Portable AL-AgNPs hydrogel and application thereof in visual detection of carbaryl

Abstract

The invention discloses portable AL-AgNPs hydrogel and application thereof in visual detection of carbaryl, and relates to the technical field of food safety detection. Lignin and AgNO3 serve as raw materials, under the action of acrylic acid and ammonium persulfate, AL-AgNPs hydrogel is prepared and mixed with TMB, H2O2 and an HAC-NaAC buffer solution to react, the AL-AgNPs hydrogel is taken out and then soaked in a carbaryl standard solution to be incubated, the AL-AgNPs hydrogel is taken out after incubation, an image of the taken-out AL-AgNPs hydrogel is shot through a mobile phone, RGB analysis is carried out, a B / G value is obtained, and the value of the B / G value is obtained. And establishing a quantitative relationship between B / G and carbaryl concentration, and calculating to obtain the carbaryl concentration in the to-be-detected object. The lowest detection limit of carbaryl detected by the method is 0.1 mu mol / L, which is lower than the maximum residual limit of carbaryl in vegetables in the national food safety standard.

Description

Technical Field

[0001] This invention relates to the field of food safety testing technology, specifically to a portable AL-AgNPs hydrogel and its application in the visual detection of Sevin. Background Technology

[0002] Carbaryl, a broad-spectrum carbamate insecticide, is widely used for pest and disease control in vegetables, fruits, and other crops. However, excessive carbaryl residues in agricultural products can enter the human body through the food chain, inhibiting cholinesterase activity and causing health risks such as damage to the nervous system. Therefore, establishing a rapid, sensitive, and portable method for detecting carbaryl is of great significance for ensuring food safety.

[0003] Currently, the detection of sevin mainly relies on instrumental analytical methods such as high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS). While these methods offer high detection precision and accuracy, they suffer from drawbacks such as expensive equipment, complex operating procedures, long detection cycles, and the need for specialized technical personnel, making them unsuitable for rapid on-site screening. In contrast, colorimetric sensing technology has become a current research hotspot due to its ease of operation, rapid detection, low cost, and ability to provide visual detection through intuitive color changes.

[0004] Nanozymes have attracted widespread attention in the field of colorimetric sensing due to their advantages such as high catalytic activity, strong stability, and low preparation cost. Among them, AL-AgNPs, as a typical peroxidase-like enzyme, can catalyze the reaction of 3,3',5,5'-tetramethylbenzidine (TMB) with hydrogen peroxide (H2O2) to generate a blue oxidation product (oxTMB), providing a technical basis for the colorimetric detection of pesticide residues. However, existing silver nanozymes suffer from problems such as easy aggregation and catalytic activity degradation due to environmental influences, which limits their practical application. Hydrogels, as a polymer material with a three-dimensional network structure, possess good biocompatibility, porosity, and optical clarity, and can be used to immobilize nanozymes, improving their catalytic stability and reusability. In existing technologies, CuMn bimetallic nanozymes are immobilized using sodium alginate hydrogels, and Au@Pt nanozymes are encapsulated in hyaluronic acid to construct sensing systems. However, these hydrogel materials do not incorporate natural renewable materials and have insufficient compatibility for the detection of carbaryl, making it difficult to balance environmental friendliness and detection performance. In addition, smartphone colorimetry technology, with its portability, widespread availability, and image acquisition and data processing capabilities, provides a convenient means of signal reading for on-site testing.

[0005] Therefore, it is of practical significance to develop a stable, easy-to-operate material based on AL-AgNPs that is suitable for smartphone detection, and to construct a Sevin sensing and detection system to achieve rapid detection of Sevin. Summary of the Invention

