Application of non-enzyme sensor in hypersensitivity detection of organophosphorus pesticide

Abstract

The invention belongs to the technical field of electrochemical sensors, and particularly relates to application of a non-enzyme sensor in hypersensitivity detection of organophosphorus pesticides, and a working electrode of the non-enzyme sensor is a Fe3O4 / graphene oxide / GCE composite electrode. According to the invention, the Fe3O4 / graphene oxide / GCE composite electrode is taken as the electrode of the sensor, the non-enzymatic sensor with wide detection linear range and high sensitivity is obtained, and the technical defect that high-sensitivity detection of organophosphorus pesticide can be carried out only by depending on acetylcholin esterase in the prior art is overcome. The principle of the non-enzymatic sensor is as follows: active groups of pesticide molecules are utilized, and the surface of the working electrode is modified, so that the electrochemical performance is improved, and the electrochemical direct detection is realized; when no pesticide exists, the electrochemical signal is relatively strong, and when the pesticide exists, the macromolecular substance inhibits the current signal, so that the detection is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical sensors and relates to the application of non-enzymatic sensors in the ultrasensitive detection of organophosphorus pesticides. Background Art

[0002] In modern agriculture, pesticides are often used to prevent food damage and increase food production. Organophosphorus pesticides (OPs) are a widely used type of pesticide. The use of pesticides has brought huge economic benefits, but their excessive use has also brought pollution problems and food safety issues.

[0003] Currently, the inherent idea of those skilled in the art for the detection of organophosphorus pesticides is that acetylcholinesterase is required, and a micro-enzymatic reactor is prepared using acetylcholinesterase for detection. However, enzymes are not only expensive but also prone to denaturation and difficult to preserve. The use of enzymes not only increases the detection cost but also has a certain impact on the accuracy of the detection results. Such detection methods can no longer meet the needs of rapid detection of large quantities of agricultural products and on-site rapid detection of food at home and abroad. Therefore, there is an urgent need to develop a simple, enzyme-free, highly sensitive, and low-cost method for rapid detection of organophosphorus pesticides. Summary of the Invention

[0005] In view of the above technical deficiencies, the present invention provides the application of a non-enzymatic sensor in the ultrasensitive detection of organophosphorus pesticides. The present invention uses a Fe3O4 / graphene oxide / GCE composite electrode as the working electrode of the sensor, and obtains a non-enzymatic sensor with a wide detection linear range and high sensitivity, solving the technical defect that the prior art needs to rely on acetylcholinesterase to achieve high-sensitivity detection of organophosphorus pesticides.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The application of a non-enzymatic sensor in the ultrasensitive detection of organophosphorus pesticides, wherein the working electrode of the non-enzymatic sensor is a Fe3O4 / graphene oxide / GCE composite electrode, and the Fe3O4 / graphene oxide / GCE composite electrode is prepared according to the following steps:

[0008] Prepare Fe3O4 nanoparticles;

[0009] Ultrasonically disperse the Fe3O4 nanoparticles in ultrapure water to obtain Solution I; ultrasonically disperse graphene oxide in glacial acetic acid solution to obtain Solution II; mix Solution I and Solution II to obtain a Fe3O4 / GO modification solution;

[0010] Drop the Fe3O4 / GO modification solution onto the polished GCE and dry it to obtain a Fe3O4 / graphene oxide / GCE composite electrode.

[0011] Preferably, the Fe3O4 nanoparticles are prepared according to the following steps:

[0012] Dissolve soluble Fe 3+ salt and soluble Fe 2+ salt in water and mix them. Then, heat and stir the mixture, and add ammonia water dropwise until the pH reaches 9 - 10, and continue stirring for 0.5 - 1 h to obtain the precursor of Fe3O4 particles;

[0013] Among them, the molar ratio of soluble Fe 3+ salt to soluble Fe 2+ salt is 2 - 2.2:1;

[0014] Hydrothermally react the precursor of Fe3O4 particles at 160 - 170 °C for 4 - 5 h, and then wash it with water until it is neutral to obtain Fe3O4 nanoparticles.

[0015] Preferably, the mass ratio of the Fe3O4 nanoparticles to graphene oxide is 1:3 - 7.

[0016] Preferably, the operation of drop - coating is as follows: Drop - coat Fe3O4 / GO on the surface of the polished GCE and then dry it to obtain the Fe3O4 / graphene oxide / GCE composite electrode. Repeat the operations of drop - coating the Fe3O4 / GO modification solution and drying on the surface of the dried Fe3O4 / graphene oxide / GCE composite electrode.

