A flexible wearable long-term stable ruthenium oxide pH sensing electrode

Abstract

The application discloses a flexible wearable long-term stable ruthenium oxide pH sensing electrode, and belongs to the technical field of sensing and detection. The ruthenium oxide pH sensing electrode comprises, from bottom to top, a flexible substrate layer, an electrode, a pH sensitive layer and a polymer layer. The pH sensitive layer is composed of ruthenium oxide, conductive fillers and a polymer. The polymer layer is combined to enhance the electrode performance. The structures of the electrode can be processed by a drop coating method or a printing method, avoiding complex and harsh processing procedures. The electrode is suitable for electrode processing on common flexible materials, has good processing consistency, and is expected to realize batch production. In the use process, the electrode is combined with simple and convenient electrode electroactivation treatment, and the electrode shows excellent sensitivity in the detection of the pH in the physiological range, shows good storage and use stability, can meet the application requirement of long-time continuous monitoring of body fluid by a flexible wearable sensor, and has wide practical application potential.

Description

Technical Field

[0001] This invention belongs to the field of sensing and detection technology, and in particular relates to a long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable devices. Background Technology

[0002] With the development of materials science and microelectronics technology, flexible wearable sensors hold promise for non-invasive, continuous detection of biochemical markers in bodily fluids such as sweat and interstitial fluid, providing new tools for disease prevention, diagnosis, and management. Compared to traditional rigid materials, flexible materials such as organic polymers, paper, or fabrics can adapt to a certain degree of curvature and shape changes, exhibiting minimal mechanical mismatch with skin contact surfaces and demonstrating great application potential in wearable bodily fluid detection. However, flexible materials typically have low melting or ignition points, making them unable to withstand harsh conditions such as high temperatures, thus placing higher demands on electrode fabrication processes. Therefore, developing simple, convenient, and mild electrode fabrication processes is crucial for the mass production of flexible wearable sensors.

[0003] pH is a crucial parameter for human health. Changes in body fluid pH can reflect inflammation, organ function, and other conditions, making it an important indicator for wearable body fluid detection. Previous research (Long-Long-term stable pH sensor array with synergistic bilayer structure for 2D real-time mapping in cell culture monitoring, Biosensors and Bioelectronics, 254, 116223) has shown that various metal oxides, including iridium oxide, ruthenium oxide, cerium oxide, titanium dioxide, tin oxide, tantalum pentoxide, and tungsten trioxide, exhibit good pH detection sensitivity. Among them, ruthenium oxide shows the second-best pH response after iridium oxide, and also has lower raw material costs and better long-term stability. Therefore, ruthenium oxide demonstrates good application potential in pH sensing. The literature (Fabrication, potentiometric characterization, and application of screen-printed ruthenium oxide pHelectrodes for water quality testing, Sensor, 21, 16, 5399) discloses a method for preparing ruthenium oxide-modified pH sensing electrodes on alumina substrates by combining screen printing and high-temperature sintering processes; the literature (Application of ruthenium oxide pH sensitive electrode to samples with highredox interference, Sensors and Actuators B: Chemical, 273, 1222-1225) discloses a scheme for depositing ruthenium oxide on the electrode surface using radio frequency magnetron sputtering, which enables pH detection of samples containing reducing agents such as wine and citrus juice; the literature (Gan Weiping, Qin Zhenghui, Liu Hongshi, The effect of the initial pH value of the electrodeposition solution on the electrodeposition preparation of tantalum-based RuO2·nH2O thin films, Materials Reports, 2008, No. 5, 143-145) discloses a method for electrodepositing hydrated ruthenium oxide on the surface of aluminum foil using a constant current method. However, the methods disclosed above all have certain drawbacks. High-temperature sintering can damage flexible materials, making them difficult to use for the preparation of pH sensing electrodes in flexible wearable sensors. Radio frequency magnetron sputtering is costly and complex, making it difficult to achieve mass production. Electrodeposition methods are time-consuming and have low product consistency. Furthermore, thin film electrodes deposited on flexible substrates often have poor mechanical stability and are prone to cracking and delamination.

[0004] Therefore, developing a ruthenium oxide pH sensing electrode that is simple to process, can be fabricated at room temperature, and has a low cost is of great significance for building accurate, sensitive, stable, and reliable flexible wearable sensors, and will help promote the mass production of high-performance devices. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable devices.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] One of the objectives of this invention is to provide a long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearables, comprising, from bottom to top: a flexible substrate layer, an electrode, a pH-sensitive layer, and a polymer layer;

[0008] The pH-sensitive layer is composed of ruthenium oxide, conductive filler, and polymer.

[0009] The pH-sensitive layer is composed of ruthenium oxide, conductive filler, and polymer. Ruthenium oxide serves as the core sensing material, generating a signal response to the pH of the target sample. The conductive filler enhances the conductivity of the pH-sensitive layer, improving the conversion and transmission of electrochemical signals. The polymer enhances the adhesion of the pH-sensitive layer to the electrode surface, improving the stability of the pH electrode. The addition of the polymer layer enhances the adhesion of the pH-sensitive layer to the electrode surface, reducing cracking and delamination during long-term storage and improving the mechanical stability of the electrode. Furthermore, the polymer layer also provides ion selection, offering physical protection for the pH-sensitive layer, improving the specificity and stability of pH detection, and extending the lifespan of the sensing electrode.

