A copper-based MOFs nanoscale enzyme, a MOFs functionalized nanofiber membrane, and respective preparation methods and a wearable sweat vitamin C sensing patch

Abstract

This invention belongs to the field of colorimetric biosensing and wearable detection technology, specifically relating to a copper-based MOF nanozyme, a MOF-functionalized nanofiber membrane, their respective preparation methods, and a wearable sweat vitamin C sensing patch. The patch comprises a bottom adhesive layer, a middle sensing layer, and a top encapsulation layer. The sensing layer contains a nanofiber membrane made of copper-based metal-organic framework and polycaprolactone electrospun. This membrane exhibits oxidase-like activity, catalyzing TMB color development under H2O2-free conditions. The presence of ascorbic acid inhibits this reaction, causing a color change from blue-green to a lighter shade, with the degree of change linearly related to the ascorbic acid concentration. The patch's structural design facilitates sweat flow and optical reading, supporting visual interpretation or smartphone image analysis. It offers advantages such as ease of operation, rapid response, high specificity, high stability, and non-invasive wearability, making it suitable for real-time health monitoring of sweat vitamin C.

Description

Technical Field

[0001] This invention belongs to the field of colorimetric biosensing and wearable detection technology, specifically involving a copper-based MOF nanozyme, a MOF functionalized nanofiber membrane and their respective preparation methods, as well as a wearable sweat vitamin C sensing patch. Background Technology

[0002] Ascorbic acid (AA), also known as vitamin C, is an essential water-soluble vitamin for the human body, playing a vital role in physiological processes such as antioxidant reactions, collagen synthesis, and immune regulation. Changes in ascorbic acid levels in the body are closely related to nutritional status, oxidative stress levels, and the development of various diseases (such as scurvy and cancer). Therefore, accurate and timely detection of ascorbic acid is of great significance.

[0003] Existing methods for detecting ascorbic acid mainly include high-performance liquid chromatography (HPLC), spectrophotometry, and electrochemical detection. These methods typically require complex sample pretreatment, rely on bulky and expensive instruments, and are operated by specialized personnel, making them unsuitable for real-time monitoring and on-site testing. Furthermore, most of these methods use blood or urine as the detection target, resulting in highly invasive sampling and inconvenient operation.

[0004] In recent years, with the development of wearable technology, non-invasive biodetection based on sweat has received widespread attention. Sweat is continuously secreted and easily obtained, and its composition can reflect the physiological state of the human body to a certain extent. However, sweat has a low content of ascorbic acid and contains various interfering substances such as uric acid, lactic acid, and glucose, which places higher demands on the sensitivity and selectivity of sensing materials.

[0005] Current reports on sweat ascorbic acid sensors mostly rely on external oxidants (such as hydrogen peroxide) or electrochemical detection methods, which suffer from problems such as insufficient system stability, complex device structures, and difficulty in achieving intuitive and visual detection. Meanwhile, how to stably and uniformly integrate highly active sensing materials into flexible wearable substrates remains a technical challenge in this field.

[0006] Metal-organic frameworks (MOFs) have shown promising applications in biosensing due to their large specific surface area, tunable structure, and designable catalytic activity. However, when MOF powder materials are used directly in wearable devices, they often suffer from poor mechanical stability, easy shedding, and poor sweat transmission, which limits their practical application.

[0007] Therefore, there is an urgent need to develop an ascorbic acid detection patch that is structurally stable, has a simple preparation process, requires no exogenous oxidants, and is suitable for wearable applications, so as to achieve non-invasive, rapid, and visual detection of ascorbic acid in sweat. Summary of the Invention

[0008] The purpose of this invention is to solve the problems of complex operation, slow response, poor specificity, reliance on large instruments or exogenous oxidants (such as H2O2) in existing vitamin C detection technologies in sweat, and difficulty in achieving wearable real-time monitoring. The invention provides a flexible wearable sensing patch that is easy to operate, fast to detect, has good specificity, high stability, and does not require the addition of external oxidants.

