A reference electrode for dopamine detection and its preparation method

Abstract

A reference electrode for dopamine detection and its preparation method belong to the field of electrochemistry. In the present invention, carbon cloth is used as the electrode substrate material, silver is deposited by electrochemistry deposition method to obtain a carbon cloth-silver electrode, and then the carbon cloth-silver electrode is chlorinated by electrochemistry chlorination method to prepare a carbon cloth-silver / silver chloride electrode. Finally, a polyvinyl alcohol hydrogel is cast on its surface to obtain a polyvinyl alcohol hydrogel-carbon cloth-silver / silver chloride reference electrode. The reference electrode prepared in the present invention has good conductivity and high softness, and is improved in terms of electrode stability and service life. The reference electrode of the present invention can be used to detect dopamine and obtain good detection results.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemistry, and particularly relates to a reference electrode for dopamine detection and a preparation method thereof. Background Art

[0002] The silver / silver chloride electrode is one of the widely used electrodes in reference electrodes. However, traditional reference electrodes are often prepared using rigid materials. Therefore, the prepared reference electrodes have poor softness and also need to be improved in terms of electrode stability and service life. For example, Zhang Zhifeng [1] Designed a silver / silver chloride reference electrode by sequentially setting a coating and a Nafion film layer on the surface of the silver / silver chloride electrode. Although the coating can alleviate the shedding or dissolution rate of the silver chloride coating on the silver / silver chloride electrode, the prepared reference electrode still uses a rigid material as the housing. In addition, Liu Jingquan et al. [2] Sputtered a metal seed layer on a silicon substrate and then etched it to obtain a silver chloride layer. This electrode has miniaturization, but the substrate is a rigid material with a large hardness.

[0003] Although there have been studies on the preparation of flexible reference electrodes in the prior art, there are significant differences in the preparation methods and material selections. For example, Jin Qinghui et al. [3] Prepared a reference electrode by screen printing using carbon powder ink and silver-silver chloride paste, detected heavy metal ions by stripping voltammetry, and applied it to the sensor field; Sun Jing et al. [4] Prepared a silver / silver chloride reference electrode using PDMS as the substrate, and peeled off the cured PDMS from ITO-Ag to obtain PDMS-Ag as the substrate; Sun Jing et al. [5] Prepared a silver / silver chloride reference electrode using PDMS as the substrate, and carried out chlorination by a chemical method during the preparation process to obtain the reference electrode. The electrodes prepared by the above methods still need to be improved in terms of stability and service life. Summary of the Invention

[0004] To make up for the deficiencies of the electrodes prepared in the prior art, such as large hardness, low stability, and short service life, the present invention discloses a reference electrode for dopamine detection (i.e., a polyvinyl alcohol hydrogel-carbon cloth-silver chloride reference electrode) and a preparation method thereof.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows: Using carbon cloth as the substrate of the reference electrode, depositing silver by electrochemically depositing method to obtain a carbon cloth-silver electrode, then chlorinating the carbon cloth-silver electrode by electrochemically chlorinating method to prepare a carbon cloth-silver / silver chloride electrode, and finally pouring polyvinyl alcohol hydrogel on its surface to obtain a polyvinyl alcohol hydrogel-carbon cloth-silver / silver chloride reference electrode. The specific steps are as follows:

[0006] Step 1: Hydrophilic modification of carbon cloth.

[0007] After cleaning the carbon cloth with deionized water, acetone, and ethanol, soak it in hydrochloric acid and air-dry it at room temperature for later use.

[0008] Step 2: Preparation of the carbon cloth-silver / silver chloride electrode.

[0009] Using a three-electrode system, with the hydrophilically modified carbon cloth as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum wire as the counter electrode, place them in a mixed solution of AgNO3 and NaNO3 and perform chronoamperometry for electrochemical deposition of silver to obtain a carbon cloth-silver electrode. Then, chlorinate the carbon cloth-silver electrode by electrochemical chlorination to prepare a carbon cloth-silver / silver chloride electrode.

[0010] Step 3: Preparation of the polyvinyl alcohol hydrogel-carbon cloth-silver / silver chloride electrode.

[0011] Using a one-step freeze-thaw method, uniformly pour the PVA solution onto the surface of the carbon cloth-silver / silver chloride electrode to obtain a polyvinyl alcohol hydrogel-carbon cloth-silver / silver chloride electrode. Then, soak this electrode in a saturated KCl solution and dry it in a vacuum oven to obtain a polyvinyl alcohol hydrogel-carbon cloth-silver / silver chloride reference electrode.

