A method for detecting paraquat based on GSH-Zn-Ag-In-S quantum dots

Abstract

The present invention belongs to the technical field of fluorescent nano-quantum dot material preparation and chemical analysis and detection technology, specifically to a method for detecting paraquat based on GSH-Zn-Ag-In-S quantum dots. The present invention utilizes GSH-Zn-Ag-In-S quantum dots to undergo a specific redox reaction with paraquat, resulting in significant aggregation and changes in fluorescence color and intensity, thereby enabling qualitative and quantitative detection of the paraquat pesticide in food. The present invention has the advantages of good specificity, high sensitivity, and fast response speed, providing a new method for determining paraquat content.

Description

Technical Field

[0001] The present invention belongs to the technical field of fluorescent nano-quantum dot material preparation and chemical analysis detection, and specifically relates to a method for detecting paraquat based on GSH-Zn-Ag-In-S quantum dots. Background Art

[0002] Paraquat, a bipyridine pesticide, was widely used in my country early on due to its powerful herbicidal properties. Paraquat is extremely toxic and can cause multiple organ damage if accidentally ingested. There is no effective treatment, and even a small amount can cause irreversible damage. Consequently, China revoked paraquat's registration and production license on July 1, 2014. Its sale in the Chinese market is currently suspended, and its use in fruit and vegetable cultivation is strictly prohibited. However, China still relies to varying degrees on imports for some types of fruits and vegetables. In fact, more than half of the world's countries, such as the United States, Japan, and France, use paraquat. Because fruits and vegetables are essential for daily supplementation of essential vitamins and trace elements, and are also a major route for pesticides to enter the human body, developing new methods for detecting paraquat is of great practical significance for regulating pesticide residues and maintaining public safety.

[0003] Common paraquat detection methods include chromatography, spectroscopy, and chromatography / mass spectrometry. While these methods offer advantages such as high sensitivity, good reproducibility, and stability, they still suffer from low efficiency, high instrument costs, complex operation, and the inability to achieve rapid, immediate detection outside the laboratory. Given the shortcomings of existing detection methods, the development of new paraquat detection methods is of great practical significance.

[0004] In recent years, nanomaterial-based fluorescence visualization array sensing methods have become increasingly popular for pesticide detection. Nanomaterials offer not only high stability, ease of synthesis, and good biocompatibility, but also unique quantum effects and size advantages. Therefore, developing a nanomaterial-based fluorescence visualization sensing method for paraquat identification could provide a new strategy for rapid detection and real-time monitoring of paraquat in food. Summary of the Invention

[0005] To address the shortcomings of the prior art, the present invention provides a method for detecting paraquat using a nanofluorescent quantum dot colorimetric sensor. This method utilizes the strong khaki fluorescence of the GSH-Zn-Ag-In-S quantum dots in the nanofluorescent quantum dot colorimetric sensor, with a fluorescence spectrum showing two emission peaks. The GSH-Zn-Ag-In-S quantum dots undergo a specific redox reaction with paraquat, resulting in significant aggregation that alters the fluorescence color and intensity at 540±5 nm. This method enables the qualitative and quantitative detection of paraquat in samples including food and agricultural products. This method offers the advantages of simple operation, rapidity, and sensitivity, enabling rapid and accurate identification of paraquat in food and agricultural products.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for detecting paraquat using a nano-fluorescent quantum dot colorimetric sensor, comprising: a GSH-Zn-Ag-In-S quantum dot stock solution and a Tris-HCl buffer solution; mixing the nano-fluorescent quantum dot colorimetric sensor with a sample solution to be tested, allowing the mixture to react; collecting a fluorescent visualization image of paraquat identified by the GSH-Zn-Ag-In-S quantum dots; utilizing the color difference in the fluorescent color response of paraquat at different concentrations; and detecting the paraquat content in the sample solution to be tested (determining whether the paraquat pesticide residue exceeds the standard) based on the fluorescent color of the detection system obtained after the reaction of the sample solution to be tested; wherein the paraquat concentration in the sample solution to be tested is preferably no more than 1 mg / L, more preferably between 0.01 mg / L and 1 mg / L, and the solution exhibits a fluorescent color difference from dark blue to bluish purple to khaki as the paraquat concentration decreases; and / or

[0008] The nano fluorescent quantum dot colorimetric sensor is mixed with the sample solution to be tested, allowed to react, and the fluorescence emission spectrum of the resulting detection system is measured. If the ratio of the fluorescence intensity at 540±5 nm before and after the addition of the sample solution to be tested, F0 / F>2 (F0 refers to the fluorescence intensity before the addition of the sample solution to be tested, and F refers to the fluorescence intensity after the addition of the sample solution to be tested), it is determined that the sample solution to be tested contains paraquat; otherwise, the sample solution to be tested does not contain paraquat.

