A preparation method and application of carbon dots for detecting thiophanate-methyl

Abstract

The present invention discloses a method for preparing carbon dots for detecting thiophanate-methyl, comprising the following steps: mixing nitropyrene with a sodium hydroxide solution and fully dissolving it under ultrasonic conditions; placing the mixed solution in a stainless steel high-pressure reactor and reacting it under high temperature and high pressure conditions; cooling it to room temperature after the reaction and purifying it by centrifugation, filtration and dialysis to obtain the carbon dots. The present invention also discloses the application of the carbon dots prepared by the method for preparing the carbon dots in the detection of thiophanate-methyl. The carbon dots prepared by the method of the present invention have the advantages of simple preparation, high fluorescence quantum yield, rich surface functional groups, relatively uniform particle size distribution, good water solubility and biocompatibility, and high stability. In addition, the carbon dots have a specific response effect to thiophanate-methyl, and can achieve qualitative and semi-quantitative detection of thiophanate-methyl.

Description

Technical Field

[0001] The invention belongs to the field of fluorescent sensing materials, and particularly relates to a preparation method of carbon dots for detecting thiophanate methyl and an application thereof. Background Art

[0002] Carbon dots (Cdots) are a novel carbon-based nanomaterial with excellent fluorescence properties, biocompatibility, and chemical stability. As sensor materials, their high sensitivity and selectivity enable rapid response to minute changes in analytes, holding broad application prospects in areas such as environmental sanitation, food safety, and disease diagnosis. Furthermore, their low cost, ease of preparation, environmental friendliness, and versatility make them suitable for large-scale production and rapid on-site detection.

[0003] Thiophanate methyl is a broad-spectrum thiocarbamate fungicide widely used in agriculture to control crop diseases such as powdery mildew, gray mold, and leaf spot. As a highly effective pesticide, its residues in agricultural products may pose a potential threat to food safety and the environment. Therefore, rapid and sensitive detection of thiophanate methyl is particularly important. Specific detection of thiophanate methyl can effectively control pesticide residues, ensuring that agricultural products meet international food safety standards while minimizing its negative impact on the ecological environment. This is not only important for protecting consumer health but also promotes quality control of agricultural product export trade. Carbon dot-based detection technology, with its high selectivity and sensitivity, provides an efficient and convenient solution for rapid monitoring of thiophanate methyl, with broad application prospects. Existing methods for detecting thiophanate methyl include high-performance liquid chromatography (HPLC), gas chromatography (GC), enzyme-linked immunosorbent assay (ELISA), and fluorescence and electrochemical sensing technologies. HPLC and GC offer high sensitivity and accuracy, but their instruments are expensive, complex, and require time-consuming sample pretreatment, making them unsuitable for rapid on-site testing. ELISA is simple and efficient, suitable for batch testing, but sensitivity and antibody specificity may be compromised. Fluorescence and electrochemical sensing technologies have the advantages of high sensitivity and portability, but may suffer from insufficient selectivity. Summary of the Invention

[0004] One of the objectives of the present invention is to provide a method for preparing carbon dots for detecting thiophanate-methyl. The prepared carbon dots have the advantages of simple preparation, high fluorescence quantum yield, rich surface functional groups, relatively uniform particle size distribution, good water solubility and biocompatibility, and high stability.

[0005] A second object of the present invention is to provide an application of carbon dots prepared by the carbon dot preparation method in the detection of thiophanate methyl, thereby achieving qualitative and semi-quantitative detection of thiophanate methyl through the specific interaction between the carbon dots and thiophanate methyl.

[0006] The present invention provides a method for preparing carbon dots for detecting thiophanate methyl, comprising the following steps:

[0007] S11. nitropyrene was mixed with a NaOH solution and sonicated to fully dissolve it to obtain a pyrene-NaOH solution;

[0008] S12. Add the pyrene-NaOH solution into the high-pressure reactor. After the reaction is completed, centrifuge, filter, and dialyze to obtain the carbon dots.

[0009] Furthermore, in step S11, the concentration of the NaOH solution is 0.01 to 10 M; the dosage ratio of nitropyrene to the NaOH solution is (1 to 4): (1 to 6) mg / ml; and the ultrasonic treatment time is 30 to 90 min.

[0010] Furthermore, in step S12, the reaction process conditions are: pressure of 1-20 MPa, temperature of 150-240°C, and reaction time of 5-30 h; the centrifugal process conditions are: rotation speed of 5000-12000 rpm, time of 10-30 min; the pore size of the microporous filter membrane for filtration is 0.22-0.45 μm; the molecular retention capacity of the dialysis bag used for dialysis is 500-5000 Da, and the dialysis time is 24-72 h.

