A flexible enzyme-free sweat glucose sensor based on a nickel-cobalt sulfide composite thin film and its preparation method

Abstract

This invention discloses a flexible, enzyme-free sweat glucose sensor based on a nickel-cobalt sulfide composite film and its preparation method, belonging to the field of flexible electronics and biosensing technology. The sensor uses a flexible insulating film as a substrate and integrates a screen-printed carbon electrode system. It adopts a short-time electrodeposition-intermediate treatment cycle process: after applying a 5V voltage to the carbon working electrode for 30 seconds, the electrode is removed, residual droplets in the non-working area are wiped off, and the electrode is air-dried at room temperature. This process is repeated 3 to 4 times, thereby growing a uniform, dense, and strongly adherent nickel-cobalt sulfide nanocatalytic film in situ on the electrode surface. This process effectively avoids the swelling of the flexible porous carbon electrode and the cracking of the catalytic film by controlling the single reaction time and the forced interruption treatment, realizing the stable integration of high-performance materials. The sensor has excellent flexibility, mechanical stability, and high sensitivity and high selectivity electrochemical response to glucose.

Description

Technical Field

[0001] This invention relates to the fields of flexible electronics and biosensing technology, and in particular to a flexible enzyme-free sweat glucose sensor based on a nickel-cobalt sulfide composite film and its preparation method. Background Technology

[0002] As a typical chronic metabolic disease, diabetes relies heavily on frequent monitoring of blood glucose levels for effective management. Traditional finger-prick blood glucose testing is an invasive procedure that not only causes physical pain to patients but also poses a risk of wound infection and makes it difficult to achieve continuous dynamic monitoring of blood glucose. Various metabolites in sweat are correlated with the concentrations of corresponding substances in the blood, among which glucose concentration has a clear correlation with blood glucose levels. Therefore, non-invasive blood glucose monitoring by detecting glucose in sweat has become a cutting-edge research direction in the field of biosensing.

[0003] Currently, the research and application of sweat glucose sensors still face two major technological challenges: First, mainstream sweat glucose sensing technology relies on glucose oxidase as the recognition element. This enzyme is extremely sensitive to environmental conditions such as temperature, humidity, and pH. It is prone to inactivation in the complex environment of the human body surface, resulting in poor sensor environmental stability, short service life, and stringent storage requirements. Second, in order to achieve good conformal adhesion to human skin, the sensor needs to have excellent flexibility. However, high-performance inorganic catalytic materials are difficult to form a uniform, stable, and strongly adherent sensitive film on a flexible substrate. When traditional electrodeposition processes are directly applied to porous, hydrophilic flexible carbon electrodes, the electrodes are prone to swelling, cracking, or detachment of the catalytic film due to prolonged immersion in the electrolyte and accumulation of reaction stress.

[0004] Therefore, developing a simple, low-cost method for preparing a sweat glucose sensor that can stably construct a highly active enzyme-free catalytic layer on a flexible electrode and also possesses good mechanical properties has significant scientific research value and practical application prospects. Summary of the Invention

[0005] Purpose of the invention The purpose of this invention is to provide a flexible, enzyme-free sweat glucose sensor with good flexibility, high detection sensitivity, and strong environmental stability. At the same time, it provides a simple and controllable preparation method to solve the technical problems of poor stability of traditional enzyme-based glucose sensors and the difficulty in achieving uniform and firm modification of enzyme-free catalytic films on rigid / flexible substrates.

[0006] Technical solution To achieve the above objectives, the present invention adopts the following technical solution: A flexible enzyme-free sweat glucose sensor based on a nickel-cobalt sulfide composite film and its preparation method are disclosed. The sensor uses a flexible polyethylene terephthalate (PET) film as a substrate and a three-electrode system is prepared by screen printing. The three-electrode system includes a carbon working electrode, a carbon counter electrode, and an Ag / AgCl reference electrode. A nickel-cobalt sulfide catalytic film is modified on the surface of the carbon working electrode by an improved electrochemical deposition method.

