s peaks, respectively. The high-resolution spectrum of Zn 2p has two peaks at 1044.61 eV and 1021.64 eV, corresponding to Zn 2p 1 / 2 and Zn 2p 3 / 2 ( Figure 5b ). Figure 5c The C 1s high-resolution spectra of Zn-MOF and RhB@Zn-MOF show three peaks at 284.26 eV, 286.00 eV and 287.84 eV, respectively, attributed to CC / C=C, CN / CO and C=O bonds. Compared with Zn-MOF, the C=O bond of RhB@Zn-MOF moves to the high wavenumber direction, indicating that Zn-MOF and RhB are successfully combined. The N 1s high-resolution spectrum shows two peaks at 400.46 eV and 398.45 eV ( Figure 5d ). The weak peak at 400.46 eV is attributed to the NH group in RhB, and the strong peak at 398.45 eV is attributed to the CN bond in RhB. Figure 5e The O 1s high-resolution spectra of Zn-MOF and RhB@Zn-MOF, the peak at 530.99 eV comes from the CO and C=O bonds of Zn-MOF and RhB. No new binding energy peaks of RhB@Zn-MOF were observed in the XPS total spectrum, thus excluding the possibility of new chemical bonds between Zn-MOF and RhB. XPS also confirmed the atomic percentages of elements in RhB@Zn-MOF, with the atomic percentages of Zn 2p, C 1s, N 1s and O 1s being 2.05%, 73.3%, 11.46% and 12.54%, respectively, which are consistent with the EDS results. Similarly, we found that the atomic percentages of elements hardly changed before and after RhB loading, indicating the successful synthesis of RhB@Zn-MOF. The results show that Zn-MOF after RhB loading has more abundant chemical recognition sites, laying the foundation for the monitoring of DQ.

[0022] 3. Luminescence properties of Zn-MOF and RhB@Zn-MOF

[0023] First, the solid-state and liquid-state emission spectra of Zn-MOF and RhB@Zn-MOF were tested at an excitation wavelength of 310 nm. Figure 6a-b, the main emission wavelength of Zn-MOF is 352 nm, showing a single emission state. The emission peak of RhB in aqueous solution is at 580 nm, while solid RhB shows almost no fluorescence. As designed, after RhB is loaded into the framework of Zn-MOF, the fluorescence spectrum of RhB@Zn-MOF shows dual emission characteristics. The maximum emission peak of RhB@Zn-MOF is located at 356 nm, which is attributed to the emission of ligands in the Zn-MOF framework; the lower emission peak is located at 580 nm, which is attributed to the emission of RhB. Compared with the emission peak of the ligand H3TATB, the emission peaks of Zn-MOF and RhB@Zn-MOF are blue-shifted by about 50 nm, which may be caused by the charge transfer between the ligand H3TATB and the Zn(Ⅱ) center. The emission band of RhB appears in RhB@Zn-MOF because the framework of Zn-MOF limits the quenching of RhB caused by aggregation. Compared with Zn-MOF, the emission band of RhB@Zn-MOF has a slight change, which is mainly due to the interaction between RhB and Zn-MOF during the formation of the composite material. In order to verify the luminescence mechanism of RhB@Zn-MOF, the spectral properties of RhB and Zn-MOF were studied. Figure 6c -d shows that the absorption spectrum of RhB and the broad emission spectrum of Zn-MOF overlap significantly, indicating the existence of FRET between them. In addition, RhB@Zn-MOF has an absorption peak corresponding to Zn-MOF at 285 nm, which is mainly attributed to the π-π* electronic transition of the benzene ring.

[0024] In order to clarify the feasibility of RhB@Zn-MOF as a dual-emission sensing platform for DQ, the fluorescence signal changes of RhB, Zn-MOF and the composite material RhB@Zn-MOF as a DQ sensing platform were studied. Figure 7a As shown in the figure, the fluorescence intensity of RhB is slightly weakened before and after the addition of DQ, which can be used as a reference signal for DQ monitoring. Under the excitation wavelength of 310 nm, after the addition of DQ, the fluorescence intensity of Zn-MOF at 352 nm gradually increases, which makes Zn-MOF an "ON" type fluorescence sensor for DQ detection ( Figure 7b ). To confirm this result, DQ was added to the composite material RhB@Zn-MOF and its fluorescence signal changes were observed ( Figure 7c ). The experimental data showed that as the fluorescence intensity at Zn-MOF gradually increased, the fluorescence intensity at RhB gradually decreased, successfully verifying the feasibility of RhB@Zn-MOF as a dual-emission sensing platform for DQ.

