Fluorescent ion probe based on dihydroxynaphthalene and its preparation and application in detecting diquat

Abstract

The application discloses a fluorescent ion probe based on dihydroxynaphthalene, and preparation and application thereof in detection of monuron, wherein the fluorescent ion probe can realize rapid, sensitive and specific detection of monuron residues, the fluorescent ion probe is loaded on paper to develop fluorescent paper, the demand of a portable device is met, and a new method is provided for convenient detection of monuron in a complex matrix.

Description

(1) Technical field

[0001] The invention relates to a fluorescent ion probe based on dihydroxynaphthalene, and its preparation and application in detecting diquat. (2) Background technology

[0002] Diquat (DQ), also known as 1,1'-ethylene-2,2'-bipyridinium dibromide, is a classic commercial quaternary ammonium herbicide widely used for crop weed control and desiccation. Several studies have shown that diquat is a strong electron transfer agent that produces oxidative stress, thereby promoting the formation of superanion radicals and leading to cell apoptosis in the biological microenvironment. Its strong irritation and residues pose serious health risks to organisms, such as irritation to the eyes, skin, mouth, stomach, and throat. As food safety issues related to pesticide residues have become increasingly important, China has established maximum residue limits (MRLs) for diquat in various foods, such as 2 mg / kg for wheat and 0.05 mg / kg for corn and potatoes. Several classic analytical techniques, such as high-performance liquid chromatography (HPLC), electrochemical analysis, and surface-enhanced Raman spectroscopy, have been explored for detection. However, these traditional detection methods and large instrumentation often suffer from cumbersome handling, difficult operation, and low sensitivity. Therefore, a simple, rapid, and sensitive detection method is urgently needed.

[0003] Fluorescent probe detection technology has become one of the important means besides some traditional technologies due to its good sensitivity, selectivity and real-time monitoring. The choice of fluorescent material is an important factor in determining the sensitivity of fluorescent probes. The new material ionic liquids (ILs) have become more attractive in the field of analysis due to their high tunability and unique optical properties. The charge characteristics of ionic liquids also give them a signal amplification effect. According to the structural characteristics of the analyte, the anions or cations can be precisely adjusted in a targeted manner, and the fluorescence, color, weak interaction force, etc. of the probe can be optimized, which makes ionic liquids a unique sensor. Therefore, as long as the tunability of ionic liquids is fully utilized, it is expected that a fluorescent ion probe for the rapid and sensitive detection of diquat can be developed. (3) Summary of the invention

[0004] The present invention aims to provide a dihydroxynaphthalene-based fluorescent ion probe, its preparation, and application in the detection of diquat. The fluorescent ion probe can achieve rapid, sensitive, and specific detection of diquat residues. At the same time, the fluorescent ion probe is loaded on paper to develop a fluorescent paper base, which meets the needs of portable devices and provides a new method for the convenient detection of diquat in complex matrices.

[0005] The technical solution adopted in the present invention is:

[0006] The present invention provides a fluorescent ion probe based on dihydroxynaphthalene, wherein the structure of the fluorescent ion probe is shown in one of the following:

[0007]

[0008] The invention provides a preparation method of the fluorescent ion probe. The method comprises: placing trihexyl (tetradecyl) phosphine hydroxide and dihydroxynaphthalene in a single-necked flask, dissolving them with anhydrous ethanol, fully stirring and reacting at a temperature of 40 to 120° C. for 5 to 18 hours (preferably at 60° C. for 12 hours), evaporating under reduced pressure to remove the solvent after the reaction is completed, and continuing to dry under nitrogen at 60 to 100° C. (preferably 80° C.) to obtain a viscous product, which is the fluorescent ion probe; the dihydroxynaphthalene includes 1,3-dihydroxynaphthalene, 1,4-dihydroxynaphthalene, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 1,7-dihydroxynaphthalene, 1,8-dihydroxynaphthalene, 2,3-dihydroxynaphthalene, 2,6-dihydroxynaphthalene and 2,7-dihydroxynaphthalene.