[0009] Therefore, a first aspect of the present invention provides a method for preparing copper-based MOF nanozymes, the method comprising: Step 1: Dissolve benzimidazole compounds and copper salts in the first solvent, react at 120-160℃, cool, and obtain a dark green suspension; Step 2: Rotary evaporation precipitates the solid; Step 3: After washing the precipitated solid with deionized water by centrifugation, collect the solid, dry it, and obtain the copper-based MOF nanozyme; The benzimidazole compound is 5,6-dimethylbenzimidazole and / or benzimidazole.

[0010] The ratio of ligand to metal ions directly affects the stability of the framework structure and the number of catalytic active sites. As a preferred method, in the preparation method of the copper-based MOF nanozyme described above, in step 1, the molar ratio of benzimidazole compound to copper ions in copper salt is 2:1-3:1. For example, 172 mg of 5,6-dimethylbenzimidazole and 121 mg of Cu(NO3)2·3H2O (at this time, the molar ratio of 5,6-dimethylbenzimidazole to Cu(NO3)2·3H2O is about 2.35:1) are dissolved in 4 mL of the first solvent and transferred to a glass pressure tube.

[0011] As a preferred embodiment, in the above-mentioned method for preparing copper-based MOF nanozymes, in step 1, the copper salt is at least one of copper nitrate, copper carbonate, copper sulfate, and copper chloride.

[0012] As a preferred embodiment, in the above-mentioned method for preparing copper-based MOF nanozymes, in step 1, the first solvent is at least one of methanol, ethanol, and deionized water. A moderately polar solvent is beneficial for the complete dissolution and coordination of the ligands with the metal ions; selecting a solvent with a suitable boiling point ensures that the reaction system maintains a stable pressure at 120-160°C.

[0013] As a preferred embodiment, in the above-mentioned method for preparing copper-based MOF nanozymes, the reaction time in step 1 is 4-10 hours, such as heating in an oil bath at 140°C for 7.5 hours. Four hours ensures complete reaction and avoids crystal defects, 10 hours prevents particle agglomeration due to overgrowth, and approximately 7.5 hours achieves uniform crystal size and optimal catalytic activity.

[0014] As a preferred embodiment, in the above-mentioned method for preparing copper-based MOF nanozymes, step 1, cooling refers to cooling to room temperature.

[0015] In step 2 of the above-mentioned method for preparing copper-based MOF nanozymes, the product can be transferred to a round-bottom flask, the solid can be precipitated using a rotary evaporator, deionized water can be added to the flask to transfer the solid to a centrifuge tube, the solid can be washed with water and collected by centrifugation (e.g., 8000 rpm, 5 min / time, for a total of 3 times).

[0016] As a preferred embodiment, in the above-mentioned method for preparing copper-based MOF nanozymes, the drying temperature in step 3 is 35-45℃; optionally, the drying method is vacuum drying. A dark green solid powder is obtained after drying.

[0017] A second aspect of the present invention provides a copper-based MOF nanozyme, which is prepared by the preparation method described above.

[0018] A third aspect of the present invention provides a method for preparing MOF-functionalized nanofiber membranes, the method comprising: Step a: Disperse copper-based MOF nanozymes in a second solvent to obtain a first solution; disperse polycaprolactone in a third solvent to obtain a second solution; mix the first and second solutions uniformly and stir continuously to form a uniform and stable spinning precursor solution; Step b: Perform electrospinning, and after spinning, dry to obtain the MOFs functionalized nanofiber membrane; In step a, the copper-based MOF nanozyme is the copper-based MOF nanozyme described above.

[0019] As a preferred embodiment, in the above-mentioned method for preparing MOF-functionalized nanofiber membranes, in step a, the mass ratio of copper-based MOF nanozyme to polycaprolactone is 0.05-0.15:1. This range ensures basic catalytic activity and avoids insufficient sensitivity; prevents nanozyme aggregation and ensures the flexibility of the fiber membrane; and achieves an optimal balance between catalytic activity and mechanical strength.

