A flexible multi-modal sweat sensor array based on indium tin oxide substrate and a preparation method thereof

Abstract

The application relates to a flexible multi-modal sweat sensor array based on an indium tin oxide substrate and a preparation method thereof, and belongs to the technical field of flexible electronics and biosensing. The application innovatively takes a cheap industrial-grade ITO / PET conductive film as a core substrate, solves the core problems such as potential drift caused by the sparseness of intrinsic surface electrochemical active sites of the ITO substrate, poor catalytic performance and small interface capacitance through laser etching and electrochemical interface engineering, and the like. A platinum nano layer is modified on the ITO surface through a constant potential in-situ deposition method, and the conductivity and electrochemical performance of the electrode are improved. The array single chip integrates three detection modes of glucose, pH and sodium ions, and there is no crosstalk between the electrodes. The application realizes the combination of high-performance sensing and low material cost, has a simple preparation process, excellent flexible conformal adhesion capacity and high detection stability, and has a wide industrialization prospect in the field of wearable health monitoring.

Description

Technical Field

[0001] This invention relates to a flexible multimodal sweat sensor array based on an indium tin oxide substrate and its fabrication method, belonging to the field of flexible electronics and biosensing technology. Background Technology

[0002] With the rapid development of wearable health monitoring devices, non-invasive or minimally invasive detection technologies based on body fluids have become a research hotspot. Sweat, as one of the most readily available body fluids, is rich in physiological markers such as glucose, lactic acid, electrolytes (sodium and potassium ions), and pH. Real-time continuous monitoring of these indicators is of great significance for assessing exercise function, managing diabetes, early warning of dehydration, and diagnosing cystic fibrosis.

[0003] Currently, the development of flexible electrochemical sweat sensors faces a structural contradiction between cost and performance. On the one hand, high-performance sensors often rely on expensive gold and platinum vacuum deposition processes, making it difficult to achieve low-cost, large-scale manufacturing on flexible substrates. On the other hand, inexpensive screen-printed carbon electrodes cannot meet the high-sensitivity detection requirements due to their slow electron transfer rate and poor consistency. While indium tin oxide (ITO) films, as a potential alternative, possess mature patterning processes and cost advantages, their intrinsic surface electrochemical active sites are sparse, making them unable to effectively catalyze hydrogen peroxide. More seriously, existing research is mostly limited to single-parameter detection, lacking multi-parameter collaborative calibration mechanisms. Therefore, how to overcome the electrochemical activity limitations of ITO on a single flexible substrate and construct a multimodal self-calibrating sensor array that combines low cost, mass production capability, and high reliability has become a core technical challenge that urgently needs to be overcome. Summary of the Invention

[0004] This invention aims to overcome the shortcomings of existing technologies and provide a flexible multimodal sweat sensor array based on an indium tin oxide (ITO) substrate and its fabrication method. Firstly, this invention focuses on overcoming the intrinsic performance bottleneck of low-cost ITO electrodes, addressing how to achieve high-performance electrochemical detection sensitivity while maintaining low cost through surface modification engineering. Secondly, this invention delves into the universality and specificity of electrode interface construction, solving how to simultaneously achieve functional differentiation in different electrode regions of the same substrate, achieving high catalytic activity (for enzyme electrodes) and high potential stability (for ion electrodes), using only a standardized electrochemical deposition process. Thirdly, at the system integration level, this invention addresses how to integrate glucose, pH, and sodium ion sensing modalities on a single flexible chip with low interference.

[0005] The present invention is achieved through the following technical solution.

[0006] A flexible multimodal sweat sensor array based on an indium tin oxide substrate includes: Flexible substrate: 200µm thick PET film; Conductive pattern layer: An ITO film laminated on the PET substrate, with five mutually insulated electrode regions formed by laser etching; Functionalized electrode array: Five mutually insulated electrode regions integrate a platinum counter electrode, an Ag / AgCl reference electrode, a glucose detection electrode, a pH detection electrode, and a sodium ion detection electrode, all located on the surface of an ITO thin film.

[0007] In the five mutually insulated electrode regions, the platinum counter electrode is located at the outer end of the electrode array and is distributed in an arc shape; the Ag / AgCl reference electrode is located at the top of the outer periphery of the electrode array and on the opposite side of the opposite end, and is distributed in an arc shape, forming an outer ring structure around the inner region together with the platinum counter electrode; the glucose detection electrode is located in the inner region surrounded by the platinum counter electrode and the Ag / AgCl reference electrode.

[0008] Among the five mutually insulated electrode regions, the pH detection electrode is located to the upper right of the inner region enclosed by the Ag / AgCl reference electrode and the platinum counter electrode, and is adjacent to the inner edge of the platinum counter electrode; the sodium ion detection electrode is located below the inner region enclosed by the Ag / AgCl reference electrode and the platinum counter electrode, and is adjacent to the inner edge of the Ag / AgCl reference electrode 8.

