Self-powered sweat uric acid sensor and method based on air cell

Abstract

The application relates to a self-powered sweat uric acid sensor based on an air cell and a method, which comprises a negative metal electrode, a uric acid oxidase, a positive electrode capable of adsorbing oxygen in air, a flexible hydrophilic layer and a uric acid concentration indicator. Under normal environmental humidity, oxygen in the positive electrode of the cell is reduced, and oxidation reaction occurs in the negative electrode of the cell; under high humidity, ion conductive channels are formed, thus forming a complete loop, so that the output voltage can be measured by a voltmeter. After adding sweat, uric acid is oxidized under the action of the uric acid oxidase in the positive electrode and oxygen. Since oxygen is consumed in the oxidation process of uric acid, the oxygen content in the positive electrode of the air cell is reduced, and the output voltage of the cell is reduced, so the change trend of the uric acid concentration can be calculated according to the size of the output open circuit voltage. The uric acid sensor of the application is a self-powered sensor, does not need an external power supply, actively reflects the uric acid concentration information to an output electric signal through the air cell, and thus realizes real-time monitoring of the uric acid concentration.

Description

Technical Field

[0001] This invention belongs to the fields of sensor technology, self-powered technology, and biomarker detection, specifically relating to a self-powered sweat uric acid sensor based on an air battery and its working method and preparation method. Background Technology

[0002] Uric acid (UA), or 2,6,8-trioxopurine, is the final product of purine metabolism. The level of UA in body fluids (such as serum and urine) is a major characteristic of various diseases. When uric acid levels in the body are abnormally high, it can lead to various diseases, such as hyperuricemia and gout. Hyperuricemia is the pathophysiological basis of gout. Gouty arthritis often occurs at night, with a sudden onset, progressively increasing pain that peaks in about 12 hours, and symptoms usually subside spontaneously within several days or two weeks. In addition to joint damage, long-term hyperuricemia can also cause kidney disease and cardiovascular damage. Therefore, there is an urgent need for real-time and accurate monitoring of individual uric acid levels.

[0003] Since Gallban developed the phosphotungstic acid reduction method in 1894, numerous methods for uric acid detection have emerged. Existing methods for uric acid detection include chemiluminescence, fluorescence, spectrophotometry, HPLC-MS / ID-MS, ion chromatography, capillary electrophoresis / amperometrics, capillary electrophoresis with chemiluminescence detection, colorimetry, enzyme assay kits, and electrochemical methods. Among these, electrochemical methods for uric acid detection offer advantages such as rapid detection, high sensitivity, simple operation, and low cost, making them the most commonly used method. The principle of electrochemical uric acid detection is that uric acid undergoes an oxidation reaction catalyzed by uricase or uricase-like enzymes. During this redox reaction, electrons are transferred, and the change in current or voltage signal generated by this electron transfer is used to detect the uric acid concentration. Uric acid oxidase-based sensors exhibit excellent specificity, making them highly advantageous for uric acid detection. However, due to the high cost of enzymes and their susceptibility to inactivation during immobilization, much research currently focuses on constructing highly selective enzyme-like materials. In recent years, advancements in nanomaterials have significantly propelled the development of biosensors. Materials at the nanoscale exhibit unique properties that can enhance sensor performance. For example, nanomaterials possess high catalytic activity; combining them with the specificity of biomolecules (antibodies, neurotransmitters, etc.) can yield highly selective biosensors. Furthermore, the large specific surface area of ​​nanomaterials also contributes to improved sensor sensitivity.