[0017] Preferably, the non - enzymatic sensor consists of a three - electrode system, with the Fe3O4 / graphene oxide / GCE composite electrode as the working electrode, the saturated calomel electrode as the reference electrode, and the platinum wire electrode as the counter electrode.

[0018] Preferably, the specific steps for detecting organophosphorus pesticides are as follows:

[0019] Take the saturated calomel electrode as the reference electrode, the platinum wire electrode as the counter electrode, and together with the Fe3O4 / graphene oxide / GCE composite electrode as the working electrode to form a three - electrode system, connect it to an electrochemical workstation, use PBS solution as the electrolyte, and adopt cyclic voltammetry to draw a working curve according to the current - potential.

[0020] Preferably, the organophosphorus pesticides include methamidophos, phorate, parathion, and dimethoate.

[0021] Preferably, the detection limit of the Fe3O4 / graphene oxide / GCE composite electrode for the concentration of dimethoate is 5.2013×10 -7 g / L, and the linear range is 2.56×10 -7 g / L~8×10 -4 g / L.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1. The present invention uses a Fe3O4 / graphene oxide / GCE composite electrode as the electrode of the sensor, obtaining a non-enzyme sensor with a wide detection linear range and high sensitivity, and solving the technical defect that the prior art needs to rely on acetylcholinesterase to achieve highly sensitive detection of organophosphorus pesticides. The principle of the non-enzyme sensor of the present invention is as follows: By utilizing the active groups carried by pesticide molecules themselves and modifying the electrode surface, the electrochemical performance is improved, thereby realizing direct electrochemical detection. When there is no pesticide, the electrochemical signal is relatively strong, and when there is pesticide, macromolecular substances inhibit the current signal, thus realizing detection.

[0024] 2. The present invention prepares a Fe3O4 / GO / GCE electrochemical sensor, conducts electrochemical tests on the prepared electrode with the help of an electrochemical workstation, and uses it for the detection research of dimethoate. Through cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV), the optimal reaction conditions are determined. The pH of the PBS solution is selected as 5.0, the scanning rate is 0.09 V / s, and the enrichment time is 300 s. After optimization, the response peak current value of dimethoate detected shows a linear relationship with the concentration in the range of 2.56×10 -7 g / L to 8×10 -4 g / L, and the detection limit is 5.2013×10 -7 g / L. Finally, a spike recovery experiment is carried out with tap water. The experimental results show that the recovery rate is between 95.98% and 99.21%, and the recovery rate is relatively high. Based on this, the modified electrode provides a choice for the detection of dimethoate.

[0025] 3. The present invention prepares iron oxide nanoparticles by a hydrothermal method, characterizes Fe3O4 by Fourier transform infrared spectroscopy, and characterizes the Fe3O4 / GO modified material by scanning electron microscopy (SEM) and transmission electron microscopy (TEM); based on the research of non-enzyme electrochemical sensors, a composite material is prepared by combining Fe3O4 nanoparticles with graphene oxide to fabricate a non-enzyme electrochemical sensor. The electrode material is tested by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). The conditions such as the pH of the buffer solution, the scanning rate, and the enrichment time are optimized for the detection of organophosphorus pesticides. Taking the detection of dimethoate residues in tap water as an example, it provides a basis for the detection of organophosphorus pesticides in the future. Description of the Drawings

[0026] Figure 1 It is the infrared spectrum diagram of the Fe3O4 nanoparticles in Example 1;

[0027] Figure 2 In (a) is the SEM diagram of the Fe3O4 nanoparticles in Example 1, and in (b) is the SEM diagram of the Fe3O4 / GO in Example 1;

[0028] Figure 3 In (a) and (b), they are TEM images of Fe3O4 / GO in Example 1 at different magnifications respectively;

[0029] Figure 4 In (a), it is the linear relationship diagram between PBS buffer solutions with different pH values and peak current, and in (b), it is the influence diagram of pH on Fe3O4 / GO / GCE in Example 1;

[0030] Figure 5 In (a), it is the cyclic voltammogram of Fe3O4 / GO / GCE in Example 1 at different scanning rates, and in (b), it is the linear relationship diagram between Fe3O4 / GO / GCE in Example 1 at different scanning rates and peak current;

[0031] Figure 6 It is the linear relationship diagram between different enrichment times and oxidation peak current of Fe3O4 / GO / GCE in Example 1;

