A cyclodextrin polymer-graphene modified electrode, an electrochemical sensor and preparation and application thereof

Abstract

The application belongs to the technical field of analysis and detection, and discloses a cyclodextrin polymer-graphene modified electrode and a preparation and application thereof. The preparation of the cyclodextrin polymer-graphene modified electrode comprises the following steps: preparing nitrogen-doped reduced graphene oxide; dissolving beta-cyclodextrin in an ethanol aqueous solution, adding Si-69 and heating to perform a cross-linking polymerization reaction to obtain Si-69-beta-CD; dropping a dispersion liquid of the nitrogen-doped reduced graphene oxide on the surface of a glassy carbon electrode, and drying to obtain an N-rGO / GCE modified electrode; dropping a Si-69-beta-CD suspension on the surface of the N-rGO / GCE modified electrode, and drying to obtain a Si-69-beta-CD / N-rGO / GCE modified electrode. The electrochemical sensor prepared based on the Si-69-beta-CD / N-rGO / GCE working electrode can specifically detect fipronil, and has good selectivity.

Description

Technical Field

[0001] This invention belongs to the field of analytical detection technology, and specifically relates to a cyclodextrin polymer-graphene modified electrode, an electrochemical sensor, and their preparation and application. Background Technology

[0002] With rapid economic and technological development, pesticides are essential for pest control in agricultural production. Consequently, my country's agricultural departments have formulated relevant laws and regulations to control pesticide use. However, many people still illegally use pesticides, resulting in a significant increase in pesticide residues and causing substantial environmental harm. Fipronil is still widely used in crop pest control, household pest control, and veterinary medicine. Fipronil residues spread and accumulate through the food chain, potentially causing serious harm to animals and humans. Therefore, rapid detection of fipronil is crucial. Currently, fipronil residue detection mainly relies on traditional large-scale instrumental methods such as HPLC. While these methods offer high sensitivity and accuracy, they generally suffer from drawbacks such as long experimental times, complex operation, and large, portable instruments, failing to meet the market demand for rapid on-site detection. Electrochemical methods, as an emerging detection approach, have gained widespread application due to their advantages of fast detection speed, low cost, and portable equipment. With the widespread application of electrochemical sensors, increasingly higher requirements will be placed on the sensitivity, selectivity, and detection range of electrodes. Therefore, researching and developing electrode modification materials with larger surface area, stronger conductivity, strong enrichment ability, good thermodynamic stability and mechanical properties will become an important research trend.

[0003] In recent years, the broad and cutting-edge field of supramolecular chemistry has developed rapidly. The binding of supramolecular molecules is based on molecular recognition, which is the selective binding of a host to a guest to produce a specific function. This recognition is specific, particular, and selective, similar to a "lock and key." This specific recognition differs from covalent bonding forces and is related to electrostatic interactions, hydrogen bonds, van der Waals forces, π-π interactions, and hydrophobic interactions. Cyclodextrins, as second-generation supramolecular hosts, have been widely used due to their advantages. For example, cyclodextrin is an ideal host molecule for fipronil, a hydrophobic organic pesticide with a small molecular structure. However, the binding constant of natural cyclodextrins to small guest molecules is relatively small, and direct use may not yield good encapsulation effects. Therefore, it is necessary to modify natural cyclodextrins by introducing effective groups, such as thiol cyclodextrins, carboxyl cyclodextrins, and amino cyclodextrins, and further, bridging cyclodextrins, to improve molecular recognition ability and binding constant.

[0004] Bis-(γ-triethoxysilylpropyl)-tetrasulfide, also known as Si-69, is a pale yellow, oily liquid currently used primarily in the rubber and plastics industry to improve physical properties. In recent years, many researchers have developed it as an emerging research material in electrochemistry. Most organosulfur compounds exhibit good electrochemical performance, and their redox potentials can be adjusted over a wide range, resulting in relatively high capacities. Furthermore, the extra intermediate sulfur atom in tetrasulfide compounds lowers the dissociation energy of the disulfide bridge; this low dissociation energy supports rapid electrode kinetics, promotes electron transport, and demonstrates excellent electrochemical performance.

[0005] Since its discovery in 2004, graphene has attracted widespread attention from researchers due to its excellent electrical conductivity, high specific surface area, and good mechanical properties. Functional modification of graphene endows it with new properties and improves its electronic structure and chemical properties; nitrogen atoms are the most commonly used dopant atoms.

