CN116087294A

CN116087294A - Preparation method of wearable sensor

Info

Publication number: CN116087294A
Application number: CN202310144044.0A
Authority: CN
Inventors: 罗细亮; 许珍颖; 魏臻; 李艳欣
Original assignee: Qingdao University of Science and Technology
Current assignee: Qingdao University of Science and Technology
Priority date: 2023-02-21
Filing date: 2023-02-21
Publication date: 2023-05-09

Abstract

The invention discloses a preparation method of a wearable sensor, which specifically comprises the following steps: (1) preparing TA-Ag nano particles; (2) preparing TA-Ag-CNT-PANI hydrogel; (3) preparing agarose water gel; (4) constructing a wearable electrode array; and (5) modifying the wearable electrode array. The sensor of the present invention is a highly integrated flexible wearable sweat sensor that can successfully detect pH and Tyr concentration in sweat.

Description

Preparation method of wearable sensor

Technical Field

The invention relates to the technical field of wearable electrochemical sweat sensors, in particular to a preparation method of a wearable sensor.

Background

Wearable devices and sensors have gained great attention for their advantage of monitoring physiological information of a person in real time.

Currently, wearable devices track mainly respiratory rate, body movements and electrocardiograms, but do not provide information at the molecular level. This challenge encourages rapid development of wearable electrochemical sensors, providing a window for non-invasive detection of analytes in biological fluids. Among the different types of biological fluids, noninvasive monitoring is difficult to obtain in blood and interstitial fluid. In addition, sweat contains abundant necessary indicators related to physiological status information of human body, including various molecules and biomolecules (uric acid, ascorbic acid and proteins), and metabolites (lactic acid and urea) and electrolytes (k+ and na+), as compared to tears, saliva and urine. In particular, tyrosine (Tyr) is a semi-essential amino acid and has physiological concentration in sweat ranging from 6 to 240. Mu.M, and Tyr concentration abnormalities are associated with various diseases such as tyrosinemia, chronic low inflammation, liver disease and bulimia nervosa. However, electrochemical monitoring of Tyr is always susceptible to pH changes, whereas the pH in human sweat is susceptible to health conditions. Therefore, developing a wearable sweat sensor to detect Tyr with reliable accuracy is of considerable interest.

Since the wearable electrochemical sweat device is in intimate contact with human skin, flexible materials with good conductivity and biocompatibility are essential in designing such sensor constructions. Therefore, the conductive polymer hydrogel is an ideal material for detecting sweat due to the advantages of excellent biological performance, large three-dimensional elastic crosslinked polymer network, good sweat storage capacity, adjustable mechanical performance, good electrocatalytic performance and the like. Among other things, the conductive polymer Polyaniline (PANI) exhibits interesting pH and Tyr sensing properties, which are useful for identifying Tyr and pH in sweat. However, PANI-based hydrogels with good electrical conductivity, antimicrobial properties, and mechanical properties have yet to be explored.

Meanwhile, as a wearable sensor for detecting sweat in real time, the sweat discharging process is very important. Perspiration may depend on environmental conditions (such as temperature and humidity), activity levels, and chemical irritation. While exercise is always used to induce perspiration, it is difficult to meet on-demand perspiration analysis and sedentary individuals. Thus, there is a need for an appropriate perspiration stimulation method to induce perspiration in a controlled manner for in situ detection. Iontophoresis is a conventional process of delivering chemicals such as pilocarpine, which can stimulate sweat glands to produce sweat by applying an imperceptible local current to the skin. Therefore, in sweat sensor systems, integrating the iontophoresis electrode as a sweat induction module is critical to achieving sweat in situ analysis.

Therefore, how to prepare a wearable sensor based on multifunctional conductive hydrogel for simultaneously and accurately detecting pH and Tyr concentration in sweat is a problem to be solved by those skilled in the art.

Disclosure of Invention

Accordingly, the present invention is directed to a method for manufacturing a wearable sensor, which solves the drawbacks of the prior art. The sensor is a highly integrated flexible wearable sweat sensor that can successfully detect pH and Tyr concentration in sweat.

