Temperature self-calibration wearable sweat sensor system, preparation method and equipment

Abstract

The invention discloses a temperature self-calibration wearable sweat sensor system, a preparation method and equipment, and relates to the technical field of wearable sweat sensors. The system comprises a flexible multifunctional sensing electrode which is used for synchronously monitoring sodium ion concentration, potassium ion concentration and skin temperature in sweat; the micro-fluidic module is integrated with the flexible multifunctional sensing electrode and is used for guiding sweat to flow to the flexible multifunctional sensing electrode along a preset path and isolating direct contact between the flexible multifunctional sensing electrode and the skin; and the signal detector is connected with the flexible multifunctional sensing electrode. The skin temperature sensor is integrated, the skin temperature change can be monitored in real time in different activity states, the output result of the potassium and sodium ion sensor is corrected in real time by introducing a temperature compensation item into the Nernst equation, temperature interference is effectively eliminated, and continuous monitoring of Na and Kelectrolyte in sweat can be achieved.

Description

Technical Field

[0001] This invention relates to the field of wearable sweat sensor technology, specifically to a temperature self-calibrating wearable sweat sensor system, its preparation method, and equipment. Background Technology

[0002] Hydration plays a crucial role in maintaining normal bodily functions. In high-temperature environments, during strenuous exercise, or heavy physical labor, the body dissipates heat through profuse sweating, leading to rapid fluid loss and increasing the risk of dehydration. Mild dehydration typically manifests as thirst, decreased urine output, fatigue, and muscle cramps. Without timely intervention, it can progress to moderate or severe dehydration, even causing life-threatening conditions like heatstroke. Athletes, in particular, face the potential health threats of dehydration during high-intensity training under extreme heat conditions. An imbalance in hydration can severely impact athletic performance and potentially cause irreversible physiological damage. Therefore, continuous, real-time monitoring of bodily hydration can effectively prevent dehydration risks and provide valuable data for adjusting and optimizing training programs.

[0003] Currently, various methods exist for assessing human hydration status, including weight changes, plasma osmolality, urine specific gravity, urine color, urine osmolality, and bioelectrical impedance. While these methods possess a degree of accuracy, they often rely on specialized equipment and operators, making continuous, real-time monitoring difficult and limiting their practical application in dynamic environments such as high-temperature work or sports training. In contrast, sweat, as a non-invasive and continuously obtainable bodily fluid, contains a variety of biomarkers, providing a wealth of biochemical information closely related to human health, comparable in quantity to that of blood. Among these, the composition of inorganic ions (such as Na⁺, K⁺, Cl⁻), organic molecules, amino acids, hormones, proteins, and peptides in sweat is closely related to hydration status, making it a hot topic in wearable sensor research in recent years. In particular, the concentrations of sodium (Na⁺) and potassium (K⁺) ions show significant changes early in dehydration, thus becoming important markers of hydration status in sweat.

[0004] However, existing potassium and sodium ion sensors often overlook a crucial influencing factor: the interference of temperature on the sensor response. Currently, most sensors use calibration curves obtained with standard solutions at room temperature to estimate ion concentration. This method fails to account for response deviations caused by temperature changes during practical applications. This oversight can easily lead to significant errors, especially when the Nernst response itself exhibits a significant temperature dependence. In wearable applications, particularly during high-intensity activities such as sports, skin surface temperature rises significantly. If timely compensation is not provided, the estimation of ion concentration will be greatly interfered with, severely affecting the accuracy of the data and the reliability of the monitoring results. Therefore, this invention proposes a temperature-self-calibrated wearable sweat sensor system, its preparation method, and equipment. Summary of the Invention

[0005] The purpose of this invention is to provide a wearable sweat sensor system with self-calibrated temperature to solve the problems mentioned in the background art.

[0006] According to a first aspect of the present invention, in order to achieve the above-mentioned objective, the present invention provides the following technical solution: a wearable sweat sensor system with self-calibrated temperature, comprising: A flexible, multifunctional sensing electrode for simultaneously monitoring sodium and potassium ion concentrations in sweat and skin temperature. A microfluidic module, integrated with the flexible multifunctional sensing electrode, is used to guide sweat along a preset path to the flexible multifunctional sensing electrode and to isolate the flexible multifunctional sensing electrode from direct contact with the skin. A signal detector, connected to the flexible multifunctional sensing electrode, is used to collect, process, and transmit the electrical signals output by the flexible multifunctional sensing electrode. The signal detector integrates a temperature calibration module for real-time compensation of the measurement results of sodium ion concentration and potassium ion concentration based on skin temperature.

[0007] Furthermore, it also includes a protective cover and a protective shell. The flexible multifunctional sensing electrode, microfluidic module and signal detector are all integrated in the protective cover and protective shell through mutual adaptation between the protective cover and the protective shell.

[0008] Furthermore, the signal detector includes an STM32 microcontroller power supply, a power management module, a front-end analog circuit consisting of an amplifier circuit and a low-pass filter, and a low-power Bluetooth transmission module. The front-end analog circuit, the low-power Bluetooth transmission module, and the temperature calibration module are all electrically connected to the STM32 microcontroller power supply. The collected real-time data is transmitted to the front-end analog circuit and the temperature calibration module, and after calibration and processing, it is output in real time through the low-power Bluetooth transmission module.

[0009] Furthermore, the microfluidic module includes, from top to bottom, a waste liquid collection layer 41, an outlet layer 42, a paper-based microfluidic layer 43, and a sample introduction layer 44, with a flexible multifunctional sensing electrode 5 disposed between the paper-based microfluidic layer 43 and the sample introduction layer 44; The waste liquid collection layer is made of medical cotton cloth, which is used to absorb the discharged waste liquid and maintain the continuous flow of sweat; The outlet layer is made of polydimethylsiloxane material, and a rectangular outlet 421 is opened at the center of the outlet layer for the discharge or evaporation of waste liquid; The sample introduction layer is made of polydimethylsiloxane material, and multiple circular inlets 441 are opened on the sample introduction layer to guide sweat into the paper-based microfluidic 43. The paper-based microfluidic layer 43 is made by engraving filter paper. The paper-based microfluidic layer 43 includes a collection area and a collection area. The collection area is set as a rectangular area corresponding to the rectangular outlet of the outlet layer, which is used for temporary storage and detection of sweat. The collection area is set as multiple circular collection pieces with the same size as the multiple circular inlets of the sample injection layer. The circular collection pieces are connected to the collection area through strip channels, and the circular collection pieces correspond one-to-one with the multiple circular inlets of the sample injection layer, which is used for sweat collection and guidance.

