A highly sensitive flexible breathable electrode for sweat lactate detection

Abstract

The present invention provides a flexible breathable electrode composed of a graphene nanofiber membrane and polypyrrole for electrochemical monitoring of lactic acid in human sweat. The main characteristics of the electrode are enzyme-free, high sensitivity and wide linear response range. The electrode is doped with lactic acid into polypyrrole at a specific potential to generate electron transfer, and then transmitted to the detection circuit via highly conductive graphene nanofibers to form a response current to achieve continuous dynamic monitoring of lactic acid concentration. Compared with traditional enzyme electrodes, the electrode has higher stability, and its sensitivity retention rate is about 100% when stored at room temperature for more than 20 days. Compared with traditional enzyme-free electrodes, the electrode does not need to rely on alkaline media to work, and can be directly used in wearable electrochemical sensors. The skin surface test results show that the lactic acid concentration measured simultaneously by the electrode and the commercial lactate meter has a good correlation.

Description

Technical Field

[0001] The invention relates to the field of human body monitoring equipment, and in particular to a high-sensitivity flexible breathable electrode for sweat lactic acid detection. Background Art

[0002] Lactate, as a product of glycolysis and anaerobic glucose metabolism, is considered one of the key markers of hypoxia in the body. Since the lactate concentration in the blood is an important basis for preventing drug poisoning and diagnosing a variety of diseases, the development of a reliable lactate detection method is very important in clinical analysis. In addition, sports medicine also needs to monitor lactate concentration to assess the endurance limit of athletes in high-intensity activities to avoid excessive lactate accumulation in muscles that squeezes blood vessels, restricts blood flow, and causes cellular acidosis.

[0003] Traditional technologies such as high performance liquid chromatography, enzymatic colorimetry, and portable analyzers have been used for blood lactate determination, which is important in sports, military, and healthcare. However, these invasive blood sampling methods usually bring pain, inconvenience, and the risk of bacterial infection during the test.

[0004] Wearable biosensors, which enable non-invasive and continuous physiological monitoring to maintain optimal health and assess body function, have received extensive attention in recent research. In recent years, the measurement of lactate in body fluids by electrochemical devices such as smart contact lenses, electronic patches, and tattoos, thereby avoiding invasive and painful sampling processes, has opened up new horizons for personalized healthcare. Currently, electrochemical biosensors for surface lactate detection mostly use expensive lactate oxidase or lactate dehydrogenase. The inherent properties of enzyme molecules are affected by temperature, oxygen, pH, humidity, and organic reagents, resulting in high costs and poor stability of enzyme sensors.

[0005] Compared with enzyme biosensors, non-enzyme biosensors have the characteristics of low cost, good stability, and easy operation. However, most non-enzyme electrodes based on transition metal oxides and layered double hydroxides (NiO, Ni(OH)2, Co(OH)2, NiCo LDH, etc.) require an unfriendly alkaline environment to oxidize lactate. Therefore, how to design an enzyme-free high-performance lactate biosensor that can be directly used for surface testing is a problem that needs to be solved at this stage. In response to the above problems, a solution is proposed below. Summary of the invention

[0006] The purpose of the present invention is to provide a high-sensitivity flexible breathable electrode for sweat lactic acid detection, which has the advantages of good stability and can monitor the lactic acid concentration in sweat in real time.

[0007] The above technical objectives of the present invention are achieved through the following technical solutions:

[0008] A highly sensitive flexible breathable electrode for sweat lactate detection comprises a signal conversion layer and a conductive skeleton. The signal conversion layer is used to undergo a redox reaction with lactic acid to generate transfer electrons, and the conductive skeleton is used to transmit the transfer electrons to generate an electrical signal.

[0009] Preferably, the signal conversion layer is a polypyrrole signal conversion layer, and the polypyrrole signal conversion layer is made of pyrrole as a raw material.