[0009] Platinum counter electrode 4 is formed by electrochemically depositing a platinum nanolayer on the surface of an ITO thin film.

[0010] The Ag / AgCl reference electrode 8 is obtained by depositing a silver layer on the surface of an ITO thin film and then chlorinating it to obtain Ag / AgCl.

[0011] The glucose detection electrode 6 is formed by electrochemically depositing a platinum nanolayer on the surface of an ITO thin film and then covering it with a glucose oxidase membrane.

[0012] pH detection electrode 5 is formed by in-situ polymerization and deposition of a PANI film on the surface of an ITO film.

[0013] The sodium ion detection electrode 7 is formed by depositing a platinum nanolayer on the surface of an ITO thin film and then covering it with a sodium ion selective film.

[0014] A method for fabricating a flexible multimodal sweat sensor array based on an indium tin oxide substrate includes the following steps: S1. Conductive substrate patterning: Five mutually insulated electrode regions 3 and leads are formed on the ITO-PET film by chemical etching; S2. Simultaneous construction of platinum nanolayers: Platinum nanolayers were simultaneously deposited on the ITO surfaces of glucose detection electrode 6 and sodium ion detection electrode 7 using a single electroplating solution and pulse voltammetry. S3, pH-sensitive membrane polymerization: PANI film is deposited in situ by constant potential polymerization on pH detection electrode 5. The electroplating solution used is a solution containing 0.5~1M dilute hydrochloric acid and 0.1~0.2M aniline, the voltage is 2.2~2.4V, and the time is 60~120 s. S4. Modification of working electrodes: sequentially coat glucose oxidase composite membrane onto glucose detection electrode 6 and sodium ion selective membrane onto sodium ion detection electrode 7.

[0015] The electroplating solution in S2 is an aqueous solution containing 2~5mM chloroplatinic acid and 0.2~0.5M sulfuric acid. The pulse voltammetric deposition potential is set to -0.8V~0.1V, and the deposition time is 60~120s.

[0016] Limitations of key process features The electrochemical deposition of the platinum nanolayer uses the same electroplating solution formulation and deposition parameters, and is completed simultaneously or stepwise in the Ag / AgCl reference electrode integration region, the glucose detection electrode integration region, and the sodium ion detection electrode integration region. The electroplating solution for depositing the platinum nanolayer is an acidic aqueous solution containing chloroplatinic acid (H2PtCl6) with a concentration of 5 mM, and the supporting electrolyte is 0.5 M sulfuric acid. The deposition potential is in pulse voltammetry mode, with a potential of -0.8 V to -0.1 V relative to the external Ag / AgCl reference electrode, and the deposition time is preferably 60 to 120 seconds.

[0017] Preparation limitations of each functional membrane The glucose oxidase composite membrane layer in the integrated region of the glucose detection electrode contains glucose oxidase, a film-forming polymer, and a cross-linking agent; the film-forming polymer is selected from chitosan, Nafion, or polyvinyl alcohol; and the cross-linking agent is a glutaraldehyde solution.

[0018] The polyaniline thin film layer in the pH electrode integrated region is prepared by potentiostatic polymerization. The polymerization solution is an aqueous solution containing 0.5M aniline monomer and 0.8M sulfuric acid. The potential relative to the external Ag / AgCl reference electrode is 2.4V, and the deposition time is preferably 60 seconds.

[0019] The sodium ion selectively permeable membrane layer in the sodium ion detection electrode integrated area comprises, by mass percentage: 26% polyvinyl chloride (PVC), 70% dioctyl sebacate (DOS), 2% sodium ion carrier (NaIonophoreX), and 2% sodium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate (NaTFPB); the solvent is tetrahydrofuran (THF).

[0020] The beneficial effects of this invention are: 1. Excellent skin conformal adhesion ability: This invention uses ultra-thin PET (200µm thick) as a flexible substrate, which can form a conformal physical adhesion with human skin.

[0021] 2. High integration: The sensor achieves multimodal functionality in sweat analysis through five electrodes, significantly improving the sensor's integration level.

[0022] 3. Simple preparation process, simple formula, and low cost: This invention creatively uses a single electroplating solution and the same set of deposition parameters to simultaneously complete the functionalization modification of Pt nanolayers on glucose electrodes and sodium ion electrodes, thus rapidly realizing electrode preparation. Attached Figure Description

[0023] Figure 1 This invention presents a schematic diagram of the flexible multimodal sweat sensor array structure and electrode array based on an indium tin oxide substrate. Figure I .

[0024] Figure 2 This invention presents a schematic diagram of the flexible multimodal sweat sensor array structure and electrode array based on an indium tin oxide substrate. Figure II .

[0025] Figure 3 This is a schematic flowchart of the method for fabricating a flexible multimodal sweat sensor array on an indium tin oxide substrate according to the present invention.