[0010] Furthermore, the flexible multifunctional sensing electrode comprises, from top to bottom, a functional layer 51, a transduction layer 52, and an electrode carrier layer, wherein: The functional layer includes a potassium ion selective membrane 511, a sodium ion selective membrane 512, a polyvinyl butyral (PVB) membrane 513, and multi-walled carbon nanotubes, wherein the multi-walled carbon nanotubes are temperature-sensitive materials used for temperature sensing. The transduction layer 52 is made of a highly conductive polymer PEDOT:PSS and is used to convert the ion change signal sensed by the ion-selective membrane into an electronic signal. The electrode carrier layer consists of an insulating layer 531, a carbon layer 532, a silver / silver chloride layer 533, and a PET substrate 534, which are all prepared sequentially by screen printing.

[0011] Furthermore, the insulating layer 531 is prepared using UV-cured insulating ink to isolate the silver / silver chloride leads on the PET substrate 534 from contact with sweat and prevent short circuits. The carbon layer is formed by electro-carbon paste printing. The carbon layer is a circular area with a diameter of 3 mm, which is used to support the upper transconducting layer 52 to achieve stable electron transport. The silver / silver chloride layer 533 is used for signal acquisition and transmission, transmitting electrical signals of potassium and sodium ions and temperature to an external receiving circuit.

[0012] Furthermore, the temperature calibration module incorporates a temperature correction term into the Nernst equation to achieve temperature compensation, as detailed below: The Nernst equation for an ion-selective electrode is: After adding temperature calibration, it becomes: After formula transformation, we get: In the formula, ∆E is the electrode potential; T0 is selected as 20℃; γ is the standard potential at T0; β and K are the slope and intercept of the sensor sensitivity relative to the temperature change, respectively; a is the ion concentration; and T is the real-time temperature of the skin.

[0013] According to a second aspect of the present invention, the present invention provides a method for fabricating a flexible multifunctional sensing electrode, used to fabricate the flexible multifunctional sensing electrode described in the first aspect, specifically comprising: (1) Screen printing electrode design: A flexible multifunctional sensing electrode printing template was designed using CorelDRAW software. Each flexible multifunctional sensing electrode includes two working electrodes, one reference electrode, and one temperature sensing electrode. The working electrode and reference electrode areas are both circular structures with a diameter of 3 mm, and the thermistor material area of ​​the temperature sensor is 1.2 × 1 mm in size. (2) Fabrication of screen-printed substrate electrodes: The PET film substrate was pretreated by washing the PET film 534 in anhydrous ethanol for 5 minutes, air drying it naturally, and then ultrasonically cleaning it in deionized water for 5 minutes. Finally, it was placed in a 70°C oven to dry it thoroughly, ensuring that the surface was clean and had good adhesion. The screen printing process involves printing three layers of materials in sequence: first, silver / silver chloride paste is printed, then conductive carbon paste is printed, and finally green insulating ink is printed. The silver / silver chloride layer and the carbon layer were respectively heat-cured at 90°C for 20 minutes; The green insulating layer is cured by irradiation under a UV curing lamp for 1 minute. (3) Preparation of Na⁺ and K⁺ ion sensors: First, a potassium ion selective membrane mixture was prepared by dissolving 2 mg of valine, 0.5 mg of sodium tetraphenylborate, 64.7 mg of dioctyl phthalate and 32.7 mg of polyvinyl chloride in 350 μL of cyclohexanone and ultrasonically stirring for 20 minutes at room temperature. Next, a sodium ion-selective membrane mixture was prepared by dissolving 2 mg of tetraethyl 4-tert-butylcalixarenetetraacetate, 130.9 mg of dioctyl phthalate, 1.1 mg of sodium tetraborate and 66 mg of polyvinyl chloride in 1320 μL of tetrahydrofuran and ultrasonically stirring at room temperature for 20 minutes. Finally, the prepared ion-selective membrane mixture was sealed and stored in a 4°C refrigerator for later use. Na + and K + The ion sensor uses PEDOT:PSS as the ion electron transduction layer and employs a three-electrode system. An external Ag / AgCl reference electrode and a Pt electrode are used in an electrolyte containing 0.01 mol EDOT and 0.1 mol PSS. The electrodeposition of PEDOT:PSS is performed using a chronoamperometric method, with a constant current of 14 μA, a sampling interval of 5 ms, and a total electroplating time of 714 seconds. The electroplating is considered successful when the voltage is maintained at 0.9 volts. After electroplating, the sample was rinsed with deionized water and dried overnight. Finally, it was plated separately on the modified Na... + and K + Five microliters of K⁺-ISM and Na⁺-ISM were dropped onto the electrodes in three separate drops, with a one-hour interval between each drop. The modified electrodes were dried overnight. Then, 0.1 mol of NaCl and 0.01 mol of KCl solution were microinjected into the working electrode regions of the sodium ion electrode and potassium ion electrode, respectively, and conditioned at room temperature for at least 12 hours. (4) Fabrication of the temperature sensor: Two milligrams of multi-walled carbon nanotubes were dispersed in 1 milliliter of tetrahydrofuran and ultrasonically stirred for 2 hours to ensure that the MWCNTs were uniformly dispersed in the solution. One microliter of the mixture was then dropped between two Ag / AgCl plates. Finally, the electrode was dried at 60°C for 60 minutes to remove any water content. (5) Preparation of reference electrode: 79.1 mg of polyvinyl butyral powder and 50 mg of sodium chloride were added to 1 mL of anhydrous ethanol, magnetically stirred for 2 minutes, and then ultrasonically vibrated for 30 minutes to fully dissolve. Subsequently, 5 μL of the prepared PVB solution was dropped onto the surface of the reference electrode and dried overnight at room temperature.

[0014] According to a third aspect of the present invention, the present invention provides a method for fabricating a microfluidic module, used to fabricate the microfluidic module described in the first aspect, specifically comprising: (1) Use scissors to cut medical cotton cloth to a size of 45×25 mm to prepare waste liquid collection layer 41; (2) Cut the PET substrate into a circle with a diameter of 100 mm to serve as the substrate for spin coating; (3) Mix the liquid PDMS and the pre-curing agent thoroughly at a ratio of 10:1, place them in a vacuum chamber for 5 minutes, and remove the air bubbles from the mixture; (4) Place the PET substrate on the suction plate of the spin coater, drop 2 mL of PDMS onto the center of the PET substrate, spin coat at 500 rpm for 1 minute, remove the PET substrate, and cure in an oven at 60°C for 3 hours to obtain a PDMS film with a thickness of 1 mm. Peel the cured PDMS film off the PET substrate to obtain the PDMS film. (5) Use scissors and a punch to cut and punch the PDMS membrane to obtain the microfluidic outlet layer and sample inlet layer; (6) Using a carving knife, a paper-based microfluidic layer 43 is carved on the filter paper according to the set pattern, including 8 3 mm circular sampling pieces, 1 15 × 7 mm rectangular sweat collection area and 8 strip channels with a width of 1 mm; (7) Stack the waste liquid collection layer, outlet layer, paper-based microfluidic layer, flexible multifunctional sensing electrode, and sample injection layer in sequence and press gently to complete the assembly.