[0009] Furthermore, the molar ratio of trihexyl (tetradecyl) phosphine hydroxide to dihydroxynaphthalene is 2:1.

[0010] Furthermore, the preparation of trihexyl (tetradecyl) phosphine hydroxide comprises adding trihexyl (tetradecyl) phosphine chloride to a chromatography column filled with a strongly basic anion exchange resin, slowly flushing with anhydrous ethanol at a rate of 6 to 8 seconds per drop until the effluent changes from alkaline to neutral. The collected alkaline effluent is the trihexyl (tetradecyl) phosphine hydroxide solution. This process is a dechlorination treatment. The strongly basic anion exchange resin is AMberlite IRA-400 (Cl). The mass ratio of trihexyl (tetradecyl) phosphine chloride to the strongly basic anion exchange resin is 1:6.

[0011] The present invention also provides an application of the fluorescent ion probe in detecting diquat in actual samples.

[0012] Furthermore, the application includes grinding and pulverizing the sample to be tested, ultrasonically extracting the sample with methanol at 100-350W and immersing for 5-30 minutes, centrifuging the sample, adding the fluorescent ion probe to the supernatant, detecting the fluorescence spectrum at 350-550nm, and calculating the diquat content in the sample to be tested based on a standard curve of diquat concentration and fluorescence quenching intensity.

[0013] Furthermore, the fluorescent ion probe is added to the supernatant at a concentration of 5 to 500 μM.

[0014] Furthermore, the standard curve of diquat concentration and fluorescence quenching intensity was prepared according to the following steps: a fluorescent ion probe methanol solution was added to a centrifuge tube, and then different volumes of diquat methanol solution were added to make the probe concentration 50 μM and the final concentration of diquat was 0, 0.5, 1, 2, 2.5, 3, 4, 5, 6, 7, 7.5, 8, 9, 10, 25, 50, 75, 100, 250, 500, and 1000 μM. After mixing evenly, the mixture was poured into a quartz dish, and the fluorescence spectrum at 350 to 550 nm was measured. The fluorescence quenching intensity (ΔF=F0-F) of the fluorescent ion probe at 410 nm was used as the vertical coordinate, and the diquat concentration was used as the horizontal coordinate to form a standard curve.

[0015] The present invention also provides a diquat test strip made of a fluorescent ion probe, wherein the test strip is made by mixing filter paper in a fluorescent ion probe methanol solution (preferably 5.0×10 -4 M) soaked and then naturally dried; the test strip is used as follows: immerse the front end of the test strip into the solution to be tested, take it out after 10 seconds, observe the fluorescence change of the test strip under a 365nm ultraviolet lamp, and compare the test strip fluorescence quenching standard colorimetric card to determine the concentration range of diquat in the test solution;

[0016] The test strip fluorescence quenching standard colorimetric card was prepared according to the following steps: the front end of the test strip was immersed in a methanol solution containing different concentrations of diquat (0, 1, 5, 10, 50, 100, 500, and 1000 μM), and the test strip was removed after 10 seconds. The changes in the fluorescence of the test strip were recorded under a 365 nm ultraviolet lamp to prepare a fluorescence quenching standard colorimetric card. The color gradually changed from strong blue fluorescence to dark to no fluorescence.

[0017] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in:

[0018] (1) The fluorescent ion probe of the present invention has high sensitivity.

[0019] The present invention successfully synthesized a series of dihydroxynaphthalene-based fluorescent ion probes through a proton exchange reaction between dihydroxynaphthalene with different substitution sites and trihexyl (tetradecyl)phosphine hydroxide. Due to the strong electrostatic attraction and π-π stacking interaction between diquat and the fluorescent ion probe, diquat can rapidly quench the fluorescence of the fluorescent ion probe and be captured by the detector. In particular, the fluorescence of 18-DHNP can be rapidly quenched (less than 5 seconds). Using fluorescence titration, the linear range of 18-DHNP fluorescence detection for diquat is determined to be 0.05 to 100 μM, with a LOD of 0.1 μM.