[0004] To achieve real-time monitoring and facilitate convenient and quick use, the development of miniaturized, integrated, and self-powered sensors is essential. Traditional power supply methods for sensors limit their usability. With societal development and technological advancements, it has become possible to directly obtain energy from the human body and the surrounding environment (including various types of environmental and bioenergy, such as biomechanical energy, biochemical energy, thermal and solar energy, motion, bending, strain, and molecular concentration). Energy directly obtained from the human body and the surrounding environment can be converted into the energy required by the sensor, allowing it to operate sustainably without external power. Therefore, developing a self-powered uric acid biosensor is of great practical significance for real-time, non-invasive monitoring of human physiological health indicators. Such self-powered sensing systems are also strong candidates for wearable electronics and the Internet of Things (IoT). Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a self-powered sweat uric acid sensor based on an air battery, addressing the problems existing in the prior art.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0007] A self-powered sweat uric acid sensor based on an air battery includes a positive electrode 3 at the bottom that can adsorb oxygen from the air, a flexible hydrophilic layer 4 attached to the positive electrode 3, a uricosuric enzyme 2 coated on the flexible hydrophilic layer 4, and a negative metal electrode 1 above the uricosuric enzyme 2. The positive electrode 3, the flexible hydrophilic layer 4, the uricosuric enzyme 2, and the negative metal electrode 1 are in close contact in sequence, and a uric acid concentration indicator 5 is connected between the negative metal electrode 1 and the positive electrode 3. The negative metal electrode 1, the positive electrode 3, and the flexible hydrophilic layer 4 constitute an air battery. Because the reaction at the positive electrode involves oxygen from the air, it is called an air battery.

[0008] The negative metal electrode 1 and the positive electrode 3 of the air battery generate electrical energy through a chemical reaction, providing power to the sensor to achieve self-driven sweat monitoring. The uricosuric enzyme 2 in the positive electrode 3 reacts with oxygen to catalyze the oxidation of uric acid, consuming the oxygen adsorbed by the positive electrode, resulting in a decrease in oxygen in the positive electrode 3. As a result, the amount of oxygen participating in the battery chemical reaction decreases, thus reducing the output voltage. The trend of uric acid concentration change can be calculated from the magnitude of the output voltage; the smaller the output voltage, the greater the uric acid concentration.

[0009] As a preferred embodiment, the negative metal electrode 1 is selected from one of the following metals: iron, zinc, magnesium, aluminum, lithium, sodium, and potassium.

[0010] As a preferred embodiment, uricosuric oxidase 2 is a nanomaterial capable of catalyzing the oxidation of uric acid, selected from a composite of one or more of the following: metal oxides TiO2, Fe2O3, WO3, ZnO, Cu2O, SnO2, metal sulfides CdS, ZnS, MoS2, or two-dimensional material MXene.

[0011] As a preferred embodiment, the positive electrode 3, which can adsorb oxygen from the air, is a conductive material with lower reactivity than the negative electrode metal electrode.

[0012] Alternatively, it can be selected from porous activated carbon or graphite paper.

[0013] As a preferred embodiment, the flexible hydrophilic layer 4 is hydrophilic to adsorb the test liquid for detection, and is selected from a composite or composition of one or more materials such as aqueous MXene, water-absorbing resin, and hydrogel.

[0014] As a preferred embodiment, the uric acid concentration indicator 5 is made by modifying a voltmeter or an LED array.

[0015] The second objective of this invention is to provide a method for operating the sensor: the positive and negative electrodes of the battery generate electrical energy through a chemical reaction, providing energy to the sensor to achieve self-driven sweat monitoring; the uricosuric enzyme 2 in the positive electrode 3 reacts with oxygen to catalyze the oxidation of uric acid, consuming the oxygen adsorbed by the positive electrode, resulting in a reduction of oxygen in the positive electrode 3. As a result, the amount of oxygen participating in the battery chemical reaction decreases, thus reducing the output voltage. The trend of uric acid concentration change can be calculated from the magnitude of the output voltage; the smaller the output voltage, the greater the uric acid concentration.

[0016] A third objective of this invention is to provide a method for preparing the aforementioned self-powered sweat uric acid sensor based on an air battery, comprising the following steps;

[0017] S1: The negative electrode metal electrode 1 of the air battery is prepared by vapor deposition or electrochemical deposition.

