Preparation method of flexible fishbone-shaped Ag / AgCl reference electrode and application thereof in wearable industry

Abstract

The application relates to a preparation method of a flexible fishbone-shaped Ag / AgCl reference electrode and application of the electrode in the wearable industry, and belongs to the field of electrochemical preparation of reference electrodes. In the application, self-adhesive cloth is used as electrode base material, silver nanowires are uniformly coated on the surface of the cloth, the cloth is placed in a mixed solution of AgNO3 and NaNO3, deposition is carried out by using a chronocoulometry method, and then fishbone-shaped Ag / AgCl reference electrodes are obtained after electrochemical chlorination. Compared with existing reference electrodes, the reference electrode has improved stability, conductivity and service life, can improve the electronic transmission rate, has low manufacturing cost, and can be used for electroencephalogram, electrocardiogram and electromyogram monitoring. The reference electrode uses self-adhesive cloth as the base, can be bonded on various cloths, and does not need to be hydrophilically modified, and is more suitable for preparing wearable medical devices.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemical preparation of reference electrodes, and specifically relates to a preparation method of a flexible fishbone-shaped Ag / AgCl reference electrode and its application in the wearable industry. Background Art

[0002] In recent years, the rapid development of medical equipment has led to the development of medical services in the direction of low cost and high quality. More and more people are pursuing more comfortable and fast health services, which has made wearable devices more thoroughly penetrated into the medical industry. [1] . As the core component of wearable devices, flexible sensors can be used in different products according to the measurement parameters. The functions and performance of wearable devices are inseparable from the support of sensor core technology. In the future, the core technology of wearable flexible sensors will mainly focus on the development and application of new sensor materials, improving the wearability of wearable devices, reducing sensor power consumption, and improving the battery life of wearable devices. The reference electrode is an electrode used as a reference for comparison when measuring the potential of various electrodes. As an indispensable part of flexible sensors, it is crucial to achieve high repeatability, simple structure, stable performance, and cost-effectiveness. The Ag / AgCl reference electrode is composed of porous metal silver covered with silver chloride on the surface and immersed in a Cl-containing - The electrode formed in the solution is one of the commonly used reference electrodes [2] .

[0003] Screen printing [3] and inkjet printing [4] Screen printing is a commonly used method for preparing sheet-type Ag / AgCl reference electrodes. Screen printing utilizes the principle that the mesh holes in the imaged portion of a screen printing plate are permeable to ink, while the mesh holes in the non-imaged portion are impermeable. During printing, the ink on the plate is squeezed by a squeegee and transferred through the holes on the plate to the substrate, completing the printing process. Inkjet printing, on the other hand, is a contactless, pressureless, and plate-free printing and replication technology. It directly sprays nanosized solutions onto flexible or rigid substrates, allowing for the formation of patterned thin films without the need for a mask. Currently, reference electrodes prepared using both methods are composed of silver nanoparticles. These reference electrodes suffer from poor stability, low reproducibility, and a short service life. Furthermore, the performance of the resulting pseudo-Ag / AgCl sheet-type reference electrodes still lags significantly behind that of traditional commercial glass reference electrodes. Key factors influencing reference electrode performance are stability, polarization resistance, reaction rate, reproducibility, and shelf life. At present, the sheet-like pseudo Ag / AgCl reference electrode has not yet shown good performance in the above aspects, and few researchers have conducted in-depth research on the performance of these electrodes. In the previous research of the applicant of the present invention, a flexible reference electrode in the form of nanowire particles was prepared on a PDMS substrate using AgNWs.[5,6] The reference electrode has excellent performance in terms of stability, service life, repeatability and storage period. However, later studies found that the performance of this nanowire granular flexible reference electrode still failed to reach the level of commercial glass Ag / AgCl reference electrode. Summary of the Invention

[0004] To overcome the performance deficiencies of existing sheet-like Ag / AgCl reference electrodes, the present invention discloses a flexible fishbone-shaped Ag / AgCl reference electrode (Fishbone-Ag / AgCl RE) and its applications. The prepared Fishbone-Ag / AgCl RE has high stability, strong conductivity, and a long service life. While improving the electron transfer rate, it has a low production cost and can be used for EEG, EKG, and EMG monitoring.

