Flexible electrochemical sensing platform for real-time detection of nicotine level of sweat

Abstract

The invention discloses a flexible electrochemical sensing platform for real-time detection of the nicotine level of sweat, and belongs to the field of electrochemical analysis and detection. The flexible electrochemical sensing platform is constructed by modifying the polydimethylsiloxane loaded with the single-walled carbon nanotubes with the conductive hydrogel PMAMA, and can be used for noninvasive real-time detection of the nicotine level in human sweat. The modification of PMAMA greatly increases the conductivity of the electrochemical sensing platform, can sensitively and specifically detect nicotine in a wide linear range, has a low detection limit, and is suitable for detection of trace nicotine in sweat. In addition, the constructed electrochemical sensing platform not only has excellent repeatability, reproducibility and stability, but also can realize real-time dynamic monitoring of the nicotine level in human sweat.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical analysis and detection, specifically relating to a flexible electrochemical sensing platform for real-time detection of nicotine levels in sweat. Background Technology

[0002] Traditional methods for detecting nicotine mainly include high-performance liquid chromatography (HPLC), gas chromatography-mass spectrometry (GC-MS), and enzyme-linked immunosorbent assay (ELISA). These methods often rely on large laboratory instruments, require a fixed laboratory environment and specialized personnel, and involve complex sample pretreatment processes. The time from sample collection to result acquisition can typically take several hours or even days. This lag prevents them from being used for dynamic monitoring of real-time changes in human nicotine metabolism.

[0003] Flexible electrochemical sensing platforms based on flexible substrates (such as polydimethylsiloxane, nonwoven fabric, and polyethylene terephthalate) are lightweight, wearable, and portable. They can directly contact the skin to collect sweat without complex sample pretreatment and can be integrated into devices such as wristbands and patches. This enables in-situ detection of nicotine levels in sweat, suitable for various scenarios including outdoor and bedside applications. The flexible electrochemical sensing platform can output detection results within minutes or even seconds, supporting continuous, real-time nicotine concentration tracking. Furthermore, the platform can selectively identify nicotine by modifying conductive materials with excellent conductivity and electrocatalytic activity, and can be combined with electrochemical techniques such as cyclic voltammetry and chronoamperometry for real-time dynamic monitoring of nicotine levels in sweat.

[0004] Therefore, this invention provides a flexible electrochemical sensing platform for real-time detection of nicotine levels in sweat. Summary of the Invention

[0005] One objective of this invention is to provide a flexible electrode, which is prepared using the following steps: Step 1: Vacuum filter the aqueous solution of single-walled carbon nanotubes through a filter membrane to form a uniform single-walled carbon nanotube membrane on the surface of the filter membrane. Step 2: Prepare polydimethylsiloxane substrate, then attach the filter membrane loaded with single-walled carbon nanotube membrane to the surface of polydimethylsiloxane substrate, dry and cure, and then peel off the filter membrane to obtain polydimethylsiloxane substrate SWCNT / PDMS loaded with single-walled carbon nanotube membrane. Step 3: Adhesive tape is pasted on the surface of the single-walled carbon nanotube film of SWCNT / PDMS, then holes are made in the tape, and conductive hydrogel PMAMA is dropped into the holes. After drying and curing, the flexible electrode PMAMA / SWCNT / PDMS is obtained. The preparation process of the conductive hydrogel PMAMA is as follows: acrylamide is dissolved in water, then poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) and α-methylpropylene are added, and then N,N'-methylenebisacrylamide and ammonium persulfate are added to obtain the conductive hydrogel PMAMA.

[0006] Further, the concentration of the single-walled carbon nanotube aqueous solution in step 1 is 0.25-1 mg / mL, preferably 0.75 mg / mL.

[0007] Furthermore, the drying and curing conditions in step 2 are 60°C for 2 hours.

[0008] Furthermore, the drying and curing conditions in step 3 are 60°C for 30 minutes.

[0009] Furthermore, in the preparation of the conductive hydrogel PMAMA, the proportions of acrylamide, water, poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate), α-methylpropylene, N,N'-methylenebisacrylamide, and ammonium persulfate are 3g:8 mL:0.5 g:0.6 g:0.03 g:0.03 g.