[0006] This invention utilizes Si-69 hydrophobically modified cyclodextrin and nitrogen-doped reduced graphene oxide to form a composite material through non-covalent interactions. The composite material exhibits the advantages and performance of synergistic effects. Si-69 hydrophobically modified cyclodextrin improves molecular recognition performance and enrichment ability, while nitrogen-doped graphene provides a large specific surface area, high conductivity, and electrocatalytic performance, thus preparing a rapid detection and highly sensitive fipronil electrochemical sensor. Summary of the Invention

[0007] In order to overcome the shortcomings and deficiencies of the prior art, the primary objective of this invention is to provide a method for preparing a cyclodextrin polymer-graphene modified electrode.

[0008] Another object of the present invention is to provide a cyclodextrin polymer-graphene modified electrode prepared by the above method.

[0009] Another object of the present invention is to provide an electrochemical sensor comprising the above-mentioned cyclodextrin polymer-graphene modified electrode.

[0010] Another object of the present invention is to provide the application of the above-mentioned cyclodextrin polymer-graphene electrochemical sensor in the detection of the cockroach bait fipronil.

[0011] The objective of this invention is achieved through the following solution:

[0012] A method for preparing a cyclodextrin polymer-graphene modified electrode includes the following steps:

[0013] (1) Take graphene oxide, urea and sodium citrate and mix them in water. Transfer the mixed solution to a polytetrafluoroethylene reactor for hydrothermal reaction. After the reaction is completed, filter the solution, wash the filter residue with water, and dry it to obtain nitrogen-doped reduced graphene oxide, abbreviated as N-rGO.

[0014] (2) Dissolve β-cyclodextrin in an ethanol aqueous solution, add Si-69 and heat to carry out cross-linking polymerization reaction. After the reaction is completed, purify to obtain a slightly yellow Si-69 modified cyclodextrin powder, abbreviated as Si-69-β-CD;

[0015] (3) The nitrogen-doped reduced graphene oxide prepared in step (1) is dispersed in an organic solvent and then ultrasonically dispersed to obtain a uniform dispersion. The dispersion is then drop-coated onto the surface of a polished glassy carbon electrode (d = 3 mm) and dried to obtain an N-rGO / GCE modified electrode.

[0016] (4) The Si-69-β-CD prepared in step (2) is ultrasonically dispersed in water to obtain a uniform Si-69-β-CD suspension. The Si-69-β-CD suspension is drop-coated onto the surface of the N-rGO / GCE modified electrode and dried to obtain the Si-69-β-CD / N-rGO / GCE modified electrode, which is the aforementioned cyclodextrin polymer-graphene modified electrode.

[0017] In this invention, the graphene oxide can be prepared by those skilled in the art according to existing technology, and the modified Marcano method can be used as a reference for preparing graphene oxide.

[0018] Further, in step (1), the weight ratio of urea:sodium citrate:graphene oxide is 1-2:1.5-1:0.1-0.05; water is only used as a reaction medium, so the amount of water used does not need to be limited; the hydrothermal reaction refers to the reaction at 120-180℃ for 8-10 hours; the product obtained after the hydrothermal reaction can be separated by filtration through filter paper. The drying in step (1) is preferably freeze drying.

[0019] Further, the ethanol-water solution mentioned in step (2) is 60%-70% (V%); the weight ratio of Si-69:β-cyclodextrin is 0.6-1.4; the crosslinking polymerization reaction refers to the reaction at 60-80℃ for 6-10h.

[0020] Further, the purification described in step (2) refers to the removal of excess ethanol-water solution by rotary evaporation after the reaction, followed by washing away unreacted Si-69 with anhydrous ethanol, then dissolving it in water, removing unreacted cyclodextrin by dialysis (cutoff: 1500 Da), and finally drying to obtain Si-69-β-CD.

[0021] Furthermore, before use, the glassy carbon electrode after grinding and polishing described in step (3) is preferably rinsed with deionized water and anhydrous ethanol in sequence, and then subjected to Fe[(CN)6] 3- / 4-Cyclic voltammetry scans were performed in a KCl mixed solution until the curves were stable and symmetrical. Stable and symmetrical curves are an indicator of whether the electrode has been properly treated, so as to ensure that the state of the electrode is similar in each experiment.