[0012] In the above method, in step 2, the concentration of AgNO3 is 500 - 800 mmol / L, and the concentration of NaNO3 is 500 - 800 mmol / L. Preferably, the concentration of the AgNO3 solution is 500 mmol / L, and the concentration of the NaNO3 solution is 500 mmol / L.

[0013] In the above method, in step 2, for the chronoamperometric deposition of silver, the deposition potential is -0.2 to -0.5 V, and the deposition time is 500 - 2000 s. Preferably, the deposition potential is -0.2 V, and the deposition time is 1000 s.

[0014] In the above method, in step 2, for electrochemical chlorination, use a 0.1 - 0.3 mol / L hydrochloric acid solution, the chlorination time is 1000 - 2400 s, and the chlorination potential is 230 - 350 mV. Preferably, use a 0.1 mol / L hydrochloric acid solution for electrochemical chlorination, the chlorination time is 1500 s, and the chlorination potential is 300 mV.

[0015] In the above method, in step 3, the specific one-step freeze-thaw method is as follows: use glycerol / water as a co-solvent and tannic acid as a cross-linking agent, and dissolve polyvinyl alcohol (PVA) powder at 90 - 100 °C. After the PVA is completely dissolved, place the dried carbon cloth-silver / silver chloride electrode in a petri dish, uniformly pour the PVA solution onto the electrode surface, and place it at -20 °C for 2 h to obtain a polyvinyl alcohol hydrogel-carbon cloth-silver / silver chloride electrode.

[0016] In the above method, in step 3, the soaking time in the saturated KCl solution is 12 h.

[0017] In the above method, in step 3, the temperature of the vacuum oven is 20°C - 60°C, and the drying time is 2 h - 3 h. Preferably, the temperature of the vacuum oven is 60°C and the drying time is 2 h.

[0018] In the above method, in step 3, the temperature of the vacuum oven is 20°C - 60°C, and the drying time is 2 h - 3 h. Preferably, the temperature of the vacuum oven is 30°C and the drying time is 2.5 h.

[0019] The present invention also protects the application of a polyvinyl alcohol hydrogel - carbon cloth - silver / silver chloride reference electrode in dopamine detection.

[0020] Carbon cloth, also known as carbon fiber cloth, is composed of carbonized oxidized polyacrylonitrile fiber fabric or woven carbon fiber. Carbon cloth has properties such as high strength, strong durability, low density, good electrical conductivity, and good flexibility. Therefore, its application range is very wide. For example, it is used in battery research as the negative electrode for electron acceptance and transfer; it is used in supercapacitor research as the current collector, for electron transmission, and as a structure or part for collecting current; it is used as the substrate material for electrochemistry, and metal oxides are deposited on the carbon cloth to test the performance of metal oxides.

[0021] Hydrogel is a class of extremely hydrophilic three - dimensional network structure gels. Its formation principle is through certain chemical cross - linking and physical cross - linking, so that it can quickly swell in water and store water in this swollen state without dissolving. The water absorption amount is closely related to the cross - linking degree. The higher the cross - linking degree, the lower the water absorption. The synthesized hydrophilic polymer hydrogels include alcohols, acrylic acid and its derivatives (polyacrylic acid, polymethacrylic acid, polyacrylamide), and can be widely applied in industrial, agricultural, medical and other fields.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention uses carbon cloth as the substrate for the first time, which is easy to use, has good electrical conductivity and high softness. The present invention adopts the electrochemical chlorination method, which has better controllability and can more accurately control the chlorination degree and time. The present invention uses a polyvinyl alcohol hydrogel with high softness and excellent ion permeability as the surface film, which can reduce the pollution of the reference electrode, increase the stability of the reference electrode, and improve the service life of the reference electrode. The reference electrode prepared by the present invention has high softness, good electrical conductivity and strong stability, and can be applied to the detection of dopamine in the field of electrochemistry. Description of the Drawings

[0023] Figure 1 : Flow chart of reference electrode preparation and detection;

[0024] Figure 2 : XRD of Ag;

[0025] Figure 3 : SEM of carbon cloth-Ag electrode;

[0026] Figure 4 : XRD of Ag / AgCl electrode;

[0027] Figure 5 : SEM of carbon cloth-Ag / AgCl electrode;

[0028] Figure 6 : Stability test of the reference electrode of the present invention;

[0029] Figure 7 : Electrochemical detection comparison between the reference electrode of the present invention and a commercial hard glass silver / silver chloride reference electrode. Detailed implementation manners

[0030] The present invention is described in detail below through specific embodiments, but the protection scope of the present invention is not limited. Unless otherwise specified, the experimental methods adopted in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can all be obtained from commercial channels.