[0026] Figure 4 This is an optical microscope image of the platinum nanolayer modified ITO electrode prepared in Preparation 1 of the present invention, scale bar 200 µm.

[0027] Figure 5 These are the current-time response curves and corresponding operating curves of the glucose detection electrode prepared in preparation 2 of this invention; wherein, Figure 5 'a' represents the it curve when glucose standard solutions of different concentrations are continuously added. After continuous addition of glucose standard solutions, the current rises rapidly in a stepwise manner, with each step reaching a steady state within 5 seconds. Within the range of 40–400 μM, the current value shows a good linear relationship with the glucose concentration. R (²=0.998), sensitivity is 54.71 μA / M, detection limit is 2.5 μM. Figure 5 b is a graph showing the anti-interference performance of the prepared glucose detection electrode.

[0028] Figure 6 These are the open-circuit potential response curves and corresponding calibration curves of the pH detection electrode prepared in preparation 3 of this invention; wherein, Figure 6 a represents the open-circuit potential-time response curve in standard buffer solutions with pH values ​​ranging from 4.0 to 8.0. Figure 6b. Interference resistance test diagram of the pH detection electrode prepared by the method.

[0029] Figure 7 These are the open-circuit potential response curves and corresponding calibration curves of the sodium ion detection electrode prepared in preparation 4 of this invention; wherein, Figure 7 a is in Na + Open-circuit potential-time response curves within the concentration range of 12.5–200 mM. Figure 7 b. Interference resistance test diagram of the sodium ion detection electrode prepared by the method.

[0030] Figure 8 These are the test results of each functional electrode of the sensor array in Embodiment 1 of the present invention, wherein Figure 8 'a' represents the it curves of the sensor array when different concentrations of glucose standard solution are continuously added. After continuous addition of glucose standard solution, the current rises rapidly in a stepwise manner, with each step reaching steady state within 5 seconds. Within the range of 100–500 μM, the current value shows a good linear relationship with the glucose concentration. R (²=0.997) Figure 8 b is the sensor array in Na + Open-circuit potential-time response curves within the concentration range of 12.5–200 mM. Figure 8 c is the open-circuit potential-time in a standard buffer solution with pH = 4.0~8.0.

[0031] Figure 9 These are the test results of each functional electrode of the sensor array in human sweat in Embodiment 1 of the present invention.

[0032] The labels in the figure are as follows: 1-flexible substrate layer, 2-conductive pattern layer, 3-five mutually insulated electrode regions, 4-platinum counter electrode, 5-pH detection electrode, 6-glucose detection electrode, 7-sodium ion detection electrode, 8-Ag / AgCl reference electrode. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0034] I. Individual fabrication and performance characterization of key functional modules To systematically verify the independent feasibility and process compatibility of each functional electrode involved in this invention, the glucose detection electrode, pH detection electrode, sodium ion detection electrode, counter electrode and reference electrode were first prepared for the experiment. The individual modules were prepared and their performance was characterized. Based on this, the integrated preparation of the five-electrode integrated array was carried out.

[0035] Preparation before the experiment 1. Preparation and characterization of platinum nanolayer modified ITO electrode The purpose of this experiment was to verify the effect of electrochemically deposited platinum nanolayers on enhancing the electrochemical activity of the ITO substrate, and to provide basic process parameters for subsequent glucose and sodium ion electrodes.

[0036] 1.1 Electrode Preparation: A 1 cm × 2 cm ITO / PET conductive film (sheet resistance 7 Ω / sq, PET thickness 200 mm) was ultrasonically cleaned sequentially in acetone, anhydrous ethanol, and deionized water for 8 minutes, and then dried with nitrogen. A UV-ozone cleaning machine was used for 15 minutes to improve surface hydrophilicity. The cleaned ITO / PET film was used as the working electrode, an external Ag / AgCl electrode (saturated KCl) as the reference electrode, and a platinum sheet electrode as the counter electrode, forming a three-electrode system. The electroplating solution was an aqueous solution of H₂PtCl₆ (2~5 mM) + H₂SO₄ (0.2~0.5 M). Pulse voltammetry deposition was used, with a potential set to -0.8 V to 0.1 V. vs Ag / AgCl), deposition time 60-120 seconds. After deposition, rinse with deionized water, dry with nitrogen, and place in an oven at 180-200℃ for 1-2 minutes.

[0037] 1.2 Morphology and Structure Characterization: Optical microscopy revealed that the deposited ITO surface was uniformly covered with a layer of platinum nanoparticles. (Image scale bar 200 mm) Figure 4 As shown.