In order to achieve the above purpose, the present invention adopts the following technical scheme:

the preparation method of the wearable sensor specifically comprises the following steps:

(1) Preparation of TA-Ag nanoparticles

Firstly, dissolving Tannic Acid (TA) powder into water to obtain tannic acid solution; then silver nitrate (AgNO) ₃ ) Dissolving the powder in water to obtain a silver nitrate solution; mixing and stirring the tannic acid solution and the silver nitrate solution; finally, centrifugally washing to obtain TA-Ag nano particles;

(2) Preparation of TA-Ag-CNT-PANI hydrogel

Ammonium Persulfate (APS), carbon Nano Tubes (CNT) and TA-Ag nano particles are dissolved in water to obtain solution A; then dissolving 3-Aminobenzene Borate (ABA) in hydrochloric acid, and then adding aniline and water to obtain a solution B; dropwise adding the solution B into a polyvinyl alcohol (PVA) aqueous solution under magnetic stirring to obtain a solution C; finally, adding the solution A into the solution C, and rapidly stirring to obtain TA-Ag-CNT-PANI hydrogel for later use;

(3) Preparation of agarose water gel

Dissolving agarose in potassium phosphate buffer solution, continuously stirring until the agarose is completely dissolved, pouring the solution on a die, and cooling the solution to room temperature to obtain agarose hydrogel for later use;

(4) Construction of wearable electrode arrays

Forming an ion-introducing electrode and an electrochemical sensor into a wearable electrode array; wherein the electrochemical sensor has a three-electrode system comprising an Ag/AgCl reference electrode, a carbon counter electrode and a carbon working electrode;

(5) Modification of wearable electrode arrays

Firstly, dripping TA-Ag-PANI-CNT hydrogel on a carbon working electrode; then cutting agarose gel into the same size as the ion-introducing electrode and covering the ion-introducing electrode before electric stimulation; and finally, dripping pilocarpine alkali solution into agarose water gel and keeping the pilocarpine alkali solution to obtain the wearable sensor.

The application principle of the wearable sensor is as follows:

the invention prepares an iontophoresis system and an electrochemical sensing system based on pilocarpine, and couples the same to an electrochemical sensing electrode array on a single wearable detection patch (figure 1). The device is intended to achieve local sweat stimulation and accurate Tyr detection. Iontophoresis electrodes (i.e., IP electrodes, including Ag cathodes and Ag anodes) and three electrode sensing systems (including Ag/AgCl reference electrodes, carbon counter electrodes, and carbon working electrodes) were mass produced using screen printing techniques (fig. 2) in combination with medical tape to facilitate peeling from the skin. First, serpentine wires and electrodes were printed on a flexible Polyimide (PI) substrate using a 300 mesh screen; next, an insulating layer is printed in the same manner; then, the electrode array is dried at 60 ℃ for 30min; the width of the anode of the IP electrode is 1cm, the length of the anode is 2cm, the width of the cathode is 1cm, and the length of the cathode is 1cm; agarose gel loaded on the IP electrode consists of agarose and potassium phosphate buffer solution so as to avoid potential pH value change on the epidermis caused by ion accumulation of sampling points in the repeated sensing process; in addition, agarose gel is used as an anode medicine storage layer, and 3% pilocarpine alkali solution is preloaded; upon energization, the anode repels the positively charged pilocarpine drug into the skin to induce perspiration (fig. 3); the TA-Ag-CNT-PANI hydrogel is modified on a carbon working electrode by adopting a dripping method, and under the synergistic effect of PANI and CNT, the electrocatalytic performance of the modified electrode to Tyr detection is enhanced; meanwhile, since protonation of polyaniline may cause OCP change, pH may be detected.

Further, in the above step (1), the mass concentration of the tannic acid solution is 10 to 30mg/mL, preferably 10mg/mL, 20mg/mL or 30mg/mL; the mass concentration of the silver nitrate solution is 10-75mg/mL, preferably 10mg/mL, 20mg/mL, 30mg/mL and 75mg/mL; the mixing and stirring time is 20-40min, preferably 30min.