[0020] As a preferred embodiment, in the above-mentioned method for preparing MOF-functionalized nanofiber membranes, in step a, the second solvent is at least one selected from methanol, ethanol, propanol, and trifluoroethanol, such as 2,2,2-trifluoroethanol. For example, 100 mg of copper-based MOF nanozyme is dispersed in 1 mL of 2,2,2-trifluoroethanol.

[0021] As a preferred embodiment, in the above-mentioned method for preparing MOF-functionalized nanofiber membranes, in step a, the third solvent is at least one selected from methanol, ethanol, propanol, and trifluoroethanol, such as 2,2,2-trifluoroethanol. For example, 100 mg of polycaprolactone is dispersed in 9 mL of 2,2,2-trifluoroethanol.

[0022] 2,2,2-Trifluoroethanol has good solubility and dispersibility for both PCL and MOFs, making it suitable for electrospinning processes and easy to form uniform fibers; it also has relatively low toxicity and the residual solvent is easy to remove.

[0023] As a preferred embodiment, in the above-mentioned method for preparing MOF-functionalized nanofiber membranes, in step a, the stirring speed is 400-800 rpm to ensure thorough mixing while avoiding bubble generation, and the stirring time is 8-16 hours to ensure uniform dispersion of MOFs in the spinning solution. Preferably, the stirring method is magnetic stirring, which provides a gentle yet effective hybrid mixing. For example, magnetic stirring at 600 rpm for 12 hours forms a uniform and stable spinning precursor solution. This spinning solution is then loaded into a disposable plastic syringe with a 21G flat-tipped needle and deposited onto smooth silicone paper using electrospinning technology.

[0024] As a preferred embodiment, in the above-described method for preparing MOF-functionalized nanofiber membranes, the drying temperature in step b is 35-40℃. After drying, a flexible and porous MOF-functionalized nanofiber membrane can be obtained.

[0025] As a preferred embodiment, in the above-mentioned method for preparing MOF-functionalized nanofiber membranes, in step b, the electrospinning process parameters satisfy at least one of the following characteristics: The voltage of the high-voltage power supply is 16-18kV; when the voltage is below 16kV, the electric field force is insufficient to overcome the surface tension of the solution, resulting in spinning difficulties; when the voltage is above 18kV, jet instability is likely to occur, affecting fiber morphology. The distance between the nozzle and the receiver is 15-18cm. This distance ensures that the solvent evaporates fully and prevents the fiber from curing prematurely. The feed rate is 0.6-0.8 mL / h; The ambient temperature should be 25-30℃ to ensure a moderate solvent evaporation rate. The relative humidity is kept below 40%RH to prevent moisture from affecting fiber formation.

[0026] A fourth aspect of this invention provides a MOF-functionalized nanofiber membrane, which is prepared by the above-described preparation method. MOF-functionalized nanofiber membranes are a class of nanomaterials with unique structures and excellent catalytic performance. Their core is a copper-based MOF nanozyme, which is formed into the MOF-functionalized nanofiber membrane through electrospinning. The nanofibers, with their large specific surface area, can not only efficiently load nanozymes but also enhance the exposure of active sites in the catalytic reaction, thereby improving catalytic efficiency. Applying the MOF-functionalized nanofiber membrane to the construction of wearable biosensors can achieve highly sensitive and selective detection of ascorbic acid in sweat.

[0027] This invention prepares MOF-functionalized nanofiber membranes via electrospinning. This material exhibits excellent oxidase-like activity. Testing revealed that the MOF-functionalized nanofiber membrane can efficiently catalyze the colorimetric reaction of 3,3′,5,5′-tetramethylbenzidine (TMB) at room temperature. In the presence of ascorbic acid (AA), AA acts as a strong reducing agent, inhibiting the oxidation process of TMB, resulting in a significant reduction in color intensity. Furthermore, the color change (from blue-green to colorless / light-colored) shows a good linear relationship with the AA concentration, thus achieving highly sensitive, label-free colorimetric detection of ascorbic acid.