[0010] Furthermore, the material of the flexible substrate layer is selected from one of polyimide (PI), polyester (PET), polyetheretherketone (PEEK), polyvinyl fluoride (FEP), paper, and fabric.

[0011] Furthermore, the electrode is selected from one of the following: carbon electrode, gold electrode, platinum electrode, silver electrode, immersion gold electrode, and gold-plated electrode.

[0012] Furthermore, the material of the polymer layer is selected from one or more of perfluorosulfonic acid (Nafion), polyaniline (PANi), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polystyrene sulfonate (PSS), and polypyrrole (PPy).

[0013] The polymer layer can perform ion selection and provide physical protection for the pH-sensitive layer, thereby improving the sensitivity and stability of pH detection and extending the service life of the sensing electrode.

[0014] Furthermore, the solvent is water and an organic solvent, wherein water is used when preparing the ruthenium oxide dispersion and the conductive filler dispersion, and an organic solvent is used when preparing the polymer solution, and the volume ratio of water to organic solvent is (1-10):1.

[0015] Furthermore, the ruthenium oxide has a particle size of 10-500 nm.

[0016] Furthermore, the conductive filler is selected from one or more of carbon black, carbon nanotubes, carbon nanorods, graphene, and gold nanoparticles, with a particle size of 10-100 nm.

[0017] Furthermore, the polymer in the pH-sensitive layer is selected from one or more of perfluorosulfonic acid (Nafion), polyaniline (PANi), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polystyrene sulfonate (PSS), and polypyrrole (PPy).

[0018] The second objective of this invention is to provide a method for preparing a long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable devices, comprising the following steps:

[0019] Ruthenium oxide, conductive filler, and polymer were dissolved in solvent and mixed to obtain pH-sensitive layer ink;

[0020] After cleaning, polishing and drying the electrodes on the flexible substrate, pH-sensitive layer ink is coated onto the electrodes and dried to form a pH-sensitive layer on the electrodes.

[0021] A polymer solution is obtained by dissolving a polymer in an organic solvent, and then coating it onto a pH-sensitive layer to form a polymer layer on top of the pH-sensitive layer, thus obtaining a long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearables.

[0022] This invention provides a long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearables. Using a flexible substrate, the pH-sensitive layer ink is a uniform dispersion composed of solvent, ruthenium oxide, conductive nanoparticles, and a polymer. The pH-sensitive layer is modified on the substrate using a drop-coating or printing process, and a polymer layer is further drop-coated or printed to construct the complete pH sensing electrode. Compared to other ruthenium oxide modification methods, this invention avoids the introduction of complex, demanding, and costly processing techniques such as high-temperature, radio frequency magnetron sputtering, or electropolymerization. By introducing conductive materials and polymer layers, it improves the conductivity, specificity, and stability of the sensing electrode, ensuring accurate and sensitive pH detection. The electrode's analytical characteristics show a Nernst and slightly super-Nernst response.

[0023] Furthermore, in the pH-sensitive layer ink, the mass concentration ratio of ruthenium oxide, conductive filler, and polymer is (10-100):(1-10):1, the concentration of the polymer is 0.1-10 mg / mL, and the solvent is water and an organic solvent with a volume ratio of (1-10):1.

[0024] Furthermore, the coating amount of the pH-sensitive layer ink is 0.1-10 μL / mm. 2 .

[0025] Furthermore, the concentration of the polymer solution is 0.1-10 mg / mL, and the coating amount is 0.1-10 μL / mm. 2 .

[0026] A third objective of this invention is to provide a long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable applications in the field of sensing and detection, such as the accurate detection of changes in the pH of bodily fluids (e.g., sweat or interstitial fluid).

[0027] The fourth objective of this invention is to provide a method for using a flexible, wearable, long-term stable ruthenium oxide pH sensing electrode, comprising the following steps:

[0028] 1) The ruthenium oxide pH sensing electrode and the reference electrode were placed in an electro-activation solution and activated in the electro-activation solution using the open-circuit potential method to obtain the activated electrode;

[0029] 2) The activated electrode was placed in solutions with pH = 4, 6 and 8 in sequence, and the potential of the activated electrode was recorded using the open circuit potential method to obtain the standard formula of "potential-pH".

[0030] 3) Place the activated electrode in the sample to be tested, record the potential of the activated electrode in the solution to be tested using the open circuit potential method, and calculate the pH value of the sample to be tested according to the above standard formula.

[0031] The pH detection principle of the flexible, wearable, long-term stable ruthenium oxide pH sensing electrode provided by this invention is as follows: RuO2 dissociates and adsorbs at the interface with the aqueous solution to form Ru-OH groups. These neutral surface hydroxyl groups will receive or donate a proton depending on the pH of the solution being tested, generating Ru... IV To Ru III The partial conversion of the electrode creates a potential difference between the working electrode and the reference electrode.