[0006] To address the aforementioned limitations of existing technologies, the present invention aims to provide a portable AL-AgNPs hydrogel and its application in the visual detection of carbaryl. This invention utilizes lignin and AgNO3 as raw materials, reacting them with acrylic acid and ammonium persulfate to prepare an AL-AgNPs hydrogel. The AL-AgNPs hydrogel is then mixed with TMB solution, H2O2 solution, and HAC-NaAC buffer solution for reaction. After the reaction, the AL-AgNPs hydrogel is removed and incubated in standard carbaryl solutions of different concentrations. After incubation, the AL-AgNPs hydrogel is removed, and images of the removed AL-AgNPs hydrogel are captured using a mobile phone and analyzed using RGB to obtain the B / G value. A quantitative relationship between B / G and carbaryl concentration is established, and the concentration of carbaryl in the analyte is detected based on this quantitative relationship. The limit of detection for carbaryl using the visual detection method of this invention is 0.1 μmol / L, which is lower than the maximum residue limit for carbaryl in vegetables in the national food safety standards.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides an AL-AgNPs hydrogel prepared by the following method: (1) Dissolve lignin in deionized water, add NaOH solution to adjust pH, add AgNO3 and stir to obtain AL-AgNPs suspension; (2) After mixing acrylic acid and ammonium persulfate, a mixed solution is obtained; AL-AgNPs suspension is added to the mixed solution and stirred to obtain a precursor solution; the precursor solution is placed at room temperature to obtain AL-AgNPs hydrogel.

[0008] Preferably, in step (1), the ratio of lignin to deionized water is (1-3) mg: (0.5-1.5) mL.

[0009] Preferably, in step (1), the concentration of the NaOH solution is 0.004-0.006 mol / L, and the pH is adjusted to 7.5-8.5.

[0010] Preferably, in step (1), the mass ratio of lignin to AgNO3 is 1:(15-25).

[0011] Preferably, in step (2), the mass percentage of acrylic acid in the mixed solution is 98%-99%, and the mass percentage of ammonium persulfate is 1%-2%.

[0012] Preferably, in step (2), the volume ratio of the AL-AgNPs hydrogel suspension to the mixed solution is (1-3):(1-3).

[0013] Preferably, in step (2), the stirring time is 5-10 min.

[0014] Preferably, in step (3), the settling time is 10-20 minutes.

[0015] In a second aspect, the present invention provides the application of the above-described AL-AgNPs hydrogel in the visual detection of Sevin.

[0016] A third aspect of the present invention provides a method for visually detecting seviin, comprising the following steps: (1) The above AL-AgNPs hydrogel, TMB solution, H2O2 solution and HAC-NaAC buffer solution are mixed and reacted. After the reaction, the AL-AgNPs hydrogel is taken out. (2) The AL-AgNPs hydrogel taken out in step (1) was immersed in different concentrations of carbaryl standard solution for incubation. After incubation, the AL-AgNPs hydrogel was taken out, and the image of the AL-AgNPs hydrogel after taking out was taken out with a smartphone. The image was analyzed by RGB to obtain the B / G value, and the quantitative relationship between the B / G value and the carbaryl concentration was established and a standard curve was plotted. (3) Pretreatment of the analyte to obtain sample extract; the content of carbaryl in the sample extract is calculated using the standard curve, and thus the content of carbaryl in the analyte is calculated.

[0017] Preferably, in step (1), the pH of the HAC-NaAC buffer solution is 3-4, the concentration of the TMB solution is 0.05-0.15 mM, and the concentration of the H2O2 solution is 9.5-10.0 M.

[0018] Preferably, in step (1), the volume ratio of AL-AgNPs hydrogel, HAC-NaAC buffer solution, TMB solution, and H2O2 solution is (25-75) μL: (1.5-2.5) mL: (150-250) μL: (150-250) μL.

[0019] Preferably, in step (1), the reaction time is 20-30 min.

[0020] Preferably, in step (2), the incubation time is 4-6 min.

[0021] Preferably, in step (3), the specific pretreatment operation for the test sample is as follows: Anhydrous sodium sulfate was added to the analyte for drying. The dried analyte was then added to ethanol and shaken. CaCO3 and activated carbon were added and the mixture was centrifuged. After centrifugation, the mixture was filtered, evaporated and concentrated to obtain a solid. The solid was then redissolved in PBS buffer to obtain the sample extract.

[0022] Furthermore, the ratio of the analyte, anhydrous sodium sulfate, ethanol, CaCO3, activated carbon, and PBS buffer is 25g:(30-40)g:(15-25)mL:(1.5-2.5)g:(1.5-2.5)g:(1.5-2.5)mL.

[0023] Furthermore, the oscillation time is 1.5-2.5 hours.

[0024] Furthermore, during the centrifugation process, the centrifugation speed is 3500-4500 rpm and the centrifugation time is 20-40 min.

[0025] Furthermore, a 0.45μm microporous filter membrane was used for filtration.