[0038] Preparation before the experiment 2. Individual preparation and performance characterization of glucose detection electrode 2.1 Electrochemically deposit a platinum nanolayer on the ITO / PET surface according to the method described in Preparation 1. Enzyme solution preparation: Dissolve 30-40 mg of glucose oxidase (GOD, activity ≥200 mg / mL) in 1 mL of 0.01-0.03 M PBS buffer (pH=7.0), add 1 mL of 0.3-0.5 wt% chitosan solution (solvent: 1 wt% acetic acid solution), and add 10 mL of 25-30% glutaraldehyde aqueous solution as a cross-linking agent. Mix well and place in an ice bath for later use. Using a micropipette, carefully drop 2 mL of the above enzyme mixture onto the surface of the ITO electrode with the deposited platinum nanolayer (working area diameter 3 mm). Place the electrode in a 4°C refrigerator to dry for 4 hours to allow the enzyme membrane to form a stable three-dimensional network structure. After drying, gently wash the unfixed enzyme with PBS buffer and store at 4°C for later use.

[0039] 2.2 Glucose Detection Performance Test: The current-time method (it) was used, with the prepared glucose electrode as the working electrode, an external Ag / AgCl electrode as the reference electrode, and a platinum wire as the counter electrode. The test was conducted in 0.01 M PBS buffer (pH=7.4). The working voltage was set to 0.5V~0.8V. vsAfter the background current stabilized, different volumes of glucose standard solution were added dropwise to the stirred solution every 30 seconds to create glucose concentration gradients of 0.5 mM, 1 mM, 2 mM, 5 mM, 10 mM, 15 mM, 200 mM, 40 mM, 80 mM, 160 mM, 200 mM, 240 mM, 280 mM, 320 mM, 360 mM, 400 mM, 1 mM, 2 mM, and 3 mM. Test results: The current response reached steady state within 5 seconds. The response current showed a good linear relationship with the glucose concentration in the range of 40–400 mM, and the linear regression equation was I(nA) = 54.71 × Glu + 17.03. R ²=0.998, sensitivity 54.71 mA / M, detection limit (S / N=6) calculated to be 2.5 mM, if Figure 5 As shown in a.

[0040] 2.3 Anti-interference performance test: In a PBS solution containing 0 mM glucose, 50 mM glucose, 50 mM urea, 50 mM uric acid, and 50 mM lactic acid were added respectively, and the current changes were recorded. The results showed that the current changes caused by each interfering substance were all less than 5%, indicating that the electrode has good anti-interference ability. Figure 5 As shown in b.

[0041] Preparation before the experiment: 3. Individual preparation and performance characterization of the pH detection electrode 3.1 Electrode Preparation: The cleaned ITO / PET film was used as a platform with an electrochemical workstation employing a three-electrode system (ITO electrode as the working electrode, Ag / AgCl as the reference electrode, and platinum wire as the counter electrode). The polymerization solution was 0.1–0.2 M aniline monomer in 0.5–1 M HCl aqueous solution (aniline was purified by vacuum distillation before use). A constant potential mode was used, with a potential set at 2.2–2.4 V and a deposition time of 60–120 s. During the scanning process, the electrode surface gradually changed from colorless to light green, and finally to dark green, indicating successful polyaniline (PANI) film growth. After polymerization, the electrode was scanned in 0.1–0.2 M HCl solution using cyclic voltammetry (-0.2 V to +0.5 V, 50 mV / s) until the curve stabilized, thus activating the PANI film.

[0042] 3.2 pH Response Performance Test: The open-circuit potential-time (OCPT) method was used. The prepared pH electrode was sequentially immersed in commercial standard buffer solutions with pH values ​​of 4.0, 5.0, 6.0, 7.0, and 8.0, and the steady-state potential values ​​were recorded. Test Results: The electrode potential showed a good linear relationship with the pH value to be measured in the range of 4.0 to 8.0, with a slope of -58.396 mV / pH. R²=0.999), close to the theoretical value of Nernst (-58.96 mV / pH at 25℃). The response time (T90) is 18 seconds, such as... Figure 6 As shown in a.

[0043] 3.3 Anti-interference performance test: The steady-state potential value was recorded in the original commercial standard buffer solution at pH=4.0. After rinsing with deionized water, the solution was placed in a commercial standard buffer solution at pH=5.0, and the steady-state potential value was recorded. 50 mM NH4+ was added sequentially. + 50 mMK + 50 mM Ca 2+ The steady-state potential values ​​were recorded. After rinsing the electrode with deionized water, it was immersed in a commercial standard buffer solution at pH 6.0, and the steady-state potential values ​​were recorded again. The results showed that the current changes caused by each interfering substance were all less than 5%, indicating that the electrode has good anti-interference ability. Figure 6 As shown in b.

