WO2023087332A1 - Bismuth oxide p-n type transition potential-based photoelectrochemical flexible wearable sweat ph sensor - Google Patents

Abstract

A bismuth oxide p-n type transition potential-based photoelectrochemical flexible wearable sweat pH sensor, comprising a bismuth oxide working electrode, a reference electrode, a counter electrode, a transparent flexible substrate, and a light source. An amphoteric bismuth oxide semiconductor is used for the first time as a photoelectrode, and a specific p-n type transition potential thereof is used as a sensing signal, thus preparing a photoelectrochemical flexible wearable sweat pH sensor. The sensor may adapt to complex wearing environments, and may very well resist interference from changes in light intensity and the area of the sensing electrode covered by sweat covered; in addition, the sensor has low preparation costs, is simple and portable, easy to use, achieves the accurate and continuous monitoring of sweat pH value, and has high use value, thus solving the problem in the existing technology of inaccurate measurement.

Description

A photoelectrochemical flexible wearable sweat pH sensor based on bismuth oxide p-n transition potential Technical field:

The invention relates to the technical field of photoelectrochemical sensing, in particular to a photoelectrochemical flexible wearable sweat pH sensor based on bismuth oxide p-n type transition potential.

Background technique:

The pH value of human sweat can provide a lot of important information about health status. Various skin diseases (such as dermatitis, acne and fungal infection, etc.) will cause changes in the pH value of sweat. Provide important reference [Balaji A N, Yuan C, et al.pH Watch-Leveraging pulse oximeters in existing wearables for reusable, real-time monitoring of pH in sweat[C].The 17th Annual International Conference.2019:262-274 .].

Using flexible wearable sensors to monitor sweat pH is an effective method. Compared with traditional sensors, flexible wearable sensors are not only lighter, more beautiful, and more comfortable, but also can achieve continuous monitoring [Yu Mengke, Zhang Guojun. Flexible and wearable sensors] A review of the application of wearable sensors in sweat monitoring [J]. Medical and Health Equipment, 2020, 41(12): 90-96.].

Flexible wearable sensors based on electrochemical and photoelectrochemical principles have attracted extensive attention due to their high accuracy, high sensitivity, and fast response. At present, many flexible and wearable pH sensors based on electrochemical and photoelectrochemical methods have appeared on the market [Shi X M, Mei L P, et al. A polymer dots-based photoelectrochemical pH sensor:simplicity, high sensitivity, and broad-range pH measurement [J].Analytical chemistry,2018,90(14):8300-8303.], but they are all based on the voltage (or current) signal under constant current (or constant potential) to judge the pH value, this signal mechanism is in Poor adaptability to complex and changeable wearing environments. In real usage scenarios, the vibration caused by human body movement and power consumption may cause the light intensity of the photoelectrochemical sensor to fluctuate; when the human body sweats low, the sweat may not completely cover the sensing electrodes. In these cases, traditional sensing signal mechanisms can generate large measurement errors.

Invention content:

The purpose of the present invention is to provide a photoelectrochemical flexible _wearable sweat pH sensor based on bismuth oxide (Bi ₂ O ₃ ) pn-type transition _potential . As the sensing signal, the transition potential can adapt to the complex wearing environment, and can well resist the interference of changes in light intensity and changes in the area of the sweat-covered sensing electrode, and realize accurate and continuous monitoring of the pH value of sweat, which solves the problem of inaccurate measurement in the prior art question.

The present invention is achieved through the following technical solutions:

A photoelectrochemical flexible wearable sweat pH sensor based on bismuth oxide (Bi ₂ O ₃ ) pn-type transition potential, characterized in that it includes a bismuth oxide (Bi ₂ O ₃ ) working electrode, a reference electrode, a counter electrode, a transparent flexible Substrate and light source, the preparation of bismuth oxide (Bi ₂ O ₃ ) working electrode comprises the following steps:

(1) Deposit indium-doped tin oxide (ITO) film on a transparent and flexible mica substrate by radio frequency magnetron sputtering: use an indium-doped tin oxide (ITO) target with a purity of 99.99%, and the sputtering power is 50 -150W, substrate temperature is room temperature -350°C, argon flow rate is 10-50sccm, sputtering pressure is 0.5-3pa, deposition time is 300-3600s, substrate rotation speed is 10-30r/min;