[0009] Among them, the optimal excitation wavelength of the fluorescence spectrum is 373nm.

[0010] Among them, the static reaction time is 3±0.5min.

[0011] The GSH-Zn-Ag-In-S quantum dots are glutathione-capped quaternary Zn-Ag-In-S quantum dots. They are synthesized by reacting reduced glutathione as a reducing agent and stabilizer with zinc acetate, silver nitrate, indium acetate, and sodium sulfide. The molar ratio of zinc acetate, silver nitrate, indium acetate, reduced glutathione, and sodium sulfide is 1.2:0.71:2:60:0.26, and the concentration of reduced glutathione in the reaction system is 0.055-0.060M.

[0012] The Tris-HCl buffer has a concentration of 0.2 M and a pH of 7.6.

[0013] The preparation method of the GSH-Zn-Ag-In-S quantum dot stock solution comprises the following steps:

[0014] (1) Dissolving zinc acetate, silver nitrate, indium acetate, and reduced glutathione in ultrapure water, mixing them uniformly, adjusting the pH of the mixed solution to 8.5±0.1, and then adding sodium sulfide solution to the mixed solution to obtain a reaction system;

[0015] (2) The reaction system was heated to 100±5°C, refluxed in the dark for 4±0.5 h, cooled and centrifuged, filtered with a 0.2 μm filter membrane, and dialyzed in the dark for 24-48 h to obtain a GSH-Zn-Ag-In-S quantum dot stock solution.

[0016] In step (1), the pH of the mixed solution is adjusted with a sodium hydroxide solution, wherein the concentration of the sodium hydroxide solution is 0.8-8 mol / L.

[0017] In step (2), the average particle size of the GSH-Zn-Ag-In-S quantum dots in the GSH-Zn-Ag-In-S quantum dot stock solution is 0.89±0.11 nm.

[0018] After the GSH-Zn-Ag-In-S quantum dot stock solution is diluted a certain number of times with ultrapure water (preferably, the GSH-Zn-Ag-In-S quantum dot stock solution is diluted 35-45 times), the diluted GSH-Zn-Ag-In-S quantum dot stock solution, Tris-HCl buffer and the sample solution to be tested are mixed, preferably, in a volume ratio of 1.5-2:1.5-3:3.

[0019] The detection limit of the nano fluorescent quantum dot colorimetric sensor for paraquat is 0.056 μg / L.

[0020] Furthermore, a method for detecting paraquat using a nano fluorescent quantum dot colorimetric sensor comprises the following steps:

[0021] S1: Draw a standard curve: Accurately weigh a paraquat dichloride standard and prepare a paraquat standard stock solution with ultrapure water. Then, dilute it with ultrapure water to different concentrations to obtain a paraquat linear solution. Evenly mix the diluted GSH-Zn-Ag-In-S quantum dot stock solution, Tris-HCl buffer, and the paraquat linear solution. Allow the mixture to react and measure the fluorescence emission spectrum of the detection system. Draw a standard curve with the paraquat concentration as the abscissa and the fluorescence intensity at 540±5 nm as the ordinate.

[0022] S2 pre-treats the sample to be tested to obtain a sample solution to be tested, mixes the diluted solution of the GSH-Zn-Ag-In-S quantum dot stock solution, Tris-HCl buffer and the sample solution to be tested, allows the reaction to proceed, measures the fluorescence intensity value of the detection system at 540±5nm, and calculates the paraquat concentration in the sample solution to be tested using the standard curve in S1.

[0023] The paraquat concentration in the sample solution to be tested is 0.001 mg / L to 0.01 mg / L.

[0024] The samples to be tested include food and agricultural products.

[0025] The sample to be tested is pretreated to obtain a sample solution to be tested. For solid samples, it is first crushed, then added with pure water to squeeze juice or soak, filtered, and the filtrate is diluted with pure water until it is colorless; for liquid samples, it is shaken and filtered, and the filtrate is diluted with pure water until it is colorless.

[0026] Preferably, in steps S1-S2, the dilution of the GSH-Zn-Ag-In-S quantum dot stock solution is a 40-fold dilution of the GSH-Zn-Ag-In-S quantum dot stock solution.

[0027] Preferably, in steps S1-S2, the volume ratio of the diluted solution of the GSH-Zn-Ag-In-S quantum dot stock solution, the Tris-HCl buffer solution, and the paraquat linear solution to the test sample solution is 2:3:3.