[0044] Preparation before the experiment 4. Individual preparation and performance characterization of the sodium ion detection electrode 4.1 Electrode Preparation: A platinum nanolayer was electrochemically deposited on the ITO / PET surface according to the method described in Example 1. 2-3 mg of sodium ion carrier X (sodium ion carrier IV) and 1-2 mg of NaTFPB were dissolved together in 1-1.5 mL of tetrahydrofuran (THF). The solution was sealed and stirred in the dark for 2 hours to obtain a colorless, transparent, viscous solution, which was then allowed to stand for 30 minutes to remove bubbles before use. Using a micropipette, 2.5 mL of the above film solution was continuously drop-coated onto the surface of the ITO electrode with the deposited platinum nanolayer. Immediately after drop-coating, the electrode was placed in a horizontal, dust-free, and ventilated environment and allowed to stand at room temperature for 12 hours to allow the THF solvent to evaporate slowly and completely, forming a transparent, uniform, and strongly bonded ion-selective film on the electrode surface.

[0045] 4.2 Sodium ion response performance test: A 10 mM Tris-HCl buffer solution (pH=7.0) was used as the background electrolyte solution. The Na⁺ concentration was adjusted from 12.5 mM to 200 mM by adding NaCl standard solution, and the steady-state potential values ​​were recorded. Figure 7 As shown in a.

[0046] 4.3 Anti-interference performance test: In 10mM Tris-HCl buffer (pH=7.0), the electrode pairs with NH4 were tested respectively. + K + Ca 2+ The potential response results showed that the current change caused by each interfering object was less than 5%, indicating that the electrode has good anti-interference ability. Figure 7 As shown in b. Example

[0047] like Figure 1 and 2 As shown, the flexible multimodal sweat sensor array based on an indium tin oxide substrate includes: Flexible substrate 1: a PET film with a thickness of 200µm; Conductive pattern layer 2: An ITO film laminated on the PET substrate, with five mutually insulated electrode regions 3 formed by laser etching; Functionalized electrode array: Five mutually insulated electrode regions 3 respectively integrate a platinum counter electrode 4, an Ag / AgCl reference electrode 8, a glucose detection electrode 6, a pH detection electrode 5, and a sodium ion detection electrode 7, all located on the surface of the ITO thin film. Platinum counter electrode 4: Located on the ITO surface, a platinum layer is formed by electrochemical deposition to form the current loop of the three-electrode system; Ag / AgCl reference electrode 8: Located on the ITO surface, it consists of an Ag / AgCl layer formed by electrochemically deposited silver layer and chlorination treatment, providing a stable reference potential; Glucose detection electrode 6: From bottom to top, it consists of an ITO substrate, an electrochemically deposited platinum nanolayer, and a glucose oxidase composite film; the platinum nanolayer serves as the electrocatalytic oxidation medium for hydrogen peroxide. pH detection electrode 5: From bottom to top, it consists of an ITO substrate and an electrochemically polymerized polyaniline (PANI) thin film layer; the polyaniline film is grown in situ using a potentiostatic method, and its redox potential exhibits a Nernst response with hydrogen ion activity; Sodium ion detection electrode 7: from bottom to top, it consists of an ITO substrate, an electrochemically deposited platinum nanolayer, and a sodium ion selectively permeable membrane layer; the platinum nanolayer serves as a solid contact layer to stably convert the ion potential signal into an electronic signal.

[0048] like Figure 3 As shown, the fabrication method of the flexible multimodal sweat sensor array based on an indium tin oxide substrate includes the following steps: 5.1 Substrate Patterning: A flexible ITO / PET conductive film (sheet resistance 7Ω / sq, PET thickness 200 mm) was selected and cut to a size of 4 cm × 5 cm. The ITO layer was chemically etched to form five mutually insulated working regions 3, where the working electrodes are 12 mm, 8 mm, and 8 mm in diameter, respectively, and a conductive lead extending to the edge of the film. The overall size is 4 cm × 5 cm.

[0049] 5.2 Substrate Cleaning and Activation: The etched ITO / PET film was sequentially placed in acetone, anhydrous ethanol, and deionized water, and ultrasonically cleaned for 8 minutes each to remove residual carbon particles from laser etching and surface organic contaminants. After cleaning, it was dried with high-purity nitrogen. To further improve the hydrophilicity and electrochemical activity of the ITO surface, the cleaned substrate was treated in a UV-ozone plasma cleaner for 15 minutes.

[0050] 5.3 Selective Electrochemical Deposition of Platinum Nanolayers: Electroplating Solution Preparation: Weigh 0.1035~0.2589g of chloroplatinic acid hexahydrate (H2PtCl6·6H2O), add it to a 100 mL volumetric flask, and dilute to volume with 0.5~1 M dilute hydrochloric acid to prepare a mixed electrolyte of H2PtCl6 (2~5 mM) + H2SO4 (0.5~0.1 M). Degas the electrolyte using ultrasonication for 5 minutes. Deposition Process: Use the cleaned and activated ITO / PET substrate as the working electrode, an external Ag / AgCl electrode (saturated KCl) as the reference electrode, and a platinum sheet electrode as the counter electrode, forming a three-electrode system connected to an electrochemical workstation (CHI660E, Shanghai Chenhua). Pulse voltammetry deposition was used, with a potential set to -0.8V~0.1V (…). vs. (Ag / AgCl), deposition time 60-120 seconds. Using the multi-channel selection function of the electrochemical workstation, only the alligator clips of the workstation are connected to the leads of the three regions to be modified (glucose electrode region and sodium ion electrode region). After deposition, the electrodes are quickly removed, the surface is gently rinsed with deionized water, dried with nitrogen, and placed in an oven at 180-200℃ for 2-3 minutes. At this time, a uniform, strongly adherent, gray-black platinum nanoparticle layer is formed on the ITO surface of the above two regions.