[0007] The preparation method of this flexible, enzyme-free sweat glucose sensor specifically includes the following steps: 1. Flexible substrate preparation: PET film is selected as the flexible carrier, on which a screen-printed electrode system (containing carbon working electrodes) is printed. Before use, the electrode surface is cleaned or polished as necessary.

[0008] 2. Preparation of electroplating solution: Using deionized water as solvent, add nickel acetate, cobalt acetate and sodium thiosulfate, and stir until completely dissolved. The concentration of nickel acetate is 0.005~0.02 mol / L, the concentration of cobalt acetate is 0.01~0.03 mol / L, and the concentration of sodium thiosulfate is 0.05~0.2 mol / L. The preferred concentrations are 0.0085 mol / L for nickel acetate, 0.02 mol / L for cobalt acetate, and 0.1 mol / L for sodium thiosulfate.

[0009] 3. Electrochemical deposition: The carbon working electrode area of ​​the flexible electrode is used as the cathode and the carbon counter electrode is used as the anode. They are both immersed in the electroplating solution and electrochemical deposition is performed by applying a 5V DC voltage. Due to the adsorption characteristics of the carbon electrode, the deposition time for each deposition is strictly controlled to 30 seconds.

[0010] 4. Wiping and Air-drying Process: This is a key improvement step for flexible carbon substrates. After a single 30-second deposition, the electrode is vertically removed from the electroplating solution. Using absorbent material (such as absorbent paper), residual droplets outside the working electrode area are wiped along the plane of the flexible substrate, avoiding horizontal scratching of the sensitive area of ​​the carbon working electrode. The electrode is then placed at room temperature to air-dry until the surface of the carbon working electrode changes from a wet, reflective state to a uniform matte state with no obvious liquid film.

[0011] 5. Repeated deposition: Repeat the above "deposition for 30 seconds - wipe - air dry" operation 3 to 4 times. This process can prevent the carbon electrode from absorbing too much water and swelling, while ensuring the uniform nucleation and growth of nickel-cobalt sulfide particles on the carbon slurry surface, forming a dense black catalytic film.

[0012] The reaction mechanism of the electrochemical deposition process is as follows: When a negative voltage is applied to the cathode, thiosulfate ions (S2O3) in the electrolyte... 2- A reduction reaction occurs on the electrode surface, generating reactive sulfide ions (S₂O₃). 2- Meanwhile, nickel ions (Ni) in the solution 2+) and cobalt ions (Co 2+ The ions migrate to the cathode surface, react with sulfur ions, and co-deposit to form a nickel-cobalt bimetallic sulfide (NiCo2S4) film. The overall reaction of this process can be represented as follows:

[0013] Beneficial effects Compared with the prior art, the present invention has the following significant advantages: 1. Non-invasive and wearable: The sensor is based on polyethylene terephthalate (PET) film, which is thin, light and flexible, and can fit closely to human skin to achieve non-invasive, continuous or on-demand detection of glucose in sweat, making it suitable for wearable sensing scenarios.

[0014] 2. High environmental stability: The use of inorganic nickel-cobalt sulfide materials to replace easily deactivated biological enzymes as catalytic recognition elements makes the sensor insensitive to changes in ambient temperature, pH value and humidity. This solves the problems of difficult preservation and short lifespan of traditional enzyme sensors, effectively extending the sensor's shelf life and actual service life.

[0015] 3. High detection sensitivity: The improved multi-step cyclic deposition process constructs a high specific surface area nanostructure on the surface of the porous carbon electrode. Compared with the unmodified electrode, the sensor's response sensitivity to low concentrations of sweat glucose at the micromolar level is significantly improved.

[0016] 4. Simple preparation process and low cost: The raw materials required for preparation are inexpensive and readily available. The preparation process does not require complex and precision equipment. The screen printing technology and the cyclic electrodeposition process are well compatible, making it easy to scale up and industrialize, and it has good commercialization potential. Attached Figure Description

[0017] Figure 1 : A schematic diagram of the flexible, enzyme-free sweat glucose sensor of the present invention in contact with the skin; Figure 2 : Dimensions of the screen-printed carbon electrodes used in this invention (all dimensions are in mm, R represents radius). Detailed Implementation

[0018] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] In the embodiments of the present invention, unless otherwise specified, all raw materials used are conventional commercial products purchased from the market, and all experimental operations are conventional electrochemical and material preparation operations.