[0028] A fifth aspect of the present invention provides a wearable sweat vitamin C sensing patch, the sensing patch comprising a bottom adhesive layer, an intermediate sensing layer, and a top encapsulation layer disposed sequentially. The intermediate sensing layer includes the aforementioned MOFs-functionalized nanofiber membrane, and a colorimetric card with color levels corresponding to the colorimetric responses at different concentrations of ascorbic acid, used to assist in quantitative analysis.

[0029] The color scales on the color chart correspond to ascorbic acid concentrations in sweat ranging from 0 to 1300 μM.

[0030] This patch enables non-invasive, visual detection of vitamin C in human sweat and supports image acquisition and concentration analysis via smartphone. It is suitable for scenarios such as daily health monitoring, sports nutrition assessment, and clinical auxiliary diagnosis.

[0031] As a preferred option, the aforementioned wearable sweat vitamin C sensor patch, The bottom adhesive layer uses a medical-grade substrate material and includes multiple sweat inlets to guide sweat into the intermediate sensing layer. The top encapsulation layer is provided with multiple sweat outlets corresponding to the bottom adhesive layer to promote sweat circulation and prevent internal fluid accumulation.

[0032] According to a specific embodiment of the present invention, the preparation method of the above-mentioned wearable sweat vitamin C sensor patch includes the following steps: Preparation of the bottom adhesive layer: Medical-grade double-sided tape material is cut into a circular base with a diameter of 3cm, and three circular sweat inlets with a diameter of 3mm are formed on its surface by laser drilling, which is used to guide sweat to flow into the sensing area. Construction of the intermediate sensing layer: Medical nonwoven fabric is cut into three radially intersecting strips, and a MOF-functionalized nanofiber membrane is fixed in the central area of ​​the intersection as a sensing unit; at the same time, a pre-calibrated colorimetric card is integrated around it, whose color scale corresponds to the color development response at different concentrations of AA, which is used to assist in quantitative analysis. Top layer preparation: Transparent polydimethylsiloxane (PDMS) is used for casting to form a moderately thick, flexible and transparent circular cover layer. Three circular sweat outlets with a diameter of 3mm are opened on it corresponding to the bottom layer entrance to promote sweat circulation and prevent internal liquid accumulation. Patch integration: The above three-layer structure is stacked in sequence as “bottom adhesive layer – middle sensing layer – top PDMS layer” and tightly bonded together by physical pressing to form an integrated, fully flexible, breathable and light-transmitting circular patch device with an overall diameter of 3cm.

[0033] When in use, the patch is directly applied to human skin (such as the forearm or forehead). Sweat seeps in through the bottom inlet and triggers a colorimetric reaction after contacting the sensor area of ​​the MOFs functionalized nanofiber membrane. The color change of the reaction can be initially judged by the naked eye, or by taking an image with a smartphone camera and combining it with a dedicated APP for RGB value analysis to achieve digital reading of AA concentration.

[0034] Compared with the prior art, the present invention has at least the following beneficial effects: (1) This invention utilizes the inherent oxidase activity of MOFs, without the need to add unstable reagents such as H2O2, thereby improving the stability and safety of detection.

[0035] (2) The patch of the present invention has high sensitivity and a detection limit as low as micromolar level, and can accurately respond to changes in vitamin C in the physiological concentration range of sweat.

[0036] (3) The color change of the patch during use is intuitive and obvious, supporting visual interpretation or quantitative measurement with the assistance of smartphone, reducing the threshold for use; the fully flexible structure fits the skin, and the breathable and sweat-wicking design avoids irritation, making it suitable for long-term wear.

[0037] (4) The raw materials used in this invention are readily available, and the electrospinning and lamination processes are easy to scale up for production.

[0038] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0039] Figure 1 A schematic diagram of a sweat vitamin C sensor patch; Figure 2 A schematic diagram of the synthesis of Cu-MOFs-CPNFs; Figure 3 The image shows a scanning electron microscope (SEM) image of Cu-MOFs-CPNFs obtained in Example 1. Figure 4 The image shows the sensing effect of Cu-MOFs-CPNFs prepared in Example 1 on vitamin C. Detailed Implementation

[0040] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the technical solutions provided by the present invention. However, it will be apparent to those skilled in the art that the technical solutions provided by the present invention can be implemented without one or more of these details.