[0010] A second objective of this invention is to provide an electrochemical sensor comprising a reference electrode, a working electrode, and a counter electrode, wherein the working electrode is the aforementioned flexible electrode; the electrochemical sensor is used to detect the content of nicotine.

[0011] The third objective of this invention is to provide a flexible electrochemical sensing platform for real-time monitoring of nicotine in sweat, which is prepared using the following steps: Step 1: The designed sensor pattern is drawn on polyimide tape using a cutting machine. The polyimide tape with the sensor pattern is transferred to the surface of the filter membrane and then fixed on the filter assembly. The conductive carbon paste, single-walled carbon nanotube aqueous solution and conductive silver paste are filtered sequentially through vacuum filtration to the reference electrode, working electrode and counter electrode areas of the sensor pattern, and a complete three-electrode system is obtained on the surface of the filter membrane. Step 2: Prepare a polydimethylsiloxane substrate, then attach a filter membrane with a three-electrode system onto the polydimethylsiloxane substrate, dry and cure it, and then peel off the filter membrane to obtain a polydimethylsiloxane substrate loaded with a three-electrode system. Step 3: Add conductive hydrogel PMAMA to the surface of the working electrode, dry and solidify to obtain a flexible electrochemical sensing platform; The sensor pattern includes: three circular electrodes with a diameter of 3 mm, which serve as a reference electrode, a working electrode, and a counter electrode, respectively. The circles corresponding to the reference electrode and the counter electrode are connected to a rectangle with a length of 12 mm and a width of 1 mm. The circle corresponding to the working electrode is connected to a rectangle with a length of 10 mm and a width of 1 mm. The ends of the rectangles are all connected to rectangles with a length of 1 mm and a width of 2 mm. The preparation process of the conductive hydrogel PMAMA is as follows: acrylamide is dissolved in water, then poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) and α-methylpropylene are added, and then N,N'-methylenebisacrylamide and ammonium persulfate are added to obtain the conductive hydrogel PMAMA.

[0012] Further, the concentration of the single-walled carbon nanotube aqueous solution in step 1 is 0.25-1 mg / mL, preferably 0.75 mg / mL.

[0013] Furthermore, the drying and curing conditions in step 2 are 60℃ for 2 hours; the drying and curing conditions in step 3 are 60℃ for 30 minutes.

[0014] Furthermore, in the preparation of the conductive hydrogel PMAMA, the proportions of acrylamide, water, poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate), α-methylpropylene, N,N'-methylenebisacrylamide, and ammonium persulfate are 3g:8 mL:0.5 g:0.6 g:0.03 g:0.03 g.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention can achieve rapid detection of nicotine in sweat in a short time (100 s); 2. This invention can achieve a low detection limit (0.1 µM) and a wide detection range (0.25 µM−280 µM). 3. This invention can achieve non-invasive real-time monitoring of sweat nicotine levels and can serve as a new method for sweat nicotine detection.

[0016] This invention constructs a flexible electrochemical sensor platform by modifying polydimethylsiloxane loaded with single-walled carbon nanotubes using conductive hydrogel PMAMA, for non-invasive real-time detection of nicotine levels in human sweat. PMAMA modification significantly increases the conductivity of the electrochemical sensing platform while enabling sensitive and specific detection of nicotine over a wide linear range, along with a low detection limit, making it suitable for detecting trace amounts of nicotine in sweat. Furthermore, the constructed electrochemical sensing platform exhibits excellent repeatability, reproducibility, and stability, and enables real-time dynamic monitoring of nicotine levels in human sweat. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the preparation process of conductive hydrogel PMAMA.

[0018] Figure 2 This is a schematic diagram of the fabrication process of a flexible electrochemical sensing platform based on flexible electrodes PMAMA / SWCNT / PDMS.