[0025] 4. DQ Sensing Research of RhB@Zn-MOF

[0026] 1. Study on DQ sensing characteristics

[0027] Considering the dual emission properties of RhB@Zn-MOF and its potential as a sensor, the sensing ability of RhB@Zn-MOF towards common pesticides in agriculture was explored. We selected 10 pesticides, 4 ions and 5 amino acid aqueous solutions (10 -2 M) were dispersed in the RhB@Zn-MOF aqueous solution and treated with ultrasound for 30 min to form a uniform suspension (0.4 mg.mL -1 ). The fluorescence intensity ratio at 356 nm and 580 nm ( I 356 / I 580 ) as the fluorescent signal to achieve ratiometric detection of these substances. Figure 8a It can be seen that, except for the pesticide DQ, the ratio fluorescence intensity of other substances detected by RhB@Zn-MOF remained almost unchanged. I 356 / I 580 The ratio is about 3.5 times higher than that of the original RhB@Zn-MOF, while in the presence of other interfering substances I 356 / I 580 The ratio remains almost unchanged. The research results show that RhB@Zn-MOF can detect DQ by ratiometric fluorescence.

[0028] Detection limit is one of the important indicators for measuring fluorescence sensors. In order to monitor the sensitivity of RhB@Zn-MOF to DQ, a fluorescence titration experiment was carried out. Figure 8b As shown in the figure, with the increase of DQ concentration, the fluorescence intensity at 356 nm gradually increased, while the fluorescence intensity at 580 nm gradually decreased, demonstrating the ability of RhB@Zn-MOF as a ratiometric fluorescence sensor. Under 356 nm ultraviolet light, RhB@Zn-MOF showed a fluorescence color change from orange to blue, which is consistent with the CIE coordinate diagram ( Figure 8c ). I 356 / I 580 The relationship between the ratio and DQ concentration can be expressed by the equation I 356 / I 580 = 0.02854[DQ]+0.90874 ( R 2 = 0.983). According to the equation LOD = 3 σ / k(3 is the factor at the 99% confidence level, σ is the standard deviation of repeated tests of blank solution, k is the slope of the calibration curve), the minimum detection limit was calculated to be 10.5 nM ( Figure 8d ). These seven selected pesticides are commonly used as crop growth regulators, insecticides, herbicides and antimicrobial agents, and as interfering substances, they can significantly affect the accuracy of DQ determination. Therefore, the fluorescence response of RhB@Zn-MOF to DQ in the presence of common interfering substances was investigated to illustrate the specific recognition of RhB@Zn-MOF to DQ. Figure 8e It can be seen that the interfering substances have almost no effect on the fluorescence intensity of RhB@Zn-MOF quenched by DQ, indicating that the sensor has excellent selectivity and anti-interference properties for DQ.

[0029] Since the change in the fluorescence intensity of RhB@Zn-MOF is mainly caused by the interaction between Zn-MOF and DQ, we selected Zn-MOF as the sensor to monitor the sensing ability of DQ. As the concentration of DQ increases, the fluorescence intensity of Zn-MOF gradually increases ( Figure 9a ). According to the good linear relationship between them ( R 2 = 0.992), and calculate LOD 16.9nM( Figure 9b ). The results show that encapsulating RhB in the framework of Zn-MOF can greatly improve the sensitivity to DQ. Compared with other fluorescent sensors for detecting DQ, the RhB@Zn-MOF proposed in this invention has better selectivity, lower detection limit and higher sensitivity.

