Molecularly imprinted electrochemical sensor based on chitosan modified ferroferric oxide / carboxylated multi-walled carbon nanotube as well as preparation method and application of molecularly imprinted electrochemical sensor

Abstract

The invention discloses a chitosan modified ferroferric oxide / carboxylated multi-walled carbon nanotube-based molecularly imprinted electrochemical sensor as well as a preparation method and application thereof, and relates to the technical field of electrochemical sensing. The invention aims to solve the problems that the existing method for detecting carbendazim is complicated to operate and high in cost and the traditional sensor is poor in selectivity. The invention discloses a molecularly imprinted electrochemical sensor based on chitosan modified ferroferric oxide / carboxylated multi-walled carbon nanotubes. The molecularly imprinted electrochemical sensor comprises a glassy carbon electrode, and a molecularly imprinted polymer and CS-Fe3O4-CMWCNTs which are modified on the surface of the glassy carbon electrode, the molecularly imprinted polymer is prepared by taking carbendazim as a template molecule, methacrylic acid as a functional monomer, ethylene glycol dimethacrylate as a cross-linking agent and azodiisobutyronitrile as an initiator. The molecularly imprinted electrochemical sensor is applied to detection of carbendazim.

Description

Technical Field

[0001] This invention relates to the field of electrochemical sensing technology, specifically to a molecularly imprinted electrochemical sensor based on chitosan-modified iron tetroxide / carboxylated multi-walled carbon nanotubes, its preparation method, and its application. Background Technology

[0002] Carbendazim (CBZ) is a broad-spectrum and highly effective benzimidazole fungicide widely used in the cultivation of crops and medicinal plants to control fungal diseases such as mold and leaf spot. However, excessive use of CBZ can lead to residues in agricultural products, traditional Chinese medicines, and the environment, posing potential harm to the ecological environment and human health. Therefore, establishing a rapid, accurate, and sensitive method for detecting CBZ residues is of significant practical importance.

[0003] Currently, the main detection methods for CBZ (concentrated cyanide precipitate) include high-performance liquid chromatography (HPLC), liquid chromatography-mass spectrometry (LC-MS), capillary electrophoresis, and fluorescence spectroscopy. While these methods offer high detection accuracy, they suffer from drawbacks such as complex sample pretreatment, expensive equipment, and cumbersome operation, making them unsuitable for rapid on-site detection. Electrochemical sensors, due to their advantages of rapid response, low cost, and ease of miniaturization, have become an ideal choice for on-site detection. However, traditional electrochemical sensors suffer from poor selectivity, and the conductivity and dispersibility of electrode materials can affect detection sensitivity, limiting their application in complex samples.

[0004] Molecularly imprinted polymers (MIPs) are polymeric materials with specific recognition sites, prepared through the interaction between template molecules and functional monomers. The vacancies formed after removing the template can specifically recognize target molecules, significantly improving the selectivity of sensors. Fe3O4 nanoparticles possess good catalytic activity and biocompatibility, but suffer from insufficient conductivity; multi-walled carbon nanotubes (MWCNTs) exhibit excellent conductivity but are prone to aggregation; chitosan (CS) possesses good dispersibility and film-forming ability, which can improve the stability of composite materials. By rationally combining these three materials with the specific recognition function of MIPs, it is hoped that high-performance electrochemical sensors can be constructed, overcoming the technical bottlenecks of traditional detection methods and sensors. Summary of the Invention

[0005] The purpose of this invention is to solve the problems of complex operation, high cost and poor selectivity of existing methods for detecting carbendazim, and to provide a molecularly imprinted electrochemical sensor based on chitosan-modified iron oxide / carboxylated multi-walled carbon nanotubes, its preparation method and application.

[0006] This invention provides a molecularly imprinted electrochemical sensor with high sensitivity, good selectivity, and strong stability for rapid and accurate detection of CBZ.

[0007] A molecularly imprinted electrochemical sensor based on chitosan-modified iron(III) oxide / carboxylated multi-walled carbon nanotubes includes a glassy carbon electrode and a composite material of a molecularly imprinted polymer and CS-Fe3O4-CMWCNTs modified on the surface of the glassy carbon electrode.

[0008] The molecularly imprinted polymer is prepared using carbendazim as a template molecule, methacrylic acid as a functional monomer, ethylene glycol dimethacrylate as a crosslinking agent, and azobisisobutyronitrile as an initiator.

[0009] A method for preparing a molecularly imprinted electrochemical sensor based on chitosan-modified iron(III) oxide / carboxylated multi-walled carbon nanotubes is specifically carried out according to the following steps:

[0010] 1. Polish, wash, and dry the glassy carbon electrode, then use the CV method with a scanning range of -0.2V to 0.6V and a scanning speed of 50mV·s. -1 Under certain conditions, the bare glassy carbon electrode was repeatedly scanned multiple times in a mixed solution containing potassium ferrocyanide, potassium ferricyanide, and potassium chloride. When the difference between the oxidation peak potential and the reduction peak potential of the bare glassy carbon electrode was less than 80 mV, the pretreated glassy carbon electrode was obtained.

[0011] 2. The CS-Fe3O4-CMWCNTs dispersion was drop-coated onto the surface of the pretreated glassy carbon electrode and dried to obtain CS-Fe3O4-CMWCNTs / GCE;

[0012] 3. The prepolymer solution was drop-coated onto the surface of CS-Fe3O4-CMWCNTs / GCE, dried, and then immersed in a mixture of methanol and acetic acid to elute and dry. A molecularly imprinted polymer was formed on the surface of CS-Fe3O4-CMWCNTs, resulting in a molecularly imprinted electrochemical sensor based on chitosan-modified iron(III) oxide / carboxylated multi-walled carbon nanotubes.

[0013] A molecularly imprinted electrochemical sensor based on chitosan-modified iron(III) oxide / carboxylated multi-walled carbon nanotubes is applied in the detection of carbendazim.

[0014] The principle of this invention:

[0015] The principle of this invention lies in constructing a composite nanosubstrate by modifying Fe3O4-carboxylated multi-walled carbon nanotubes (CMWCNTs) with chitosan (CS), integrating the electrochemical catalytic properties of Fe3O4, the high conductivity of CMWCNTs, and the biocompatibility and site immobilization ability of CS to form a synergistic functional system of "conductivity-catalysis-recognition-dispersion". Utilizing molecular imprinting technology, specific recognition holes complementary to the molecular size, configuration, and functional groups of carbendazim (CBZ) are constructed on the composite substrate, enabling selective binding of the target analyte to eliminate interference from complex matrices. The catalytic effect of Fe3O4 and the conductive network of CMWCNTs achieve dual amplification of the electrochemical signal, improving the sensitivity and accuracy of trace CBZ detection. Simultaneously, the detection conditions are optimized for the complex matrix characteristics of traditional Chinese medicinal materials such as Ligusticum chuanxiong, making the sensor adaptable to the detection of CBZ recovery rates in actual samples, overcoming the adaptability bottleneck of laboratory sensors in practical applications, and ultimately achieving high selectivity and high sensitivity detection of trace CBZ in complex matrices and effective application in actual samples.