[0020] Example 1 This embodiment provides detailed steps for preparing the flexible, enzyme-free sweat glucose sensor: S1. Preparation of flexible screen-printed electrodes: A commercially available or self-printed flexible three-electrode system is provided. The electrode uses a 125 μm thick polyethylene terephthalate (PET) film as a flexible insulating substrate. On the PET substrate, silver paste wires, carbon paste working electrode and counter electrode, and Ag / AgCl reference electrode are sequentially printed by screen printing process. The carbon working electrode is circular and preferably has a diameter of 3 mm. Before use, the electrode surface is ultrasonically cleaned with anhydrous ethanol and deionized water for 1-2 minutes to remove organic contaminants and dust, and then air-dried at room temperature.

[0021] S2. Preparation of electroplating solution: Weigh the following reagents into a 100mL beaker: 0.291g of nickel acetate hexahydrate (corresponding to a nickel ion concentration of 0.0085mol / L), 0.498g of cobalt acetate tetrahydrate (corresponding to a cobalt ion concentration of 0.02mol / L), and 2.48g of sodium thiosulfate pentahydrate (corresponding to a thiosulfate concentration of 0.1mol / L).

[0022] Add about 80 mL of deionized water to a beaker, place it on a magnetic stirrer, and stir at 500 rpm for about 20 minutes at room temperature until all solids are completely dissolved and the solution is a uniform light purple transparent color. Then transfer the solution to a 100 mL volumetric flask, dilute to the mark with deionized water, and shake well to obtain the nickel cobalt sulfide electrodeposition solution.

[0023] S3. Construction of the electrochemical deposition system: Take 50 mL of the electroplating solution prepared in step S2 and pour it into a clean 50 mL glass beaker (as an electrodeposition cell). Use the carbon working electrode area of ​​the flexible electrode prepared in step S1 as the cathode (working electrode) and its carbon counter electrode as the anode (counter electrode). Connect the two electrodes to the positive and negative terminals of a DC regulated power supply through alligator clip wires. Immerse the electrodes in the electroplating solution, ensuring that the entire sensitive area of ​​the carbon working electrode is completely submerged and the electrode lead part is kept above the water surface. The anode (counter electrode) can be the carbon counter electrode of the screen-printed electrode system itself, or an independent auxiliary electrode (such as a platinum sheet) can be used.

[0024] S4. Improved cyclic electrodeposition process: Turn on the DC regulated power supply and set the voltage to 5V.

[0025] 1. First cycle deposition: Maintain voltage of 5V and continue to apply power for 30 seconds. At this time, it can be observed that a small number of bubbles begin to be generated on the surface of the carbon working electrode and gradually darken.

[0026] 2. Intermediate treatment of the first cycle: After 30 seconds, immediately turn off the power and vertically remove the entire flexible electrode from the electroplating solution. Quickly use a clean, dust-free absorbent paper to gently absorb and wipe away excess droplets hanging on the outer edge of the working electrode area, the silver wire, and the PET substrate along the plane of the electrode substrate. Pay special attention to avoid forcefully scraping the surface of the sensitive area of ​​the working electrode horizontally. Then, place the electrode horizontally in a dust-free environment at room temperature (25±3℃) to air dry for about 3-5 minutes until the surface of the working electrode changes from a wet and reflective state to a uniform matte black, and there is no visible liquid film.

[0027] 3. Subsequent cycle deposition and treatment: Immerse the electrode, which has been air-dried, back into the electroplating solution and repeat the complete process of "deposit with 5V for 30 seconds -> remove and wipe -> air-dry at room temperature".

[0028] 4. Cycle count control: In this preferred embodiment, the above-mentioned complete "deposition-wiping-air drying" cycle is executed a total of 4 times.