(2) Depositing Bi metal on the ITO film obtained in step (1) by DC magnetron sputtering, using a Bi metal target with a purity of 99.99%, the sputtering power is 20-60W, and the substrate temperature is room temperature-350°C. The argon flow rate is 10-50sccm, the sputtering pressure is 0.5-3pa, the deposition time is 60-600s, and the substrate rotation speed is 10-30r/min;

(3) Heating the bismuth oxide (Bi ₂ O ₃ ) film obtained in step (2) for 30-120 min at a heating temperature of 250-350° C., and the heating tool is one of a heating table, an oven, and a tube furnace to obtain bismuth oxide (Bi ₂ O ₃ ) working electrode.

Preferably, the preparation of the bismuth oxide (Bi ₂ O ₃ ) working electrode includes the following steps:

(1) Deposit indium-doped tin oxide (ITO) film on a transparent and flexible mica substrate by radio frequency magnetron sputtering: use an indium-doped tin oxide (ITO) target with a purity of 99.99%, and the sputtering power is 100 -150W, substrate temperature is 200-350℃, argon gas flow is 10-50sccm, sputtering pressure is 1.5-2pa, deposition time is 1200-2400s, substrate rotation speed is 20-30r/min;

(2) Depositing Bi metal on the ITO film obtained in step (1) by DC magnetron sputtering, using a Bi metal target with a purity of 99.99%, the sputtering power is 40-60W, and the substrate temperature is 100-350°C. The argon flow rate is 30-50sccm, the sputtering pressure is 1-2pa, the deposition time is 100-240s, and the substrate rotation speed is 20-30r/min;

(3) Heating the bismuth oxide (Bi ₂ O ₃ ) film obtained in step (2) for 30-60 min at a heating temperature of 270-350° C., and the heating tool is one of a heating table, an oven, and a tube furnace to obtain bismuth oxide (Bi ₂ O ₃ ) working electrode.

The preparation of reference electrode comprises the following steps:

(1) Agar is added in the mixed solution of saturated KCl, the content of agar is 1wt%～5wt%, and mixed solution is heated to boiling to make agar dissolve completely;

(2) Fix Ag/AgCl on a transparent flexible substrate to obtain a flexible Ag/AgCl film, and the mixed solution obtained in step (1) is drip-coated on the surface of the flexible Ag/AgCl film, and the coating amount is 10-50 μ L/cm ² , cooled to Obtain an agar gel film comprising KCl after room temperature;

(3) On the surface of the agar gel film obtained in step (2), drop-coat Nafion solution with a content of 5 wt % in a coating amount of 5-30 μL/cm ² , and dry at room temperature to form a film to obtain a reference electrode.

Counter electrode preparation includes the following steps:

Thin films are deposited on transparent and flexible substrates by DC magnetron sputtering, using targets with a purity of 99.99%, sputtering power at 10-100W, substrate temperature at room temperature -350°C, argon gas flow at 10-50sccm, and sputtering pressure 0.5-3pa, the deposition time is 60-3600s, and the substrate rotation speed is 10-30r/min.

In the preparation of the counter electrode, the substrate is one of flexible polyester (PET), mica, and polyimide (PI). The target material is one of graphite and Pt.

Preferably, the width of the working electrode, the reference electrode and the counter electrode is 0.5-5mm, and the distance between the electrodes is 0.5-2mm.

Preferably, the light source is 0.1-1W, and the wavelength is 400-500nm.

The packaging of the photoelectrochemical flexible wearable sweat pH sensor based on bismuth oxide (Bi ₂ O ₃ ) pn-type transition potential includes the following steps:

1) Select a flexible polyester (PET) film with a thickness of 45-55mm as the transparent flexible substrate;

2) Paste the working electrode, reference electrode and counter electrode on the transparent flexible polyester (PET) film with polydimethylsiloxane (PDMS) glue;

3) Encapsulate the film obtained in step 2) with PDMS glue, exposing the detection end and the wire connection end;

4) Curing the film obtained in step (3) at 95-105° C. for 50-70 minutes to obtain the finished product.