[0016] Advantages of this invention:

[0017] I. This invention combines Fe3O4, carboxylated multi-walled carbon nanotubes (CMWCNTs), and chitosan (CS) to leverage their synergistic effects: CMWCNTs provide excellent conductivity, Fe3O4 enhances catalytic activity, and CS improves dispersibility and stability, significantly enhancing the electrochemical performance of the electrode; combined with the specific recognition function of MIP, an integrated "conductivity-catalysis-recognition-dispersion" system is constructed to achieve highly sensitive and selective detection of CBZ.

[0018] Second, the sensor of this invention has a wide linear detection range (0.1~50.75μM and 50.75~239.75μM) and a low detection limit (0.0423μM), meeting the requirements of relevant national standards; it also exhibits good repeatability (RSD=1.51%), reproducibility (RSD=1.75%), and long-term stability (maintaining 90.83% of the initial response after 25 days).

[0019] Third, the sensor of this invention has strong anti-interference ability and good selectivity for common pesticides and coexisting substances; the recovery rate in the detection of actual samples of Ligusticum chuanxiong reached 100.16%~103.05%, the detection results are reliable, and it is suitable for rapid on-site detection.

[0020] Fourth, the preparation process of this invention is simple and low in cost. By changing the template molecule, it can be extended to the detection of other pesticides or environmental pollutants, and has broad application prospects in the fields of food safety, environmental monitoring and agricultural product quality control. Attached Figure Description

[0021] Figure 1Images (a)–(f) are SEM images of various composite materials and sensors; images (g)–(h) are TEM images; image (i) is an EDS image; and image (j) is a mapping image. In the images, (a) represents CMWCNTs; (b) represents Fe3O4-CMWCNTs; (c) represents CS-Fe3O4-CMWCNTs; (d) represents NIP / CS-Fe3O4-CMWCNTs; (e) represents MIP / CS-Fe3O4-CMWCNTs (CBZ); (f) represents MIP / CS-Fe3O4-CMWCNTs; (g) is a low-magnification transmission electron microscope image of Fe3O4-CMWCNTs; (h) is a high-magnification transmission electron microscope image of Fe3O4-CMWCNTs; (i) is an EDS image of Fe3O4-CMWCNTs; and (j) is a mapping image of Fe3O4-CMWCNTs.

[0022] Figure 2 The image shows the FT-IR spectrum of the molecularly imprinted polymer prepared in Example 1.

[0023] Figure 3 In Figure (a), the MIP / CS-Fe3O4-CMWCNTs / GCE prepared in Example 1 was analyzed at a scan rate of 10 mV·s. -1 ~100mV·s -1 (a) CV plot at time; (b) CV plot of different types of sensors at a scan rate of 100 mV·s -1 CV diagram at time;

[0024] Figure 4 EIS plots for different sensors;

[0025] Figure 5 The graph shows the effect of different MAA dosages on the sensor response current.

[0026] Figure 6 This is a diagram showing the sensor's anti-interference performance.

[0027] Figure 7 (a) shows the DPV of MIP / CS-Fe3O4-CMWCNTs / GCE prepared in Example 1 in 0.1M PBS solution (pH=5.0) with different concentrations of CBZ; (b) shows the linear relationship between CBZ concentration and oxidation peak response current.

[0028] Figure 8 The graphs show the repeatability, reproducibility, short-term stability, and long-term stability of the sensor prepared in Example 1. Detailed Implementation

[0029] Specific implementation method one: This implementation method is a molecularly imprinted electrochemical sensor based on chitosan-modified iron(III) oxide / carboxylated multi-walled carbon nanotubes, including a glassy carbon electrode and a molecularly imprinted polymer and CS-Fe3O4-CMWCNTs composite material modified on the surface of the glassy carbon electrode.

[0030] The molecularly imprinted polymer is prepared using carbendazim as a template molecule, methacrylic acid as a functional monomer, ethylene glycol dimethacrylate as a crosslinking agent, and azobisisobutyronitrile as an initiator.

[0031] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the preparation method of the CS-Fe3O4-CMWCNTs composite material is completed according to the following steps:

[0032] 1. Disperse multi-walled carbon nanotubes in a mixed solution of sulfuric acid and nitric acid, sonicate, filter, wash until neutral, and dry to obtain CMWCNTs;

[0033] The mass ratio of the multi-walled carbon nanotubes mentioned in step one to the volume ratio of the mixed solution of sulfuric acid and nitric acid is 200 mg: 20 mL.

[0034] 2. FeCl3·6H2O and CH3COONa were dispersed in ethylene glycol and stirred. Then CMWCNTs were added, stirred and ultrasonically dispersed, and then transferred to a hydrothermal reactor for hydrothermal reaction. After the reaction was completed, the mixture was cooled to room temperature, washed, and dried to obtain Fe3O4-CMWCNTs.

[0035] The mass-to-volume ratio of FeCl3·6H2O, CH3COONa, CMWCNTs and ethylene glycol in step two is 0.162g:0.246g:60mg:30mL;

[0036] 3. Disperse Fe3O4-CMWCNTs in a mixture of anhydrous ethanol and a 5 wt% naphthol solution, and sonicate to obtain solution A;

[0037] The mass ratio of Fe3O4-CMWCNTs in step three to the volume ratio of the mixture of anhydrous ethanol and a 5 wt% naphthol solution is 0.6 mg: 500 μL.

[0038] IV. Dissolve chitosan in a 1% (v / v) acetic acid solution to obtain solution B;

[0039] The mass ratio of chitosan to the volume of a 1% acetic acid solution in step four is 1 mg: 0.5 mL.

[0040] 5. Mix solution A and solution B, stir magnetically and sonicate to obtain CS-Fe3O4-CMWCNTs dispersion, and dry to obtain CS-Fe3O4-CMWCNTs composite material;

[0041] In step five, the mass ratio of Fe3O4-CMWCNTs to chitosan in the CS-Fe3O4-CMWCNTs dispersion is 0.6 mg:1 mg. Other steps are the same as in specific embodiment one.

[0042] The 5 wt% naphthol solution described in this embodiment was purchased from Sigma-Aldrich.