[0029] S5. Post-processing and sensor completion: After completing the fourth cycle and air-drying, a uniform, dense, and well-adhered pure black film can be observed on the surface of the carbon working electrode. This is the in-situ grown nickel-cobalt sulfide nanocatalytic layer. Rinse the electrode surface very gently with deionized water for 1-2 seconds to remove loose ions adsorbed on the surface, and then dry it thoroughly at room temperature (e.g., let it stand for 1 hour).

[0030] Thus, a flexible, enzyme-free sweat glucose sensor based on a nickel-cobalt sulfide composite film has been successfully fabricated.

[0031] Example 2 This embodiment aims to illustrate that the composition of the electroplating solution can be adjusted within a certain range while still achieving the purpose of the present invention.

[0032] Except for the different electroplating solution ratio, the other steps are exactly the same as in Example 1.

[0033] When preparing the electroplating solution, the following concentration combination is used: nickel acetate concentration: 0.008 mol / L, cobalt acetate concentration: 0.015 mol / L, sodium thiosulfate concentration: 0.08 mol / L.

[0034] Following steps S3-S5 of Example 1, the electrode modification process resulted in a sensor that could also form a uniform nickel-cobalt sulfide film on the carbon working electrode. Its current response sensitivity to glucose was on the same order of magnitude as that of the sensor prepared in Example 1, demonstrating the effectiveness of the concentration range (nickel salt 0.005-0.02 mol / L, cobalt salt 0.01-0.03 mol / L, sulfur source 0.05-0.2 mol / L) required by the present invention.

[0035] Example 3 This embodiment is used to verify the validity of the boundary parameters within the scope of the claims.

[0036] 1. Low concentration boundary verification: Except for changing the composition of the electroplating solution to: nickel acetate concentration 0.005 mol / L (lower limit of the range), cobalt acetate concentration 0.01 mol / L (lower limit of the range), and sodium thiosulfate concentration 0.05 mol / L (lower limit of the range), the remaining steps are the same as in Example 1. The prepared sensor can form a uniform nickel-cobalt sulfide film on the carbon working electrode and produce a clear and repeatable electrochemical response to glucose, proving that the lower limit of the concentration range claimed in the claims is feasible and effective.

[0037] 2. High concentration boundary verification: Except for the electroplating solution composition being changed to: nickel acetate concentration 0.02 mol / L (upper limit of range), cobalt acetate concentration 0.03 mol / L (upper limit of range), and sodium thiosulfate concentration 0.2 mol / L (upper limit of range), the other steps are the same as in Example 1. The prepared sensor catalytic film is more dense and the response current is further increased, proving that the upper limit of the concentration range is effective and that the sensor performance can be controlled within a certain range by adjusting the concentration.

[0038] 3. Cycle number boundary verification: Using the formulation of Example 1, the number of deposition-wiping-air drying cycles was strictly limited to 3 times (lower limit of range) and 4 times (upper limit of range) for preparation. The test results showed that 3 cycles were sufficient to form a complete and catalytically active film; the film obtained by 4 cycles was denser and had higher sensitivity. When attempting 5 cycles, the film was too thick and prone to microcracks, resulting in decreased mechanical stability. This result proves that 3 to 4 cycles is the cycle number range for obtaining the best balance between performance and stability.

[0039] The above results demonstrate that the electroplating solution concentration range (nickel salt 0.005~0.02mol / L, cobalt salt 0.01~0.03mol / L, sulfur source 0.05~0.2mol / L) and the number of cyclic depositions (3~4 times) defined by the present invention are the optimal parameter range that balances sensor performance and stability.

[0040] Comparative Example 1 Except for omitting the intermediate "wipe-air dry" treatment, the other conditions were the same as in Example 1, that is, the working electrode was continuously deposited for 120 seconds at 5V (the total deposition time was the same as the four 30-second depositions in Example 1). The results showed that the prepared film had visible cracks after drying, and the film layer detached from the carbon electrode substrate after the electrode was slightly bent, making it impossible to detect glucose.