The technical scheme has the beneficial effects that the antibacterial activity of the silver nano particles and catechol functional groups of tannic acid are utilized, so that the efficient antibacterial activity is obtained, and the adhesive performance of the hydrogel is enhanced.

Further, in the solution A in the step (2), the mass-volume ratio of ammonium persulfate, carbon nanotubes, tA-Ag nano particles and water is 456.4mg:6mg:30mg:1.0mL.

The technical scheme has the advantage that the carbon nano tube can enhance the conductivity of the hydrogel.

Further, in the above step (2), the volume molar concentration of hydrochloric acid in the solution B is 5 to 6mol/L, preferably 6mol/L; the mass volume ratio of the 3-aminobenzene borate to the hydrochloric acid to the aniline to the water is 18.3mg:835 μl:1.5mmol: 225. Mu.L.

The technical scheme has the advantages that the step is an oxidation polymerization process of aniline, 3-aminobenzene borate is a monomer of aniline, ammonium persulfate is used as an initiator, and hydrochloric acid is used as a reaction doping agent.

Further, in the step (2), the mass percentage of the polyvinyl alcohol aqueous solution in the solution C is 10% -12%, preferably 10%; the volume of the aqueous polyvinyl alcohol solution was 3mL.

The technical proposal has the beneficial effects that the polyvinyl alcohol is used as the cross-linking agent for the aniline hydrogel reaction, so that the aniline can form hydrogel in the oxidative polymerization process.

Further, in the step (3), the molar concentration of the potassium phosphate buffer solution is 0.1mol/L and the pH is 7.0; the mass volume ratio of agarose to potassium phosphate buffer is 0.4g:10mL; the temperature of the continuous stirring is 150-170 ℃, preferably 170 ℃.

The technical proposal has the beneficial effects that the agarose water gel can be loaded with the electric stimulation medicine and the potassium phosphate buffer solution. Wherein the potassium phosphate buffer solution can avoid potential pH change on the epidermis caused by ion accumulation of sampling points in the repeated sensing process.

Further, in the step (4), the iontophoresis electrode includes an Ag cathode and an Ag anode; the diameter of the carbon working electrode was 3mm.

The technical proposal has the beneficial effects that positive charges can be accumulated at the Ag anode of the ion leading-in electrode after the electrifying, thereby repelling the pilocarpine medicine with positive charges into the skin and inducing sweating. Electrochemical sensors can perform in situ detection of pH and Tyr concentration on the sweat produced.

Further, in the above step (5), the volume of the TA-Ag-PANI-CNT hydrogel was 1. Mu.L; the mass percentage of the pilocarpine alkali solution is 2-3%, preferably 3%; the holding time is 1-2h, preferably 1h.

The technical proposal has the beneficial effects that pilocarpine belongs to cholinergic, has the effect of stimulating the secretion of exocrine glands, thereby causing sweating.

The invention also claims the application of the wearable sensor prepared by the preparation method in detecting the pH value and Tyr concentration in human sweat.

Further, the detection method specifically comprises the following steps: before detection, wiping the skin of a subject with isopropanol, and attaching the wearable sensor to the forearm of the subject with a medical double-sided tape; in actual measurement, first, using the CHI660E electrochemical workstation, a constant voltage of 2.0V was applied between the cathode and anode electrodes of the iontophoresis electrode for 20min, and sweat was induced and collected; open Circuit Potential (OCP) was then recorded for 60s and pH was determined using calibration plots obtained in vitro experiments; next, based on the measured pH value, calculating Tyr concentration from Differential Pulse Voltammetry (DPV) measurements using a calibration plot at the particular pH value; finally, the Tyr and pH levels of the collected sweat were measured using standard enzyme-linked immunosorbent assay (ELISA) methods and pH meters.