[0043] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in the following ways: In step one, the volume ratio of sulfuric acid to nitric acid in the mixed solution of sulfuric acid and nitric acid is 3:1; the mass fraction of sulfuric acid is 98%, and the mass fraction of nitric acid is 68%; the ultrasonic dispersion time in step one is 4-6 hours; the drying is performed under vacuum at 60-70°C for 8-10 hours; the stirring time in step two is 30-60 minutes; the ultrasonic dispersion time in step two is 30-60 minutes; the hydrothermal reaction temperature in step two is 180°C, and the hydrothermal reaction time is 8-10 hours; in step three, the volume ratio of 5 wt% naphthol solution to anhydrous ethanol in the mixed solution of anhydrous ethanol is 20 μL:480 μL; the ultrasonication time in step three is 1-2 hours. Other steps are the same as in Specific Implementation Method One or Two.

[0044] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the preparation method of the molecularly imprinted polymer is specifically carried out according to the following steps:

[0045] Methacrylic acid and N,N-dimethylformamide were mixed to obtain a mixture of methacrylic acid and N,N-dimethylformamide; carbendazim was added to the mixture of methacrylic acid and N,N-dimethylformamide, and the mixture was sonicated and stirred. Then ethylene glycol dimethacrylate and azobisisobutyronitrile were added, and the mixture was sonicated and stirred to obtain a prepolymer solution. After drying, the molecularly imprinted polymer can be obtained.

[0046] The mass-to-volume ratio of carbendazim, methacrylic acid, N,N-dimethylformamide, ethylene glycol dimethacrylate, and azobisisobutyronitrile is 38 mg:(300 μL~700 μL):10 mL:1 mL:33 mg;

[0047] The ultrasound duration is 15-20 minutes; the stirring duration is 15-20 minutes. Other steps are the same as in embodiments one to three.

[0048] Specific Implementation Method 5: This implementation method is a method for preparing a molecularly imprinted electrochemical sensor based on chitosan-modified iron(III) oxide / carboxylated multi-walled carbon nanotubes, specifically completed according to the following steps:

[0049] 1. Polish, wash, and dry the glassy carbon electrode, then use the CV method with a scanning range of -0.2V to 0.6V and a scanning speed of 50mV·s. -1 Under certain conditions, the bare glassy carbon electrode was repeatedly scanned multiple times in a mixed solution containing potassium ferrocyanide, potassium ferricyanide, and potassium chloride. When the difference between the oxidation peak potential and the reduction peak potential of the bare glassy carbon electrode was less than 80 mV, the pretreated glassy carbon electrode was obtained.

[0050] 2. The CS-Fe3O4-CMWCNTs dispersion was drop-coated onto the surface of the pretreated glassy carbon electrode and dried to obtain CS-Fe3O4-CMWCNTs / GCE;

[0051] 3. The prepolymer solution was drop-coated onto the surface of CS-Fe3O4-CMWCNTs / GCE, dried, and then immersed in a mixture of methanol and acetic acid to elute and dry. A molecularly imprinted polymer was formed on the surface of CS-Fe3O4-CMWCNTs, resulting in a molecularly imprinted electrochemical sensor based on chitosan-modified iron(III) oxide / carboxylated multi-walled carbon nanotubes.

[0052] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in the following ways: In Step One, the concentration of potassium ferrocyanide in the mixed solution containing potassium ferrocyanide, potassium ferricyanide, and potassium chloride is 5 mmol / L, the concentration of potassium ferricyanide is 5 mmol / L, the concentration of potassium chloride is 0.1 mol / L, and the solvent is water; in Step Two, the drop volume of the CS-Fe3O4-CMWCNTs dispersion is 6 μL to 14 μL; in Step Three, the volume ratio of methanol to acetic acid in the mixed solution of methanol and acetic acid is 9:1; the elution time in Step Three is 1 h; the drying temperature in Step Three is 60°C, and the drying time is 20 h to 24 h; the drop volume of the prepolymerization solution in Step Three is 10 μL. Other steps are the same as in Specific Implementation Methods One to Five.

[0053] Specific Implementation Method Seven: This implementation method describes the application of the sensor in detecting carbendazim.

[0054] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the sensor is used to detect carbendazim in traditional Chinese medicine, food, soil, or water; the traditional Chinese medicine is Ligusticum chuanxiong. Other steps are the same as in Specific Implementation Methods One to Seven.

[0055] Specific Implementation Method Nine: The difference between this implementation method and Specific Implementation Methods One to Eight is that the method of applying the sensor in the qualitative detection of carbendazim is as follows:

[0056] The sensor was placed in the test solution, and differential pulse voltammetry was used for detection. Compared with the blank solution, the test solution showed a peak value. When carbendazim standard sample was added to the test solution, the peak position remained unchanged, and the peak response current increased with the increase of carbendazim concentration, proving that the test solution contained carbendazim; the detection limit was 0.0423 μmol / L. Other steps were the same as in specific implementation methods one to eight.

[0057] Specific Implementation Method Ten: The difference between this implementation method and Specific Implementation Methods One to Nine is that the method for applying the sensor in the quantitative detection of carbendazim is as follows:

[0058] The sensor was placed in a PBS buffer solution containing carbendazim, and the differential pulse voltammetry was used for detection.

[0059] The PBS buffer solution has a pH of 5.0 and a concentration of 0.1 mol / L.

[0060] When the concentration of carbendazim in the PBS buffer solution is between 0.1 μmol / L and 50.75 μmol / L, there is a linear relationship between the concentration of carbendazim and the peak current response value. PA =0.254C-0.017, R 2 =0.993;

[0061] When the concentration of carbendazim in the PBS buffer solution is between 50.75 μmol / L and 239.75 μmol / L, there is a linear relationship between the concentration of carbendazim and the peak current response value. PA =0.057C+9.826, R 2 =0.995. The other steps are the same as those in Specific Implementation Methods One through Nine.

[0062] The beneficial effects of the present invention are verified using the following embodiments:

[0063] Example 1: A method for preparing a molecularly imprinted electrochemical sensor based on chitosan-modified iron(III) oxide / carboxylated multi-walled carbon nanotubes, specifically completed according to the following steps:

[0064] I. Preparation of CS-Fe3O4-CMWCNTs dispersion:

[0065] ① Disperse 200 mg of multi-walled carbon nanotubes (MWCNTs) in 20 mL of a mixed solution of sulfuric acid and nitric acid, sonicate for 5 h, filter, wash with distilled water until neutral (pH=7), and vacuum dry at 60 °C for 10 h to obtain CMWCNTs;

[0066] In step one, the volume ratio of sulfuric acid to nitric acid in the mixed solution is 3:1; the mass fraction of sulfuric acid is 98%, and the mass fraction of nitric acid is 68%.

