A flexible pH sensor based on a conductive polymer layer and its preparation method

Abstract

The present invention belongs to the field of biosensor technology, specifically a flexible pH sensor based on a conductive polymer layer and a preparation method thereof. The flexible pH sensor includes a three-dimensional flexible substrate and a conductive polymer layer deposited on the surface of the three-dimensional flexible substrate; the conductive polymer layer includes Ti4O7, sulfur-containing acid ions and conductive polymer materials. The flexible pH sensor provided by the present invention has a uniform and complete structure, and has the characteristics of flexibility, customizable electrode area, super-Nernstian response, no ion interference, excellent long-term service performance, and good biocompatibility. It can be used as the main sensing unit of an implantable / wearable pH sensor, can meet the accuracy of measurement within the pH range of common biological media, and achieve reliability when working continuously for a long time in situ or in vivo. The preparation process of the present invention is simple and has broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the field of biosensor technology, and in particular relates to a flexible pH sensor based on a conductive polymer layer and a preparation method thereof. Background Art

[0002] pH is crucial for many chemical and biological reactions. Some physiological processes, such as implant degradation, microbial infection, tumor metastasis, and wound healing, can be determined by changes in pH to determine the status of these processes. Once deviations occur, pH will reliably indicate abnormalities and diseases. Currently, many materials have been developed for pH sensing, such as glass electrodes, modern extended gate field effect transistor (EGFET) pH sensors, ion field effect transistor (ISFET) pH sensors, optical fiber pH sensors, hydrogel membranes, etc. However, these technologies still have disadvantages in the field of healthcare, such as rigidity, high cost, short battery life, and cytotoxicity.

[0003] Patent CN117554447A discloses a method for preparing a flexible conductive polymer layer pH sensor. The specific steps are: first, prepare a printed anode flexible film, and then realize the synthesis of metal-doped polyaniline composite materials on its surface by cyclic voltammetry. This method can achieve high bending stability, but there is no test to reflect its long-term service stability. Patent CN117990657A discloses a fiber optic pH value detection method using a polyaniline reaction deposition film layer. The refractive index of the polyaniline sensitive film changes after contact with the liquid to be measured. The swept laser is reflected by the fiber optic pH sensor and then incident on the fiber optic Bragg grating demodulator for spectrum extraction. The pH value of the liquid to be measured is obtained by analysis and processing. The preparation method of this invention is complex and costly, and it cannot achieve long-term continuous monitoring in wearable / implantable environments. Patent CN113670999A discloses a metal oxide-based pH sensing electrode and its preparation method and application, which is electrochemically transferred to WO 3- H intercalated in the lattice + , and transform its crystal structure from monoclinic to cubic, significantly improving its conductivity and thus the ion-electron conversion efficiency of the sensing layer. However, this method requires the addition of adhesives and is also difficult to meet the requirements of long-term continuous monitoring in wearable / implantable environments.

[0004] Despite the development of numerous pH sensors, practical applications in the biomedical field remain limited. Conductive polymers exhibit promising potential for pH sensing due to their excellent electrochemical properties. Their high biocompatibility, flexibility, stretchability, antibacterial and antioxidant properties, and ease of deposition on any flexible substrate, give them unique potential for biomedical applications. To date, development of conductive polymer layer pH sensors has primarily focused on nanofabrication and multi-component composites. However, major bottlenecks hindering the widespread application of conductive polymers in biomedical sensing include: First, many conductive polymer layer pH sensors exhibit only sub-Nernstian responses, resulting in low sensitivity. This is particularly important for narrow-range detection, where pH sensitivity is crucial, such as accuracy at neutral pH, which is particularly relevant for physiological measurements. Second, for practical applications, these polymers suffer from limited chemical stability and low mechanical strength. This makes it difficult to maintain sensor sensitivity over long periods of time in situ or in vivo, resulting in short service lives and significant potential drift, hindering their full potential. Therefore, it is of great practical significance to improve its chemical stability and develop pH sensors with long-term stability for early detection of pH fluctuations and abnormal conditions when implanted in or on the surface of organisms. Summary of the Invention

[0005] The purpose of the present invention is to provide a flexible pH sensor based on a conductive polymer layer and a preparation method thereof, so as to improve the long-term stability of the pH sensor and solve the technical problems that conductive polymer materials are easily degraded and have a short service life when used for pH sensing.