[0011] The present invention also provides an application of the carbon dots prepared by the carbon dot preparation method in the detection of thiophanate-methyl.

[0012] The application of carbon dots in the detection of thiophanate-methyl includes the following steps:

[0013] S1. preparing carbon dots according to the method;

[0014] S2. The carbon dots obtained in step S1 are dispersed in water, a predetermined concentration of thiophanate-methyl is added dropwise, and the fluorescence intensity of the system is detected to obtain a corresponding relationship between the fluorescence intensity of the carbon dot system and the concentration of thiophanate-methyl;

[0015] S3. Disperse the carbon dots obtained in step S1 in water, add the sample to be tested, and detect the fluorescence intensity of the system. According to the corresponding relationship between the fluorescence intensity of the carbon dot system obtained in step S2 and the concentration of thiophanate methyl, qualitative and semi-quantitative detection of thiophanate methyl is achieved.

[0016] Furthermore, in step S2, when the carbon dots are dispersed in water, the ratio of carbon dots to water is (1-50): (1-3) μg / ml; when testing the fluorescence intensity, it is necessary to use light excitation with a wavelength of 400-600 nm.

[0017] Beneficial effects of the present invention:

[0018] (1) The method of the present invention utilizes the high fluorescence quantum yield and excellent photostability of carbon dots to produce significant fluorescence changes even in the presence of low concentrations of thiophanate-methyl, thereby ensuring high sensitivity and selectivity of detection;

[0019] (2) The method of the present invention utilizes a simple hydrothermal method to synthesize carbon dots, which is easy to operate and can be detected by simple mixing and fluorescence measurement, without the need for complex sample pretreatment and expensive instruments and equipment;

[0020] (3) The carbon dot preparation process of the present invention is environmentally friendly, the raw materials are cheap and readily available, the method cost is low, and it is suitable for large-scale promotion and application;

[0021] (4) The method of the present invention is mainly suitable for the rapid detection of methyl thiophanate in environmental samples and foods. It can be applied to many fields such as environmental monitoring, agricultural product quality control and food safety. It is of great significance to the protection of ecological environment and food quality, and shows high practical value and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 a is the TEM image of carbon dots. Figure 1 b is the size distribution diagram of carbon dots;

[0023] Figure 2 a is the spectrum of carbon dots; Figure 2 b is the high-resolution XPS spectrum of C1s; Figure 2 c is the high-resolution XPS spectrum of O1s; Figure 2 d is the high-resolution XPS spectrum of N1s;

[0024] Figure 3 a is the Raman spectrum of carbon dots, Figure 3 b is the infrared spectrum of carbon dots;

[0025] Figure 4 is the fluorescence spectrum of carbon dot solution at different excitation wavelengths;

[0026] Figure 5 a is the fluorescence spectra of carbon dot aqueous solution at different pH; Figure 5 b is the UV absorption spectra of carbon dot aqueous solution at different pH; Figure 5 c is the normalized linear relationship between the fluorescence intensity and UV absorption of carbon dots at different pH values;

[0027] Figure 6 a is the fluorescence spectra of carbon dots in sodium chloride solutions with different concentrations; Figure 6 b is the linear relationship between the fluorescence intensity of carbon dots in sodium chloride solutions with different concentrations and the sodium chloride concentration;

[0028] Figure 7 a is the fluorescence spectrum of carbon dot aqueous solution after 7 days; Figure 7 b is the linear relationship between the fluorescence intensity of carbon dot aqueous solution and time;

[0029] Figure 8 a is a schematic diagram of the mechanism of carbon dots detecting thiophanate-methyl; Figure 8 b is the fluorescence spectra of carbon dots in different concentrations of thiophanate-methyl; Figure 8 c is the linear relationship between the fluorescence intensity ratio (F0 / F) of carbon dots in different concentrations of thiophanate methyl and the concentration of thiophanate methyl; Figure 8 d is the UV absorption spectra of carbon dots in different concentrations of thiophanate-methyl;

[0030] Figure 9 The selectivity test results of carbon dots for thiophanate-methyl. DETAILED DESCRIPTION

[0031] To facilitate those skilled in the art to understand the technical content of the present invention, the present invention is further explained below with reference to the accompanying drawings.