Compared with the prior art, the invention has the following beneficial effects:

1. the integrated wearable sensor system of the present invention combines a composite hydrogel electrochemical sensor with an iontophoresis electrode for direct sweat stimulation. The composite hydrogel consists of polyaniline hydrogel modified with tannic acid chelated silver nano particles (TA-AgNPs) and Carbon Nanotubes (CNTs), and the PANI hydrogel with large specific surface area has higher catalytic activity on pH value and Tyr concentration detection. For better application to skin surfaces, tA-AgNPs were introduced to ensure efficient antimicrobial activity of the hydrogels; the addition of CNTs can improve the conductivity, the catalytic performance and the mechanical performance of the hydrogel. With the help of the pH sensing results, the Tyr concentration in various sweat samples will be corrected to ensure reliable accuracy. This approach will have profound effects on personalized medicine for the design of wearable sweat sensors.

2. The invention designs a wearable sensor, which integrates two important functions in a single wearable sensing patch: sweat-stimulating iontophoresis systems and electrochemical sensors based on TA-Ag-CNT-PANI hydrogels induced to sweat by fabrication of iontophoresis electrodes and non-invasive detection of pH and Tyr concentration using electrochemical sensors. In order to be better applied to human skin, the TA-Ag-CNT-PANI hydrogel with good antibacterial property, good mechanical property and good structural stability is designed, and the sensor based on the hydrogel can simultaneously detect the pH value and Tyr level in human sweat and has good correlation with detection results of a commercial pH meter and an ELISA kit. More importantly, by means of pH calibration, reliable and accurate detection of Tyr levels in human sweat can be achieved. Ultimately, this study will help build a stable wearable sensor for accurate sweat detection.

Drawings

FIG. 1 is a schematic diagram of the structure of a wearable sensor (IP electrode and three electrode sensing system);

FIG. 2 is a schematic diagram of a screen printed sensor array;

FIG. 3 is a schematic diagram of the operation of an IP electrode;

FIG. 4 is a graph comparing the results of six sweat sample pH measurements using the wearable sensor of example 2 and a conventional pH meter;

FIG. 5 is a linear calibration of the ELISA method for detecting Tyr concentration;

fig. 6 is a graph comparing the detection results of Tyr concentration in six sweat samples using the wearable sensor of example 2 (before and after calibration) and ELISA method.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and completely, and it is apparent that the described embodiments are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

Example 1

(1) Preparation of TA-Ag nanoparticles

Firstly, dissolving tannic acid powder into water to obtain tannic acid solution with the mass concentration of 10 g/mL; then, dissolving silver nitrate powder into water to obtain a silver nitrate solution with the mass concentration of 10 mg/mL; mixing and stirring the tannic acid solution and the silver nitrate solution for 20min; finally, centrifugally washing to obtain TA-Ag nano particles;

(2) Preparation of TA-Ag-CNT-PANI hydrogel

456.4mg of ammonium persulfate, 46mg of carbon nanotubes and 30mgTA-Ag nano particles are dissolved in 1.0mL of water to obtain a solution A; then 18.3mg of 3-aminobenzene borate was dissolved in 835. Mu.L of 5mol/L hydrochloric acid by volume and molar concentration, followed by addition of 1.5mmol of aniline and 225. Mu.L of water to obtain a solution B; then dropwise adding the solution B into 3mL of 10% polyvinyl alcohol water solution under magnetic stirring to obtain a solution C; finally, adding the solution A into the solution C, and rapidly stirring to obtain TA-Ag-CNT-PANI hydrogel for later use;

(3) Preparation of agarose water gel

Dissolving 0.4g agarose in 10mL potassium phosphate buffer solution with the volume molar concentration of 0.1mol/L and the pH value of 7.0, continuously stirring at 150 ℃ until the agarose is completely dissolved, pouring the solution on a die, and cooling the solution to room temperature to obtain agarose hydrogel for later use;

(4) Construction of wearable electrode arrays

Forming a wearable electrode array from an ion-introducing electrode comprising an Ag cathode and an Ag anode and an electrochemical sensor comprising an Ag/AgCl reference electrode, a carbon counter electrode and a carbon working electrode with a diameter of 3 mm;

(5) Modification of wearable electrode arrays

Firstly, 1 mu LTA-Ag-PANI-CNT hydrogel is dripped on a carbon working electrode; then cutting agarose gel into the same size as the ion-introducing electrode and covering the ion-introducing electrode before electric stimulation; and finally, dripping pilocarpine alkali solution with the mass percentage of 3% into agarose gel and keeping for 1h to obtain the wearable sensor.