[0041] Comparative Example 2 Four 30-second depositions were performed, but after each deposition, the electrode was not removed and wiped to air dry. Instead, it was placed directly in the solution for 10 seconds before the next deposition. The results showed that the flexible carbon electrode swelled due to prolonged immersion in the electrolyte, resulting in an uneven film morphology, poor adhesion to the electrode substrate, and low sensing performance stability.

[0042] Comparative Example 3 To demonstrate the synergistic necessity of the wiping and air-drying steps, the following comparative example is set up: 1. Wipe but do not air dry: Four 30-second depositions were performed. After each deposition, the electrode was removed and excess droplets were wiped off, but it was not air dried. The electrode was immediately immersed in the solution for the next deposition. The results showed that the electrode surface was unstable due to the residual liquid film, resulting in a rough, uneven film with weak adhesion.

[0043] 2. Air-drying without wiping: Four 30-second depositions were performed. After each deposition, the film was removed and air-dried directly without wiping. The results showed that the droplets around the working electrode area migrated under the influence of gravity and capillary action, forming a significant "coffee ring" effect after drying. The film thickness was extremely uneven (thick at the edges and thin in the center), and the performance could not be reproduced.

[0044] The above comparison demonstrates that wiping and air drying are two operations that must be performed consecutively and work synergistically in the intermediate processing steps of this invention. Together, they ensure the uniform removal of the electrolyte film and the gentle evaporation of the solvent, which are key to achieving film uniformity and adhesion.

[0045] Comparative Example 4 To highlight the specific compatibility and advantages of the nickel-cobalt sulfide material system and the flexible PET substrate in the aforementioned process, a material substitution was attempted: 1. Comparison of monometallic sulfides: Using only nickel acetate and sodium thiosulfate (attempt to prepare NiSx) or only cobalt acetate and sodium thiosulfate (attempt to prepare CoSx), deposition was carried out under the same process. The results showed that the catalytic activity of the formed monometallic sulfide film for glucose was significantly lower than that of the nickel-cobalt sulfide film, and its current response value was less than 30% of the latter.

[0046] 2. Comparison of different flexible substrates: When the PET substrate was replaced with polydimethylsiloxane (PDMS) film and carbon electrodes were screen-printed, under the same deposition process, due to the poor compatibility between the hydrophobicity of the PDMS surface and the carbon paste, the carbon electrodes were easily peeled off from the PDMS substrate or wrinkled under the mechanical action and swelling stress of repeated immersion and wiping in the electrodeposition solution, making it impossible to complete the process.

[0047] This comparison demonstrates that the "short-time deposition-intermediate processing" cycle process of the present invention forms an optimal synergy with the "screen-printed carbon electrode on PET substrate" and the specific high-performance catalytic material system of "nickel-cobalt sulfide", jointly ensuring the excellent performance of the sensor.

[0048] Performance testing methods and results To comprehensively evaluate the performance of the flexible enzyme-free sweat glucose sensor prepared in this invention, the following tests were conducted using an electrochemical workstation: 1. Sensitivity and Linearity Range Tests: A three-electrode system of an electrochemical workstation was used, with the prepared sensor as the working electrode, the Ag / AgCl electrode as the reference electrode, and the platinum wire electrode as the counter electrode. Tests were conducted in 0.1M NaOH electrolyte. Using a chronoamperometric method, different concentrations of glucose standard solution were continuously added at a constant working potential of +0.55V (vs. Ag / AgCl), and the steady-state current response was recorded. A calibration curve was plotted with glucose concentration on the x-axis and the corresponding response current value on the y-axis. The slope within the linear range represents the sensitivity (unit: μA·mM). -1 ·cm -2 or μA·mM -1 The linear range is determined by the linear correlation coefficient (R²). 2 >0.99) confirmed; 2. Detection Limit Calculation: Based on the data in the low concentration region of the sensitivity test, the detection limit (LOD) is calculated using the formula LOD=3σ / S, where σ is the standard deviation of the current response of the blank solution (0.1M NaOH) (tested 10 times), and S is the sensitivity of the calibration curve.

