Integrated flexible sweat wearable sensor array chip based on metal aerogel

Abstract

This invention relates to an integrated flexible wearable sweat sensor array chip based on metal aerogel, belonging to the field of microfluidics technology. The chip includes a microfluidic chip layer for sweat collection and storage, comprising multiple storage chambers. Each storage chamber has multiple microchannels arranged circumferentially. Each microchannel collects sweat based on sweat gland pressure and capillary force, transporting the collected sweat to its corresponding storage chamber. An electrochemical sensor array layer includes a flexible PET substrate and five working electrodes, one counter electrode, and three reference electrodes placed on it. The five working electrodes correspond to the multiple storage chambers of the microfluidic chip layer, uniformly covering the detection areas of the five working electrodes. This invention enables the simultaneous detection of glucose, lactic acid, sodium ions, potassium ions, and pH in sweat.

Description

Technical Field

[0001] This invention belongs to the fields of metal nanomaterials, electrochemical detection and microfluidics, and specifically relates to an integrated flexible sweat wearable sensor array chip based on metal aerogel. Background Technology

[0002] The human body is a complex physiological system. A comprehensive and accurate assessment of health requires the simultaneous action of multiple target substances. Compared to single-function devices, multifunctional wearable sweat sensors offer greater practicality and functionality, providing more comprehensive data for health monitoring. Among common biomarkers, glucose and lactic acid are the most typical metabolites, while sodium ions, potassium ions, and pH are the most important inorganic ions. Glucose is the primary energy source for living organisms, and maintaining glucose levels within an appropriate range is crucial for health. High blood sugar is closely related to diseases such as diabetes; while low blood sugar can lead to neurological dysfunction. Lactic acid is an intermediate product of anaerobic metabolism in human tissues, and its expression level is closely related to the body's health status. For example, tissue hypoxia, tumor growth and metastasis, cancer, and sepsis are all closely related to lactic acid levels in the body. Sodium ions are the main inorganic salt determining extracellular fluid osmotic pressure, playing a vital role in maintaining extracellular fluid volume, osmotic pressure, and cellular physiological functions. For instance, a severe imbalance in sodium ion ratio can lead to dehydration, and in severe cases, shock. Potassium ions are also an important inorganic salt in human body fluids, playing a crucial role in maintaining acid-potassium balance, participating in protein and carbohydrate metabolism, and maintaining neuromuscular stress responses. Human body pH is an indicator of the acidity or alkalinity of body fluids and plays a vital role in maintaining physiological homeostasis. In summary, the synergistic effects of these target substances jointly maintain the body's healthy balance. Therefore, simultaneous monitoring of changes in the levels of these target substances has an urgent application need in the early diagnosis and clinical treatment of diseases.

[0003] Existing technologies already include wearable sweat detection devices that integrate microfluidic structures, nanomaterials, and electrochemical sensing arrays, indicating that this research area is not entirely unexplored. However, existing technologies still have the following shortcomings: Firstly, in existing multi-index sweat sensors, glucose and lactic acid detection still largely rely on enzyme electrodes, or use conventional metal oxide powders, nanoparticles or thin films as the sensitive layer, which has problems such as high cost and easy inactivation. Secondly, regarding the detection of glucose / lactic acid by current and Na... + K + In cases where pH potential detection and other types of detection coexist, simply placing multiple sensors side-by-side on the same chip can easily affect the stability and accuracy of the detection due to problems such as low sweat flow, uneven liquid distribution, differences in reaction time, and cross-contamination between detection zones.

[0004] Therefore, it remains necessary to provide an integrated flexible wearable sweat sensor array chip that is co-designed in both material system and microfluidic structure, enabling it to detect glucose, lactic acid, and sodium. + K + It can simultaneously detect pH and is also suitable for the stable collection, distribution and detection of trace sweat samples in flexible devices. Summary of the Invention

[0005] The technical problem to be solved: To overcome the shortcomings of existing technologies, this invention provides an integrated flexible wearable sweat sensor array chip based on metal aerogel. It utilizes a prepared gold-nickel hydroxide aerogel as the working electrode material selectively responding to glucose, and a nickel-doped copper oxide aerogel as the working electrode material selectively responding to lactic acid. Simultaneously, it employs a sodium ion selectively permeable membrane, a potassium ion selectively permeable membrane, a polyaniline film combined with a PEDOT:PSS solid-state transconducting layer as sensitive films selectively responding to sodium ions, potassium ions, and pH. This enables the simultaneous detection of glucose, lactic acid, sodium ions, potassium ions, and pH in sweat. Combined with a self-designed and fabricated microfluidic device, an enzyme-free integrated flexible wearable sweat sensor array chip integrating sweat collection and electrochemical detection is constructed.

[0006] The technical solution of this invention is: an enzyme-free sweat detection method, the specific steps of which include: An integrated flexible sweat wearable sensor array chip based on metal aerogel is attached to the surface of human skin; the chip includes a microfluidic chip layer and an electrochemical sensor array layer. Sweat is collected and guided to different working electrodes in the electrochemical sensing array layer via a microfluidic chip layer; The concentration of glucose in sweat is obtained by acquiring the current signal of sweat in the corresponding region of the microfluidic chip layer using a glucose detection working electrode modified with gold-nickel hydroxide aerogel. The concentration of lactic acid in sweat is obtained by acquiring the current signal of sweat in the corresponding region of the microfluidic chip layer using a working electrode modified with nickel-doped copper oxide aerogel. The concentration of sodium ions in sweat is obtained by acquiring the current signal of sweat in the corresponding region of the microfluidic chip layer through a sodium ion detection working electrode modified with a sodium ion selective permeation membrane. The concentration of potassium ions in sweat is obtained by acquiring the current signal of sweat in the corresponding region of the microfluidic chip layer through a potassium ion detection working electrode modified with a potassium ion selective permeation membrane. The pH value in sweat is obtained by acquiring the current signal of sweat in the corresponding region of the microfluidic chip layer through a pH detection working electrode modified with polyaniline film. Complete the coordinated detection of glucose, lactic acid, sodium ions, potassium ions, and pH value.