[0041] Example 1 This embodiment provides a copper-based MOF nanozyme, a MOF-functionalized nanofiber membrane, and their respective preparation methods.

[0042] Preparation methods of Cu-MOFs-CPNFs nanofiber membranes, such as Figure 2 As shown, the steps are as follows: (1) Solvent-thermal synthesis of Cu-MOF nanozymes: 5,6-dimethylbenzimidazole (172 mg) and copper nitrate trihydrate (Cu(NO3)2·3H2O, 121 mg) were added to 4 mL of anhydrous methanol and sonicated for 5 minutes until completely dissolved to form a homogeneous transparent solution. The solution was transferred to a 25 mL pressure-resistant glass reaction tube, sealed, and placed in an oil bath at 140 °C for 7.5 hours. After the reaction was completed, the solution was naturally cooled to room temperature to obtain a dark green suspension. The product was transferred to a round-bottom flask and most of the solvent was removed by rotary evaporation at 40 °C. The obtained solid was repeatedly washed by centrifugation with deionized water (8000 rpm, 5 min / time, for a total of 3 times). Finally, it was dried in a vacuum drying oven at 40 °C for 12 hours to obtain dark green Cu-MOF nanozyme powder.

[0043] (2) Preparation of Cu-MOFs spinning solution: Weigh 100mg of the above Cu-MOFs powder and disperse it in 1mL of 2,2,2-trifluoroethanol (TFEA), and sonicate it for 30 minutes to make it uniformly dispersed; separately, dissolve 1g of polycaprolactone (PCL) in 9mL of TFEA and stir magnetically until completely dissolved; then mix the Cu-MOFs dispersion with the PCL solution and stir magnetically at 600rpm for 12 hours to form a uniform and stable spinning precursor solution.

[0044] (3) Electrospinning film formation: The above spinning solution was drawn into a 10mL disposable plastic syringe and fitted with a 21G flat-tipped stainless steel needle; under the conditions of ambient temperature 28℃ and relative humidity 35%RH, the high voltage power supply voltage was set to 17kV, the distance between the nozzle and the receiver (an aluminum foil roller covered with silicone paper) was 16cm, and the feed rate of the feed pump was 0.7mL / h, and electrospinning was carried out for 2 hours; after spinning, the collected fiber membrane was placed in a vacuum drying oven at 38℃ and dried overnight to completely remove residual solvent, and finally a flexible and self-supporting nanofiber membrane: Cu-MOFs-CPNFs was obtained. The scanning electron microscope image is shown in [reference]. Figure 3 .

[0045] Figure 4 The image shows the sensing effect of Cu-MOFs-CPNFs prepared in Example 1 on vitamin C. Among them, (1) is a graph showing the color change of Cu-MOFs-CPNFs on vitamin C solutions of different concentrations, and (2) is a graph showing the linear relationship between the difference in color development effect and the concentration of vitamin C.

[0046] Example 2 This embodiment provides a wearable sweat vitamin C sensor patch (see...). Figure 1 The assembly method and its detection mechanism were verified. (1) Bottom layer: Cut a 3cm diameter medical double-sided tape disc and laser-drill three 3mm diameter inlets; (2) Intermediate layer: Cut three 4mm wide medical non-woven fabrics and intersect them in a "Y" shape. 6mm diameter Cu-MOFs-CPNFs are attached to the center point, and colorimetric cards (corresponding to AA concentrations of 0, 50, 100, 300, 500, 700, 900, 1100, and 1300μM) are printed on the side. (3) Top layer: After casting and curing PDMS prepolymer (main agent: curing agent = 10:1), three outlets with a diameter of 3mm are made; (4) Three layers are aligned and pressed together to obtain a complete patch.