[0005] The present invention provides a method for preparing Fishbone-Ag / AgCl RE, which comprises the following steps:

[0006] Step 1: Prepare the self-adhesive cloth base material.

[0007] Step 2: Evenly coat the AgNWs solution on the surface of the self-adhesive cloth substrate and place it in a dry environment at room temperature for one day to obtain an AgNWs electrode.

[0008] Step 3: Take the AgNWs electrode obtained in step 2, place it in a mixed solution of AgNO3 and NaNO3 and deposit it using the chronoamperometry method to obtain a Fishbone-Ag electrode after deposition.

[0009] Step 4: After deposition, the surface of the Fishbone-Ag electrode was cleaned with ultrapure water and then dried with N2.

[0010] Step 5: Using the three-electrode system of CHI660E electrochemical system, with Fishbone-Ag electrode as working electrode, Ag / AgCl electrode as reference electrode, and platinum electrode as counter electrode, placed in HCl solution, chlorination was performed using chronoamperometry to prepare Fishbone-Ag / AgCl electrode.

[0011] Step 6: The surface of the Fishbone-Ag / AgCl electrode obtained after chlorination was cleaned three times with deionized water and then blown dry with N2.

[0012] In the above method, in step 1, the self-adhesive cloth base material is a combination of hot melt adhesive mesh and polyester material.

[0013] In the above method, in step 2, the concentration of the AgNWs solution is 1 to 10 mg / mL, preferably, the concentration of the AgNWs solution is 5 mg / mL.

[0014] In the above method, in step 3, the concentration of the AgNO3 solution is 0.005-0.015 moL / L, and the concentration of NaNO3 is 0.05-0.15 moL / L. Preferably, the concentration of the AgNO3 solution is 0.012 moL / L, and the concentration of the NaNO3 solution is 0.12 moL / L.

[0015] In the above method, in step 3, silver is deposited by chronoamperometry, the deposition potential is -0.4 V, and the deposition time is 2000 s.

[0016] In the above method, in step 5, the concentration of the HCl solution is 0.05 to 0.15 mol / L, preferably, the concentration of the HCl solution is 0.12 mol / L.

[0017] In the above method, in step 5, chlorination is performed using chronoamperometry, the chlorination potential is 250 mV higher than the open circuit potential, and the chlorination time is 1600 s.

[0018] The present invention also protects the application of Fishbone-Ag / AgCl RE in the wearable industry, especially in EEG monitoring, ECG monitoring and myoelectric monitoring.

[0019] Beneficial effects: The Fishbone-Ag / AgCl RE disclosed in the present invention has significant improvements in electrode stability, conductivity and service life compared to existing electrodes. It has a low production cost while improving the electron transfer rate and can be used for EEG, ECG and EMG monitoring. The reference electrode prepared by the present invention uses self-adhesive cloth as a substrate, which can be adhered to various fabrics by heating and does not require hydrophilic modification, and is more suitable for the preparation of wearable medical devices. The present invention adopts an electrochemical deposition method to prepare a reference electrode. The method is simple to operate, highly practical, and can be applied to mass production. The present invention prepares a reference electrode with a fishbone-shaped nanostructure for the first time. Since the fishbone-shaped silver nanowires have a thicker diameter, their electron transfer rate will not be affected even after chlorination or slight oxidation, and they have outstanding stability and a longer service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is the SEM image of the fishbone-shaped Ag / AgCl reference electrode;

[0021] Figure 2 SEM images of AgNWs;

[0022] Figure 3 SEM image of AgNWs-Ag / AgCl reference electrode prepared by electrochemical chlorination method;

[0023] Figure 4OCP curves of Fishbone-Ag / AgCl reference electrode and AgNWs-Ag / AgCl reference electrode;

[0024] Figure 5 The OCP curves of Fishbone-Ag / AgCl reference electrode and commercial Ag / AgCl reference electrode are shown in Figure 2.