[0006] To achieve the above objectives, the present invention provides a flexible pH sensor based on a conductive polymer layer, comprising a three-dimensional flexible substrate and a conductive polymer layer deposited on the surface of the three-dimensional flexible substrate; the conductive polymer layer comprises Ti4O7, sulfur-containing acid ions and a conductive polymer material.

[0007] Furthermore, the Ti4O7 is hydroxylated Ti4O7, and there is a chemical bonding between the hydroxylated Ti4O7 and the sulfur-containing acid ion;

[0008] The sulfur-containing acid radical ions are derived from sulfuric acid, sulfonic acid, or sulfonate, for example, one or more of sulfuric acid, sodium p-toluenesulfonate, sodium polystyrenesulfonate, sodium dodecylbenzenesulfonate, and β-naphthalenesulfonic acid, preferably sodium p-toluenesulfonate.

[0009] Furthermore, the three-dimensional flexible substrate is a three-dimensional flexible conductive substrate, preferably a three-dimensional flexible carbon substrate; the three-dimensional flexible carbon substrate includes carbon nanotubes, graphene, carbon paper, natural carbon fiber, carbon cloth, foam carbon or MXene, preferably foam carbon;

[0010] The conductive polymer material includes one or more of polypyrrole, polyaniline and polythiophene, preferably polypyrrole.

[0011] The present invention also provides a method for preparing a flexible pH sensor based on a conductive polymer layer as described in any of the above, comprising: preparing a deposition solution containing Ti4O7, sulfur-containing acid ions and conductive polymer material monomers, and depositing them on a three-dimensional flexible substrate to obtain a flexible pH sensor.

[0012] Furthermore, the preparation method of the deposition liquid includes: hydroxylating Ti4O7, reacting it with sulfur-containing acid ions to obtain sulfur-containing acid ion-modified Ti4O7, and then adding the monomer corresponding to the conductive polymer material to obtain the deposition liquid.

[0013] Furthermore, the preparation method of the deposition liquid is as follows: methanesulfonic acid is used for the hydroxylation; and the average particle size of the Ti4O7 is 100 to 500 nm.

[0014] Furthermore, the deposition liquid is deposited on the three-dimensional flexible substrate by electrochemical deposition; the electrochemical deposition method uses the three-dimensional flexible substrate as the working electrode, a saturated calomel electrode as the reference electrode, a platinum sheet as the counter electrode, and the deposition liquid as the electrolyte solution.

[0015] Furthermore, the concentration of the conductive polymer monomer in the deposition solution is 0.1-1 mol / L, the concentration of Ti4O7 is 10-50 g / L, and the concentration of the sulfur-containing acid ion is 0.1-5 mol / L. The conductive polymer monomer includes pyrrole, aniline, or thiophene.

[0016] Furthermore, the electrochemical deposition method adopts constant current, constant potential or pulsed electrodeposition, preferably constant current; the power consumed per square centimeter of electrode surface is 8 to 12C.

[0017] Furthermore, the three-dimensional flexible carbon substrate is activated with an activator selected from the group consisting of sulfuric acid, nitric acid, phosphoric acid, potassium hydroxide, potassium carbonate, and zinc chloride; preferably, 4-8 mol / L sulfuric acid. The activation treatment temperature is 80-160°C for 4-8 hours. The three-dimensional flexible carbon substrate can also be activated by physical activation methods, such as plasma etching.

[0018] The method for preparing a flexible pH sensor based on a conductive polymer layer of the present invention specifically comprises:

[0019] (1) A three-dimensional flexible porous carbon substrate with a surface rich in oxygen-containing functional groups was obtained through activation modification;

[0020] (2) preparing dopant particles Ti4O7 powder by Ti reduction method;

[0021] (3) A ternary composite pH sensing electrode consisting of Ti4O7, a conductive polymer layer and a three-dimensional flexible porous carbon substrate was prepared in one step by electrochemical method.

[0022] In some embodiments, step (1) uses a chemical activation method to prepare modified three-dimensional flexible carbon, including: first, ultrasonically cleaning the three-dimensional flexible carbon substrate using deionized water, ethanol, and acetone, respectively, and drying for use. Take 2 to 3 cleaned three-dimensional flexible carbon electrodes and add them to 10 mL of a chemical activator prepared in a certain proportion. After mixing and impregnating for a period of time, transfer them to a 50 mL polytetrafluoroethylene reactor liner, place them at a certain temperature for a certain period of time for hydrothermal reaction, and after cooling to room temperature, take out the sample, rinse it with ethanol and acetone, respectively, and dry it for use, thereby obtaining modified three-dimensional flexible carbon.