[0019] Figure 3 In the figure, A and B are flexible electrodes SWCNT / PDMS and PMAMA / SWCNT / PDMS, respectively, in 5 mM Fe(CN)6. 3− / 4− Cyclic voltammetry and electrochemical impedance spectroscopy in solution, C and D are respectively the results of the flexible electrode PMAMA / SWCNT / PDMS after undergoing different numbers of bending cycles (radius = 3 mm) and 30% stretching cycles at 5 mM Fe(CN)6. 3− / 4− Cyclic voltammetry in solution (insets are photographs of the electrodes being bent and stretched, respectively).

[0020] Figure 4 In the diagram, A is a schematic diagram of the reaction mechanism of nicotine on the surface of the flexible sensing platform; B is the response current value of the flexible electrode PMAMA / SWCNT / PDMS loaded with different concentrations of SWCNT to 250 µM nicotine; C is the cyclic voltammogram of the flexible electrode SWCNT / PDMS and PMAMA / SWCNT / PDMS in phosphate buffer solutions without and with 250 µM nicotine; and D is the cyclic voltammogram of the flexible electrode PMAMA / SWCNT / PDMS in phosphate buffer solutions with different concentrations of nicotine.

[0021] Figure 5 In the figure, A is the chronocurrent curve of the flexible sensing platform based on PMAMA / SWCNT / PDMS with different concentrations of nicotine added at +0.8 V voltage; B is the linear calibration curve of response current versus nicotine concentration; C, D, E and F are the test results of specificity, repeatability, reproducibility and stability of nicotine detection by the flexible sensing platform based on PMAMA / SWCNT / PDMS, respectively.

[0022] Figure 6 In the figure, A is the time-current curve of nicotine in the sweat of 12 volunteers detected by the flexible sensing platform, and B is the concentration of nicotine in the sweat of these 12 volunteers calculated based on the linear equation between nicotine concentration and response current.

[0023] Figure 7 In the image, A shows a photo of a volunteer wearing the constructed flexible electrochemical sensing platform while exercising, and B shows the timing current response curve recorded by the flexible sensing platform during the exercise. Detailed Implementation

[0024] The preferred embodiments of the present invention will now be described in detail with reference to specific examples. It should be understood that the following examples are given for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications and substitutions to the present invention without departing from its spirit and essence.

[0025] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0026] Unless otherwise specified, all materials and reagents used in the following examples are commercially available. Example 1

[0027] This embodiment provides a flexible electrode composed of a flexible substrate polydimethylsiloxane (PDMS), single-walled carbon nanotubes (SWCNTs), and conductive hydrogel PMAMA.

[0028] 1. Synthesis of conductive hydrogel PMAMA like Figure 1 As shown, 3 g of acrylamide (AAM) was dissolved in 8 mL of deionized water, and then sonicated for 3 min to ensure uniform dispersion. Next, 0.5 g of poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) and 0.6 g of α-methylpropylene (MAA) were slowly added sequentially to the acrylamide solution. Finally, 0.03 g of N,N'-methylenebisacrylamide (MBAAM) and 0.03 g of ammonium persulfate (APS) were added to the above mixed solution to obtain a liquid conductive hydrogel PMAMA. The liquid conductive hydrogel PMAMA was poured into a mold and placed in a vacuum oven at 60°C for 30 min to obtain a solid conductive hydrogel PMAMA.

[0029] 2. Fabrication of flexible electrodes PMAMA / SWCNT / PDMS First, a 1.5 mg / mL SWCNT aqueous dispersion was diluted with deionized water to concentrations of 0.25, 0.5, 0.75, and 1 mg / mL, respectively. Then, the SWCNT aqueous solutions of different concentrations were vacuum filtered through a 0.22 µM filter membrane to form a uniform SWCNT membrane on the filter membrane surface. Next, the prepolymer and crosslinking agent from a commercially available PDMS (Dow Corning DC184) reagent were mixed at a mass ratio of 10:1, degassed under vacuum to remove air bubbles, and cured in a vacuum oven at 60°C for 30 min to obtain a semi-dry PDMS substrate. The filter membrane loaded with the SWCNT membrane was then attached to the surface of the semi-dry PDMS substrate and cured in a vacuum oven at 60°C for 2 h. After peeling off the top layer of filter membrane, the SWCNT membrane was successfully transferred to the PDMS substrate, resulting in an SWCNT / PDMS mixture. Finally, the prepared SWCNT / PDMS was cut into 16×8 mm rectangles, and an 8×8 mm plastic tape was attached to its surface with a 4 mm diameter hole. 10 µL of the synthesized liquid conductive hydrogel PMAMA was dropped onto the SWCNT / PDMS, and the mixture was placed in a vacuum oven at 60 °C for 30 min to obtain the flexible electrode PMAMA / SWCNT / PDMS.