[0020] (2) The fluorescent ion probe of the present invention exhibits high selectivity and anti-interference properties.

[0021] The fluorescent ion probe of the present invention can specifically identify diquat from 20 different common pesticides and 5 quaternary ammonium salt pesticides, and has good selectivity and anti-interference properties.

[0022] (3) Fluorescent ion probe-based preparations can detect diquat rapidly, portablely, and sensitively.

[0023] The fluorescent ion probe is loaded onto paper and assembled into a fluorescent paper base, which is portable and can detect diquat quickly and in real time.

[0024] (4) The present invention provides a method for rapid, sensitive, and quantitative detection of diquat, which has good applicability in a variety of real food samples; it meets the demand for portable devices and provides a new approach for on-site semi-quantitative detection of diquat. (IV) Description of the accompanying drawings

[0025] Figure 1 This is the fluorescence titration emission spectrum of 18-DHNP detecting different concentrations of diquat.

[0026] Figure 2 Graph (a) showing the fluorescence quenching intensity (ΔF) at 410 nm and the relationship between the concentration of diquat (0-1000 μM) and the calibration curve (b) showing the linear range of the fluorescence quenching intensity and the relationship between the concentration of diquat (0-100 μM) and the detection of different concentrations of diquat by 18-DHNP.

[0027] Figure 3 The fluorescence spectra of 18-DHNP detecting diquat at different response times (a) and the line graph with fluorescence intensity as the vertical axis and response time as the horizontal axis (b) are shown.

[0028] Figure 4 Selectivity and anti-interference ability of 18-DHNP in detecting different pesticides; a represents the structural formula and number of 20 pesticides: 1 diquat, 2 bensulfuron-methyl, 3 carbendazim, 4 beta-cypermethrin, 5 dimethoate, 6 beta-cypermethrin, 7 pentachloronitrobenzene, 8 triazophos, 9 deltamethrin, 10 methyl parathion, 11 chlorpyrifos, 12 fomesafen, 13 phoxim, 14 pretilachlor, 15 acephate, 16 diazinon, 17 butachlor, 18 acetochlor, 19 profenofos, and 20 dichlorvos; b represents the bar graph of fluorescence quenching intensity and pesticide type in detecting different pesticides by 18-DHNP.

[0029] Figure 5 Figure 2 shows the selectivity and anti-interference ability of 18-DHNP in detecting different quaternary ammonium pesticides. a represents the structural formula of quaternary ammonium pesticides: diquat DQ, paraquat PQ, diquat FQ, mepiquat MQ, and chlormequat-chloride CQ. b represents a bar graph showing the fluorescence quenching intensity of 18-DHNP in detecting different quaternary ammonium pesticides and the types of quaternary ammonium pesticides.

[0030] Figure 6 The Job plot's curve shows the fluorescence quenching intensity of 18-DHNP detecting different contents of diquat and the molar concentration ratio of diquat to the total amount of substances.

[0031] Figure 7 The fluorescence visualization photos were taken under 365 nm light when 18-DHNP solution was not added (blank) and when diquat was added.

[0032] Figure 8 The preparation and use process of 18-DHNP fluorescent paper (a) and the fluorescence photos taken under 365nm light after detecting different concentrations of diquat (0-1000μM) (b). (V) Specific implementation methods

[0033] The present invention is further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto:

[0034] The chemical reagents and solvents used in the examples were all commercially available analytical grade.

[0035] The fluorescence spectrum measurement conditions were set as an excitation wavelength of 345 nm, an emission wavelength of 350-600 nm, and excitation and emission slit widths of 2.5 nm and 2.5 nm, respectively.