[0022] Further, the organic solvent mentioned in step (3) is N,N-dimethylformamide (DMF).

[0023] Furthermore, the ultrasonic dispersion time of the dispersion in step (3) is 30-60 min; the concentration of the N-rGO dispersion is 0.5%-1% (wt%); and for a glassy carbon electrode with d=3 mm, the amount of nitrogen-doped reduced graphene oxide dispersion used for drop coating is 5-10 μL.

[0024] Furthermore, the drying in step (3) is preferably done by irradiation with an infrared lamp.

[0025] Further, the ultrasonic dispersion time of the Si-69-β-CD suspension in step (4) is 20-40 min; the concentration of the Si-69-β-CD suspension is 0.5%-1.5% (wt%); and for a glassy carbon electrode with d=3 mm, the amount of Si-69-β-CD suspension used for drop coating is 5-10 μL. That is, the volume ratio of the nitrogen-doped reduced graphene oxide dispersion dropped in step (3) to the Si-69-β-CD suspension dropped in step (4) is (5-10):(5-10).

[0026] Furthermore, the drying in step (4) is preferably done by irradiation with an infrared lamp.

[0027] A cyclodextrin polymer-graphene modified electrode prepared by the above method.

[0028] A cyclodextrin polymer-graphene electrochemical sensor is provided, wherein the aforementioned cyclodextrin polymer-graphene modified electrode is used as the working electrode, the calomel electrode is used as the reference electrode, and the platinum electrode is used as the auxiliary electrode.

[0029] The present invention also provides the application of the above-mentioned cyclodextrin polymer-graphene electrochemical sensor in the detection of fipronil in cockroach bait.

[0030] The composite modified electrode Si-69-β-CD / N-rGO / GCE prepared in this invention serves as a working electrode for constructing a sensor that provides an excellent electrochemical platform for the qualitative and quantitative determination of fipronil. The multi-cavity synergistic effect of Si-69-β-CD expands the hydrophobic environment, resulting in a stronger attraction for fipronil. Furthermore, Si-69, as a tetrasulfide compound, exhibits excellent electrochemical performance. Combined with N-rGO as a composite material, it produces a synergistic effect, enabling the construction of a rapid and highly sensitive electrochemical sensor for the detection of fipronil, and its practical application in the detection of fipronil cockroach bait samples.

[0031] A method for detecting fipronil in cockroach bait includes the following steps:

[0032] (1) An electrochemical sensor was prepared by using the Si-69-β-CD / N-rGO / GCE modified electrode as the working electrode, the calomel electrode as the reference electrode, and the platinum electrode as the auxiliary electrode.

[0033] (2) Add different amounts of acetonitrile solution of fipronil standard to the electrolyte solution to obtain fipronil solutions of different concentrations. Immerse the working electrode and stir to fully adsorb and capture the adsorbed fipronil. Then, use differential pulse voltammetry to quantitatively detect the electrochemical behavior of fipronil standard and plot the standard working curve. The horizontal axis of the standard working curve is the concentration of fipronil in the electrolyte solution, and the vertical axis is the peak current intensity.

[0034] (3) Take the sample to be tested, ultrasonically disperse it in acetonitrile, centrifuge it, take the supernatant, filter and purify it, and use the sample solution to replace the acetonitrile solution of the fipronil standard in step (2) to perform the operation in step (2). Then calculate the concentration of fipronil in the sample to be tested based on the peak current intensity and the standard working curve.

[0035] Further, the electrolyte solution mentioned in step (2) is a 0.1M Britton-Robinson buffer solution with pH = 8-10; the stirring mentioned in step (2) refers to stirring for 200-400s.

[0036] Further, the sample to be tested in step (3) is fipronil cockroach bait, and the ultrasonic time is 10-30 min; the centrifugation speed is 6000-12000 rpm, and the time is 5-15 min; the sample is filtered through a 0.22 μm microporous membrane, and the pH of the clear liquid is adjusted to 8-10 with 0.1 M Britton-Robinson buffer.

[0037] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0038] (1) The electrochemical sensor based on Si-69-β-CD / N-rGO / GCE obtained in this invention has a low cost of raw materials required for chemical synthesis. The synergistic effect of Si-69-β-CD and N-rGO results in high sensitivity to fipronil and short sample detection and analysis time.