[0007] A further technical solution of the present invention is: the preparation method of the gold-nickel hydroxide aerogel includes: A mixed precursor solution was prepared by dissolving HAuCl4 and NiCl2 in deionized water, wherein the volume ratio of HAuCl4 to NiCl2 was 1:200. Under stirring conditions, 1 mol / L sodium hydroxide solution was added dropwise to the mixed precursor solution to adjust the pH of the reaction system to 10; Add 1 mL of sodium borohydride solution with a concentration of 20 mg / mL to the pH-adjusted mixture, continue stirring for 10 min, then stop stirring and let stand at room temperature for 12 hours to obtain gold-nickel hydroxide hydrogel. The gold-nickel hydroxide hydrogel was washed with ultrapure water to remove unreacted substances and byproducts, and then freeze-dried at -50°C, under a vacuum of 10 Pa for 12 hours to obtain gold-nickel hydroxide aerogel. The gold-nickel hydroxide aerogel was formulated into a dispersion with a concentration of 2 mg / mL for subsequent modification of the glucose detection working electrode.

[0008] A further technical solution of the present invention is: the preparation method of the nickel-doped copper oxide aerogel includes: A mixed precursor solution was prepared by dissolving CuCl2 and NiCl2 in deionized water, wherein the volume ratio of CuCl2 to NiCl2 was 4:1. Under stirring conditions, 1 mL of 20 mg / mL NaBH4 solution was added to the mixed precursor solution, stirring was continued for 5 min and then stopped. The mixture was allowed to stand at room temperature for 12 h to obtain nickel-copper hydrogel. The initial nickel-copper hydrogel was washed with ultrapure water to remove unreacted substances and byproducts, and then freeze-dried at -50℃, vacuum degree of 10Pa, and drying time of 12h to obtain the nickel-copper aerogel precursor. The nickel-copper aerogel precursor was pyrolyzed in an air atmosphere furnace, heated to 300°C at a rate of 5°C / min, and held at that temperature for 2 hours. After the holding period, it was cooled to room temperature by natural cooling to obtain nickel-doped copper oxide aerogel. The nickel-doped copper oxide aerogel was prepared into a dispersion with a concentration of 2 mg / mL for subsequent modification of the working electrode for lactic acid detection.

[0009] An integrated flexible sweat wearable sensor array chip based on metal aerogel, comprising: The microfluidic chip layer is used for the collection and storage of sweat. It includes multiple liquid storage chambers, and each liquid storage chamber is provided with multiple microchannels in the circumference. Each microchannel collects sweat based on the sweat gland pressure and the capillary force of the microchannel, and delivers the collected sweat to its corresponding liquid storage chamber. The electrochemical sensing array layer includes a flexible PET substrate and five working electrodes, one counter electrode and three reference electrodes placed thereon. The five working electrodes correspond to multiple liquid storage cavities of the microfluidic chip layer, and each liquid storage cavity is uniformly covered by the detection area of ​​the five working electrodes. The five working electrodes are as follows: The first working electrode has a surface modified with gold-nickel hydroxide aerogel, which is used for enzyme-free catalytic oxidation of glucose in sweat. The second working electrode is surface-modified with nickel-doped copper oxide aerogel, which is used for enzyme-free catalytic oxidation of lactic acid in sweat. The third working electrode has a surface modified with a sodium ion selectively permeable membrane. The fourth working electrode has a surface modified with a potassium ion selectively permeable membrane; The fifth working electrode has a surface modified with a polyaniline film.

[0010] A further technical solution of the present invention is: the microfluidic chip layer includes three sequentially connected liquid storage chambers: The central liquid storage chamber has two microchannels arranged around its circumference as liquid inlets and one liquid outlet; the liquid outlet is used to discharge the sweat in the liquid storage chamber in real time, so as to realize the circulation of sweat in the liquid storage chamber. Three microchannels are arranged circumferentially as liquid inlets in the liquid storage chambers located at both ends; The three liquid storage chambers correspond one-to-one with the three detection areas on the electrode layer of the sensor array; the first liquid storage chamber covers the glucose detection working electrode and the sodium ion detection working electrode, the second liquid storage chamber covers the lactic acid detection working electrode and the potassium ion detection working electrode, and the third liquid storage chamber covers the pH detection working electrode.

[0011] A further technical solution of the present invention is: the diameter of the liquid inlet is 2µm, the width of the microchannel is 0.2µm and the depth is 0.2µm, and the diameter of the liquid inlet is 2µm.

[0012] A further technical solution of the present invention is: the three liquid storage chambers of the microfluidic chip layer are provided with grooves on their circumferential outer edges as microfluidic isolation walls to achieve isolation of the three parts of sweat in the detection area of ​​the electrochemical sensing array layer.

[0013] A further technical solution of the present invention is: the microfluidic chip layer is treated with oxygen plasma hydrophilic treatment to enhance the capillary driving force of the microchannel, so that sweat can automatically fill the microchannel and reduce evaporation and external pollution. A further technical solution of the present invention is: the electrochemical sensing array layer is prepared by screen printing technology, and a chitosan immobilization layer is provided on the surface of each working electrode; The sodium ion detection working electrode and the potassium ion detection working electrode are further provided with a PEDOT:PSS solid-state transconducting layer between the corresponding ion-selective permeable membrane and the working electrode.

[0014] A method for simultaneously monitoring glucose, lactic acid, sodium ions, potassium ions and pH in sweat, using the aforementioned integrated flexible wearable sweat sensor array chip based on metal aerogel.