[0032] Further, the electroactivation solution is a buffer solution with pH = 2-12. Preferably, it is electroactivated sequentially in phosphate-buffered saline (PBS) with pH = 4, pH = 6 and pH = 8, or sequentially in phosphate-buffered saline (PBS) with pH = 4 and pH = 6.

[0033] Furthermore, the activation time is 10-120 seconds.

[0034] Compared with the prior art, the present invention has the following advantages and technical effects:

[0035] This invention provides a long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable devices. The electrode is fabricated using a drop-coating or printing method, avoiding the stringent, complex, and costly processing required by traditional electrode modification methods. The manufacturing process is simple and efficient, facilitating mass production. It is suitable for processing and modifying electrodes on flexible materials that are not heat-resistant, such as polymers, paper, and fabrics. The fabricated electrode exhibits supernernsian response sensitivity and linearity within the physiological pH range, demonstrating good stability and consistency, and showing broad application prospects in the construction of flexible wearable sensors.

[0036] The electrode preparation method of this invention is simple, efficient, and low in cost. The constructed ruthenium oxide pH sensing electrode is accurate, sensitive, and stable over a long period of time, enabling electrochemical detection of pH. It can be used as a pH sensing electrode for flexible wearable sensors to accurately detect changes in the acidity and alkalinity of body fluids. Attached Figure Description

[0037] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0038] Figure 1 A schematic diagram of the structure of the long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable devices provided by the present invention;

[0039] Figure 2 The flowchart shows the fabrication process of the long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable devices prepared in Example 1 of the present invention.

[0040] Figure 3 The chronoscopic potential (a) and sensitivity (b) of the long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable devices prepared in Example 1 of this invention are shown.

[0041] Figure 4 This refers to the intra-batch (a) and inter-batch (b) consistency of the long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable devices prepared in Example 1 of this invention.

[0042] Figure 5 This describes the change in sensitivity of the long-term stable ruthenium oxide pH sensing electrode prepared in Example 1 of this invention, which is suitable for flexible wearable devices, when stored at room temperature.

[0043] Figure 6 This describes the change in sensitivity of the long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable devices prepared in Example 1 of this invention during accelerated aging testing.

[0044] Figure 7 The long-term stable ruthenium oxide pH sensing electrode prepared in Example 1 of this invention is used without electroactivation and under different electroactivation conditions to show the effect on sensitivity. Detailed Implementation

[0045] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0046] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0047] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0048] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0049] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0050] Figure 1 This is a schematic diagram of the structure of a long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable devices, provided by the present invention.

[0051] This invention provides a method for fabricating a long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable devices (see [link]). Figure 2 The process includes the following steps:

[0052] (1) Formulation of pH-sensitive layer ink

[0053] A) Preparation of pH ink stock solution

[0054] Ruthenium oxide was dispersed in water to obtain a ruthenium oxide dispersion;

[0055] The conductive filler is dispersed in water to obtain a conductive filler dispersion.

[0056] A polymer solution is obtained by dissolving a polymer in an organic solvent.

[0057] B) Formulation of pH-sensitive layer ink

[0058] The obtained ruthenium oxide dispersion, conductive filler dispersion and polymer solution are mixed to obtain pH-sensitive layer ink;

[0059] (2) Electrode cleaning

[0060] Rinse the electrode surface on the flexible substrate with deionized water, polish it with alumina with a particle size of 0.05-0.5μm, sonicate it, rinse the electrode surface with deionized water, and dry it.

[0061] (3) pH-sensitive layer modification

[0062] The pH-sensitive layer ink obtained in step (1) is coated onto the electrode in step (2) and dried to form a pH-sensitive layer on the electrode.

[0063] (4) Polymer layer modification

[0064] The polymer is dissolved in an organic solvent to obtain a polymer solution, which is then coated onto the electrode containing the pH-sensitive layer obtained in step (3). A polymer layer is formed on top of the pH-sensitive layer, thus obtaining a long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable devices.

[0065] In the following embodiments of the present invention, in step (1), the particle size of the ruthenium oxide is 10-500 nm.

[0066] In the following embodiments of the present invention, in step (1), the conductive filler is selected from one or more of carbon black, carbon nanotubes, carbon nanorods, graphene, and gold nanoparticles, with a particle size of 10-100 nm. Preferably, it is carbon black with a particle size of 10-100 nm.

[0067] In the following embodiments of the present invention, in step (1), the polymer is selected from one or more of perfluorosulfonic acid (Nafion), polyaniline (PANi), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polystyrene sulfonate (PSS), and polypyrrole (PPy). Preferably, it is Nafion R-1100 resin.

[0068] In the following embodiments of the present invention, in step (1), the mass concentration ratio of ruthenium oxide, conductive filler, and polymer in the pH-sensitive layer ink is (10-100):(1-10):1, preferably 10:5:1, 10:10:1, or 15:10:1. The concentration of the polymer is 0.1-10 mg / mL. The volume ratio of water to organic solvent is (1-10):1, preferably 7:3 or 1:1.