[0018] S2: Use a conductive material with weaker reactivity than the negative electrode metal electrode as the positive electrode 3;

[0019] S3: Attach the flexible hydrophilic layer 4 to the surface of the positive electrode 3;

[0020] S4: Prepare a uricosuric acid oxidase dispersion. Weigh 2 mg of uricosuric acid oxidase, 10 μL of naphthol solution, and 1 mL of ethanol and deionized water in a volume ratio of 1:1. Disperse the uricosuric acid oxidase dispersion by ultrasonication. Then, use the drop-coating method to coat it onto the surface of the flexible hydrophilic layer 4. After drying at room temperature, a self-powered uric acid biosensor based on an air battery is obtained.

[0021] S5: Connect the negative metal electrode 1 and the positive electrode 3 to the uric acid concentration indicator 5 using wires.

[0022] As a preferred embodiment, the method for preparing the flexible hydrophilic layer 4 includes the following steps;

[0023] S01: Weigh 1.4-2.8g of acrylamide AAM into a 25mL beaker, add 8.6-17.2mL of deionized water and stir well;

[0024] SO2: Weigh 1-2 mg of N,N-methylenebisacrylamide (MBAA), 1-2 mg of ammonium persulfate (APS), and 2.9-5.8 g of LiCl into a beaker and stir at room temperature for 20-30 min to obtain the precursor solution;

[0025] S03: Add 5-10 μL of tetramethyldiethylamine (TEMED) to the precursor solution, mix well, and pour into a mold;

[0026] S04: Irradiate with ultraviolet light at 60-70℃ for 30-40 minutes to obtain the flexible hydrophilic layer 4 of the flexible polyacrylamide hydrogel.

[0027] As a preferred method, the preparation of uricase CdS includes the following steps:

[0028] S001: Add 30-60 mL of ethanol and deionized water in a 1:1 volume ratio to a 100 mL beaker and stir continuously with a magnetic force at room temperature;

[0029] S002: Add 1-2 mmol of Cd(NO3)2·4H2O and 1-2 mmol of CH3CSNH2 to the mixed solution of ethanol and deionized water and stir for 30-40 min until the solution is homogeneous;

[0030] S003: Transfer the solution into a 100mL Teflon-lined stainless steel autoclave and hydrothermally react at 120-200℃ for 12-20h. After the reaction is complete, cool to room temperature.

[0031] S004: Collect the product after centrifugation in a high-speed centrifuge at a speed of 4000-5000 rpm for 1-2 min, and wash it 5-10 times with a mixture of deionized water and ethanol.

[0032] S005: Dry in a constant temperature drying oven at 55-65℃ for 2-6 hours, and then grind to obtain the product urate oxidase CdS.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] This invention provides a non-invasive detection method that avoids the inconvenience caused by pollution, irritation, or other non-invasive biological fluids (such as saliva, tears, and urine).

[0035] The uric acid sensor of the present invention is a self-powered sensor that does not require an external power source. Compared with traditional sensors that require an external power source, the present invention uses an air battery to spontaneously and actively reflect uric acid concentration information to the output electrical signal, converting chemical energy into electrical energy to power the sensor, thereby realizing real-time monitoring of uric acid concentration.

[0036] Compared to a conventional primary battery, the open-circuit voltage of the air battery sensor of this invention is approximately 0V in a completely dry environment, which enables it to have a longer shelf life and makes long-term storage possible. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the structure of a self-powered sweat uric acid sensor based on an air battery according to Embodiment 1 of the present invention;

[0038] Figure 2 This is a schematic diagram illustrating the principle of a self-powered sweat uric acid sensor based on an air battery, according to Embodiment 1 of the present invention.

[0039] Figure 3 This is a schematic diagram illustrating an application example of a self-powered sweat uric acid sensor based on an air battery, according to Embodiment 1 of the present invention.

[0040] Wherein, a indicates that the uric acid concentration indicator has no deflection; b indicates that the uric acid concentration indicator has the largest deflection angle when the liquid absorbed by the sensor does not contain uric acid; c indicates that when the human body sweats and the flexible hydrophilic layer of the sensor absorbs the sweat, the uric acid concentration can be accurately determined based on the degree (deflection angle) of the uric acid concentration indicator.

