Rapid detection method for thiamethoxam residue content

Abstract

The application discloses a kind of for the fast detection method of thiamethoxam residual content, this method respectively prepares nano silver particle, nano silver surface molecular imprinting polymer and fluorescence response signal cadmium telluride quantum dot, thiamethoxam standard solution is placed in black centrifuge tube with the nano silver surface molecular imprinting polymer diluted by MES buffer solution, add fluorescence response signal cadmium telluride quantum dot diluted by MES buffer solution;The relationship between the change value of quantum dot fluorescence intensity and thiamethoxam concentration is used to establish standard curve, and the residual content of thiamethoxam is calculated according to standard curve.This method can specifically identify and adsorb thiamethoxam molecules from sample solution, thiamethoxam molecules and nano silver particles interact by electrostatic and hydrogen bond, cause nano silver particles to gather, weaken the internal filter effect between quantum dot and nano silver particles, improve quantum dot fluorescence intensity;This method is simple and fast, high sensitivity, good selectivity, realizes the quantitative detection of thiamethoxam residual content.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical hazard detection, and particularly relates to a rapid detection method for thiamethoxam residue content. BACKGROUND

[0002] Thiamethoxam is a second-generation neonicotinoid insecticide, which not only has stomach toxicity, contact killing and systemic activity on pests, but also has the characteristics of high activity, good safety, wide insecticidal range, rapid effect and long action time, and can replace most high-toxicity pesticides such as organophosphorus and organochlorine. However, long-term exposure to thiamethoxam pesticides can cause irreversible harm to the human body, and the damage to the nervous system is the most significant. In addition, the damage of thiamethoxam to the ecosystem and the accumulation in pollination media such as bees have also attracted widespread attention. Therefore, corresponding laws and regulations have been introduced in China to limit the residue of such pesticides in food such as agricultural products and aquatic products, in order to ensure food safety.

[0003] Gas chromatography, high performance liquid chromatography and gas / liquid chromatography-mass spectrometry (GC / LC-MS) are currently commonly used standard methods for pesticide residue detection. However, these methods are complex, time-consuming and expensive, and cannot meet the demand for on-site rapid detection of pesticide residues.

[0004] The electrostatic and hydrogen bond interactions between silver nanoparticles and thiamethoxam cause the aggregation of silver nanoparticles, thereby weakening the inner filter effect between quantum dots and silver nanoparticles, improving the fluorescence intensity of quantum dots, and realizing the quantitative detection of thiamethoxam residue content. However, this method has poor selectivity for thiamethoxam and cannot realize specific detection of thiamethoxam in samples.

[0005] Therefore, it is urgent to develop a rapid, accurate and sensitive method for rapid detection of thiamethoxam residue content. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a rapid detection method for thiamethoxam residue content, which overcomes the defects of traditional on-site rapid detection of pesticide residues, can specifically identify and adsorb thiamethoxam molecules from sample solution, has the characteristics of simple and fast operation, high sensitivity and good selectivity, and realizes quantitative detection of thiamethoxam residue content.

[0007] To solve the above technical problems, the rapid detection method for thiamethoxam residue content of the present application comprises the following steps:

[0008] Step one, preparation of silver nanoparticles: 17 mg of silver nitrate was dissolved in 100 mL of water and heated to boiling; under constant stirring speed, 1 mL of 0.039 mol / L sodium citrate aqueous solution was quickly added, and the stirring and heating was continued for 30 min until the solution turned yellow-green; the solution was cooled to room temperature and stored at 4°C for standby;

[0009] Step two, preparation of silver nanoparticles surface molecularly imprinted polymer: 15 mg of thiamethoxam and 16.2 μL of methacrylic acid were dispersed in 20 mL of acetonitrile, and stirring was continued for 12 h; then 10 mL of silver nanoparticles, 99.11 μL of EGDMA crosslinking agent and 73.96 μL of AIBN initiator were added, and after mixing, ultrasonic dispersion was carried out for 30 min, and the reaction was continuously stirred at 60°C oil bath for 24 h;

[0010] Step three, the prepared silver nanoparticles surface molecularly imprinted polymer was washed with ethanol and acetonitrile until no absorbance of the template molecule was detected under ultraviolet-visible light, and the silver nanoparticles surface molecularly imprinted polymer after washing the template molecule was dried in a 60°C oven for 24 h, and after cooling, it was stored at room temperature for standby;

[0011] Step four, preparation of fluorescence response signal cadmium telluride quantum dots: 46 mg of cadmium chloride, 83.2 μL of mercaptoacetic acid and 34 mg of zinc chloride were sequentially dissolved in 38 mL of ultrapure water, and 0.6 mL of 0.5M NaOH solution was used to adjust the pH value to 7.9-8.0, and then nitrogen was passed for 20 min to obtain a first solution; 11 mg of sodium tellurite was dissolved in 1 mL of water to obtain a second solution; 5 mg of sodium borohydride was dissolved in 1 mL of water to obtain a third solution; in the process of stirring, the second solution and the third solution were sequentially added to the first solution, and after mixing at room temperature, it was transferred to a 50 mL reaction kettle, and reacted in a 200°C oven for 23 min; after the reaction was completed, isopropyl alcohol was used to wash away the unreacted substances, and then the product was dispersed in water and stored at 4°C;