[0015] According to a fourth aspect of the present invention, the present invention provides a wearable device that integrates a temperature self-calibrating wearable sweat sensor system as described in the first aspect.

[0016] This invention has at least the following beneficial effects: (1) The system disclosed in this invention integrates a skin temperature sensor, which can monitor skin temperature changes in real time under different activity states. By introducing a temperature compensation term into the Nernst equation, it can realize real-time correction of the output results of the potassium and sodium ion sensor, effectively eliminating temperature interference and significantly improving the accuracy of electrolyte detection. At the same time, the sensor system can be integrated into a sports headband, which is convenient to install. It can realize continuous monitoring of Na⁺ and K⁺ electrolytes in sweat, thereby realizing real-time assessment of the body's hydration status. This invention has good stability and detection accuracy, and is suitable for continuous and non-invasive health monitoring. It has broad application prospects in the field of smart wearable devices.

[0017] (2) The present invention designs a flexible multifunctional sensing electrode that can simultaneously detect potassium and sodium ion concentration and skin temperature. The potassium ion sensor has a sensitivity of 59.6±0.35 mV / dec, the sodium ion sensor has a sensitivity of 58.6±0.01 mV / dec, and the temperature sensor has a TCR of -0.664% / °C. The electrode is fabricated using screen printing technology, which has low cost and simple manufacturing process, and can be mass-produced.

[0018] (3) The present invention also prepares a microfluidic device that can be highly integrated with a flexible multifunctional sensing electrode. The microfluidic device is made of PDMS, which has good air permeability and biocompatibility, and can adhere to the skin surface to achieve efficient collection and guidance of sweat.

[0019] (4) The present invention uses filter paper as a paper-based fluid channel to absorb sweat and guide it to the working area of ​​the electrode. Therefore, the electrochemical electrode does not need to come into contact with human skin, which not only ensures the accuracy of signal acquisition, but also effectively reduces the stimulation and other discomfort to the wearer's skin.

[0020] (5) This invention constructs a wearable device integrating a flexible multifunctional sensing electrode array, a microfluidic module, and a signal detection circuit, which can be integrated into a sports headband. This structural design not only improves wearing comfort but also effectively reduces interference caused by vibration during exercise, ensuring the stability and accuracy of the detection data. In addition, the assembly of the microfluidic chip and the PCB device is detachable, allowing for the replacement of microfluidic components, and the circuit components are reusable, resulting in a long service life.

[0021] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall structure of the system described in this invention; Figure 2 This is a dimensional diagram of the protective cover in this invention; Figure 3 This is a dimensional diagram of the protective shell in this invention; Figure 4 This is a schematic diagram of the acquisition circuit inside the signal detector in this invention; Figure 5 This is an exploded view of the microfluidic module in this invention; Figure 6 This is a diagram of the sweat transport path of the microfluidic module in this invention; Figure 7 This is a diagram showing the dimensions of the outlet layer of the microfluidic module in this invention; Figure 8 This is a diagram showing the sample introduction layer dimensions of the microfluidic module in this invention; Figure 9 This is a dimension diagram of the paper-based microfluidic layer of the microfluidic module in this invention; Figure 10 This is an exploded view of the flexible multifunctional sensing electrode in this invention. Figure 11 This is a schematic diagram showing the dimensions of the flexible multifunctional sensing electrode in this invention; Figure 12 This is a flowchart of the temperature calibration module in this invention. Figure 13 This is a schematic diagram of the signal acquisition circuit in this invention. Figure 14 This is a schematic diagram of the STM32 microcontroller in the signal acquisition circuit of this invention; Figure 15 This is a schematic diagram of the analog circuit of the front end of the Na⁺ and K⁺ ion sensor in the signal acquisition circuit of the present invention; Figure 16 This is a schematic diagram of the analog circuit at the front end of the temperature sensor in the signal acquisition circuit of this invention; Figure 17 This is a schematic diagram of the Bluetooth transmission module in the signal acquisition circuit of the present invention; Figure 18 This is a schematic diagram of the connection interface circuit in the signal acquisition circuit of the present invention; Figure 19 This is a schematic diagram of the power management module in the signal acquisition circuit of the present invention; Figure 20 This is a schematic diagram of the real-time detection results of human body hydration status in this invention.

[0023] Figure label: 1. Protective cap; 2. Button battery; 3. Signal detector; 4. Microfluidic module; 41. Waste liquid collection layer; 42. Outlet layer; 43. Paper-based microfluidic layer; 44. Sample injection layer; 441. Circular inlet; 421. Rectangular outlet; 5. Flexible multifunctional sensing electrode; 51. Functional layer; 52. Transduction layer; 53. Electrode carrier layer; 511. Potassium ion selective membrane; 512. Sodium ion selective membrane; 513. PVB membrane; 514. Multi-walled carbon nanotubes; 531. Insulating layer; 532. Carbon layer; 533. Silver / silver chloride layer; 534. PET substrate; 6. Protective shell. Detailed Implementation

[0024] The technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0025] Example 1: Please see Figures 1-20 The present invention provides a technical solution: a temperature self-calibrating wearable sweat sensor system, including a flexible multifunctional sensing electrode 5, for simultaneously monitoring the concentration of sodium ions, potassium ions and skin temperature in sweat; The microfluidic module 4 is integrated with the flexible multifunctional sensing electrode 5 to guide sweat along a preset path to the flexible multifunctional sensing electrode 5 and to isolate the flexible multifunctional sensing electrode 5 from direct contact with the skin. The signal detector 3 is connected to the flexible multifunctional sensing electrode 5 and is used to collect, process and transmit the electrical signals output by the flexible multifunctional sensing electrode 5. The signal detector 3 integrates a temperature calibration module for real-time compensation of the measurement results of sodium ion concentration and potassium ion concentration based on skin temperature.