[0041] The attached diagram lists the components represented by each number as follows:

[0042] 1 is the negative metal electrode; 2 is a uricase-like enzyme; 3 is the positive electrode; 4 is a flexible hydrophilic layer; 5 is a uric acid concentration indicator. Detailed Implementation

[0043] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0044] Example 1

[0045] like Figure 1As shown, this embodiment of the invention provides a self-powered sweat uric acid sensor based on an air battery. The sensor includes a positive electrode 3 at the bottom that can adsorb oxygen from the air, a flexible hydrophilic layer 4 attached to the positive electrode 3, a uricosuric enzyme 2 coated on the flexible hydrophilic layer 4, and a negative metal electrode 1 above the uricosuric enzyme 2. The positive electrode 3, the flexible hydrophilic layer 4, the uricosuric enzyme 2, and the negative metal electrode 1 are in close contact in sequence. A uric acid concentration indicator 5 is connected between the negative metal electrode 1 and the positive electrode 3. The negative metal electrode 1, the positive electrode 3, and the flexible hydrophilic layer 4 constitute an air battery. The reaction that occurs at the positive electrode involves oxygen from the air, hence the name air battery.

[0046] The negative metal electrode 1 and the positive electrode 3 of the air battery generate electrical energy through a chemical reaction, providing power to the sensor to achieve self-driven sweat monitoring. The uricosuric enzyme 2 in the positive electrode 3 reacts with oxygen to catalyze the oxidation of uric acid, consuming the oxygen adsorbed by the positive electrode, resulting in a decrease in oxygen in the positive electrode 3. As a result, the amount of oxygen participating in the battery chemical reaction decreases, thus reducing the output voltage. The trend of uric acid concentration change can be calculated from the magnitude of the output voltage; the smaller the output voltage, the greater the uric acid concentration.

[0047] The negative metal electrode 1 is selected from one of the following metals: iron, zinc, magnesium, aluminum, lithium, sodium, and potassium.

[0048] Uric acid oxidase 2 is a nanomaterial that catalyzes the oxidation of uric acid, and is a composite of one or more of the following materials: metal oxides TiO2, Fe2O3, WO3, ZnO, Cu2O, SnO2, metal sulfides CdS, ZnS, MoS2, or two-dimensional material MXene.

[0049] The positive electrode 3, which can adsorb oxygen from the air, is a conductive material with weaker activity than the negative electrode metal; or it can be selected from porous activated carbon or graphite paper.

[0050] The flexible hydrophilic layer 4 is hydrophilic to adsorb the test liquid for detection, and is selected from a composite or composition of one or more materials such as aqueous MXene, water-absorbing resin, and hydrogel.

[0051] The uric acid concentration indicator 5 is made by modifying a voltmeter or an LED array.

[0052] The working method of this embodiment is as follows: After sweat is added, the flexible hydrophilic layer absorbs the sample, placing the sensor in a high-humidity environment. The positive and negative electrodes of the battery generate electrical energy through a chemical reaction, providing energy for the sensor to achieve self-driven sweat monitoring. The uricosuric enzyme 2 in the positive electrode 3 reacts with oxygen to catalyze the oxidation of uric acid, consuming the oxygen adsorbed by the positive electrode, resulting in a decrease in oxygen in the positive electrode 3. As a result, the oxygen participating in the battery chemical reaction decreases, thus reducing the output voltage. The trend of uric acid concentration change can be calculated from the output voltage. The smaller the output voltage, the greater the uric acid concentration.

[0053] The self-driving principle and uric acid detection principle of this sensor are as follows: Figure 2 As shown, the negative metal electrode of the battery undergoes a redox reaction with oxygen at the positive electrode, converting chemical energy into electrical energy. In a dry environment, no ionic conductivity pathway is formed, so the battery's open-circuit voltage is 0. When the hydrophilic layer absorbs the sample, the battery forms an ionic conductivity pathway, connecting the two ends of the electrode to the external circuit, forming a complete loop. At this point, the battery's output voltage can be measured. In this invention, metallic Zn is used as the negative metal electrode, and graphite paper is used as the positive electrode. Zn reacts with O2 in a redox reaction, converting chemical energy into electrical energy to power the sensor, thus achieving self-driven sweat monitoring.

