Magnetic nanoelectrochemical sensor and preparation method and application thereof

Abstract

The application relates to a diacylpyrimidinamine detection technical field, in particular to a magnetic nano electrochemical sensor and a preparation method and application thereof. The Ag@PDA@Fe3O4 nano magnetic material is prepared by the following method: adding ammonia water into AgNO3 drop by drop until the solution is clear to prepare an ammonia silver solution; then, PDA@Fe3O4 dispersion liquid is added, and ultrasonic stirring is carried out for 4-6 minutes; then, L-ascorbic acid is added, and ultrasonic oscillation is carried out for 20-30 minutes; after oscillation, the solution is separated by a magnet, the liquid is discarded, the solid is reserved, and the solid is washed by water and ethanol respectively to obtain the Ag@PDA@Fe3O4 nano magnetic material. An active electrode Ag@PDA@Fe3O4 / MGCE and a diacylpyrimidinamine pesticide detection method are also provided. Advantages are that the active electrode has stability, reproducibility and specificity, and can be reused; the diacylpyrimidinamine detection time is short, the sensitivity is high, and the specificity is good.

Description

Technical Field

[0001] This invention relates to the field of acetamiprid detection technology, and in particular to a magnetic nanoelectrochemical sensor, its preparation method, and its application. Background Technology

[0002] Acetamiprid (AAP) is a neonicotinoid insecticide with broad-spectrum inhibitory effects on insect neurotransmission and is widely used in agricultural production. However, excessive use of acetamiprid can lead to pesticide residues. The national standard (GB 2763-2021) stipulates a maximum residue limit of 1 mg / kg. Accumulation of acetamiprid can contaminate soil, water, and food, endangering human health. Currently, commonly used methods for detecting acetamiprid residues include enzyme-linked immunosorbent assay (ELISA), high-performance liquid chromatography (HPLC), liquid / gas chromatography-mass spectrometry (LC / GC-MS), fluorescence methods, and colorimetric methods. While these methods are effective, they also have several drawbacks, such as complex sample pretreatment, expensive instruments, and difficulties or time-consuming real-time monitoring, which hinder rapid on-site detection and large-scale sample screening.

[0003] Electrochemical sensors, characterized by high speed, high sensitivity, simple operation, and low cost, have attracted widespread attention in the food detection field. Furthermore, the use of magnetic nanomaterials and magnetic electrodes enhances the reusability and stability of these sensors. In electrochemical sensors, the functional properties of the electrodes are altered through modification, thereby enabling rapid and convenient qualitative and quantitative analysis of target analytes. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a magnetic nanoelectrochemical sensor, its preparation method, and its applications.

[0005] The primary objective of this invention is to provide an Ag@PDA@Fe3O4 nanomagnetic material, prepared by the following method: Ammonia water is added dropwise to AgNO3 until clear, to prepare an ammonia-silver solution; then, a PDA@Fe3O4 dispersion is added and ultrasonically stirred for 4-6 minutes; L-ascorbic acid is then added and ultrasonically vibrated for 20-30 minutes; after vibration, the mixture is separated using a magnet, the liquid is discarded, and the solid is retained. The solid is washed with water and ethanol respectively to obtain the Ag@PDA@Fe3O4 nanomagnetic material.

[0006] Preferably, the concentration of the ammoniacal silver solution is 0.1 mol / L; and the concentration of the L-ascorbic acid is 1 mmol / L.

[0007] Preferably, the PDA@Fe3O4 dispersion is obtained by dispersing the PDA@Fe3O4 nanocomposite in an aqueous phase, and the preparation method of the PDA@Fe3O4 nanocomposite includes the following steps: S1. Preparation of Fe3O4MNPs dispersion; S2. Preparation of PDA@Fe3O4 nanocomposite: S201. Add C2H5OH and Tris-HCl buffer solution, sonicate for 4-6 min, then add Fe3O4MNPs dispersion, sonicate for 4-10 min to ensure uniform dispersion of Fe3O4MNPs in the solution. S202. Weigh dopamine, add water to dissolve it completely, add it to the mixed solution in step S201, stir for 7-9 hours, separate with a magnet, discard the liquid and keep the solid; S2O3 and solid were washed with water and ethanol respectively to obtain PDA@Fe3O4 nanocomposite.