[0032] Figure 7 It is the cyclic voltammetry (CV) test diagram of Fe3O4 / GO / GCE in Example 1;

[0033] Figure 8 It is the differential pulse voltammetry (DPV) test diagram of Fe3O4 / GO / GCE in Example 1;

[0034] Figure 9 It is the electrochemical impedance spectroscopy (EIS) test diagram of Fe3O4 / GO / GCE in Example 1;

[0035] Figure 10 In (a), it is the DPV test diagram of Fe3O4 / GO / GCE in Example 1 at different concentrations, and in (b), it is the standard curve diagram. Detailed implementation manners

[0036] The following is a detailed description of the specific implementation manners of the present invention, but it should be understood that the protection scope of the present invention is not limited by the specific implementation manners. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the protection scope of the present invention. The experimental methods described in each embodiment of the present invention are conventional methods unless otherwise specified.

[0037] Example 1

[0038] A preparation method of a Fe3O4 / GO / GCE composite electrode includes the following steps:

[0039] (1) Preparation of Fe3O4 nanoparticles:

[0040] Synthesized by hydrothermal method: Fe 2+ + 2Fe 3+ + 8OH - = Fe3O4 + 4H2O. Measure 50 mL (0.087 mol / L) aqueous solution of FeCl3·6H2O and 50 mL (0.04 mol / L) aqueous solution of FeCl2·4H2O and put them into a 250 mL round-bottom flask, stir and mix evenly, then place it in an oil bath at 60 °C, quickly add concentrated ammonia water dropwise to the mixed solution while stirring, adjust the pH of the solution to within the range of 9, react for 0.5 h to obtain the precursor of Fe3O4 particles; transfer the precursor of Fe3O4 particles to a polytetrafluoroethylene hydrothermal reactor, react at 160 °C for 5 h, then rinse the product with distilled water, use a strong magnet to precipitate it, and then pour off the supernatant above. Repeat this rinsing 4 - 5 times until the pH of the supernatant is 7; remove the precipitate and dry it in a vacuum dryer at 60 °C for 10 h to obtain dry nano-Fe3O4 particles;

[0041] (2) Preparation of Fe3O4 / graphene oxide / GCE composite electrode;

[0042] S1. Disperse 5 mg of the Fe3O4 nanoparticles prepared in step (1) in 5 mL of ultrapure water for 2 h to obtain a 1 mg / mL Fe3O4 solution; dissolve 25 mg of GO in 5 mL of 1% glacial acetic acid solution to obtain a 5 mg / mL GO solution; combine the two solutions in a volume ratio of 1:1 to obtain a Fe3O4 / GO modification solution;

[0043] S2. Take 5 μL of the modification solution and disperse and drop-coat it on the polished GCE, dry it at room temperature to finally obtain a modified electrode, which is denoted as Fe3O4 / GO / GCE.

[0044] Example 2

[0045] Preparation method of Fe3O4 / GO / GCE composite electrode, including the following steps:

[0046] (1) Preparation of Fe3O4 nanoparticles:

[0047] Synthesized by hydrothermal method: Fe 2+ + 2Fe 3+ + 8OH -= Fe3O4 + 4H2O. Measure 50 mL (0.08 mol / L) of FeCl3·6H2O and 50 mL (0.04 mol / L) of FeCl2·4H2O solutions and put them into a 250 mL round-bottom flask. Stir and mix them evenly, then place them in a 60 °C oil bath. Rapidly add concentrated ammonia water to the mixed solution while stirring, adjust the pH of the solution to within the range of 10, and react for 45 min to obtain the precursor of Fe3O4 particles; transfer the precursor of Fe3O4 particles to a polytetrafluoroethylene hydrothermal reactor, react at 165 °C for 4.5 h, then rinse the product with distilled water, use a strong magnet to make it precipitate, and then pour off the supernatant above. Repeat this rinsing 4 - 5 times until the pH of the supernatant is 7; remove the precipitate and dry it in a vacuum dryer at 60 °C for 10 h to obtain dry nano-Fe3O4 particles;

[0048] (2) Preparation of Fe3O4 / graphene oxide / GCE composite electrode;

[0049] S1. Dissolve 5 mg of the Fe3O4 nanoparticles prepared in step (1) in 5 mL of ultrapure water and disperse for 2 h to obtain a 1 mg / mL Fe3O4 solution; dissolve 15 mg of GO in 5 mL of 1% glacial acetic acid solution to obtain a 3 mg / mL GO solution; combine the two solutions in a volume ratio of 1:1 to obtain a Fe3O4 / GO modification solution;

[0050] S2. Take 5 μL of the modification solution and disperse and drop-coat it on the polished GCE, dry it at room temperature, and finally obtain a modified electrode, which is denoted as Fe3O4 / GO / GCE.