[0015] Beneficial effects The beneficial effects of this invention are as follows: (1) In this invention, gold-nickel hydroxide aerogel and nickel-doped copper oxide aerogel are used as enzyme-free sensing materials for glucose and lactic acid, respectively. The three-dimensional self-supporting porous structure is beneficial for providing a large specific surface area. According to the test results of the examples, the glucose detection working electrode shows a linear response in the range of 1 μM-3 mM, and the linear correlation coefficient R between the low concentration region and the high concentration region is [value missing]. 2 The values ​​were 0.997 and 0.991, respectively, with a detection limit of 0.1 μM. The working electrode for lactate detection exhibited a linear response in the range of 0.5 mM–30 mM, with a corresponding linear correlation coefficient R0. 2 The values ​​were 0.994 and 0.987, respectively, with a detection limit of 0.1 mM.

[0016] (2) Under the interference conditions set in the example, the glucose detection working electrode was subjected to the addition of 5 mM lactic acid, 5 mM urea, and 1 mM Na. + 1 mM K + After applying 0.1 mM uric acid and 0.05 mM ascorbic acid, the current response was less than 5.4%; the working electrode for lactic acid detection showed a significantly higher current change signal induced by lactic acid than that induced by glucose, urea, and sodium. + K + The material system used in this invention contains interfering substances such as ascorbic acid. The change in current caused by these interfering substances is only 3.1% of the change in lactic acid current, indicating that the material system used in this invention has good selectivity and anti-interference ability for the target material.

[0017] (3) The present invention integrates the sensor array electrode layer and the microfluidic chip layer by stacking and integrating them, and sets multiple liquid inlets, microchannels and partitioned liquid storage chambers in the microfluidic chip layer, so that sweat is collected from the skin side and enters the corresponding detection area along a fixed path. It is suitable for stable transport under the condition of a small amount of sweat, which helps to reduce sample evaporation, external pollution and cross-influence between different detection areas.

[0018] (4) The present invention integrates glucose, lactic acid, and Na+ on the same flexible chip. + K+ It includes five detection units: pH, glucose, lactic acid, and Na. + K + pH is detected using a potentiometric method. The combination of a zoned microfluidic structure and a multi-electrode array provides a structural basis for the simultaneous monitoring of multiple indicators, and can be applied to sports and health monitoring, dehydration risk assessment, and continuous monitoring of disease-related physiological parameters. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall structure of the integrated flexible sweat wearable sensor array chip in an embodiment of the present invention; Figure 2 These are SEM images (A) and XRD images (B) of the gold-nickel hydroxide aerogel in the embodiments of the present invention. Figure 3 These are SEM images (A) and XRD images (B) of nickel-doped copper oxide aerogels in this embodiment of the invention. Figure 4 This is a comparison (D) of the cyclic voltammetry curves and catalytic current magnitudes of glucose catalyzed by electrodes modified with gold-nickel hydroxide aerogel (A), nickel hydroxide aerogel (B), and gold aerogel (C) in the embodiments of the present invention. Figure 5 These are the it curve (A), calibration curve (B), and anti-interference test results (CD) of the gold-nickel hydroxide aerogel modified electrode used in this invention for monitoring glucose. Figure 6 These are the cyclic voltammetry curves of the nickel-doped copper oxide aerogel (A) and copper oxide aerogel (B) modified electrodes in this embodiment of the invention in response to lactic acid. Figure 7 The diagrams shown in this invention are: the it curve (A), calibration curve (B), and anti-interference test results (CD) of the nickel-doped copper oxide aerogel modified electrode for monitoring lactic acid. Figure 8 Yes + K + H + Detection graphs related to selectively modified membrane electrodes; AC is Na + Selective membrane-modified electrode for monitoring Na + Detection diagram, OCP-t curve and calibration curve; DF is K + Selective membrane modified electrode monitoring K + Detection diagram, OCP-t curve and calibration curve; GI is H + Selective membrane-modified electrode for monitoring H + The detection diagram, OCP-t curve, and calibration curve; Figure 9This is a schematic diagram of the microfluidic chip layer structure in an embodiment of the present invention; Figure 10 This is a schematic diagram of the fabrication process of the microfluidic chip layer in an embodiment of the present invention; Figure 11 These are simulation results (A) and actual liquid collection performance results (B) of the microfluidic chip in this embodiment of the invention. Figure 12 This is a flowchart illustrating the fabrication process of the electrochemical sensing array layer in an embodiment of the present invention; Figure 13 This is a physical image of the electrochemical sensing array layer in an embodiment of the present invention; Figure 14 The images shown are optical photographs (A) of the electrochemical sensing array layer under different bending angles and the electrochemical changes in the target object response (B) in the embodiments of the present invention. Figure 15 This is a physical image of the wearable microfluidic sensor array chip in an embodiment of the present invention; Figure 16 The figures shown are (A) and (B) comparisons of the array electrode test results with those of commercial methods in this invention embodiment.

[0020] Explanation of reference numerals in the attached figures: 1. Electrochemical sensing array layer, 11. First detection area, 12. Second detection area, 13. Third detection area; 2. Microfluidic chip layer, 21. Liquid inlet, 22. Microchannel, 23. Liquid storage chamber, 24. Liquid outlet. Detailed Implementation

[0021] The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the invention, and should not be construed as limiting the invention.

[0022] Among existing multi-object simultaneous sensing technologies, there is no invention utilizing integrated sweat wearable sensors constructed with gold-nickel hydroxide aerogel or nickel-doped copper oxide aerogel. Multi-object wearable sensors similar to this invention generally employ enzyme electrodes, which are costly, lack stability, and have poor detection accuracy. This invention, however, utilizes the excellent electrocatalytic activity of gold-nickel hydroxide aerogel and nickel-doped copper oxide aerogel to accurately and stably respond to the concentration of target substances in sweat. Furthermore, combining it with a microfluidic chip effectively avoids the performance degradation caused by difficulties in sweat collection, sample contamination, and evaporation.