[0051] 5.4 Electrochemical Polymerization of pH-Sensitive Electrode: Polymerization Solution Preparation: 1.15–2.3 mL of aniline monomer (purified by vacuum distillation before use) was dissolved in 10 mL of 0.5–1 M dilute hydrochloric acid aqueous solution and ultrasonically mixed to obtain a 0.1–0.2 M aniline / 0.5–1 M dilute hydrochloric acid polymerization solution. Electropolymerization: The cleaned, unmodified pH electrode region ITO was used as the working electrode, with an external Ag / AgCl as the reference electrode and a platinum wire as the counter electrode. A constant potential mode was used, with a deposition time of 60–120 s within a potential window of 2.2–2.4 V. During the process, the electrode surface was observed to gradually change from colorless to light green, and finally to dark green, indicating successful polyaniline (PANI) film growth. After polymerization, the electrode was scanned in 0.1–0.2 M dilute hydrochloric acid solution using cyclic voltammetry (-0.2 V to +0.5 V, 50 mV / s) until the curve stabilized, thus completing the activation of the PANI film.

[0052] 5.5 Preparation of Glucose-Sensitive Membrane. Enzyme Solution Preparation: Dissolve 40 mg of glucose oxidase (derived from Aspergillus niger, activity >200 mg / mL) in 1 mL of 0.01 M PBS buffer (pH=7.0), add 1-2 mL of 0.5 wt% chitosan solution (solvent: 1 wt% acetic acid solution), and add 10-20 mL of 25% glutaraldehyde aqueous solution as a cross-linking agent. Mix thoroughly and place in an ice bath for later use. Modification: Using a micropipette, carefully drop 2 mL of the above enzyme mixture onto the glucose detection electrode area where a platinum nanolayer has been deposited. Place the electrode in a 4°C refrigerator to dry for 4 hours to allow the enzyme membrane to form a stable three-dimensional network structure. After drying, gently wash the unfixed enzyme with PBS buffer and store at 4°C for later use.

[0053] 5.6 Preparation of Sodium Ion Selective Sensitive Membrane: Membrane Solution Preparation: Weigh PVC powder (26 mg), DOS plasticizer (70 mg), sodium ion carrier X (2 mg), and NaTFPB (2 mg) sequentially, and dissolve them together in 1 mL of tetrahydrofuran (THF). Seal and protect from light, stir for 2 hours to obtain a colorless, transparent, viscous solution, and allow it to stand for 30 minutes to remove bubbles before use. Modification: Using a micropipette, take 2.5 mL of the above membrane solution and drop it continuously onto the sodium ion detection electrode area where a platinum nanolayer has been deposited. Due to the high volatility of THF, the electrode should be placed in a horizontal, dust-free, and ventilated environment immediately after drop coating. Allow it to stand at room temperature for 12 hours to allow the solvent to slowly evaporate completely, forming a transparent, uniform, and firmly bonded ion-selective membrane on the electrode surface.

[0054] 5.7 Preparation of the Ag / AgCl reference electrode: A silver layer was electrochemically deposited on an ITO / PET substrate using a three-electrode system. The patterned ITO electrode region served as the working electrode, a platinum sheet as the counter electrode, and Ag / AgCl (saturated KCl) as the external reference electrode. The electrolyte was a mixed aqueous solution containing 0.05–0.2 M AgNO3 and 0.05–0.2 M KNO3. A potentiostatic deposition method was used, with the deposition potential set to -0.5 V to -0.2 V. vs A uniform and dense metallic silver layer was obtained on the ITO surface by deposition of Ag / AgCl at a time of 240–600 s. After deposition, the electrode was rinsed with deionized water and dried with nitrogen gas.

[0055] Subsequently, the deposited silver layer was subjected to anodic chlorination. Using the prepared Ag / ITO electrode as the working electrode, a constant current of 0.2–1.0 mA·cm⁻¹ was applied in 0.05–0.2 M KCl solution. -2The anolyte current density was adjusted, and the treatment time was 30–120 s to partially convert the silver layer surface into an AgCl layer. After chlorination, the electrode was rinsed with deionized water and stored in a 1–3 M KCl solution away from light for later use to obtain a stable reference potential.