[0030] In order to obtain better detection results, the loading amount of RhB was investigated. Different amounts of RhB were loaded into the framework of Zn-MOF to prepare three composite materials with dual emission characteristics. As the RhB content increased, the emission peak position slightly blue-shifted. The RhB emission band of the composite material with the largest loading amount had a weaker intensity, indicating that there was a weaker FRET ( Fig.10a ). The UV-visible absorption spectra also show that their absorption peak intensities gradually weaken ( Fig.10b ). Among them, the composite material with the largest loading amount showed the lowest absorption peak intensity. Considering that the addition of DQ led to a gradual enhancement of the emission band of Zn-MOF, while the emission band of RhB changed weakly, the optimal loading amount of RhB was 0.01 mmol.

[0031] 2. Research on DQ sensing mechanism

[0032] In order to explore the possible sensing mechanism of RhB@Zn-MOF to DQ, experimental analysis was carried out. Fig.11aAs shown in Figure 2, after sensing DQ, the PXRD pattern of RhB@Zn-MOF is almost consistent with that of the original material. First, the fluorescence "on-off" phenomenon caused by the collapse of the skeleton is ruled out. Fig.11b As shown in the figure, compared with the FT-IR spectrum of RhB@Zn-MOF, the FT-IR spectrum of RhB@Zn-MOF after adding DQ has no new peaks, and no new functional groups are generated, proving that no new complexes are generated. Under 310nm excitation, compared with the RhB@Zn-MOF aqueous solution with the addition of DQ, the fluorescence intensity of the DQ aqueous solution is negligible, excluding the influence of DQ itself on the mechanism ( Fig.11c ).like Fig.11d As shown in Figure 2, after adding DQ, the fluorescence lifetime of RhB@Zn-MOF remains almost unchanged, indicating that it is a static quenching process. The excitation spectrum, emission spectrum of RhB@Zn-MOF and absorption spectrum of DQ were recorded ( Fig.11e ). The absorption peak of DQ overlaps significantly with the excitation peak of RhB@Zn-MOF, which verifies that DQ can absorb the excitation light of Tb(Ⅲ)@1, thereby reducing the total effective energy of RhB@Zn-MOF, resulting in a decrease in the excited state energy of RhB@Zn-MOF and fluorescence quenching. This behavior is mainly caused by IFE. In order to further explore its mechanism, the interaction and FRET between RhB@Zn-MOF and DQ were studied. Figure 8b It can be seen that with the gradual increase of the concentration of added DQ, the broad emission signal in the range of 330~450 nm is significantly enhanced, confirming the intermolecular interaction and FRET between RhB@Zn-MOF and DQ. These results indicate that the mechanism of RhB@Zn-MOF detection of DQ may be the interaction of IFE, FRET and static quenching.

[0033] 3. Actual sample sensor test

[0034] Tap water and apples (Gansu, China) were used as real samples. Different concentrations of DQ aqueous solution were added to the tap water sample (100 mL), filtered and directly tested. Take an appropriate amount of apple sample, crush it in a mortar, put it in a beaker, add 20 mL of deionized water and stir it with a magnetic stirrer for 1 hour. Different concentrations of DQ aqueous solution were added to the sample solution, diluted 100 times with water, and centrifuged at 3000 rpm for 30 min. The collected supernatant was filtered with a 0.22μm filter membrane and directly tested. Subsequently, the RhB@Zn-MOF sensor developed by the present invention was used to detect the DQ residue in the real sample. The results are shown in Table 2.

[0035] Table 2 Determination of DQ in actual samples

[0036]

[0037] As can be seen from the table above, in tap water samples, the recovery of DQ was 90.30-109.6%, with an RSD lower than 2.38%. In apple samples, the recovery of DQ was 89.22-110.30%, with an RSD lower than 1.87%. The DQ level detected by this method was good, which verified the convenience of the detection method based on this sensor.

[0038] In summary, the present invention constructs a ratiometric fluorescence sensor (RhB@Zn-MOF) by encapsulating RhB into a Zn-MOF framework for ratiometric fluorescence detection of DQ. In the presence of DQ, the fluorescence intensity of Zn-MOF gradually increases, and the fluorescence intensity of RhB gradually decreases, forming an "on-off" type ratiometric fluorescence sensor. The sensor has self-calibration capability, avoids interference from the external environment, effectively improves the precision and accuracy of the sensor, and is applied to the detection of DQ in actual samples, with a detection limit as low as 10.5nM. Based on the above advantages, we believe that the ratiometric fluorescence sensor (RhB@Zn-MOF) will have broader application prospects in the field of food safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 (a) Asymmetric structural unit of Zn-MOF; (b) 2D layer of Zn-MOF; (cf) 2D supramolecular layer formed by π-π interaction; (g) 3D supramolecular stacking diagram formed by π-π interaction.