[0051] Example 3

[0052] A preparation method of Fe3O4 / GO / GCE composite electrode, comprising the following steps:

[0053] (1) Preparation of Fe3O4 nanoparticles:

[0054] Synthesized by hydrothermal method: Fe 2+ + 2Fe 3+ + 8OH -= Fe3O4 + 4H2O. Measure 50 mL (0.088 mol / L) of FeCl3·6H2O and 50 mL (0.04 mol / L) of FeCl2·4H2O solutions and put them into a 250 mL round-bottom flask. Stir and mix them evenly, then place them in a 60 °C oil bath. Rapidly add concentrated ammonia water to the mixed solution while stirring, adjust the pH of the solution to within the range of 9.5, and react for 1 h to obtain the precursor of Fe3O4 particles; transfer the precursor of Fe3O4 particles to a polytetrafluoroethylene hydrothermal reactor, react at 170 °C for 4 h, then rinse the product with distilled water, use a strong magnet to precipitate it, and then pour off the supernatant above. Repeat this rinsing 4 - 5 times until the pH of the supernatant is 7; remove the precipitate and dry it in a vacuum dryer at 60 °C for 10 h to obtain dry nano-Fe3O4 particles;

[0055] (2) Preparation of Fe3O4 / graphene oxide / GCE composite electrode;

[0056] S1. Disperse 5 mg of the Fe3O4 nanoparticles prepared in step (1) in 5 mL of ultrapure water for 2 h to obtain a 1 mg / mL Fe3O4 solution; dissolve 35 mg of GO in 5 mL of 1% glacial acetic acid solution to obtain a 7 mg / mL GO solution; combine the two solutions in a volume ratio of 1:1 to obtain a Fe3O4 / GO modification solution;

[0057] S2. Take 5 μL of the modification solution and disperse it by dropping on the polished GCE, dry it at room temperature, and finally obtain a modified electrode, which is denoted as Fe3O4 / GO / GCE.

[0058] In Examples 1 - 3 of the present invention, Fe3O4 / GO / GCE composite electrodes with a wide detection linear range and high sensitivity were all prepared, and the effects were parallel. Below, the Fe3O4 / GO / GCE composite electrode prepared in Example 1 was taken as an example for research, and the Fe3O4 / GO / GCE composite electrode prepared in Example 1 was used as the working electrode to construct an electrochemical sensor to detect the residue of dimethoate in tap water. The specific research methods and research results are as follows:

[0059] I. Preparation of solutions

[0060] (1) Preparation of glacial acetic acid

[0061] Use a measuring cylinder to measure 1 mL of glacial acetic acid, dissolve it with a small amount of ultrapure water, quantitatively transfer it to a 100 mL volumetric flask, add ultrapure water to dilute to the scale, shake well, and store it in the refrigerator for later use.

[0062] (2) Preparation of electrolyte solution (PBS)

[0063] Weigh 0.1646 g of K3[Fe(CN)6], 0.2112 g of K4[Fe(CN)6], 3.7275 g of KCl, 10.9233 g of Na2HPO4·12H2O, and 2.6552 g of NaH2PO4·2H2O. Mix them and dissolve in ultrapure water, then make up the volume to 1 L in a volumetric flask and store in the refrigerator for later use.

[0064] (3) Preparation of dimethoate standard solution

[0065] Dissolve 2 mL of 1×10 -2 g / L dimethoate stock solution in 95% ethanol, quantitatively transfer it to a 25 mL volumetric flask, add 95% ethanol solution to dilute to the mark, shake well to obtain 8×10 -4 g / L dimethoate standard solution. Then take 5 mL of the 8×10 -4 g / L standard solution and dissolve it in 95% ethanol solution, quantitatively transfer it to a 25 mL volumetric flask, add 95% ethanol to dilute to the mark, shake well to obtain 1.6×10 -4 g / L dimethoate standard solution. The dilution method is the same as the previous step, and sequentially dilute to obtain 3.2×10 -5 g / L, 6.4×10 - 6 g / L, 1.28×10 -6 g / L, 2.56×10 -7 g / L dimethoate standard solutions.