[0012] Step five, detection of thiamethoxam residue content: 400 μL of thiamethoxam standard solution with concentrations of 0 mg / L, 0.01 mg / L, 0.1 mg / L, 1 mg / L and 10 mg / L was placed in a black centrifuge tube with 400 μL of silver nanoparticles surface molecularly imprinted polymer diluted with MES buffer, and reacted at room temperature for 25 min; then 50 μL of fluorescence response signal cadmium telluride quantum dots diluted 200 times with MES buffer was added and continued to react for 1-5 min; the standard curve was established by using the change value of quantum dot fluorescence intensity and the concentration of thiamethoxam, and the residual content of thiamethoxam was calculated according to the standard curve.

[0013] Further, in the step three, the volume ratio of the ethanol and acetonitrile is 9:1.

[0014] Further, in the step five, the MES buffer is 0.004M, pH=5.4 MES buffer.

[0015] Since the method for rapid detection of thiamethoxam residue content in the application adopts the above technical scheme, i.e., the method respectively prepares nano-silver particles, nano-silver surface molecular imprinting polymer and fluorescence response signal cadmium telluride quantum dots, places thiamethoxam standard solution and nano-silver surface molecular imprinting polymer diluted by MES buffer in a black centrifuge tube, and adds fluorescence response signal cadmium telluride quantum dots diluted by MES buffer; the standard curve is established by using the relationship between the change value of quantum dot fluorescence intensity and the concentration of thiamethoxam, and the residual content of thiamethoxam is calculated according to the standard curve. The method can specifically identify and adsorb thiamethoxam molecules from the sample solution, the adsorbed thiamethoxam molecules interact with nano-silver particles through electrostatic and hydrogen bonds, resulting in aggregation of the nano-silver particles, thereby weakening the inner filter effect between quantum dots and nano-silver particles and improving the fluorescence intensity of the quantum dots. The method has the characteristics of simple and quick operation, high sensitivity and good selectivity, and realizes quantitative detection of the residual content of thiamethoxam. BRIEF DESCRIPTION OF DRAWINGS

[0016] The application will be further described in detail below in combination with the drawings and embodiments:

[0017] Figure 1 The figure shows the change of fluorescence intensity after adding different concentrations of thiamethoxam in the method. DETAILED DESCRIPTION

[0018] The method for rapid detection of thiamethoxam residue content in the application comprises the following steps:

[0019] Step one, preparation of nano-silver particles:

[0020] 17 mg of silver nitrate was weighed and dissolved in 100 mL of water, and heated to boiling; under a constant stirring speed, 1 mL of 0.039 mol / L sodium citrate aqueous solution was quickly added, and the stirring and heating were continued for 30 min until the solution turned yellow-green; the solution was cooled to room temperature and stored at 4℃ for standby;

[0021] Step two, preparation of nano-silver surface molecular imprinting polymer:

[0022] The 15 mg thiamethoxam and 16.2 μL methacrylic acid were dispersed in 20 mL acetonitrile, and stirred for 12 h; then the silver nanoparticles prepared in step 1 (10 mL), crosslinking agent EGDMA (99.11 μL) and initiator AIBN (73.96 μL) were added into the above solution, and after mixing, ultrasonic dispersion was performed for 30 min, and the reaction was continuously stirred at 60°C for 24 h;

[0023] Step three, the prepared polymer was washed with ethanol and acetonitrile (9:1, v / v) until no absorbance of the template molecule was detected under ultraviolet-visible light; the nanosilver surface molecularly imprinted polymer after washing the template molecule was dried in a 60°C oven for 24 h, and after cooling, it was stored at room temperature for standby;

[0024] Step four, preparation of fluorescence response signal cadmium telluride quantum dots:

[0025] The 46 mg cadmium chloride, 83.2 μL mercaptoacetic acid and 34 mg zinc chloride were sequentially dissolved in 38 mL ultrapure water, and 0.6 mL, 0.5M NaOH solution was used to adjust the pH value to 7.9-8.0, and then nitrogen was passed for 20 min to obtain a first solution; 11 mg sodium tellurite was weighed and dissolved in 1 mL water to obtain a second solution; 5 mg sodium borohydride was weighed and dissolved in 1 mL water to obtain a third solution; during stirring, the second solution and the third solution were sequentially added to the first solution, and after mixing at room temperature, it was transferred to a 50 mL reaction kettle, and reacted in a 200°C oven for 23 min; after the reaction was completed, isopropyl alcohol was used for multiple washing to remove unreacted substances, and then the product was dispersed in water and stored in a 4°C refrigerator.