[0008] Preferably, the volume ratio of C2H5OH, Tris-HCl buffer, and Fe3O4MNPs dispersion is 5:3:1.

[0009] Preferably, the Fe3O4MNPs dispersion in step S1 is prepared by the following method: S101. Weigh FeCl3 and C6H5Na3O7, dissolve and disperse them in (CH2OH)2; S102. Add CH3COONa to the dispersion solution while stirring, and continue stirring for 25-35 minutes; after stirring, react at 180-220°C for 9-11 hours. S103. After the reaction is complete, cool to room temperature; finally wash with water and ethanol respectively, and dilute with 30% ethanol.

[0010] Preferably, in step S102, the reaction is carried out at 200°C for 10 hours.

[0011] Preferably, in step S1, FeCl3 108g, C6H5Na3O7 0.40g, CH3COONa 2.40g, and (CH2OH)2 40mL are used.

[0012] The second objective of this invention is to provide an active electrode Ag@PDA@Fe3O4 / MGCE, prepared using Ag@PDA@Fe3O4 nanomagnetic material and a magnetic glassy carbon electrode, specifically comprising: Ag@PDA@Fe3O4 was dispersed to form a dispersion, which was then dropped onto the surface of a magnetic glassy carbon electrode MGCE and dried. Cyclic voltammetry was performed in NaOH solution using an electrochemical workstation. After stabilization and drying, the active electrode Ag@PDA@Fe3O4 / MGCE was obtained.

[0013] The third objective of this invention is to provide a method for detecting acetamiprid pesticide, specifically including: Take the sample to be tested, pretreat it, and prepare the test solution; add NaOH solution and hydrolyze it for 15-25 minutes under pH=13~14 conditions; A three-electrode system was prepared by using the active electrode Ag@PDA@Fe3O4 / MGCE, platinum wire, and Ag / AgCl electrode as the working electrode, counting electrode, and reference electrode, respectively. Hydrolysis signals of acetamiprid and oxidation signals of nano-silver were collected to determine and analyze the concentration of acetamiprid pesticide in the test samples.

[0014] Preferably, the pH is 14 and the hydrolysis time is 20 minutes; the measurement voltage range is 0.1 to 1.1 V.

[0015] Compared with the prior art, the present invention can achieve the following beneficial effects: (1) This invention develops a magnetic electrochemical sensor (MEC) based on Ag@PDA@Fe3O4 nanocomposite material to detect acetamiprid pesticide. It requires no complex instruments or processing, and is simple to operate, requiring only an electrochemical workstation and low-cost magnetic electrodes to complete sample detection. The detection process takes only 30 minutes (including sample pretreatment), providing a highly effective method for sensitive and rapid detection of acetamiprid. This overcomes the drawbacks of high cost, time-consuming operation, and the need for specialized personnel.

[0016] (2) Achieving high repeatability and reusability of the detection. The detection results did not change significantly after multiple tests. The detection results also did not change significantly after being left for several days. Furthermore, by utilizing the properties of the material, a dual-signal strategy was constructed to reduce background interference.

[0017] (3) By modifying the working electrode in the already mature electrochemical detection technology, the sensitivity of the sensor can be further improved. MEC has stability, reproducibility and specificity, and can adapt to special situations in real life, laying the foundation for the application of MEC in real life. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of (A) the preparation process of Ag@PDA@Fe3O4 nanomagnetic materials and (B) the detection principle of acetamiprid provided in the embodiments of the present invention.