Example 2

(1) Preparation of TA-Ag nanoparticles

Firstly, dissolving tannic acid powder into water to obtain tannic acid solution with the mass concentration of 20 mg/mL; then, dissolving silver nitrate powder into water to obtain a silver nitrate solution with the mass concentration of 30mg/mL; mixing and stirring the tannic acid solution and the silver nitrate solution for 30min; finally, centrifugally washing to obtain TA-Ag nano particles;

(2) Preparation of TA-Ag-CNT-PANI hydrogel

456.4mg of ammonium persulfate, 46mg of carbon nanotubes and 30mgTA-Ag nano particles are dissolved in 1.0mL of water to obtain a solution A; then 18.3mg of 3-aminobenzene borate was dissolved in 835. Mu.L of 6mol/L hydrochloric acid by volume and molar concentration, followed by addition of 1.5mmol of aniline and 225. Mu.L of water to obtain a solution B; then dropwise adding the solution B into 3mL of 10% polyvinyl alcohol water solution under magnetic stirring to obtain a solution C; finally, adding the solution A into the solution C, and rapidly stirring to obtain TA-Ag-CNT-PANI hydrogel for later use;

(3) Preparation of agarose water gel

Dissolving 0.4g agarose in 10mL potassium phosphate buffer solution with the volume molar concentration of 0.1mol/L and the pH value of 7.0, continuously stirring at 170 ℃ until the agarose is completely dissolved, pouring the solution on a die, and cooling the solution to room temperature to obtain agarose hydrogel for later use;

(4) Construction of wearable electrode arrays

(5) Modification of wearable electrode arrays

Example 3

(1) Preparation of TA-Ag nanoparticles

Firstly, dissolving tannic acid powder into water to obtain tannic acid solution with the mass concentration of 30mg/mL; then, dissolving silver nitrate powder into water to obtain a silver nitrate solution with the mass concentration of 75mg/mL; mixing and stirring the tannic acid solution and the silver nitrate solution for 40min; finally, centrifugally washing to obtain TA-Ag nano particles;

(2) Preparation of TA-Ag-CNT-PANI hydrogel

456.4mg of ammonium persulfate, 46mg of carbon nanotubes and 30mgTA-Ag nano particles are dissolved in 1.0mL of water to obtain a solution A; then 18.3mg of 3-aminobenzene borate was dissolved in 835. Mu.L of 6mol/L hydrochloric acid by volume and molar concentration, followed by addition of 1.5mmol of aniline and 225. Mu.L of water to obtain a solution B; then dropwise adding the solution B into 3mL of 12-percent polyvinyl alcohol water solution under magnetic stirring to obtain a solution C; finally, adding the solution A into the solution C, and rapidly stirring to obtain TA-Ag-CNT-PANI hydrogel for later use;

(3) Preparation of agarose water gel

(4) Construction of wearable electrode arrays

(5) Modification of wearable electrode arrays

Firstly, 1 mu LTA-Ag-PANI-CNT hydrogel is dripped on a carbon working electrode; then cutting agarose gel into the same size as the ion-introducing electrode and covering the ion-introducing electrode before electric stimulation; and finally, dripping pilocarpine alkali solution with the mass percentage of 3% into agarose gel and keeping for 2 hours to obtain the wearable sensor.

Performance testing

First, human sweat samples were collected from 6 volunteers, and sweat pH values were measured using the wearable sensor (electrochemical sensor) and conventional pH meter prepared in example 2, respectively, and the results are shown in fig. 4. As can be seen from fig. 4, the wearable sensor of example 2 was close to the sweat sample pH as measured by a conventional pH meter. It is obvious that the pH varies from person to person.