[0010] Preferably, the manufacturing process of the polypyrrole signal conversion layer comprises the following steps:

[0011] S1: treating the graphene nanofiber membrane with plasma for 1-10 minutes, and soaking the treated graphene nanofiber membrane in a pyrrole monomer aqueous solution for 1 hour;

[0012] S2: removing excess pyrrole monomer aqueous solution, placing the graphene nanofiber membrane in a hydrochloric acid aqueous solution containing an oxidant, and keeping it at room temperature for 1 hour for polymerization;

[0013] S3: After the polymerization is completed, the graphene nanofiber membrane is washed with 0.1M hydrochloric acid and deionized water in sequence to obtain a graphene nanofiber membrane with a polypyrrole signal conversion layer attached to the surface.

[0014] Preferably, the mass fraction of the pyrrole monomer aqueous solution in S1 is 0.5-10 wt %.

[0015] Preferably, the oxidant in S2 is ferric chloride, and the mass fraction of the oxidant is 0.5-2wt%.

[0016] Preferably, the conductive skeleton is constructed of graphene nanofibers, and the specific surface area of ​​the graphene nanofibers is about 500-1000m 2 g -1 .

[0017] The beneficial effects of the present invention are as follows: first, the present solution does not rely on alkaline medium to work, and overcomes the defect that the traditional enzyme-free electrode needs to be in alkaline medium to oxidize lactic acid. The electrode can be directly used for electrochemical detection of lactic acid concentration in human body fluids including sweat, tears, saliva, tissue fluid and blood, and does not respond to interfering substances such as glucose, fructose, urea, chloride ions, sodium ions and potassium ions.

[0018] Secondly, it has high electrochemical stability. The electrode overcomes the problem of easy inactivation and difficult preservation of traditional enzyme electrodes. Experimental results show that long-term storage for more than 20 days at room temperature will not lead to significant degradation of electrochemical performance. Then, it has high sensitivity. The graphene nanofiber membrane gives polypyrrole abundant electrochemical active sites, ensuring that lactic acid is fully doped with polypyrrole to produce a large number of transferred electrons. At the same time, the binder-free highly conductive graphene nanofibers can effectively collect and accelerate transferred electrons to quickly generate a response current. The electrode has an electrochemical response sensitivity to lactic acid greater than 50μA mM under mild conditions close to the pH value of human body fluids (5-7). -1 cm -2 , which is better than the sensitivity of most lactase electrodes in the same concentration range. Finally, the linear response range is large. The electrode can produce a linear response to lactate in the concentration range of 1-50mM. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a diagram of the electrospinning solution of Example 1.

[0020] Figure 2 This is the SEM image of the graphene nanofiber membrane of Example 1.

[0021] Figure 3 This is the SEM image of the graphene / polypyrrole nanofiber membrane of Example 1.

[0022] Figure 4 This is the It response curve of Example 1.

[0023] Figure 5 Schematic diagram of the working mechanism of the lactic acid electrochemical sensor electrode of Example 1.

[0024] Figure 6 This is the electrode selectivity test result of Example 2.

[0025] Figure 7 The long-term placement stability test results of the electrode in Example 3 are shown.

[0026] Figure 8 This is a schematic diagram of the structure of the real-time sweat lactate analysis patch of Example 5 and a diagram of its actual application scenario. DETAILED DESCRIPTION

[0027] The present invention is specifically described below through examples. The examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Those skilled in the art may make some non-essential changes and adjustments based on the contents of the above invention, which all fall within the scope of protection of the present invention.

[0028] Embodiment 1:

[0029] (1) Dissolve 0.5 g of sodium polyacrylate in 25 mL of deionized water to form a concentration of 20 mg mL -1 of a clear solution and then mixed with 25 mL of a 20 mg mL -1 The graphene oxide aqueous solution and Triton X-100 were uniformly mixed in a ratio of 1:1:0.05. After removing possible impurities and performing degassing treatment, the graphene oxide / sodium polyacrylate / Triton X-100 spinning solution was obtained. The solution was a dark brown viscous liquid (see Figure 1 ).

[0030] (2) Electrospinning was performed using graphene oxide / sodium polyacrylate / Triton X-100 spinning solution in an electric field of 30 kV, with a spinning solution discharge rate of 0.15 mL min -1 To prevent the fiber from collapsing due to water absorption, the humidity and temperature in the spinning machine were set to 10% and 60°C, respectively. After spinning, the collected graphene oxide / sodium polyacrylate nanofiber membrane was reduced in hydroiodic acid vapor at 95°C for 12 h, and then heated in an argon atmosphere at 10°C min -1 The graphene nanofiber membrane was obtained by heating to 3000℃ at a rate of 1000℃ and annealing. Figure 2 ).