[0030] Using SWCNT (0.75 mg / mL) / PDMS and PMAMA / SWCNT (0.75 mg / mL) / PDMS as working electrodes, respectively, at 5 mM Fe(CN)6 3− / 4− Cyclic voltammetry and electrochemical impedance spectroscopy were used for detection in solution; subsequently, PMAMA / SWCNT (0.75 mg / mL) / PDMS was subjected to different numbers of bending cycles (radius = 3 mm) and 30% stretching cycles, respectively, and then detected in 5 mM Fe(CN)6. 3− / 4− Cyclic voltammetry was used for detection in the solution.

[0031] like Figure 3 As shown in Figure A, at 5 mM Fe(CN)6 3− / 4− In solution, compared with the flexible electrode SWCNT (0.75 mg / mL) / PDMS, the flexible electrode PMAMA / SWCNT (0.75 mg / mL) / PDMS exhibits a pair of distinct and reversible redox peaks with a peak potential difference of 280 mV. This indicates that the modification of the conductive hydrogel PMAMA can accelerate the electron transfer rate on the electrode surface, thereby giving the flexible electrode PMAMA / SWCNT (0.75 mg / mL) / PDMS excellent conductivity. Figure 3As shown in Figure B, the electrochemical impedance spectroscopy of the flexible electrodes SWCNT (0.75 mg / mL) / PDMS and PMAMA / SWCNT (0.75 mg / mL) / PDMS further confirms that modification with PMAMA, which has excellent conductivity, significantly reduces the resistance of the flexible electrode PMAMA / SWCNT (0.75 mg / mL) / PDMS. To characterize the electrochemical stability of this flexible electrode under different mechanical deformations, the changes in conductivity of the flexible electrode PMAMA / SWCNT (0.75 mg / mL) / PDMS after different numbers of bending and stretching cycles were investigated. Figure 3 As shown in Figure C, after 100 bending cycles, the redox peak current and potential difference of the electrode did not change significantly. Under 30% stretching for 100 cycles, the cyclic voltammetry curve of the electrode was only slightly affected, as shown in Figure C. Figure 3 As shown in Figure D. The above results demonstrate that the flexible electrode PMAMA / SWCNT (0.75 mg / mL) / PDMS exhibits good electrochemical stability under different mechanical deformations, laying a solid foundation for the subsequent fabrication of a flexible electrochemical sensing platform.