The present invention also protects the application of the above-mentioned photoelectrochemical flexible wearable sweat pH sensor based on bismuth oxide (Bi ₂ O ₃ ) pn-type transition potential for detecting sweat pH, comprising the following steps:

(1) Using a three-electrode system, add 1-7μL/mm ² artificial sweat to the test area of the flexible wearable pH sensor, scan the dark current by cyclic voltammetry under no light conditions, and use cyclic voltammetry to obtain dark current under light conditions. An method to scan to get photocurrent;

(2) Test the artificial sweat with different pH in sequence to obtain the p-n transition potential (potential at the intersection of photocurrent and dark current) at different pH, and then fit the data and obtain a standard curve;

3) Attach the flexible wearable pH sensor to the skin. After the sweat infiltrates the test area, the dark current is scanned by cyclic voltammetry under no light conditions, and the photocurrent is obtained by cyclic voltammetry scanning under light conditions. The p-n transition potential at this time is obtained, and the pH value of the sweat at this time is obtained by comparing with the standard curve.

The beneficial effects of the present invention are:

1) In the present invention, the amphoteric bismuth oxide (Bi ₂ O ₃ ) semiconductor is used as the photoelectrode for the first time, and its unique pn-type transition potential is used as the sensing signal to prepare a photoelectrochemical flexible wearable sweat pH sensor. The sensor can adapt to the complex wearing environment, and can well resist the interference of changes in light intensity and changes in the area of the sensing electrode covered by sweat.

2) The magnetron sputtering coating method is easy to achieve low-cost mass production of bismuth oxide (Bi ₂ O ₃ ) working electrodes.

In a word, the sensor of the present invention has low preparation cost, is simple and portable, easy to use, has strong anti-interference ability, realizes accurate and continuous monitoring of sweat pH value, has high application value, and solves the problem of inaccurate measurement in the prior art.

Description of drawings:

Figure 1 is a schematic top view of the structure of the present invention.

Fig. 2 is a schematic side view of the structures of the reference electrode and the working electrode of the present invention.

3 is an X-ray diffraction pattern (XRD) of the working electrode prepared in Example 1.

Fig. 4 shows the cyclic voltammetry scanning results of the flexible wearable sweat pH sensor under different pH values of sweat.

Figure 5 is the standard curve of the wearable sweat pH sensor.

Figure 6 shows the cyclic voltammetry scanning results of the wearable sweat pH sensor under different light intensities.

Figure 7 shows the cyclic voltammetry scanning results of the wearable sweat pH sensor at different sweat coverage rates.

Detailed ways:

The following is a further description of the present invention, rather than a limitation of the present invention.

Example 1:

A photoelectrochemical flexible wearable sweat pH sensor based on Bi ₂ O ₃ pn transition potential, including Bi ₂ O ₃ working electrode, reference electrode, counter electrode, transparent flexible substrate and light source. The width of the working electrode, the reference electrode and the counter electrode is 5mm, the distance between the electrodes is 1.5mm (as shown in Figure 1), the light source is 0.2W, and the wavelength is 440nm.

Preparation steps _{of Bi2O3} working electrode:

(1) Deposit an indium-doped tin oxide (ITO) film on a transparent and flexible mica substrate by radio frequency magnetron sputtering, using an indium-doped tin oxide (ITO) target with a purity of 99.99%, and a sputtering power of 100W , the substrate temperature is 200° C., the argon flow rate is 30 sccm, the sputtering pressure is 1.5 pa, the deposition time is 2400 s, and the substrate rotation speed is 20 r/min.

(2) Deposit Bi metal on the ITO thin film obtained in step (1) by DC magnetron sputtering, using a Bi metal target with a purity of 99.99%, sputtering power of 40W, substrate temperature of 100°C, and argon flow of 30sccm, the sputtering pressure is 1.0pa, the deposition time is 240s, and the substrate rotation speed is 20r/min.

(3) The Bi ₂ O ₃ thin film obtained in step (2) was calcined on a heating platform for 60 min at a calcining temperature of 270° C. to obtain a Bi ₂ O ₃ working electrode (as shown in FIG. 2 ).

The resulting Bi ₂ O ₃ working electrode was analyzed by X-ray diffractometer (XRD) (as shown in Figure 3), and the working electrode film was made of α-Bi ₂ O ₃ (PDF#76-1730) and β-Bi2O3 (PDF# 78-1793) composition.

Preparation steps of the reference electrode:

(1) Agar is added in the mixed solution of saturated KCl (the content of agar is 1%), and the mixed solution is heated to boiling to completely dissolve the agar.