[0031] Example 1 A preparation method of a polyvinyl alcohol hydrogel-carbon cloth-silver / silver chloride reference electrode, the specific steps are as follows:

[0032] Step 1: Hydrophilic modification of carbon cloth

[0033] Cut the carbon cloth into 1.2 * 4 cm, place it in ionic water and ultrasonicate at 15 °C for 30 min, dry it with nitrogen, then put it into an acetone solution and ultrasonicate for 30 min, dry it with nitrogen, and finally put it into ethanol and ultrasonicate for 30 min, dry it with nitrogen to clean and remove impurities on the surface of the carbon cloth. Immerse the cleaned carbon cloth in 0.1 mol / L hydrochloric acid for 10 hours, and let it dry naturally at room temperature for standby.

[0034] Step 2: Preparation of carbon cloth-silver / silver chloride electrode

[0035] Adopt a three-electrode system, use the chronoamperometry method in an electrochemical workstation, use the hydrophilically modified carbon cloth as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum wire as the counter electrode, and put it into a mixed solution of 500 mmol / L AgNO3 and 500 mmol / L NaNO3 as the electrolyte solution for electrochemical deposition of silver. The deposition potential is -0.2 V, and the deposition time is 1000 s. After electrochemical deposition, nano-sized silver particles are deposited on the surface of the carbon cloth. Figure 2 is the X-ray diffraction pattern of silver. It can be seen from the figure that the deposition of nano-silver on the surface of the carbon cloth is completed. Figure 3 is the scanning electron microscope image of carbon cloth-silver, and its electrode morphology is a granular nanostructure.

[0036] The carbon cloth-silver electrode was chlorinated by electrochemical chlorination method using 0.1 mol / L hydrochloric acid solution. The electrochemical chlorination time was 1500 s and the chlorination potential was 300 mV, to obtain a carbon cloth-silver / silver chloride reference electrode. The preparation process of the electrode working layer is as Figure 1 shown. Figure 4 Figure Figure 1 is the X-ray diffraction pattern of the silver / silver chloride electrode. It can be seen from the figure that there is chlorine element on the nano silver, indicating that the nano silver chlorination is completed. Figure 5 Figure Figure 4 is the scanning electron microscope image of the carbon cloth-silver / silver chloride electrode. It can be seen from the electron microscope image that the electrode morphology is a spherical nano structure with a rough surface, and the electrode surface has a large specific surface area.

[0037] Step 3: Preparation of polyvinyl alcohol hydrogel-carbon cloth-silver / silver chloride electrode

[0038] Pour polyvinyl alcohol hydrogel on the surface of the prepared carbon cloth-silver / silver chloride electrode. First, the hydrogel was prepared by a one-step freeze-thaw method, using glycerol / water as a co-solvent and tannic acid as a cross-linking agent. The PVA powder was dissolved at 90 °C. After the PVA was completely dissolved, the dried carbon cloth-silver / silver chloride electrode was placed in a petri dish, and the PVA solution was evenly poured on the electrode surface and placed at -20 °C for 2 h to obtain a polyvinyl alcohol hydrogel-carbon cloth-silver / silver chloride electrode. Then the polyvinyl alcohol hydrogel-carbon cloth-silver / silver chloride electrode was immersed in saturated KCl solution for 12 h, and then the electrode was transferred to a vacuum oven and dried at 60 °C for 2 h to obtain a polyvinyl alcohol hydrogel-carbon cloth-silver / silver chloride reference electrode.

[0039] Example 2 A preparation method of a polyvinyl alcohol hydrogel-carbon cloth-silver / silver chloride reference electrode, the specific steps are as follows:

[0040] Step 1: Hydrophilic modification of carbon cloth

[0041] The carbon cloth was cut into 1.2 * 4 cm, placed in deionized water and ultrasonically treated at 15 °C for 30 min, dried with nitrogen, then placed in acetone solution and ultrasonically treated for 30 min, dried with nitrogen, and finally placed in ethanol and ultrasonically treated for 30 min, dried with nitrogen to remove impurities on the surface of the carbon cloth. The cleaned carbon cloth was soaked in 0.1 mol / L hydrochloric acid for 10 hours and left to dry naturally at room temperature for later use.