[0032] like Figure 4 As shown in Figure A, the nicotine detection mechanism involves the demethylation reaction of nicotine on the surface of a flexible electrode to generate demethylated nicotine. This process is accompanied by electron transfer, and real-time detection of nicotine is achieved by capturing changes in the current signal during the reaction. PMAMA / SWCNT / PDMS flexible electrodes loaded with 0.25, 0.5, 0.75, and 1 mg / mL of SWCNT were used in a 0.1 mol / L phosphate buffer solution at pH 7.0 to record the response current values ​​to 250 µM nicotine using cyclic voltammetry. The effect of the SWCNT concentration loaded on the PDMS substrate on the sensing performance of the PMAMA / SWCNT / PDMS flexible electrode was investigated by recording the oxidation peak current generated by the flexible electrode PMAMA / SWCNT / PDMS in a 0.1 mol / L phosphate buffer solution containing 250 µM nicotine at pH 7.0. Figure 4As shown in Figure B, the oxidation peak current gradually increased with the increase of SWCNT concentration from 0.25 mg / mL to 0.75 mg / mL; however, when the SWCNT concentration was further increased to 1 mg / mL, the oxidation peak current decreased instead. Therefore, a flexible electrode PMAMA / SWCNT / PDMS was prepared using a 0.75 mg / mL SWCNT aqueous solution. Cyclic voltammetry was then used to record the cyclic voltammetry curves of the flexible electrodes SWCNT (0.75 mg / mL) / PDMS and PMAMA / SWCNT (0.75 mg / mL) / PDMS in phosphate buffer solutions containing and without 250 µM nicotine. The electrochemical response of different electrodes to 250 µM nicotine was compared in phosphate buffer solution to characterize the electrocatalytic performance of the conductive hydrogel PMAMA for nicotine. Figure 4 As shown in Figure C, without the addition of nicotine, no observable current signal was generated on the surfaces of SWCNT (0.75 mg / mL) / PDMS and PMAMA / SWCNT (0.75 mg / mL) / PDMS. Upon addition of 250 µM nicotine, both electrodes exhibited significant oxidation peaks, corresponding to the oxidation process of nicotine. Compared to SWCNT (0.75 mg / mL) / PDMS, the oxidation peak current of PMAMA / SWCNT (0.75 mg / mL) / PDMS was significantly larger, due to the superior electrocatalytic performance of PMAMA for nicotine. Finally, cyclic voltammetry curves were recorded using cyclic voltammetry after adding different concentrations of nicotine to the flexible electrode PMAMA / SWCNT (0.75 mg / mL) / PDMS in phosphate buffer solution. Figure 4 As shown in Figure D, the oxidation peak current increases with increasing nicotine concentration, indicating that PMAAM / SWCNT / PDMS can be used for the quantitative detection of nicotine. Example 2

[0033] This embodiment provides a flexible sensing platform, which is composed of a flexible substrate polydimethylsiloxane (PDMS), single-walled carbon nanotubes (SWCNT), conductive hydrogel PMAMA, conductive carbon paste, and conductive silver paste.

[0034] Fabrication of the flexible sensing platform: The fabrication process of the flexible sensing module is as follows Figure 2As shown in the diagram, the sensor pattern was first drawn using drawing software. The pattern included three circular electrodes, each 3 mm in diameter, serving as the reference electrode, working electrode, and counter electrode, respectively. The circles corresponding to the reference and counter electrodes were then connected to a 12 × 1 mm rectangle, and the circle corresponding to the working electrode was connected to a 10 × 1 mm rectangle. Each rectangle's end was connected to a 1 × 2 mm rectangle. The designed sensor pattern was then drawn onto polyimide (PI) tape adhered to polyethylene terephthalate (PET) using a programmable mechanical cutter. The PI tape with the sensor pattern was transferred from the PET membrane to the surface of a 0.22 µM filter membrane and then fixed to the filter assembly. Conductive carbon paste, 0.75 mg / mL SWCNT aqueous solution, and conductive silver paste were sequentially filtered into the reference, working, and counter electrode areas using a vacuum filtration device, resulting in a complete three-electrode system on the filter membrane surface. The prepolymer and crosslinking agent in a commercially available PDMS (Dow Corning DC184) reagent were mixed at a mass ratio of 10:1, degassed under vacuum to remove air bubbles, and cured to a semi-dry state in a vacuum oven at 60°C. A filter membrane with a three-electrode system was then attached to the semi-dry PDMS substrate and cured in a vacuum oven at 60°C for 2 hours. After peeling off the top filter membrane, the three-electrode system was successfully transferred to the PDMS substrate. Finally, the working electrode was modified with the prepared liquid PMAMA to obtain a flexible sensing platform. This flexible sensing platform can be used for non-invasive real-time monitoring of dynamic changes in nicotine levels in sweat, facilitating personalized assessment of tobacco exposure levels and providing crucial early warning of health risks associated with tobacco exposure.