[0019] Figure 2The following are the UV-Vis spectra, particle size, and zeta potential variation diagrams of PDA@Fe3O4 provided according to embodiments of the present invention: (A) UV-Vis spectra of PDA@Fe3O4 prepared at different stirring times; (B) UV-Vis spectra of PDA and PDA@Fe3O4 prepared at different stirring times; (C) Particle size of PDA@Fe3O4 prepared at different stirring times; and (D) zeta potential variation diagrams.

[0020] Figure 3 The images provided in this invention are (A) scanning electron microscope images of PDA@Fe3O4 and (B) Ag@PDA@Fe3O4; (C) elemental spectra of iron, nitrogen and silver on the Ag@PDA@Fe3O4 magnetic nanomaterial; and (D) elemental energy spectrum of Ag@PDA@Fe3O4.

[0021] Figure 4 According to embodiments of the present invention, (A) the effect of Ag@PDA@Fe3O4 / MGCE placement time on the detection of AAP signal, (B) the reproducibility of ten measurements of acetamiprid signal detection, (C) the structural formulas of eight pesticides, and (D) the specificity results of MEC detection of AAP.

[0022] Figure 5 The results are as follows: (A) Comparison of AAP detection results in cowpea samples by MEC method and HPLC-MS method; (B) Correlation between MEC method and HPLC-MS method for detecting AAP in cowpea samples.

[0023] Figure 6 The values ​​are electrochemical signals collected under different hydrolysis conditions of acetamiprid according to embodiments of the present invention; (A) different pH; (B) different time.

[0024] Figure 7 The (A) solution of acetamiprid at different concentrations (0.01~2.0 mg / L) provided according to embodiments of the present invention is an example of this invention. -1 (a) DPV curves of acetamiprid solutions of different concentrations and the linear relationship between the electrochemical hydrolysis peak intensity IAAP of acetamiprid; (b) Linear relationship between the electrochemical signal intensity Iag of silver nanoparticle oxidation of acetamiprid solutions of different concentrations; (c) Linear relationship between the electrochemical signal IAAP / Iag of acetamiprid solutions of different concentrations. Detailed Implementation

[0025] In the following description, embodiments of the invention will be described with reference to the accompanying drawings. In the description below, the same modules are denoted by the same reference numerals. Where the same reference numerals are used, their names and functions are also the same. Therefore, their detailed description will not be repeated.

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0027] Example 1 Ag@PDA@Fe3O4 nanomagnetic materials were prepared for use as a magnetic electrochemical sensor (MEC). Figure 1 A illustrates the preparation process; specifically, it includes the following steps: Preparation of S1 and Fe3O4MNPs: S101. Accurately weigh 108g FeCl3 and 0.40g sodium citrate (C6H5Na3O7), dissolve and disperse them in 40.00 mL ethylene glycol (CH2OH)2; S102. Add 2.40 g of sodium acetate (CH3COONa) to the dispersion solution with stirring and continue stirring for 30 minutes. After stirring, transfer to a polytetrafluoroethylene reactor and react at 200°C for 10 h. S103. After the reaction is complete, remove the reactor and allow it to cool naturally to room temperature. Finally, wash the reactor five times with water and ethanol, dilute with 30% ethanol (C2H5OH), and store at 4°C for later use.

[0028] Preparation of S2, PDA@Fe3O4 nanocomposites: S201. Add 25 mL of C2H5OH and 15 mL of Tris-HCl buffer (pH=8.8) to the flask, sonicate for 5 min, then add 5 mL of Fe3O4MNPs, sonicate for 5 min, so that Fe3O4MNPs are evenly dispersed in the solution. S202. Accurately weigh 0.04g of dopamine (PDA, C8H) into a centrifuge tube. 11 NO2), add 22.5 mL of ultrapure water to dissolve it completely, then add it all to the flask, place the flask on an electric stirrer and stir for 8 hours, separate with a magnet, discard the liquid and keep the solid; S203 and solid were washed twice with water and ethanol respectively to obtain PDA@Fe3O4, which was then dispersed in 10 mL of aqueous phase for later use.