[0026] The overall structure of the system is as follows Figure 1 As shown, the system mainly includes a protective cover 1, a button battery 2, a signal detector 3, a microfluidic module 4, a flexible multifunctional sensing electrode 5, and a protective shell 6. This system can be comfortably attached to the skin of multiple parts of the human body, such as the forehead, arms, and wrists. The system can collect the liquid in the sweat glands through the microfluidic module and transmit it to the electrode detection point. It can also transmit the calibrated signal to the mobile device via Bluetooth. It can achieve dynamic and real-time monitoring of the concentration of Na⁺ and K⁺ ions in sweat and skin temperature in different body positions. The application of this system is expected to provide a scientific basis for assessing hydration status during outdoor training and help regulate exercise status and personalize health management.

[0027] Regarding the technical solution of this embodiment, the outer protective cover 1 and protective shell 6 are made of resin and manufactured using 3D printing technology. The recommended overall dimensions are 65×50×18 mm. To ensure stable Bluetooth signal transmission, a 3×3 mm through hole is specially designed on the protective cover. Simultaneously, a rectangular opening measuring 19×8 mm is opened on the side wall of the protective shell to achieve effective connection between the electrodes and the internal circuitry. For detailed structural and dimensional design, please refer to... Figure 2 , 3 This protective case, while possessing good mechanical strength and structural stability, also features lightweight, compactness, and functional practicality, making it suitable for long-term sweat monitoring applications in dynamic environments.

[0028] Regarding the technical solution of this embodiment, the signal detector 3 integrates an STM32 microcontroller power supply, a power management module, a front-end analog circuit consisting of an amplifier circuit and a low-pass filter, and a low-power Bluetooth transmission module. It acquires, calibrates, processes, and transmits signals. The acquired real-time data is transmitted to the system's built-in algorithm module. After precise calibration and processing by the front-end analog circuit and the low-power Bluetooth transmission module, the accuracy of the data output is ensured. Subsequently, the processed data is transmitted in real-time via the Bluetooth communication module. A schematic diagram of the acquisition circuit is shown below. Figure 4 As shown, the overall dimensions are 41 × 60 mm.

[0029] Regarding the technical solution of this embodiment, the microfluidic module 4 and the flexible multifunctional sensing electrode 5 together constitute a microfluidic chip. A recommended overall size is 45×25 mm. If the size is too large, it will affect the comfort of wearing it; conversely, if the size is too small, the collected sweat may not effectively cover the electrode area, leading to signal acquisition failure. Figure 5 As shown, the overall structure of this microfluidic chip is mainly divided into five functional layers, namely: a waste liquid collection layer 41, an outlet layer 42, a paper-based microfluidic layer 43, a flexible multifunctional sensing electrode 5, and a sample introduction layer 44. These five layers are assembled sequentially. The outlet layer 42 has a rectangular outlet 421 at its center for waste liquid discharge or evaporation. The sample introduction layer has multiple circular inlets 441 to guide sweat into the paper-based microfluidic layer 43. The sweat transport path is as follows: Figure 6 As shown.

[0030] Furthermore, the waste liquid collection layer 41 is made of medical cotton cloth with good water absorption properties, which is used to efficiently absorb the waste liquid discharged from the outlet area 421, thereby maintaining the continuous flow of sweat and ensuring continuous and stable monitoring of metabolites and electrolytes in sweat. Its size is designed to be 45×25 mm to ensure good liquid carrying capacity.

[0031] Both the outlet layer 42 and the sample inlet layer 44 are made of polydimethylsiloxane (PDMS). PDMS is widely used in wearable sensors due to its excellent light transmittance, biocompatibility, and skin adhesion. Both PDMS films are 1 mm thick, a thickness that ensures sufficient mechanical strength while maintaining good flexibility, suitable for assembling multilayer flexible structures. In terms of structural design, the sample inlet layer 44 has eight 3 mm diameter circular inlets 441 to guide sweat into the paper-based microfluidic system 43. Figure 8 As shown, the outlet layer 42 is provided with a rectangular outlet 421 with dimensions of 15×7 mm for the discharge or evaporation of waste liquid, such as... Figure 7 As shown.

[0032] The paper-based microfluidic layer 43 was fabricated directly on ordinary filter paper using a carving tool, such as... Figure 9 As shown, this process is simple, low-cost, and can be mass-produced. This layer mainly includes two functional areas: a collection area and a sampling area. The collection area has eight circular collection plates with a diameter of 3 mm, corresponding to the circular inlet 441 of the sample layer 44, to collect and guide sweat. The sampling area is a rectangular liquid storage structure, corresponding to the rectangular outlet 421 of the outlet layer 42, located above the flexible multifunctional electrode, and is used as a sweat temporary storage and detection pool to ensure that the electrode can stably contact the sweat and achieve accurate electrochemical signal acquisition. The collection area and the sampling area are connected by eight strip channels with a width of 1 mm, which are used to guide the sweat from the collection point to the detection area evenly. This structural design not only improves the reliability of sweat transmission, but also enhances the stability and response consistency of the sensor in dynamic environments.

[0033] Regarding the technical solution of this embodiment, such as Figure 10As shown, the flexible multifunctional sensing electrode 5 comprises, from top to bottom, a functional layer 51, a transduction layer 52, and an electrode support layer 53. The functional layer 51 integrates a variety of key functional materials, including a potassium ion selective membrane 511, a sodium ion selective membrane 512, a polyvinyl butyral (PVB) membrane 513, and multi-walled carbon nanotubes (MWCNTs) 514. The potassium / sodium ion selective membranes (511, 512) can specifically identify and screen target ions (K+, Na+) in sweat, allowing them to effectively enter the transduction layer (52). The PVB membrane 513 serves as a stable coating for the reference electrode, helping to maintain the consistency and reliability of its potential. The multi-walled carbon nanotubes 514 serve as a temperature-sensitive material. The transduction layer 52 is composed of a highly conductive polymer, PEDOT:PSS, which has excellent ion-electron transduction performance and can convert the ion change signal sensed by the ion selective membrane into a stable electronic signal, which is then transmitted to the carbon layer 532. The electrode carrier layer 53 comprises four structural layers: an insulating layer 531, a carbon layer 532, a silver / silver chloride layer 533, and a PET substrate 534, all fabricated sequentially using a screen printing process. The insulating layer 531 uses UV-cured insulating ink (with resin as the main component) to isolate the silver / silver chloride leads on the PET substrate 534 from sweat, preventing short circuits. The carbon layer 532 is formed by printing conductive carbon paste, forming a circular area with a diameter of 3 mm, supporting the upper transducer layer 52 for stable electron transmission. The silver / silver chloride layer 533 is used for signal acquisition and transmission, transmitting electrical signals of potassium and sodium ions and temperature to the external receiving circuit. The bottom layer is the PET substrate 534, serving as a flexible support substrate, providing mechanical stability and skin-friendly properties for the entire electrode structure.