[0023] Step (2) of preparing Ti4O7 powder by a Ti reduction method includes: weighing Ti and TiO2 in a certain mass ratio (the mass ratio of TiO2 to Ti is 7:(1-2)), grinding them evenly in an agate mortar, and then placing the mixed powder in a tube furnace, heating it to a certain temperature at a certain heating rate under an Ar atmosphere, and calcining it for a certain time (4-8 hours). After the calcination is completed, the furnace temperature is naturally cooled to room temperature, and the sample powder that has turned black, i.e., the product Ti4O7, is taken out, ground, and packaged for later use.

[0024] In some embodiments, step (2) hydroxylating the prepared Ti4O7 powder and uniformly dispersing the modified Ti4O7 particles with a sulfur-containing acid ion solution specifically comprises:

[0025] The Ti4O7 particles obtained through the above steps are etched and activated with methanesulfonic acid, making their surfaces rich in hydroxyl groups, which serve as active sites for subsequent reactions. Specifically, a certain amount of Ti4O7 particles is added to 100 mL of methanesulfonic acid diluted to a certain concentration and stirred at reflux for 24 hours. The modified Ti4O7 particles are centrifuged, washed with distilled water, and dried in a 60°C oven for 24 hours. A certain amount of modified Ti4O7 particles is then added to a sulfur-containing acid ion solution and stirred. During this process, the hydroxyl groups on the surface of the Ti4O7 particles fully react with the sulfur-containing groups in the solution.

[0026] Preferably, the concentration of Ti4O7 in the synthetic solution is 10-50 g / L, and the concentration of the sulfur-containing acid radical ion p-toluenesulfonic acid is 0.1-5 mol / L.

[0027] In some embodiments, step (3) uses an electrochemical method to uniformly deposit the complex on the modified three-dimensional flexible carbon substrate to obtain a ternary complex pH sensor, specifically comprising:

[0028] Take 100 mL of the sulfur-containing acid radical ion-modified Ti4O7 mixed solution from step (2), add the corresponding monomer of the conductive polymer and introduce N2 for 10 minutes to degas the polymer solution to serve as the electrolyte solution. The synthesis uses a traditional three-electrode system, with the modified three-dimensional flexible carbon prepared in step (1) as the working electrode, a platinum sheet (2×2 cm) as the counter electrode, and a saturated calomel electrode (SCE) with a glass salt bridge as the reference electrode. The electrochemical deposition process is carried out using a Gmary 3000 electrochemical workstation. The entire deposition process is carried out under low-speed stirring. After the deposition is completed, the obtained ternary complex is washed with deionized water and naturally dried for use.

[0029] According to another aspect of the present invention, a pH sensor with long-term stability is provided for the early detection of pH fluctuations and abnormal conditions in implants or on the surface of biological bodies, thereby achieving accurate measurement of pH values ​​in common physiological media and stability for long-term continuous operation in situ or in vivo.

[0030] In general, the above technical solutions conceived by the present invention have the following technical advantages compared with the existing technology:

[0031] 1. According to density functional theory (DFT) calculations, the new ceramic material Ti4O7 can produce strong bonding with various sulfur elements. Therefore, the present invention bonds the new ceramic material Ti4O7 with sulfur-containing acid ions, and the sulfur-containing acid ions then combine with the conductive polymer material through electrostatic interaction, thereby stabilizing the doped ions in the conductive polymer layer, inhibiting the collapse of the conductive polymer layer, effectively delaying the degradation of the conductive polymer layer, and improving long-term stability.

[0032] 2. The conductive polymer layer proposed in this invention comprises TiO, sulfur-containing acid ions, and a conductive polymer material. The conductive polymer material undergoes a reversible protonation-deprotonation reaction. Its conjugated structure allows for the free movement of π electrons within the energy band shared by the entire molecule, resulting in excellent conductivity. This allows for highly sensitive and rapid detection of solution pH. Furthermore, the conductive polymer layer exhibits excellent antibacterial and antioxidant properties, facilitating its application in implantable and wearable healthcare applications.