[0025] Figure 6 is the storage life graph of Fishbone-Ag / AgCl reference electrode;

[0026] Figure 7 Human EEG monitoring graph for sheet-shaped Fishbone-Ag / AgCl reference electrode;

[0027] Figure 8 Conduct human electrocardiogram monitoring for sheet-type Fishbone-Ag / AgCl reference electrodes;

[0028] Figure 9 Figure 3. Human electromyography monitoring using a sheet-like Fishbone-Ag / AgCl reference electrode. DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to the embodiments.

[0030] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods. Unless otherwise specified, the materials, reagents, etc. used in the following examples are all commercially available.

[0031] Example 1

[0032] A method for preparing Fishbone-Ag / AgCl RE, comprising the following steps:

[0033] Step 1: Prepare the self-adhesive fabric base: Prepare a clean, thin polyester fabric, spread the hot melt adhesive film on its surface, and use a pressing device to heat and iron one side of the fabric to make it completely adhered. This base can be sewn onto any fabric.

[0034] Step 2: Prepare AgNWs electrodes: Take an appropriate amount of 5 mg / mL AgNWs solution and evenly apply it on the surface of the self-adhesive cloth substrate. Place it in a dry environment at room temperature for one day.

[0035] Step 3: Place the AgNWs electrode obtained in Step 2 in a mixed solution of 0.012 mol / L AgNO₃ and 0.12 mol / L NaNO₃. Deposit silver using chronoamperometry, setting a constant deposition potential of -0.4 V and a deposition time of 2000 s. This results in a fishbone-Ag electrode.

[0036] Step 4: The Fishbone-Ag electrode obtained after deposition is washed with ultrapure water to remove surface impurities and then blown dry with N2.

[0037] Step 5: Using the three-electrode system of CHI660E electrochemical system, with Fishbone-Ag electrode as working electrode, Ag / AgCl electrode as reference electrode, and platinum electrode as counter electrode, placed in 0.12 mol / L HCl solution, chlorination was performed using chronoamperometry at a potential higher than 250 mV and a chlorination time of 1600 s to prepare Fishbone-Ag / AgCl electrode.

[0038] Step 6: The surface of the Fishbone-Ag / AgCl electrode obtained after chlorination was cleaned three times with deionized water and blown dry with N2.

[0039] Comparative Example 1. Performance comparison of Fishbone-Ag / AgCl RE and existing electrodes.

[0040] The present invention prepares a Fishbone-Ag / AgCl RE based on the original silver nanowire granular reference electrode. The differences between the present electrode and the prior art are shown in Table 1:

[0041] Table 1: Differences between the electrodes of the present invention and the prior art

[0042]

[0043]

[0044] (1) Compare the performance of nanowire (NWs) reference electrode and fishbone reference electrode.

[0045] Figure 2 is the SEM image of the AgNWs reference electrode surface. Figure 2 It can be seen that the surface of the AgNWs reference electrode is very smooth. Figure 3 The SEM image of the AgNWs-Ag / AgCl reference electrode shows that the surface of the reference electrode is relatively rough and has many AgCl nanoparticles attached to it, indicating that the AgNWs-Ag / AgCl reference electrode was successfully prepared. The open circuit potential method was then used to test the OCP of the AgNWs-Ag / AgCl reference electrode and the Fishbone-Ag / AgCl reference electrode to see if the potential difference between the working electrode and the two different reference electrodes is the same when there is no load. The test results are shown in Figure 2. Figure 4The results show that the OCP curve of the AgNWs-Ag / AgCl reference electrode fluctuates greatly, while the OCP curve of the Fishbone-Ag / AgCl reference electrode is smoother, indicating that the Fishbone-Ag / AgCl reference electrode has higher stability. The electrochemical impedance spectroscopy of the two reference electrodes was compared successively.

[11] The results show that the Fishbone-Ag / AgCl reference electrode has a faster charge transfer rate and better electrolyte diffusion capacity. Through the above research, we analyzed that the AgNWs structure has a smaller diameter, and after chlorination, the inner layer of the silver wire is damaged, which affects electron transport and leads to unstable electron transport rate. Fishbone silver nanowires have a thicker diameter, and chlorination occurs only in the nanostructure of the surface layer, without destroying the inner silver structure. Therefore, even after chlorination, the electron transport rate is not affected. Therefore, the performance of the Fishbone-Ag / AgCl reference electrode is far superior to that of the AgNWs-Ag / AgCl reference electrode.