[0023] Based on the problems existing in the prior art, this invention proposes an enzyme-free sweat detection method, the specific steps of which include: An integrated flexible sweat wearable sensor array chip based on metal aerogel is attached to the surface of human skin; the chip includes a microfluidic chip layer and an electrochemical sensor array layer. Sweat is collected and guided to different working electrodes in the electrochemical sensing array layer via a microfluidic chip layer; The concentration of glucose in sweat is obtained by acquiring the current signal of sweat in the corresponding region of the microfluidic chip layer using a glucose detection working electrode modified with gold-nickel hydroxide aerogel. The concentration of lactic acid in sweat is obtained by acquiring the current signal of sweat in the corresponding region of the microfluidic chip layer using a working electrode modified with nickel-doped copper oxide aerogel. The concentration of sodium ions in sweat is obtained by acquiring the current signal of sweat in the corresponding region of the microfluidic chip layer through a sodium ion detection working electrode modified with a sodium ion selective permeation membrane. The concentration of potassium ions in sweat is obtained by acquiring the current signal of sweat in the corresponding region of the microfluidic chip layer through a potassium ion detection working electrode modified with a potassium ion selective permeation membrane. The pH value in sweat is obtained by acquiring the current signal of sweat in the corresponding region of the microfluidic chip layer through a pH detection working electrode modified with polyaniline film. Complete the coordinated detection of glucose, lactic acid, sodium ions, potassium ions, and pH value.

[0024] This invention also proposes an integrated flexible sweat wearable sensor array chip based on metal aerogel, comprising: The microfluidic chip layer is used for the collection and storage of sweat. It includes multiple liquid storage chambers, and each liquid storage chamber is provided with multiple microchannels in the circumference. Each microchannel collects sweat based on the sweat gland pressure and the capillary force of the microchannel, and delivers the collected sweat to its corresponding liquid storage chamber. The electrochemical sensing array layer includes a flexible PET substrate and five working electrodes, one counter electrode and three reference electrodes placed thereon. The five working electrodes correspond to multiple liquid storage cavities of the microfluidic chip layer, and each liquid storage cavity is uniformly covered by the detection area of ​​the five working electrodes. The five working electrodes are as follows: The first working electrode has a surface modified with gold-nickel hydroxide aerogel, which is used for enzyme-free catalytic oxidation of glucose in sweat. The second working electrode is surface-modified with nickel-doped copper oxide aerogel, which is used for enzyme-free catalytic oxidation of lactic acid in sweat. The third working electrode has a surface modified with a sodium ion selectively permeable membrane. The fourth working electrode has a surface modified with a potassium ion selectively permeable membrane; The fifth working electrode has a surface modified with a polyaniline film.

[0025] This invention also proposes a method for simultaneous monitoring of glucose, lactic acid, sodium ions, potassium ions and pH in sweat, using the aforementioned integrated flexible sweat wearable sensor array chip based on metal aerogel.

[0026] The technical solution will be further analyzed below with reference to examples and accompanying figures: In one embodiment, refer to Figure 1 As shown, an integrated flexible sweat sensor chip based on metal aerogel includes a sensor array electrode layer 1 and a microfluidic chip layer 2. The sensor array electrode layer 1 includes a flexible PET substrate and five working electrodes, one counter electrode, and three reference electrodes disposed on the flexible PET substrate. The microfluidic chip layer 2 consists of eight liquid inlets 21, microchannels 22 communicating with the eight liquid inlets, three liquid storage chambers 23, and one liquid outlet 24. The microfluidic chip layer 2 has the function of directionally collecting and storing sweat and precisely guiding it to the corresponding working electrode detection area. Human sweat enters the microfluidic chip... After the liquid outlet, under the combined action of sweat gland pressure and microchannel capillary force, the liquid is transported along the microchannel to the storage chamber and covers the corresponding working electrode detection area. The detection chambers are physically separated by microchannel isolation walls and are not directly connected. The five working electrodes are: a glucose detection working electrode modified with gold-nickel hydroxide aerogel, a lactic acid detection working electrode modified with nickel-doped copper oxide aerogel, a sodium ion detection working electrode modified with a sodium ion selective permeable membrane, a potassium ion detection working electrode modified with a potassium ion selective permeable membrane, and a pH detection working electrode modified with a polyaniline film.

[0027] In one embodiment, refer to Figure 9-11 As shown, the microfluidic chip layer 2 is molded using PDMS after the mold is prepared by photolithography. The microfluidic chip layer includes 8 liquid inlets, 3 mutually isolated detection chambers, and liquid outlet channels. The diameter of each liquid inlet is 2 µm, the width of each microchannel is 0.2 µm, the depth is 0.2 µm, and the diameter of each liquid outlet is 2 µm.

[0028] In one embodiment, the microfluidic chip layer is treated with oxygen plasma hydrophilicity to enhance the capillary drive force of the microchannels, enabling sweat to automatically fill within the microchannels and reducing evaporation and external contamination.

[0029] In one embodiment, the method for preparing the gold-nickel hydroxide aerogel includes: A mixed precursor solution was prepared by dissolving HAuCl4 and NiCl2 in deionized water, wherein the volume ratio of HAuCl4 to NiCl2 was 1:200. Under stirring conditions, 1 mol / L sodium hydroxide solution was added dropwise to the mixed precursor solution to adjust the pH of the reaction system to 10; Add 1 mL of sodium borohydride solution with a concentration of 20 mg / mL to the pH-adjusted mixture, continue stirring for 10 min, then stop stirring and let stand at room temperature for 12 hours to obtain gold-nickel hydroxide hydrogel. The gold-nickel hydroxide hydrogel was washed with ultrapure water to remove unreacted substances and byproducts, and then freeze-dried at -50°C, under a vacuum of 10 Pa for 12 hours to obtain gold-nickel hydroxide aerogel. The gold-nickel hydroxide aerogel was formulated into a dispersion with a concentration of 2 mg / mL for subsequent modification of the glucose detection working electrode.