[0028] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0029] 1. The detection method of the present invention has high sensitivity, short detection time, simple operation, does not involve expensive instruments and reagents, and is low in cost;

[0030] 2. The detection method of the present invention can be used to directly determine with the naked eye whether the paraquat pesticide residue exceeds the standard. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the detection principle of the nano fluorescent quantum dot colorimetric sensor of the present invention;

[0032] Figure 2 The fluorescence spectra of the GSH-Zn-Ag-In-S quantum dots in the nano-fluorescent quantum dot colorimetric sensor of the present invention before and after the reaction with paraquat (red line: GSH-ZAIS-QDs+ultrapure water; black line: GSH-ZAIS-QDs+PQCl2), with the abscissa being the wavelength and the ordinate being the fluorescence intensity;

[0033] Figure 3 TEM images and particle size distribution diagrams of GSH-Zn-Ag-In-S quantum dots before and after the reaction with paraquat, where (AB) is before the reaction and (CD) is after the reaction;

[0034] Figure 4 The infrared spectra of GSH-Zn-Ag-In-S quantum dots before and after the reaction with paraquat;

[0035] Figure 5 This is the pH optimization diagram for the detection of paraquat by GSH-Zn-Ag-In-S quantum dots. The horizontal axis is pH, and the vertical axis is the ratio of the fluorescence intensity change before and after the reaction to the fluorescence intensity value before the reaction, that is, (F0-F) / F0;

[0036] Figure 6 Comparison of fluorescence visualization of optimized dilution factors for paraquat detection using GSH-Zn-Ag-In-S quantum dots;

[0037] Figure 7 This is the optimization diagram of the volume ratio of each solution for the detection of paraquat by the nano fluorescent quantum dot colorimetric sensor. The horizontal axis is the reaction ratio, and the vertical axis is the ratio of the change in fluorescence intensity before and after the reaction to the fluorescence intensity value before the reaction, that is, (F0-F) / F0;

[0038] Figure 8 The specificity of the nano fluorescent quantum dot colorimetric sensor in detecting paraquat is shown in Figure 2. The horizontal axis represents the type of pesticide, and the vertical axis represents the ratio of fluorescence intensity before and after the reaction, i.e., F0 / F.

[0039] Figure 9 The anti-interference performance of the nano fluorescent quantum dot colorimetric sensor in detecting paraquat. The horizontal axis represents the type of interfering pesticides, and the vertical axis represents the ratio of fluorescence intensity before and after the reaction, i.e., F0 / F.

[0040] Figure 10 The colorimetric effect diagram of the reaction between the nano fluorescent quantum dot colorimetric sensor and paraquat is visualized after color extraction and refilling;

[0041] Figure 11After constructing the sensor, a paraquat standard solution of known concentration was added to construct a fluorescence spectrum diagram (the horizontal axis is wavelength, the vertical axis is fluorescence intensity) and a linear regression diagram (the horizontal axis is concentration, the vertical axis is fluorescence intensity) of the standard curve.

[0042] In the present invention, GSH-Zn-Ag-In-S quantum dots, GSH-ZnAgInS QDs, GSH-ZAIS-QDs and ZAIS-QDs all have the same meaning. DETAILED DESCRIPTION

[0043] The present invention will be further described below with reference to the embodiments and accompanying drawings, but the scope of protection of the present invention is not limited to these embodiments. Those skilled in the art should understand that equivalent substitutions or corresponding improvements made to the technical features of the present invention still fall within the scope of protection of the present invention.

[0044] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. The materials and reagents used are all commercially available unless otherwise specified. Paraquat dichloride standard was purchased from Sinopharm Group with a purity of 99.8% and a size of 25 mg.

[0045] Example 1: Preparation of quantum dots

[0046] A method for preparing a colorimetric sensor based on glutathione-capped quaternary high-luminescence Zn-Ag-In-S quantum dots comprises the following steps:

[0047] 0.0022g (12μmol) of zinc acetate was added to 1mL of ultrapure water, 0.0012g (7.1μmol) of silver nitrate was added to 0.2mL of ultrapure water, 0.0058g (20μmol) of indium acetate was added to 2mL of ultrapure water, and 0.1843g (600μmol) of reduced glutathione was added to 5mL of ultrapure water. The four solutions were mixed under stirring, and the pH of the mixed solution was adjusted to 8.5 with 8mol / L sodium hydroxide solution (approximately 0.1mL). Then, 2mL of 1.3mmol / L sodium sulfide solution was added to the mixed solution to obtain a yellow clear solution. The mixed solution was heated to 100° C., refluxed in the dark for 4 h, cooled, centrifuged at 10,000 r / min, filtered with a 0.2 μm filter membrane, and dialyzed in the dark for 24 h to obtain a GSH-Zn-Ag-In-S quantum dot stock solution, which emitted a khaki fluorescence (Ex=373 nm).