[0040] Figure 2 shows (a) PXRD of RhB, RhB@Zn-MOF, Zn-MOF and Zn-MOF simulation; (b) FT-IR spectra of RhB, RhB@Zn-MOF and Zn-MOF.

[0041] Figure 3 shows (a) TGA curve of Zn-MOF and (b) TGA curve of RhB@Zn-MOF.

[0042] Figure 4 (a) SEM image of Zn-MOF, (b) SEM magnified image of Zn-MOF, (c) SEM image of RhB@Zn-MOF, (d) SEM magnified image of RhB@Zn-MOF; (ei) is EDS of RhB@Zn-MOF.

[0043] Figure 5 shows (a) the overall XPS spectra of Zn-MOF and RhB@Zn-MOF; (b) Zn 2p, (c) C 1s, (d) N 1s and (e) O 1s high-resolution spectra of Zn-MOF and RhB@Zn-MOF.

[0044] Figure 6 shows (a) liquid emission spectra of RhB, Zn-MOF, RhB@Zn-MOF and H3TATB; (b) solid emission spectra of RhB, Zn-MOF and RhB@Zn-MOF; (c) liquid emission spectrum of Zn-MOF and UV-vis absorption spectrum of RhB; (d) UV-vis absorption spectrum of RhB, Zn-MOF and RhB@Zn-MOF.

[0045] Figure 7 Emission spectra of (a) RhB, (b) Zn-MOF, and (c) RhB@Zn-MOF after adding DQ.

[0046] Figure 8 (a) RhB@Zn-MOF I 356 / I 580 Interaction with different substances; (b) Fluorescence spectrum of RhB@Zn-MOF after adding DQ; (c) CIE color coordinates of RhB@Zn-MOF at different DQ concentrations; (d) I 356 / I 580 Linear relationship between fluorescence intensity ratio and DQ concentration; (e) Selectivity of RhB@Zn-MOF for DQ in the presence of other interfering substances.

[0047] Figure 9: Fluorescence spectrum of Zn-MOF after adding DQ; (b) I 352 / I There is a linear relationship between the fluorescence intensity ratio and the DQ concentration.

[0048] Figure 10 (a) Solid-state emission spectra of RhB, Zn-MOF, and RhB@Zn-MOF composites containing different concentrations of RhB. (b) UV-vis spectra of RhB@Zn-MOF composites.

[0049] Figure 11 shows (a) PXRD and (b) FT-IR spectra of RhB@Zn-MOF before and after immersion in DQ aqueous solution; (c) emission spectra of RhB@Zn-MOF after DQ and mixed with DQ; (d) fluorescence lifetime of RhB@Zn-MOF before and after adding DQ; (e) UV-vis spectrum of DQ, FL emission spectrum of RhB@Zn-MOF (λ ex = 310 nm) and FL excitation spectra of RhB@Zn-MOF and DQ. DETAILED DESCRIPTION

[0050] The present invention is further explained below with reference to specific embodiments. Example

[0051] Reagents and instruments:

[0052] H3TATB, bimb, ZnCl2, NH4Cl, CaCl2, MgCl2, KCl, cystine (Cys), glycine (Gly), glutamic acid (Glu), valine (Val), arginine (Arg), and rhodamine B (RhB) were purchased from Anaiji Chemical (Anhui, China). Ethanol, methanol, DMSO, and DMF were purchased from Aladdin (Shanghai, China). 2,4-Dichlorophenoxyacetic acid (2,4-D), glyphosate (GLYP), profenofos (PF), alachlor (ALA), dichlorvos (DDVP), carbendazim (CZ), diquat (DQ), thiamethoxam (TH), alatazine (ATZ), and methylthiophanate (TM) were purchased from J&K Scientific (Beijing, China).