[0034] To reduce the error caused by temperature, a temperature correction term is added to the Nernst equation for the technical solution in this embodiment, as follows: The Nernst equation for an ion-selective electrode is: After adding temperature calibration, it becomes: After formula transformation, we get: The standard temperature T0 is set to 20℃, ∆E is the electrode potential, γ is the standard potential at T0, β and K are the slope and intercept of the sensor sensitivity relative to temperature change, respectively, a is the ion concentration, and T is the real-time skin temperature. β, K, and γ are calculated using experimental data. The specific calibration flowchart is shown below. Figure 12 As shown.

[0035] The technical solution of the present invention for detecting human hydration status will be verified by experimental testing using specific embodiments: To evaluate the platform's potential for accurate and non-invasive monitoring of dehydration, this embodiment assembles flexible integrated sensing electrodes, microfluidic devices, and circuit boards, and fixes them onto a sports headband to create a "smart headband." Figure 1 The subjects underwent outdoor running tests. The flexible, multifunctional sensing electrodes and detection circuitry were encapsulated in a silicone case and mounted on a sports headband for easy wear. To prevent the electrodes from shifting during running, the microfluidic chip was secured to the skin with waterproof tape. Before wearing the device, the subjects' foreheads were wiped with alcohol and deionized water, and the sensors were calibrated before testing.

[0036] In this embodiment, subjects underwent two 1-hour continuous outdoor running experiments, with real-time monitoring of changes in sodium (Na⁺) and potassium (K⁺) ion concentrations and temperature in their sweat. To verify the accuracy of the compensated sensor, sweat collected from subjects at different exercise time periods (20, 30, 40, 50, 60 minutes) was placed in centrifuge tubes, and the actual Na⁺ and K⁺ concentrations in the sweat were analyzed using inductively coupled plasma mass spectrometry (ICP-MS). Figure 20 As shown in Figure a, during the hydration experiment (drinking 150ml of water every 5 minutes), the body temperature fluctuated between 29℃ and 38℃. Simultaneously, for the ion sensor, there was a significant difference between the data without temperature calibration and the data after calibration. Without temperature compensation, the measured electrolyte concentrations showed significant deviations, with the largest deviation for Na⁺ concentration being 28% and the largest deviation for K⁺ concentration being 56%. After temperature calibration, the error between the obtained concentration data and the actual values ​​was significantly reduced to within ±4.2%. Furthermore, in this experiment, the K⁺ ion concentration in sweat initially showed a decreasing trend, while the Na⁺ ion concentration showed an increasing trend followed by stabilization. For the dehydration experiment (exercise without drinking water), as... Figure 20 As shown in Figure b, the human body temperature varies within the range of 28℃ to 38℃. The maximum deviation in Na⁺ ion concentration is 36%, and the maximum deviation in K⁺ ion concentration is 45%. After temperature calibration, the error between the obtained concentration data and the actual values ​​is significantly reduced to within ±3%. Furthermore, after 40 minutes of running, the Na⁺ ion concentration shows a rapid upward trend. The K⁺ concentration also increases, but the increase is not significant, possibly due to the release of K⁺ caused by changes in cell metabolism, leading to a slight increase. Therefore, the constructed wearable sensor platform can achieve stable and highly reliable monitoring of hydration status during exercise.

[0037] In summary, the system disclosed in this invention integrates a skin temperature sensor, enabling real-time monitoring of skin temperature changes under different activity states. By introducing temperature compensation, it effectively eliminates temperature interference, significantly improving the accuracy of electrolyte detection. Furthermore, this sensor system can be integrated into a sports headband, making installation convenient. It allows for continuous monitoring of Na⁺ and K⁺ electrolytes in sweat, thereby achieving real-time assessment of the body's hydration status. This invention possesses good stability and detection accuracy, making it suitable for continuous, non-invasive health monitoring and showing broad application prospects in the field of smart wearables.

[0038] Example 2: The flexible multifunctional sensing electrode includes a potassium ion electrode, a sodium ion electrode, and a temperature sensing electrode. The potassium / sodium ion sensor adopts a two-electrode system. All electrodes can be prepared by methods such as magnetron sputtering and vacuum coating. However, this embodiment recommends the use of screen printing process because it has the advantages of low cost, simple process, and high preparation efficiency.

[0039] This embodiment provides a method for fabricating a flexible multifunctional sensing electrode, used to prepare the flexible multifunctional sensing electrode described in Embodiment 1, as follows: (1) Screen printing electrode design: The screen printing stencil was designed using the graphic design software CorelDRAW. Each flexible multifunctional sensing electrode includes two working electrodes, one reference electrode, and one temperature sensing electrode. The working and reference electrode areas are both circular structures with a diameter of 3 mm. The temperature sensor's thermistor material area measures 1.2 × 1 mm. Furthermore, the stencil supports printing multiple sensors simultaneously. The specific pattern dimensions and structure of each sensor are as follows... Figure 11 As shown; (2) Fabrication of screen-printed substrate electrodes: Before screen printing, the PET film substrate needs to be pretreated: First, a 20×30 cm, 100 micrometer thick PET film 534 was cleaned in anhydrous ethanol for 5 minutes, air-dried, and then ultrasonically cleaned in deionized water for 5 minutes. It was then thoroughly dried in a 70°C oven to ensure a clean surface and good adhesion. Figure 10 As shown, the screen printing process involves printing three layers of material sequentially: first, silver / silver chloride paste, then conductive carbon paste, and finally green insulating ink; the silver / silver chloride layer 533 and the carbon layer 532 need to be heat-cured at 90°C for 20 minutes each; the green insulating layer 531 needs to be cured by irradiation under a UV curing lamp (175 watts) for 1 minute. The prepared substrate electrode can be used without any pretreatment. (3) Preparation of Na⁺ and K⁺ ion sensors: First, a potassium ion selective membrane mixture (K⁺-ISM) was prepared by dissolving 2 mg of valinemycin, 0.5 mg of sodium tetraphenylborate, 64.7 mg of dioctyl phthalate and 32.7 mg of polyvinyl chloride in 350 μL of cyclohexanone and ultrasonically stirring at room temperature for 20 minutes. A similar method was used to prepare a sodium ion selective membrane mixture (Na⁺-ISM). 2 mg of tetraethyl 4-tert-butylcalixarenetetraacetate, 130.9 mg of dioctyl phthalate, 1.1 mg of sodium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate, and 66 mg of polyvinyl chloride were dissolved in 1320 μL of tetrahydrofuran (THF) and ultrasonically stirred at room temperature for 20 minutes. Note that high temperatures should be avoided during stirring to prevent changes in material properties. Finally, the prepared ion-selective membrane mixture was sealed and stored in a 4°C refrigerator for later use. For the Na+ and K+ ion sensors, PEDOT:PSS was used as the ion electron transduction layer. A three-electrode system was employed, with an external Ag / AgCl reference electrode and a Pt electrode. PEDOT:PSS was electrodeposited in an electrolyte containing 0.01 mol EDOT and 0.1 mol PSS using a chronoamperometric method. The constant current was 14 μA, the sampling interval was 5 ms, and the total plating time was 714 seconds. A final voltage of 0.9 V indicated successful plating. After electroplating, the electrodes were rinsed with deionized water and dried overnight. Finally, 5 μL of K⁺-ISM and Na⁺-ISM were drop-coated onto the modified Na⁺ and K⁺ electrodes, respectively, in three separate applications with a 1-hour interval between each application. The modified electrodes were then dried overnight. To prevent potential drift, 0.1 mol NaCl and 0.01 mol KCl solutions were microinjected into the working electrode regions of the sodium and potassium ion electrodes, respectively (avoiding contact with the temperature sensor and reference electrode), and conditioned at room temperature for at least 12 hours. (4) Fabrication of the temperature sensor: 2 mg of MWCNTs were dispersed in 1 mL of THF and ultrasonically stirred for 2 h to ensure that the MWCNTs were uniformly dispersed in the solution. 1 μL of the mixture was dropped between two Ag / AgCl plates. Finally, the electrode was dried at 60 °C for 60 min to remove any water content. (5) Preparation of reference electrode: 79.1 mg of polyvinyl butyral (PVB) powder and 50 mg of sodium chloride were added to 1 mL of anhydrous ethanol, magnetically stirred for 2 minutes and then ultrasonically vibrated for 30 minutes to fully dissolve. Then, 5 μL of the prepared PVB solution was dropped onto the surface of the reference electrode and dried overnight at room temperature.