[0032] Example 1 Preparation of carbon dots

[0033] The preparation of carbon dots specifically includes the following steps:

[0034] 0.01 g of nitropyrene was added to 10 mL of 0.1 M NaOH solution and sonicated for 60 minutes to fully dissolve it. The mixed solution was transferred to a 50 mL stainless steel autoclave and heated at 200°C and 10 MPa for 12 hours. After the reaction, the crude carbon dot product was centrifuged at 9000 rpm for 15 minutes. The resulting supernatant was filtered through a 0.22 μM pore size filter membrane and dialyzed using a 1000 Da molecular weight cutoff dialysis bag for 48 hours to remove impurities, yielding the carbon dots. 10 mg of carbon dots was dispersed in 10 mL of water to obtain a 1 mg / mL carbon dot aqueous solution, which was stored at 2-8°C for subsequent use.

[0035] Figure 1 This is a transmission electron microscope image of the carbon dots prepared in Example 1. Figure 1 It can be seen that the carbon dots prepared by this method have a particle size of 2.90 nm and are evenly distributed.

[0036] Figure 2 is the X-ray electron spectrum of the carbon dots prepared in Example 1. Figure 2 It can be seen that the carbon dots mainly contain C=O, CN, CO, CC and ON.

[0037] Figure 3 The Raman and infrared spectra of the carbon dots prepared in Example 1 are shown in FIG. Figure 3 a It can be seen that the carbon dots are rich in sp 2structure, but also contains a certain number of defects or imperfect structures (such as oxidized groups, edge defects, etc.). This means that while maintaining a certain order in the electronic structure, carbon dots also have sufficient reactivity, which has a positive impact on their performance in applications such as biomarkers, sensors, and catalysis. Figure 3 b It can be seen that the carbon dots contain OH, CH, C=O, C=C, CN and CO functional groups.

[0038] Figure 4 This is an excitation wavelength-dependent spectrum of the carbon dots prepared in Example 1. As can be seen from the figure, the carbon dots have no excitation wavelength dependence, and the optimal excitation wavelength is 490 nm.

[0039] Example 2 pH Effect Test of Carbon Dots

[0040] Prepare a PBS buffer solution with a pH of 3.8 to 8.0 by mixing 8.5 g of sodium chloride, 2.2 g of disodium hydrogen phosphate, and 0.4 g of sodium dihydrogen phosphate with 1000 mL of ultrapure water, sonicating to fully dissolve, and dispensing into 11 centrifuge tubes. Adjust the pH to 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, and 8, respectively, using 0.01 mol / L HCl and 0.01 mol / L NaOH.

[0041] 20 μL of the carbon dot aqueous solution obtained in Example 1 was dispersed in 2 mL of PBS solutions with different pH values ​​(pH=3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8), and the fluorescence and UV absorption spectra were tested.

[0042] Figure 5 Figure 1 shows the fluorescence intensity and UV absorption changes of the carbon dots prepared in Example 1 in PBS buffer solutions at different pH values, and their linear relationship. As can be seen from the figure, as the pH gradually increases, the fluorescence of the carbon dots gradually increases, while the UV absorption remains almost unchanged, indicating that the carbon dots may undergo protonation / deprotonation under different pH conditions, leading to changes in fluorescence intensity. The essentially unchanged absorption spectrum indicates that the core skeleton of the carbon dots remains stable under different pH conditions.

[0043] Example 3 Salt tolerance test of carbon dots

[0044] Mix 0.2338 g of sodium chloride with 2 mL of ultrapure water and sonicate to fully dissolve it. Disperse 20 μL of the carbon dot aqueous solution obtained in Example 1 in 2 mL of ultrapure water. Add 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 μL of a 2 mol / L sodium chloride solution dropwise, respectively. Measure the fluorescence intensity of the mixed solution.

[0045] Figure 6The fluorescence spectra and linear relationship of the carbon dots prepared in Example 1 in sodium chloride solutions of varying concentrations are shown. As shown, the carbon dots are stable in an electrolyte environment and are not significantly affected by changes in ion concentration in the solution. The fluorescence of the carbon dots exhibits strong chemical stability, indicating that their surface groups and core structure remain unchanged in the salt solution.

[0046] Example 4 7-day stability test of carbon dots

[0047] 20 μL of the carbon dot aqueous solution obtained in Example 1 was dispersed in 2 mL of ultrapure water, and its fluorescence spectrum was measured every other day for 7 consecutive days.

[0048] Figure 7 The fluorescence change spectrum and its linear relationship of the carbon dots prepared in Example 1 over 7 days are shown. As can be seen from the figure, the fluorescence intensity of the carbon dots is basically unaffected by time, indicating that the fluorescence performance of the carbon dots has long-term stability.