[0049] 3. Repeatability test: Five independent sensors prepared in the same batch were tested on glucose solutions of the same concentration (e.g., 1.0 mM) under the same conditions. The relative standard deviation (RSD) of the response current was calculated to evaluate the repeatability of the preparation process. 4. Stability Test: (1) Operational stability: The same sensor was used continuously for multiple measurement cycles (e.g., after measuring 1.0 mM glucose solution, it was placed in a blank solution to recover, and the cycle was >20 times), and the decay rate of the response current was recorded; (2) Long-term storage stability: The prepared sensor was dried and stored at 4°C, and its response to a fixed concentration of glucose was tested periodically (e.g., on the 1st, 7th, 14th and 30th days) to examine its performance retention rate. 5. Anti-interference test: In a 0.1M NaOH solution containing a fixed concentration of glucose (e.g., 0.5mM), potentially coexisting interfering substances (such as uric acid, ascorbic acid, lactic acid, sodium chloride, etc., with concentrations typically 5-10 times the glucose concentration) are added separately. The changes in current response are measured, and the deviation from the response value of the glucose solution alone is calculated to evaluate the selectivity of the sensor. 6. Mechanical flexibility test: The sensor is attached to the surface of a cylinder with different radii of curvature (or subjected to a certain number of bending cycles, such as 1000 cycles), and the current response to the same concentration of glucose solution is tested before and after bending. The response retention rate is calculated to evaluate its flexibility and practicality. 7. Actual sample recovery test: Using the standard addition method, a known concentration of glucose standard was added to artificial sweat or diluted real sweat samples, and the sensor was used for detection. The recovery rate was calculated (recovery rate (%) = measured value / spiked value × 100%) to verify its analytical reliability in complex matrices.

[0050] The results are shown in Tables 1 and 2: Table 1. Sensor performance data from the examples

[0051] Table 2. Performance data of the comparative sensor

[0052] To quantitatively evaluate the advantages of the process of this invention, the sensors prepared in the examples and comparative examples were subjected to systematic electrochemical performance tests. The key data are summarized in Tables 1 and 2. As shown in Table 1, the sensors (Examples 1-3) prepared using the 'short-time deposition-wiping-air drying' cycle process of this invention exhibit high sensitivity, wide linear range, low detection limit, and excellent repeatability (RSD<4%) and stability (current retention rate>88%) over a wide range of parameters. In contrast, Table 2 shows that the performance of the comparative examples that did not use complete intermediate treatment or had material / substrate defects deteriorated across the board, especially the poor reproducibility (RSD>12%) and low sensitivity caused by thin film morphology problems. The extremely high RSD values ​​(>15%) of Comparative Examples 1, 3a, and 3b conclusively prove from a data perspective that the synergistic effect of the three elements of short-time deposition, wiping, and air drying is indispensable. The results of Comparative Example 4 confirm the specific advantages of the nickel-cobalt sulfide material and PET substrate system.

[0053] The sensors prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to the same electrochemical performance tests (glucose was detected by chronoamperometry in 0.1M NaOH solution). The sensors in Examples 1-3 all showed high and stable current response, wide linear range and good repeatability. However, the sensors in Comparative Example 1 (continuous deposition) and Comparative Example 2 (no processing cycle) had weak response signals, high noise and poor stability. Moreover, the signal was severely attenuated after mechanical bending test. The sensor prepared in Comparative Example 3 (missing step) could not reproduce the performance and had serious defects in film morphology. Comparative Example 4 (material replacement) could not obtain an effective sensing interface or the performance was significantly degraded.

[0054] The above results fully demonstrate that the cyclic process of "short-time electrodeposition (controlling the depth of a single reaction) - forced interruption and wiping and air drying (eliminating swelling, releasing stress, and homogenizing the liquid film)" designed in this invention is a key technology for solving the problem of the firm and uniform growth of nickel-cobalt sulfide catalytic films on flexible porous carbon electrodes. At the same time, Example 3 verifies the full feasibility of the parameter range of the claims, and Comparative Examples 3 and 4 demonstrate from the opposite perspective the non-obviousness of the synergistic effect between the process steps and the material system, which is by no means a simple superposition of conventional technologies in the field or an easily conceived improvement.