(2) Fix Ag/AgCl on a transparent flexible substrate to obtain a flexible Ag/AgCl film. The mixed solution obtained in step (1) is drop-coated on the surface of the flexible Ag/AgCl film with a coating amount of 10 μL/cm ² , and cooled to room temperature An agar gel film containing KCl was obtained.

(3) The Nafion solution with a content of 5% was drip-coated on the surface of the agar gel film obtained in step (2), and the coating amount was 5 μL/cm ² , and dried at room temperature to form a film to obtain a reference electrode (as shown in Figure 2 Show).

The preparation steps of the counter electrode:

Pt metal was deposited on flexible polyester (PET) by DC magnetron sputtering, using a Pt metal target with a purity of 99.99%, the sputtering power was 50W, the substrate temperature was room temperature, the argon flow rate was 30sccm, and the sputtering pressure was 1.0pa, the deposition time is 600s, and the substrate rotation speed is 20r/min to obtain the counter electrode.

The packaging steps of the sensor are as follows:

(1) A flexible polyester (PET) film with a thickness of 50 mm was selected as the transparent flexible substrate.

(2) Using polydimethylsiloxane (PDMS) glue to stick the working electrode, reference electrode and counter electrode on the transparent flexible polyester (PET) film.

(3) Encapsulating the thin film obtained in step (2) with PDMS glue, exposing the detection end and the wire connection end.

(4) Curing the film obtained in step (3) at 100°C for 60 minutes to obtain the finished product.

Example 2

Referring to Example 1, the difference lies in the preparation of Bi ₂ O ₃ working electrode, reference electrode and counter electrode.

Preparation steps _{of Bi2O3} working electrode:

(1) Deposit an indium-doped tin oxide (ITO) film on a transparent and flexible mica substrate by radio frequency magnetron sputtering, using an indium-doped tin oxide (ITO) target with a purity of 99.99%, and a sputtering power of 150W , the substrate temperature is 350° C., the argon flow rate is 30 sccm, the sputtering pressure is 2 pa, the deposition time is 1200 s, and the substrate rotation speed is 30 r/min.

(2) Deposit Bi metal on the ITO thin film obtained in step (1) by DC magnetron sputtering, using a Bi metal target with a purity of 99.99%, sputtering power of 60W, substrate temperature of 350°C, and argon flow of 50sccm, the sputtering pressure is 2pa, the deposition time is 100s, and the substrate rotation speed is 30r/min.

(3) Calcining the Bi ₂ O ₃ film obtained in step (2) for 30 min on a heating platform at a temperature of 350° C. to obtain a Bi ₂ O ₃ working electrode.

Preparation steps of the reference electrode:

(1) Agar is added in the mixed solution of saturated KCl (the content of agar is 5%), and the mixed solution is heated to boiling to completely dissolve the agar.

(2) Fix Ag/AgCl on a transparent flexible substrate to obtain a flexible Ag/AgCl film. The mixed solution obtained in step (1) is drop-coated on the surface of the flexible Ag/AgCl film with a coating amount of 50 μL/cm ² , and cooled to room temperature An agar gel film containing KCl was obtained.

(3) Drop-coat 5% Nafion solution on the surface of the agar gel film obtained in step (2), the coating amount is 30 μL/cm ² , and dry at room temperature to form a film to obtain a reference electrode.

The preparation steps of the counter electrode:

Pt metal was deposited on flexible polyester (PET) by DC magnetron sputtering, using a Pt metal target with a purity of 99.99%, the sputtering power was 70W, the substrate temperature was 150°C, the argon gas flow rate was 50sccm, and the sputtering pressure was is 2.0pa, the deposition time is 100s, and the substrate rotation speed is 30r/min to obtain the counter electrode.

Example 3

Referring to Example 1, the difference lies in the preparation of the counter electrode.

The preparation steps of the counter electrode:

Graphite was deposited on flexible polyester (PET) by DC magnetron sputtering, using a graphite target with a purity of 99.99%, the sputtering power was 100W, the substrate temperature was 200°C, the argon flow rate was 30sccm, and the sputtering pressure was 1.0 pa, the deposition time is 60 min, and the substrate rotation speed is 30 r/min to obtain the counter electrode.