[0029] Preparation of S3, Ag@PDA@Fe3O4 nanomagnetic materials: S301. Weigh 0.034 g AgNO3 into a centrifuge tube, add ammonia water dropwise in a fume hood until clear, and prepare a 0.1 mol / L ammonia silver solution; S302, then add 1 mL of PDA@Fe3O4 dispersion (aqueous phase), and sonicate for 5 minutes; then add 1 mL of L-ascorbic acid (1 mmol / L), and sonicate for 25 minutes; S303 was separated using a magnet, the liquid was discarded and the solid was retained. The solid was washed twice with water and ethanol respectively to obtain Ag@PDA@Fe3O4 nanomagnetic materials.

[0030] The prepared Ag@PDA@Fe3O4 nanomagnetic material was dispersed in 1 ml of aqueous phase to prepare Ag@PDA@Fe3O4 dispersion for later use.

[0031] Characterization and physicochemical property analysis: 1. During the preparation of PDA@Fe3O4, 500 μL of PDA@Fe3O4 solution was taken as a sample every hour, washed with water and ethanol, and characterized by UV-Vis spectroscopy. The UV spectrum of PDA exhibits specific UV absorption. Figure 2 In A, as the stirring time increased, the absorption peak of the sample near the wavelength of 440 nm gradually disappeared, and the change was more obvious at 6 h. Figure 2 In section B, the UV-Vis spectrum of PDA@Fe3O4 showed the gradual appearance of an absorption peak near 285 nm, indicating that PDA had been successfully coated onto the surface of the magnetic nanoparticles. With increasing reaction time, the absorption peak near 440 nm gradually disappeared, with a more pronounced change after 6 hours. To further confirm the synthesis of PDA@Fe3O4, the particle size and potential of PDA@Fe3O4 were further investigated. Figure 2 As shown in Figure C, the particle size of PDA@Fe3O4 increases significantly with increasing stirring time. The particle size also increases with increasing stirring time, while the thickness of the PDA film does not reach several hundred nanometers. However, it is speculated that the viscosity of the system continuously increases due to dopamine polymerization, leading to particle agglomeration and resulting in an inflated particle size measurement. According to the particle size measurement data, the average particle size of PDA@Fe3O4 is approximately 1365.9 nm. With increasing reaction time, PDA polymerization occurs, and the system potential becomes negative.

[0032] 2. Characterization analysis of Ag@PDA@Fe3O4: like Figure 3 As shown in Figure A, the Fe3O4 surface is coated with a PDA film. The particle size distribution in the figure ranges from 200 to 280 nm, and the average particle size of the PDA@Fe3O4 particles is approximately 241 nm. Figure 3 Compared to A, Figure 3 Numerous small particles were observed on the surface of PDA@Fe3O4 in sample B, and these particles were unevenly distributed on the surface of PDA@Fe3O4. This indicates that silver nanoparticles have formed on the surface of PDA@Fe3O4. Figure 3Figure C shows the EDS elemental spectrum of Ag@PDA@Fe3O4, indicating that Fe3O4@Au@Pt contains iron, silver, and nitrogen. Furthermore, the contents of iron, silver, and nitrogen in Ag@PDA@Fe3O4 reach 19.5%, 69.5%, and 11.1%, respectively. Figure 3 D). As can be seen from the SEM morphology and EDS energy spectrum, both PDA and AgNPs were successfully modified onto Fe3O4.

[0033] Example 2 The preparation of the active electrode Ag@PDA@Fe3O4 / MGCE specifically includes: Five μL of the Ag@PDA@Fe3O4 dispersion prepared in Example 1 was dropped onto the surface of a magnetic glassy carbon electrode (MGCE) and allowed to dry naturally. After drying, cyclic voltammetry (CV) was performed in NaOH solution using an electrochemical workstation. After stabilization, the electrode was dried again to obtain the active electrode Ag@PDA@Fe3O4 / MGCE, which is ready for use.