[0067] ② Disperse 0.162g FeCl3·6H2O and 0.246g CH3COONa in 30mL ethylene glycol and stir magnetically for 30min at room temperature. Then add 60mg CMWCNTs, stir and sonicate for 30min, and then transfer to a 50mL hydrothermal reactor. React hydrothermally at 180℃ for 10h. After the reaction is completed, cool to room temperature, wash repeatedly with anhydrous ethanol and distilled water, and dry at 60℃ for 10h to obtain Fe3O4-CMWCNTs.

[0068] ③ Disperse 0.6 mg Fe3O4-CMWCNTs in a mixture of 480 μL anhydrous ethanol and 20 μL of 5 wt% naphthol solution (purchased from Sigma-Aldrich), and sonicate for 1 h to obtain solution A;

[0069] ④ Dissolve 1 mg of chitosan (CS) in 0.5 mL of 1% (v / v) acetic acid solution to obtain solution B;

[0070] ⑤ Mix solution A and solution B, stir magnetically and sonicate for 1 hour to obtain CS-Fe3O4-CMWCNTs dispersion;

[0071] II. Preparation of prepolymerization solution:

[0072] Mix 300 μL of methacrylic acid (MAA) with 10 mL of N,N-dimethylformamide to obtain a mixture of methacrylic acid and N,N-dimethylformamide; add 38 mg of carbendazim (CBZ) to the mixture of methacrylic acid (MAA) and N,N-dimethylformamide, sonicate, stir for 15 min, then add 1 mL of ethylene glycol dimethacrylate (EGDMA) and 33 mg of azobisisobutyronitrile (AIBN), sonicate for 20 min, stir for 20 min to obtain a prepolymerization solution;

[0073] 3. Polish the glassy carbon electrode to a mirror finish using 0.3μm and 0.05μm alumina powders sequentially, rinse with distilled water, and air dry. Then immerse the glassy carbon electrode in a mixed solution containing potassium ferrocyanide, potassium ferricyanide, and potassium chloride at 50mV·s. -1The scanning rate was cyclically scanned in the range of -0.2 to 0.6 V until the redox peak potential difference was less than 80 mV, thus obtaining the pretreated glassy carbon electrode.

[0074] In step three, the concentration of potassium ferrocyanide in the mixed solution containing potassium ferrocyanide, potassium ferricyanide, and potassium chloride is 5 mmol / L, the concentration of potassium ferricyanide is 5 mmol / L, the concentration of potassium chloride is 0.1 mol / L, and the solvent is water.

[0075] IV. Drop application:

[0076] ① 12 μL of CS-Fe3O4-CMWCNTs dispersion was drop-coated onto the surface of the pretreated glassy carbon electrode and dried to obtain CS-Fe3O4-CMWCNTs / GCE;

[0077] ② 10 μL of prepolymer solution was drop-coated onto the surface of CS-Fe3O4-CMWCNTs / GCE, dried at 60℃ for 24 h, then immersed in a mixture of methanol and acetic acid for 1 h to elute, rinsed with distilled water and air-dried at room temperature. A molecularly imprinted polymer was formed on the surface of CS-Fe3O4-CMWCNTs, resulting in a molecularly imprinted electrochemical sensor based on chitosan-modified iron(III) oxide / carboxylated multi-walled carbon nanotubes (denoted as MIP / CS-Fe3O4-CMWCNTs / GCE).

[0078] In step four, the volume ratio of methanol to acetic acid in the methanol-acetic acid mixture is 9:1 (v / v).

[0079] Example 2: The difference between this example and Example 1 is as follows: In step two, 100 μL of methacrylic acid (MAA) and 10 mL of N,N-dimethylformamide are mixed to obtain a mixture of methacrylic acid and N,N-dimethylformamide; 38 mg of carbendazim (CBZ) is added to the mixture of methacrylic acid (MAA) and N,N-dimethylformamide, and the mixture is sonicated and stirred for 15 min. Then, 1 mL of ethylene glycol dimethacrylate (EGDMA) and 33 mg of azobisisobutyronitrile (AIBN) are added, and the mixture is sonicated for 20 min and stirred for 20 min to obtain a prepolymerized solution. All other steps and parameters are the same as in Example 1.

[0080] Example 3: The difference between this example and Example 1 is as follows: In step two, 500 μL of methacrylic acid (MAA) and 10 mL of N,N-dimethylformamide are mixed to obtain a mixture of methacrylic acid and N,N-dimethylformamide; 38 mg of carbendazim (CBZ) is added to the mixture of methacrylic acid (MAA) and N,N-dimethylformamide, and the mixture is sonicated and stirred for 15 min. Then, 1 mL of ethylene glycol dimethacrylate (EGDMA) and 33 mg of azobisisobutyronitrile (AIBN) are added, and the mixture is sonicated for 20 min and stirred for 20 min to obtain a prepolymerized solution. All other steps and parameters are the same as in Example 1.

[0081] Example 4: The difference between this example and Example 1 is as follows: In step two, 700 μL of methacrylic acid (MAA) and 10 mL of N,N-dimethylformamide are mixed to obtain a mixture of methacrylic acid and N,N-dimethylformamide; 38 mg of carbendazim (CBZ) is added to the mixture of methacrylic acid (MAA) and N,N-dimethylformamide, and the mixture is sonicated and stirred for 15 min. Then, 1 mL of ethylene glycol dimethacrylate (EGDMA) and 33 mg of azobisisobutyronitrile (AIBN) are added, and the mixture is sonicated for 20 min and stirred for 20 min to obtain a prepolymerized solution. All other steps and parameters are the same as in Example 1.

[0082] Example 5: The difference between this example and Example 1 is as follows: In step two, 900 μL of methacrylic acid (MAA) and 10 mL of N,N-dimethylformamide are mixed to obtain a mixture of methacrylic acid and N,N-dimethylformamide; 38 mg of carbendazim (CBZ) is added to the mixture of methacrylic acid (MAA) and N,N-dimethylformamide, and the mixture is sonicated and stirred for 15 min. Then, 1 mL of ethylene glycol dimethacrylate (EGDMA) and 33 mg of azobisisobutyronitrile (AIBN) are added, and the mixture is sonicated for 20 min and stirred for 20 min to obtain a prepolymerized solution. All other steps and parameters are the same as in Example 1.