[0033] 3. After activation and modification, the three-dimensional flexible carbon material has a rich surface of oxygen-containing functional groups that can form hydrogen bonds with N, O, etc. in the conductive polymer layer, which is conducive to the directional arrangement of the conductive polymer chains, thereby improving the electron transfer efficiency and structural stability of the polymer, and further promoting the improvement of conductivity and. At the same time, due to the large specific surface area and high porosity of the three-dimensional flexible carbon material, it has abundant active sites, which can greatly increase the sensing area and sensing sensitivity. In addition, the three-dimensional flexible carbon material also gives the conductive polymer layer pH sensor the advantages of good flexibility and customizable electrode shape and area.

[0034] 4. The pH sensor based on the conductive polymer layer prepared by the present invention improves the stability of the conductive polymer layer by modifying the new ceramic material Ti4O7, so that the pH sensor not only has excellent pH sensing ability and can achieve super-Nernstian response, but also can maintain good response ability after long-term service for 90 days.

[0035] 5. The electrochemical method used in the present invention has a simple preparation and synthesis process, a stable process, and the raw materials used can be directly purchased on the market and are easily available, thus having broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 In the figure, a, b, c, and d are scanning electron microscope images of the novel ceramic material Ti4O7, the activated foam carbon substrate prepared in Examples 1 and 2, the ternary composite electrode in Example 1, and the binary composite electrode in Example 2, respectively.

[0037] Figure 2 This is a graph showing the pH responsiveness changes during 90 days of service in 37°C human body simulation fluid in Examples 1 and 2.

[0038] Figure 3 This is a graph showing the open circuit potential fluctuations during 90 days of service in 37°C human body simulation fluid in Examples 1 and 2.

[0039] Figure 4 These are scanning electron microscope images of Example 1 at different scales after being immersed in human body simulation fluid at 37°C for 90 days.

[0040] Figure 5 These are scanning electron microscope images of Example 2 at different scales after being immersed in human body simulation fluid at 37°C for 90 days. DETAILED DESCRIPTION

[0041] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0042] The flexible pH sensor based on a conductive polymer layer provided by the present invention serves as the main sensing unit in practical applications. The pH sensor is a ternary composite electrode composed of a modified three-dimensional flexible substrate loaded with a new ceramic material Ti4O7 and a conductive polymer layer.

[0043] The present invention preferably uses modified three-dimensional porous flexible carbon materials as conductive supports to support active materials, thereby improving the sensing area, conductivity and stability of the sensing material, and achieving the requirements of flexibility and customizable design appearance of the composite electrode; a new ceramic material Ti4O7 (one of the Magn'eli phases, Ti) with excellent conductivity and dielectric chemical inertness is used. n O 2n-1 , n≥4) as a composite material to enhance the dielectric stability of the conductive polymer layer, thereby greatly improving the long-term stability of the composite pH sensor and solving the technical problems of easy degradation and short service life of conductive polymer materials used in pH sensing.

[0044] The method for preparing a pH sensor based on a conductive polymer layer of the present invention comprises the following steps:

[0045] (1) Preparation of modified three-dimensional flexible carbon materials by chemical activation method;

[0046] (2) preparing Ti4O7 powder by Ti reduction method, then hydroxylating it, and uniformly mixing and dispersing the hydroxylated Ti4O7 particles with sulfur-containing acid radical ion solution for chemical bonding;

[0047] (3) A conductive polymer layer doped with Ti4O7 particles is grown on the modified three-dimensional flexible carbon material prepared in step (1) by an electrochemical method, thereby obtaining a ternary composite pH sensor.

[0048] The electrochemical method uses the modified three-dimensional porous flexible carbon material as the working electrode, a saturated calomel electrode as the reference electrode, a platinum sheet as the counter electrode, and a mixed solution of a conductive polymer monomer, sulfur-containing acid ions, and the novel ceramic material Ti4O7 as the electrolyte solution. The concentration of the conductive polymer monomer in the electrolyte solution is 0.1 to 1 mol / L, the concentration of the Ti4O7 is 10 to 50 g / L, and the concentration of the sulfur-containing acid ions is 0.1 to 1 mol / L.

[0049] When the ternary complex sensing electrode is placed in media with varying pH values, it exhibits different open-circuit potentials, which can be used to monitor changes in the medium's pH. This method can monitor changes in the medium's pH over a 90-day operating period based on the potential, ensuring both accuracy for small-scale pH measurements in physiological media and stability during long-term continuous operation in situ or in vivo. Furthermore, the pH sensor offers advantages such as flexibility, customizable electrode shape and area, and lack of cytotoxicity.