[0046] (2) Compare the performance of Fishbone-Ag / AgCl reference electrode with that of commercial Ag / AgCl reference electrode.

[0047] In order to determine whether the performance of the prepared Fishbone-Ag / AgCl reference electrode has reached the performance standard of a commercial hard glass Ag / AgCl reference electrode, the research group of the applicant of the present invention conducted the following tests.

[0048] First, the stability of the two reference electrodes was compared by OCP test. The test results are as follows: Figure 5 As shown in the figure, the test curves of the Fishbone-Ag / AgCl reference electrode and the commercial hard glass Ag / AgCl reference electrode are very stable, with no significant fluctuations and little difference. This shows that the stability of the flexible sheet-shaped Fishbone-Ag / AgCl reference electrode prepared by the present invention has reached the level of commercial hard glass Ag / AgCl reference electrode and is far superior to other flexible sheet-shaped reference electrodes.

[0049] The service life of the Fishbone-Ag / AgCl reference electrode was tested in succession: in a dark open environment without N2 protection, the stability of the Fishbone-Ag / AgCl electrode after 3 days, 50 days, 100 days and 150 days of storage was tested. The experimental results are as follows Figure 6As shown, the results show that the reference electrode prepared by the present invention can be stored stably for 50 days at a potential difference below 0.002V, and can be stored for 100 days and 150 days at potential differences below 0.003V and 0.006V, respectively. A slight increase in the potential difference does not affect the normal use of the electrode, indicating that the Fishbone-Ag / AgCl reference electrode has a longer storage life. We analyzed that the reason for the superior stability of the Fishbone-Ag / AgCl reference electrode is similar to the above view. The diameter of its fishbone-shaped silver nanowires is thicker. Even if the silver nanowire surface is slightly oxidized, its interior is not affected. The internal Ag can still maintain the conductivity of the reference electrode. Therefore, the Fishbone-Ag / AgCl reference electrode has very outstanding stability, longer service life and storage period.

[0050] (3) The Fishbone-Ag / AgCl reference electrode prepared by electrochemical deposition was compared with the reference electrodes prepared by screen printing and inkjet printing.

[0051] Screen printing cannot guarantee the quality of the reference electrode thin film produced, resulting in a high probability of waste and defective products. Furthermore, this method is not suitable for mass production due to the complex operation procedures. While inkjet printing offers advantages over other thin-film fabrication techniques, such as ease of use, cost-effectiveness, and ease of pattern deposition, it still presents certain technical difficulties. These include limitations in equipment functionality, the tendency for printing precision errors to occur, the limited film drop volume range of the printhead, the increased difficulty in fabrication, and the instability of inkjet and nozzle clogging. Furthermore, most reference electrodes prepared by inkjet and screen printing methods are nanoparticles. The performance of these nanowire-granular Ag / AgCl reference electrodes has yet to reach the level of commercial hard glass Ag / AgCl reference electrodes.

[0052] The present invention uses an electrochemical deposition method to prepare a reference electrode. This method exhibits greater stability and a longer lifespan than reference electrodes prepared using screen printing and inkjet printing. Furthermore, the stability of the Fishbone-Ag / AgCl reference electrode prepared in this invention has reached the level of commercial hard glass Ag / AgCl reference electrodes, demonstrating the practicality of the present invention's technical solution.

[0053] Example 2. Application of a Fishbone-Ag / AgCl reference electrode in EEG monitoring, ECG monitoring, and EMG monitoring.