[0047] Detection mechanism description: Before use, Cu-MOFs-CPNFs adsorb trace amounts of oxygen from the air, and the Cu on their surface... 2+Site activation of O2 generates reactive oxygen species, which in turn oxidize the colorless TMB substrate to blue oxidized TMB (oxTMB), resulting in a blue-green color. When the patch comes into contact with sweat containing ascorbic acid, AA is preferentially converted to Cu. 2+ Catalytic oxidation simultaneously reduces the generated oxTMB back to its colorless state, causing the overall color to change from blue-green to light green or white. The degree of colorimetric inhibition is positively correlated with the AA concentration, enabling visual quantitative detection.

[0048] The patch was applied to the volunteer's forearm, and color development was completed within 5-10 minutes after sweating during exercise. Images were captured using a smartphone, and the corresponding values ​​were analyzed using RGB analysis software to establish a standard curve (standard curve reference) with ΔR = R0 - R (R0 being the R value without AA). Figure 4 The linear range is 5–150 μM, and the detection limit is approximately 5 μM. In simulated sweat containing interfering substances such as uric acid, lactic acid, and glucose, the response signal change is less than 5%, indicating excellent selectivity.

[0049] Comparative Example 1 This comparative example provides a method for preparing MOF functionalized nanofiber membranes.

[0050] The difference from Example 1 lies in the substitution of 5,6-dimethylbenzimidazole with an equimolar amount of imidazole in the Cu-MOF synthesis step, while the remaining raw material ratios, reaction conditions, and subsequent electrospinning process remain unchanged. The resulting material exhibits a significantly weakened ability to catalyze TMB color development, and the color change is not obvious at the same AA concentration, indicating that the methyl substituent of 5,6-dimethylbenzimidazole plays a crucial role in stabilizing the Cu active center and enhancing enzyme-like activity.

[0051] Imidazole lacks a benzene ring conjugated structure and a methyl electron-donating group, and is associated with Cu 2+ The coordination ability is weak, the crystallinity of the MOF formed is poor and the density of active sites is low. The oxidase-like activity is lower than that of Cu-MOF constructed from 5,6-dimethylbenzimidazole. Therefore, it cannot effectively catalyze the TMB colorimetric reaction, resulting in a significant decrease in the detection sensitivity of ascorbic acid.

[0052] Comparative Example 2 This comparative example provides a method for preparing MOF functionalized nanofiber membranes.

[0053] The difference from Example 1 lies in the substitution of Cu(NO3)2·3H2O with an equimolar amount of Zn(NO3)2·6H2O in the Cu-MOF synthesis step. All other raw materials, solvents, reaction temperatures, times, and film formation processes remain the same as in Example 1. This film exhibits almost no catalytic TMB color development ability, showing no significant color formation even in the absence of AA, and thus fails to achieve a colorimetric response against ascorbic acid. This demonstrates that copper ions are a necessary metal center for achieving oxidase-like activity and AA-specific detection.

[0054] Comparative Example 3 This comparative example provides a method for preparing MOF functionalized nanofiber membranes.

[0055] The difference from Example 1 is that the solvothermal reaction temperature of Cu-MOF was reduced from 140℃ to 100℃, while the reaction time remained at 7.5 h. Other raw material composition, post-treatment, and electrospinning parameters remained unchanged. The resulting product exhibited poor crystallinity, severe particle agglomeration, and a significant decrease in enzyme-like activity. In AA detection, the response was slow (>15 min), with low color contrast and poor repeatability, indicating that approximately 140℃ is a necessary condition for forming highly active and highly dispersed Cu-MOF nanostructures.

[0056] Comparative Example 4 This comparative example provides a method for preparing MOF functionalized nanofiber membranes.

[0057] The difference from Example 1 lies in the Cu-MOF synthesis step, where the molar ratio of 5,6-dimethylbenzimidazole to Cu(NO3)2·3H2O was adjusted from 2.35:1 to 1:1, while the remaining solvent volume, reaction temperature, reaction time, and subsequent film-forming process remained unchanged. The resulting product contained a large number of uncoordinated copper salt impurities, exhibited decreased MOF crystallinity, and showed severe nanoparticle aggregation. The fabricated patch showed a dark background color and low color contrast in AA detection, with a significantly increased detection limit, indicating that a suitable ligand / metal molar ratio is a key condition for forming highly active and pure Cu-MOF nanozymes.