[0026] The beneficial effects of this invention are: This invention utilizes lignin and AgNO3 as raw materials to prepare AL-AgNPs hydrogels through a reaction with acrylic acid and ammonium persulfate. A visual method for detecting carbaryl is then constructed using this AL-AgNPs hydrogel. Specifically, the AL-AgNPs hydrogel, TMB, H2O2, and HAC-NaAC buffer solution are mixed and reacted. After the reaction, the AL-AgNPs hydrogel is removed and incubated in standard carbaryl solutions of different concentrations. After incubation, the AL-AgNPs hydrogel is removed, and images of the removed AL-AgNPs hydrogel are captured using a smartphone and subjected to RGB analysis to obtain the B / G value. A quantitative relationship between the B / G value and the carbaryl concentration is then established, and this quantitative relationship is used to detect the carbaryl concentration in the analyte. The limit of detection for carbaryl using this visual method is 0.1 μmol / L, which is lower than the maximum residue limit for carbaryl in vegetables according to national food safety standards.

[0027] Furthermore, the visual detection method for carbaryl of this invention possesses strong anti-interference capabilities, high sensitivity, and selectivity, making it suitable for detecting carbaryl in various agricultural product samples (such as cabbage, carrots, and corn). Sample pretreatment is simple and rapid, with an actual sample detection recovery rate of 91.84%-98.25% and a relative standard deviation (RSD) ≤ 7.01%. The detection results show no significant difference from those obtained by ultraviolet spectrophotometry, demonstrating broad prospects for practical application. Attached Figure Description

[0028] Figure 1a) Michael-Lis-Menten curves of TMB oxidation by AL-AgNPs in the presence of H2O2 at different concentrations; b) Lineweaver-Burk plots corresponding to the data in a; c) Michael-Lis-Menten curves of TMB oxidation by AL-AgNPs in the presence of H2O2 at different concentrations; d) Lineweaver-Burk plots corresponding to the data in c. Figure 2 SEM images of the AL-AgNPs hydrogel prepared in Example 1 at scale bars of 10 μm and 10 μm; Figure 3 In Experiment 2, the standard curve for the detection of seviin by AL-AgNPs hydrogel; Figure 4 In Experiment 3, the anti-interference results of AL-AgNPs hydrogel detection of carbaryl are shown in the figure. a: No interfering substance; b: Lysine; c: Histidine; d: Glucose; e: K. + CO3 2- f:Br - Na + , g: Ni + NO3 - h: methamidophos, i: methamidophos, j: isoprocarb, k: Fe 3+ SO4 2- 、l:Ca 2+ Cl - . Detailed Implementation

[0029] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0030] In the existing technology, the methods for detecting sevin include high performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS). Although these methods have high detection precision and accuracy, they have drawbacks such as expensive equipment, complex operation procedures, long detection cycles, and the need for professional technicians to operate them, making it difficult to meet the needs of rapid on-site screening.

[0031] Based on this, the present invention provides an AL-AgNPs hydrogel and constructs a method for visual detection of Sevin based on the hydrogel, overcoming the shortcomings of existing Sevin detection methods, such as complex operation, high equipment dependence, poor stability and insufficient environmental friendliness of existing nanoenzyme sensing systems.

[0032] This invention utilizes lignin and AgNO3 as raw materials to prepare AL-AgNPs hydrogels through a reaction in the presence of acrylic acid and ammonium persulfate. The synthesis principle is based on a lignin-silver dynamic dual-catalytic system, which can induce rapid free radical polymerization at room temperature to form a hydrogel. Specifically, the catechol groups in lignin spontaneously reduce silver ions to silver nanoparticles and then oxidize them to semiquinones or quinones. This oxidation product synergistically activates ammonium persulfate (APS) with silver ions, generating sulfate free radicals in situ, thereby efficiently initiating the polymerization of acrylic acid monomers at room temperature. Therefore, by adding the AL-AgNPs nanoparticle suspension to a solution containing acrylic acid and APS, AL-AgNPs hydrogels can be rapidly formed at room temperature without heating.

[0033] This invention utilizes the abundant phenolic hydroxyl groups in lignin molecules to achieve in-situ reduction and stable dispersion of silver nanozymes. Through multiple interactions such as hydrogen bonding and hydrophobicity, it inhibits the aggregation of silver nanoparticles, effectively solving the technical problems of easy aggregation and catalytic activity decay of existing silver nanozymes. At the same time, lignin, as a natural renewable material, is widely available, inexpensive, and biocompatible, significantly improving the environmental friendliness and sustainability of the system, which is in line with the development trend of green sensing technology.