[0050] It should be noted that, because the conductive polymer material itself has conductivity and pH responsiveness, the three-dimensional flexible substrate of the present invention is not limited to three-dimensional flexible carbon materials. That is, by preparing a deposition solution containing Ti4O7, sulfur-containing acid ions, and the corresponding monomer of the conductive polymer material, and depositing it on the three-dimensional flexible substrate, a flexible pH sensor can also achieve long-term stability. When activated three-dimensional flexible carbon materials are preferred, it is conducive to the directional arrangement of the conductive polymer chains, thereby improving the electron transfer efficiency and structural stability of the conductive polymer, and further promoting the improvement of conductivity and stability.

[0051] Example 1

[0052] A pH sensor based on a conductive polymer with long-term stability is prepared by the following method:

[0053] Step 1: Prepare modified activated foam carbon by chemical activation

[0054] First, ultrasonically clean the carbon foam substrate (1×1 cm) using deionized water, ethanol, and acetone, respectively, and dry it for later use. Then, prepare an 8 mol / L H2SO4 aqueous solution, take two to three cleaned carbon foam electrodes, add them to the prepared 10 mL H2SO4 solution, and place them in a 50 mL polytetrafluoroethylene reactor for hydrothermal reaction at 120°C for 4 hours. After cooling to room temperature, remove the sample, rinse it with ethanol and acetone, and dry it to obtain the activated carbon foam electrode for later use.

[0055] Step 2: Prepare Ti4O7 powder using Ti reduction method

[0056] Weigh TiO2 and Ti powder in a mass ratio of 7:1, grind them evenly in an agate mortar, then put the mixed powder into a tube furnace, heat it to 850°C at a certain heating rate in an Ar environment and calcine it for 4 hours. After the calcination is completed, wait for the furnace temperature to cool naturally to room temperature, take out the sample powder that has turned black, that is, the product Ti4O7, and package it after grinding for use. Then add the Ti4O7 particles to 100mL of diluted methanesulfonic acid and stir and reflux for 24 hours. After centrifugation, the modified Ti4O7 particles are washed with distilled water and dried in a 60°C oven for 24 hours. Then 5g of modified Ti4O7 particles are added to 100mL of 0.1M sodium p-toluenesulfonate (pTS) solution (the solvent is water) and stirred. In this process, the hydroxyl groups on the surface of the Ti4O7 particles react with the pTS in the solution. - The reaction is sufficient to form a pTS-Ti4O7 composite solution with strong interaction.

[0057] Step 3: Distill and purify the pyrrole monomer

[0058] Take 100 mL of pyrrole monomer in a 150 mL round-bottom flask, add 2 to 3 zeolites, and purify by distillation. Collect the purified pyrrole solution and store it in a refrigerator in the dark.

[0059] Step 4: Electrochemically deposit the composite uniformly on the activated carbon foam substrate. The resulting ternary composite is designated as Ti4O7+PPy / ACF.

[0060] Take 100 mL of the pTS-Ti4O7 composite solution from step 2, add pyrrole monomer to a concentration of 0.1 M, and degas the polymer solution by passing N2 for 10 minutes to obtain an electrolyte solution. The synthesis uses a traditional three-electrode system, with the activated carbon foam prepared in step 1 as the working electrode, a platinum sheet (2×2 cm) as the counter electrode, and a saturated calomel electrode (SCE) with a glass salt bridge as the reference electrode. The electrochemical deposition process is carried out using a constant current deposition method in a Gmary 3000 electrochemical workstation with a deposition current density of 4 mA cm -2 The deposition time was 2000s. The entire deposition process was carried out with low-speed stirring. After the deposition was completed, the obtained ternary composite was washed with deionized water and naturally dried for later use. The scanning electron microscope image of the prepared ternary composite electrode Ti4O7+PPy / ACF is shown in Figure 2. Figure 1 As shown in c.

[0061] Example 2

[0062] The difference between this embodiment and embodiment 1 is that after the three-dimensional flexible foam carbon substrate is chemically activated, the conductive polymer layer is grown by electrochemical method with only sulfuric acid doped, without doping the new ceramic material Ti4O7 (i.e., the electrolyte solution is composed of only 0.1M conductive polymer pyrrole monomer and 0.1M sodium p-toluenesulfonate). The obtained product is recorded as a binary composite electrode PPy / ACF, and its scanning electron microscope image is shown as follows: Figure 1 As shown in d.

