Electrochemical sensor as well as preparation method and application thereof

Abstract

The invention discloses an electrochemical sensor as well as a preparation method and application thereof. The surface of the SnO2 / Gr / GCE electrode is modified by using DMF, and weak interaction (hydrogen bond and Van der Waals force) between carbonyl (C = O) and amino (-N (CH3) 2) in DMF molecules and hydroxyl (-OH) or graphene defect sites on the surface of SnO2 is utilized, so that the interface resistance of the electrode is effectively reduced, the conductivity is enhanced, the electron transfer dynamic resistance of the electrode is as low as 4.78 omega, and the electrode can be effectively applied to detection of 6-BA in plants or environments.

Description

Technical Field

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

[0002] In recent years, sensor technology has become an important technical means to improve agricultural production efficiency, reduce agricultural production costs, and promote the sustainable development of agriculture, showing great application potential in the field of smart agriculture. The new sensor technology can provide more refined and intelligent technical means and decision-making support for agricultural production, and also provides a more sustainable, efficient, environmentally friendly, and safe solution to address the challenges faced by modern agriculture.

[0003] With the continuous development of various sensing technologies, the traditional agricultural production mode is transforming towards the modern development path of smart agriculture. Smart agriculture relies on various advanced technologies such as the Internet of Things, big data, and artificial intelligence, and realizes the real-time monitoring of information such as the agricultural production environment, meteorological climate, and crop growth status by constructing an intelligent wireless sensor network (WSNs). Therefore, sensors are playing an increasingly important role in smart agriculture. Various sensing nodes and plant wearable devices can be deployed according to their spatial resolution and detection range to collect data such as temperature, humidity, light intensity, and CO2 concentration in real time, and upload them to the cloud for analysis and processing, so as to realize the whole-process automatic monitoring and control of agricultural information.

[0004] At present, the commonly used methods in the agricultural production system can be used to a certain extent to monitor and evaluate plant growth characteristics in order to timely detect crop stress and resource deficiencies. However, due to their own characteristics and limitations, the application of these technologies in the field of agricultural monitoring also faces some problems and challenges.

[0005] 6-Benzylaminopurine (6-BA), as the first artificially synthesized cytokinin, has been widely used in agricultural production in recent years. 6-BA can promote cell division, accelerate fruit growth, promote bud formation, and increase fruit setting rate and yield. However, excessive use of 6-BA can stimulate 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 detection method to detect 6-BA residues in food and environmental samples.

[0006] At present, the main methods for determining 6-BA are UV-visible spectrophotometry, high performance liquid chromatography, enzyme-linked immunosorbent assay, surface enhanced Raman (Raman) spectroscopy and fluorescence analysis. However, these methods have many limitations, such as expensive instruments, time-consuming experiments, and the need for skilled operators. Compared with the above methods, electrochemical methods have the advantages of high sensitivity, fast response speed, low cost, etc., and have great application potential. At present, electrochemical analysis is a detection method with relatively promising application prospects. It has the advantages of high sensitivity, short response time, low cost, simple operation, miniaturization of instruments, and long service life, and has received widespread attention. However, at the same time, the modified materials in electrochemical sensors need to have the characteristics of large specific surface area, rich resources, biocompatibility and excellent electrochemical performance, so as to achieve the conductivity of the electrode and the adsorption of the target analyte. At present, the accuracy and sensitivity are relatively general. 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, the accuracy of the electrode 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 be reduced, making it difficult to capture low-concentration 6-BA residues (such as trace pollution in the environment or agricultural products). 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] In view of the above problems, the present invention provides an electrochemical sensor and its preparation method and application. The surface of the SnO2 / Gr / GCE electrode is modified by using DMF to effectively reduce the electrode interface resistance and enhance the conductivity. The electron transfer kinetic resistance of the electrode is as low as 4.78Ω.

[0008] Specifically, the present invention is prepared by the following method: (1) Preparation of SnO2 / Gr materials: SnCl4·5H2O and NaOH were added to an ethanol-water (1:1, volume ratio) mixed solution, stirred until translucent, polyethylene glycol and graphene were added, and stirred for 1 h, heated at 180 °C for 12 h, cooled to room temperature, and the precipitate was collected and washed alternately with water and anhydrous ethanol by centrifugation to obtain a pure composite material, which was then heated at 60 °C for 24 h. After cooling, it was collected in a medicine bottle for later use.