[0056] 5.8 Preparation of platinum counter electrode: The preparation process is the same as in 5.3.

[0057] 5.9 Electrochemical Performance Testing of the Integrated Array: The five-electrode integrated sensor array prepared in Example 1 underwent full-function testing. All tests were conducted at room temperature, using the sensor's built-in counter and reference electrodes. The operating potentials were for the glucose electrode, pH electrode, and sodium ion electrode, respectively. The test medium was artificial sweat. Glucose detection: operating potential +0.6 V ( vs On-chip Ag / AgCl detection showed a sensitivity of 57 mA / mM at concentrations ranging from 100 to 500 mM, a linear correlation coefficient of 0.997, and a detection limit of 3.1 mM. pH detection, in open-circuit potential mode, exhibited a slope of -57.9 mV / pH at pH 4.0–8.0, a linear correlation coefficient of 0.999, and a response time of 20 seconds. Sodium ion detection, in open-circuit potential mode, showed a slope of 55.2 mV / decade at concentrations ranging from 12.5 to 200 mM, and a linear correlation coefficient of 0.996. These results indicate that the integrated process did not significantly affect the performance of individual electrodes, there was no crosstalk between electrodes, and the sensor array could stably achieve simultaneous detection of multiple parameters, such as… Figure 8 As shown, from Figure 8 As can be seen, regardless of step changes in glucose concentration, sodium ion concentration, or pH value, all sensors respond rapidly after the addition of the analyte and reach a stable plateau within a short time, with smooth signals and no significant fluctuations. Furthermore, subsequent tests using artificial sweat... Figure 9 As shown, from Figure 8 As can be seen, during the continuous monitoring lasting 1800 seconds, the glucose, sodium ion, and pH sensing units exhibited excellent stability in their current or potential signals after a brief initial stabilization, with no significant signal drift. This confirms the device's excellent anti-interference capability and reliability during long-term continuous operation in complex matrices. Furthermore, the sensor's ability to quantitatively analyze samples of unknown concentrations was verified. Figure 9 (Right side). Based on the stable signal output by the sensor in artificial sweat, combined with the previously established linear calibration curve, we successfully deduced that the glucose concentration in this artificial sweat sample was 225 mM, the sodium ion concentration was 85 mM, and the pH value was 5.6. These results fully demonstrate that this integrated sensor array can meet the needs of accurate, stable, and long-term synchronous monitoring of multiple parameters in bodily fluids in real-world application scenarios.

[0058] Example 2: Optimization Experiment of Electropolymerization Process Parameters for pH-Sensitive Membrane (PANI) This embodiment aims to investigate the effects of polymerization voltage and polymerization time on the morphology and pH detection performance of PANI membranes during the constant potential electropolymerization of polyaniline (PANI) in order to determine the optimal process window.

[0059] 6.1 Experimental Design: Keeping other conditions constant, PANI films were prepared on ITO / PET substrates according to the method described in Preparation 3 before the experiment. The constant potential polymerization voltage was changed to 2.0 V, 2.2 V, and 2.4 V respectively. vs The pH detection electrode was integrated according to the method described in Example 1, and its response slope (mV / pH) and response time (T90) in the pH range of 4.0~8.0 were tested. The morphology and adhesion state of the film were observed at the same time.

[0060] 6.2 Results Analysis: (1) Effect of Polymerization Voltage: With a fixed polymerization time of 60 s, the effects of different constant potential polymerization voltages on the properties of PANI film are as follows: 2.0V Light green, uniform film layer good -51.7±1.8 2.2V Dark green, with a uniform and dense film layer. Excellent -58.1±0.9 2.4V Dark green, with a relatively thick film layer good -58.4±1.1 The results showed that when the polymerization voltage was below 2.0V, the driving force for aniline monomer oxidation was insufficient, the polymerization rate was too slow, the film layer was too thin, resulting in a low pH response slope (<-52mV / pH) and a sluggish response. When the polymerization voltage was 2.2V, the PANI film was uniformly dark green, with good adhesion, and the pH response slope was close to the theoretical Nernst value (-58.1~-58.4mV / pH). When the polymerization voltage increased to 2.0V, overpotential caused aniline peroxidation, resulting in a rough and loose film layer, decreased adhesion, and deterioration in both the response slope and response time. In summary, the preferred polymerization voltage window of this invention is 2.2V~2.4V, with the optimal value being 2.2V.