[0039] (2) The electrochemical sensor based on Si-69-β-CD / N-rGO / GCE prepared in this invention can specifically detect fipronil with good selectivity. The method is low in cost, simple to operate, stable, strong anti-interference ability and good repeatability. Ultimately, it can establish a rapid on-site detection system for various foods and agricultural products in fields, wholesale markets and other places. Attached Figure Description

[0040] Figure 1 Characterization of nitrogen-doped graphene oxide prepared in Example 1 of the present invention: (a) is a scanning electron microscope image; (b) is a Raman spectrum.

[0041] Figure 2 Characterization of Si-69-β-CD prepared in Example 1 of the invention: (a) is a scanning electron microscope image and EDS analysis; (b) is an infrared spectrum; (c) is a Raman spectrum; and (d) is an XRD spectrum.

[0042] Figure 3 Electrochemical performance testing of the Si-69-β-CD / N-rGO / GCE composite electrode prepared in Example 1 of the invention: (a) is the cyclic voltammetry curve; (b) is the electrochemical impedance spectroscopy.

[0043] Figure 4 Optimization of performance parameters for the fipronil electrochemical sensor prepared in Example 2 of the invention: (a) shows the effect of scanning speed; (b) shows the linear relationship between scanning speed and peak current; (c) shows the effect of pH; (d) shows the coating concentration of N-rGO; (e) shows the coating concentration of Si-69-β-CD; and (f) shows the stirring enrichment time.

[0044] Figure 5 The device performance of the fipronil electrochemical sensor of Example 2 of the invention is as follows: (a) is selectivity; (b) is repeatability; (c) is reproducibility; and (d) is stability.

[0045] Figure 6 The detection range of the fipronil electrochemical sensor in Example 2 of the invention was determined for standard samples and actual sample analysis: (a) is the differential pulse voltammetry curve of fipronil at different concentrations, with the inset being the standard curve; (b) is the differential pulse voltammetry curve of cockroach bait. Detailed Implementation

[0046] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0047] Unless otherwise specified, all reagents used in the examples are commercially available.

[0048] Example 1: Preparation of a rapid detection, high-sensitivity fipronil electrochemical sensor

[0049] (1) Disperse 0.1 g of GO powder in 30 mL of deionized water and sonicate for 30 min. Then add 1.0 g of urea and 1.0 g of sodium citrate, and after complete dissolution, transfer the solution to a polytetrafluoroethylene reactor. The reactor is placed in an electrically heated constant temperature drying oven at 180 °C for 10 h. After the reaction, wash the filter residue with deionized water several times and freeze-dry to obtain nitrogen-doped reduced graphene oxide (N-rGO).

[0050] (2) Weigh 5g of β-cyclodextrin and place it in a 150mL three-necked flask equipped with a condenser. Add 100mL of 70% ethanol aqueous solution and heat in an oil bath at 80℃ for several minutes with stirring until β-CD is completely dissolved. Adjust the pH to 4 with glacial acetic acid, then slowly add 5mL of Si-69 and maintain the reaction at 80℃ for 8 hours. After the reaction is complete, evaporate the excess ethanol aqueous solution using a rotary evaporator, filter, and wash several times with anhydrous ethanol to remove unreacted Si-69. Dissolve the filter residue in a small amount of deionized water and dialyze it using a 1500Da dialysis bag for 1 day. After dialysis, dry in a vacuum drying oven to obtain a slightly yellow Si-69-β-CD powder.

[0051] (3) Take 10 μL of N-rGO with a mass fraction of 0.5% dispersed in DMF and drop it onto the surface of GCE (d = 3 mm). After drying in an infrared oven, the N-rGO / GCE modified electrode is obtained. Take 10 μL of Si-69-β-CD with a mass fraction of 1% dispersed in water and drop it onto the surface of N-rGO / GCE. After slightly drying in an infrared oven, the Si-69-β-CD / N-rGO / GCE modified electrode is obtained.

[0052] Figure 1 The SEM and Raman spectra of nitrogen-doped reduced graphene oxide prepared in Example 1 of this invention show that the graphene oxide was successfully reduced and N was successfully doped into the carbon quantum dots.

[0053] Figure 2 The SEM, infrared, XRD, and Raman spectra of Si-69-β-CD prepared in Example 1 of this invention show that Si-69-β-CD was successfully prepared.