[0083] Comparative Example 1: The difference between this example and Example 1 is that elution is omitted in step four ②. That is, in step four ②, 10 μL of prepolymerization solution is drop-coated onto the surface of CS-Fe3O4-CMWCNTs / GCE and dried at 60°C for 24 h to obtain the sensor (denoted as MIP / CS-Fe3O4-CMWCNTs / GCE(CBZ)). Other steps and parameters are the same as in Example 1.

[0084] Comparative Example 2: The difference between this example and Example 1 is that the use of carbendazim (CBZ) is omitted in step two. Specifically, in step two, 300 μL of methacrylic acid (MAA) is mixed with 10 mL of N,N-dimethylformamide to obtain a mixture of methacrylic acid and N,N-dimethylformamide; 1 mL of ethylene glycol dimethacrylate (EGDMA) and 33 mg of azobisisobutyronitrile (AIBN) are added to the mixture of methacrylic acid and N,N-dimethylformamide, and the mixture is sonicated for 20 min and stirred for 20 min to obtain a prepolymerized solution; the sensor obtained in step four is designated as NIP / CS-Fe3O4-CMWCNTs / GCE. All other steps and parameters are the same as in Example 1.

[0085] Comparing with Example 3: The fabrication method of the sensor (MIP / GCE) is specifically completed according to the following steps:

[0086] I. Preparation of prepolymerization solution:

[0087] Mix 300 μL of methacrylic acid (MAA) with 10 mL of N,N-dimethylformamide to obtain a mixture of methacrylic acid and N,N-dimethylformamide; add 38 mg of carbendazim (CBZ) to the mixture of methacrylic acid (MAA) and N,N-dimethylformamide, sonicate, stir for 15 min, then add 1 mL of ethylene glycol dimethacrylate (EGDMA) and 33 mg of azobisisobutyronitrile (AIBN), sonicate for 20 min, stir for 20 min to obtain a prepolymerization solution;

[0088] 2. Polish the glassy carbon electrode to a mirror finish using 0.3μm and 0.05μm alumina powders sequentially, rinse with distilled water, and air dry. Then immerse the glassy carbon electrode in a mixed solution containing potassium ferrocyanide, potassium ferricyanide, and potassium chloride at 50mV·s. -1 The scanning rate was cyclically scanned in the range of -0.2 to 0.6 V until the redox peak potential difference was less than 80 mV, thus obtaining the pretreated glassy carbon electrode.

[0089] In step two, the concentration of potassium ferrocyanide in the mixed solution containing potassium ferrocyanide, potassium ferricyanide, and potassium chloride is 5 mmol / L, the concentration of potassium ferricyanide is 5 mmol / L, the concentration of potassium chloride is 0.1 mol / L, and the solvent is water.

[0090] III. Drop application:

[0091] 10 μL of prepolymer solution was drop-coated onto the surface of the pretreated glassy carbon electrode, dried at 60 °C for 24 h, then immersed in a mixture of methanol and acetic acid for 1 h to wash off, rinsed with distilled water and air-dried at room temperature. A molecularly imprinted polymer was formed on the surface of the glassy carbon electrode, and the sensor (denoted as MIP / GCE) was obtained.

[0092] In step three, the volume ratio of methanol to acetic acid in the methanol-acetic acid mixture is 9:1 (v / v).

[0093] Comparative Example 4: The difference between this example and Comparative Example 3 is that elution is omitted in step three; that is, in step three, 10 μL of prepolymerization solution is drop-coated onto the surface of the pretreated glassy carbon electrode and dried at 60°C for 24 h to obtain the sensor (denoted as MIP / GCE(CBZ)); the volume ratio of methanol to acetic acid in the methanol-acetic acid mixture in step three is 9:1 (v / v). All other steps and parameters are the same as in Comparative Example 3.

[0094] Figure 1 Images (a)–(f) are SEM images of various composite materials and sensors; images (g)–(h) are TEM images; image (i) is an EDS image; and image (j) is a mapping image. In the images, (a) represents CMWCNTs; (b) represents Fe3O4-CMWCNTs; (c) represents CS-Fe3O4-CMWCNTs; (d) represents NIP / CS-Fe3O4-CMWCNTs; (e) represents MIP / CS-Fe3O4-CMWCNTs (CBZ); (f) represents MIP / CS-Fe3O4-CMWCNTs; (g) is a low-magnification transmission electron microscope image of Fe3O4-CMWCNTs; (h) is a high-magnification transmission electron microscope image of Fe3O4-CMWCNTs; (i) is an EDS image of Fe3O4-CMWCNTs; and (j) is a mapping image of Fe3O4-CMWCNTs.

[0095] Figure 1 As shown in (a), MWCNTs treated with carboxylation exhibit a tangled and uniformly dispersed tubular structure. Figure 1 In the middle (b), carboxylated carbon nanotubes (Fe3O4-CMWCNTs) functionalized with iron oxide are shown. It can be seen that a large number of regularly shaped nanospheres are uniformly loaded on the carbon nanotubes, and the loose overall structure of the carbon nanotubes helps to improve the conductivity of the composite material. Figure 1 As can be seen in (c), the addition of chitosan makes the composite material uniformly distributed and presents a smooth film. Figure 1 The surface morphology of (d) and (e) is similar, and the surface of the composite material has a dense and smooth polymer film. Figure 1 Compared with Figure (e), Figure (f) shows that some pores appear on the surface after the template molecule (CBZ) is removed, indicating that the elution operation can expose more imprinted cavities in the polymer film to accommodate the target molecule without changing the structure. Figure 1 Image (g) is a TEM image of Fe3O4-CMWCNTs, which clearly shows that Fe3O4 nanospheres are uniformly embedded in carboxylated carbon nanotubes. Figure 1The image in (h) is a partial TEM image of Fe3O4-CMWCNTs at a higher magnification. The distance between the crystal folds was calculated to be 0.21 nm, which is consistent with the (311) crystal plane of Fe3O4. Figure 1 In the middle (i), the EDS spectrum of Fe3O4-CMWCNTs shows that the material contains three elements: C, O and Fe, proving that Fe3O4-CMWCNTs was successfully composited. Figure 1 The middle (j) diagram is a mapping diagram of Fe3O4-CMWCNTs, which shows that C, O and Fe elements are uniformly loaded in this material.

[0096] Figure 2 The image shows the FT-IR spectrum of the molecularly imprinted polymer prepared in Example 1.