[0069] The organic solvent used to prepare the polymer solution is selected from one or more of isopropanol, ethanol, methanol, cyclohexane, n-hexane, chloroform, dichloromethane, and dimethyl sulfoxide, preferably isopropanol.

[0070] Controlling the composition and concentration of the pH-sensitive layer ink can improve the conductivity of the sensitive layer while maintaining pH sensitivity, thereby enhancing signal response and detection sensitivity. The addition of polymeric molecules helps reduce cracking and delamination of the pH-sensitive layer during long-term storage, improving electrode stability. Adjusting the ratio of water to organic reagents in the formulation solution can control the diffusion of the ink on the electrode surface, helping to precisely limit the modification range of the pH-sensitive layer and improve processing accuracy.

[0071] In this invention, all liquids are uniformly dispersed by vortexing and ice bath sonication. The pH-sensitive layer ink is sealed and stored, and before use, it is vortexed and sonicated in an ice bath for at least 15 minutes to ensure uniform dispersion.

[0072] In the following embodiments of the present invention, the material of the flexible substrate layer is selected from polyimide (PI), polyester (PET), polyetheretherketone (PEEK), polyvinyl fluoride (FEP), paper, and fabric, preferably PI. The electrode is selected from carbon electrode, gold electrode, platinum electrode, silver electrode, immersion gold electrode, and gold-plated electrode, preferably gold electrode.

[0073] Maintaining a clean electrode surface facilitates subsequent electrode modification, enhances ink adhesion to the electrode surface, and improves the stability and sensitivity of the pH sensing electrode.

[0074] In the following embodiments of the present invention, in step (3), the coating amount of the pH-sensitive layer ink is 0.1-10 μL / mm. 2 Preferably 1 μL / mm 2 or 2μL / mm 2 The coating method can be either drop coating or printing, with drop coating being preferred. Multiple drop coatings or printings can ensure a complete and dense pH-sensitive layer is deposited on the surface of the flexible electrode, ensuring a stable pH response.

[0075] In the following embodiments of the present invention, in step (4), the material of the polymer layer is selected from one or more of perfluorosulfonic acid (Nafion), polyaniline (PANi), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polystyrene sulfonate (PSS), and polypyrrole (PPy). Preferably, it is Nafion R-1100 resin.

[0076] The organic solvent used to prepare the polymer solution is selected from one or more of isopropanol, ethanol, methanol, cyclohexane, n-hexane, chloroform, dichloromethane, and dimethyl sulfoxide, preferably isopropanol.

[0077] In the following embodiments of the present invention, in step (4), the concentration of the polymer solution is 0.1-10 mg / mL, preferably 2.5 mg / mL, 5 mg / mL or 10 mg / mL, and the coating amount is 0.1-10 μL / mm. 2 Preferably 1 μL / mm 2 or 2μL / mm 2 The coating method can be either drop coating or printing, with drop coating being preferred. Multiple drop coatings or printings can be performed to ensure a complete and dense polymer layer is deposited on the electrode surface, ensuring complete coverage of the pH-sensitive layer and achieving good ion selectivity and mechanical protection. As a proton exchange membrane with good mechanical strength and chemical stability on the electrode surface, it helps improve the electrode's sensitivity, specificity, and stability.

[0078] The drying process involved in this invention involves temperatures below 300°C to protect the flexible substrate material.

[0079] Using the above preparation method, a long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearables can be prepared, which includes, from bottom to top: a flexible substrate layer, an electrode, a pH sensitive layer, and a polymer layer;

[0080] The pH-sensitive layer is composed of ruthenium oxide, conductive filler, and polymer.

[0081] The method of using the flexible, wearable, long-term stable ruthenium oxide pH sensing electrode includes the following steps:

[0082] 1) Electrode activation: The ruthenium oxide pH sensing electrode and the reference electrode are placed in an electro-activation solution. The open-circuit potential method is used to activate the electrodes by working in the electro-activation solution for 10-120s (preferably 30s) to obtain the activated electrode.

[0083] 2) Electrode calibration: The activated electrode was placed in solutions with pH = 4, 6 and 8 in sequence. The potential of the activated electrode was recorded using the open circuit potential method to obtain the standard formula of "potential-pH".

[0084] 3) Sample detection: Place the activated electrode in the sample to be tested, use the open circuit potential method to record the potential of the activated electrode in the solution to be tested, and calculate the pH value of the sample to be tested according to the above standard formula.

[0085] In some embodiments of the present invention, the electroactivation solution is a buffer solution with pH = 2-12. Preferably, electroactivation is performed sequentially in phosphate-buffered saline (PBS) with pH = 4, pH = 6 and pH = 8, or sequentially in phosphate-buffered saline (PBS) with pH = 4 and pH = 6.

[0086] Unless otherwise specified, "room temperature" and "normal temperature" in this invention refer to 20-30℃.

[0087] All raw materials used in this invention were purchased from the market.

[0088] The technical solution of the present invention will be further illustrated by the following embodiments.