[0034] The AL-AgNPs hydrogel prepared by this invention combines the porosity of hydrogels with the high catalytic activity of silver nanozymes. The three-dimensional network structure of the hydrogel provides ample channels for the diffusion of substrates and targets, and its excellent optical clarity ensures the accuracy of colorimetric detection. The immobilization effect of the hydrogel not only improves the catalytic stability of nanozymes, but also simplifies the operation process of the sensing system, making it easy to carry and store on site.

[0035] This invention presents a method for visually detecting carbaryl based on AL-AgNPs hydrogel. The specific steps are as follows: AL-AgNPs hydrogel, TMB, H2O2, and HAC-NaAC buffer solution are mixed and reacted. After the reaction, the AL-AgNPs hydrogel is removed and incubated in standard carbaryl solutions of different concentrations. After incubation, the AL-AgNPs hydrogel is removed, and images of the removed AL-AgNPs hydrogel are captured using a smartphone and subjected to RGB analysis to obtain the B / G value. A quantitative relationship between the B / G value and the carbaryl concentration is then established, and this quantitative relationship is used to detect the carbaryl concentration in the analyte.

[0036] The detection principle is as follows: AL-AgNPs hydrogel, TMB, H2O2, and HAC-NaAC buffer solution are mixed and reacted. Due to the combination of the porosity of hydrogels and the high catalytic activity of silver nanozymes, AL-AgNPs hydrogel can catalyze the oxidation of colorless TMB by H2O2 to generate blue oxTMB. Then, the AL-AgNPs hydrogel is removed and added to a carbaryl standard solution, at which point the blue oxTMB is reduced back to colorless TMB. Finally, the B / G value is obtained using a mobile phone, and a quantitative relationship between the B / G value and the carbaryl concentration is established, thereby achieving rapid and visual detection of carbaryl.

[0037] The present invention provides a visual detection method for Sevin, which does not rely on large analytical instruments. It can achieve the acquisition and quantitative analysis of detection signals through ordinary smartphones. It is easy to operate, has a short detection cycle (the entire detection time is ≤30min), and low detection cost. It is suitable for rapid on-site screening scenarios such as agricultural product production areas, farmers' markets, and grassroots supervision.

[0038] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0039] The experimental materials used in the embodiments of this invention are all conventional experimental materials in the art and can be purchased through commercial channels.

[0040] Example 1: Preparation of AL-AgNPs hydrogel (1) Dissolve 10 mg of lignin in 10 mL of deionized water, add 0.005 mol / L NaOH solution to adjust the pH to 8.0, then add 200 mg of AgNO3 and stir to obtain AL-AgNPs hydrogel suspension; (2) After mixing acrylic acid and ammonium persulfate, a mixed solution was obtained, wherein the mass percentage of acrylic acid in the mixed solution was 98.82% and the mass percentage of ammonium persulfate was 1.18%. 3 mL of AL-AgNPs hydrogel suspension was added to 2 mL of the mixed solution and magnetically stirred for 8 min to obtain a precursor solution. The precursor solution was transferred to a 96-well plate and allowed to stand at room temperature for 15 min to obtain AL-AgNPs hydrogel.

[0041] The morphology of the AL-AgNPs hydrogel prepared in this embodiment is shown in the figure below. Figure 2 As shown. By Figure 2 As can be seen, the prepared AL-AgNPs hydrogel exhibits a rough porous structure with relatively uniform pore size. This loose and porous structure is a typical characteristic of hydrogels, thus proving the successful synthesis of AL-AgNPs hydrogel.

[0042] Example 2: Preparation of AL-AgNPs hydrogel (1) Dissolve 10 mg of lignin in 5 mL of deionized water, add 0.004 mol / L NaOH solution to adjust the pH to 7.5, then add 150 mg of AgNO3 and stir to obtain an AL-AgNPs suspension; (2) After mixing acrylic acid and ammonium persulfate, a mixed solution was obtained, wherein the mass percentage of acrylic acid in the mixed solution was 98.82% and the mass percentage of ammonium persulfate was 1.18%; 3 mL of AL-AgNPs suspension was added to 3 mL of the mixed solution and magnetically stirred for 5 min to obtain a precursor solution; the precursor solution was transferred to a 96-well plate and allowed to stand at room temperature for 10 min to obtain AL-AgNPs hydrogel.