[0097] from Figure 2 It can be determined that: 749cm -1 The peak at 1648 cm⁻¹ is caused by the CH bending vibration of the benzene ring (ortho-disubstituted benzene) of carbendazim. -1 The peak at 2990 cm⁻¹ represents the C=C vibration of the benzene ring in carbendazim, indicating that the MIPs contain carbendazim. -1 and 2957cm -1 The peak at 1731 cm⁻¹ originates from the CH vibration of the crosslinking agent EGDMA. -1 The distinct peak at 1156 cm⁻¹ represents the C=O stretching vibration of EGDMA. -1 The peak at 3445 cm⁻¹ represents the CO stretching vibration of EGDMA, confirming the presence of the crosslinking agent EGDMA in the MIPs. -1 The absorption peak at that point is the OH group of the functional monomer MAA. The smaller peak is attributed to the polymerization reaction between the functional monomer MAA and the template molecule carbendazim due to hydrogen bonding.

[0098] The MIP / CS-Fe3O4-CMWCNTs / GCE prepared in Example 1 was impregnated into a substrate containing [Fe(CN)6]. 3- [Fe(CN)6] 4- The test was conducted in a mixed solution of KCl, see [reference needed]. Figure 3 As shown, the [Fe(CN)6] content 3- [Fe(CN)6] 4- [Fe(CN)6] in KCl solution 3- The concentration was 5 mmol / L, [Fe(CN)6] 4- The concentration of [unspecified substance] is 5 mmol / L, and the concentration of KCl is 0.1 mol / L;

[0099] Figure 3In Figure (a), the MIP / CS-Fe3O4-CMWCNTs / GCE prepared in Example 1 was analyzed at a scan rate of 10 mV·s. -1 ~100mV·s -1 (a) CV plot at time; (b) CV plot of different types of sensors at a scan rate of 100 mV·s -1 CV diagram at time;

[0100] Figure 3 Image (a) shows a clear pair of redox peaks, and the peak current gradually increases with increasing scan rate. The linear equation obtained is I... pa =3.578×10 -4 v 1 / 2 -1.358×10 -5 (R 2 =0.998). Following the Randles-Sevcik equation, the calculated electrochemically active surface area of ​​this electrode is 0.096 cm². 2 Approximately the electrochemically active surface area of ​​a bare glassy carbon electrode (0.052 cm²). 2 The electron transport capability of the composite electrode is 1.8 times that of the bare electrode, indicating that the electron transport capability of the composite electrode is significantly improved compared to the bare electrode. Figure 3 Figure (b) shows that MIP / CS-Fe3O4-CMWCNTs / GCE, MIP / CS-Fe3O4-CMWCNTs / GCE(CBZ), NIP / CS-Fe3O4-CMWCNTs / GCE, MIP / GCE, and MIP / GCE(CBZ) have a concentration of 5 mM [Fe(CN)6]. 3- 5mM [Fe(CN)6] 4- The CV curves for a 10 mL mixed solution of 0.1 M KCl are also shown. The peak current value of MIP / CS-Fe3O4-CMWCNTs / GCE is significantly higher than that of MIP / GCE, indicating that the functionalized material CS-Fe3O4-CMWCNTs can improve the electron transfer rate of the electrode. The dense, non-molecularly imprinted polymer film on the surface of NIP / CS-Fe3O4-CMWCNTs / GCE hinders the transfer ability of probe molecules, resulting in unsatisfactory conductivity. Furthermore, the peak current value of MIP / CS-Fe3O4-CMWCNTs / GCE is larger than that of MIP / CS-Fe3O4-CMWCNTs / GCE (CBZ), indicating that the charge transport ability of the electrode after removing template molecules is significantly enhanced, which also confirms the better elution effect.

[0101] In the presence of [Fe(CN)6] 3- [Fe(CN)6] 4- Different sensors were tested in a mixed solution of KCl, see [link / reference]. Figure 4As shown; the [Fe(CN)6] content 3- [Fe(CN)6] 4- In a mixed solution of Fe(CN)6 and KCl 3- The concentration was 5 mmol / L, [Fe(CN)6] 4- The concentration of [unspecified substance] is 5 mmol / L, and the concentration of KCl is 0.1 mol / L;

[0102] Figure 4 EIS plots for different sensors;

[0103] In EIS spectra, the diameter of the semicircle typically represents the charge transfer resistance (Rct). A smaller semicircle diameter indicates a lower charge transfer resistance, meaning a faster electrochemical reaction rate. (This is illustrated in 10 mL of a solution containing 5 mM [Fe(CN)6]). 3- 5mM [Fe(CN)6] 4- And tests were conducted in a mixed solution of 0.1M KCl. The test results are as follows: Figure 4 As shown, the charge transfer resistance (Rct) from largest to smallest is: MIP / GCE(CBZ) > MIP / GCE > NIP / CS-Fe3O4-CMWCNTs / GCE > MIP / CS-Fe3O4-CMWCNTs / GCE(CBZ) > MIP / CS-Fe3O4-CMWCNTs / GCE. The electrode resistance of the drop-coated CS-Fe3O4-CMWCNTs material is significantly reduced, demonstrating that this material coating enhances charge transfer capability. The electrode resistance after template molecule removal is significantly smaller than that after template molecule removal because the polymer film on the surface of the unremoved composite electrode is too dense, lacking sufficient sites to accommodate probe molecules. Similarly, the dense polymer film on the surface of NIP / CS-Fe3O4-CMWCNTs / GCE also affects probe molecule transport. Furthermore, the resistivity of MIP / CS-Fe3O4-CMWCNTs / GCE is significantly lower than that of other types of electrodes, demonstrating that the modified material and the imprinted cavity within the polymer film work synergistically to enhance the electron transport rate. The EIS test results are consistent with the CV method results described above, proving that this molecularly imprinted composite electrode has excellent electron transport capabilities.

[0104] Figure 5 The graph shows the effect of different MAA dosages on the sensor response current.

[0105] The amount of methacrylic acid (MAA) used in Examples 1-5 was different to study the effect of the amount of the functional monomer methacrylic acid (MAA) on the sensor's performance in detecting carbendazim; the sensors prepared in Examples 1-5 were tested for response changes to 50 μM carbendazim in 0.1 M PBS solution (pH=5.0) (n=5). Figure 5 As shown, when the volume of MAA used is 300 μL, the prepared sensor exhibits the highest response current to carbendazim. When the volume of MAA added is too small, the number of recognition sites formed after the template molecules bind to it is relatively small, resulting in a weak specific recognition effect and thus a low current response value. As the volume of MAA increases, the template molecules can bind sufficiently, forming a significantly larger number of specific recognition sites, leading to a substantial increase in the peak current response value. However, when the volume of MAA is excessive, the current response value gradually decreases. This may be attributed to the dense imprinted membrane formed after the template molecules bind to it, making it difficult to completely remove the template molecules and reducing the number of specifically recognizable imprinted cavities, thus lowering the response current of the composite electrode. Therefore, the molecularly imprinted composite electrode prepared with 300 μL of MAA shows the best results.