Experimental example 1

1. Obtain the standard curve

Using a three-electrode system, add 3 μL/mm ² of artificial sweat to the test area of the flexible wearable pH sensor obtained in Example 1 above, scan the dark current by cyclic voltammetry under no light conditions, and use cyclic voltammetry under light conditions to obtain the dark current. Photocurrent was obtained by voltammetry scan. The artificial sweat with different pH was tested sequentially, and the results shown in Figure 4 were obtained. The pn-type transition potentials (potentials at the intersection of photocurrent and dark current) at different pHs were obtained, and a standard curve as shown in Figure 5 was obtained by fitting, and the fitting degree was good.

Attach the flexible wearable pH sensor to the skin. After the sweat infiltrates the test area, the dark current is scanned by cyclic voltammetry under no light conditions, and the photocurrent is obtained by cyclic voltammetry scanning under light conditions. When the p-n type transition potential is compared with the standard curve, the pH value of the sweat at this time is obtained.

Experimental example 2

1. Anti-light interference test

Add 3 μL/mm ² of artificial sweat with a pH of 5 to the test area of the flexible wearable pH sensor prepared in the above-mentioned Example 1, and test under the light intensity of 15mW/cm ² -35mW/cm ² respectively, when the light intensity changes , the pn-type transition potential basically does not change, but the current has a huge change, as shown in Figure 6. It can be seen that when the light intensity changes, the accuracy of the pH detection result obtained by using the pn-type transition potential as a signal will be much higher than the pH detection result obtained by using the current as a signal.

2. Partial coverage of sweat interferes with the test

Add 3 μL/mm ² of artificial sweat with a pH of 5 to the test area of the flexible wearable pH sensor prepared in the above-mentioned Example 1, control the area of the working electrode covered by the artificial sweat, and test separately under different coverage degrees. It is also found that in When sweat partially covers the electrode, the pn-type transition potential basically does not change, but the current changes greatly, as shown in Figure 7. It can be seen that when sweat partially covers the electrode, the accuracy of the pH detection result obtained by using the pn-type transition potential as a signal will be much higher than that obtained by using the current as a signal.

The description of the above embodiments is only used to help understand the technical scheme of the present invention and its core idea, it should be pointed out that for

For those skilled in the art, without departing from the principles of the present invention, some improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims (10)