[0048] The prepared GSH-Zn-Ag-In-S quantum dot stock solution was scanned with a transmission electron microscope, and the obtained TEM image was as shown in the figure below. Figure 3As shown in A and B. TEM images show that the quantum dots are uniform in size and are regular spherical, with an average particle size of 0.89±0.11nm.

[0049] Example 2: Analytical method establishment

[0050] Accurately weigh the paraquat dichloride standard and prepare a 10 mg / L paraquat standard stock solution with ultrapure water. Then dilute the paraquat standard stock solution with ultrapure water to obtain paraquat standard solutions of different concentrations.

[0051] A 40-fold dilution of the GSH-Zn-Ag-In-S quantum dot stock solution prepared in Example 1, Tris-HCl buffer (0.2 M, pH 7.6), and a 1 mg / L paraquat standard solution were mixed at a volume ratio of 1:1:1. In the blank group, paraquat was replaced with an equal volume of ultrapure water. The fluorescence spectra of the two mixed solutions were collected using a fluorescence spectrophotometer. The results are shown in FIG. Figure 2 As shown. Figure 2 It can be seen that GSH-Zn-Ag-In-S quantum dots have two obvious fluorescence characteristic peaks in the buffer solution. After adding paraquat, the characteristic peak of GSH-Zn-Ag-In-S quantum dots at 540nm disappears.

[0052] The GSH-Zn-Ag-In-S quantum dot stock solution of Example 1, Tris-HCl buffer (0.2M, pH 7.6), and 1 mg / L paraquat standard solution were mixed at a volume ratio of 1:1:1, and a microscopic image of the mixed solution was taken using a transmission electron microscope. The results are shown in FIG. Figure 3 As shown in C and D. Figure 3 From C and D, we can see that the particle size of GSH-Zn-Ag-In-S quantum dots becomes significantly larger after reacting with paraquat, with an average particle size of 3.69±0.23nm.

[0053] Figure 4 The infrared spectra of GSH-Zn-Ag-In-S quantum dots before and after the reaction with paraquat. -1 、1680cm -1 、1590cm -1 , 1400cm -1 , 1300cm -1 and 1000cm -1 The characteristic peaks at 2990 cm-1 in the FT-IR spectrum of paraquat correspond to the carboxyl group, amide bond, and thiol group in the GSH chemical structure, respectively. -1、1640cm -1 、1560cm -1 、1440cm -1 、1180cm -1 The characteristic peaks are methyl CH stretching vibration, conjugated C=C stretching vibration, pyridine ring plane deformation vibration, 4,4-bipyridine skeleton CH stretching vibration, CN stretching vibration, which are consistent with the nitrogen methyl bipyridine structure of paraquat; and the FT-IR spectrum after the reaction of the two is at 500~600cm -1 and 2880cm -1 New SS stretching vibration and methylene CH asymmetric stretching vibration characteristic peaks appeared at 1590 cm -1 The CN stretching vibration characteristic peak signal at 1640 cm -1 The characteristic peak signal of conjugated C=C stretching vibration weakened. It was inferred that a special chemical reaction occurred between GSH-Zn-Ag-In-S quantum dots and paraquat.

[0054] pH optimization for paraquat detection using GSH-Zn-Ag-In-S quantum dots:

[0055] The following concentrations of paraquat standard solutions were taken respectively: 1, 0.5, 0.01, and 0 mg / L (replaced with ultrapure water), and then GSH-Zn-Ag-In-S quantum dot stock solution, Tris-HCl buffer of different pH values ​​(0.2M, pH 7.0-8.0), and paraquat standard solutions of different concentrations were added in the order of 1:1:1 volume ratio. After mixing, the mixture was reacted for 3 minutes, and the colorimetric effect was captured by a camera under a 365 nm ultraviolet lamp. The results are shown in FIG. Figure 5 As shown in Figure A, a to f correspond to the colorimetric effects at pH 7.0, pH 7.2, pH 7.4, pH 7.6, pH 7.8, and pH 8.0, respectively; 4 samples in a to f: upper left: blank control, upper right: 0.01 mg / L, lower left: 0.5 mg / L, lower right: 1 mg / L; with pH as the horizontal axis, the ratio of the change in 540 nm fluorescence intensity of GSH-Zn-Ag-In-S quantum dots before and after the reaction with 0.5 mg / L paraquat standard solution to the fluorescence intensity value before the reaction, i.e., (F0-F) / F0, is plotted as the vertical axis, see Figure 5 In Figure B, it can be seen that the change in (F0-F) / F0 before and after the reaction is the largest when the pH of the buffer solution is 7.6. Therefore, pH = 7.6 is selected as the condition for subsequent experiments.