[0009] The carbon-based material is combined with the semiconductor material through mechanical mixing (ball milling, ultrasonic dispersion). Through the collision and shear of the grinding balls and the materials, the aggregates of the carbon-based material and the semiconductor can be effectively broken, improving the dispersion uniformity. At the same time, the composite interface is optimized, and the mechanical force promotes the formation of close contact between the carbon-based material and the semiconductor particles, and in some cases, interface chemical bonding is induced. The uniform dispersion of the carbon-based material can construct a conductive network (carbon nanotubes bridging semiconductor particles), reducing the electrode interface resistance and enhancing the conductivity.

[0010] (2)Preparation of the modified electrode The glassy carbon electrode is polished to a mirror surface on the cortex containing Al2O3 powder, cleaned, and then dried for later use; the SnO2 / Gr material is dispersed in N,N-dimethylformamide (DMF), and ultrasonic treatment is carried out for 2 h to obtain a suspension. Then, the above suspension is dropped onto the electrode surface and transferred to an infrared drying oven for drying, and cooled to room temperature.

[0011] Further, the mass ratio of the SnCl4·5H2O, NaOH, ethanol-water (1:1, volume ratio) mixture is 1 - 1.1:1:98.

[0012] Further, the mass ratio of the NaOH, polyethylene glycol, and graphene is (5.2 - 6):(5.2 - 6):1.

[0013] Further, the concentration of the SnO2 / Gr material in step (2) in DMF is 6 mg / ml.

[0014] The surface functional groups (-COOH, -OH) of the carbon material are coupled with DMF. As a highly polar solvent, DMF effectively disperses SnO2 nanoparticles and graphene sheets, reducing aggregation. Its strong dissolution ability makes the SnO2 precursor (SnCl4) uniformly distributed on the surface of graphene, forming a tight heterostructure. The carbonyl (C=O) and amino (-N(CH3)2) in the DMF molecule can have weak interactions (hydrogen bonds and van der Waals forces) with the hydroxyl (-OH) on the surface of SnO2 or the defect sites of graphene, promoting the combination of the two-phase interface and reducing the contact resistance. At the same time, DMF is inserted between the graphene layers, weakening the π-π interaction, reducing the re-stacking of the sheets, maintaining a high specific surface area (up to 800 - 1200 m² / g), and increasing the exposure rate of active sites.

[0015] The present invention also provides an electrochemical sensor prepared by the above method and the application of the above electrochemical sensor in the detection of 6-BA.

[0016] Further, the 6-ba exists in the environment or plants, and the environment is water or soil.

[0017] The advantages of the present invention are as follows: DMF modification significantly enhances the interfacial bonding strength between SnO2 nanoparticles and graphene, reduces phase separation, and decreases the contact resistance. Meanwhile, the active sites are fully exposed, improving the efficiency of the electrochemical reaction. Its detection accuracy for 6-BA in plants is significantly improved compared to the unmodified electrode.

[0018] The specific capacity of the DMF-modified SnO2 / Gr composite material reaches 1200 mAh / g at 0.1C (only 780 mAh / g for pure SnO2), and the capacity retention rate is >85% after 100 cycles (the unmodified material <60%). The performance improvement is due to enhanced interfacial bonding and structural stability. Description of the Drawings

[0019] Figure 1 It is the scanning electron microscope image of Example 1. Figure 1 In (a) is the scanning electron microscope image of Gr. Figure 1 In (b) is the scanning electron microscope image of SnO2. Figure 1 In (c) is the scanning electron microscope image of SnO2 / Gr. Figure 1 In (d) is the scanning electron microscope image of SnO2 / Gr. Detailed Embodiments

[0020] The following examples are used to further illustrate the present invention, and their purpose is to explain the present invention rather than to limit the scope of the present invention. Unless otherwise specified, weight parts and weight percentages are used hereinafter.

[0021] The raw materials used in the present invention are all conventional commercially available products unless otherwise specified; the methods used in the present invention are all conventional methods in the art unless otherwise specified.

[0022] The embodiments of the present invention will be further described in multiple examples below.

[0023] It should be clear that the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative work belong to the scope of protection of the present application.