[0061] (2) Effect of polymerization time: With a fixed polymerization voltage of 2.2V, the effects of different polymerization times on the properties of the PANI film are as follows: 30s Light green, discontinuous film layer ultra-thin -31.5±1.8 60s Dark green, with a uniform and dense film layer. Moderate -58.1±0.9 80s Dark green, uniform film layer Thicker -58.3±1.1 The results showed that at a polymerization time of 30 s, the PANI film failed to completely cover the ITO substrate, resulting in insufficient active sites and a pH response slope of only -31.5 mV / pH. At a polymerization time of 60 s, the PANI film formed a uniform and dense network structure, with a pH response slope stabilizing at -58.1 to -58.3 mV / pH, exhibiting the best overall performance. After a polymerization time of 80 s, the excessively thick film layer led to a prolonged proton diffusion path, significantly increasing the response time. Furthermore, the increased internal stress of the excessively thick film layer resulted in decreased long-term stability. In summary, the preferred polymerization time window of this invention is 60–80 s, with the optimal value being 60 s.

[0062] The specific embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A flexible multimodal sweat sensor array based on an indium tin oxide substrate, characterized in that: include: Flexible substrate (1): PET film with a thickness of 200µm; Conductive pattern layer (2): An ITO film composited on the PET substrate, which forms five mutually insulated electrode regions (3) by laser etching. Functionalized electrode array: Five mutually insulated electrode regions (3) are respectively integrated with a platinum counter electrode (4), an Ag / AgCl reference electrode (8), a glucose detection electrode (6), a pH detection electrode (5), and a sodium ion detection electrode (7) located on the surface of the ITO film.

2. The flexible multimodal sweat sensor array based on an indium tin oxide substrate according to claim 1, characterized in that: In the five mutually insulated electrode regions (3), the platinum counter electrode (4) is located on the outer side of the electrode array and is distributed in an arc shape; the Ag / AgCl reference electrode (8) is located on the top of the outer side of the electrode array and on the other side of the opposite end, and is distributed in an arc shape, and together with the platinum counter electrode (4), it forms an outer ring structure surrounding the inner region; the glucose detection electrode (6) is located in the inner region surrounded by the platinum counter electrode (4) and the Ag / AgCl reference electrode (8).

3. The flexible multimodal sweat sensor array based on an indium tin oxide substrate according to claim 1, characterized in that: Among the five mutually insulated electrode regions (3), the pH detection electrode (5) is located to the upper right of the inner region enclosed by the Ag / AgCl reference electrode (8) and the platinum counter electrode (4), and is adjacent to the inner edge of the platinum counter electrode (4); the sodium ion detection electrode (7) is located below the inner region enclosed by the Ag / AgCl reference electrode (8) and the platinum counter electrode (4), and is adjacent to the inner edge of the Ag / AgCl reference electrode (8).

4. The flexible multimodal sweat sensor array based on an indium tin oxide substrate according to claim 1, characterized in that: The platinum counter electrode (4) is formed by electrochemically depositing a platinum nanolayer on the surface of an ITO thin film.

5. The flexible multimodal sweat sensor array based on an indium tin oxide substrate according to claim 1, characterized in that: The Ag / AgCl reference electrode (8) is obtained by depositing a silver layer on the surface of an ITO thin film and then chlorinating it to obtain Ag / AgCl.

6. The flexible multimodal sweat sensor array based on an indium tin oxide substrate according to claim 1, characterized in that: The glucose detection electrode (6) is formed by electrochemically depositing a platinum nanolayer on the surface of an ITO thin film and then covering it with a glucose oxidase film.

7. The flexible multimodal sweat sensor array based on an indium tin oxide substrate according to claim 1, characterized in that: The pH detection electrode (5) is formed by in-situ polymerization and deposition of a PANI film on the surface of an ITO film.

8. The flexible multimodal sweat sensor array based on an indium tin oxide substrate according to claim 1, characterized in that: The sodium ion detection electrode (7) is formed by depositing a platinum nanolayer on the surface of an ITO thin film and then covering it with a sodium ion selective film.

9. A method for fabricating a flexible multimodal sweat sensor array based on an indium tin oxide substrate according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Conductive substrate patterning: Five mutually insulated electrode regions (3) and leads are formed on the ITO-PET film by chemical etching; S2. Simultaneous construction of platinum nanolayers: Platinum nanolayers were simultaneously deposited on the ITO surfaces of glucose detection electrode (6) and sodium ion detection electrode (7) using a single electroplating solution and pulse voltammetry. S3, pH-sensitive membrane polymerization: PANI film is deposited in situ by constant potential method on pH detection electrode (5). The electroplating solution used is a solution containing 0.5~1M dilute hydrochloric acid solution and 0.1~0.2M aniline solution, the voltage is 2.2~2.4V, and the time is 60~120s. S4. Modification of working electrodes: sequentially coat the glucose detection electrode (6) with a glucose oxidase composite membrane and the sodium ion detection electrode (7) with a sodium ion selective membrane.

10. The method for fabricating a flexible multimodal sweat sensor array based on an indium tin oxide substrate according to claim 9, characterized in that: The electroplating solution in S2 is an aqueous solution containing 2~5mM chloroplatinic acid and 0.2~0.5M sulfuric acid. The pulse voltammetric deposition potential is set to -0.8V~0.1V, and the deposition time is 60~120s.

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