[0042] Step 2: Preparation of carbon cloth-silver / silver chloride electrode

[0043] A three - electrode system was adopted. Using the chronoamperometry method in an electrochemical workstation, the hydrophilically modified carbon cloth was used as the working electrode, the saturated calomel electrode was used as the reference electrode, and the platinum wire was used as the counter electrode. They were placed in a mixed solution of 500 mmol / L AgNO3 and 500 mmol / L NaNO3 as the electrolyte solution for electrochemical deposition of silver. The deposition potential was - 0.2 V and the deposition time was 1000 s. After electrochemical deposition, nano - granular silver was deposited on the surface of the carbon cloth. Figure 2 It is the X - ray diffraction pattern of silver. It can be seen from the figure that the deposition of nano - silver on the surface of the carbon cloth is completed. Figure 3 It is the scanning electron microscopy image of carbon cloth - silver. The electrode morphology is a granular nanostructure.

[0044] The carbon cloth - silver electrode was chlorinated by electrochemical chlorination method using 0.1 mol / L hydrochloric acid solution. The electrochemical chlorination time was 1500 s and the chlorination potential was 300 mV to prepare a carbon cloth - silver / silver chloride reference electrode. The preparation process of the electrode working layer is as Figure 1 shown. Figure 4 It is the X - ray diffraction pattern of the silver / silver chloride electrode. It can be seen from the figure that there is chlorine element on the nano - silver, indicating that the chlorination of nano - silver is completed. Figure 5 It is the scanning electron microscopy image of the carbon cloth - silver / silver chloride electrode. It can be seen from the electron microscopy image that the electrode morphology is a spherical nanostructure with a rough surface, and the electrode surface has a large specific surface area.

[0045] Step 3: Preparation of polyvinyl alcohol hydrogel - carbon cloth - silver / silver chloride electrode

[0046] Polyvinyl alcohol hydrogel was poured on the surface of the prepared carbon cloth - silver / silver chloride electrode. First, the hydrogel was prepared by a one - step freeze - thaw method. Using glycerol / water as the co - solvent and tannic acid as the cross - linker, the PVA powder was dissolved at 90 °C. After the PVA was completely dissolved, the dried carbon cloth - silver / silver chloride electrode was placed in a petri dish, and the PVA solution was evenly poured on the surface of the electrode. It was placed at - 20 °C for 2 h to obtain a polyvinyl alcohol hydrogel - carbon cloth - silver / silver chloride electrode. Then the polyvinyl alcohol hydrogel - carbon cloth - silver / silver chloride electrode was soaked in saturated KCl solution for 12 h, and then the electrode was transferred to a vacuum oven and dried at 30 °C for 2.5 h to obtain a polyvinyl alcohol hydrogel - carbon cloth - silver / silver chloride reference electrode.

[0047] Comparative Example 1: Comparison of the polyvinyl alcohol conductive hydrogel - carbon cloth - silver / silver chloride reference electrode with the existing technology electrode

[0048] Compared with the electrodes of the prior art, the present invention uses carbon cloth as the substrate, which has good electrical conductivity and high flexibility. The present invention prepares the reference electrode by electrochemical chlorination method, which has better controllability and can more accurately control the chlorination degree and time. And the present invention uses polyvinyl alcohol hydrogel as the surface film, which can increase the softness and stability of the electrode while improving the service life of the electrode. Therefore, the reference electrode prepared by the present invention has better performance. The differences between the electrode of the present invention and the prior art are shown in Table 1:

[0049] Table 1: Differences between the electrode of the present invention and the prior art

[0050]

[0051] Example 3 Stability test of polyvinyl alcohol hydrogel-carbon cloth-silver / silver chloride reference electrode

[0052] Taking the polyvinyl alcohol hydrogel-carbon cloth-silver / silver chloride electrode prepared by the present invention as the working electrode, a platinum wire as the counter electrode, and silver / silver chloride as the reference electrode, and placing them in a 3 mol / L KCl aqueous solution for OCP stability test. The test results are as Figure 6 shown, and the results show that the electrode can still maintain a stable state after working for 10,000 s.