[0089] Example 1

[0090] A method for fabricating a long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable use includes the following steps:

[0091] (1) Formulation of pH-sensitive layer ink

[0092] A) Preparation of pH ink stock solution

[0093] Ruthenium oxide was dispersed in water to obtain a ruthenium oxide dispersion with a concentration of 50 mg / mL;

[0094] The conductive filler (carbon black) was dispersed in water to obtain a conductive filler dispersion with a concentration of 25 mg / mL.

[0095] The polymer (Nafion R-1100 resin) was dissolved in an organic solvent (isopropanol) to obtain a polymer solution with a concentration of 5 mg / mL.

[0096] B) Formulation of pH-sensitive layer ink

[0097] The obtained ruthenium oxide dispersion with a concentration of 50 mg / mL, conductive filler dispersion with a concentration of 25 mg / mL, and polymer solution with a concentration of 5 mg / mL were mixed. The resulting mixed solution contained ruthenium oxide with a concentration of 25 mg / mL, conductive filler with a concentration of 2.5 mg / mL, and polymer solution with a concentration of 0.5 mg / mL. The volume ratio of water to isopropanol in the solvent was controlled to be 7:3, thus obtaining the pH-sensitive layer ink.

[0098] (2) Electrode cleaning

[0099] The surface of the gold electrode on the flexible PI substrate was rinsed with deionized water, polished with alumina with a particle size of 0.05μm, sonicated for 10 minutes, rinsed with deionized water, and dried in an oven at 60℃.

[0100] (3) pH-sensitive layer modification

[0101] The pH-sensitive layer ink obtained in step (1) was drop-coated onto the electrode surface obtained in step (2) and dried. The ink usage was 1 μL / mm. 2 Dry in a 60℃ oven to ensure that the pH-sensitive layer densely covers the entire electrode surface and forms a pH-sensitive layer on the electrode;

[0102] (4) Polymer layer modification

[0103] A polymer (Nafion R-1100 resin) was dissolved in an organic solvent (isopropanol) to obtain a polymer solution with a concentration of 5 mg / mL. This solution was then drop-coated onto the electrode surface containing the pH-sensitive layer obtained in step (3). The amount of polymer solution used was 1 μL / mm. 2 The ruthenium oxide pH sensing electrode is dried in a 60°C oven to form a polymer layer on top of the pH-sensitive layer, thus obtaining a long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable devices.

[0104] The method for using the long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable devices prepared in this embodiment includes the following steps:

[0105] 1) Electrode activation: The ruthenium oxide pH sensing electrode and the Ag / AgCl reference electrode prepared in Example 1 were placed in electro-activation solutions (phosphate buffer) with pH=4, pH=6 and pH=8 respectively. The open circuit potential method was used to work in each electro-activation solution for 30s to obtain the activated electrode.

[0106] 2) Electrode calibration: The activated electrode obtained in step 1) was placed in phosphate buffer solutions with pH=4, pH=6 and pH=8 in sequence. The potential of the activated electrode was recorded using the open circuit potential method to obtain the standard formula of "potential-pH".

[0107] 3) Sample detection: Place the activated electrode in the sample to be tested, use the open circuit potential method to record the potential of the activated electrode in the solution to be tested, and calculate the pH value of the sample to be tested according to the above standard formula.

[0108] Performance testing

[0109] 1. The long-term stable ruthenium oxide pH sensing electrode prepared in this embodiment can be used to monitor the pH of body fluids such as sweat, saliva, and interstitial fluid in real time within the physiological pH range (pH=4-8), and should be calibrated before use.

[0110] Buffer solutions with pH values ​​of 4, 5, 6, 7, and 8 were prepared in 10 mM PBS. After electroactivating the ruthenium oxide pH sensing electrode, the open-circuit potential of these buffer solutions was measured using the open-circuit potential method. The open-circuit potential decreased as the pH increased. Figure 3 In (a), the specific formula is: E = -63.037pH + 462.26;

[0111] Where E is the open-circuit potential, in mV. The E value is obtained by measuring the ruthenium oxide pH-sensing flexible electrode prepared in this invention, and the pH value is then calculated.

[0112] The results show that the potential obtained by the open-circuit potential method has a linear relationship with the pH value (see [reference]). Figure 3 (b) in the middle, R 2 At around 0.99, the sensitivity reaches -63.037 mV / pH, showing good response performance that slightly exceeds the theoretical Nernst response (59.1 mV / pH).

[0113] 2. The preparation method of the flexible wearable long-term stable ruthenium oxide pH sensing electrode prepared in Example 1 of the present invention is simple and convenient, and has the potential for mass production. Therefore, the consistency of the flexible wearable long-term stable ruthenium oxide pH sensing electrode prepared in Example 1 was tested.

[0114] Electrodes prepared in the same batch (three groups) and electrodes prepared in different batches (three groups) were electroactivated, and then immersed in PBS with pH values ​​of 4, 6, and 8, respectively. The open-circuit potential method was used to measure the open-circuit potential, and the relationship between the open-circuit potential and pH value was calculated and compared. Figure 4 As shown, the ruthenium oxide pH sensing electrode prepared according to the method proposed in this invention has good intra-batch and inter-batch consistency, indicating that the electrode preparation method proposed in this invention is simple and reliable, and is expected to be applied to the mass production of flexible wearable sensors.