[0040] Example 3: This embodiment provides a method for fabricating a microfluidic module, used to fabricate the microfluidic module described in Embodiment 1, specifically including: The waste liquid collection layer 41 is made from purchased medical cotton cloth; the outlet layer 42 and the sample injection layer 44 are prepared by spin coating and can be completed by simple cutting; the paper-based microfluidic layer 43 is prepared from ordinary filter paper; the specific preparation process is as follows: (1) Use scissors to cut medical cotton cloth to a size of 45×25 mm to prepare waste liquid collection layer 41; (2) Cut the PET substrate into a circle. Its diameter should be greater than the length and width of the top layer of the device. A diameter of 100 mm is recommended as the substrate for spin coating. (3) Mix the liquid PDMS and the pre-curing agent thoroughly at a ratio of 10:1, place them in a vacuum chamber for 5 minutes, and remove the air bubbles from the mixture; (4) Place the PET substrate on the spin coater and drop an appropriate amount of PDMS onto the center of the PET substrate, 2 mL is recommended. Spin coat at 500 rpm for 1 minute, remove the PET substrate, and cure in an oven at 60°C for 3 hours to obtain a PDMS film with a thickness of 1 mm. Peel the cured PDMS film off the PET substrate to obtain the PDMS film. (5) Use tools such as scissors and hole punches according to Figure 7 , 8 The PDMS membrane is cut and perforated according to its shape and size to obtain the microfluidic outlet layer 42 and sample injection layer 44; (6) Using a carving knife, a paper-based microfluidic layer 43 is carved on the filter paper according to the pattern. It consists of 8 circular (3 mm) sample inlets, 1 rectangular (15 × 7 mm) sweat collection area, and 8 capillary channels (1 mm wide); (7) The prepared flexible multifunctional sensing electrode 5 can be put into use without any processing; (8) Arrange the waste liquid collection layer 41, outlet layer 42, paper-based microfluidic layer 43, flexible multifunctional sensing electrode 5, and sample introduction layer 44 according to... Figure 5 The microfluidic chip is assembled by stacking the relative positions of the components in sequence and pressing them gently.

[0041] Example 4: Detection circuit design and fabrication This embodiment designs a detection circuit for electrical signals of potassium and sodium ions and temperature, creating a highly flexible detector. The specific idea is as follows: The front-end module of the detection circuit receives the electrical signal output from the flexible multifunctional sensing electrode. For the potassium and sodium ion sensor, the electrical signal is the potential difference between the shared reference electrode and the working electrode of the potassium and sodium sensor. This potential difference is first buffered by an operational amplifier, then passed through a differential amplifier to reduce external noise interference, and finally filtered and rectified by a low-pass filter. For the temperature sensor, the electrical signal is the resistance value of the sensitive material. First, a constant current source converts the resistance signal into a voltage signal, where the constant current source converts the voltage through an operational amplifier. When current flows through the temperature sensor, a voltage drop is generated. Finally, the weak voltage drop signal is amplified to output the desired voltage signal. The filtered voltage is then converted from digital to analog by an STM32 microcontroller, and data calibration is performed based on the detected skin temperature. Finally, the signal is transmitted to a computer or mobile phone via a Bluetooth module. The overall framework diagram of the detection circuit is shown below. Figure 13 As shown.

[0042] (1) First, use AD software to design the circuit schematic, such as Figures 14 to 19 As shown; The microcontroller, as the control core of the detector, is responsible for processing digital signals within the system. Based on its main functions, technical parameters, and logic design requirements, this embodiment selects the STM32F103RET6 programmable microcontroller (STMicroelectronics), and designs the circuit in conjunction with the characteristics of its related peripheral modules. (See attached diagram.) Figure 14 This microcontroller can process the signals acquired by the front-end analog circuit and convert them into digital signals through an ADC. In order to achieve temperature compensation of the signal and Bluetooth wireless transmission, a temperature calibration module and a data processing module are also embedded in the program, so that data from different channels can be calibrated and sent alternately to the user's mobile application terminal.

[0043] The front-end analog circuit of the potential sensor uses AD8606 and AD8608 operational amplifier chips, which feature low offset, low noise, and high speed. Due to the different potentials caused by ion migration, a potential difference is formed between the working electrode (WE) and the reference electrode (RE). This potential difference is processed by the instrumentation amplifier circuit, which consists of two non-inverting amplifiers and one differential amplifier. This structure significantly improves the circuit's input impedance and minimizes attenuation of weak input signals. In addition, to eliminate high noise and ensure stable signal output, a fourth-order low-pass filter is introduced, such as... Figure 15 ; For the front-end analog circuit of the temperature sensor, the voltage is converted into a constant current source by an operational amplifier. When current flows through the temperature sensor, a voltage drop is generated. This weak voltage drop signal is amplified to output the desired voltage signal. The schematic diagram is shown below. Figure 16 As shown; For the Bluetooth module, this embodiment uses the CH9140 low-power Bluetooth module, which is compatible with the BLE4.2 protocol and meets the device's requirements for low power consumption and compact structure. This module uses asynchronous serial communication with a baud rate of 115,200 bps, and can seamlessly interface with commonly used serial port software and tools. Its circuit schematic is shown below. Figure 17 As shown, in this module, the Bluetooth protocol stack is responsible for implementing the communication protocol functions, while the microcontroller is responsible for data acquisition, processing, and data interaction with the Bluetooth module.