[0056] Optimization of the dilution factor for paraquat detection using GSH-Zn-Ag-In-S quantum dots:

[0057] Take 1 mL of the GSH-Zn-Ag-In-S quantum dot stock solution prepared in Example 1, add 9 mL of ultrapure water and mix evenly to obtain a 10-fold dilution of the GSH-Zn-Ag-In-S quantum dot stock solution. Similarly, prepare a 20-fold dilution of the GSH-Zn-Ag-In-S quantum dot stock solution and a 40-fold dilution of the GSH-Zn-Ag-In-S quantum dot stock solution for later use. The following concentrations of paraquat standard solutions were taken respectively: 1, 0.8, 0.5, 0.1, 0.08, 0.05, 0.03, 0.01, 0 mg / L (replaced with ultrapure water), and then the dilutions of the GSH-Zn-Ag-In-S quantum dot stock solution at different dilution multiples, Tris-HCl buffer (0.2M, pH 7.6), and paraquat standard solutions at different concentrations were added in the order of 1:1:1 volume ratio. After mixing evenly, the mixture was reacted for 3 minutes, and the colorimetric effect was captured by a camera under a 365nm ultraviolet lamp. The results are shown as follows: Figure 6 As shown, A to C are the colorimetric effects of 10-fold, 20-fold, and 40-fold dilutions of the GSH-Zn-Ag-In-S quantum dot stock solution, respectively. There are nine samples in A to C: from top to bottom, the first row from left to right: 1, 0.8, 0.5 mg / L, the second row from left to right: 0.1, 0.08, 0.05 mg / L, and the third row from left to right: 0.03, 0.01, 0 mg / L. As shown in the figure, when 10- and 20-fold dilutions of the GSH-Zn-Ag-In-S quantum dot stock solution were added, the fluorescence intensity of GSH-ZAIS-QDs after reacting with paraquat was high, with a wide range of fluorescence color differences between high and low concentrations, and almost no fluorescence color difference between high concentrations, making it difficult to distinguish. When the GSH-Zn-Ag-In-S quantum dot stock solution was diluted 40-fold, the fluorescence intensity of GSH-ZAIS-QDs after reacting with paraquat was moderate, with a clear and distinct fluorescence color change from blue to purple to yellow as the paraquat concentration decreased. Therefore, a 40-fold dilution of the GSH-Zn-Ag-In-S quantum dot stock solution was selected for subsequent experiments.

[0058] Optimization of the ratio of each solution for GSH-Zn-Ag-In-S quantum dots detection of paraquat:

[0059] The following concentrations of paraquat standard solutions were taken respectively: 1, 0.8, 0.5, 0.1, 0.08, 0.05, 0.03, 0.01, 0 mg / L (replaced with ultrapure water), and then added in the order of 40-fold dilution of GSH-Zn-Ag-In-S quantum dot stock solution (V1), Tris-HCl buffer (0.2M, pH 7.6) (V2), and paraquat standard solutions of different concentrations (V3). After mixing evenly according to the volume ratio of V1:V2:V3 of 1:1:1, 1:1:2, 2:3:3, 1:2:1, 3:2:1, 3:3:1, and 2:1:1, the mixture was reacted for 3 minutes, and the colorimetric effect was photographed by a camera under a 365nm ultraviolet lamp. The results are shown as follows: Figure 7 As shown in Figure A, a to g correspond to the colorimetric effects under 1:1:1, 1:1:2, 2:3:3, 1:2:1, 3:2:1, 3:3:1, and 2:1:1, respectively. The 9 samples in a to g are from top to bottom, the first row from left to right: 1, 0.8, 0.5 mg / L, the second row from left to right: 0.1, 0.08, 0.05 mg / L, the third row from left to right: 0.03, 0.01, 0 mg / L; with the reaction ratio as the horizontal axis, the ratio of the 540 nm fluorescence intensity change value before and after the reaction of GSH-Zn-Ag-In-S quantum dots with 0.5 mg / L paraquat standard solution to the fluorescence intensity value before the reaction, that is, (F0-F) / F0, is plotted as the vertical axis, see Figure 7 In Figure B, it can be seen that the change effect of the reaction system (F0-F) / F0 is best when the volume ratio of V1:V2:V3 is 1:1:2. However, when the fluorescence ratio is similar, the fluorescence color change of the paraquat standard solution with different concentrations in response to GSH-ZAIS-QDs is more obvious when the volume ratio of V1:V2:V3 is 2:3:3. At this volume ratio, the colorimetric effect diagram is taken by a camera under a 365nm ultraviolet lamp for color extraction and refilling. The colorimetric effect diagram is shown in the figure below. Figure 10 As shown ( Figure 10 The concentration order is Figure 7 The concentration order corresponds one to one). Figure 10 It can be seen that the colorimetric sensing system changes from blue to purple and then to yellow according to the concentration of the paraquat standard solution from high to low, which can be clearly observed with the naked eye. The colorimetric sensing method for identifying sulfur-containing pesticides constructed by the present invention is satisfactory.