[0035] The flexible electrochemical sensing platform based on the flexible electrode PMAMA / SWCNT (0.75 mg / mL) / PDMS was timed after adding different concentrations of nicotine at +0.8 V. Figure 5 As shown in Figure A, the response current increases with increasing nicotine concentration; even when the added nicotine concentration is as low as 0.25 µM, a detectable current signal can still quickly appear on the surface of the sensing platform and stabilize within 3 seconds. Figure 5As shown in Figure B, within a wide linear range of 0.25 µM to 280 µM, the response current increases proportionally with increasing nicotine concentration, exhibiting a linear relationship with nicotine concentration. The limit of detection was calculated to be 0.1 µM (S / N=3). Subsequently, the specificity, repeatability, reproducibility, and stability of nicotine detection were investigated using a flexible electrochemical sensing platform based on the flexible electrode PMAMA / SWCNT (0.75 mg / mL) / PDMS. The selectivity of the electrode was evaluated using a chronoamperometry method by sequentially adding 20 µM of common interfering substances present in sweat, including sodium chloride (NaCl), potassium chloride (KCl), glucose (Glu), lactic acid (LA), dopamine (DA), uric acid (UA), and ascorbic acid (AA), to a phosphate buffer solution. Figure 5 As shown in Figure C, when 2 µM nicotine is added, the sensing platform generates a very significant current signal, while the response current generated by adding interfering substances is almost negligible. Figure 5 As shown in Figure D, the response current of the same flexible electrochemical sensing platform to 2 µM nicotine was measured five times consecutively using the chronoamperometry method. The relative standard deviation of the five measurements was calculated to be 4.46%, indicating good repeatability of the sensing platform. Figure 5 As shown in Figure E, the relative standard deviation of the response current values ​​of 2 µM nicotine detected by the chronoamperometry using five flexible electrochemical sensing platforms prepared using the same method was 5.74%, demonstrating the excellent reproducibility of the sensing platforms. Figure 5 As shown in Figure F, the flexible sensing platform measures the response current to 2 µM nicotine every 4 days using the chronoamperometry method. After 16 days, it can still maintain 90.2% of its original response current to 2 µM nicotine, which is satisfactory in terms of stability.

[0036] The 12 selected subjects were first divided into three groups based on their tobacco exposure levels: subjects 1–4 were non-smokers, subjects 5–8 were light smokers, and subjects 9–12 were heavy smokers. Before sweat collection, subjects had to clean their foreheads with alcohol pads and cotton balls. These subjects were asked to ride a bicycle with a constant output power of 100 watts. Then, approximately 10 minutes after they began exercising, sweating began. Once sweating started, the sweat from their foreheads was collected using centrifuge tubes and stored in a refrigerator for subsequent in vitro experiments. During actual monitoring, the collected sweat was injected into the sensor surface using a syringe pump at 1 µL / min, and the resulting electrochemical signal was recorded using chronoamperometry. Figure 6 As shown in Figure A, with increasing tobacco exposure, the nicotine response current in the volunteers' sweat also increased. The nicotine concentration in the sweat of these 12 volunteers was calculated based on the linear equation between the response current and nicotine concentration. Figure 6As shown in Figure B, the nicotine concentration in non-smokers was much lower than that in smokers, while the nicotine concentration in the sweat of heavy smokers was higher than that of light smokers. The range of nicotine concentrations measured in different populations was consistent with previous literature reports.

[0037] A flexible electrochemical sensing platform was constructed and worn by a volunteer during exercise. The current signal from the platform during the volunteer's exercise was then recorded using chronoamperometry. Figure 7 As shown in Figure A, the selected volunteers wore the fabricated flexible electrochemical sensing platform while riding a bicycle with a constant output power of 100 watts. Over a period of time, the sensing platform measured the current signal generated by nicotine in sweat using a chronoamperometry method, as shown below. Figure 7 As shown in Figure B, this demonstrates the great potential of this flexible electrochemical sensing platform in long-term dynamic tracking of nicotine levels in sweat.

