An electrochemical sensor and its preparation method and application

Abstract

This invention discloses an electrochemical sensor, its preparation method, and its application. By using DMF to modify the surface of a SnO2 / Gr / GCE electrode, the carbonyl (C=O) and amino (-N(CH3)2) groups in the DMF molecules interact weakly (hydrogen bonding and van der Waals forces) with hydroxyl (-OH) groups on the SnO2 surface or graphene defect sites, effectively reducing the electrode interface resistance and enhancing conductivity. The electrode exhibits an electron transfer kinetic resistance as low as 4.78Ω, making it suitable for the detection of 6-BA in plants or the environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and in particular relates to an electrochemical sensor and a preparation method and application thereof. Background Art

[0002] In recent years, sensor technology has become a crucial tool for improving agricultural production efficiency, reducing agricultural costs, and promoting sustainable agricultural development. It has demonstrated tremendous potential for application in smart agriculture. New sensor technologies can provide more refined and intelligent technical tools and decision-making support for agricultural production, offering more sustainable, efficient, environmentally friendly, and safe solutions to address the challenges facing modern agriculture.

[0003] With the continuous development of various sensing technologies, traditional agricultural production methods are transitioning towards a modernized path of smart agriculture. Smart agriculture relies on advanced technologies such as the Internet of Things, big data, and artificial intelligence. By building intelligent wireless sensor networks (WSNs), it enables real-time monitoring of information such as the agricultural production environment, weather and climate, and crop growth. Therefore, sensors are playing an increasingly important role in smart agriculture. Various sensor nodes and plant wearable devices can be deployed based on their spatial resolution and detection range to collect real-time data such as temperature, humidity, light intensity, and CO2 concentration, and upload this data to the cloud for analysis and processing, thereby enabling fully automated monitoring and control of agricultural information.

[0004] Currently, commonly used methods in agricultural production systems can be used to monitor and assess plant growth characteristics to a certain extent, allowing for the timely detection of crop stress and resource shortages. However, due to their inherent characteristics and limitations, the application of these technologies in agricultural monitoring also faces several problems and challenges.

[0005] 6-benzylaminopurine (6-BA), the first synthetic cytokinin, has been widely used in agricultural production in recent years. 6-BA promotes cell division, accelerates fruit growth, promotes bud formation, and increases fruit set and yield. However, excessive use of 6-BA can irritate and damage the upper respiratory tract, mucous membranes, eyes, and tibia, and can cause symptoms such as anorexia and vomiting. Therefore, there is an urgent need for a rapid, simple, and reliable method to detect 6-BA residues in food and environmental samples.

[0006] Currently, the main methods for determining 6-BA include UV-visible spectrophotometry, high-performance liquid chromatography, enzyme-linked immunosorbent assay (ELISA), surface-enhanced Raman spectroscopy, and fluorescence analysis. However, these methods have many limitations, such as expensive instrumentation, time-consuming experiments, and the requirement for skilled operators. Compared to these methods, electrochemical methods offer advantages such as high sensitivity, rapid response, and low cost, and thus have great application potential. Currently, electrochemical analysis is a promising detection method, attracting widespread attention due to its high sensitivity, short response time, low cost, simple operation, miniaturization, and long service life. However, the modified materials used in electrochemical sensors must possess large surface area, abundant resources, biocompatibility, and excellent electrochemical properties to achieve good electrode conductivity and adsorption of target analytes. Currently, their accuracy and sensitivity are relatively limited. The core performance of electrochemical sensors (such as detection limit, selectivity, and stability) is highly dependent on the accuracy of the electrode. As the key interface between signal conversion and target recognition, electrode accuracy directly determines the adsorption efficiency, electron transfer rate, and specific recognition ability of 6-BA molecules. If the specific surface area of ​​the electrode surface modification material is insufficient or the electrochemical active sites are unevenly distributed, the detection sensitivity will decrease, making it difficult to capture low-concentration 6-BA residues (such as trace pollution in the environment or agricultural products); and the inaccuracy of the electrode structure may cause background current fluctuations, reducing the repeatability and accuracy of the test results, and thus affecting the timely warning of excessive use of 6-BA. Summary of the Invention

[0007] To address these issues, the present invention provides an electrochemical sensor, its preparation method, and its application. By using DMF to modify the surface of a SnO2 / Gr / GCE electrode, the electrode's interfacial resistance is effectively reduced, enhancing its conductivity. The electrode's electron transfer kinetic resistance is as low as 4.78Ω.