[0054] Figure 3 Electrochemical performance tests were conducted on the Si-69-β-CD / N-rGO / GCE modified electrode prepared in Example 1 of this invention. It can be seen that the peak current of Si-69-β-CD / N-rGO / GCE is the largest in the cyclic voltammetry curve; the capacitive expansion portion of the semicircle in the impedance plot approximates the charge transfer resistance, with a smaller radius indicating a smaller impedance value, and Si-69-β-CD / N-rGO / GCE having the smallest semicircle diameter. Therefore, all of the above demonstrates that the Si-69-β-CD / N-rGO composite material exhibits a synergistic effect and possesses excellent electrochemical performance.

[0055] Example 2: Application of a rapid and highly sensitive electrochemical sensor in the detection of fipronil in cockroach bait.

[0056] (1) Examine the optimal test parameters

[0057] Using the Si-69-β-CD / N-rGO / GCE modified electrode prepared in Example 1 as the working electrode, the saturated calomel electrode as the reference electrode, and the platinum electrode as the auxiliary electrode, a three-electrode electrochemical sensor was prepared, and the measurement was performed using this electrochemical sensor.

[0058] First, the effects of coating concentrations of N-rGO and Si-69-β-CD, scan rate, electrolyte solution pH, and stirring enrichment time on the sensor response current were investigated. The scan rate was studied using cyclic voltammetry (CV) with 10 μmol / L fipronil standard in Britton-Robinson buffer at pH 10. The scan potential ranged from -0.5 to 1.5 V, and the scan rate ranged from 20 to 120 mV / s. The effects of coating concentration of N-rGO and Si-69-β-CD, electrolyte pH, and fipronil (FIP) enrichment time on stirring were investigated using differential pulse voltammetry. The pulse amplitude was 30 mV, the potential increment was 5 mV, and the period was 0.2 s. The effect of different pH values ​​was studied using Britton-Robinson buffers (pH = 4.0–10.0) containing 10 μmol / L FIP as the supporting electrolyte. The effect of stirring enrichment time was studied by enriching in Britton-Robinson buffer (pH = 10) containing 10 μmol / L FIP for different times (0.5–30 min). Then, under the optimal electrolyte pH and fipronil (FIP) enrichment time, the coating concentrations of N-rGO and Si-69-β-CD in Example 1 were individually varied to investigate their effects.

[0059] Figure 4 This section describes the factors affecting sensor detection performance in Example 2 of this invention, including the coating concentration of N-rGO, the coating concentration of Si-69-β-CD, the scan rate, the pH of the electrolyte solution, and the enrichment time. It can be seen that the optimal test conditions are 0.5% (wt%), 1% (wt%), 100 mV / s, pH = 10, and 5 min. Specifically, the supporting electrolyte solution is Britton-Robinson buffer with pH = 10, the stirring time is 5 min, the scan rate is 100 mV / s, the coating concentration of N-rGO is 0.5%, and the coating concentration of Si-69-β-CD is 1%.

[0060] Using the Si-69-β-CD / N-rGO / GCE modified electrode prepared in Example 1 as the working electrode, the saturated calomel electrode as the reference electrode, and the platinum electrode as the auxiliary electrode, a three-electrode electrochemical sensor was prepared. Subsequent experiments were conducted using this electrochemical sensor under optimal testing conditions.