[0036] Example 1. Synthesis of fluorescent ion probe

[0037] (1) Dechlorination of trihexyl (tetradecyl) phosphine chloride:

[0038] Trihexyl(tetradecyl)phosphine chloride was added to a chromatography column containing a strongly basic anion exchange resin (Model Amberlite IRA-400(Cl)) at a mass ratio of 1:6. The column was slowly rinsed with anhydrous ethanol at a rate of 8 seconds / drop until the effluent became neutral. The collected alkaline effluent was the trihexyl(tetradecyl)phosphine hydroxide solution obtained after dechlorination treatment. Its concentration was determined to be 0.3027 M by acid-base titration.

[0039] (2) Synthesis of fluorescent ion probe 18-DHNP:

[0040] 0.1602 g of 1,8-dihydroxynaphthalene and a solution containing 1.0010 g of trihexyl (tetradecyl) phosphine hydroxide obtained in step (1) (solution volume 6.61 mL), with a molar ratio of trihexyl (tetradecyl) phosphine hydroxide to 1,8-dihydroxynaphthalene of 2:1, were added to a round-bottom flask and dissolved in anhydrous ethanol. The mixture was then stirred thoroughly in a 60°C oil bath and reacted for 12 hours. After the reaction was completed, the reaction solution was evaporated under reduced pressure to remove the solvent and then heated to 80°C in a nitrogen atmosphere for further drying to obtain 1.0265 g of a viscous liquid product, which was a fluorescent ion probe, designated 18-DHNP. The mixture was sealed and stored at room temperature.

[0041] The 1,8-dihydroxynaphthalene was replaced by 1,3-dihydroxynaphthalene, 1,4-dihydroxynaphthalene, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 1,7-dihydroxynaphthalene, 2,3-dihydroxynaphthalene, 2,6-dihydroxynaphthalene and 2,7-dihydroxynaphthalene, respectively. The other operations were the same to prepare the fluorescent ion probes 13-DHNP, 14-DHNP, 15-DHNP, 16-DHNP, 17-DHNP, 23-DHNP, 26-DHNP and 27-DHNP, respectively.

[0042] Example 2: Selectivity and Anti-interference of Fluorescent Ion Probe for Diquat Detection

[0043] Accurately weigh the solid diquat and dissolve it in methanol to prepare 1.0×10 -2 M diquat standard stock solution. Accurately weigh 18-DHNP and dissolve it in methanol to prepare 1.0×10 -3 M 18-DHNP standard stock solution.

[0044] (1) Fluorescence detection of diquat by 18-DHNP:

[0045] When performing fluorescence titration, first add 50 μL of 1.0×10 -3 M 18-DHNP standard stock solution was added to a centrifuge tube, and then different volumes of diquat standard stock solution were added. The volume was then adjusted to 1.0 mL with methanol to make the final concentration of the probe 50 μM. The final concentrations of diquat were 0, 0.5, 1, 2, 2.5, 3, 4, 5, 6, 7, 7.5, 8, 9, 10, 25, 50, 75, 100, 250, 500, and 1000 μM. After mixing evenly, the mixture was poured into a quartz dish. The fluorescence spectra of samples containing different concentrations of diquat (0-1000 μM) were measured at 350-550 nm. The results are shown in Figure 2. Figure 1 As shown, as the concentration of diquat increased from 0 to 1000 μM, the fluorescence of the probe was gradually quenched and the fluorescence intensity at 410 nm gradually decreased.

[0046] according to Figure 1The graph with the fluorescence quenching intensity of 18-DHNP at 410 nm (ΔF = F0-F) as the ordinate and the diquat concentration (0-1000 μM) as the abscissa is shown in FIG. Figure 2 As shown in a, Figure 2 Figure b is a calibration curve of the linear range of fluorescence quenching intensity and diquat concentration (0-100 μM), which shows a good linear relationship between the quenching intensity and the diquat concentration.

[0047] like Figure 2 As shown, in the linear range of 0.05 to 10 μM, the linear standard calibration curve equation is fitted as ΔF = 51.9C + 13.0 (R 2 =0.9934); In the linear range of 10-100 μM, the linear standard calibration curve equation was fitted as ΔF=2.8C+486.3(R 2 =0.9939). The limit of detection (LOD) of 18-DHNP for diquat was calculated to be 0.1 μM.