[0008] Specifically, the present invention is prepared by the following method:

[0009] (1) Preparation of SnO2 / Gr materials:

[0010] SnCl₄·5H₂O and NaOH were added to an ethanol-water (1:1, volume ratio) mixture and stirred until translucent. Then, polyethylene glycol and graphene were added. Stirring was continued for 1 hour, and the mixture was heated at 180°C for 12 hours. After cooling to room temperature, the precipitate was collected and washed by centrifugation with water and anhydrous ethanol several times, yielding a pure composite material. The mixture was then heated at 60°C for 24 hours. After cooling, the precipitate was collected in a vial for later use.

[0011] Carbon-based materials are combined with semiconductor materials through mechanical mixing (ball milling, ultrasonic dispersion). The collision and shearing between the milling balls and the materials effectively break up carbon-based material and semiconductor agglomerates, improving dispersion uniformity. This also optimizes the composite interface. Mechanical forces promote close contact between the carbon-based material and semiconductor particles, in some cases inducing interfacial chemical bonding. The uniform dispersion of the carbon-based material builds a conductive network (carbon nanotubes bridging semiconductor particles), reducing electrode interface resistance and enhancing conductivity.

[0012] (2) Preparation of modified electrodes

[0013] The glassy carbon electrode was polished to a mirror surface on a cortex containing Al2O3 powder, cleaned, and dried for later use; the SnO2 / Gr material was dispersed in N,N-dimethylformamide (DMF) and ultrasonically treated for 2 h to obtain a suspension, which was then dropped onto the electrode surface, transferred to an infrared drying oven for drying, and cooled to room temperature.

[0014] Furthermore, the mass ratio of the SnCl4·5H2O, NaOH, and ethanol-water (1:1, volume ratio) mixed solution is 1-1.1:1:98.

[0015] Furthermore, the mass ratio of NaOH, polyethylene glycol, and graphene is (5.2-6): (5.2-6):1.

[0016] Furthermore, the concentration of the SnO2 / Gr material in DMF in step (2) is 6 mg / ml.

[0017] By coupling the surface functional groups (-COOH, -OH) of carbon materials with DMF, DMF, a highly polar solvent, effectively disperses SnO2 nanoparticles and graphene sheets, minimizing agglomeration. Its strong solubility enables the SnO2 precursor (SnCl4) to be evenly distributed on the graphene surface, forming a compact heterostructure. The carbonyl (C=O) and amino (-N(CH3)2) groups in DMF molecules interact weakly (hydrogen bonding and van der Waals forces) with hydroxyl (-OH) groups on the SnO2 surface or with graphene defects, promoting interfacial bonding and reducing contact resistance. Furthermore, DMF intercalates between graphene layers, weakening π-π interactions and reducing sheet re-stacking, maintaining a high surface area (up to 800-1200 m² / g) and increasing active site exposure.

[0018] The present invention also provides an electrochemical sensor prepared by the method and application of the electrochemical sensor in 6-BA detection.

[0019] Furthermore, the 6-ba exists in the environment or in plants, and the environment is water or soil.

[0020] The present invention is beneficial in that:

[0021] Modification with DMF significantly enhances the interfacial bonding strength between SnO2 nanoparticles and graphene, reducing phase separation and lowering contact resistance. This also fully exposes active sites, boosting electrochemical reaction efficiency. The accuracy of 6-BA detection in plants is significantly improved compared to unmodified electrodes.

[0022] The DMF-modified SnO2 / Gr composite material has a specific capacity of 1200 mAh / g at 0.1C (pure SnO2 is only 780 mAh / g), and the capacity retention rate after 100 cycles is >85% (unmodified material <60%). The performance improvement is due to enhanced interface bonding and structural stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a scanning electron microscope image of Example 1, Figure 1 (a) is the scanning electron microscope image of Gr; Figure 1 (b) is a scanning electron microscope image of SnO2; Figure 1 (c) is the scanning electron microscope image of SnO2 / Gr; Figure 1 (d) in the figure is a scanning electron microscope image of SnO2 / Gr. DETAILED DESCRIPTION

[0024] The following examples are used to further illustrate the present invention. Their purpose is to illustrate the present invention and should not be construed as limiting the scope of the present invention. Unless otherwise specified, all references are by weight and weight percentage.

[0025] Unless otherwise specified, the raw materials used in the present invention are conventional commercial products; the methods used in the present invention are conventional methods in the art unless otherwise specified.

[0026] The embodiments of the present invention are further described below with reference to a number of embodiments.

[0027] It should be clear that the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0028] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "an", "the" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0029] Example 1

[0030] (1) Preparation of SnO2 / Gr materials:

[0031] 0.07012 g of SnCl₄·5H₂O and 0.0625 g of NaOH were added to 6.25 ml of a 1:1 ethanol-water mixture. The mixture was stirred vigorously on a magnetic stirrer until translucent. Then, 0.0625 g of polyethylene glycol and 0.012 g of graphene were added. The mixture was stirred at a constant speed on the magnetic stirrer for 1 hour. The mixture was then transferred to a 20 mL Teflon-lined stainless steel autoclave and heated in a forced air drying oven at 180°C for 12 hours. After cooling to room temperature, the precipitate was collected and washed by alternating centrifugation with water and anhydrous ethanol to obtain a pure composite material. The composite material was then transferred to a forced air drying oven and heated at 60°C for 24 hours. After cooling, the precipitate was collected in a vial for later use.