[0054] The prepared sheet-shaped Fishbone-Ag / AgCl reference electrode is used in human EEG monitoring, ECG monitoring, and myoelectric monitoring:

[0055] The electroencephalogram (EEG) is a graph obtained by amplifying and recording the spontaneous bioelectricity of the brain on the scalp using electronic instruments. It is the spontaneous, rhythmic electrical activity of a group of brain cells recorded by electrodes. It can be used clinically to diagnose epilepsy, sleep disorders, depth of anesthesia, coma, encephalopathy and brain death. There are mainly video EEG, dynamic EEG and conventional EEG, and the corresponding monitoring method is selected according to the patient's condition. Currently, EEG is mainly used for the diagnosis and treatment of epilepsy. It can evaluate the origin of epileptic seizures, the effectiveness of anti-epileptic drugs, and the indications for surgical operations. However, while it plays an important role in diagnosis and treatment, it also has certain limitations, namely sensitivity and specificity. We placed the Fishbone-Ag / AgCl reference electrode on a fixed position on the scalp surface according to the international 10-20 system electrode placement method. A chemical reaction occurred between the ions in the conductive gel and the electrode to form a primary battery, which significantly reduced the contact resistance compared to the traditional electrode resistance. When the resistance is reduced, the signal generated is also more stable, thereby increasing the sensitivity of EEG monitoring. EEG such as Figure 7 shown.

[0056] Electrocardiogram is a graph that uses an electrocardiograph to record the changes in electrical activity of the heart during each cardiac cycle from the body surface, providing a basis for clinical diagnosis, treatment and nursing.

[12] . Currently, the commonly used ECG in clinical practice is 12-lead, which can be used for routine ECG monitoring and 24-hour dynamic ECG monitoring. The chest lead of the ECG is adsorbed on the body surface through the negative pressure of the ECG lead ball to monitor ECG activity. However, during work, we found that as the patient's chest rises and falls with breathing or because the patient is too thin, the lead ball is prone to fall off and affect the ECG wave pattern. Therefore, we use the electrode sheet of the Fishbone-Ag / AgCl reference electrode to replace the lead ball, stick it to the patient, connect it to the ECG machine, and then record ECG changes. This method can effectively prevent the lead ball from falling off. ECG such as Figure 8 shown.

[0057] Surface electromyography is a measurement method that records bioelectric signals from the activity of the adjacent neuromuscular system by attaching electrodes to the surface of the skin. It can be used to evaluate whether muscles are normal, and is of great significance for the diagnosis of the causes of muscle pain, numbness, atrophy or weakness. At present, when measuring surface electromyography, most reference electrodes made of nanosilver / silver chloride are used. This type of reference electrode is relatively expensive and has poor sensitivity. Fishbone-Ag / AgCl reference electrodes have low production costs and high sensitivity, which is more conducive to data collection and disease diagnosis. The research team of the applicant of the present invention applied Fishbone-Ag / AgCl reference electrodes to surface electromyography monitoring, and monitored the electromyographic morphology of the ulnar nerve, tibial nerve, median nerve and common peroneal nerve, such as Figure 9 shown.

[0058] The above embodiments are merely examples and illustrations of the present invention and are not intended to limit the present invention to the scope of the described embodiments. Furthermore, it will be understood by those skilled in the art that the present invention is not limited to the above embodiments and that various variations and modifications may be made based on the teachings of the present invention, all of which fall within the scope of protection claimed by the present invention.

[0059] References

[0060] [1] Zhou Xuesi, Zhong Ronghua, Wang Tianhui. Flexible sensing technology and its application in health care [J]. Military Medicine, 2015, 11(39): 876-880.

[0061] [2] Wang Jinlong, Wang Jia, Jia Honggang, et al. Current status and progress of research and application of Ag / AgCl solid reference electrode [J]. Journal of Chinese Society for Corrosion and Protection, 2013, 2(33): 81-89.

[0062] [3]Cardoso RM,Kalinke C,Rocha RG,et al.Additive-manufactured(3D-printed)electrochemical sensors:A criticalreview[J].Analytica chimica acta,2020,1118:73-91.

[0063] [4] Wei Yunge, Cao Quanxi, Lei Mengbi, et al. Research on the preparation process of all-solid-state Ag / AgCl electrode [J]. Functional Materials, 2013, 3(41): 441-444.

[0064] [5] Sun J, Wang Q, Luo G, et al. A novel flexible Ag / AgCl quasi-reference electrode based on silver nanowires toward ultracomfortable electrophysiology and sensitive electrochemical glucose detection [J]. Journal of Materials Research and Technology, 2020, 9 (6): 13425-13433.