[0054] When the sensor absorbs sweat, its CdS layer selectively catalyzes the oxidation of uric acid, causing the uric acid to lose two electrons and gain two H atoms. + Meanwhile, the oxygen at the positive electrode is consumed in this process, which reduces the amount of oxygen that reacts with Zn and decreases the output voltage of the battery. Therefore, the uric acid concentration can be calculated from the output voltage signal, thereby enabling the monitoring of uric acid.

[0055] In the above embodiments, the two electrodes are respectively connected to the two ends of a voltmeter or an LED array, and the uric acid concentration is evaluated by the meter reading (deflection angle) or the number of LEDs lit in the LED array.

[0056] like Figure 3 As shown, a voltmeter is used as a uric acid concentration indicator. The self-powered sweat uric acid sensor based on an air battery, prepared according to an embodiment of the present invention, is used for uric acid concentration detection. In a dry environment, such as... Figure 3 The uric acid concentration indicator shown in Figure a has no deflection; when the liquid absorbed by the sensor does not contain uric acid, as... Figure 3 As shown in Figure b, the uric acid concentration indicator deflects at its maximum angle; when the human body sweats, the sensor's flexible hydrophilic layer absorbs the sweat, as... Figure 3 The uric acid concentration can be accurately determined based on the reading (deflection angle) of the uric acid concentration indicator.

[0057] Example 2

[0058] This embodiment provides a method for preparing a self-powered sweat uric acid sensor based on an air battery, including the following steps:

[0059] S1: The negative electrode metal electrode 1 of the air battery is prepared by vapor deposition or electrochemical deposition.

[0060] S2: Use a conductive material with weaker reactivity than the negative electrode metal electrode as the positive electrode 3;

[0061] S3: Attach the flexible hydrophilic layer 4 to the surface of the positive electrode 3;

[0062] S4: Prepare a uricosuric acid oxidase dispersion. Weigh 2 mg of uricosuric acid oxidase, 10 μL of naphthol solution, and 1 mL of ethanol and deionized water in a volume ratio of 1:1. Disperse the uricosuric acid oxidase dispersion by ultrasonication. Then, use the drop-coating method to coat it onto the surface of the flexible hydrophilic layer 4. After drying at room temperature, a self-powered uric acid biosensor based on an air battery is obtained.

[0063] S5: Connect the negative metal electrode 1 and the positive electrode 3 to the uric acid concentration indicator 5 using wires.

[0064] Example 3

[0065] This embodiment provides a method for preparing a flexible hydrophilic layer 4, including the following steps;

[0066] S01: Weigh 1.4-2.8g of acrylamide AAM into a 25mL beaker, add 8.6-17.2mL of deionized water and stir well;

[0067] SO2: Weigh 1-2 mg of N,N-methylenebisacrylamide (MBAA), 1-2 mg of ammonium persulfate (APS), and 2.9-5.8 g of LiCl into a beaker and stir at room temperature for 20-30 min to obtain the precursor solution;

[0068] S03: Add 5-10 μL of tetramethyldiethylamine (TEMED) to the precursor solution, mix well, and pour into a mold;

[0069] S04: Irradiate with ultraviolet light at 60-70℃ for 30-40 minutes to obtain the flexible hydrophilic layer 4 of the flexible polyacrylamide hydrogel.

[0070] Example 4

[0071] This embodiment provides a method for preparing urate oxidase CdS, including the following steps:

[0072] S001: Add 30-60 mL of ethanol and deionized water in a 1:1 volume ratio to a 100 mL beaker and stir continuously with a magnetic force at room temperature;

[0073] S002: Add 1-2 mmol of Cd(NO3)2·4H2O and 1-2 mmol of CH3CSNH2 to the mixed solution of ethanol and deionized water and stir for 30-40 min until the solution is homogeneous;

[0074] S003: Transfer the solution into a 100mL Teflon-lined stainless steel autoclave and hydrothermally react at 120-200℃ for 12-20h. After the reaction is complete, cool to room temperature.

[0075] S004: Collect the product after centrifugation in a high-speed centrifuge at a speed of 4000-5000 rpm for 1-2 min, and wash it 5-10 times with a mixture of deionized water and ethanol.

