Preparation method and application of carbon dots for detecting thiophanate methyl

Abstract

The invention discloses a preparation method of carbon dots for detecting thiophanate methyl, which comprises the following steps: mixing nitropyrene with a sodium hydroxide solution, and fully dissolving under an ultrasonic condition; putting the mixed solution into a stainless steel high-pressure reactor, and reacting under high-temperature and high-pressure conditions; and after the reaction is finished, cooling to room temperature, and carrying out purification treatment through centrifugation, filtration and dialysis to obtain the carbon dots. The invention also discloses application of the carbon dots prepared by the preparation method of the carbon dots in detection of thiophanate methyl. The carbon dots prepared by the method have the advantages of simple preparation, high fluorescence quantum yield, abundant surface functional groups, uniform particle size distribution, good water solubility and biocompatibility, high stability and the like. In addition, the carbon dots have a specific response effect on the thiophanate methyl, and qualitative and semi-quantitative detection of the thiophanate methyl can be realized.

Description

Technical Field

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

[0002] Carbon dots are a new type of carbon-based nanomaterial with excellent fluorescence properties, good biocompatibility and chemical stability. As a sensor material, the high sensitivity and high selectivity of carbon dots enable them to quickly respond to trace changes in the analyte, and have broad application prospects in environmental hygiene, food safety, disease diagnosis and other fields. In addition, the low cost, easy preparation, environmental friendliness and versatility of carbon dots 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 residue 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. By specifically detecting thiophanate-methyl, the pesticide residue can be effectively controlled to ensure that agricultural products meet international food safety standards while reducing its negative impact on the ecological environment. This is not only of great significance for protecting consumer health, but also promotes the quality supervision of agricultural product export trade. The detection technology based on carbon dots, with its high selectivity and sensitivity, provides an efficient and convenient solution for rapid monitoring of thiophanate-methyl, and has 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 have high sensitivity and accuracy, but the instruments are expensive and complicated to operate, and the sample pretreatment takes a long time, which is not suitable for rapid on-site detection. The ELISA method is simple and efficient, suitable for batch detection, but the sensitivity and antibody specificity may be affected. 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 purposes of the present invention is to provide a method for preparing carbon dots for detecting thiophanate-methyl, wherein 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] The 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 methyl thiophanate, so as to achieve qualitative and semi-quantitative detection of methyl thiophanate through the specific interaction between the carbon dots and methyl thiophanate.

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

[0007] S11. mixing nitropyrene with a NaOH solution, and subjecting it to ultrasonic treatment to fully dissolve it, thereby obtaining a pyrene-NaOH solution;

[0008] S12. Adding the pyrene-NaOH solution into the high-pressure reactor, after the reaction is completed, centrifuging, filtering and dialyzing 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 process conditions of the reaction are: pressure of 1-20 MPa, temperature of 150-240°C, reaction time of 5-30 h; the process conditions of centrifugation 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 dots 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. dispersing the carbon dots obtained in step S1 in water, adding a certain preset concentration of thiophanate methyl, and then detecting the fluorescence intensity of the system to obtain the 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, drop the sample to be tested, detect the fluorescence intensity of the system, and achieve qualitative and semi-quantitative detection of methyl thiophanate based on the corresponding relationship between the fluorescence intensity of the carbon dot system obtained in step S2 and the concentration of methyl thiophanate.

[0016] Furthermore, in step S2, when the carbon dots are dispersed in water, the usage ratio of the 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, and can produce significant fluorescence changes in the presence of low concentrations of thiophanate-methyl, thereby ensuring high sensitivity and high 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 easily 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 thiophanate-methyl in environmental samples and foods, and can be applied to multiple fields such as environmental monitoring, agricultural product quality control and food safety. It is of great significance to the protection of the 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 spectra of carbon dot solutions under 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] Fig. 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] 0.01g of nitropyrene was added to 10mL of 0.1M NaOH solution and ultrasonicated for 60min to fully dissolve it. The mixed solution was transferred to a 50mL stainless steel autoclave and heated at 200℃ and 10MPa for 12h. After the reaction, the crude carbon dot product was centrifuged at 9000rpm for 15min. The supernatant obtained was filtered with a filter membrane with a pore size of 0.22μM, and then dialyzed with a dialysis bag with a molecular cutoff of 1000Da to remove impurities. The dialysis time was 48h to obtain carbon dots. 10mg of carbon dots was dispersed in 10ml of water to obtain a 1mg / ml carbon dot aqueous solution, which was stored at 2-8℃ 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 have abundant 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 the excitation wavelength dependence spectrum of the carbon dots prepared in Example 1. It can be seen from the figure that 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. The specific steps are as follows: 8.5 g of sodium chloride, 2.2 g of disodium hydrogen phosphate and 0.4 g of sodium dihydrogen phosphate are mixed with 1000 mL of ultrapure water, ultrasonically dissolved, and dispensed into 11 centrifuge tubes, and the pH is adjusted to 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, and 8 respectively with 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 of different pH values ​​(pH=3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8), and its fluorescence spectrum and UV absorption spectrum were tested.