[0026] Step five, detection of thiamethoxam residue content:

[0027] 400 μL (0, 0.01, 0.1, 1, 10 mg / L) thiamethoxam standard solution and 400 μL nanosilver surface molecularly imprinted polymer diluted with MES buffer (0.004M, pH=5.4) were placed in a black centrifuge tube, and reacted at room temperature for 25 min; 50 μL of fluorescence response signal cadmium telluride quantum dots diluted 200 times with MES buffer (0.004M, pH=5.4) were added to the above solution and continued to react for 1-5 min; the standard curve was established by using the change value of quantum dot fluorescence intensity and the concentration of thiamethoxam, and the residual content of thiamethoxam was calculated according to the standard curve.

[0028] As Figure 1The fluorescence intensity corresponding to 0, 0.01, 0.1, 1, 10 mg / L thiamethoxam standard solution is shown. The nano-silver surface molecular imprinting polymer selectively recognizes thiamethoxam molecules from the sample solution. The electrostatic and hydrogen bond interaction between the nano-silver particles wrapped inside the imprinting polymer and thiamethoxam makes the nano-silver particles aggregate, thereby weakening the inner filter effect between the quantum dots and the nano-silver particles, improving the fluorescence intensity of the quantum dots, and realizing the quantitative detection of thiamethoxam.

[0029] The nano-silver surface molecular imprinting polymer in the method has the advantages of structural predetermination, specific recognition ability, strong environmental tolerance, and easy large-scale preparation, and is an important recognition material. Thus, the method innovatively coats thiamethoxam molecular imprinting polymer on the surface of silver nanoparticles and combines with fluorescent quantum dots to realize specific detection of thiamethoxam. The detection time of the method is 25 min, and the detection sensitivity of thiamethoxam reaches 0.01 mg / L. Thus, the method has great application potential in the rapid detection of thiamethoxam residues. Moreover, by changing the template molecules, the method can be easily extended to the development of other neonicotinoid pesticide rapid detection methods.

Claims

1. A method for rapid detection of thiamethoxam residues, characterized in that The method comprises the following steps: Step one, preparation of nano-silver particles: 17 mg of silver nitrate is dissolved in 100 mL of water and heated to boiling; under constant stirring speed, 1 mL of 0.039 mol / L sodium citrate aqueous solution is quickly added, and stirring and heating are continued for 30 min until the solution turns yellow-green; the solution is cooled to room temperature and stored at 4°C for standby; Step two, preparation of nano-silver surface molecularly imprinted polymer: 15 mg of thiamethoxam and 16.2 μL of methacrylic acid are dispersed in 20 mL of acetonitrile, and stirring is continued for 12 h; then 10 mL of nano-silver particles, 99.11 μL of EGDMA crosslinking agent and 73.96 μL of AIBN initiator are added, ultrasonic dispersion is carried out for 30 min, and continuous stirring reaction is carried out in a 60°C oil bath for 24 h; Step three, the prepared nano-silver surface molecularly imprinted polymer is washed with ethanol and acetonitrile until no light absorption value of the template molecule is detected under ultraviolet-visible light, the nano-silver surface molecularly imprinted polymer after washing the template molecule is dried in a 60°C oven for 24 h, and after cooling, it is stored at room temperature for standby; Step four, preparation of fluorescence response signal cadmium telluride quantum dots: 46 mg of cadmium chloride, 83.2 μL of mercaptoacetic acid and 34 mg of zinc chloride are sequentially dissolved in 38 mL of ultrapure water, and 0.6 mL of 0.5M NaOH solution is used to adjust the pH value to 7.9-8.0, then nitrogen is passed for 20 min to obtain a first solution; 11 mg of sodium tellurite is dissolved in 1 mL of water to obtain a second solution; 5 mg of sodium borohydride is dissolved in 1 mL of water to obtain a third solution; in the process of stirring, the second solution and the third solution are sequentially added to the first solution, and after uniform mixing at room temperature, it is transferred to a 50 mL reaction kettle, and reacted in a 200°C oven for 23 min; After the reaction is completed, isopropyl alcohol is used for multiple washing to remove unreacted substances, then the product is dispersed in water and stored at 4°C; Step five, detection of thiamethoxam residue content: 400 μL of thiamethoxam standard solution with concentrations of 0 mg / L, 0.01 mg / L, 0.1 mg / L, 1 mg / L and 10 mg / L is placed in a black centrifuge tube with 400 μL of nano-silver surface molecularly imprinted polymer diluted with MES buffer, and reacts at room temperature for 25 min; then 50 μL of fluorescence response signal cadmium telluride quantum dots diluted 200 times with MES buffer is added and continues to react for 1-5 min; a standard curve is established by using the change value of quantum dot fluorescence intensity and the concentration of thiamethoxam, and the residual content of thiamethoxam is calculated according to the standard curve.

2. The method for rapid detection of thiamethoxam residue according to claim 1, characterized in that: In step three, the volume ratio of ethanol and acetonitrile is 9:

1.

3. The method for rapid detection of thiamethoxam residue according to claim 1, characterized in that: In step five, the MES buffer is 0.004M, pH=5.4 MES buffer.

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