[0034] Example 3 A method for detecting acetamiprid pesticide, specifically including the following steps: S4. Take the sample to be tested, dissolve it in an organic solvent, pretreat it, centrifuge it, and collect the supernatant. S5. Take 500 μL of supernatant, add 1 mL of NaOH solution (1 mol / L), and make up to 4 mL with ultrapure water. Hydrolyze for 20 minutes at pH=14. S6. Preparation of a three-electrode system: The active electrode Ag@PDA@Fe3O4 / MGCE, platinum wire, and Ag / AgCl electrode were used as the working electrode, counting electrode, and reference electrode, respectively. S7. Differential pulse voltammetry was used to collect the hydrolysis signal of acetamiprid and the oxidation signal of nano-silver to determine and analyze the concentration of acetamiprid pesticide in the test sample; the voltage range for each detection was 0.1 to 1.1 V.

[0035] Experiments were conducted to determine the stability, reproducibility, and specificity of acetamiprid; results are as follows: Figure 4 As shown.

[0036] like Figure 4 As shown in Figure A, one month later, ΔI of MEC AAP / ΔI Ag The ratio signal remained at 94.5% of the initial response. The results indicate that the designed MEC has good stability.

[0037] In addition, reproducibility is another important parameter of the sensor. The same modified electrode was repeatedly tested 10 times. The results show that the sensor has good reproducibility. Figure 4 B).

[0038] To determine the specificity of MEC and to prevent interference from other pesticides during actual sample testing, further research on MEC specificity is necessary. Chlorpyrifos, imidacloprid, acephate, parathion, furadan, phorate, and chlorpyrifos were used as controls. Figure 4 Figure C shows the structural formula), testing the specificity of this invention for detecting acetamiprid. Figure C shows the pesticides commonly used in fruits and vegetables and their molecular structures. Clearly, other pesticides do not interfere with AAP detection. However, using MEC can detect signals of other pesticides at low concentrations (…). Figure 4 D).

[0039] Example 4 The specific detection process for acetamiprid pesticide in actual cowpea samples is as follows: According to the national standard GB23200.121-2021, the actual sample was pretreated as follows: 10 g of cowpeas were taken, 10 mL of acetonitrile was added, and the mixture was shaken for 1 minute; 4 g of magnesium sulfate, 1 g of sodium chloride, 1 g of trisodium citrate dihydrate and 0.5 g of disodium hydrogen citrate trihydrate were added, and the mixture was mixed for 1 minute; the supernatant was collected after centrifugation. Take 500 μL of supernatant, add 1 mL of NaOH solution (1 mol / L), and bring the volume to 4 mL with ultrapure water. Hydrolyze for 20 minutes. After incubation, collect the electrochemical signal using Ag@PDA@Fe3O4 / MGCE.

[0040] Using the HPLC-MS standard method as a comparison, the content of cowpeas in actual samples was measured and compared with the detection method of this invention (MEC method). The results are as follows: Figure 5 . Figure 5 A shows the comparison results of MEC method and HPLC-MS detection of AAP in cowpea samples. The results show that the difference in detection results is not significant, indicating that the reliability and stability of the method of the present invention can reach those of the traditional method. The MEC quantitative results of acetamiprid in cowpea are in good agreement with the HPLC-MS quantitative results. Figure 5 Figure B shows the correlation between the MEC method and HPLC-MS in the detection of AAP in cowpea samples. The results indicate that the detection performance of the MEC method is close to that of the traditional HPLC-MS method.

[0041] Example 5 The optimization experiments for the detection conditions of acetamiprid pesticide included: 1. Effects of hydrolysis time and reaction pH on detection First, the hydrolysis time and reaction pH were evaluated using MGCE. The pH of the electrolyte was varied (strongly alkaline range, pH from 13 to above 14) using NaOH solution (1 mol / L), with the same hydrolysis time. Differential pulse voltammetry was used to collect signals from the hydrolysis of acetamiprid and the oxidation of nano-silver.

[0042] Then, the electrolyte was prepared using the same method, and different hydrolysis times were controlled (5, 10, 15, 20, and 25 min, respectively). The hydrolysis signal of acetamiprid and the oxidation signal of nano-silver were collected using differential pulse voltammetry.