[0042] Figure 5 The fluorescence intensity change and ultraviolet absorption change of the carbon dots prepared in Example 1 in PBS buffer solutions of 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, and the ultraviolet absorption hardly changes, indicating that the carbon dots may be protonated / deprotonated under different pH conditions, resulting in changes in their fluorescence intensity. The absorption spectrum remains basically unchanged, indicating that the core skeleton of the carbon dots remains stable under different pH conditions.

[0043] Example 3 Salt tolerance test of carbon dots

[0044] 0.2338 g of sodium chloride was mixed with 2 mL of ultrapure water and fully dissolved by ultrasound. 20 μL of the carbon dot aqueous solution obtained in Example 1 was dispersed in 2 mL of ultrapure water, and 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 μL of 2 mol / L sodium chloride solution were added dropwise in sequence to test the fluorescence intensity of the mixed solution.

[0045] Figure 6The fluorescence spectra of the carbon dots prepared in Example 1 in sodium chloride solutions of different concentrations and their linear relationships are shown in the figure. As can be seen from the figure, the carbon dots are stable in the electrolyte environment and are not significantly affected by changes in ion concentration in the solution. The fluorescence of the carbon dots shows strong chemical stability, indicating that its 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 tested 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 within 7 days are shown in the figure. As can be seen from the figure, the fluorescence intensity of the carbon dots is basically not affected 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 1 mmol / L thiophanate-methyl aqueous solution were added dropwise in sequence to test the ultraviolet absorption spectrum and fluorescence spectrum of the mixed solution.

[0051] Figure 8 The following are 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 carbon dots through hydrogen bonding and π-π stacking, and then reduces the fluorescence of carbon dots through static quenching. As the concentration of thiophanate-methyl increases, the fluorescence intensity and ultraviolet absorption of carbon dots gradually weaken, and there is a good linear relationship between the two, indicating that the carbon dots can achieve qualitative and semi-quantitative detection of thiophanate-methyl.

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

[0053] Take 20 μL of the carbon dot aqueous solution obtained in Example 1 and disperse it in 2 mL of ultrapure water, and add 50 μL of 1 mmol / L DDT, BHC, permethrin, imidacloprid, avermectin, cyhalothrin, fipronil, mancozeb, carbendazim, thiophanate-methyl, difenoconazole, atrazine, glyphosate, diquat, and acetochlor, respectively, to test the change in the fluorescence intensity of the solution. Then add 50 μL of 1 mmol / L thiophanate-methyl to the above solution, and test the fluorescence intensity of the mixed system.

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

Claims

1. A method for preparing carbon dots for detecting thiophanate-methyl, characterized in that: The following steps are involved: S11. mixing nitropyrene with a NaOH solution, and subjecting it to ultrasonic treatment to fully dissolve it, thereby obtaining a pyrene-NaOH solution; S12. Adding the pyrene-NaOH solution into the high-pressure reactor, after the reaction is completed, centrifuging, filtering and dialyzing to obtain the carbon dots.

2. The method for preparing carbon dots for detecting thiophanate-methyl 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 method for preparing carbon dots for detecting thiophanate-methyl according to claim 1, characterized in that: In step S11, the ultrasonic treatment time is 30 to 90 minutes.

4. The method for preparing carbon dots for detecting thiophanate-methyl according to claim 1, characterized in that: 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.

5. The method for preparing carbon dots for detecting thiophanate-methyl according to claim 1, characterized in that: The process conditions of centrifugation are: rotation speed of 5000-12000 rpm and time of 10-30 min.

6. According to the method for preparing carbon dots for detecting thiophanate-methyl according to claim 1, 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.

7. Use of the carbon dots prepared by the method according to any one of claims 1 to 6 in the detection of thiophanate-methyl.

8. The use according to claim 7, characterized in that: The following steps are involved: S1. preparing carbon dots according to the method according to any one of claims 1 to 6; S2. dispersing the carbon dots obtained in step S1 in water, adding a certain preset concentration of thiophanate methyl, and then detecting the fluorescence intensity of the system to obtain the corresponding relationship between the fluorescence intensity of the carbon dot system and the concentration of thiophanate methyl; S3. Disperse the carbon dots obtained in step S1 in water, drop the sample to be tested, detect the fluorescence intensity of the system, and achieve qualitative and semi-quantitative detection of methyl thiophanate based on the corresponding relationship between the fluorescence intensity of the carbon dot system obtained in step S2 and the concentration of methyl thiophanate.

9. The use according to claim 8, characterized in that: In step S2, when the carbon dots are dispersed in water, the usage ratio of the carbon dots to water is (1-50): (1-3) μg / ml.

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

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