[0076] S005: Dry in a constant temperature drying oven at 55-65℃ for 2-6 hours, and then grind to obtain the product urate oxidase CdS.

[0077] Example 5

[0078] This embodiment provides a method for preparing a self-powered sweat uric acid sensor based on an air battery, including the following steps:

[0079] S1: The negative electrode metal electrode 1 of the air battery is prepared by vapor deposition or electrochemical deposition.

[0080] S2: Use a conductive material with weaker reactivity than the negative electrode metal electrode as the positive electrode 3;

[0081] S301: Weigh 1.4-2.8g of acrylamide AAM into a 25mL beaker, add 8.6-17.2mL of deionized water and stir well;

[0082] S302: Weigh 1-2 mg of N,N-methylenebisacrylamide (MBAA), 1-2 mg of ammonium persulfate (APS), and 2.9-5.8 g of LiCl into a beaker and stir at room temperature for 20-30 min to obtain the precursor solution;

[0083] S303: Add 5-10 μL of tetramethyldiethylamine (TEMED) to the precursor solution, mix well, and pour into a mold;

[0084] S304: At 60-70℃, irradiate with ultraviolet light for 30-40 minutes to obtain the flexible hydrophilic layer 4 of the flexible polyacrylamide hydrogel.

[0085] S305: Attach the flexible hydrophilic layer 4 to the surface of the positive electrode 3;

[0086] S4001: Add 30-60 mL of ethanol and deionized water in a 1:1 volume ratio to a 100 mL beaker and stir continuously with a magnetic force at room temperature;

[0087] S4002: Add 1-2 mmol of Cd(NO3)2·4H2O and 1-2 mmol of CH3CSNH2 to the mixed solution of ethanol and deionized water and stir for 30-40 min until the solution is homogeneous;

[0088] S4003: Transfer the solution into a 100mL Teflon-lined stainless steel autoclave and hydrothermally react at 120-200℃ for 12-20h. After the reaction is complete, cool to room temperature.

[0089] S4004: Collect the product after centrifugation in a high-speed centrifuge at a speed of 4000-5000 rpm for 1-2 min, and wash it 5-10 times with a mixture of deionized water and ethanol.

[0090] S4005: Dry in a constant temperature drying oven at 55-65℃ for 2-6 hours, and then grind to obtain the product urate oxidase CdS.

[0091] S4006: Prepare a uricosuric acid oxidase dispersion. Weigh 2 mg of uricosuric acid oxidase, 10 μL of naphthol solution, and 1 mL of ethanol and deionized water in a volume ratio of 1:1. Disperse the uricosuric acid oxidase dispersion by ultrasonication. Then, use the drop-coating method to coat it onto the surface of the flexible hydrophilic layer 4. After drying at room temperature, a self-powered uric acid biosensor based on an air battery is obtained.

[0092] S5: Connect the negative metal electrode 1 and the positive electrode 3 to the uric acid concentration indicator 5 using wires.

[0093] Example 6

[0094] This embodiment provides a method for preparing a self-powered sweat uric acid sensor based on an air battery, including the following steps:

[0095] Step 1: Add 30 mL of ethanol and deionized water in a volume ratio of 1:1 to a 100 mL beaker and stir continuously with a magnetic force at room temperature.

[0096] Step 2: Add 1 mmol Cd(NO3)2·4H2O and 1 mmol CH3CSNH2 to the ethanol and water mixture respectively and stir for 30 min until the solution is homogeneous;

[0097] Step 3: Transfer the solution into a 100mL Teflon-lined stainless steel autoclave and perform a hydrothermal reaction at 160℃ for 16 hours. After the reaction is complete, cool to room temperature.

[0098] Step 4: Collect the product after high-speed centrifugation at 5000 rpm for 1 min, and wash it 5 times with a mixture of deionized water and ethanol.

[0099] Step 5: Dry the product CdS at 60℃ for 4 hours in a constant temperature drying oven, and then grind it to obtain the product.