[0024] 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", "the", and "said" used in the embodiments of the present application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0025] Example 1 (1) Preparation of SnO2 / Gr material: 0.07012 g of SnCl4·5H2O and 0.0625 g of NaOH were added to 6.25 ml of ethanol-water (1:1, volume ratio) mixed solution. After being vigorously stirred on a magnetic stirrer until it became translucent, 0.0625 g of polyethylene glycol and 0.012 g of graphene were added. Then, it was continuously stirred evenly on the magnetic stirrer for 1 h, and then transferred to a 20 mL Teflon-lined stainless steel autoclave. Subsequently, it was transferred to a forced-air drying oven and heated at 180 °C for 12 h. After cooling to room temperature, the precipitate was collected and centrifugally washed alternately with water and absolute ethanol for multiple times to obtain a pure composite material. Then, it was transferred to a forced-air drying oven and heated at 60 °C for 24 h. After cooling, it was collected in a medicine bottle for standby.

[0026] (2)Preparation of modified electrode The electrode was polished on a cortex containing 0.3 and 0.5 µm of Al2O3 powder until it became mirror-like. After ultrasonic cleaning and being washed clean with water, it was dried for standby. 3 mg of SnO2 / Gr material was dispersed into a small centrifuge tube containing 0.5 ml of N,N-dimethylformamide (DMF) solution and ultrasonically treated for 2 h. Then, 2.5 µL of the above suspension was dropped onto the electrode surface and transferred to an infrared drying oven for drying. After cooling to room temperature, it was used for standby.

[0027] (3)Electrochemical tests A three-electrode system was adopted, 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. The detection equipment was a CHI660E electrochemical workstation. Cyclic voltammetry (CV), linear sweep voltammetry (LSV), and square wave voltammetry (SWV) were used for testing. The concentration of the buffer solution used was 0.1 mol / L PBS buffer solution; the electrode test solution was a 5 mmol / L potassium ferricyanide solution. The specific capacity of the DMF-modified SnO2 / Gr composite material reached 1200 mAh / g at 0.1C (only 780 mAh / g for pure SnO2). After 100 cycles, the capacity retention rate was >85% (less than 60% for the unmodified material). The performance improvement was due to the 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.

[0028] The electron transfer ability of glassy carbon electrode (GCE), SnO2 / GCE, Gr / GCE, and SnO2 / Gr / GCE was investigated by Electrochemical Impedance Spectroscopy (EIS). The diameter of the semicircle at higher frequencies was related to the electron transfer kinetic resistance (Rct) of the electrode.

[0029] Table 1 Values of the charge transfer resistance (Rct) of the electrode GCE <![CDATA[SnO2 / GCE]]> Gr / GCE <![CDATA[SnO2 / Gr / GCE]]> Rct (Ω) 12.44 19.75 7.05 4.78 The results show that SnO2 / Gr / GCE has better conductivity and is more suitable as the electrode material for electrochemical sensors.

[0030] The constructed SnO2 / Gr / GCE sensor was used to determine 6-BA in mung bean sprouts, and the results are shown in Table 2. Table 2 Determination of 6-BA content in mung bean sprouts Sample Scalar / (μmol / L) Measured quantity / (μmol / L) 1 0 - 2 3 3.22 3 6 6.42 4 12 12.01 5 24 24.32 6 48 48.12 Based on the above data, it shows that the sensor has good detection ability and can be used for actual detection.

[0031] Example 2 (1) Preparation of SnO2 / Gr material: 0.0625 g of SnCl4·5H2O and 0.0625 g of NaOH were added to 6.25 ml of ethanol-water (1:1, volume ratio) mixed solution. After being vigorously stirred on a magnetic stirrer until it became translucent, 0.0625 g of polyethylene glycol and 0.0104 g of graphene were added. Then, it was continuously stirred evenly on the magnetic stirrer for 1 h. Then, it was transferred to a 20 mL Teflon-lined stainless steel autoclave, and then transferred to a blast drying oven and heated at 180 °C for 12 h. After cooling to room temperature, the precipitate was collected and centrifugally washed alternately with water and absolute ethanol for multiple times to obtain a pure composite material. Then, it was transferred to a blast drying oven and heated at 60 °C for 24 h. After cooling, it was collected with a medicine bottle for standby.

[0032] (2) Preparation of the modified electrode The electrode was polished on the cortex containing 0.3 and 0.5 µm of Al2O3 powder until it became mirror-like. After ultrasonic cleaning and being washed clean with water, it was dried for standby. 3 mg of SnO2 / Gr material was dispersed into a small centrifuge tube containing 0.5 ml of N,N-dimethylformamide (DMF) solution and ultrasonically treated for 2 h. Then, 2.5 µL of the above suspension was dropped onto the electrode surface and transferred to an infrared drying oven for drying. After cooling to room temperature, it was for standby.