[0044] The circuit design of the connection interface between the detector and the sensor is as follows: Figure 18 As shown, this is used for data acquisition by potassium and sodium ion sensors and temperature sensors.

[0045] Based on the operating current parameters and battery life of each module, this embodiment selects a 3.7V rechargeable button battery 2. The system is powered by four voltage converters, including a boost converter chip TPS613222ADBVR and a buck converter chip TPS76333DBVR. The TPS613222ADBVR boosts the standard 3.3V voltage to 5V to power the AD8606, AD8608 operational amplifier chips and related peripheral modules; the TPS76333DBVR can reduce the 3.7V output voltage from the battery to 3.3V to power the microprocessor and Bluetooth module. The circuit schematic is shown below. Figure 19 As shown.

[0046] (2) After completing the circuit connection and component layout design on the printed circuit board (PCB), verify the rationality and connectivity of the circuit through the design rule check (DRC), and hand over the design documents to a commercial customization manufacturer to make a physical circuit board. (3) Manually solder various electronic components. After soldering, use a microscope and multimeter to inspect the solder joints to ensure they are firm and correctly connected, and avoid cold solder joints or short circuits; (4) Use Keil5 software to write and develop programs, and connect the computer port to the circular pad on the PCB board through temporary wires to realize firmware burning to the microcontroller; (5) Connect the flexible multifunctional sensing electrode to the designated interface, and install the button battery on the PCB circuit board to provide support for subsequent experiments or practical applications. The actual object is shown in the figure. Figure 1 As shown.

[0047] Figure 20 This is a schematic diagram of the real-time detection results of human body hydration status in this embodiment.

[0048] Example 5: This embodiment provides a wearable device that integrates a temperature self-calibrating wearable sweat sensor system as described in Embodiment 1.

[0049] It should be noted that the temperature self-calibrating wearable sweat sensor system provided in this application, and other components of the wearable device, can be designed, manufactured, and sold separately, or they can be assembled together and sold as a whole. Whether they are individual components formed before assembly or as a whole formed after assembly, they all fall within the protection scope of this application.

[0050] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0051] For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances. When an element is referred to as being "assembled on," "mounted on," "fixed to," or "set on" another element, it may be directly on the other element or there may be an intermediate element present. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be an intermediate element present. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible embodiments.

[0052] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0053] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

Claims

1. A wearable sweat sensor system with self-calibrated temperature, characterized in that, include: A flexible, multifunctional sensing electrode for simultaneously monitoring sodium and potassium ion concentrations in sweat and skin temperature. A microfluidic module, integrated with the flexible multifunctional sensing electrode, is used to guide sweat along a preset path to the flexible multifunctional sensing electrode and to isolate the flexible multifunctional sensing electrode from direct contact with the skin. A signal detector, connected to the flexible multifunctional sensing electrode, is used to collect, process, and transmit the electrical signals output by the flexible multifunctional sensing electrode. The signal detector integrates a temperature calibration module for real-time compensation of the measurement results of sodium ion concentration and potassium ion concentration based on skin temperature.

2. The wearable sweat sensor system with self-calibrated temperature according to claim 1, characterized in that: It also includes a protective cover and a protective shell. The flexible multifunctional sensing electrode, microfluidic module and signal detector are all integrated in the protective cover and protective shell through mutual adaptation between the protective cover and the protective shell.

3. The wearable sweat sensor system with self-calibrated temperature according to claim 2, characterized in that: The signal detector includes an STM32 microcontroller power supply, a power management module, a front-end analog circuit consisting of an amplifier circuit and a low-pass filter, and a low-power Bluetooth transmission module. The front-end analog circuit, the low-power Bluetooth transmission module, and the temperature calibration module are all electrically connected to the STM32 microcontroller power supply. The collected real-time data is transmitted to the front-end analog circuit and the temperature calibration module, and after calibration and processing, it is output in real time through the low-power Bluetooth transmission module.

4. The wearable sweat sensor system with self-calibrated temperature according to claim 3, characterized in that: The microfluidic module comprises, from top to bottom, a waste liquid collection layer 41, an outlet layer 42, a paper-based microfluidic layer 43, and a sample introduction layer 44, with a flexible multifunctional sensing electrode 5 disposed between the paper-based microfluidic layer 43 and the sample introduction layer 44. The waste liquid collection layer is made of medical cotton cloth, which is used to absorb the discharged waste liquid and maintain the continuous flow of sweat; The outlet layer is made of polydimethylsiloxane material, and a rectangular outlet 421 is opened at the center of the outlet layer for the discharge or evaporation of waste liquid; The sample introduction layer is made of polydimethylsiloxane material, and multiple circular inlets 441 are opened on the sample introduction layer to guide sweat into the paper-based microfluidic 43. The paper-based microfluidic layer 43 is made by engraving filter paper. The paper-based microfluidic layer 43 includes a collection area and a collection area. The collection area is set as a rectangular area corresponding to the rectangular outlet of the outlet layer, which is used for temporary storage and detection of sweat. The collection area is set as multiple circular collection pieces with the same size as the multiple circular inlets of the sample injection layer. The circular collection pieces are connected to the collection area through strip channels, and the circular collection pieces correspond one-to-one with the multiple circular inlets of the sample injection layer, which is used for sweat collection and guidance.

5. The wearable sweat sensor system with self-calibrated temperature according to claim 4, characterized in that: The flexible multifunctional sensing electrode comprises, from top to bottom, a functional layer 51, a transduction layer 52, and an electrode carrier layer, wherein: The functional layer includes a potassium ion selective membrane 511, a sodium ion selective membrane 512, a polyvinyl butyral (PVB) membrane 513, and multi-walled carbon nanotubes, wherein the multi-walled carbon nanotubes are temperature-sensitive materials used for temperature sensing. The transduction layer 52 is made of a highly conductive polymer PEDOT:PSS and is used to convert the ion change signal sensed by the ion-selective membrane into an electronic signal. The electrode carrier layer consists of an insulating layer 531, a carbon layer 532, a silver / silver chloride layer 533, and a PET substrate 534, which are all prepared sequentially by screen printing.