[0043] During signal acquisition, the voltage range was 0.1–1.1 V. Furthermore, the AAP solution was diluted to different concentrations using ultrapure water, and a linear relationship between concentration and electrochemical signal was obtained under optimal conditions for quantitative analysis.

[0044] During measurement, the electrochemical workstation used differential pulse voltammetry to acquire the hydrolysis signal of acetamiprid and the oxidation signal of nano-silver, employing a three-electrode system (using an active electrode Ag@PDA@Fe3O4 / MGCE, a platinum wire, and an Ag / AgCl electrode as the working electrode, counting electrode, and reference electrode, respectively). The voltage range for each measurement was 0.1–1.1 V.

[0045] The results are as follows Figure 6 As shown, it can be observed that as the pH value of the hydrolysis reaction increases, the rate of increase in the signal value decreases continuously after pH 14. With the extension of the hydrolysis time, the signal value remains almost constant after 20 minutes. Therefore, the optimal pH and hydrolysis time for the hydrolysis reaction are 14 and 20 minutes, respectively.

[0046] 2. Linear relationship between acetamiprid concentration and electrochemical signal intensity Different concentrations of acetamiprid solutions (0.01, 0.05, 0.1, 0.5, 1.0, 2.0 mg / L) were prepared, and the electrochemical signal intensity at different concentrations was measured. The results are as follows: Figure 7 As shown. Figure 7 A represents the DPV curves of acetamiprid solutions at different concentrations (0.01, 0.05, 0.1, 0.5, 1.0, 2.0 mg / L); Figure 7 B is a linear relationship between the electrochemical hydrolysis peak intensity (IAAP) of acetamiprid solutions of different concentrations and acetamiprid. Figure 7 C represents the electrochemical signal intensity of the oxidation of silver nanoparticles with different concentrations of acetamiprid solutions. Ag A linear relationship graph; Figure 7 D represents different concentrations of acetamiprid solutions and electrochemical signals. AAP / I AgThe graph shows the linear relationship between acetamiprid solutions of different concentrations and the electrochemical signal intensity I of silver nanoparticle oxidation. Ag It exhibits a good linear relationship between acetamiprid solutions of different concentrations and the electrochemical signal I. AAP / I Ag It exhibits a good linear relationship.

[0047] The key technical points of this invention are: (1) This invention solves the shortcomings of traditional methods for detecting acetamiprid, such as high cost, time consumption, and the need for professional personnel, and develops a method for detecting acetamiprid pesticide based on a magnetic electrochemical sensor of Ag@PDA@Fe3O4 nanocomposite material. In this case, no professional personnel are required; only an electrochemical workstation and a low-cost magnetic electrode are needed to complete the sample detection, and the detection process only takes 30 minutes (including sample pretreatment).

[0048] (2) A novel magnetic nanomaterial, Ag@PDA@Fe3O4, was developed, achieving high repeatability and reusability in detection. The detection results did not change significantly after multiple tests. Even after being stored for several days, the detection results remained largely unchanged. Furthermore, the material's properties were utilized to construct a dual-signal strategy to reduce background interference.

[0049] (3) To verify the accuracy of this method in actual sample detection, HPLC-MS was used for comparative evaluation. The results showed that the MEC quantitative results of acetamiprid in cowpeas were in good agreement with the HPLC-MS quantitative results. This method does not require complex equipment and has good sensitivity and accuracy in actual conditions, providing a simple and effective method for the detection of acetamiprid pesticides.

[0050] (4) To simulate various situations that may occur in practice, experiments were conducted on the stability, reproducibility, and specificity of MEC. Through these experiments, it was found that MEC can adapt to special situations in real life, laying the foundation for the application of MEC in real life.