[0061] (2) Selectivity, repeatability, reproducibility and stability

[0062] (2.1) Selectivity Analysis

[0063] Prepare anhydrous ethanol solutions of FIP, abamectin, emamectin benzoate, fludioxonil, matrine, acetamiprid, and imidacloprid, respectively. Then prepare Ca... 2+ aqueous solution, Fe 3+ Aqueous solution of NH4+ 4+ aqueous solution, K + aqueous solution of Na + Aqueous solution, SO4 2- Aqueous solution of H2PO4 - Aqueous solutions were prepared. Under optimal detection conditions (supporting electrolyte solution Britton-Robinson buffer pH = 10, stirring time 5 min, scan rate 100 mV / s; N-rGO coating concentration 0.5%; Si-69-β-CD coating concentration 1%), FIP solution and interference solutions were added respectively. (All substances prepared in this section except fipronil are interference solutions. The final concentration of FIP in the electrolyte was 10 μmol / L. When the interference solution was one of the following: anhydrous ethanol solution of abamectin, anhydrous ethanol solution of emamectin benzoate, anhydrous ethanol solution of fludioxonil, anhydrous ethanol solution of matrine, anhydrous ethanol solution of acetamiprid, or anhydrous ethanol solution of imidacloprid, the final concentration of the corresponding interference substance was 10 μmol / L.) 2+ aqueous solution, Fe 3+ Aqueous solution of NH4+ 4+ aqueous solution of K + aqueous solution of Na + Aqueous solution, SO4 2- Aqueous solution of H2PO4 - When the interfering substance is in an aqueous solution (with a final concentration of 100 μmol / L), the selectivity of the sensor to FIP is studied by differential pulse voltammetry, with a pulse amplitude of 30 mV, a potential increment of 5 mV, and a period of 0.2 s.

[0064] (2.2) Repeatability, reproducibility and stability tests

[0065] The electrode prepared in Example 1 was used to conduct 20 repeated experiments.

[0066] The same sensor was fabricated using seven electrodes prepared in Example 1, and a reproducibility experiment was conducted.

[0067] Stability tests were conducted on the sensors after they were placed for several days.

[0068] Figure 5 The selectivity, repeatability, reproducibility and stability of the electrochemical sensor prepared by the Si-69-β-CD / N-rGO composite electrode in Example 2 of this invention were tested. It can be seen that the electrochemical sensor has good selectivity, good stability, strong anti-interference ability and good repeatability.

[0069] (3) Standard curve and detection limit

[0070] Prepare electrolyte solutions of FIP standards with concentrations ranging from 0.01 to 20 μmol / L. Perform standard curve and detection limit tests under the optimal test conditions determined in the previous experiments.

[0071] Preparation of the sample solution to be analyzed: Weigh 10 mg of FIP cockroach bait, add 10 mL of deionized water, and shake for 10 min to form a paste. Dilute with acetonitrile in a 100 mL volumetric flask and bring to volume. Extract the FIP by ultrasonication, filter through a 0.22 μm microporous membrane to obtain the stock solution for the test sample, and adjust the pH of the supernatant to 10 with 0.1 M Britton-Robinson buffer. Detect the actual sample of fipronil cockroach bait under optimal test conditions.

[0072] Figure 6 The standard curve, detection limit, and sample detection of the Si-69-β-CD / N-rGO composite electrode in this embodiment of the invention are shown. It can be seen that the Si-69-β-CD / N-rGO composite electrode exhibits linearity in the range of 0.01-20 μmol / L, with a detection limit of 0.00229 μmol / L. Furthermore, although the cockroach bait contains complex components, it has minimal interference with the detection of fipronil, indicating that the Si-69-β-CD / N-rGO composite electrode has good anti-interference ability.

[0073] (4) Verify the accuracy of the method of the present invention for detecting fipronil in cockroach bait.

[0074] This invention highlights its accuracy by comparing numerical values ​​with those obtained using high-performance liquid chromatography (HPLC). The HPLC detection method involves: weighing 10 mg of FIP cockroach bait, adding 10 mL of deionized water, and shaking for 10 min to form a paste. Dilute with acetonitrile in a 100 mL volumetric flask and bring to volume. Extract the FIP using ultrasonication, and filter through a 0.22 μm microporous membrane to obtain the test sample stock solution. The chromatographic column used is a Shimadzu C18 4.6 mm (id) × 15 cm stainless steel column (Japan), with a detection wavelength of 280 nm, a mobile phase V(acetonitrile-water) = 65-35, a flow rate of 1 mL / min, and a column temperature of 25 °C. The FIP retention time is approximately 9 min.