[0032] (2) Preparation of modified electrodes

[0033] The electrode was polished to a mirror finish on a cortex containing 0.3 and 0.5 µm Al2O3 powders. After ultrasonic cleaning, it was rinsed with water and dried for later use. 3 mg of SnO2 / Gr material was dispersed in a small centrifuge tube containing 0.5 mL of N,N-dimethylformamide (DMF) solution and ultrasonicated for 2 h. Then, 2.5 µL of this suspension was added dropwise to the electrode surface, transferred to an infrared drying oven for drying, and cooled to room temperature before use.

[0034] (3) Electrochemical testing

[0035] A three-electrode system was used, with SnO2 / Gr / GCE as the working electrode, a platinum electrode as the auxiliary electrode, and Ag / AgCl (3 mol / L KCl) as the reference electrode. Cyclic voltammetry (CV), linear sweep voltammetry (LSV), and square wave voltammetry (SWV) were performed on a CHI660E electrochemical workstation. The buffer used was 0.1 mol / L PBS; the electrode test solution was 5 mmol / L potassium ferricyanide solution. The DMF-modified SnO2 / Gr composite exhibited a specific capacity of 1200 mAh / g at 0.1C (compared to 780 mAh / g for pure SnO2). After 100 cycles, the capacity retention was >85% (compared to <60% for the unmodified material). This performance improvement was attributed to enhanced interfacial bonding and structural stability. The specific capacitance reached 450 F / g at a current density of 1 A / g, attributed to the enhanced ion diffusion rate and conductive network.

[0036] Electrochemical impedance spectroscopy (EIS) was used to investigate the electron transfer capabilities of glassy carbon electrode (GCE), SnO2 / GCE, Gr / GCE, and SnO2 / Gr / GCE. The diameter of the semicircle at higher frequencies was related to the electron transfer kinetic resistance (Rct) of the electrode.

[0037] Table 1 Electrode electron transfer kinetic resistance (Rct) values

[0038] GCE <![CDATA[SnO2 / GCE]]> Gr / GCE <![CDATA[SnO2 / Gr / GCE]]> Rct (Ω) 12.44 19.75 7.05 4.78

[0039] The results show that SnO2 / Gr / GCE has better conductivity and is more suitable as an electrode material for electrochemical sensors.

[0040] The constructed SnO2 / Gr / GCE sensor was used to determine 6-BA in bean sprouts. The results are shown in Table 2

[0041] Table 2 Determination of 6-BA content in bean sprouts

[0042] sample Scalar / (μmol / L) Measured amount / (μmol / L) 1 0 - 2 3 3.22 3 6 6.42 4 12 12.01 5 24 24.32 6 48 48.12

[0043] According to the above data, it shows that the sensor has good detection ability and can be used for actual detection.

[0044] Example 2

[0045] (1) Preparation of SnO2 / Gr materials:

[0046] 0.0625 g of SnCl₄·5H₂O and 0.0625 g of NaOH were added to 6.25 ml of a 1:1 ethanol-water mixture. The mixture was stirred vigorously on a magnetic stirrer until translucent. Then, 0.0625 g of polyethylene glycol and 0.0104 g of graphene were added. The mixture was stirred at a constant speed on the magnetic stirrer for 1 hour. The mixture was then transferred to a 20 mL Teflon-lined stainless steel autoclave and heated in a forced air drying oven at 180°C for 12 hours. After cooling to room temperature, the precipitate was collected and washed by alternating centrifugation with water and anhydrous ethanol several times to obtain a pure composite material. The composite material was then transferred to a forced air drying oven and heated at 60°C for 24 hours. After cooling, the precipitate was collected in a vial for later use.

[0047] (2) Preparation of modified electrodes

[0048] The electrode was polished to a mirror finish on a cortex containing 0.3 and 0.5 µm Al2O3 powders. After ultrasonic cleaning, it was rinsed with water and dried for later use. 3 mg of SnO2 / Gr material was dispersed in a small centrifuge tube containing 0.5 mL of N,N-dimethylformamide (DMF) solution and ultrasonicated for 2 h. Then, 2.5 µL of this suspension was added dropwise to the electrode surface, transferred to an infrared drying oven for drying, and cooled to room temperature before use.