[0043] Example 3: Preparation of AL-AgNPs hydrogel (1) Dissolve 10 mg of lignin in 15 mL of deionized water, add 0.006 mol / L NaOH solution to adjust the pH to 8.5, then add 250 mg of AgNO3 and stir to obtain AL-AgNPs hydrogel suspension; (2) After mixing acrylic acid and ammonium persulfate, a mixed solution was obtained, wherein the mass percentage of acrylic acid in the mixed solution was 98.82% and the mass percentage of ammonium persulfate was 1.18%; 3 mL of AL-AgNPs hydrogel suspension was added to 1 mL of the mixed solution and magnetically stirred for 10 min to obtain a precursor solution; the precursor solution was transferred to a 96-well plate and allowed to stand at room temperature for 20 min to obtain AL-AgNPs hydrogel.

[0044] Experimental Example 1: Detection of Nanozyme Activity in AL-AgNPs Hydrogels The activity of AL-AgNPs hydrogel was verified by TMB colorimetry to confirm that the AL-AgNPs hydrogel possesses catalase activity. The specific steps are as follows: Add 2 mL of HAC-NaAC buffer solution (pH 3.5), 200 μL of H2O2 solution, and 10 μL of the AL-AgNPs hydrogel suspension prepared in step (1) of Example 1 to 200 μL of TMB solution. At this point, TMB changes from colorless to blue. The absorbance at 652 nm is measured using a UV-Vis spectrophotometer, and the absorbance change curve at 652 nm is plotted. During the detection process, measurements are taken every 30 seconds, with a total reaction time of 120 seconds. The results are as follows: Figure 1 As shown.

[0045] Depend on Figure 1 It can be seen that the Vmax of LA-AgNPs is larger when TMB is used as the substrate, while the Km of LA-AgNPs is smaller when H2O2 is used as the substrate. This proves that LA-AgNPs have a faster catalytic rate and better affinity.

[0046] The AL-AgNPs prepared in this invention are rich in phenol-quinone redox pairs on their outer surface. These groups can continuously transfer electrons to peroxides, and the outer quinone groups further activate silver nanoparticles, enabling them to continuously supply electrons to maintain the redox activity of the phenol-quinone pairs. Simultaneously, AL-AgNPs are the core foundation for constructing a dual-catalytic system, capable of efficiently driving hydrogel self-gelling under conditions without external stimulation. The catechol groups in the lignin molecules can reduce silver ions to silver nanoparticles, while the lignin itself is oxidized by silver ions to semiquinones or quinone groups. The generated semiquinone / quinone groups synergistically activate ammonium persulfate with silver ions, producing sulfate free radicals, which accelerate the free radical polymerization of acrylic monomers without the introduction of external energy, achieving rapid in-situ gelation of the hydrogel.

[0047] Experimental Example 2: Using cabbage as the analyte, the carbaryl content in cabbage was detected using a visual detection method. The specific steps are as follows: (1) Place 50 μL of the AL-AgNPs hydrogel prepared in Example 1 into a 5 mL centrifuge tube, add 2 mL of HAC-NaAC buffer solution with pH 3.5, 200 μL of TMB solution with a concentration of 0.1 mM and 200 μL of H2O2 solution with a concentration of 9.79 M, react for 25 min, and then take out the AL-AgNPs hydrogel. (2) Immerse the AL-AgNPs hydrogel taken in step (1) in carbaryl standard solutions with concentrations of 0.1 μmol / L, 0.5 μmol / L, 1 μmol / L, 10 μmol / L, 50 μmol / L, 100 μmol / L and 200 μmol / L for 5 min. After incubation, remove the AL-AgNPs hydrogel. Take an image of the removed AL-AgNPs hydrogel with a smartphone and convert the image to red-green-blue (RGB) mode. Then use ImageJ software to analyze the image to quantify the intensity of color changes, obtain the B / G value (the intensity ratio of the blue channel to the green channel), establish the quantitative relationship between the B / G value and the carbaryl concentration, and plot a standard curve with the carbaryl standard solution concentration as the x-axis and B / G as the y-axis, as shown in the figure. Figure 3 As shown; (3) Add 35g of anhydrous sodium sulfate to 25g of the sample in three portions, and after drying by absorbing water, transfer it to a 50mL centrifuge tube, add 20mL of ethanol and shake for 2h, then add 2g of CaCO3 and 2g of activated carbon and mix well. Centrifuge the mixture at 4000rpm for 30min, take the supernatant, filter it through a 0.45 μm microporous membrane, and then concentrate it using a rotary evaporator to obtain a solid. Redissolve the solid in 2mL of PBS buffer to obtain the sample extract. Using the sample extract instead of the carbaryl standard solution, repeat steps (1)-(2) to obtain the B / G value; the concentration of carbaryl in the sample extract was calculated to be 9.47 × 10⁻⁶ using the standard curve. -5 The concentration of carbaryl was determined to be mol / L, resulting in a carbaryl content of 1.14 mg / kg in the analyte.