[0030] In one embodiment, the method for preparing the nickel-doped copper oxide aerogel includes: A mixed precursor solution was prepared by dissolving CuCl2 and NiCl2 in deionized water, wherein the volume ratio of CuCl2 to NiCl2 was 4:1. Under stirring conditions, 1 mL of 20 mg / mL NaBH4 solution was added to the mixed precursor solution, stirring was continued for 5 min and then stopped. The mixture was allowed to stand at room temperature for 12 h to obtain nickel-copper hydrogel. The initial nickel-copper hydrogel was washed with ultrapure water to remove unreacted substances and byproducts, and then freeze-dried at -50℃, vacuum degree of 10Pa, and drying time of 12h to obtain the nickel-copper aerogel precursor. The nickel-copper aerogel precursor was pyrolyzed in an air atmosphere furnace, heated to 300°C at a rate of 5°C / min, and held at that temperature for 2 hours. After the holding period, it was cooled to room temperature by natural cooling to obtain nickel-doped copper oxide aerogel. The nickel-doped copper oxide aerogel was prepared into a dispersion with a concentration of 2 mg / mL for subsequent modification of the working electrode for lactic acid detection.

[0031] In one embodiment, refer to Figure 12 As shown, the electrochemical sensing array layer 1 is prepared by screen printing technology, and a chitosan immobilization layer is provided on the surface of each working electrode; the sodium ion detection working electrode and the potassium ion detection working electrode are further provided with a PEDOT:PSS solid transconducting layer between the corresponding ion selective permeable membrane and the working electrode.

[0032] In one embodiment, a method for fabricating an integrated flexible sweat sensor chip based on metal aerogel includes the following steps: Step 1: Preparation of sensitive electrode material; (1) Preparation of gold-nickel hydroxide aerogel: HAuCl4 and NiCl2 were used as precursors, with HAuCl4 solution concentration of 10 wt% and NiCl2 solution concentration of 0.1 M, and the volume ratio of HAuCl4 to NiCl2 was 1:200. After mixing the two precursors, the mixture was magnetically stirred at 25 °C for 30 min; then the pH of the system was adjusted to 10 with 1 mol / L freshly prepared NaOH solution. 1 mL of 20 mg / mL freshly prepared NaBH4 solution was added dropwise to the above mixture, and the mixture was stirred at 25 °C for 10 min and then allowed to stand to form a gel. The standing temperature was 25 °C and the standing time was 12 h to obtain the gold-nickel hydroxide hydrogel. The gel was then washed 10 times with ultrapure water for 30 min each time to remove unreacted substances and byproducts. The cleaned hydrogel was freeze-dried in a freeze dryer at -50 °C, a vacuum of 10 Pa, and a drying time of 12 h to obtain a gold-nickel hydroxide aerogel. Figure 2 As shown. The obtained aerogel was prepared into a dispersion with a concentration of 2 mg / mL for subsequent modification of the glucose working electrode.

[0033] By changing the feed ratio of the metal precursor (introducing only NiCl2 or HAuCl4 as the precursor, while keeping other experimental parameters unchanged), Ni(OH)2 and gold aerogels can be obtained. The obtained Ni(OH)2 aerogel and gold aerogel were prepared into dispersions with a concentration of 2 mg / mL as control materials for subsequent modification of the glucose working electrode.

[0034] (2) Preparation of nickel-doped copper oxide aerogel: CuCl2 and NiCl2 were used as precursors, with CuCl2 solution concentration of 0.1 M and NiCl2 solution concentration of 0.1 M, and the volume ratio of CuCl2 to NiCl2 was 4:1. After mixing, the mixture was stirred at 25 °C for 30 min, followed by the addition of 1 mL of freshly prepared 20 mg / mL NaBH4 solution. The mixture was stirred at 25 °C for another 5 min and then allowed to stand for 12 h to form a gel, thus obtaining a nickel-copper hydrogel. The obtained nickel-copper hydrogel was washed 10 times with ultrapure water for 30 min each time. Then it was placed in a freeze dryer and dried at -50 °C, 10 Pa, and for 12 h to obtain the nickel-copper aerogel precursor. The nickel-copper aerogel precursor was pyrolyzed in an air atmosphere furnace at a heating rate of 5 °C / min, reaching 300 °C and holding for 2 h. After holding, it was cooled to room temperature naturally to obtain nickel-doped copper oxide aerogel. Figure 3 As shown.

[0035] When there is no Ni doping, only CuCl2 needs to be introduced as a precursor, and the subsequent steps are the same as above, and finally the control material copper oxide (CuO) aerogel can be obtained.

[0036] Among them, the comparison of cyclic voltammetry curves and catalytic current magnitudes of glucose catalyzed by gold-nickel hydroxide aerogel, nickel hydroxide aerogel, and gold aerogel modified electrodes is as follows: Figure 4 As shown.

[0037] Step 2: Fabrication and modification of the electrochemical sensing array layer; Flexible array electrodes were fabricated on a PET substrate using screen printing technology. Figure 12 It includes 5 working electrodes, 1 platinum counter electrode, and 3 Ag / AgCl reference electrodes (see physical sample). Figure 13 Optical photographs of the array electrodes at different bending angles and the electrochemical changes in the target object's response are shown below. Figure 14 As shown.