[0063] Test Example 1

[0064] Long-term service behavior of simulated samples in human body simulated fluid at 37°C

[0065] The samples prepared in Examples 1 and 2 were fixed with working electrode clamps and the sides were sealed with silicone rubber, leaving only 1 cm 2 Place the work surface on a plate and then immerse it in 150 mL of human body simulation fluid at 37°C. Replace the fluid with 150 mL of fresh fluid every 7 days to simulate the dynamic body fluids of the human body. The human body simulation fluid is primarily composed of sodium chloride, potassium chloride, magnesium chloride, calcium chloride, sodium bicarbonate, potassium dihydrogen phosphate, and magnesium sulfate. Adjust the prepared solution to pH 7.2-7.4 with 0.1M sodium hydroxide and store at room temperature until use.

[0066] (1) pH responsiveness changes of Examples 1 and 2 in human body simulated fluid:

[0067] The changes in pH responsiveness of Examples 1 and 2 in human body simulation fluid are as follows: Figure 2 As shown, Figures a and c refer to the open circuit potential and linear fitting of Examples 1 and 2 taken out and tested in solutions with different pH values ​​after being immersed for 0, 7, 30, 60, and 90 days, respectively; Figures b and d refer to the slope fluctuations of the electrode potential of Examples 1 and 2 as the pH value changes after being immersed for 0, 7, 30, 60, and 90 days, respectively.

[0068] When polypyrrole undergoes a reversible protonation-deprotonation reaction of nitrogen atoms in a solution, it can be described by the following equation:

[0069]

[0070] The degradation of polypyrrole causes the structure to transform into a quinone structure, accompanied by the removal of doped ions. When the degradation time is long enough, the quinone structure will further hydrolyze and undergo a ring-opening reaction to generate the final degradation products, including C=O, C=N and -CH=CH-. Its electrochemical activity and conductivity will undergo irreversible degradation, resulting in the loss of pH responsiveness. Figure 2 It can be seen that both newly prepared composite electrodes have good performance, but the PPy / ACF electrode loses sensitivity, has poor linear fit, and has large individual differences during the 90-day immersion period (the error bar in Figure d is large). The Ti4O7+PPy / ACF electrode can maintain the Nernst response during the 90-day service period.

[0071] (2) Other response performance changes of Examples 1 and 2 in human body simulation fluid:

[0072] Other responsiveness tests of the two newly prepared composite electrodes in human body simulated fluid, including electrode response time test, repeatability test, reversibility test, interfering ion selectivity test, stability test, etc., all show that both composite electrodes have excellent performance in these aspects. When the same responsiveness test was performed again after 90 days of service, the Ti4O7+PPy / ACF electrode showed no significant difference from before immersion except for a slightly prolonged response time, indicating that it can maintain good performance during the 90-day service period. However, the response time of the PPy / ACF electrode after immersion was significantly longer, and the potential deviation and potential drift were serious.

[0073] (3) Fluctuation of open circuit potential of Examples 1 and 2 in human body simulation fluid:

[0074] The open circuit potential changes of the composite electrode in human body simulated fluid are as follows: Figure 3As shown, the potential variation patterns of the two sensors are basically the same. Within the first seven days, there is an activation period with a continuous potential rise. Then, over a longer period of time, the electrodes experience smaller potential fluctuations. The PPy / ACF electrode fluctuates within 20mV over 60 days, while the Ti4O7+PPy / ACF electrode fluctuates within 17mV over a longer period of 80 days. The error bars for the Ti4O7+PPy / ACF electrode also reflect smaller individual differences between the electrodes within the group. This indicates that the conductive polymer layer ternary composite pH sensor of the present invention has basically no sensitivity loss within 90 days, and the performance test meets the requirements.

[0075] Test Example 2

[0076] The morphology of Examples 1 and 2 after being immersed in 37°C human body simulation fluid for different times

[0077] The surface morphology of the composite electrode after being immersed in human body simulation fluid for 90 days was photographed by scanning electron microscope. Figure 4 and 5 As shown in the figure, compared with the PPy / ACF electrode, the PPy still maintains its original morphology and a large amount of Ti4O7 powder remains on the surface of the Ti4O7+PPy / ACF electrode, indicating that the electrode has good integrity.