[0048] Experiment 3: Anti-interference test To investigate the specific recognition ability of the AL-AgNPs hydrogel prepared in Example 1 for carbaryl, three structural analogues (tsumacide, methomyl, and isoprocarb) at concentrations equal to carbaryl, along with 10 times the concentration of lysine, histidine, and glucose, and 100 times the concentration of inorganic salts (K+) were selected. + CO3 2- ,Br - Na + Ni + NO3 - Fe 3+ SO4 2- Ca 2+ Cl - Interference tests were conducted on interfering ions such as ions.

[0049] The specific method is as follows: The AL-AgNPs hydrogel prepared in Example 1 was immersed in carbaryl solution, and methimazole, methomyl, and isoprocarb solutions of equal concentration to carbaryl solution, lysine solution, histidine solution, glucose solution and inorganic salt solution of 10 times concentration as interfering substances were added. After incubation for 5 min, the AL-AgNPs hydrogel was taken out. The extracted AL-AgNPs hydrogel was mixed with HAC-NaAC buffer solution (pH 3.5), 0.1 mM TMB solution, and 9.79 M H2O2 solution at a volume ratio of 50 μL: 2 mL: 200 μL: 200 μL and reacted for 25 min to obtain a colorimetric sensing system. Images of this system were acquired using a smartphone and converted to red-green-blue (RGB) mode. ImageJ software was then used to analyze the images to quantify the intensity of color changes and obtain the B / G value. A control group was also set up, which contained no interfering substances. The results are as follows. Figure 4 As shown.

[0050] Depend on Figure 4It can be seen that there is no significant difference in the B / G value between the absence of interfering substances and the presence of interfering substances. This proves that structural analogs such as methomyl, isoprocarb, lysine, histidine, glucose, and inorganic salts do not interfere with the detection of carbaryl by the AL-AgNPs hydrogel. Therefore, the AL-AgNPs hydrogel prepared in this invention exhibits good specificity for carbaryl.

[0051] Experimental Example 4: The AL-AgNPs hydrogel prepared in Example 1 was used for sample addition and recovery experiments. The specific steps are as follows: Weigh 25g of the sample to be tested (corn, carrot), add 35g of anhydrous sodium sulfate to the sample in three portions, grind and absorb and dry, transfer the ground solid into a stoppered conical flask, and select three different concentrations (10, 50, 100µM) from the calibration curve for the addition and recovery experiment of the actual sample.

[0052] Add 10 mL of the corresponding concentration of carbaryl solution to a stoppered conical flask and soak for 30 min. Then add 100 mL of ethanol and soak for 2 h. Filter and collect the filtrate. Add 2 g of CaCO3 and 2 g of activated carbon to the filtrate, mix well and soak for 30 min. Filter coarsely with filter paper. Concentrate the solution using a rotary evaporator to remove organic solvents and obtain a solid. Redissolve the solid with 10 mL of PBS buffer solution and filter through a 0.45 μm microporous membrane to obtain the test sample solution. Then use the method in Experiment Example 2 to detect the concentration of carbaryl in the test sample. Each concentration is measured in triplicate. Calculate the RSD and recovery rate (%). The results are shown in Table 1.

[0053] Table 1 As shown in Table 1, the actual sample detection recovery rate was 91.84%-98.25%, and the relative standard deviation (RSD) was ≤7.01%. This demonstrates that the visual detection method for Sevin of the present invention has good applicability and accuracy, providing reliable technical support for the detection of Sevin in real-world environments.