[0038] (1) Glucose detection working electrode: Gold-nickel hydroxide aerogel was dispersed in a dispersion medium to form a modification solution. The aerogel concentration in the modification solution was 2 mg / mL, and the dispersion medium was a mixture of deionized water and ethanol (volume ratio 1:1). The ultrasonic dispersion time was 60 min. 5 μL of the modification solution was drop-coated onto the surface of the first working electrode for glucose detection and dried at 25 ℃ for 60 min to form a sensitive layer. A chitosan immobilization layer was drop-coated onto the surface of the sensitive layer. The chitosan solution concentration was 1 wt%, the drop-coating volume was 3 μL, and the film thickness was 1 μm. In this process, no additional cross-linking was used; the film was fixed by the natural formation of chitosan.

[0039] (2) Working electrode for lactic acid detection: Nickel-doped copper oxide aerogel was dispersed in a deionized water / ethanol mixture (volume ratio 1:1) at a concentration of 2 mg / mL and sonicated for 60 min to form a modification solution; 5 μL of the modification solution was dropped onto the surface of the second working electrode for lactic acid detection and dried at 25 °C for 60 min to form a sensitive layer. A chitosan immobilization layer was further deposited on the surface of the sensitive layer, with a chitosan solution concentration of 1 wt%, a drop volume of 3 μL, and a film thickness of 1 μm.

[0040] (3) Sodium and potassium ion selective electrode: in Na + and K +A solid-state transconducting layer is first formed on the surface of the working electrode. This solid-state transconducting layer is preferably a PEDOT:PSS layer, prepared by electrochemical deposition, specifically as follows: In a mixed solution containing 0.1 M sodium polystyrene sulfonate (NaPSS) and 0.01 M 3,4-ethylenedioxythiophene (EDOT), the electrodeposition time is controlled at 740 s and the electrodeposition current at 14 µA to obtain the PEDOT:PSS layer. Subsequently, a sodium ion-selective membrane dispersion and a potassium ion-selective membrane dispersion are drop-coated onto the surface of the PEDOT:PSS layer, respectively.

[0041] The sodium ion selective membrane dispersion was prepared as follows: 1 mg of 4-tert-butylcalix[4] aryl-tetraethyl acetate, 0.6 mg of sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, 33 mg of polyvinyl chloride and 65.4 mg of di(2-ethylhexyl) sebacate were weighed, dissolved in 0.66 mL of tetrahydrofuran, and ultrasonically mixed to obtain the sodium ion selective membrane dispersion. The potassium ion selective membrane dispersion was prepared as follows: 2 mg of valproic acid, 0.55 mg of sodium tetraphenylborate, 33 mg of PVC and 64.5 mg of DOS were weighed and dissolved in 0.35 mL of cyclohexanone and ultrasonically mixed until homogeneous.

[0042] (4) pH electrode: A polyaniline sensitive layer is formed on the surface of the pH detection working electrode. The polyaniline layer can be formed by electrochemical deposition, and the preparation process is as follows: In a mixed solution containing 0.1 M aniline and 1 M HCl, a polyaniline thin film (potential range -0.2) is electrodeposited on the electrode substrate by cyclic voltammetry. 1.0 V, scan rate 100 mVs 1. The cycle is repeated 25 times.

[0043] Step 3: Structural design, simulation, and fabrication of microfluidic chips The microfluidic chip has a segmented structure, including eight 2 µm diameter inlets, two circular reservoirs on the left and right, a central elliptical reservoir, a 2 µm diameter outlet, and microchannels connecting the reservoirs to the inlets and outlet. The left and right reservoirs are each 10 mm in diameter, the central reservoir has a major axis of 10 mm and a minor axis of 6 mm, the microchannels are 0.2 µm wide, and all areas are 0.2 µm deep. Multiple inlets are located at the chip's edge for collecting sweat from the skin contact layer. After entering the branched microchannels through the inlets, the sweat is directed into reservoirs corresponding to different detection areas; the first reservoir corresponds to glucose and sodium. + The detection showed that the second reservoir corresponds to lactic acid and K+. +The third liquid storage chamber corresponds to pH detection; the compartmentalized design is intended to reduce liquid crosstalk between different detection zones.

[0044] Microfluidic drawings were created using AutoCAD, and molds were fabricated using photolithography. PDMS was mixed with monomer and curing agent at a mass ratio of 10:1, and after vacuum degassing for 20 min, it was poured onto the mold surface and cured at 60 ℃ for 30 min. After demolding, inlet and outlet ports were formed by punching to obtain the PDMS microfluidic layer.

[0045] The sweat filling process was simulated by establishing a corresponding two-dimensional geometric model in COMSOL. During the simulation, the sweat was approximated as an incompressible Newtonian fluid with a density of 1000 kg / m³ and a dynamic viscosity of 1.0 mPa·s. The microchannel walls were set as no-slip boundaries, the inlet pressure was set to 0.5-5 kPa for parameter scanning, and the outlet was set as a pressure outlet boundary with an outlet pressure of 0 Pa gauge pressure to simulate the state of communication between the microfluidic outlet and the external atmosphere.

[0046] Step 4: The electrochemical sensing array layer prepared in Step 2 and the PDMS microfluidic layer prepared in Step 3 are stacked and assembled. The PDMS microfluidic layer is subjected to oxygen plasma hydrophilic treatment at a power of 120 W for 60 s to enhance the capillary driving force of the microchannels; subsequently, it is precisely aligned and bonded to the array electrode layer.

[0047] In one embodiment, a method for monitoring glucose, lactic acid, sodium ions, potassium ions, and pH in sweat includes the following steps: Step 1: Glucose monitoring based on a gold-nickel hydroxide aerogel modified electrode The modified glucose detection electrode was connected to an electrochemical workstation, and detection was performed using chronoamperometry at a working potential of +0.1 V. The sensor exhibited a stepwise current response in the concentration range of 1 μM to 3 mM, with a linear correlation coefficient R0 between the low and high concentration regions. 2 The values ​​were 0.997 and 0.991, respectively, with a detection limit of 0.1 μM. 5 mM lactic acid, 5 mM urea, and 1 mM Na were added to the detection system. + 1 mM K + When 0.1 mM uric acid and 0.05 mM ascorbic acid were used as interfering agents, the current response showed no significant fluctuation and was 5.4% of the glucose response current, indicating that the electrode has good selectivity for glucose. The it curve, calibration curve, and anti-interference test results of the gold-nickel hydroxide aerogel modified electrode for monitoring glucose are shown below. Figure 5 As shown.