[0115] 3. The flexible, wearable, long-term stable ruthenium oxide pH sensing electrode needle prepared in Example 1 of this invention can maintain good detection performance under long-term storage and use conditions. Therefore, the electrode performance over time was tested for two storage and application scenarios: room temperature storage and immersion in body fluids.

[0116] Ruthenium oxide pH sensing electrodes were treated with air exposure and PBS immersion at pH 6.5 at room temperature. Electrodes stored under different conditions were randomly selected at each test time point. After electroactivation, they were immersed in PBS at pH 4, 6, and 8, respectively. The open-circuit potential method was used to measure the open-circuit potential, calculate the relationship between open-circuit potential and pH value, and compare the electrode sensitivity. Figure 5 As shown, under both test scenarios, the ruthenium oxide pH sensing electrode prepared in this embodiment of the invention consistently exhibited good sensitivity during a storage period of up to 40 days, and the sensitivity did not change significantly with changes in storage or application scenarios. This indicates that the flexible wearable long-term stable ruthenium oxide pH sensing electrode has good storage and usage stability and can meet the application requirements of flexible wearable sensors for long-term continuous monitoring of body fluids.

[0117] 4. The flexible, wearable, long-term stable ruthenium oxide pH sensing electrode prepared in Example 1 of this invention can maintain good detection performance over a long shelf life. Therefore, for practical applications requiring room temperature storage, an accelerated aging test was designed based on the Arrhenius equation to verify its storage stability.

[0118] Under dry conditions, the ruthenium oxide pH sensing electrode was stored at a constant temperature of 60°C. Three sensing electrodes were randomly selected at each test time point, and after electroactivation, they were immersed in PBS with pH values ​​of 4, 6, and 8, respectively. The open-circuit potential method was used for measurement, the relationship between open-circuit potential and pH value was calculated, and the sensitivity of the electrodes was compared. Figure 6As shown, the ruthenium oxide pH sensing electrode prepared in Example 1 of the present invention consistently exhibited good sensitivity during a storage period of up to 27 days at 60°C. This result is equivalent to the ruthenium oxide pH sensing electrode consistently exhibiting good sensitivity during a storage period of up to 12 months at room temperature. This indicates that the flexible wearable long-term stable ruthenium oxide pH sensing electrode provided by the present invention has long-term stability, can maintain good sensitivity within a shelf life of at least one year, and its performance is not affected by extreme high-temperature conditions that may exist during storage.

[0119] 5. The ruthenium oxide pH sensing electrode prepared in Example 1 of this invention needs to be electroactivated before use to reduce electrode potential drift and sensitivity decrease caused by electrode aging or drift. Therefore, electroactivation with a certain buffer solution before electrode calibration and sample measurement can ensure the sensitivity and stability of electrode detection.

[0120] The pH sensing electrode and reference electrode were sequentially placed in PBS solutions with pH values ​​of 4, 6, and 8, or 4 and 6. Using the open-circuit potential method, the pH sensing electrode was placed in each of the three buffer solutions for 30 seconds to activate it, while an unactivated electrode was used as a control. Subsequently, the unactivated or differently activated pH sensing electrodes and reference electrodes were sequentially placed in solutions with pH values ​​of 4, 6, and 8. The open-circuit potential method was used to observe the electrode potential drift, and the pH sensing electrode potential was recorded to obtain the standard formula for "potential-pH". Figure 7 As shown, the open-circuit potential of the unactivated pH sensing electrode drifts severely, resulting in abnormal detection sensitivity; while the open-circuit potential of the activated pH sensing electrode is relatively stable and the sensitivity is better. Moreover, the two activation methods have similar activation effects and can achieve good test sensitivity and stability. The activation steps can be easily adjusted according to the needs of the application scenario.

[0121] In summary, the advantages of this invention lie in its use of drop-coating or printing to prepare ruthenium oxide pH sensing electrodes. This method is simple, low-cost, and easy to operate, avoiding the need for demanding, costly, or complex processing techniques. It is suitable for integration with flexible materials and circuits to construct flexible wearable sensors, and has potential for mass production. The electrodes exhibit good consistency, and combined with a simple electrode electroactivation procedure, they demonstrate excellent sensitivity and accuracy in pH detection within the physiological range. They also exhibit good stability and detection performance under both room temperature storage and body fluid immersion storage scenarios, showing broad application prospects in the field of commercial flexible wearable body fluid pH detection.

[0122] Example 2

[0123] A method for fabricating a long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable use includes the following steps:

[0124] (1) Preparation of pH sensing electrode

[0125] A) Preparation of pH ink stock solution

[0126] Ruthenium oxide was dispersed in water to obtain a ruthenium oxide dispersion with a concentration of 25 mg / mL;

[0127] Carbon black was dispersed in water to obtain a conductive filler dispersion with a concentration of 25 mg / mL.