[0054] Experiment 5: Accuracy Test Chinese cabbage and cabbage were used as the test samples. The content of carbaryl in the test samples was detected by the visual detection method of carbaryl in Experiment 2 and the ultraviolet spectrophotometer, respectively. The results are shown in Table 2.

[0055] Table 2 As can be seen from Table 2, there was no significant difference in the concentration of carbaryl detected by the method of the present invention and by the ultraviolet spectrophotometer (p<0.05, n=3), which verifies the detection accuracy of the visual detection method of carbaryl of the present invention.

[0056] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An AL-AgNPs hydrogel, characterized in that, It is prepared by the following method: (1) Dissolve lignin in deionized water, add NaOH solution to adjust pH, add AgNO3 and stir to obtain AL-AgNPs suspension; (2) After mixing acrylic acid and ammonium persulfate, a mixed solution is obtained; AL-AgNPs suspension is added to the mixed solution and stirred to obtain a precursor solution; The precursor solution was left to stand at room temperature to obtain AL-AgNPs hydrogel.

2. The AL-AgNPs hydrogel as described in claim 1, characterized in that, In step (1), the ratio of lignin to deionized water is (1-3) mg: (0.5-1.5) mL; the concentration of NaOH solution is 0.004-0.006 mol / L, and the pH is adjusted to 7.5-8.5; the mass ratio of lignin to AgNO3 is 1: (15-25).

3. The AL-AgNPs hydrogel as described in claim 1, characterized in that, In step (2), the volume ratio of AL-AgNPs hydrogel suspension to mixed solution is (1-3):(1-3); the stirring time is 5-10 min.

4. The AL-AgNPs hydrogel as described in claim 1, characterized in that, In step (3), the settling time is 10-20 minutes.

5. The application of the AL-AgNPs hydrogel according to any one of claims 1-4 in the visual detection of Sevin.

6. A method for visually detecting sesquitin, characterized in that, Includes the following steps: (1) The AL-AgNPs hydrogel according to any one of claims 1-4, TMB solution, H2O2 solution and HAC-NaAC buffer solution are mixed and reacted, and the AL-AgNPs hydrogel is taken out after the reaction. (2) The AL-AgNPs hydrogel taken out in step (1) was immersed in different concentrations of carbaryl standard solution for incubation. After incubation, the AL-AgNPs hydrogel was taken out, and the image of the AL-AgNPs hydrogel after taking out was taken out with a smartphone. The image was analyzed by RGB to obtain the B / G value, and the quantitative relationship between the B / G value and the carbaryl concentration was established and a standard curve was plotted. (3) Pretreatment of the analyte to obtain sample extract; the content of carbaryl in the sample extract is calculated using the standard curve, and thus the content of carbaryl in the analyte is calculated.

7. The method for visually detecting Sevin as described in claim 6, characterized in that, In step (1), the pH of the HAC-NaAC buffer solution is 3-4, the concentration of the TMB solution is 0.05-0.15 mM, and the concentration of the H2O2 solution is 9.5-10.0 M; the volume ratio of AL-AgNPs hydrogel, HAC-NaAC buffer solution, TMB solution, and H2O2 solution is (25-75) μL : (1.5-2.5) mL : (150-250) μL : (150-250) μL; and the reaction time is 20-30 min.

8. The method for visually detecting Sevin as described in claim 6, characterized in that, In step (2), the incubation time is 4-6 minutes.

9. The method for visually detecting Sevin as described in claim 6, characterized in that, In step (3), the specific pretreatment operations for the test sample are as follows: Anhydrous sodium sulfate was added to the analyte for drying. The dried analyte was then added to ethanol and shaken. CaCO3 and activated carbon were added and the mixture was centrifuged. After centrifugation, the mixture was filtered, evaporated and concentrated to obtain a solid. The solid was then redissolved in PBS buffer to obtain the sample extract.

10. The method for visually detecting Sevin as described in claim 9, characterized in that, The ratio of the analyte, anhydrous sodium sulfate, ethanol, CaCO3, activated carbon, and PBS buffer is 25g:(30-40)g:(15-25)mL:(1.5-2.5)g:(1.5-2.5)g:(1.5-2.5)mL; the shaking time is 1.5-2.5h; during centrifugation, the centrifugation speed is 3500-4500rpm and the centrifugation time is 20-40min.

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