[0048] (2) Response time of 18-DHNP to Diquat:

[0049] Add the 18-DHNP standard stock solution to a centrifuge tube, then add the diquat standard stock solution, and then dilute to 1.0 mL with methanol to make the probe concentration 50 μM and the final diquat concentration 5 μM. Mix well and pour into a quartz dish. Measure the fluorescence spectrum from 350 to 550 nm at 0 (no diquat), 5, 15, 30, 45, 60, 75, 90, 105, and 120 s, respectively. The results are as follows: Figure 3 As shown in a, the line graph with the fluorescence intensity of 18-DHNP at 410 nm as the vertical axis and the response time as the horizontal axis is shown in Figure 3 As shown in b.

[0050] like Figure 3 As shown in the figure, when 5 μM diquat was added, the fluorescence intensity of 50 μM 18-DHNP immediately decreased significantly, responded to diquat within 5 s and remained stable within 120 s, indicating that the probe has the characteristics of rapid response.

[0051] (3) Selectivity of 18-DHNP for Diquat Detection:

[0052] 20 pesticides (including diquat and 19 interfering pesticides): 1. Diquat (DQ), 2. Bensulfuron-methyl, 3. Carbendazim, 4. Beta-cypermethrin, 5. Dimethoate, 6. Beta-cypermethrin, 7. Quintozene, 8. Triazophos, 9. Deltamethrin, 10. Methyl parathion, 11. Chlorpyrifos, 12. Fomesafen, 13. Phoxim, 14. Pretilachlor, 15. Acephate, 16. Diazinon, 17. Butachlor, 18. Acetochlor, 19. Profenofos, and 20. Dichlorvos. See the structural formula for the following: Figure 4 As shown in a.

[0053] In order to explore the selectivity of the probe for diquat detection, the 18-DHNP standard stock solution was added to a centrifuge tube, and then methanol solutions of 20 pesticides were added respectively. The volume was then fixed to 1.0 mL with methanol, so that the probe concentration was 50 μM and the final concentration of the pesticides was 5 μM. After mixing evenly, the solution was poured into a quartz dish and the fluorescence spectrum was detected at 350-550 nm. A bar graph was drawn with the fluorescence quenching intensity (ΔF) as the vertical axis and the type of pesticide as the horizontal axis ( Figure 4 The selectivity of the probe was shown in b), demonstrating that the probe has excellent selectivity.

[0054] (4) Anti-interference of 18-DHNP on Diquat Detection

[0055] In order to investigate the interference of interfering pesticides on the detection of paraquat by the probe, the 18-DHNP standard stock solution was added to a centrifuge tube, and then the 20 pesticides (diquat and equivalent interfering pesticides) in step (3) were added at the same time. The volume was then adjusted to 1.0 mL with methanol to make the probe concentration 50 μM and the final concentration of the pesticides 5 μM. The fluorescence spectrum was recorded and a bar graph was drawn using the same method as step (3). Figure 4 As shown in the anti-interference of b, it is proved that the probe also has good anti-interference performance.

[0056] (5) Selectivity and anti-interference of the probe for the detection of the same type of quaternary ammonium pesticides

[0057] Selectivity: Using the same detection method and conditions as step (3), the detection probe is sensitive to the same type of quaternary ammonium pesticides ( Figure 5 The detection selectivity of a) is shown in Figure 5 As shown in the selectivity of b.

[0058] Anti-interference: Using the same detection method and conditions as step (4), the detection probe is sensitive to the same type of quaternary ammonium pesticides ( Figure 5 The anti-interference performance of a) is shown in Figure 5 As shown in b, the anti-interference.

[0059] Figure 5 In Figure b, it can be found that even pesticides with highly similar structures will not interfere with the specific recognition of diquat by 18-DHNP, which is due to the "size matching" between the two.