[0060] The reaction principle is as follows: Paraquat aqueous solution is mainly composed of paraquat dichloride, which exists in the form of pyridine methyl nitrogen cations, and GSH-Zn-Ag-In-S quantum dots are encapsulated by glutathione containing two carboxyl groups. In aqueous solution, the carboxyl groups dissociate into negatively charged hydrogen ions, so the two attract each other and facilitate the reaction. Further reference shows that the nitrogen pyridine structure is easily reduced, while the sulfhydryl group of glutathione has strong reducing properties. Through analysis of experimental results such as infrared spectroscopy, new methylene structures and disulfide bonds appear after the reaction between the two, which is in line with the laws of chemical reactions. After the reaction, TEM shows that the particle size of the quantum dots increases to 3.69±0.23nm. This is because glutathione is encapsulated on the outside of the quantum dots. When the reduction reaction occurs, the sulfhydryl groups between the quantum dots form disulfide bonds, causing the quantum dots to aggregate and increase in particle size. Furthermore, after the quantum dots react with paraquat, the emission peak at 540nm is quenched, and the solution changes color from dark blue to bluish-purple and then to khaki as the paraquat concentration decreases from high to low (1mg / L-0.01mg / L). This enables quantitative and qualitative detection of low-concentration paraquat.

[0061] Example 3: Validation of analytical methods

[0062] (1) Linearity, limit of quantification, and limit of detection

[0063] Preparation of paraquat linear solutions: Take the paraquat standard stock solution in Example 2 and dilute the stock solution with ultrapure water to 0.01 mg / L, 0.007 mg / L, 0.006 mg / L, 0.005 mg / L, 0.004 mg / L, 0.003 mg / L, 0.002 mg / L, and 0.001 mg / L, respectively.

[0064] To the EP tube, a 40-fold dilution of the GSH-Zn-Ag-In-S quantum dot stock solution prepared in Example 1, Tris-HCl buffer (0.2M, pH 7.6), and a linear solution of 0.01mg / L to 0.001mg / L paraquat were added in sequence at a volume ratio of 2:3:3; to the EP tube, a 40-fold dilution of the GSH-Zn-Ag-In-S quantum dot stock solution prepared in Example 1, Tris-HCl buffer (0.2M, pH 7.6), and ultrapure water were added in a volume ratio of 2:3:3 as a blank control. Mix well, react for 3 minutes, and collect the fluorescence spectrum of the reaction system. Figure 11 In Figure A, record the fluorescence intensity at 540 nm; plot a standard curve with the concentration of paraquat linear solution as the horizontal axis and the absorbance value at 540 nm as the vertical axis. Figure 11 Figure B. The fluorescence intensity of the reaction system at 540 nm showed a linear relationship with the paraquat concentration in the range of 10 μg / L to 1 μg / L. The standard curve equation for paraquat is as follows:

[0065] Y=-40.052193x+1199.45 (Formula 1)

[0066] Where x is the concentration of paraquat, and Y is the fluorescence intensity after the reaction of paraquat with GSH-Zn-Ag-In-S quantum dots.

[0067] The method's limit of quantitation (LOQ) was calculated using the formula: LOQ = (10σ) / k, where σ is the standard deviation of 10 blank absorbance measurements and k is the slope of the standard curve. The calculated limit of quantitation for paraquat was 0.187 μg / L.

[0068] The limit of detection (LOD) of the method was calculated using the formula: LOD = (3σ) / k, where σ is the standard deviation of 10 blank absorbance measurements and k is the slope of the standard curve. The calculated limit of detection for paraquat was 0.056 μg / L.

[0069] (2) Accuracy

[0070] About 5 g of green tea, apple, cabbage, and wolfberry samples were crushed, and 20 mL of ultrapure water was added to squeeze the juice (cabbage, apple) or soak (green tea, wolfberry, soak in boiling water for 5 minutes), filtered, and the filtrate was diluted 20 times with ultrapure water until colorless to obtain food extract.

[0071] The paraquat standard stock solution in Example 2 was diluted with the above-mentioned food extract to three concentration levels of high (10 μg / L), medium (5 μg / L), and low (2 μg / L) to obtain a recovery determination solution; a reaction system was constructed according to the method in Example (1) (three parallel reaction systems were set up), and the fluorescence intensity at 540 nm was measured; the fluorescence intensity value was substituted into the standard curve equation in (1) to obtain the test concentration of paraquat, and the recovery of paraquat in the actual sample was calculated according to the formula: spiked recovery = (test concentration / sample concentration) * 100%. The results are shown in Table 1 below.