[0033] (3) Electrochemical test A three - electrode system was adopted. The SnO2 / Gr / GCE was used as the working electrode, the platinum electrode as the auxiliary electrode, and the Ag / AgCl (3 mol / L KCl) as the reference electrode. The detection equipment was a CHI660E electrochemical workstation. Cyclic voltammetry (CV), linear sweep voltammetry (LSV) and square wave voltammetry (SWV) were used for testing. The concentration of the buffer solution used was 0.1 mol / L PBS buffer solution; the electrode test solution was a 5 mmol / L potassium ferricyanide solution.

[0034] The electron transfer ability of SnO2 / Gr / GCE was investigated by Electrochemical Impedance Spectroscopy (EIS), and the value of its charge transfer resistance (Rct) of the electrode was 4.9 Ω.

[0035] The results showed that SnO2 / Gr / GCE had better conductivity and was more suitable as the electrode material for electrochemical sensors.

[0036] Comparative Example 1 (1) Preparation of SnO2 / Gr material: 0.07012 g of SnCl4·5H2O and 0.0625 g of NaOH were added to 6.25 ml of ethanol - water (1:1, volume ratio) mixed solution. After being vigorously stirred on a magnetic stirrer until it became translucent, 0.0625 g of polyethylene glycol and 0.012 g of graphene were added. Then it was continuously stirred evenly on the magnetic stirrer for 1 h, and then transferred to a 20 mL Teflon - lined stainless - steel autoclave. Then it was transferred to a forced - air drying oven and heated at 180 °C for 12 h. After cooling to room temperature, the precipitate was collected and centrifugally washed alternately with water and absolute ethanol for several times to obtain a pure composite material. Then it was transferred to a forced - air drying oven and heated at 60 °C for 24 h. After cooling, it was collected and stored in a medicine bottle for later use.

[0037] (2) Preparation of the modified electrode The electrode was polished on a leather pad containing 0.3 and 0.5 µm of Al2O3 powder until it became mirror - like. After ultrasonic cleaning and being washed clean with water, it was dried for later use.

[0038] (3) Electrochemical testing A three - electrode system was adopted. The SnO2 / Gr / GCE was used as the working electrode, the platinum electrode as the auxiliary electrode, and the Ag / AgCl (3 mol / L KCl) as the reference electrode. The detection equipment was a CHI660E electrochemical workstation. Cyclic voltammetry (CV), linear sweep voltammetry (LSV) and square wave voltammetry (SWV) were used for testing. The concentration of the buffer solution used was 0.1 mol / L PBS buffer solution; the electrode test solution was a 5 mmol / L potassium ferricyanide solution. The value of the electrode electron transfer kinetic resistance (Rct) was 6.5 Ω.

[0039] The prepared sensor was used to determine 6 - BA in mung bean sprouts, and the results are shown in Table 3. Table 3 Determination of 6 - BA Content in Mung Bean Sprouts

[0040] Based on the above data, it shows that the detection accuracy of this unmodified sensor is weaker than that of Example 1.

[0041] The above embodiments have detailed the structure, features and function effects of the present invention. The above are only the preferred embodiments of the present invention. Any changes made according to the concept of the present invention, or equivalent embodiments modified into equivalent changes, still within the scope covered by the specification, shall be within the protection scope of the present invention.

Claims

1. A method for preparing an electrochemical sensor, characterized in that, It includes the following steps: (1) Prepare the SnO2 / Gr material; (2) Polish the glassy carbon electrode on the cortex containing Al2O3 powder until it becomes mirror-like. After cleaning and drying, reserve it for use. Disperse the SnO2 / Gr material into N,N-dimethylformamide (DMF), and perform ultrasonic treatment for 2 h to obtain a suspension. Then, drop the above suspension onto the electrode surface, transfer it to an infrared drying oven for drying, and cool it to room temperature.

2. The method according to claim 1, wherein The method for preparing the SnO2 / Gr material is as follows: Add SnCl4·5H2O and NaOH to an ethanol-water mixed solution with a volume ratio of 1:

1. After stirring until it becomes semi-transparent, add polyethylene glycol and graphene, continue stirring for 1 h, then heat at 180 °C for 12 h. After cooling to room temperature, collect the precipitate and wash it by centrifugation alternately with water and absolute ethanol to obtain a pure composite material, and then heat at 60 °C for 24 h.

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

98.

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

1.

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

6. An electrochemical sensor prepared by the method according to claim 1.

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

8. The application according to claim 7, wherein The 6-ba exists in the environment or plants, and the environment is water or soil.

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