Claims

1. A flexible electrode, characterized in that, It is prepared by the following steps: Step 1: Vacuum filter the aqueous solution of single-walled carbon nanotubes through a filter membrane to form a uniform single-walled carbon nanotube membrane on the surface of the filter membrane. Step 2: Prepare polydimethylsiloxane substrate, then attach the filter membrane loaded with single-walled carbon nanotube membrane to the surface of polydimethylsiloxane substrate, dry and cure, and then peel off the filter membrane to obtain polydimethylsiloxane substrate SWCNT / PDMS loaded with single-walled carbon nanotube membrane. Step 3: Adhesive tape is pasted on the surface of the single-walled carbon nanotube film of SWCNT / PDMS, then holes are made in the tape, and conductive hydrogel PMAMA is dropped into the holes. After drying and curing, the flexible electrode PMAMA / SWCNT / PDMS is obtained. The preparation process of the conductive hydrogel PMAMA is as follows: acrylamide is dissolved in water, then poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) and α-methylpropylene are added, and then N,N'-methylenebisacrylamide and ammonium persulfate are added to obtain the conductive hydrogel PMAMA.

2. The flexible electrode according to claim 1, characterized in that, The concentration of the single-walled carbon nanotube aqueous solution in step 1 is 0.25-1 mg / mL.

3. The flexible electrode according to claim 1, characterized in that, The drying and curing conditions in step 2 are 60℃ for 2 hours.

4. The flexible electrode according to claim 1, characterized in that, The drying and curing conditions in step 3 are 60℃ for 30 minutes.

5. The flexible electrode according to claim 1, characterized in that, In the preparation of conductive hydrogel PMAMA, the ratio of acrylamide, water, poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate), α-methylpropylene, N,N'-methylenebisacrylamide and ammonium persulfate is 3 g: 8 mL: 0.5 g: 0.6 g: 0.03 g: 0.03 g.

6. An electrochemical sensor, characterized in that, It includes a reference electrode, a working electrode, and a counter electrode, wherein the working electrode is the flexible electrode as described in any one of claims 1-5; the electrochemical sensor is used to detect the content of nicotine.

7. A flexible electrochemical sensing platform, characterized in that, It is prepared by the following steps: Step 1: The designed sensor pattern is drawn on polyimide tape using a cutting machine. The polyimide tape with the sensor pattern is transferred to the surface of the filter membrane and then fixed on the filter assembly. The conductive carbon paste, single-walled carbon nanotube aqueous solution and conductive silver paste are filtered sequentially through vacuum filtration to the reference electrode, working electrode and counter electrode areas of the sensor pattern, and a complete three-electrode system is obtained on the surface of the filter membrane. Step 2: Prepare a polydimethylsiloxane substrate, then attach a filter membrane with a three-electrode system onto the polydimethylsiloxane substrate, dry and cure it, and then peel off the filter membrane to obtain a polydimethylsiloxane substrate loaded with a three-electrode system. Step 3: Add conductive hydrogel PMAMA to the surface of the working electrode, dry and solidify to obtain a flexible electrochemical sensing platform; The sensor pattern includes: three circular electrodes with a diameter of 3 mm, which serve as a reference electrode, a working electrode, and a counter electrode, respectively. The circles corresponding to the reference electrode and the counter electrode are connected to a rectangle with a length of 12 mm and a width of 1 mm. The circle corresponding to the working electrode is connected to a rectangle with a length of 10 mm and a width of 1 mm. The ends of the rectangles are all connected to rectangles with a length of 1 mm and a width of 2 mm. The preparation process of the conductive hydrogel PMAMA is as follows: acrylamide is dissolved in water, then poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) and α-methylpropene are added, and then N,N'-methylenebisacrylamide and ammonium persulfate are added to obtain the conductive hydrogel PMAMA. The flexible electrochemical sensing platform is used for real-time monitoring of nicotine in sweat.

8. The flexible electrochemical sensing platform according to claim 7, characterized in that, The concentration of the single-walled carbon nanotube aqueous solution in step 1 is 0.25-1 mg / mL, preferably 0.75 mg / mL.

9. The flexible electrochemical sensing platform according to claim 7, characterized in that, The drying and curing conditions in step 2 are 60℃ for 2 hours; the drying and curing conditions in step 3 are 60℃ for 30 minutes.

10. The flexible electrochemical sensing platform according to claim 7, characterized in that, In the preparation of conductive hydrogel PMAMA, the ratio of acrylamide, water, poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate), α-methylpropylene, N,N'-methylenebisacrylamide and ammonium persulfate is 3 g: 8 mL: 0.5 g: 0.6 g: 0.03 g: 0.03 g.

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