[0072] Table 1

[0073]

[0074]

[0075] As shown in Table 1, the recoveries of paraquat at three concentration levels in apple, wolfberry, green tea, and cabbage were all between 95% and 110%, and the RSDs were all less than 10%, confirming that the colorimetric sensor of the present invention has satisfactory detection effects in real samples.

[0076] (3) Specificity

[0077] The following pesticides were taken respectively, with a concentration of 100 mg / L: triadimefon, glyphosate, carbofuran, imidacloprid, acetamiprid, dipterex, cypermethrin, and cartap (all eight were solved with ultrapure water); highly effective chlorflucythrin, highly effective cypermethrin, quinalphos, dimethoate, and deltamethrin (five were solved with methanol); isoprocarb, procymidone, thiophanate-methyl, bispyribac, quinclorac, and bifenthrin (six were solved with ethanol), a total of 19 pesticide solutions, as well as 100 mg / L sodium chloride solution and 1 mg / L paraquat standard solution. Then, a 40-fold dilution of the GSH-Zn-Ag-In-S quantum dot stock solution prepared in Example 1, Tris-HCl buffer (0.2 M, pH 7.6), and pesticide were added in the order of 2:3:3 volume ratio and mixed evenly. A fluorescence spectrophotometer was used to collect fluorescence spectra of the above mixed solutions. The ratio of the fluorescence intensity at 540 nm before and after the reaction of GSH-Zn-Ag-In-S quantum dots with each pesticide, i.e., F0 / F, was used as the ordinate, and the type of pesticide was used as the abscissa to draw a bar graph. Figure 8 The results showed that the fluorescence intensity changed the most only after paraquat reacted with GSH-Zn-Ag-In-S quantum dots. Therefore, quantum dots have a strong specificity in detecting paraquat.

[0078] (4) Anti-interference

[0079] In order to investigate the anti-interference performance of GSH-ZAIS-QDs in detecting PQCl2, a total of 20 pesticides, including triadimefon, glyphosate, carbofuran, imidacloprid, acetamiprid, trichlorfon, cypermethrin, cartap, high-efficiency chlorflucythrin, high-efficiency cypermethrin, quinalphos, dimethoate, deltamethrin, isoprocarb, procymidone, thiophanate-methyl, temephos, quinclorac, bifenthrin and sodium chloride, were prepared into three interference mixed samples according to different solvents. Pesticides in the same solvent were prepared into mixed samples with each pesticide concentration of 100 mg / L. Interference mixed sample group 1, i.e., the group using ultrapure water as solvent, includes sodium chloride, triadimefon, glyphosate, chlorpyrifos, imidacloprid, acetamiprid, trichlorfon, cypermethrin, and cartap; interference mixed sample group 2, i.e., the group using methanol as solvent, includes highly effective chlorflucythrin, highly effective cypermethrin, quinalphos, dimethoate, and deltamethrin; interference mixed sample group 3, i.e., the group using ethanol as solvent, includes isoprocarb, procymidone, thiophanate-methyl, bispyribac, quinclorac, and cypermethrin.

[0080] Then, according to the order of adding a 40-fold dilution of the GSH-Zn-Ag-In-S quantum dot stock solution prepared in Example 1, Tris-HCl buffer (0.2 M, pH 7.6), and interference mixed sample (or interference mixed sample containing 1 mg / L paraquat, or ultrapure water), the samples were evenly mixed in a volume ratio of 2:3:3. The fluorescence spectra of the GSH-Zn-Ag-In-S quantum dots before and after the reaction with each interference mixed sample were collected using a fluorescence spectrophotometer. The ratio of the fluorescence intensity at 540 nm before and after the reaction of the GSH-Zn-Ag-In-S quantum dots with the interference mixed sample, i.e., F0 / F, was used as the ordinate, and the type of interference mixed sample was used as the abscissa to plot the graph. Figure 9 The results are as follows Figure 9 As shown in the figure, in the complex system of mixed pesticides, the mixed sample containing paraquat standard solution still has the highest reactivity, which confirms that GSH-ZAIS-QDs has strong anti-interference performance in the detection of paraquat.

Claims

1. A method for detecting paraquat using a nano fluorescent quantum dot colorimetric sensor, characterized in that: The GSH-Zn-Ag-In-S quantum dots in the nanofluorescent quantum dot colorimetric sensor undergo a specific redox reaction with paraquat, resulting in significant aggregation, which changes the fluorescence color and the fluorescence intensity at 540±5 nm, thereby enabling the detection of paraquat pesticide in the sample to be tested. The GSH-Zn-Ag-In-S quantum dots are synthesized by reacting reduced glutathione as a reducing agent and stabilizer with zinc acetate, silver nitrate, indium acetate and sodium sulfide; the molar ratio of zinc acetate, silver nitrate, indium acetate, reduced glutathione and sodium sulfide is 1.2:0.71:2:60:0.26, and the concentration of reduced glutathione in the reaction system is 0.055-0.060 M.