[0078] In summary, the conductive polymer layer-based pH sensor prepared by the present invention not only has excellent pH sensing capabilities, achieving a super-Nernstian response and resistance to ionic interference, but also exhibits excellent response time, electrode repeatability, reversibility, and stability. Furthermore, after 90 days of long-term service, the electrode still maintains good response capabilities, with a response slope maintained at 59 mV / pH or above. Therefore, the pH sensor of the present invention can monitor changes in pH based on different potential values ​​over a period of up to 90 days, achieving accurate pH measurement in common physiological media and stable operation for long periods of time in situ or in vivo.

[0079] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A flexible pH sensor based on a conductive polymer layer, characterized in that: It includes a three-dimensional flexible substrate and a conductive polymer layer deposited on the surface of the three-dimensional flexible substrate; the conductive polymer layer includes Ti4O7, sulfur-containing acid ions and conductive polymer materials; The Ti4O7 is hydroxylated Ti4O7, and there is a chemical bonding between the hydroxylated Ti4O7 and the sulfur-containing acid ions; The sulfur-containing acid radical ions are derived from one or more of sulfuric acid, sodium p-toluenesulfonate, sodium polystyrenesulfonate, sodium dodecylbenzenesulfonate, and β-naphthalenesulfonic acid.

2. The flexible pH sensor based on a conductive polymer layer according to claim 1, characterized in that: The sulfur-containing acid radical ion is sodium p-toluenesulfonate.

3. The flexible pH sensor based on a conductive polymer layer according to claim 1, characterized in that: The three-dimensional flexible substrate is a three-dimensional flexible conductive substrate.

4. The flexible pH sensor based on a conductive polymer layer according to claim 3, characterized in that: The three-dimensional flexible conductive substrate is a three-dimensional flexible carbon substrate, and the three-dimensional flexible carbon substrate is a carbon nanotube, graphene, carbon paper, natural carbon fiber, carbon cloth, foam carbon or MXene material; The conductive polymer material is one or more of polypyrrole, polyaniline and polythiophene.

5. The flexible pH sensor based on a conductive polymer layer according to claim 4, characterized in that: The three-dimensional flexible carbon substrate is foam carbon; The conductive polymer material is polypyrrole.

6. A method for preparing a flexible pH sensor based on a conductive polymer layer according to any one of claims 1 to 5, characterized in that: include: A deposition solution containing Ti4O7, sulfur-containing acid ions, and monomers corresponding to conductive polymer materials is prepared and deposited on a three-dimensional flexible substrate to obtain a flexible pH sensor; Ti4O7 is hydroxylated and then reacted with sulfur-containing acid radical ions to obtain sulfur-containing acid radical ion-modified Ti4O7, and then a monomer corresponding to the conductive polymer material is added to obtain a deposition solution.

7. The preparation method according to claim 6, characterized in that The hydroxylation is carried out using methanesulfonic acid; the average particle size of the Ti4O7 is 100 to 500 nm.

8. The preparation method according to claim 6, characterized in that In the deposition solution, the concentration of the monomer corresponding to the conductive polymer material is 0.1 to 1 mol / L, the concentration of the Ti4O7 is 10 to 50 g / L, and the concentration of the sulfur-containing acid radical ion is 0.1 to 5 mol / L.

9. The preparation method according to any one of claims 6 to 8, characterized in that The deposition liquid is deposited on the three-dimensional flexible substrate by electrochemical deposition; the electrochemical deposition method uses the three-dimensional flexible substrate as a working electrode, a saturated calomel electrode as a reference electrode, a platinum sheet as a counter electrode, and the deposition liquid as an electrolyte solution.

10. The preparation method according to claim 9, characterized in that The electrochemical deposition method adopts constant current, constant potential or pulse electrodeposition, and the power consumption per square centimeter of electrode surface is 8 to 12 C.

11. The preparation method according to claim 10, characterized in that: The electrochemical deposition method adopts constant current.

12. The preparation method according to claim 6, characterized in that The three-dimensional flexible substrate is a substrate that has been activated by an activator, and the activator is one of sulfuric acid, nitric acid, phosphoric acid, potassium hydroxide, potassium carbonate, and zinc chloride; the activation treatment temperature is 80 to 160°C and the time is 4 to 8 hours.

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