[0031] (3) The graphene nanofiber membrane was treated with plasma for 2 minutes and then immersed in an aqueous solution containing 2 wt% pyrrole monomer. After 1 hour, the excess pyrrole solution was removed and transferred to a hydrochloric acid (1 M) aqueous solution containing 1 wt% ferric chloride and kept at room temperature for 1 hour. After the polymerization was completed, it was washed with 0.1 M hydrochloric acid and deionized water respectively, and dried in an oven at 60°C to obtain a graphene / polypyrrole nanofiber membrane (see Figure 3 ).

[0032] The lactate sensing electrode obtained through the above steps has an electrochemical response sensitivity of 58.9 μA mM to lactate in PBS buffer with a pH value of 7. -1 cm -2 , corresponding It response curve and linear response interval. The graphene / polypyrrole nanofiber membrane produced a fast step-like response current to lactic acid, and it had a good linear relationship with the lactic acid concentration (see Figure 4 ).

[0033] like Figure 5 As shown, the response mechanism of the electrode to lactic acid is achieved by doping lactic acid into polypyrrole at a specific potential to produce electron transfer, which is then conducted to the detection circuit via highly conductive graphene nanofibers to form a response current to monitor the lactic acid concentration.

[0034] Embodiment 2:

[0035] (1) Dissolve 0.5 g of sodium polyacrylate in 50 mL of deionized water to form a concentration of 10 mg mL -1 of a clear solution and then mixed with 50 mL of a 10 mg mL -1 The graphene oxide aqueous solution and Triton X-100 are uniformly mixed in a ratio of 1:1:0.05. After removing possible impurities and performing degassing treatment, a graphene oxide / sodium polyacrylate / Triton X-100 spinning solution is obtained.

[0036] (2) Electrospinning was performed using graphene oxide / sodium polyacrylate / Triton X-100 spinning solution in an electric field of 30 kV, with a spinning solution discharge rate of 0.15 mL min -1 To prevent the fiber from collapsing due to water absorption, the humidity and temperature in the spinning machine were set to 10% and 60°C, respectively. After spinning, the collected graphene oxide / sodium polyacrylate nanofiber membrane was reduced in hydroiodic acid vapor at 95°C for 12 hours, and then heated to 3000°C at a rate of 10°C min-1 in an argon atmosphere to obtain a graphene nanofiber membrane after annealing.

[0037] (3) The graphene nanofiber membrane was treated with plasma for 2 minutes and then immersed in an aqueous solution containing 2 wt% pyrrole monomer. After 1 hour, the excess pyrrole solution was removed and transferred to a hydrochloric acid (1 M) aqueous solution containing 1 wt% ferric chloride and kept at room temperature for 1 hour. After the polymerization was completed, it was washed with 0.1 M hydrochloric acid and deionized water respectively, and dried in an oven at 60°C to obtain a graphene / polypyrrole nanofiber membrane.

[0038] The lactate sensing electrode obtained through the above steps has an electrochemical response sensitivity of 53.58 μA mM to lactate in PBS buffer with a pH value of 5. -1 cm -2 .

[0039] like Figure 6 As shown in the figure, the selectivity of the electrode was tested, proving that it has a selective response to lactic acid compared to common interfering substances in sweat, such as glucose, fructose, urea, sodium chloride and potassium chloride. Among them, LA is lactic acid, Glu is glucose, Fru is fructose, and Urea is urea.

[0040] Embodiment 3:

[0041] (1) Dissolve 0.5 g of sodium polyacrylate in 25 mL of deionized water to form a concentration of 20 mg mL -1 of a clear solution and then mixed with 25 mL of a 20 mg mL -1The graphene oxide aqueous solution and Triton X-100 are uniformly mixed in a ratio of 1:1:0.05. After removing possible impurities and performing degassing treatment, a graphene oxide / sodium polyacrylate / Triton X-100 spinning solution is obtained.