[0053] Example 4 Electrochemical detection using polyvinyl alcohol hydrogel-carbon cloth-silver / silver chloride reference electrode

[0054] Taking the polyvinyl alcohol hydrogel-carbon cloth-silver / silver chloride electrode prepared by the present invention and a commercial hard glass silver / silver chloride reference electrode as the reference electrodes respectively, a gold electrode as the working electrode, and a platinum wire as the counter electrode to form a three-electrode system and fix it in an electrochemical workstation. The differential pulse method is used to electrochemically detect dopamine, where the potential is -0.15 to 0.5 V, the concentration of dopamine is 100 μmol / L, and the buffer solution is 0.1 mol / L phosphate buffer solution. The experimental results are as Figure 7 shown. The results show that the polyvinyl alcohol hydrogel-carbon cloth-silver / silver chloride reference electrode prepared by the present invention can provide a stable potential and can be used for detecting dopamine in the electrochemical field to obtain good detection results.

[0055] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

[0056] References

[0057] [1] Zhang Zhifeng. A silver / silver chloride reference electrode [P]. Sichuan Province: CN210155069U, 2020-03-17.

[0058] [2] Liu Jingquan, Wang Longchun, Guo Zhejun, Xi Ye, Cao Jiawei, Wang Zhuo. A method for preparing an in-situ micro silver chloride reference electrode on a chip and the electrode [P]. Shanghai: CN113916954A, 2022-01-11.

[0059] [3] Jin Qinghui, Huang Shanluo, Liu Dan, Jin Yan, Wang Xiaodong, Shao Yun, Zhao Jianlong. A graphene screen-printed electrode for heavy metal ion detection and the method [P]. Shanghai: CN105784804A, 2016-07-20.

[0060] [4] Sun Jing, Wang Qingxiang, Shen Guijun, Lang Mingfei. A preparation method and application of a reusable PDMS-based Ag / AgCl microelectrode [P]. Liaoning Province: CN108195911B, 2020-05-19.

[0061] [5] Sun Jing, Wang Qingxiang, Shen Guijun, Lang Mingfei. A preparation method and application of a reusable PDMS-based Ag / AgCl microelectrode [P]. Liaoning: CN108195911A, 2018-06-22.

Claims

1. A preparation method of a reference electrode for dopamine detection, characterized in that, The specific steps are as follows: Step 1: Hydrophilic modification of carbon cloth The carbon cloth is successively washed with deionized water, acetone, and ethanol, then immersed in hydrochloric acid, and dried at room temperature for standby; Step 2: Preparation of carbon cloth-silver / silver chloride electrode Using a three-electrode system, with the hydrophilically modified carbon cloth as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum wire as the counter electrode, place them in a mixed solution of AgNO3 with a concentration of 500 - 800 mmol / L and NaNO3 with a concentration of 500 - 800 mmol / L, and use chronoamperometry for electrochemical deposition of nano-sized silver particles. Set the deposition potential to -0.2 - -0.5 V and the deposition time to 500 - 2000 s to obtain a carbon cloth-silver electrode. Electrochemically chlorinate the carbon cloth-silver electrode with a 0.1 - 0.3 mol / L hydrochloric acid solution, with a chlorination time of 1000 - 2400 s and a chlorination potential of 230 - 350 mV to prepare a carbon cloth-silver / silver chloride reference electrode; Step 3: Preparation of polyvinyl alcohol hydrogel-carbon cloth-silver / silver chloride reference electrode Using a one-step freeze-thaw method, uniformly pour the PVA solution on the surface of the carbon cloth-silver / silver chloride electrode to obtain a polyvinyl alcohol hydrogel-carbon cloth-silver / silver chloride electrode. Then, immerse this electrode in a saturated KCl solution and dry it in a vacuum oven. The temperature of the vacuum oven is 20°C - 60°C, and the drying time is 2 - 3 h to obtain a polyvinyl alcohol hydrogel-carbon cloth-silver / silver chloride reference electrode. nano-sized particles 2. The method according to claim 1, wherein In Step 2, the concentration of the AgNO3 solution is 500 mmol / L, the concentration of the NaNO3 solution is 500 mmol / L, and chronoamperometry is used for silver deposition. Set the deposition potential to -0.2 V and the deposition time to 1000 s.

3. The method according to claim 1, wherein In Step 2, electrochemical chlorination is carried out with a 0.1 mol / L hydrochloric acid solution, with a chlorination time of 1500 s and a chlorination potential of 300 mV.

4. The method according to claim 1, wherein In Step 3, the immersion time in the saturated KCl solution is 12 h.

5. A reference electrode for dopamine detection, characterized in that, Prepared by using the method described in any one of claims 1 - 4.

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