2. The method according to claim 1, characterized in that The nano-fluorescent quantum dot colorimetric sensor comprises a GSH-Zn-Ag-In-S quantum dot stock solution and a Tris-HCl buffer solution, wherein the nano-fluorescent quantum dot colorimetric sensor is mixed with a sample solution to be tested, and the mixture is allowed to react. A fluorescent visualization image of paraquat is obtained by the detection system based on the GSH-Zn-Ag-In-S quantum dots. The paraquat content in the sample solution to be tested is detected and whether the paraquat pesticide residue exceeds the standard is determined based on the fluorescence color of the detection system obtained after the reaction of the sample solution to be tested, utilizing the color difference in the fluorescence color response of paraquat at different concentrations; and / or The fluorescence emission spectrum of the obtained detection system is measured. If the ratio of the fluorescence intensity at 540±5 nm before and after adding the test sample solution is greater than 2, the test sample solution is determined to contain paraquat; otherwise, the test sample solution does not contain paraquat.

3. The method according to claim 2, characterized in that The Tris-HCl buffer has a concentration of 0.2 M and a pH of 7.

6.

4. The method according to claim 2, characterized in that The preparation method of the GSH-Zn-Ag-In-S quantum dot stock solution comprises the following steps: (1) Dissolve zinc acetate, silver nitrate, indium acetate and reduced glutathione in ultrapure water, mix well, adjust the pH of the mixed solution to 8.5±0.1, and then add sodium sulfide solution to the mixed solution to obtain a reaction system; (2) Heat the reaction system to 100±5°C, reflux in the dark for 4±0.5 h, cool and centrifuge, filter with a 0.2 μm filter membrane, and dialyze in the dark for 24-48 h to obtain the GSH-Zn-Ag-In-S quantum dot stock solution.

5. The method according to any one of claims 2 to 4, characterized in that: The GSH-Zn-Ag-In-S quantum dot stock solution was diluted with ultrapure water by a certain multiple, and then the diluted GSH-Zn-Ag-In-S quantum dot stock solution, Tris-HCl buffer solution and the sample solution to be tested were mixed.

6. The method according to claim 5, characterized in that Dilute the GSH-Zn-Ag-In-S quantum dot stock solution 35-45 times; and / or The diluted solution of the GSH-Zn-Ag-In-S quantum dot stock solution, the Tris-HCl buffer solution and the sample solution to be tested are mixed in a volume ratio of 1.5-2:1.5-3:

3.

7. The method according to any one of claims 2 to 4, characterized in that: The static reaction time was 3±0.5 min.

8. The method according to claim 2, characterized in that The steps include: S1. Draw a standard curve: Accurately weigh the paraquat dichloride standard and prepare a paraquat standard stock solution with ultrapure water. Then dilute it with ultrapure water to different concentrations to obtain a paraquat linear solution. Mix the diluted GSH-Zn-Ag-In-S quantum dot stock solution, Tris-HCl buffer, and the paraquat linear solution. Let the mixture stand for reaction. Measure the fluorescence emission spectrum of the detection system and draw a standard curve with the paraquat concentration as the horizontal axis and the fluorescence intensity at 540±5 nm as the vertical axis. S2 pre-treats the sample to be tested to obtain a sample solution to be tested, mixes the diluted solution of the GSH-Zn-Ag-In-S quantum dot stock solution, Tris-HCl buffer and the sample solution to be tested, allows the reaction to proceed, measures the fluorescence intensity value of the detection system at 540±5 nm, and calculates the paraquat concentration in the sample solution to be tested using the standard curve in S1.

9. The method according to claim 8, characterized in that The paraquat concentration in the sample solution to be tested is 0.001 mg / L to 0.01 mg / L.

10. The method according to claim 8, characterized in that In steps S1-S2, the dilution of the GSH-Zn-Ag-In-S quantum dot stock solution is a 40-fold dilution of the GSH-Zn-Ag-In-S quantum dot stock solution; and / or The volume ratio of the dilution solution of the GSH-Zn-Ag-In-S quantum dot stock solution, Tris-HCl buffer and paraquat linear solution / test sample solution is 2:3:

3.

11. The method according to claim 8, characterized in that In step S2, the sample to be tested includes food and agricultural products; for solid samples, they are first crushed, then added with pure water to squeeze juice or soak, filtered, and the filtrate is diluted with pure water until it is colorless; For liquid samples, shake well and filter, then dilute the filtrate with pure water until it is colorless.

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