[0053] Scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) (ZEISS GeminiSEM 500), powder X-ray diffraction (PXRD) (Philips PW 1710-BASED), single crystal X-ray diffraction (XRD) (Rigaku-Oxford), thermogravimetric analysis (TGA) (PerkinElmer TG-7analyzer), Fourier transform infrared spectroscopy (FT-IR) (VERTEX70, Germany), fluorescence spectroscopy (F-7000 fluorescence spectrophotometer, Japan), UV-visible spectroscopy (Hitachi UV-3900spectrometer, Japan), fluorescence lifetime (FLSP920 steady-state / transient fluorescence spectrometer, UK), K-Alpha X-ray photoelectron spectrometer (ThermoKalpha, USA).

[0054] Synthesis of Zn-MOF

[0055] H3TATB (0.01mmol, 4.4mg), bimb (0.01mmol, 2.4mg), CdCl2·2.5H2O (0.015mmol, 3.5mg) were dissolved in 10mL ethanol / water (V:V = 1:1), ultrasonicated for 30min, and transferred to a 25mL Teflon-lined autoclave. The mixture was kept in an oven at 90℃ for 3 days and heated at 10℃h. -1 The mixture was cooled to room temperature at a rate of 1.5 ℃. The mixture was washed with water and ethanol several times to obtain colorless block crystals. Finally, the mixture was dried in an oven at 60 ℃ for 24 h.

[0056] Synthesis of RhB@Zn-MOF

[0057] Dye (RhB) (0.01 mmol, 0.025 mmol, 0.05 mmol), H3TATB (0.01 mmol, 4.4 mg), bimb (0.01 mmol, 2.4 mg), CdCl2·2.5H2O (0.015 mmol, 3.5 mg) were dissolved in 10 mL ethanol / water (V:V = 1:1), sonicated for 30 min, and transferred to a 25 mL Teflon-lined autoclave. The mixture was kept in an oven at 90 °C for 3 days and heated at 10 °C for 3 h. -1 The mixture was cooled to room temperature at a rate of 1.5 ℃. The mixture was washed with water and ethanol several times to obtain colorless block crystals. Finally, the mixture was dried in an oven at 60 ℃ for 24 h.

[0058] Structural characterization and performance evaluation are described above.

Claims

1. A ratio fluorescence sensor based on dye-encapsulated Zn-MOF for detecting diquat (DQ) residues in tap water and apple samples, characterized in that: The preparation method of the ratio fluorescence sensor based on dye encapsulation Zn-MOF is to dissolve rhodamine B, 4,4',4''-[1,3,5]triazine-2,4,6-triyl-tribenzoic acid, 1,4-bis((1H-imidazole-1-yl)methyl)benzene and ZnCl2 in a mixed solvent of ethanol and water, mix them uniformly by ultrasonication, keep them warm at 85-100°C for 48-96h, cool them to room temperature at a rate of 8-12°C / h, wash and dry them; the rhodamine B The molar ratio of 4,4',4''-[1,3,5]triazine-2,4,6-triyl-tribenzoic acid is 1:1~5:1; the molar ratio of 4,4',4''-[1,3,5]triazine-2,4,6-triyl-tribenzoic acid to 1,4-bis((1H-imidazole-1-yl)methyl)benzene is 0.3:1~3:1; the molar ratio of 4,4',4''-[1,3,5]triazine-2,4,6-triyl-tribenzoic acid to ZnCl2 is 0.3:3~3:0.3; the volume ratio of ethanol and water in the mixed solvent is 1:1~2:1; according to I 356 / I 580 The linear relationship between the fluorescence intensity ratio and the DQ concentration was used to detect the DQ residue.

2. The use of the ratiometric fluorescence sensor based on dye-encapsulated Zn-MOF as claimed in claim 1 for detecting diquat (DQ) residues in tap water and apple samples, characterized in that: In tap water samples, the recoveries of DQ were 90.30-109.6%, with RSD lower than 2.38%; in apple samples, the recoveries of DQ were 89.22-110.30%, with RSD lower than 1.87%.

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