[0051] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0052] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for detecting acetamiprid pesticide, characterized in that, Specifically, it includes: Take the sample to be tested, pretreat it, and prepare the test solution; Add NaOH solution and hydrolyze for 15-25 minutes at pH 13-14; A three-electrode system was prepared by using the active electrode Ag@PDA@Fe3O4 / MGCE, platinum wire, and Ag / AgCl electrode as the working electrode, counting electrode, and reference electrode, respectively. The active electrode Ag@PDA@Fe3O4 / MGCE was prepared using Ag@PDA@Fe3O4 nanomagnetic material and a magnetic glassy carbon electrode. The preparation method of the active electrode Ag@PDA@Fe3O4 / MGCE specifically includes: dispersing Ag@PDA@Fe3O4 to form a dispersion, dropping it onto the surface of the magnetic glassy carbon electrode MGCE, and drying it; using an electrochemical workstation to perform cyclic voltammetry scanning in NaOH solution, and after stabilization and drying, obtaining the active electrode Ag@PDA@Fe3O4 / MGCE; Ag@PDA@Fe3O4 nanomagnetic materials were prepared by the following method: AgNO3 was added dropwise with ammonia water until clear to prepare an ammonia silver solution; then PDA@Fe3O4 dispersion was added and ultrasonically stirred for 4-6 minutes; L-ascorbic acid was then added and ultrasonically vibrated for 20-30 minutes; after vibration, the solid was separated with a magnet, the liquid was discarded and the solid was retained, and washed with water and ethanol respectively to obtain Ag@PDA@Fe3O4 nanomagnetic materials. Hydrolysis signals of acetamiprid and oxidation signals of nano-silver were collected to determine and analyze the concentration of acetamiprid pesticide in the test samples.

2. The method for detecting acetamiprid pesticide according to claim 1, characterized in that: The concentration of the ammonia silver solution is 0.1 mol / L; the concentration of the L-ascorbic acid is 1 mmol / L.

3. The method for detecting acetamiprid pesticide according to claim 2, characterized in that: The PDA@Fe3O4 dispersion is obtained by dispersing the PDA@Fe3O4 nanocomposite in an aqueous phase. The preparation method of the PDA@Fe3O4 nanocomposite includes the following steps: S1. Preparation of Fe3O4MNPs dispersion; S2. Preparation of PDA@Fe3O4 nanocomposite: S201. Add C2H5OH and Tris-HCl buffer solution, sonicate for 4-6 min, then add Fe3O4MNPs dispersion, sonicate for 4-10 min to ensure uniform dispersion of Fe3O4MNPs in the solution. S202. Weigh dopamine, add water to dissolve it completely, add it to the mixed solution in step S201, stir for 7-9 hours, separate with a magnet, discard the liquid and keep the solid; S2O3 and solid were washed with water and ethanol respectively to obtain PDA@Fe3O4 nanocomposite.

4. The method for detecting acetamiprid pesticide according to claim 3, characterized in that: The volume ratio of C2H5OH, Tris-HCl buffer solution, and Fe3O4MNPs dispersion is 5:3:

1.

5. The method for detecting acetamiprid pesticide according to claim 4, characterized in that: The Fe3O4MNPs dispersion in step S1 is prepared by the following method: S101. Weigh FeCl3 and C6H5Na3O7, dissolve and disperse them in (CH2OH)2; S102. Add CH3COONa to the dispersion solution while stirring, and continue stirring for 25-35 minutes; after stirring, react at 180-220°C for 9-11 hours. S103. After the reaction is complete, cool to room temperature; finally wash with water and ethanol respectively, and dilute with 30% ethanol.

6. The method for detecting acetamiprid pesticide according to claim 5, characterized in that: In step S102, the reaction is carried out at 200°C for 10 hours.

7. The method for detecting acetamiprid pesticide according to claim 6, characterized in that: In step S1, FeCl3 108g, C6H5Na3O7 0.40g, CH3COONa 2.40g, and (CH2OH)2 40mL are used.

8. The method for detecting acetamiprid pesticide according to claim 1, characterized in that: The pH value is 14, and the hydrolysis time is 20 minutes; the measurement voltage range is 0.1 to 1.1 V.

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