A photoelectrochemical flexible wearable sweat pH sensor based on bismuth oxide p-n type transition potential is characterized in that it includes a bismuth oxide working electrode, a reference electrode, a counter electrode, a transparent flexible substrate and a light source, and the preparation of the bismuth oxide working electrode includes the following step: (1) Deposit indium-doped tin oxide film on a transparent and flexible mica substrate by radio frequency magnetron sputtering: use an indium-doped tin oxide target with a purity of 99.99%, sputtering power is 50-150W, and the substrate temperature is Room temperature -350°C, argon gas flow rate of 10-50sccm, sputtering pressure of 0.5-3pa, deposition time of 300-3600s, substrate rotation speed of 10-30r/min; (2) Depositing Bi metal on the ITO film obtained in step (1) by DC magnetron sputtering, using a Bi metal target with a purity of 99.99%, the sputtering power is 20-60W, and the substrate temperature is room temperature-350°C. The argon flow rate is 10-50sccm, the sputtering pressure is 0.5-3pa, the deposition time is 60-600s, and the substrate rotation speed is 10-30r/min; (3) Heating the bismuth oxide thin film obtained in step (2) for 30-120 min at a heating temperature of 250-350° C., and the heating tool is one of a heating table, an oven, and a tube furnace to obtain a bismuth oxide working electrode. The photoelectrochemical flexible wearable sweat pH sensor based on the bismuth oxide p-n type transition potential according to claim 1, wherein the preparation of the bismuth oxide working electrode comprises the following steps: (1) Deposit indium-doped tin oxide film on a transparent and flexible mica substrate by radio frequency magnetron sputtering: use an indium-doped tin oxide target material with a purity of 99.99%, the sputtering power is 100-150W, and the substrate temperature is 200-350°C, argon gas flow rate of 10-50sccm, sputtering pressure of 1.5-2pa, deposition time of 1200-2400s, substrate rotation speed of 20-30r/min; (2) Depositing Bi metal on the ITO film obtained in step (1) by DC magnetron sputtering, using a Bi metal target with a purity of 99.99%, the sputtering power is 40-60W, and the substrate temperature is 100-350°C. The argon flow rate is 30-50sccm, the sputtering pressure is 1-2pa, the deposition time is 100-240s, and the substrate rotation speed is 20-30r/min; (3) Heating the bismuth oxide thin film obtained in step (2) for 30-60min, the heating temperature is 270-350°C, and the heating tool is one of a heating table, an oven, and a tube furnace to obtain a bismuth oxide working electrode. The photoelectrochemical flexible wearable sweat pH sensor based on bismuth oxide p-n type transition potential according to claim 1, wherein the preparation of the reference electrode comprises the following steps: (1) Agar is added in the mixed solution of saturated KCl, the content of agar is 1wt%～5wt%, and mixed solution is heated to boiling to make agar dissolve completely; (2) Fix Ag/AgCl on a transparent flexible substrate to obtain a flexible Ag/AgCl film, and the mixed solution obtained in step (1) is drip-coated on the surface of the flexible Ag/AgCl film, and the coating amount is 10-50 μ L/cm ² , cooled to Obtain an agar gel film comprising KCl after room temperature; (3) On the surface of the agar gel film obtained in step (2), drop-coat Nafion solution with a content of 5 wt % in a coating amount of 5-30 μL/cm ² , and dry at room temperature to form a film to obtain a reference electrode. According to the photoelectrochemical flexible wearable sweat pH sensor based on bismuth oxide p-n type transition potential according to claim 1, it is characterized in that the preparation of the counter electrode comprises the following steps: depositing a thin film on a transparent flexible substrate by DC magnetron sputtering, using For a target with a purity of 99.99%, the sputtering power is 10-100W, the substrate temperature is room temperature-350°C, the argon flow rate is 10-50sccm, the sputtering pressure is 0.5-3pa, the deposition time is 60-3600s, and the substrate rotation speed is 10-30r/min. The photoelectrochemical flexible wearable sweat pH sensor based on bismuth oxide p-n type transition potential according to claim 4, wherein the substrate is one of flexible polyester, mica, and polyimide. The photoelectrochemical flexible wearable sweat pH sensor based on bismuth oxide p-n type transition potential according to claim 4, wherein the target material is one of graphite and Pt. According to the photoelectrochemical flexible wearable sweat pH sensor based on bismuth oxide p-n type transition potential according to claim 1 or 2, it is characterized in that the width of the working electrode, reference electrode and counter electrode is 0.5-5mm, and the electrode spacing is 0.5-5mm. 2mm. According to claim 1 or 2, the photoelectrochemical flexible wearable sweat pH sensor based on bismuth oxide p-n type transition potential is characterized in that the light source is 0.1-1W and the wavelength is 400-500nm. The encapsulation method of the photoelectrochemical flexible wearable sweat pH sensor based on the p-n type transition potential of bismuth oxide described in claim 1, is characterized in that, comprises the steps: 1) Select a flexible polyester film with a thickness of 45-55mm as the transparent flexible substrate; 2) Paste the working electrode, reference electrode and counter electrode on the transparent flexible polyester film with polydimethylsiloxane glue; 3) Encapsulate the film obtained in step 2) with PDMS glue, exposing the detection end and the wire connection end; 4) Curing the film obtained in step (3) at 95-105° C. for 50-70 minutes to obtain the finished product. The application of the photoelectrochemical flexible wearable sweat pH sensor based on bismuth oxide p-n type transition potential according to claim 1 is characterized in that, for detecting sweat pH, comprising the following steps: 1) Using a three-electrode system, add 1-7μL/mm ² artificial sweat to the test area of the flexible wearable pH sensor, scan the dark current by cyclic voltammetry under no light conditions, and use cyclic voltammetry under light conditions to obtain the dark current. Scanning method to obtain photocurrent; 2) Test the artificial sweat with different pH in turn, obtain the potential at the intersection of photocurrent and dark current at different pH, then fit the data and obtain a standard curve; 3) Attach the flexible wearable pH sensor to the skin. After the sweat infiltrates the test area, the dark current is scanned by cyclic voltammetry under no light conditions, and the photocurrent is obtained by cyclic voltammetry scanning under light conditions. The p-n transition potential at this time is obtained, and the pH value of the sweat at this time is obtained by comparing with the standard curve.

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