[0060] (6) The mixing ratio of 18-DHNP to diquat:

[0061] The combination ratio of the probe and diquat was determined according to the Job plot's method, and the total molar concentration of the probe and diquat was determined to be 240 μM. The fluorescence spectra at 350-550 nm were measured when the concentration ratios of the probe and diquat were 0:10, 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, 9:1, and 10:0, respectively.

[0062] Taking a 1:9 ratio as an example, 100 μL of 18-DHNP standard stock solution and 100 μL of diquat standard stock solution were added to a centrifuge tube, and then the volume was adjusted to 1.0 mL with methanol, so that the probe concentration was 24 μM and the diquat concentration was 216 μM. After mixing evenly, the mixture was poured into a quartz dish for measurement. The other concentration ratios were the same as above. The Job plot was drawn with the fluorescence quenching intensity (ΔF) as the vertical axis and the molar concentration ratio of diquat to the total amount of substance as the horizontal axis. Figure 6 When the quenching intensity reaches the maximum, the proportion of diquat is about 0.5, indicating that the mixing ratio of 18-DHNP to diquat is about 1:1.

[0063] Example 3: Sensitivity and Accuracy of Spiked Recovery Detection of 18-DHNP for Diquat in Real Samples

[0064] Cereals (rice, wheat, sorghum, corn, and soybeans) and teas (Longjing, Maojian, and Biluochun) were collected as authentic samples, and recoveries were determined through spiked recovery experiments. 1.0 g of each cereal was crushed or ground, then added to 10 mL of methanol as the extractant. Ultrasonication at 250 W for 10 minutes was performed, followed by centrifugation to remove insoluble impurities. Extracts were obtained. 0.1 g of each tea leaf was soaked in 10 mL of methanol, ultrasonicated at 250 W for 5 minutes, and then the tea residue was removed to obtain the tea extracts.

[0065] Diquat was added to 100 μL of the extract of each sample, and then 18-DHNP standard stock solution (same as in Example 2) was added to make the concentration of the added diquat 50 μM, wherein the final concentration of diquat was 5, 10 and 80 μM, and the fluorescence spectra at 350-550 nm were measured respectively. Figure 2 The standard curve obtained in the HPLC analysis was used to calculate the recovery rate of diquat, and the recovered concentration was verified by HPLC analysis. The results are shown in Table 1. As can be seen, the probe's recovery rate for diquat spiked in real samples ranged from 96.1% to 103.4%, with a relative standard deviation (RSD) of less than 3.5%. Furthermore, a P value greater than 0.05 confirmed that there was no significant difference in the results between the two methods.

[0066] The HPLC analysis conditions were based on HG_T 5246-2017. The instrument model for this experiment was Chromai Leaps, using a C18 chromatographic column. The specific operating conditions were as follows: the mobile phase was 3.64 g of sodium heptanesulfonate, dissolved in 900 mL of distilled water, 16 mL of phosphoric acid was added, the pH was adjusted to 2 with triethylamine, and 100 mL of acetonitrile was added. The mixture was mixed evenly and filtered; the flow rate was 1.0 mL / min, the column chamber temperature was low, the detection wavelength was 310 nm, and the injection volume was 10 μL.

[0067] Table 1 Results of spike recovery experiments in food samples

[0068]

[0069] ND a :Notdetected.

[0070] Example 4, 18-DHNP portable paper base

[0071] 1. Study on the quenching of probe by diquat

[0072] A 50 μM 18-DHNP methanol solution emitted bright blue fluorescence under a 365 nm lamp. When 5 μM diquat was added, the fluorescence of the solution was rapidly quenched. Figure 7 , which provides a basis for the production of fluorescent paper base.

[0073] 2. Production of portable paper base

[0074] A circular filter paper (9 cm in diameter) was soaked in 2 mL of 5.0 × 10 -4 M of 18-DHNP methanol solution, and after natural air drying, the 18-DHNP-based paper substrate ( Figure 8 In a), the paper base can be cut into various desired shapes.