[0066] II. Preparation of sensor and electrochemical measurement

[0067] (1) Pretreatment and electrochemical measurement of glassy carbon electrode (GCE):

[0068] Since an oxide film will form on the surface of GCE after long-term storage, in order not to affect its use, it needs to be polished. Sprinkle alumina powders with different particle sizes (1.0 μm, 0.03 μm, 0.05 μm) evenly on three glass plates pasted with deerskin, moisten with ultrapure water, and then place the electrodes on the three plates respectively and polish them in an "8" shape until the surface of the electrode shows a bright mirror surface. Before performing electrochemical tests, it is necessary to turn on the electrochemical workstation and preheat it for half an hour. Using a saturated calomel electrode as the reference electrode, a platinum wire electrode as the counter electrode, and GCE as the working electrode, a three-electrode system is built accordingly. Use cyclic voltammetry to perform electrochemical performance tests on the bare glassy carbon electrode in PBS solution. Set the potential range of CV measurement to -0.05 V to +0.6 V, and the scanning rate to 50 mV / s. When the potential difference of the oxidation-reduction peak is about 65 mV, it indicates that this electrode is a quasi-reversible reaction and subsequent experiments can be carried out; if this voltage value is not reached, grind the electrode according to the above grinding method and ultrasonically clean it until this voltage value reaches about 65 mV.

[0069] (2) Preparation and Electrochemical Measurement of the Sensor:

[0070] The Fe3O4 / GO / GCE electrode of Example 1 was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) to study the electrochemical behavior of the electrode. The test method of cyclic voltammetry (CV) was the same as that of the above-mentioned bare electrode.

[0071] For all electrochemical characterizations of electrochemical impedance spectroscopy (EIS), the test conditions were: frequency 0.1 - 1×10 5 HZ, amplitude 0.05 mV. The measurement was carried out in PBS electrolyte solution. After the current was stable, the generated EIS diagram was recorded.

[0072] The electrochemical behavior of the electrode was tested by differential pulse voltammetry (DPV) with the parameters: potential range -0.1 V - +0.6 V (vs. SCE), pulse amplitude 25 mV, interval potential 4 mV, and retention time 2 s. All tests were carried out at room temperature.

[0073] (3) Sample Treatment and Determination

[0074] Tap water was selected as the real sample to detect the content of dimethoate in it. 5 mL of the prepared dimethoate standard solutions with known concentrations of 8×10 -4 g / L, 1.6×10 -4 g / L, and 3.2×10 -5 g / L were respectively transferred into 50 mL volumetric flasks, diluted to the mark with tap water and shaken well. Finally, tap water samples with concentrations of 0.8×10 -4 g / L, 1.6×10 -5 g / L, and 3.2×10 -6 g / L were obtained. 10 mL of the tap water sample was taken with a beaker, and the prepared Fe3O4 / GO / GCE electrochemical biosensor was placed in it. After soaking for 5 min, differential pulse voltammetry (DPV) at different concentrations was tested in the prepared PBS solution. The measurements were carried out in sequence from low concentration to high concentration, and the average value was taken for 3 measurements at different concentrations.

[0075] III. Results and Discussion:

[0076] 3.1.1 Fourier Transform Infrared Determination and Results:

[0077] Put the Fe3O4 and KBr obtained after vacuum drying into an agate mortar, stir evenly and then crush them into pieces to make a sample, and put it into a Fourier transform infrared spectrometer for measurement; obtain the IR spectrum of Fe3O4 and compare it with the standard spectrum. Parameter settings: detector DIGS KBr, beam splitter KBr, placed on the iD5 ATR accessory on the sample stage, scanning times 16 times, resolution 4 - 6, correction none, automatic atmospheric background subtraction, background processing select the first item or the third item. Plot with wave number as the abscissa and transmittance as the ordinate, mark the peaks, as Figure 1 shown. It can be seen from the figure that the substance has significant characteristic absorption peaks at 3440 cm -1 , 1620 cm -1 , and 567 cm -1 . By consulting the literature and analyzing, it is concluded that the absorption peaks at 3440 cm -1 and 1620 cm -1 are the stretching vibration absorption peaks of -OH on the surface of Fe3O4, and the absorption peak at 567 cm -1 is the stretching vibration absorption peak of Fe-O. Based on this, it can be preliminarily judged that the black solid substance is an iron oxide.