[0058] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing copper-based MOF nanozymes, characterized in that, The preparation method includes: Step 1: Dissolve benzimidazole compounds and copper salts in the first solvent, react at 120-160℃, cool, and obtain a dark green suspension; Step 2: Rotary evaporation precipitates the solid; Step 3: After washing the precipitated solid with deionized water by centrifugation, collect the solid, dry it, and obtain the copper-based MOF nanozyme; The benzimidazole compound is 5,6-dimethylbenzimidazole and / or benzimidazole.

2. The method for preparing copper-based MOF nanozymes according to claim 1, characterized in that, In step 1, the molar ratio of benzimidazole compounds to copper ions in copper salts is 2:1-3:

1.

3. The method for preparing copper-based MOF nanozymes according to claim 1, characterized in that, Satisfy at least one of the following characteristics: In step 1, the copper salt is at least one of copper nitrate, copper carbonate, copper sulfate, and copper chloride; In step 1, the first solvent is at least one of methanol, ethanol, and deionized water; In step 1, the reaction time is 4-10 hours; In step 1, cool to room temperature; In step 3, the drying temperature is 35-45℃; optionally, the drying method is vacuum drying.

4. A copper-based MOF nanozyme, characterized in that, The copper-based MOF nanozyme is prepared by the preparation method described in any one of claims 1-3.

5. A method for preparing MOF-functionalized nanofiber membranes, characterized in that, The preparation method includes: Step a: Disperse copper-based MOF nanozymes in a second solvent to obtain a first solution; disperse polycaprolactone in a third solvent to obtain a second solution; mix the first and second solutions uniformly and stir continuously to form a uniform and stable spinning precursor solution; Step b: Perform electrospinning, and after spinning, dry to obtain the MOFs functionalized nanofiber membrane; In step a, the copper-based MOF nanozyme is the copper-based MOF nanozyme according to claim 4.

6. The method for preparing MOFs functionalized nanofiber membranes according to claim 5, characterized in that, Satisfy at least one of the following characteristics: In step a, the mass ratio of copper-based MOF nanozyme to polycaprolactone is 0.05-0.15:1; In step a, the second solvent is at least one of methanol, ethanol, propanol, and trifluoroethanol; In step a, the third solvent is at least one of methanol, ethanol, propanol, and trifluoroethanol; In step a, the stirring speed is 400-800 rpm and the stirring time is 8-16 hours; optionally, the stirring method is magnetic stirring. In step b, the drying temperature is 35-40℃.

7. The method for preparing MOFs functionalized nanofiber membranes according to claim 5, characterized in that, In step b, the electrospinning process parameters satisfy at least one of the following characteristics: The voltage of the high-voltage power supply is 16-18kV; The distance between the nozzle and the receiver is 15-18cm; The feed rate is 0.6-0.8 mL / h; The ambient temperature is 25-30℃; Relative humidity below 40%RH.

8. A MOF-functionalized nanofiber membrane, characterized in that, The MOFs-functionalized nanofiber membrane is prepared by the preparation method of any one of claims 5-7.

9. A wearable sweat-sensing vitamin C patch, characterized in that, The sensing patch includes a bottom adhesive layer, an intermediate sensing layer, and a top encapsulation layer arranged sequentially. The intermediate sensing layer includes the MOFs functionalized nanofiber membrane as described in claim 8, and a colorimetric card whose color scale corresponds to the colorimetric response under different concentrations of ascorbic acid, for use in assisting quantitative analysis.

10. The wearable sweat vitamin C sensing patch according to claim 9, characterized in that, The bottom adhesive layer uses a medical-grade substrate material and includes multiple sweat inlets to guide sweat into the intermediate sensing layer. The top encapsulation layer is provided with multiple sweat outlets corresponding to the bottom adhesive layer to promote sweat circulation and prevent internal fluid accumulation.

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