[0128] Nafion R-1100 resin was dissolved in isopropanol to obtain a polymer solution with a concentration of 2.5 mg / mL.

[0129] B) Formulation of pH-sensitive layer ink

[0130] The above solutions are mixed to obtain a mixed solution with a ruthenium oxide concentration of 12.5 mg / mL, a conductive filler concentration of 2.5 mg / mL, and a polymer concentration of 0.25 mg / mL. The volume ratio of water to isopropanol in the solvent is controlled to be 7:3, thus obtaining the pH-sensitive layer ink.

[0131] (2) Electrode cleaning

[0132] The surface of the gold-plated electrode on the flexible PI substrate was rinsed with deionized water, polished with alumina with a particle size of 0.05μm, sonicated for 10 minutes, rinsed with deionized water, and dried in an oven at 60℃.

[0133] (3) pH-sensitive layer modification

[0134] pH-sensitive layer ink was drop-coated onto the electrode surface and dried. The ink usage was 2 μL / mm. 2 Dry in a 60℃ oven to ensure that the pH-sensitive layer densely covers the entire electrode surface and forms a pH-sensitive layer on the electrode;

[0135] (4) Polymer layer modification

[0136] Nafion R-1100 resin was dissolved in isopropanol to obtain a polymer solution with a concentration of 2.5 mg / mL. This solution was then drop-coated onto the electrode surface containing the pH-sensitive layer obtained in step (3). The amount of polymer solution used was 2 μL / mm. 2 The ruthenium oxide pH sensing electrode is dried in a 60°C oven to form a polymer layer on top of the pH-sensitive layer, thus obtaining a long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable devices.

[0137] The method for using the long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable devices prepared in this embodiment includes the following steps:

[0138] 1) Electrode activation: The prepared ruthenium oxide pH sensing electrode and Ag / AgCl reference electrode were placed in electro-activation solutions (phosphate buffer) at pH=4 and pH=6 respectively. The open-circuit potential method was used to operate each electrode in the electro-activation solution for 30s to obtain the activated electrode.

[0139] 2) Electrode calibration: The activated electrode was placed in phosphate buffer solutions with pH=4, pH=5, pH=6, pH=7 and pH=8 in sequence. The potential of the activated electrode was recorded using the open circuit potential method to obtain the standard formula of "potential-pH".

[0140] 3) Sweat sample detection: The activated electrode is placed in the sweat sample to be tested. The potential of the activated electrode in the solution is recorded using the open circuit potential method. The pH value of the sweat sample to be tested is calculated to be 4.84 according to the above standard formula.

[0141] Example 3

[0142] A method for fabricating a long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable use includes the following steps:

[0143] (1) Preparation of pH sensing electrode

[0144] A) Preparation of pH ink stock solution

[0145] Ruthenium oxide was dispersed in water to obtain a ruthenium oxide dispersion with a concentration of 75 mg / mL;

[0146] Graphene was dispersed in water to obtain a conductive filler dispersion with a concentration of 50 mg / mL.

[0147] Nafion R-1100 resin was dissolved in isopropanol to obtain a polymer solution with a concentration of 5 mg / mL.

[0148] B) Formulation of pH-sensitive layer ink

[0149] The above solutions are mixed to obtain a mixed solution with a ruthenium oxide concentration of 37.5 mg / mL, a conductive filler concentration of 5 mg / mL, and a polymer concentration of 0.5 mg / mL. The volume ratio of water to isopropanol in the solvent is controlled to be 1:1, thus obtaining the pH-sensitive layer ink.

[0150] (2) Electrode cleaning

[0151] Rinse the gold-plated electrode surface on the flexible PET substrate with deionized water, polish it with alumina with a particle size of 0.05μm, sonicate for 10 minutes, rinse the electrode surface with deionized water, and dry it in an oven at 60℃.

[0152] (3) pH-sensitive layer modification

[0153] pH-sensitive layer ink was drop-coated onto the electrode surface and dried. The ink usage was 1 μL / mm. 2 Dry in a 60℃ oven to ensure that the pH-sensitive layer densely covers the entire electrode surface and forms a pH-sensitive layer on the electrode;

[0154] (4) Polymer layer modification

[0155] Nafion R-1100 resin was dissolved in isopropanol to obtain a polymer solution with a concentration of 10 mg / mL. This solution was then drop-coated onto the electrode surface containing the pH-sensitive layer obtained in step (3). The amount of polymer solution used was 1 μL / mm. 2 The ruthenium oxide pH sensing electrode is dried in a 60°C oven to form a polymer layer on top of the pH-sensitive layer, thus obtaining a long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable devices.

[0156] The method for using the long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable devices prepared in this embodiment includes the following steps:

[0157] 1) Electrode activation: The prepared ruthenium oxide pH sensing electrode and Ag / AgCl reference electrode were placed in electro-activation solutions (phosphate buffer) at pH=4, pH=6 and pH=8 respectively. The open circuit potential method was used to work in each electro-activation solution for 30s to obtain the activated electrode.