[0078] 3.1.2 SEM characterization of Fe3O4 nanoparticles and Fe3O4 / GO:

[0079] Use SEM to scan the surface morphologies of Fe3O4 nanoparticles and Fe3O4 / GO. As Figure 2 (a), 2(b) show, the Fe3O4 nanoparticles are spherical, with a rough surface, relatively uniform size, and some agglomerated. The black flakes in Fe3O4 / GO are graphene oxide, and it can be clearly seen from the figure that Fe3O4 has been successfully combined on the GO.

[0080] Characterize the modified liquid Fe3O4 / GO by transmission electron microscopy (TEM), and the results are as Figure 3 shown. The composite material is different from single Fe3O4 nanoparticles, showing an irregular shape. The graphene oxide is sheet-like, and the circular particles attached to it are Fe3O4 particles, demonstrating the combination method of Fe3O4 and graphene. The sheet-like structure of graphene oxide serves as a composite matrix, facilitating the attachment of Fe3O4. In the presence of graphene, the Fe3O4 nanoparticles are more dispersed, indicating that GO alleviates the aggregation phenomenon of Fe3O4, making the composite material have better electrochemical properties.

[0081] 3.2 Electrode characterization

[0082] 3.2.1 Optimization of the optimal conditions

[0083] 3.2.1.1 pH optimization

[0084] In this experiment, differential pulse voltammetry (DPV) was used to investigate the oxidation peak current of Fe3O4 / GO / GCE in PBS buffer solutions with different pH values containing a certain concentration of dimethoate solution. The DPV scans were carried out with pH values of 4.0, 5.0, 6.0, 7.0, 8.0 and a dimethoate concentration of 8×10 -4 g / L solutions, and the results are as shown in Figure 4 (a). The oxidation peak current shows a trend of increasing first and then decreasing with the different pH values of the PBS buffer solution. The peak current reaches the maximum value in the PBS buffer solution with pH equal to 5.0. Then, as the pH of the buffer solution gradually increases, the oxidation peak current of dimethoate gradually decreases. As shown in Figure 4 (b), the reason for this situation may be related to the charge variation in the measurement environment. Therefore, the PBS buffer solution with a pH value of 5.0 was used for the subsequent experiments.

[0085] 3.2.1.2 Influence of scanning rate

[0086] In this experiment, the cyclic voltammetric behavior of dimethoate at different scanning rates (0.01V / s - 0.09V / s) was investigated, and the results are as shown in Figure 5 (a). The results show that at different scanning rates, there are obvious regular changes in the oxidation and reduction peaks of dimethoate. As the scanning rate increases, the oxidation peak current increases, the reduction peak current decreases, and there is a good linear relationship between the oxidation peak current and the scanning rate, as shown in Figure 5 (b). The linear equation is y = 0.8986x + 39.005 (R 2 = 0.9974), indicating that the reaction of dimethoate on the surface of Fe3O4 / GO / GCE is controlled by diffusion.

[0087] Since it takes a certain amount of time for the organophosphorus pesticide molecules to combine with the composite material on the electrochemical sensor, to accurately determine the concentration of the pesticide, it is necessary to determine the soaking time of the prepared electrochemical sensor in the pesticide. The fabricated Fe3O4 / GO / GCE was placed in a standard dimethoate solution with a concentration of 8×10 -4 g / L, and DPV scans were performed on this concentration of dimethoate. The influence of enrichment times of 60s, 120s, 180s, 240s, and 300s was investigated at an enrichment potential of 0.025V, and the results are as shown in Figure 6 . The oxidation peak current changes with the enrichment time. As the enrichment time prolongs, the oxidation peak current gradually increases. When the enrichment time reaches 300s, the oxidation peak current reaches the maximum value. It is proved that after soaking for 300s, more dimethoate is adsorbed by Fe3O4 / GO / GCE and the combination between the two is better. Therefore, the optimal enrichment time should be selected as 300s.

[0088] 3.2.2 Cyclic voltammetry (CV)

[0089] The bare electrode and the modified electrode were scanned by cyclic voltammetry (CV) in a PBS solution containing 1.2 mmol / L. As Figure 7 shown, both electrodes showed obvious oxidation peaks at about 0.20 V. Among them, the oxidation peak of the bare electrode was lower, while the oxidation peak of the Fe3O4 / GO / GCE coated with the modified solution was significantly higher. The electrochemical response signal of the bare electrode GCE was poor; the sensor signal of the electrode material modified with Fe3O4 / GO was better, and the oxidation peak current was higher. This was mainly because the aggregation of Fe3O4 was effectively alleviated after a layer of graphene oxide was loaded on the surface of Fe3O4, the impedance of the electrode was reduced, and the oxidation peak was broadened, indicating that the potential difference increased, indicating that Fe3O4 / GO had been successfully modified on the electrode surface, making Fe3O4 / GO / GCE have a more sensitive chemical response.