[0048] The obtained Ni(OH)2 aerogel and Au NPs-Ni(OH)2 were modified in the same way as described above, and their response to glucose detection was investigated.

[0049] Step 2: Lactic acid monitoring based on nickel-doped copper oxide aerogel modified electrode The modified lactic acid detection electrode was connected to an electrochemical workstation, and detection was performed using chronoamperometry at a working potential of -0.2 V. The sensor exhibited good linear response in the concentration range of 0.5 mM to 30 mM, with a linear correlation coefficient R0 in both the low and high concentration regions. 2 The concentrations were 0.994 and 0.987 respectively, with a detection limit of 0.1 mM. This was observed in glucose, urea, and sodium... + K + In the presence of interfering substances such as ascorbic acid, the current change caused by these interfering substances is only 3.1% of the lactic acid current change, indicating that the electrode has high selectivity for lactic acid. The it curve, calibration curve, and anti-interference test results of the nickel-doped copper oxide aerogel modified electrode for monitoring lactic acid are shown below. Figure 7 As shown.

[0050] The obtained CuO aerogel was modified in the same manner as described above, and its response to lactic acid detection was investigated. Cyclic voltammetric curves of the nickel-doped copper oxide aerogel and the copper oxide aerogel-modified electrode to lactic acid are shown below. Figure 6 As shown.

[0051] Step 3: Na + K + and pH working electrode detection Will Na + K + The pH working electrode was connected to the electrochemical workstation, and the open-circuit potential method was used for detection (the detection results are shown in [link to results]). Figure 8 Na + The electrode exhibits a linear response in the range of 5 mM to 160 mM, R 2 =0.992; K + The electrode exhibits a linear response in the range of 1 mM to 35 mM, R 2 =0.993; The potential of the pH electrode decreases linearly with increasing pH in the pH range of 3–8, R 2 =0.990.

[0052] In one embodiment, a wearable sensor array chip (such as...) Figure 15 A method for simultaneous monitoring of multiple targets in human sweat (as shown) includes: In human testing, the integrated flexible sensor array chip was attached to volunteers' arms, foreheads, and other areas prone to sweating. Sweat generated during human movement, under the combined action of sweat gland pressure and microchannel capillary force, enters the inlet through the sweat collection holes in the skin contact layer, then sequentially fills the corresponding reservoirs via microchannels, covering the surface of the corresponding working electrodes; glucose and lactic acid channels record changes in response current over time, while Na+ channels... + K + The pH channel records the change in open-circuit potential over time. The array electrode is used for simultaneous monitoring of multiple targets in sweat. Comparison of array electrode test results with those from commercial methods is shown below. Figure 16 As shown.

[0053] The sensor array chip measured a glucose concentration of approximately 64.5 μM, while HPLC measured approximately 65.3 μM, with an absolute error of approximately 0.8 μM and a relative error of approximately 1.2%. The chip measured a lactic acid concentration of approximately 8.1 mM, while HPLC measured approximately 8.8 mM, with an absolute error of approximately 0.7 mM and a relative error of approximately 7.7%. The chip also measured a Na... + The concentration was approximately 55.5 mM, the ICP-measured value was approximately 51.4 mM, the absolute error was approximately 4.1 mM, and the relative error was approximately 8.1%; the K measured by the chip... + The concentration was approximately 5.6 mM, while the ICP measurement was approximately 5.3 mM, with an absolute error of approximately 0.3 mM and a relative error of approximately 5.6%. The chip measured a pH value of approximately 6.4, while a commercial pH meter measured a value of approximately 6.2, with an absolute error of approximately 0.2% and a relative error of approximately 3.2%. These results indicate that the chip effectively controls glucose, lactic acid, and sodium in sweat. + K + The detection results for pH showed good consistency with commercial standard methods, and the relative deviation remained at a low level overall, which can meet the application requirements of wearable monitoring of multiple indicators of sweat.

[0054] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. An enzyme-free sweat detection method, characterized in that, The specific steps include: An integrated flexible sweat wearable sensor array chip based on metal aerogel is attached to the surface of human skin; the chip includes a microfluidic chip layer and an electrochemical sensor array layer. Sweat is collected and guided to different working electrodes in the electrochemical sensing array layer via a microfluidic chip layer; The concentration of glucose in sweat is obtained by acquiring the current signal of sweat in the corresponding region of the microfluidic chip layer using a glucose detection working electrode modified with gold-nickel hydroxide aerogel. The concentration of lactic acid in sweat is obtained by acquiring the current signal of sweat in the corresponding region of the microfluidic chip layer using a working electrode modified with nickel-doped copper oxide aerogel. The concentration of sodium ions in sweat is obtained by acquiring the current signal of sweat in the corresponding region of the microfluidic chip layer through a sodium ion detection working electrode modified with a sodium ion selective permeation membrane. The concentration of potassium ions in sweat is obtained by acquiring the current signal of sweat in the corresponding region of the microfluidic chip layer through a potassium ion detection working electrode modified with a potassium ion selective permeation membrane. The pH value in sweat is obtained by acquiring the current signal of sweat in the corresponding region of the microfluidic chip layer through a pH detection working electrode modified with polyaniline film. Complete the coordinated detection of glucose, lactic acid, sodium ions, potassium ions, and pH value.