[0106] Test the sensor's anti-interference performance;

[0107] The selectivity of this molecularly imprinted composite electrode was tested using the DPV method in PBS solution at pH 5.0. 50 μM carbendazim was used as the analyte, 250 μM of common pesticides such as chlorpyrifos, dinotefuran, benomyl, thiamethoxam, and carbaryl, and 2.5 M glucose, magnesium chloride, cobalt nitrate, potassium chloride, sodium chloride, and zinc chloride were used as interfering substances. The results are as follows: Figure 6 As shown;

[0108] Figure 6 This is a diagram showing the sensor's anti-interference performance.

[0109] Figure 6 CBZ contains only carbendazim; other interfering substances are labeled as: interfering substance + CBZ;

[0110] from Figure 6 It can be seen that the added interfering substances did not cause significant changes in the peak current and peak potential of carbendazim. This result indicates that this molecularly imprinted electrochemical sensor can specifically adsorb carbendazim and has excellent anti-interference effect.

[0111] Figure 7 The DPV diagram and linear relationship diagram of the sensor prepared in Example 1 for detecting CBZ;

[0112] Figure 7(a) shows the DPV of MIP / CS-Fe3O4-CMWCNTs / GCE prepared in Example 1 in 0.1M PBS solution (pH=5.0) with different concentrations of CBZ; (b) shows the linear relationship between CBZ concentration and oxidation peak response current.

[0113] The linear range and detection limit of the MIP / CS-Fe3O4-CMWCNTs / GCE prepared in Example 1 were investigated under optimal conditions in PBS solution at pH 5.0 using DPV technology. Figure 7 As shown in (a), the peak current response increases with increasing carbendazim concentration, but stops increasing after reaching a certain concentration. Figure 7 As shown in (b), a linear relationship exists between the concentration of carbendazim and the peak current response value in the concentration ranges of 0.1–50.75 μM and 50.75–239.75 μmol / L. The linear equation is I. PA =0.254C-0.017(R 2 =0.993), I PA =0.057C+9.826(R 2 =0.995). The detection limit for CBZ (S / N=5) was calculated to be 0.0423 μM. Compared with relevant literature on CBZ detection, the electrode's results show a wide linear range and a low detection limit. The People's Republic of China National Standard (GB2763-2021) stipulates that the maximum residue limit for carbendazim in medicinal plants is 1 mg / kg, which is calculated to be 5.2304 μM. Within the linear range observed in this experiment, it is evident that this sensor can detect carbendazim residues that meet the national standard. The experimental results demonstrate that this sensor has broad research value in the analysis of carbendazim pesticide residues.

[0114] Figure 8 The repeatability, reproducibility, short-term stability, and long-term stability graphs of the sensor prepared in Example 1 are shown.

[0115] The MIP / CS-Fe3O4-CMWCNTs / GCE prepared in Example 1 was tested in 0.1M PBS solution (pH=5.0). (a) Repeatability of detection at 50 μmol / LCBZ; (b) Reproducibility of detection at 50 μmol / LCBZ; (c) Short-term stability at 18 h; (d) Long-term stability at 25 days.

[0116] The repeatability, reproducibility, and stability of MIP / CS-Fe3O4-CMWCNTs / GCE were assessed using the DPV method in PBS solution at pH 5.0. The same sensor was used to repeatedly measure 50 μM carbendazim six times, and the results are as follows: Figure 8As shown in (a), the relative standard deviation (RSD) of the obtained current response value is 1.51%, indicating that the sensor has good repeatability. Six sensors were prepared using the same method, and each was tested for 50 μM carbendazim. Figure 8 (b) The relative standard deviation (RSD) of the six current peak values ​​is 1.75%, demonstrating the good reproducibility of the molecularly imprinted composite electrode. The short-term stability of this electrode over 18 hours was determined using the iterative method, and the experimental results are as follows: Figure 8 As shown in (c), the current response remained stable throughout, indicating good short-term stability of the electrode in PBS buffer. To analyze the long-term stability of this composite electrode, the specific procedure involved measuring the response change of 50 μM carbendazim in 0.1 M PBS (pH=5.0) every five days using the same electrode. The results are shown below. Figure 8 As shown in (d), the peak response current on day 25 was still 90.83% of the initial current, which is greater than 90% of the initial current. The RSD value was 3.24%, indicating that this electrode has ideal long-term stability for the analysis and determination of carbendazim over 25 days.

Claims

1. A molecularly imprinted electrochemical sensor based on chitosan-modified iron(III) oxide / carboxylated multi-walled carbon nanotubes, characterized in that... The sensor includes a glassy carbon electrode and a molecularly imprinted polymer and CS-Fe3O4-CMWCNTs composite material modified on the surface of the glassy carbon electrode; The molecularly imprinted polymer is prepared using carbendazim as a template molecule, methacrylic acid as a functional monomer, ethylene glycol dimethacrylate as a crosslinking agent, and azobisisobutyronitrile as an initiator.

2. The molecularly imprinted electrochemical sensor based on chitosan-modified iron(III) oxide / carboxylated multi-walled carbon nanotubes according to claim 1, characterized in that... The preparation method of the CS-Fe3O4-CMWCNTs composite material is carried out according to the following steps:

1. Disperse multi-walled carbon nanotubes in a mixed solution of sulfuric acid and nitric acid, sonicate, filter, wash until neutral, and dry to obtain CMWCNTs; The mass ratio of the multi-walled carbon nanotubes mentioned in step one to the volume ratio of the mixed solution of sulfuric acid and nitric acid is 200 mg: 20 mL.

2. FeCl3·6H2O and CH3COONa were dispersed in ethylene glycol and stirred. Then CMWCNTs were added, stirred and ultrasonically dispersed, and then transferred to a hydrothermal reactor for hydrothermal reaction. After the reaction was completed, the mixture was cooled to room temperature, washed, and dried to obtain Fe3O4-CMWCNTs. The mass-to-volume ratio of FeCl3·6H2O, CH3COONa, CMWCNTs and ethylene glycol in step two is 0.162g:0.246g:60mg:30mL; 3. Disperse Fe3O4-CMWCNTs in a mixture of anhydrous ethanol and a 5 wt% naphthol solution, and sonicate to obtain solution A; The mass ratio of Fe3O4-CMWCNTs in step three to the volume ratio of the mixture of anhydrous ethanol and a 5 wt% naphthol solution is 0.6 mg: 500 μL. IV. Dissolve chitosan in a 1% (v / v) acetic acid solution to obtain solution B; The mass ratio of chitosan to the volume of a 1% acetic acid solution in step four is 1 mg: 0.5 mL.