[0065] [6] Sun J, Li Y, Liu Y, et al. Facile fabrication of a flexible by electrode electrodeposition of palladium on silver nanowires forethanol oxidation [J]. International Journal of Hydrogen Energy, 2019, 44(12): 5990-5996.

[0066] [7] Li Gaoying, Liu Ying, Mu Jianlin, et al. Preparation of Ag / AgCl nano-dendritic structures and study of their photocatalytic properties [J] Functional Materials, 2012, 9: 1139-1142. [8] Zhang Qing, Li Ping, Bai Zhenquan, et al. Preparation of Ag / AgCl high-temperature reference electrode [J] Applied Science and Technology, 2005, 6(32): 62-63.

[0067] [9] Ma Qian, Yang Ping, Wu Changliang, et al. A sheet-like Ag / AgCl nanoheterostructure and its preparation method [p] CN201410465915.X.2015-01-28.

[0068]

[10] Sun Jing, Wang Qingxiang, Shen Guijun, et al. Preparation method and application of reusable PDMS-based micro-soft Ag / AgCl electrode [p] CN 108152348B. 2020-05-19.

[0069]

[11] Vicente N, Haro M, Garcia-Belmonte G. New approaches to thelithiation kinetics in reaction-limitedbattery electrodes through electrochemical impedance spectroscopy[J]. Chemical Communications, 2018, 54(9):1025-1040.

[0070]

[12] Wang Meihan, Guo Fei, Meng Zhaohui, et al. Research status of wearable wireless ECG monitors [J]. Biomedical Engineering and Clinic 2006, 4(10): 262-266.

Claims

1. A method for preparing a flexible fishbone-shaped Ag / AgCl reference electrode, characterized in that: The specific steps are as follows: Step 1: Prepare the self-adhesive cloth base material; Step 2: Evenly coat the AgNWs solution on the surface of the self-adhesive cloth substrate and place it in a dry environment at room temperature for one day to obtain the AgNWs electrode; Step 3: Take the AgNWs electrode obtained in step 2 and place it in a mixed solution of AgNO3 and NaNO3 for deposition using chronoamperometry to obtain a Fishbone-Ag electrode; Step 4: After deposition, the surface of the Fishbone-Ag electrode was cleaned with ultrapure water and then dried with N2; Step 5: Using a three-electrode system of a CHI660E electrochemical system, with a Fishbone-Ag electrode as the working electrode, an Ag / AgCl electrode as the reference electrode, and a platinum electrode as the counter electrode, the electrodes were placed in an HCl solution and chlorinated using chronoamperometry to prepare a Fishbone-Ag / AgCl electrode. Step 6: Wash the surface of the Fishbone-Ag / AgCl electrode obtained after chlorination with deionized water three times and blow dry with N2; The self-adhesive fabric described in step 1 is a combination of hot melt adhesive mesh and polyester material; In step 2, the concentration of the AgNWs solution is 1-10 mg / mL; In step 3, the concentration of the AgNO3 solution is 0.005~0.015 mol / L, the concentration of the NaNO3 solution is 0.05~0.15 mol / L, and silver is deposited by chronoamperometry, with a constant deposition potential of -0.4 V and a deposition time of 2000 s; In step 5, the concentration of the HCl solution is 0.05-0.15 mol / L, and chlorination is performed using chronoamperometry, with the chlorination potential set to 250 mV higher than the open circuit potential and the chlorination time being 1600 s.

2. The method according to claim 1, characterized in that In step 2, the concentration of the AgNWs solution was 5 mg / mL.

3. The method according to claim 1, characterized in that In step 3, the concentration of the AgNO3 solution is 0.012 moL / L, and the concentration of the NaNO3 solution is 0.12 moL / L.

4. The method according to claim 1, wherein In step 5, the concentration of the HCl solution is 0.12 mol / L.

5. Application of the electrode prepared by the method described in claim 1 in the wearable industry.

6. The use according to claim 5, characterized in that The electrode is used in EEG monitoring, ECG monitoring and EMG monitoring.

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