[0100] Step 6: Weigh 1.4g of acrylamide (AAm) into a 25mL beaker, add 8.6mL of deionized water and stir well;

[0101] Step 7: Weigh 1 mg of N,N-methylenebisacrylamide (MBAA), 1 mg of ammonium persulfate (APS), and 2.9 g of LiCl into a beaker and stir at room temperature for 30 min to obtain the precursor solution;

[0102] Step 8: Add 5 μL of tetramethyldiethylamine (TEMED) to the precursor solution, mix well, and pour into a mold;

[0103] Step 9: Irradiate with ultraviolet light at 60℃ for 30 minutes to obtain flexible polyacrylamide hydrogel;

[0104] Step 10: Electrochemically deposited Zn is used as the negative electrode metal electrode 1 in an air battery;

[0105] Step 11: Use 0.1mm thick graphite paper as the positive electrode 3 of the air battery;

[0106] Step 12: Attach the flexible hydrophilic layer 4 to the surface of the positive electrode 3;

[0107] Step 13: Prepare uricosuric acid oxidase dispersion. Weigh 2 mg of uricosuric acid oxidase, 10 μL of naphthol solution, and 1 mL of ethanol and deionized water in a 1:1 volume ratio. Disperse the uricosuric acid oxidase dispersion by ultrasonication. Then, coat it onto the surface of the hydrophilic layer using a drop-coating method. After drying at room temperature, a self-powered uric acid biosensor based on an air battery is obtained.

[0108] Step 14: Connect the negative metal electrode 1 and the positive electrode 3 to the uric acid concentration indicator 5 using wires.

[0109] The above is a detailed description of a self-powered sweat uric acid sensor based on an air battery proposed in this invention. The sensor size is 3×3cm. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the above embodiments should be included within the scope of protection of the technical solution.

[0110] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A self-powered sweat uric acid sensor based on an air battery, characterized in that, The sensor includes a positive electrode (3) at the bottom that can adsorb oxygen from the air, a flexible hydrophilic layer (4) attached to the positive electrode (3), a uricosuric oxidase (2) coated on the flexible hydrophilic layer (4), and a negative metal electrode (1) above the uricosuric oxidase (2). The positive electrode (3), the flexible hydrophilic layer (4), the uricosuric oxidase (2), and the negative metal electrode (1) are in close contact in sequence. A uric acid concentration indicator (5) is connected between the negative metal electrode (1) and the positive electrode (3). The negative metal electrode (1), the positive electrode (3), and the flexible hydrophilic layer (4) constitute an air battery. The reaction that occurs at the positive electrode is participated in by oxygen from the air, hence the name air battery. The negative metal electrode (1) and positive electrode (3) of the air battery generate electrical energy through chemical reaction, which provides energy for the sensor to achieve self-driven sweat monitoring. The uric acid oxidase (2) in the positive electrode (3) reacts with oxygen to catalyze the oxidation of uric acid, which consumes the oxygen adsorbed by the positive electrode, resulting in a reduction of oxygen in the positive electrode (3). As a result, the amount of oxygen participating in the battery chemical reaction decreases, so the output voltage decreases. The trend of uric acid concentration change can be calculated by the magnitude of the output voltage. The smaller the output voltage, the greater the uric acid concentration.

2. The self-powered sweat uric acid sensor based on an air battery according to claim 1, characterized in that, The negative metal electrode (1) is selected from one of the following metals: iron, zinc, magnesium, aluminum, lithium, sodium, and potassium.

3. The self-powered sweat uric acid sensor based on an air battery according to claim 1, characterized in that, Uric acid oxidase (2) is a nanomaterial that catalyzes the oxidation of uric acid, and is a composite of one or more of the following materials: metal oxides TiO2, Fe2O3, WO3, ZnO, Cu2O, SnO2, metal sulfides CdS, ZnS, MoS2, or two-dimensional material MXene.

4. The self-powered sweat uric acid sensor based on an air battery according to claim 1, characterized in that, The positive electrode (3) that can adsorb oxygen in the air is a conductive material with weaker activity than the negative electrode metal electrode. Alternatively, it can be selected from porous activated carbon or graphite paper.