[0090] 3.2.3 Differential pulse voltammetry (DPV)

[0091] Figure 8 Figure shows the DPV curves of different modified electrodes in a PBS buffer solution containing 1.2 mmol / L. In the figure, both GCE and Fe3O4 / GO / GCE showed obvious reduction peak currents at about 0.16 V. Among them, the reduction peak current of the Fe3O4 / GO / GCE modified electrode was about 4.3 times higher than that of GCE. This was due to the good adsorption of Fe3O4 in Fe3O4 / GO, the good conductivity of GO and its alleviating effect on the aggregation of Fe3O4, which increased the electrochemical response of the electrode and improved the peak current, indicating that the modified material Fe3O4 / GO effectively improved the sensitivity of the electrode.

[0092] 3.2.4 Electrochemical impedance spectroscopy (EIS)

[0093] A buffer solution containing 1.2 mmol / L PBS was used to test the electrochemical impedance (EIS) of the bare electrode GCE and the modified electrode Fe3O4 / GO / GCE respectively. The results are as Figure 9 shown. The figure shows that the impedance of Fe3O4 / GO / GCE was significantly lower than that of the bare electrode GCE. The reason for this phenomenon was that firstly, Fe3O4 had good electrical conductivity, and due to its attachment, the sensitivity of the modified electrode was greater than that of the bare electrode, effectively enriching the reaction to the medium surface; secondly, after graphene oxide GO was loaded on the surface of Fe3O4, the aggregation of Fe3O4 was greatly alleviated, and the modified electrode had a higher reaction sensitivity and lower impedance.

[0094] 3.2.5 Establishment of the standard curve

[0095] Under optimal conditions, when the pH of the PBS buffer solution is equal to 5.0, the Fe3O4 / GO / GCE was placed in dimethoate standard solutions of 8×10 -4 g / L, 1.6×10 -4 g / L, 3.2×10 -5 g / L, 6.4×10 -6 g / L, 1.28×10 -6 g / L, 2.56×10 -7 g / L for 300 s, respectively. Using the DPV method, the effect of dimethoate standard solutions with different concentrations on the peak current was investigated at a scan rate of 0.09 V / s. The results are shown in Figure 10 (a). The peak current value increased with the increase in the concentration of the dimethoate standard solution, and within the concentration range of 2.56×10 -7 g / L - 8×10 -4 g / L, a linear relationship was presented between the peak current and the concentration, as shown in Figure 10 (b). The linear equation was Ip = 2×10 -5 logc + 0.0002 (R 2 = 0.8867). The linear range was relatively wide. Through data analysis and calculation, the detection limit was 5.2013×10 -7 g / L, and the detection limit result was relatively low.

[0096] 3.2.6 Detection Results of Actual Samples

[0097] Under the optimal experimental conditions, the differential pulse voltammetry (DPV) was used to detect the content of dimethoate in tap water samples. The samples were determined in parallel three times, and the recovery experiment was carried out.

[0098] Dimethoate standard solutions of 8×10 -4 g / L, 1.6×10 -4 g / L, 3.2×10 -5 g / L were added to the same tap water respectively to obtain different current values, and the recovery rates were calculated. The results are shown in the following table.

[0099] Table 1 Detection Results of Dimethoate Content in Tap Water

[0100] Sample concentration (g / L) Measured concentration (g / L) Recovery rate (%) RSD (%) (n = 3) <![CDATA[8×10 -4 g / L]]> <![CDATA[7.9368×10 -4 g / L]]> 99.21％ 1.27％ <![CDATA[1.6×10 -4 g / L]]> <![CDATA[1.5869×10 -4 g / L]]> 99.18％ 3.44％ <![CDATA[3.2×10 -5 g / L]]> <![CDATA[3.0714×10 -5 g / L]]> 95.98％ 4.53％

[0101] As calculated and shown in the table data, the recovery rates were 99.21%, 99.18%, 95.98% respectively. The recovery rates were relatively high, and the relative deviation (RSD) was 1.27% - 4.53%, indicating that this method was reliable and could be used for the detection of dimethoate in tap water.