[0075] 3. Portable paper-based fluorescence quenching standard colorimetric card

[0076] The front end of the test strip was immersed in methanol solutions containing different concentrations of diquat (0, 1, 5, 10, 50, 100, 500, 1000 μM), and taken out after 10 seconds. The changes in the fluorescence of the test strip were recorded under a 365 nm ultraviolet light. Figure 8 As shown in middle b, the color gradually changes from strong blue fluorescence to no fluorescence.

[0077] 4. Application of portable paper base

[0078] The preliminary judgment of diquat concentration can be achieved based on the changes in paper-based fluorescence, which is expected to meet the needs of portable and rapid detection of diquat.

Claims

1. A fluorescent ion probe based on dihydroxynaphthalene, characterized in that: The structure of the fluorescent ion probe is shown below: 。 2. A method for preparing the fluorescent ion probe according to claim 1, characterized in that: The method comprises: placing trihexyl (tetradecyl) phosphine hydroxide and 1,8-dihydroxynaphthalene in a single-necked flask, dissolving them with anhydrous ethanol, fully stirring and reacting them at a temperature of 40-120°C for 5-18 hours, evaporating the solvent under reduced pressure after the reaction, and continuing to dry them under nitrogen at 60-100°C to obtain a viscous product, which is a fluorescent ion probe.

3. The method according to claim 2, wherein The molar ratio of trihexyl (tetradecyl) phosphine hydroxide to 1,8-dihydroxynaphthalene is 2:

1.

4. Use of the fluorescent ion probe according to claim 1 in detecting diquat in actual samples.

5. The use according to claim 4, characterized in that The application is as follows: grinding and crushing the sample to be tested, ultrasonicating and immersing the sample in methanol at 100-350 W for 5-30 minutes, centrifuging, adding the fluorescent ion probe to the supernatant, detecting the fluorescence spectrum at 350-550 nm, and calculating the diquat content in the sample to be tested based on a standard curve of diquat concentration and fluorescence quenching intensity.

6. The use according to claim 5, characterized in that The fluorescent ion probe was added to the supernatant at a concentration of 5-500 μM.

7. The use according to claim 5, characterized in that The standard curve of diquat concentration and fluorescence quenching intensity was prepared according to the following steps: a fluorescent ion probe methanol solution was added to a centrifuge tube, and then different volumes of diquat methanol solution were added to make the probe concentration 50 μM, and the final concentration of diquat was 0, 0.5, 1, 2, 2.5, 3, 4, 5, 6, 7, 7.5, 8, 9, 10, 25, 50, 75, 100, 250, 500, and 1000 μM. After mixing evenly, the mixture was poured into a quartz dish, and the fluorescence spectrum from 350 to 550 nm was measured. The standard curve was prepared with the fluorescence quenching intensity of the fluorescent ion probe at 410 nm as the vertical axis and the diquat concentration as the horizontal axis.

8. A diquat test strip prepared with the fluorescent ion probe according to claim 1.

9. The test strip according to claim 8, wherein The test strip is made by soaking filter paper in a fluorescent ion probe methanol solution and then naturally drying it. The test strip is used by dipping the front end of the test strip into the solution to be tested, removing it after 10 seconds, observing the fluorescence change of the test strip under a 365 nm ultraviolet lamp, and comparing the fluorescence quenching standard colorimetric card of the test strip to determine the concentration range of diquat in the solution to be tested. The test strip fluorescence quenching standard colorimetric card was prepared according to the following steps: the front end of the test strip was immersed in a diquat methanol solution with diquat concentrations of 0, 1, 5, 10, 50, 100, 500, and 1000 μM, and the test strip was removed after 10 seconds. The changes in the fluorescence of the test strip were recorded under a 365 nm ultraviolet lamp to prepare a fluorescence quenching standard colorimetric card, in which the color gradually changed from strong blue fluorescence to dark to no fluorescence.

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