[0158] 2) Electrode calibration: The activated electrode was placed in phosphate buffer solutions with pH=4, pH=6 and pH=8 in sequence. The potential of the activated electrode was recorded using the open circuit potential method to obtain the standard formula of "potential-pH".

[0159] 3) Saliva sample detection: The activated electrode is placed in the saliva sample to be tested. The potential of the activated electrode in the test solution is recorded using the open circuit potential method. The pH value of the saliva sample to be tested is calculated to be 6.97 according to the above standard formula.

[0160] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable devices, characterized in that, From bottom to top, it includes: a flexible substrate layer, electrodes, a pH-sensitive layer, and a polymer layer; The pH-sensitive layer is composed of ruthenium oxide, conductive filler, and polymer. The method for preparing the long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable devices includes the following steps: Ruthenium oxide, conductive filler, and polymer were dissolved in solvent and mixed to obtain pH-sensitive layer ink; After cleaning, polishing and drying the electrodes on the flexible substrate, the pH-sensitive layer ink is coated onto the electrodes using a drop-coating or printing method and dried at a temperature below 300°C to form a pH-sensitive layer on the electrodes. A polymer solution is obtained by dissolving a polymer in an organic solvent, then coating it onto a pH-sensitive layer and drying it at a temperature below 300°C to form a polymer layer on top of the pH-sensitive layer, thus obtaining a long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearables.

2. The long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable use according to claim 1, characterized in that, The flexible substrate layer is made of a material selected from polyimide, polyester, polyetheretherketone, polyvinyl fluoride, paper, and fabric; and / or, The electrode is selected from one of the following: carbon electrode, gold electrode, platinum electrode, silver electrode, immersion gold electrode, and gold-plated electrode; and / or, The material of the polymer layer is selected from one or more of perfluorosulfonic acid, polyaniline, polyvinyl alcohol, polyvinyl butyral, polystyrene sulfonate, and polypyrrole.

3. The long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearables according to claim 1, characterized in that, The ruthenium oxide has a particle size of 10-500 nm; and / or, The conductive filler is selected from one or more of carbon black, carbon nanotubes, carbon nanorods, graphene, and gold nanoparticles, and the particle size of the conductive filler is 10-100 nm; and / or, The high molecular weight polymer in the pH-sensitive layer is selected from one or more of perfluorosulfonic acid, polyaniline, polyvinyl alcohol, polyvinyl butyral, polystyrene sulfonate, and polypyrrole.

4. A method for preparing a long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable use as described in any one of claims 1-3, characterized in that, Includes the following steps: Ruthenium oxide, conductive filler, and polymer were dissolved in solvent and mixed to obtain pH-sensitive layer ink; After cleaning, polishing and drying the electrodes on the flexible substrate, the pH-sensitive layer ink is coated onto the electrodes by drop coating or printing, and then dried at a temperature below 300°C to form a pH-sensitive layer on the electrodes. A polymer solution is obtained by dissolving a polymer in an organic solvent, and then coating it onto an electrode containing a pH-sensitive layer. The solution is then dried at a temperature below 300°C to form a polymer layer on top of the pH-sensitive layer, thus obtaining a long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearable devices.

5. The method for preparing a flexible, wearable, long-term stable ruthenium oxide pH sensing electrode according to claim 4, characterized in that, In the pH-sensitive layer ink, the mass concentration ratio of ruthenium oxide, conductive filler and polymer is (10-100):(1-10):1, the concentration of polymer is 0.1-10 mg / mL, and the solvent is water and organic solvent with a volume ratio of (1-10):

1.

6. The method for preparing a flexible, wearable, long-term stable ruthenium oxide pH sensing electrode according to claim 4, characterized in that, The coating amount of the pH-sensitive layer ink is 0.1-10 μL / mm. 2 .

7. The method for preparing a flexible, wearable, long-term stable ruthenium oxide pH sensing electrode according to claim 4, characterized in that, The concentration of the polymer solution is 0.1-10 mg / mL, and the coating amount is 0.1-10 μL / mm. 2 .

8. The application of a long-term stable ruthenium oxide pH sensing electrode suitable for flexible wearables as described in any one of claims 1-3 in the field of sensing and detection.

9. A method of using the flexible, wearable, long-term stable ruthenium oxide pH sensing electrode as described in any one of claims 1-3, characterized in that, Includes the following steps: 1) The ruthenium oxide pH sensing electrode and the reference electrode were placed in an electro-activation solution, and the open-circuit potential method was used to perform electro-activation in the electro-activation solution to obtain the activated electrode; 2) The activated electrode was placed in solutions with pH=4, 6 and 8 in sequence, and the potential of the activated electrode was recorded using the open circuit potential method to obtain the standard formula of "potential-pH". 3) Place the activated electrode in the sample to be tested, record the potential of the activated electrode in the solution to be tested using the open circuit potential method, and calculate the pH value of the sample to be tested according to the above standard formula.

10. The method of using the flexible, wearable, long-term stable ruthenium oxide pH sensing electrode according to claim 9, characterized in that, The electroactivation solution is a buffer solution with a pH of 2-12; and / or, The activation time is 10-120 seconds.

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