[0075]

[0076]

[0077] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a cyclodextrin polymer-graphene modified electrode, characterized in that... Includes the following steps: (1) Take graphene oxide, urea and sodium citrate and mix them in water. Transfer the mixed solution to a polytetrafluoroethylene reactor for hydrothermal reaction. After the reaction is completed, filter the solution, wash the filter residue with water, and dry it to obtain nitrogen-doped reduced graphene oxide, abbreviated as N-rGO. (2) Dissolve β-cyclodextrin in an ethanol aqueous solution, add Si-69 and heat to carry out cross-linking polymerization reaction. After the reaction is completed, purify to obtain Si-69 modified cyclodextrin powder, abbreviated as Si-69-β-CD; (3) The nitrogen-doped reduced graphene oxide prepared in step (1) is dispersed in an organic solvent and then ultrasonically dispersed to obtain a uniform dispersion. The dispersion is then drop-coated onto the surface of a polished glassy carbon electrode and dried to obtain an N-rGO / GCE modified electrode. (4) The Si-69-β-CD prepared in step (2) is ultrasonically dispersed in water to obtain a uniform Si-69-β-CD suspension. The Si-69-β-CD suspension is drop-coated onto the surface of the N-rGO / GCE modified electrode and dried to obtain the Si-69-β-CD / N-rGO / GCE modified electrode, namely the cyclodextrin polymer-graphene modified electrode.

2. The method for preparing the cyclodextrin polymer-graphene modified electrode according to claim 1, characterized in that: The weight ratio of urea:sodium citrate:graphene oxide mentioned in step (1) is 1-2:1-1.5:0.1-0.05; the hydrothermal reaction refers to the reaction at 120-180℃ for 8-10 hours.

3. The method for preparing the cyclodextrin polymer-graphene modified electrode according to claim 1, characterized in that: The ethanol-water solution mentioned in step (2) is 60%-70%; the weight ratio of Si-69:β-cyclodextrin is 0.6-1.4; the cross-linking polymerization reaction refers to the reaction at 60-80℃ for 6-10h.

4. The method for preparing the cyclodextrin polymer-graphene modified electrode according to claim 1, characterized in that: The organic solvent mentioned in step (3) is N,N-dimethylformamide; The concentration of the N-rGO dispersion mentioned in step (3) is 0.5wt%-1wt%; The concentration of the Si-69-β-CD suspension mentioned in step (4) is 0.5wt%-1.5wt%; The volume ratio of the nitrogen-doped reduced graphene oxide dispersion in step (3) to the Si-69-β-CD suspension in step (4) is (5-10):(5-10).

5. A cyclodextrin polymer-graphene modified electrode prepared by the method according to any one of claims 1-4.

6. A cyclodextrin polymer-graphene electrochemical sensor, characterized in that: The cyclodextrin polymer-graphene modified electrode as described in claim 5 is used as the working electrode, the calomel electrode as the reference electrode, and the platinum electrode as the auxiliary electrode.

7. The application of the cyclodextrin polymer-graphene electrochemical sensor according to claim 6 in the detection of fipronil in cockroach bait.

8. A method for detecting fipronil in cockroach bait, characterized in that... Includes the following steps: (1) Using the cyclodextrin polymer-graphene modified electrode of claim 5 as the working electrode, the calomel electrode as the reference electrode, and the platinum electrode as the auxiliary electrode, an electrochemical sensor is prepared through a three-electrode system. (2) Add different amounts of acetonitrile solution of fipronil standard to the electrolyte solution to obtain fipronil solutions of different concentrations. Immerse the working electrode and stir to adsorb and capture fipronil. Then, use differential pulse voltammetry to quantitatively detect the electrochemical behavior of fipronil standard and plot the standard working curve. The horizontal axis of the standard working curve is the concentration of fipronil in the electrolyte solution, and the vertical axis is the peak current intensity. (3) Take the sample to be tested, disperse it in acetonitrile by ultrasonication, centrifuge it, take the supernatant, filter and purify it, and use the sample solution to replace the acetonitrile solution of the fipronil standard in step (2) to perform the operation in step (2). Then calculate the concentration of fipronil in the sample to be tested based on the peak current intensity and the standard working curve.

9. The method for detecting fipronil in cockroach bait according to claim 8, characterized in that: The electrolyte solution mentioned in step (2) is a 0.1 M Britton-Robinson buffer solution with pH=8-10; the stirring mentioned in step (2) refers to stirring for 200-400s.

10. The method for detecting fipronil in cockroach bait according to claim 8, characterized in that: The sample to be tested in step (3) is fipronil cockroach bait. The ultrasonic time is 10-30 min; the centrifugation speed is 6000-12000 rpm and the time is 5-15 min; the sample is filtered through a 0.22 μm microporous membrane, and the pH of the clear liquid is adjusted to 8-10 with 0.1 M Britton-Robinson buffer.

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