5. Mix solution A and solution B, stir magnetically and sonicate to obtain CS-Fe3O4-CMWCNTs dispersion, and dry to obtain CS-Fe3O4-CMWCNTs composite material; In step five, the mass ratio of Fe3O4-CMWCNTs to chitosan in the CS-Fe3O4-CMWCNTs dispersion is 0.6 mg:1 mg.

3. The molecularly imprinted electrochemical sensor based on chitosan-modified iron(III) oxide / carboxylated multi-walled carbon nanotubes according to claim 2, characterized in that... In step one, the volume ratio of sulfuric acid to nitric acid in the mixed solution is 3:1; the mass fraction of sulfuric acid is 98%, and the mass fraction of nitric acid is 68%; the ultrasonic dispersion time in step one is 4-6 hours; the drying is performed under vacuum at 60-70°C for 8-10 hours; the stirring time in step two is 30-60 minutes; the ultrasonic dispersion time in step two is 30-60 minutes; the hydrothermal reaction temperature in step two is 180°C, and the hydrothermal reaction time is 8-10 hours; in step three, the volume ratio of 5 wt% naphthol solution to anhydrous ethanol in the mixed solution is 20 μL:480 μL; the ultrasonication time in step three is 1-2 hours.

4. The molecularly imprinted electrochemical sensor based on chitosan-modified iron(III) oxide / carboxylated multi-walled carbon nanotubes according to claim 1, characterized in that... The preparation method of the molecularly imprinted polymer is specifically carried out according to the following steps: Methacrylic acid and N,N-dimethylformamide were mixed to obtain a mixture of methacrylic acid and N,N-dimethylformamide; carbendazim was added to the mixture of methacrylic acid and N,N-dimethylformamide, and the mixture was sonicated and stirred. Then ethylene glycol dimethacrylate and azobisisobutyronitrile were added, and the mixture was sonicated and stirred to obtain a prepolymer solution. After drying, the molecularly imprinted polymer can be obtained. The mass-to-volume ratio of carbendazim, methacrylic acid, N,N-dimethylformamide, ethylene glycol dimethacrylate, and azobisisobutyronitrile is 38 mg:(300 μL~700 μL):10 mL:1 mL:33 mg; The ultrasound time is 15-20 minutes; the stirring time is 15-20 minutes.

5. The method for preparing a molecularly imprinted electrochemical sensor based on chitosan-modified iron(III) oxide / carboxylated multi-walled carbon nanotubes as described in claim 1, characterized in that... The preparation method is specifically carried out according to the following steps:

1. Polish, wash, and dry the glassy carbon electrode, then use the CV method with a scanning range of -0.2V to 0.6V and a scanning speed of 50mV·s. -1 Under certain conditions, the bare glassy carbon electrode was repeatedly scanned multiple times in a mixed solution containing potassium ferrocyanide, potassium ferricyanide, and potassium chloride. When the difference between the oxidation peak potential and the reduction peak potential of the bare glassy carbon electrode was less than 80 mV, the pretreated glassy carbon electrode was obtained.

2. The CS-Fe3O4-CMWCNTs dispersion was drop-coated onto the surface of the pretreated glassy carbon electrode and dried to obtain CS-Fe3O4-CMWCNTs / GCE; 3. The prepolymer solution was drop-coated onto the surface of CS-Fe3O4-CMWCNTs / GCE, dried, and then immersed in a mixture of methanol and acetic acid to elute and dry. A molecularly imprinted polymer was formed on the surface of CS-Fe3O4-CMWCNTs, resulting in a molecularly imprinted electrochemical sensor based on chitosan-modified iron(III) oxide / carboxylated multi-walled carbon nanotubes.

6. The method for preparing a molecularly imprinted electrochemical sensor based on chitosan-modified iron(III) oxide / carboxylated multi-walled carbon nanotubes according to claim 5, characterized in that... In step one, the concentration of potassium ferrocyanide in the mixed solution containing potassium ferrocyanide, potassium ferricyanide, and potassium chloride is 5 mmol / L, the concentration of potassium ferricyanide is 5 mmol / L, the concentration of potassium chloride is 0.1 mol / L, and the solvent is water; in step two, the drop volume of the CS-Fe3O4-CMWCNTs dispersion is 6 μL to 14 μL; in step three, the volume ratio of methanol to acetic acid in the mixed solution of methanol and acetic acid is 9:1; the elution time in step three is 1 h; the drying temperature in step three is 60 °C, and the drying time is 20 h to 24 h; the drop volume of the prepolymerization solution in step three is 10 μL.

7. The application of the molecularly imprinted electrochemical sensor based on chitosan-modified iron(III) oxide / carboxylated multi-walled carbon nanotubes as described in claim 1, characterized in that... The sensor is used in the detection of carbendazim.

8. The application of the molecularly imprinted electrochemical sensor based on chitosan-modified iron(III) oxide / carboxylated multi-walled carbon nanotubes according to claim 7, characterized in that... The sensor is used to detect carbendazim in traditional Chinese medicine, food, soil, or water; the traditional Chinese medicine is Ligusticum chuanxiong.

9. The application of a molecularly imprinted electrochemical sensor based on chitosan-modified iron(III) oxide / carboxylated multi-walled carbon nanotubes according to claim 7, characterized in that... The method for using the sensor in the qualitative detection of carbendazim is as follows: The sensor was placed in the test solution, and differential pulse voltammetry was used for detection. Compared with the blank solution, the test solution showed a peak value. When carbendazim standard sample was added to the test solution, the peak position remained unchanged. The peak response current increased with the increase of carbendazim concentration, proving that the test solution contained carbendazim. The detection limit was 0.0423 μmol / L.

10. The application of a molecularly imprinted electrochemical sensor based on chitosan-modified iron(III) oxide / carboxylated multi-walled carbon nanotubes according to claim 7, characterized in that... The method for applying the sensor in the quantitative detection of carbendazim is as follows: The sensor was placed in a PBS buffer solution containing carbendazim, and the differential pulse voltammetry was used for detection. The PBS buffer solution has a pH of 5.0 and a concentration of 0.1 mol / L. When the concentration of carbendazim in the PBS buffer solution is between 0.1 μmol / L and 50.75 μmol / L, there is a linear relationship between the concentration of carbendazim and the peak current response value. PA =0.254C-0.017, R 2 =0.993; When the concentration of carbendazim in the PBS buffer solution is between 50.75 μmol / L and 239.75 μmol / L, there is a linear relationship between the concentration of carbendazim and the peak current response value. PA =0.057C+9.826, R 2 =0.995.

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