[0049] Example 5 Testing of Carbon Dots on Thiophanate Methyl

[0050] 20 μL of the carbon dot aqueous solution obtained in Example 1 was dispersed in 2 mL of water, and 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 μL of a 1 mmol / L thiophanate-methyl aqueous solution were added dropwise in sequence. The UV absorption spectrum and fluorescence spectrum of the mixed solution were tested.

[0051] Figure 8 The following is the mechanism of action of the carbon dots prepared in Example 1 with thiophanate methyl, as well as the fluorescence spectra and ultraviolet absorption spectra of the carbon dots in different concentrations of thiophanate methyl and their linear relationship. Figure 8 It can be seen that thiophanate methyl forms a specific interaction with the carbon dots through hydrogen bonding and Pi-Pi stacking, and then reduces the fluorescence of the carbon dots through static quenching. As the concentration of thiophanate methyl increases, the fluorescence intensity and UV absorption of the carbon dots gradually weaken, and a good linear relationship is observed between the two, indicating that the carbon dots can achieve both qualitative and semi-quantitative detection of thiophanate methyl.

[0052] Example 6 Selectivity test and anti-interference test of carbon dots for thiophanate methyl

[0053] 20 μL of the carbon dot aqueous solution obtained in Example 1 was dispersed in 2 mL of ultrapure water. 50 μL of 1 mmol / L DDT, BHC, permethrin, imidacloprid, avermectin, cyhalothrin, fipronil, mancozeb, carbendazim, chlorothalonil, difenoconazole, atrazine, glyphosate, diquat, and acetochlor were added to each solution. The fluorescence intensity of the solution was measured. Furthermore, 50 μL of 1 mmol / L thiophanate-methyl was added to each of the above solutions, and the fluorescence intensity of the mixed system was measured.

[0054] from Figure 9 It can be seen that DDT, BHC, permethrin, imidacloprid, avermectin, cyhalothrin, fipronil, mancozeb, carbendazim, chlorothalonil, difenoconazole, atrazine, glyphosate, diquat, and acetochlor do not alter the fluorescence intensity of the carbon dots, indicating that the carbon dots obtained in Example 1 have good selectivity for thiophanate-methyl. In addition, these interfering substances do not affect the response of the carbon dots to thiophanate-methyl.

Claims

1. An application of carbon dots in the detection of thiophanate-methyl, characterized in that: The method for preparing the carbon dots comprises the following steps: S11. Nitropyrene was mixed with a NaOH solution and sonicated to fully dissolve it to obtain a pyrene-NaOH solution; S12. The pyrene-NaOH solution was added to a high-pressure reactor. After the reaction, the mixture was centrifuged, filtered, and dialyzed to obtain the carbon dots. In step S12, the reaction process conditions are: pressure of 1-20 MPa, temperature of 150-240° C., and reaction time of 5-30 h.

2. The use according to claim 1, characterized in that In step S11, the concentration of the NaOH solution is 0.01-10 M; the usage ratio of nitropyrene to the NaOH solution is (1-4): (1-6) mg / ml.

3. The use according to claim 1, characterized in that In step S11, the ultrasonic treatment time is 30 to 90 minutes.

4. The use according to claim 1, characterized in that The centrifugal process conditions are: rotation speed of 5000~12000rpm, time of 10~30min.

5. The use according to claim 1, wherein the pore size of the microporous filter membrane is 0.22-0.45 μm; the molecular cutoff of the dialysis bag used for dialysis is 500-5000 Da, and the dialysis time is 24-72 h.

6. The use according to claim 1, characterized in that The application comprises the following steps: S1. preparing the carbon dots; S2. The carbon dots obtained in step S1 were dispersed in water, and a predetermined concentration of thiophanate-methyl was added dropwise. The fluorescence intensity of the system was then measured to obtain a relationship between the fluorescence intensity of the carbon dots and the concentration of thiophanate-methyl. S3. The carbon dots obtained in step S1 are dispersed in water, the sample to be tested is added dropwise, and the fluorescence intensity of the system is detected. Based on the corresponding relationship between the fluorescence intensity of the carbon dot system obtained in step S2 and the concentration of thiophanate methyl, qualitative and semi-quantitative detection of thiophanate methyl is achieved.

7. The use according to claim 6, characterized in that In step S2, when the carbon dots are dispersed in water, the dosage ratio of carbon dots to water is (1-50): (1-3) μg / ml.

8. The use according to claim 6, characterized in that When testing fluorescence intensity, it is necessary to use light excitation with a wavelength of 400 to 600 nm.

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