5. A self-powered sweat uric acid sensor based on an air battery according to claim 1, characterized in that, The flexible hydrophilic layer (4) is hydrophilic to adsorb the test liquid for detection, and is a composite of one or more materials selected from aqueous MXene, water-absorbing resin, and hydrogel.

6. A self-powered sweat uric acid sensor based on an air battery according to claim 1, characterized in that, The uric acid concentration indicator (5) is made by modifying a voltmeter or an LED array.

7. The method of operating the sensor according to any one of claims 1 to 6, characterized in that: The positive and negative electrodes of the battery generate electrical energy through chemical reactions, which provides energy for the sensor to achieve self-driven sweat monitoring. The uric acid oxidase (2) in the positive electrode (3) reacts with oxygen to catalyze the oxidation of uric acid, which consumes the oxygen adsorbed by the positive electrode, resulting in a reduction of oxygen in the positive electrode (3). As a result, the amount of oxygen participating in the chemical reaction of the battery decreases, so the output voltage decreases. The trend of uric acid concentration change can be calculated by the magnitude of the output voltage. The smaller the output voltage, the greater the uric acid concentration.

8. The method for preparing a self-powered sweat uric acid sensor based on an air battery according to any one of claims 1 to 6, characterized in that, Includes the following steps; S1: The negative metal electrode of the air battery was prepared by vapor deposition or electrochemical deposition (1); S2: Use a conductive material with weaker reactivity than the negative electrode metal electrode as the positive electrode (3); S3: Attach the flexible hydrophilic layer (4) to the surface of the positive electrode (3); S4: Prepare uricosuric acid oxidase dispersion. Weigh 2 mg uricosuric acid oxidase, 10 μL naphthol solution, and 1 mL of ethanol and deionized water in a volume ratio of 1:

1. Disperse the uricosuric acid oxidase dispersion by ultrasonication. Then, use the drop coating method to coat it on the surface of the flexible hydrophilic layer (4). After drying at room temperature, a self-powered uric acid biosensor based on an air battery is obtained. S5: Connect the negative metal electrode (1) and the positive electrode (3) to the uric acid concentration indicator (5) using wires.

9. The method for preparing a self-powered sweat uric acid sensor based on an air battery according to claim 8, characterized in that, The method for preparing the flexible hydrophilic layer (4), Includes the following steps; S01: Weigh 1.4-2.8g of acrylamide AAM into a 25mL beaker, add 8.6-17.2mL of deionized water and stir well; SO2: Weigh 1-2 mg of N,N-methylenebisacrylamide (MBAA), 1-2 mg of ammonium persulfate (APS), and 2.9-5.8 g of LiCl into a beaker and stir at room temperature for 20-30 min to obtain the precursor solution; S03: Add 5-10 μL of tetramethyldiethylamine (TEMED) to the precursor solution, mix well, and pour into a mold; S04: Irradiate with ultraviolet light at 60-70℃ for 30-40 minutes to obtain a flexible hydrophilic layer of flexible polyacrylamide hydrogel (4).

10. The method for preparing a self-powered sweat uric acid sensor based on an air battery according to claim 8, characterized in that, The preparation method of uricase CdS includes the following steps: S001: Add 30-60 mL of ethanol and deionized water in a 1:1 volume ratio to a 100 mL beaker and stir continuously with a magnetic force at room temperature; S002: Add 1-2 mmol Cd(NO3)2·4H2O and 1-2 mmol CH3CSNH2 to the mixed solution of ethanol and deionized water respectively and stir for 30-40 min until the solution is homogeneous; S003: Transfer the solution into a 100 mL Teflon-lined stainless steel autoclave and hydrothermally react at 120-200℃ for 12-20 h. After the reaction is complete, cool to room temperature. S004: Collect the product after centrifugation in a high-speed centrifuge at a speed of 4000-5000 rpm for 1-2 min, and wash it 5-10 times with a mixture of deionized water and ethanol. S005: Dry in a constant temperature drying oven at 55-65℃ for 2-6 hours, and then grind to obtain the product urate oxidase CdS.

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