[0042] (2) Electrospinning was performed using graphene oxide / sodium polyacrylate / Triton X-100 spinning solution in an electric field of 30 kV, with a spinning solution discharge rate of 0.15 mL min -1 The humidity and temperature in the spinning machine were set to 10% and 60°C, respectively. After spinning, the collected graphene oxide / sodium polyacrylate nanofiber membrane was reduced in hydroiodic acid vapor at 95°C for 12 hours, and then heated to 3000°C at a rate of 10°C min-1 in an argon atmosphere to obtain a graphene nanofiber membrane after annealing.

[0043] (3) The graphene nanofiber membrane was treated with plasma for 2 minutes and then immersed in an aqueous solution containing 5 wt% pyrrole monomer. After 1 hour, the excess pyrrole solution was removed and transferred to a hydrochloric acid (1 M) aqueous solution containing 1 wt% ferric chloride and kept at room temperature for 1 hour. After the polymerization was completed, it was washed with 0.1 M hydrochloric acid and deionized water respectively, and dried in an oven at 60°C to obtain a graphene / polypyrrole nanofiber membrane.

[0044] The lactate sensing electrode obtained through the above steps has an electrochemical response sensitivity of 59.28 μA mM to lactate in PBS buffer with a pH value of 6. -1 cm -2 .

[0045] like Figure 7 As shown, the long-term stability of the electrode was tested, proving that its electrochemical response sensitivity did not significantly decay after being placed at room temperature for 21 days.

[0046] Embodiment 4:

[0047] (1) Dissolve 0.5 g of sodium polyacrylate in 25 mL of deionized water to form a concentration of 20 mg mL -1 of a clear solution and then mixed with 25 mL of a 20 mg mL -1 The graphene oxide aqueous solution and Triton X-100 are uniformly mixed in a ratio of 1:1:0.05. After removing possible impurities and performing degassing treatment, a graphene oxide / sodium polyacrylate / Triton X-100 spinning solution is obtained.

[0048] (2) Electrospinning was performed using graphene oxide / sodium polyacrylate / Triton X-100 spinning solution in an electric field of 30 kV, with a spinning solution discharge rate of 0.15 mL min-1 The humidity and temperature in the spinning machine were set to 10% and 60°C, respectively. After spinning, the collected graphene oxide / sodium polyacrylate nanofiber membrane was reduced in hydroiodic acid vapor at 95°C for 12 h, and then heated in an argon atmosphere at 10°C min -1 The graphene nanofiber membrane was obtained by heating to 3000°C at a rate of 1.5 ℃ and annealing.

[0049] (3) The graphene nanofiber membrane was treated with plasma for 5 minutes and then immersed in an aqueous solution containing 5 wt% pyrrole monomer. After 1 hour, the excess pyrrole solution was removed and transferred to a hydrochloric acid (1 M) aqueous solution containing 2 wt% ferric chloride and kept at room temperature for 1 hour. After the polymerization was completed, it was washed with 0.1 M hydrochloric acid and deionized water respectively, and dried in an oven at 60°C to obtain a graphene / polypyrrole nanofiber membrane.

[0050] The lactate sensing electrode obtained through the above steps has an electrochemical response sensitivity of 51.76 μA mM to lactate in PBS buffer with a pH value of 5.5. -1 cm -2 .

[0051] Embodiment 5:

[0052] (1) Dissolve 0.5 g of sodium polyacrylate in 25 mL of deionized water to form a concentration of 20 mg mL -1 of a clear solution and then mixed with 25 mL of a 20 mg mL -1 The graphene oxide aqueous solution and Triton X-100 are uniformly mixed in a ratio of 1:1:0.05. After removing possible impurities and performing degassing treatment, a graphene oxide / sodium polyacrylate / Triton X-100 spinning solution is obtained.

[0053] (2) Electrospinning was performed using graphene oxide / sodium polyacrylate / Triton X-100 spinning solution in an electric field of 30 kV, with a spinning solution discharge rate of 0.15 mL min -1 To prevent the fiber from collapsing due to water absorption, the humidity and temperature in the spinning machine were set to 10% and 60°C, respectively. After spinning, the collected graphene oxide / sodium polyacrylate nanofiber membrane was reduced in hydroiodic acid vapor at 95°C for 12 h, and then heated in an argon atmosphere at 10°C min -1 The graphene nanofiber membrane was obtained by heating to 3000°C at a rate of 1.5 ℃ and annealing.