Meanwhile, the Tyr level in the sweat sample was measured using a commercial ELISA kit, and the results are shown in fig. 5.

The results of fig. 5 are used as a reference for the performance detection of the sensor with and without pH calibration, respectively, and the results are shown in fig. 6. As can be seen from fig. 6, the concentration of Tyr detected by the wearable sensor of example 2 was below or above the ELISA results in the range of 4.0-8.0 before pH calibration, and the concentration of Tyr detected by the wearable sensor of example 2 was closer to the ELISA results after calibration (using the correct calibration curve at the correct pH). Therefore, the accuracy of the wearable sensor for Tyr detection can be effectively improved by calibrating data under different pH values (measured by the same sensor).

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. The preparation method of the wearable sensor is characterized by comprising the following steps of:

(1) Preparation of TA-Ag nanoparticles

Firstly, dissolving tannic acid powder in water to obtain tannic acid solution; then, dissolving silver nitrate powder in water to obtain a silver nitrate solution; mixing and stirring the tannic acid solution and the silver nitrate solution; finally, centrifugally washing to obtain TA-Ag nano particles;

(2) Preparation of TA-Ag-CNT-PANI hydrogel

Firstly, ammonium persulfate, a carbon nano tube and TA-Ag nano particles are dissolved in water to obtain a solution A; then dissolving 3-aminobenzene borate in hydrochloric acid, and then adding aniline and water to obtain a solution B; dropwise adding the solution B into a polyvinyl alcohol water solution under magnetic stirring to obtain a solution C; finally, adding the solution A into the solution C, and rapidly stirring to obtain TA-Ag-CNT-PANI hydrogel for later use;

(3) Preparation of agarose water gel

(4) Construction of wearable electrode arrays

Forming an ion-introducing electrode and an electrochemical sensor into a wearable electrode array; wherein the electrochemical sensor has a three-electrode system comprising an Ag/AgCl reference electrode, a carbon counter electrode, and a carbon working electrode;

(5) Modification of wearable electrode arrays

2. The method for manufacturing a wearable sensor according to claim 1, wherein in the step (1), the mass concentration of the tannic acid solution is 10-30mg/mL; the mass concentration of the silver nitrate solution is 10-75mg/mL.

3. The method for manufacturing a wearable sensor according to claim 1, wherein in the step (1), the mixing and stirring time is 20-40min.

4. The method for manufacturing a wearable sensor according to claim 1, wherein in the step (2), in the solution a, the mass-volume ratio of ammonium persulfate, carbon nanotubes, tA-Ag nanoparticles and water is 456.4mg:6mg:30mg:1.0mL.

5. The method for manufacturing a wearable sensor according to claim 1, wherein in the step (2), the volume molar concentration of the hydrochloric acid in the solution B is 5-6mol/L; the mass volume ratio of the 3-aminobenzene borate to the hydrochloric acid to the aniline to the water is 18.3mg:835 μl:1.5mmol: 225. Mu.L.

6. The method for manufacturing a wearable sensor according to claim 1, wherein in the step (2), the mass percentage of the polyvinyl alcohol aqueous solution in the solution C is 10% -12% and the volume is 3mL.

7. The method of claim 1, wherein in step (3), the potassium phosphate buffer has a molar concentration of 0.1mol/L and a pH of 7.0; the mass volume ratio of the agarose to the potassium phosphate buffer solution is 0.4g:10mL; the temperature of the continuous stirring is 150-170 ℃.

8. The method of claim 1, wherein in step (4), the ion introducing electrode comprises an Ag cathode and an Ag anode.

9. The method of manufacturing a wearable sensor according to claim 1, wherein in step (4), the carbon working electrode has a diameter of 3mm.

10. The method of claim 1, wherein in step (5), the TA-Ag-PANI-CNT hydrogel has a volume of 1 μl; the mass percentage of the pilocarpine alkali solution is 2% -3%; the holding time is 1-2h.