[0102] 3.2.7 Electrode Stability and Reproducibility

[0103] The prepared electrochemical sensor was tested for stability and reproducibility. The same electrode was measured in parallel three times, and the relative standard deviation was calculated to be 3.70%. Three identical electrodes were used for measurement, and the relative standard deviation was calculated to be 5.84%, with an error less than 10%, indicating good reproducibility. The stability test was carried out on these three electrodes after they were stored in the refrigerator for 7 days. After calculation, the peak currents were 77.2%, 50.1%, and 54.2% of the first measurement, indicating that the stability of this electrochemical sensor was average. The reason for this result may be that the composite material was oxidized when storing the electrode, resulting in a decrease in the sensitivity of the electrode and a decrease in the measured peak current.

[0104] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these changes and modifications. The above-described embodiments are only preferred embodiments given to fully illustrate the present invention, and the scope of protection is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the scope of protection of the present invention, and the scope of protection of the present invention is subject to the claims.

Claims

1. Application of non-enzymatic sensor in ultrasensitive detection of organophosphorus pesticides, characterized in that, The working electrode of the non-enzymatic sensor is a Fe3O4 / graphene oxide / GCE composite electrode, and the Fe3O4 / graphene oxide / GCE composite electrode is prepared according to the following steps: Prepare Fe3O4 nanoparticles; Ultrasonically disperse the Fe3O4 nanoparticles in water to obtain Solution I; ultrasonically disperse the graphene oxide in glacial acetic acid solution to obtain Solution II; mix Solution I and Solution II to obtain the Fe3O4 / GO modification solution; Dropwise coat the Fe3O4 / GO modification solution on the polished GCE and dry it to obtain the Fe3O4 / graphene oxide / GCE composite electrode.

2. Use of the non-enzyme sensor according to claim 1 in the ultrasensitive detection of organophosphorus pesticides, characterized in that, The Fe3O4 nanoparticles are prepared according to the following steps: Dissolve soluble Fe 3+ salt and soluble Fe 2+ salt in water, mix them, heat and stir, and add ammonia water dropwise until the pH is 9 - 10, and continue stirring for 0.5 - 1 h to obtain the precursor of Fe3O4 particles; Among them, soluble Fe 3+ salt and soluble Fe 2+ salt have a molar ratio of 2-2.2:1; Hydrothermally react the Fe3O4 particle precursor at 160-170 °C for 4-5 h, then wash it with water until neutral to obtain Fe3O4 nanoparticles.

3. Use of the non-enzyme sensor according to claim 1 in the ultrasensitive detection of organophosphorus pesticides, characterized in that, The mass ratio of the Fe3O4 nanoparticles to the graphene oxide is 1:3-7.

4. Use of the non-enzyme sensor according to claim 1 in ultrasensitive detection of organophosphorus pesticides, characterized in that, The operation of the dropwise coating is as follows: dropwise coat the Fe3O4 / GO on the surface of the polished GCE and dry it to obtain the Fe3O4 / graphene oxide / GCE composite electrode, and repeat the dropwise coating of the Fe3O4 / GO modification solution and drying on the surface of the dried Fe3O4 / graphene oxide / GCE composite electrode.

5. Use of the non-enzyme sensor according to claim 1 in ultrasensitive detection of organophosphorus pesticides, characterized in that, The non-enzymatic sensor consists of a three-electrode system, with the Fe3O4 / graphene oxide / GCE composite electrode as the working electrode, the saturated calomel electrode as the reference electrode, and the platinum wire electrode as the counter electrode.

6. Use of the non-enzyme sensor according to claim 1 in ultrasensitive detection of organophosphorus pesticides, characterized in that, The specific steps for the detection of organophosphorus pesticides are as follows: Using the saturated calomel electrode as the reference electrode and the platinum wire electrode as the counter electrode, together with the Fe3O4 / graphene oxide / GCE composite electrode as the working electrode, form a three-electrode system, connect it to an electrochemical workstation, use PBS solution as the electrolyte, and adopt cyclic voltammetry to plot the working curve according to the current-potential.

7. Use of the non-enzyme sensor according to claim 1 in ultrasensitive detection of organophosphorus pesticides, characterized in that, The organophosphorus pesticides include methamidophos, phorate, parathion, and dimethoate.

8. Use of the non-enzyme sensor according to claim 7 in ultrasensitive detection of organophosphorus pesticides, characterized in that, The detection limit of the Fe3O4 / graphene oxide / GCE composite electrode for dimethoate concentration is 5.2013×10 -7 g / L, and the linear range is 2.56×10 -7 g / L~8×10 -4 g / L.

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