[0054] (3) The graphene nanofiber membrane was treated with plasma for 5 minutes and then immersed in an aqueous solution containing 10 wt% pyrrole monomer. After 1 hour, the excess pyrrole solution was removed and transferred to a hydrochloric acid (1 M) aqueous solution containing 2 wt% ferric chloride and kept at room temperature for 1 hour. After the polymerization was completed, it was washed with 0.1 M hydrochloric acid and deionized water respectively, and dried in an oven at 60°C to obtain a graphene / polypyrrole nanofiber membrane.

[0055] The lactate sensing electrode obtained through the above steps has an electrochemical response sensitivity of 60.52 μA mM to lactate in PBS buffer with a pH value of 7. -1 cm -2 .

[0056] like Figure 8 As shown, the above electrodes are integrated with a signal collection and transmission circuit containing a three-electrode test system to be used as a wireless, real-time sweat analysis patch. The sweat in the sensing area is continuously updated through a specific channel with a sweat-absorbing paper attached to the end. The integrated microfluidic channel and sensor patch can be attached to the arm of a volunteer for real-time analysis of sweat lactate, and the results have a good correlation with the lactate concentration measured by a commercial lactate tester.

[0057] In summary, this solution provides a lactic acid sensing electrode using polypyrrole as a signal conversion layer and graphene nanofibers as a conductive skeleton. The conductive skeleton of the lactic acid sensing electrode can also be made of a composite of graphene nanofiber membrane and other conductive materials.

[0058] The lactate sensing electrode can realize electrochemical detection of lactate without using lactate oxidase or lactate dehydrogenase, and does not need to rely on alkaline medium for electrochemical detection. Compared with common interfering substances in sweat such as glucose, fructose, urea, sodium chloride and potassium chloride, the electrochemical signal is selective for lactate.

[0059] The electrochemical response sensitivity of the lactate sensing electrode to lactate in the sweat pH range is greater than 50 μA mM -1 cm -2 , and the linear response range to lactate in the sweat pH range is 1-50mM.

[0060] The lactic acid sensing electrode has good stability, flexibility and air permeability, is comfortable to use, and will not cause a significant decrease in electrochemical performance when stored for a long time in an environment not exceeding 150°C. It is easy to store and not easily damaged.

[0061] The specific embodiments described above further illustrate the technical problems, technical solutions and beneficial effects solved by the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A highly sensitive flexible breathable electrode for sweat lactate detection, characterized in that: It includes a signal conversion layer and a conductive skeleton, wherein the signal conversion layer is used to undergo an oxidation-reduction reaction with lactic acid to generate transfer electrons, and the conductive skeleton is used to transmit the transfer electrons to generate electrical signals; The signal conversion layer is a polypyrrole signal conversion layer, and the polypyrrole signal conversion layer is made of pyrrole as a raw material; The manufacturing process of the polypyrrole signal conversion layer comprises the following steps: S1: treating the graphene nanofiber membrane with plasma for 1-10 minutes, and soaking the treated graphene nanofiber membrane in a pyrrole monomer aqueous solution for 1 hour; S2: removing excess pyrrole monomer aqueous solution, placing the graphene nanofiber membrane in a hydrochloric acid aqueous solution containing an oxidant, and keeping it at room temperature for 1 hour for polymerization; S3: After the polymerization is completed, the graphene nanofiber membrane is washed with 0.1M hydrochloric acid and deionized water in sequence to obtain a graphene nanofiber membrane with a polypyrrole signal conversion layer attached to the surface.

2. A highly sensitive flexible breathable electrode for sweat lactate detection according to claim 1, characterized in that: The mass fraction of the pyrrole monomer aqueous solution in S1 is 0.5-10 wt %.

3. A highly sensitive flexible breathable electrode for sweat lactate detection according to claim 1, characterized in that: The oxidant described in S2 is ferric chloride, and the mass fraction of the oxidant is 0.5-2 wt%.

4. A highly sensitive flexible breathable electrode for sweat lactate detection according to claim 1, characterized in that: The conductive skeleton is constructed of graphene nanofibers, and the specific surface area of ​​the graphene nanofibers is 500-1000 m 2 g -1 .

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