2. The enzyme-free sweat detection method according to claim 1, characterized in that: The preparation method of the gold-nickel hydroxide aerogel includes: A mixed precursor solution was prepared by dissolving HAuCl4 and NiCl2 in deionized water, wherein the volume ratio of HAuCl4 to NiCl2 was 1:

200. Under stirring conditions, 1 mol / L sodium hydroxide solution was added dropwise to the mixed precursor solution to adjust the pH of the reaction system to 10; Add 1 mL of sodium borohydride solution with a concentration of 20 mg / mL to the pH-adjusted mixture, continue stirring for 10 min, then stop stirring and let stand at room temperature for 12 hours to obtain gold-nickel hydroxide hydrogel. The gold-nickel hydroxide hydrogel was washed with ultrapure water to remove unreacted substances and byproducts, and then freeze-dried at -50°C, under a vacuum of 10 Pa for 12 hours to obtain gold-nickel hydroxide aerogel. The gold-nickel hydroxide aerogel was formulated into a dispersion with a concentration of 2 mg / mL for subsequent modification of the glucose detection working electrode.

3. The enzyme-free sweat detection method according to claim 1, characterized in that: The preparation method of the nickel-doped copper oxide aerogel includes: A mixed precursor solution was prepared by dissolving CuCl2 and NiCl2 in deionized water, wherein the volume ratio of CuCl2 to NiCl2 was 4:

1. Under stirring conditions, 1 mL of 20 mg / mL NaBH4 solution was added to the mixed precursor solution, stirring was continued for 5 min and then stopped. The mixture was allowed to stand at room temperature for 12 h to obtain nickel-copper hydrogel. The initial nickel-copper hydrogel was washed with ultrapure water to remove unreacted substances and byproducts, and then freeze-dried at -50℃, vacuum degree of 10Pa, and drying time of 12h to obtain the nickel-copper aerogel precursor. The nickel-copper aerogel precursor was pyrolyzed in an air atmosphere furnace, heated to 300°C at a rate of 5°C / min, and held at that temperature for 2 hours. After the holding period, it was cooled to room temperature by natural cooling to obtain nickel-doped copper oxide aerogel. The nickel-doped copper oxide aerogel was prepared into a dispersion with a concentration of 2 mg / mL for subsequent modification of the working electrode for lactic acid detection.

4. An integrated flexible wearable sweat sensor array chip based on metal aerogel, used to execute the enzyme-free sweat detection method according to any one of claims 1-3; characterized in that, include: The microfluidic chip layer is used for the collection and storage of sweat. It includes multiple liquid storage chambers, and each liquid storage chamber is provided with multiple microchannels in the circumference. Each microchannel collects sweat based on the sweat gland pressure and the capillary force of the microchannel, and delivers the collected sweat to its corresponding liquid storage chamber. The electrochemical sensing array layer includes a flexible PET substrate and five working electrodes, one counter electrode and three reference electrodes placed thereon. The five working electrodes correspond to multiple liquid storage cavities of the microfluidic chip layer, and each liquid storage cavity is uniformly covered by the detection area of ​​the five working electrodes. The five working electrodes are as follows: The first working electrode has a surface modified with gold-nickel hydroxide aerogel, which is used for enzyme-free catalytic oxidation of glucose in sweat. The second working electrode is surface-modified with nickel-doped copper oxide aerogel, which is used for enzyme-free catalytic oxidation of lactic acid in sweat. The third working electrode has a surface modified with a sodium ion selectively permeable membrane. The fourth working electrode has a surface modified with a potassium ion selectively permeable membrane; The fifth working electrode has a surface modified with a polyaniline film.

5. The integrated flexible sweat wearable sensor array chip based on metal aerogel according to claim 4, characterized in that: The microfluidic chip layer includes three sequentially connected liquid storage chambers: The central liquid storage chamber has two microchannels arranged around its circumference as liquid inlets and one liquid outlet; the liquid outlet is used to discharge the sweat in the liquid storage chamber in real time, so as to realize the circulation of sweat in the liquid storage chamber. Three microchannels are arranged circumferentially as liquid inlets in the liquid storage chambers located at both ends; The three liquid storage chambers correspond one-to-one with the three detection areas on the electrode layer of the sensor array; the first liquid storage chamber covers the glucose detection working electrode and the sodium ion detection working electrode, the second liquid storage chamber covers the lactic acid detection working electrode and the potassium ion detection working electrode, and the third liquid storage chamber covers the pH detection working electrode.

6. The integrated flexible sweat wearable sensor array chip based on metal aerogel according to claim 5, characterized in that: The diameter of the liquid inlet is 2µm, the width of the microchannel is 0.2µm, the depth is 0.2µm, and the diameter of the liquid inlet is 2µm.

7. The integrated flexible sweat wearable sensor array chip based on metal aerogel according to claim 5, characterized in that: The microfluidic chip layer has grooves on the outer periphery of its three liquid storage chambers, which serve as microfluidic isolation walls to isolate the three parts of sweat in the detection area of ​​the electrochemical sensing array layer.

8. The integrated flexible sweat wearable sensor array chip based on metal aerogel according to claim 4, characterized in that: The microfluidic chip layer is treated with oxygen plasma to enhance the capillary driving force of the microchannels, allowing sweat to automatically fill the microchannels and reducing evaporation and external pollution.

9. The integrated flexible sweat wearable sensor array chip based on metal aerogel according to claim 4, characterized in that: The electrochemical sensing array layer is prepared by screen printing technology, and a chitosan immobilization layer is provided on the surface of each working electrode. The sodium ion detection working electrode and the potassium ion detection working electrode are further provided with a PEDOT:PSS solid-state transconducting layer between the corresponding ion-selective permeable membrane and the working electrode.

10. A method for simultaneous monitoring of glucose, lactic acid, sodium ions, potassium ions and pH in sweat, characterized in that: The integrated flexible sweat wearable sensor array chip based on metal aerogel as described in any one of claims 4-9 is adopted.

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