6. The wearable sweat sensor system with self-calibrated temperature according to claim 5, characterized in that: The insulating layer 531 is prepared with UV-cured insulating ink and is used to isolate the silver / silver chloride leads on the PET substrate 534 from sweat to prevent short circuits. The carbon layer is formed by electro-carbon paste printing. The carbon layer is a circular area with a diameter of 3 mm, which is used to support the upper transconducting layer 52 to achieve stable electron transport. The silver / silver chloride layer 533 is used for signal acquisition and transmission, transmitting electrical signals of potassium and sodium ions and temperature to an external receiving circuit.

7. The wearable sweat sensor system with self-calibrated temperature according to claim 6, characterized in that: The temperature calibration module incorporates a temperature correction term into the Nernst equation to achieve temperature compensation, as detailed below: The Nernst equation for an ion-selective electrode is: After adding temperature calibration, it becomes: After formula transformation, we get: In the formula, ∆E is the electrode potential; T0 is selected as 20℃; γ is the standard potential at T0; β and K are the slope and intercept of the sensor sensitivity relative to the temperature change, respectively; a is the ion concentration; and T is the real-time temperature of the skin.

8. A method for fabricating a flexible multifunctional sensing electrode, used to fabricate the flexible multifunctional sensing electrode according to any one of claims 1 to 7, characterized in that, Specifically, it includes: (1) Screen printing electrode design: A flexible multifunctional sensing electrode printing template was designed using CorelDRAW software. Each flexible multifunctional sensing electrode includes two working electrodes, one reference electrode, and one temperature sensing electrode. The working electrode and reference electrode areas are both circular structures with a diameter of 3 mm, and the thermistor material area of ​​the temperature sensor is 1.2 × 1 mm in size. (2) Fabrication of screen-printed substrate electrodes: The PET film substrate was pretreated by washing the PET film 534 in anhydrous ethanol for 5 minutes, air drying it naturally, and then ultrasonically cleaning it in deionized water for 5 minutes. Finally, it was placed in a 70°C oven to dry it thoroughly, ensuring that the surface was clean and had good adhesion. The screen printing process involves printing three layers of materials in sequence: first, silver / silver chloride paste is printed, then conductive carbon paste is printed, and finally green insulating ink is printed. The silver / silver chloride layer and the carbon layer were respectively heat-cured at 90°C for 20 minutes; The green insulating layer is cured by irradiation under a UV curing lamp for 1 minute. (3) Preparation of Na⁺ and K⁺ ion sensors: First, a potassium ion selective membrane mixture was prepared by dissolving 2 mg of valine, 0.5 mg of sodium tetraphenylborate, 64.7 mg of dioctyl phthalate and 32.7 mg of polyvinyl chloride in 350 μL of cyclohexanone and ultrasonically stirring for 20 minutes at room temperature. Next, a sodium ion-selective membrane mixture was prepared by dissolving 2 mg of tetraethyl 4-tert-butylcalixarenetetraacetate, 130.9 mg of dioctyl phthalate, 1.1 mg of sodium tetraborate and 66 mg of polyvinyl chloride in 1320 μL of tetrahydrofuran and ultrasonically stirring at room temperature for 20 minutes. Finally, the prepared ion-selective membrane mixture was sealed and stored in a 4°C refrigerator for later use. Na + and K + The ion sensor uses PEDOT:PSS as the ion electron transduction layer and employs a three-electrode system. An external Ag / AgCl reference electrode and a Pt electrode are used in an electrolyte containing 0.01 mol EDOT and 0.1 mol PSS. The electrodeposition of PEDOT:PSS is performed using a chronoamperometric method, with a constant current of 14 μA, a sampling interval of 5 ms, and a total electroplating time of 714 seconds. The electroplating is considered successful when the voltage is maintained at 0.9 volts. After electroplating, the sample was rinsed with deionized water and dried overnight. Finally, it was plated separately on the modified Na... + and K + Five microliters of K⁺-ISM and Na⁺-ISM were dropped onto the electrodes in three separate drops, with a one-hour interval between each drop. The modified electrodes were dried overnight. Then, 0.1 mol of NaCl and 0.01 mol of KCl solution were microinjected into the working electrode regions of the sodium ion electrode and potassium ion electrode, respectively, and conditioned at room temperature for at least 12 hours. (4) Fabrication of the temperature sensor: Two milligrams of multi-walled carbon nanotubes were dispersed in 1 milliliter of tetrahydrofuran and ultrasonically stirred for 2 hours to ensure that the MWCNTs were uniformly dispersed in the solution. One microliter of the mixture was then dropped between two Ag / AgCl plates. Finally, the electrode was dried at 60°C for 60 minutes to remove any water content. (5) Preparation of reference electrode: 79.1 mg of polyvinyl butyral powder and 50 mg of sodium chloride were added to 1 mL of anhydrous ethanol, magnetically stirred for 2 minutes, and then ultrasonically vibrated for 30 minutes to fully dissolve. Subsequently, 5 μL of the prepared PVB solution was dropped onto the surface of the reference electrode and dried overnight at room temperature.

9. A method for fabricating a microfluidic module, used to fabricate the microfluidic module according to any one of claims 1 to 7, characterized in that, Specifically, it includes: (1) Use scissors to cut medical cotton cloth to a size of 45×25 mm to prepare waste liquid collection layer 41; (2) Cut the PET substrate into a circle with a diameter of 100 mm to serve as the substrate for spin coating; (3) Mix the liquid PDMS and the pre-curing agent thoroughly at a ratio of 10:1, place them in a vacuum chamber for 5 minutes, and remove the air bubbles from the mixture; (4) Place the PET substrate on the suction plate of the spin coater, drop 2 mL of PDMS onto the center of the PET substrate, spin coat at 500 rpm for 1 minute, remove the PET substrate, and cure in an oven at 60°C for 3 hours to obtain a PDMS film with a thickness of 1 mm. Peel the cured PDMS film off the PET substrate to obtain the PDMS film. (5) Use scissors and a punch to cut and punch the PDMS membrane to obtain the microfluidic outlet layer and sample inlet layer; (6) Using a carving knife, a paper-based microfluidic layer 43 is carved on the filter paper according to the set pattern, including 8 3 mm circular sampling pieces, 1 15 × 7 mm rectangular sweat collection area and 8 strip channels with a width of 1 mm; (7) Stack the waste liquid collection layer, outlet layer, paper-based microfluidic layer, flexible multifunctional sensing electrode, and sample injection layer in sequence and press gently to complete the assembly.

10. A wearable device, characterized in that, It integrates a wearable sweat sensor system with temperature self-calibration as described in any one of claims 1 to 7.

Images