[0055] In summary, the present invention provides a simple, low-cost, and highly effective method for preparing a flexible enzyme-free glucose sensor through the above specific embodiments. Those skilled in the art can make various changes and modifications within the scope defined by the claims, and all such changes and modifications will fall within the protection scope of the present invention.

[0056] In the description of this specification, the terms "preparation example," "example," "various examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that example or preparation example, which are included in at least one example or preparation example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same example or preparation example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more examples or preparation examples.

[0057] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a flexible, enzyme-free sweat glucose sensor based on a nickel-cobalt sulfide composite thin film, characterized in that, The preparation method includes the following steps: a. Substrate preparation: Provide a screen-printed electrode based on a flexible insulating film, the electrode system including at least a carbon working electrode, a counter electrode, and a reference electrode; b. Electroplating solution preparation: Prepare an aqueous solution containing nickel salt, cobalt salt and sulfur source as the electroplating solution. The nickel salt is nickel acetate with a concentration of 0.005~0.02 mol / L, the cobalt salt is cobalt acetate with a concentration of 0.01~0.03 mol / L, and the sulfur source is sodium thiosulfate with a concentration of 0.05~0.2 mol / L. c. Construction of the electrodeposition system: The carbon working electrode area on the flexible substrate is used as the cathode, and an auxiliary electrode is used as the anode. Both are immersed in the electroplating solution. d. Apply a 5V DC voltage between the cathode and anode for electrochemical deposition, with a single deposition time of 30 seconds; e. After each deposition, remove the electrode from the electroplating solution, wipe off any residual droplets outside the working electrode area with absorbent material, and allow the working electrode to air dry at room temperature until there is no obvious liquid film on the surface. f. Repeat steps d and e, including deposition, wiping, and air drying, 3-4 times to form a nickel-cobalt sulfide nanocatalytic film on the surface of the carbon working electrode.

2. The preparation method according to claim 1, characterized in that, The flexible insulating film is a polyethylene terephthalate film, and the conductive electrode system is a screen-printed electrode.

3. The preparation method according to claim 1, characterized in that, The preferred ratio of the electroplating solution in step b is: nickel acetate 0.0085 mol / L, cobalt acetate 0.02 mol / L, and sodium thiosulfate 0.1 mol / L.

4. The preparation method according to claim 1, characterized in that, The DC voltage mentioned in step d is 5V, and the deposition time for a single deposition is controlled to be 30 seconds.

5. The preparation method according to claim 1, characterized in that, The deposition, wiping, and air-drying process in step f is repeated 3-4 times.

6. The preparation method according to claim 1, characterized in that, Step e involves using absorbent material to wipe away residual droplets outside the working electrode area. This means wiping along the plane of the flexible substrate and avoiding lateral scraping of the sensitive area surface of the carbon working electrode.

7. The preparation method according to claim 1, characterized in that, In step e, the air drying is carried out at room temperature until the surface of the carbon working electrode changes from a wet, reflective state to a uniform matte state.

8. A flexible, enzyme-free sweat glucose sensor prepared by the method according to any one of claims 1 to 7, characterized in that, The invention includes a flexible insulating substrate and a screen-printed electrode system disposed on the substrate. The electrode system includes at least a carbon working electrode with a surface modified with a nickel-cobalt sulfide nanocatalytic film, a counter electrode, and a reference electrode.

9. A flexible, enzyme-free sweat glucose sensor as described in claim 8, characterized in that, The nickel-cobalt sulfide nanocatalytic film is a film uniformly covering the surface of a carbon working electrode, prepared by the method described in any one of claims 1 to 7.

10. A flexible, enzyme-free sweat glucose sensor as described in claim 8 or 9 for use in the preparation of a non-invasive blood glucose monitoring device or a sweat glucose detection patch.

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