[0049] (3) Electrochemical testing

[0050] A three-electrode system was used, with SnO2 / Gr / GCE as the working electrode, a platinum electrode as the auxiliary electrode, and Ag / AgCl (3 mol / L KCl) as the reference electrode. Cyclic voltammetry (CV), linear sweep voltammetry (LSV), and square wave voltammetry (SWV) were performed using a CHI660E electrochemical workstation. The buffer used was 0.1 mol / L PBS, and the electrode test solution was 5 mmol / L potassium ferricyanide solution.

[0051] The electron transfer ability of SnO2 / Gr / GCE was investigated by electrochemical impedance spectroscopy (EIS), and the electrode electron transfer kinetic resistance (Rct) value was 4.9Ω.

[0052] The results show that SnO2 / Gr / GCE has better conductivity and is more suitable as an electrode material for electrochemical sensors.

[0053] Comparative Example 1

[0054] (1) Preparation of SnO2 / Gr materials:

[0055] 0.07012 g of SnCl₄·5H₂O and 0.0625 g of NaOH were added to 6.25 ml of a 1:1 ethanol-water mixture. The mixture was stirred vigorously on a magnetic stirrer until translucent. Then, 0.0625 g of polyethylene glycol and 0.012 g of graphene were added. The mixture was stirred at a constant speed on the magnetic stirrer for 1 hour. The mixture was then transferred to a 20 mL Teflon-lined stainless steel autoclave and heated in a forced air drying oven at 180°C for 12 hours. After cooling to room temperature, the precipitate was collected and washed by alternating centrifugation with water and anhydrous ethanol to obtain a pure composite material. The composite material was then transferred to a forced air drying oven and heated at 60°C for 24 hours. After cooling, the precipitate was collected in a vial for later use.

[0056] (2) Preparation of modified electrodes

[0057] The electrodes were ground and polished to a mirror surface on a cortex containing 0.3 and 0.5 μm Al2O3 powders, ultrasonically cleaned, rinsed with water, and dried for later use.

[0058] (3) Electrochemical testing

[0059] A three-electrode system was used, with SnO2 / Gr / GCE as the working electrode, a platinum electrode as the auxiliary electrode, and Ag / AgCl (3 mol / L KCl) as the reference electrode. Cyclic voltammetry (CV), linear sweep voltammetry (LSV), and square wave voltammetry (SWV) were performed using a CHI660E electrochemical workstation. The buffer used was 0.1 mol / L PBS, and the electrode test solution was 5 mmol / L potassium ferricyanide solution. The electrode's electron transfer kinetic resistance (Rct) value was 6.5Ω.

[0060] The prepared sensor was used to measure 6-BA in bean sprouts. The results are shown in Table 3.

[0061] Table 3 Determination of 6-BA content in bean sprouts

[0062]

[0063] According to the above data, the detection accuracy of the unmodified sensor is weaker than that of Example 1.

[0064] The above embodiments describe in detail the structure, features and effects of the present invention. The above are only preferred embodiments of the present invention. Any changes made in accordance with the concept of the present invention, or modifications to equivalent embodiments with equivalent changes, which do not exceed the scope covered by the specification, should be within the scope of protection of the present invention.

Claims

1. A method for preparing an electrochemical sensor, characterized in that: The following steps are involved: (1) Preparation of SnO2 / Gr material; (2) The glassy carbon electrode was polished to a mirror surface on the cortex containing Al2O3 powder, cleaned, and dried for later use; the SnO2 / Gr material was dispersed in N,N-dimethylformamide (DMF) and ultrasonically treated for 2 h to obtain a suspension, which was then dropped onto the electrode surface, transferred to an infrared drying oven for drying, and cooled to room temperature.

2. The method according to claim 1, characterized in that The SnO2 / Gr material is prepared by adding SnCl4·5H2O and NaOH to an ethanol-water mixed solution with a volume ratio of 1:1, stirring until translucent, adding polyethylene glycol and graphene, continuing stirring for 1 hour, heating at 180°C for 12 hours, cooling to room temperature, collecting the precipitate, washing it with water and anhydrous ethanol alternately by centrifugation to obtain a pure composite material, and then heating it at 60°C for 24 hours.

3. The method according to claim 2, characterized in that The mass ratio of the SnCl4·5H2O, NaOH, and ethanol-water mixture is 1-1.1:1:

98.

4. The method according to claim 2, characterized in that The mass ratio of NaOH, polyethylene glycol and graphene is (5.2-6): (5.2-6):

1.

5. The method according to claim 1, wherein The concentration of the SnO2 / Gr material in DMF in step (2) is 6 mg / ml.

6. An electrochemical sensor prepared by the method of claim 1.

7. Use of the electrochemical sensor according to claim 6 in the detection of 6-BA.

8. The use according to claim 7, characterized in that The 6-BA exists in the environment or in plants, and the environment is water or soil.

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