Flexible ph sensor and measurement system

Abstract

A flexible pH sensor and a measurement system, belonging to the technical field of sensors. Using a material that does not react with an electrolyte, mixed with a metal, an anode substrate is printed, and by means of an electrochemical method, one-step synthesis of a metal-doped polyaniline composite material is implemented. By means of controlling the metal content, the doping amount of metal ions in the polyaniline can be changed. Adding metal increases the conductivity of the anode substrate, which facilitates deposition of polyaniline. The one-step method for preparing a polyaniline composite material is simple, low-cost, and pollution-free; compared with pure polyaniline, the composite material has improved sensitivity. The metal-doped polyaniline composite material is used in a pH sensor for the first time, thus implementing a wide pH measurement range (2-12) and a high bending stability. The flexible pH sensor can be used in saliva pH measurement, and to measure the freshness of fresh food.

Description

Flexible pH sensor and detection system Technical Field

[0001] The invention relates to a flexible pH sensor and a detection system, belonging to the technical field of sensors. Background Art

[0002] A flexible pH sensor is a sensor capable of detecting the acidity or alkalinity of a solution or medium. It consists of a pH-sensitive electrode and a pH reference electrode. The pH-sensitive electrode, as the sensor's core component, is made from a flexible substrate and sensitive materials. Its detection principle is that the sensitive material on the pH-sensitive electrode reacts with hydrogen ions, generating a potential difference proportional to the hydrogen ion concentration (i.e., the pH value). The pH value of the solution or medium is then determined based on the reference potential provided by the pH reference electrode. Due to their excellent flexibility, flexible pH sensors can adapt to applications with different shapes and surfaces. Such sensors are commonly used in fields such as biomedicine, the food industry, and environmental monitoring, particularly for detecting pH values ​​on curved or irregular surfaces.

[0003] Existing flexible pH sensors are typically made of metal oxides. However, because metal oxides are typically added in the form of solid particles, the resulting pH sensors exhibit poor bending properties and require a complex preparation process. Polyaniline (PANI) is a conductive polymer whose nitrogen-containing monomer units can accept or release protons (H+) at varying pH values. In acidic environments, the nitrogen atoms of PANI can be protonated to form positively charged NH+ groups, which induce electrostatic repulsion between polymer chains, causing the polymer to swell and increase its conductivity. Conversely, in alkaline environments, protons are released, reducing electrostatic repulsion between polymer chains and causing the polymer to shrink, reducing conductivity. Furthermore, as a polymer material, PANI exhibits excellent flexibility and processability, and can be easily synthesized through various chemical or electrochemical pathways, making it suitable for use in curved and bendable flexible sensor structures.

[0004] Although polyaniline (PAI) exhibits superior conductivity and pH sensing performance, along with greater flexibility, lower production cost, simpler preparation methods, and higher pH sensing performance compared to metal oxides, single-material PAI suffers from low pH sensitivity. Consequently, current research on PAI-based pH sensors has largely focused on composite materials. Existing PAI-based pH sensors utilize two composite materials. One is obtained by doping PAI with metal oxides. While metal oxides improve the conductivity of PAI-based pH sensors to a certain extent, the preparation methods for PAI-doped PAI (e.g., electrochemical polymerization, sol-gel, and hydrothermal synthesis) are complex and costly, and the resulting pH sensors exhibit poor bending properties. Another approach involves doping PAI with metal ions, with silver ions being a preferred choice due to their high conductivity and antibacterial properties. Currently, the main methods for doping silver ions are to add silver nitrate to the electrolyte solution or to soak the prepared polyaniline in the silver nitrate solution. However, both schemes use silver nitrate as the source of silver ions. Silver nitrate is highly corrosive and toxic, and is a controlled substance. It is not conducive to experimental safety and environmental protection, and cannot be used in the food industry. Summary of the Invention

[0005] In order to solve at least one of the above problems, the present invention provides a flexible pH sensor and detection system, the technical solution of which is as follows:

[0006] A first object of the present invention is to provide a method for preparing a flexible pH sensor, wherein the flexible pH sensor comprises a pH sensitive electrode and a pH reference electrode; wherein the preparation of the pH sensitive electrode comprises:

[0007] Step (1): preparing a first electrode using a composite conductive material as a conductive layer and a flexible film as a substrate, wherein the composite conductive material is composed of two conductive materials, which are respectively denoted as conductive material A and conductive material B;

[0008] Step (2): Prepare an electrolyte solution containing acid and aniline, use the first electrode prepared in step (1) as the working electrode, combine with a reference electrode and an auxiliary electrode, use cyclic voltammetry to prepare a polyaniline / cation composite material, and dry it to obtain a pH sensitive electrode.

[0009] In one embodiment, the conductive material A is a material that does not react with the electrolyte and serves as a growth substrate for polyaniline; the conductive material B is an insoluble and easily electrolyzed material that is oxidized when voltage is applied to provide cations for polyaniline.

[0010] In one embodiment, the material that does not react with the electrolyte is carbon, FTO, platinum, and gold.

[0011] In one embodiment, the insoluble and easily electrolytic material is one or more of silver, gold, aluminum, iron, tungsten, zinc and calcium; further, the insoluble and easily electrolytic material is in the form of powder, slurry or ion in solution.

[0012] In one embodiment, the mass ratio of the material that does not react with the electrolyte to the insoluble and easily electrolyzed material is 3 to 20:1.

[0013] In one embodiment, the acid in the electrolyte solution prepared in step (2) is one of sulfuric acid, hydrochloric acid, phosphoric acid, oxalic acid, dodecylbenzenesulfonic acid, and salicylic acid.

[0014] In one embodiment, when the acid in the electrolyte solution prepared in step (2) is sulfuric acid, the content of sulfuric acid is 0.15-0.7 mol / L, and the content of aniline is 0.15-0.7 mol / L.

[0015] In one embodiment, the reference electrode in step (2) is one of mercurous sulfate, silver / silver chloride, calomel electrode, mercury / mercuric oxide, and copper / copper sulfate.

[0016] In one embodiment, the auxiliary electrode in step (2) is one of platinum wire, nickel, tungsten, lead, and glassy carbon.

[0017] In one embodiment, the conditions of the cyclic voltammetry in step (2) are a voltage range of -0.2-1.2 V, a scan rate of 10-100 mV / s, and a cycle number of more than 4 times.

[0018] In one embodiment, the drying condition in step (2) is drying in an oven at a temperature less than 150°C.

[0019] In one embodiment, the preparation process of the pH reference electrode is as follows: a flexible film is used as a substrate, a conductive material is used to prepare a second electrode, the second electrode is used as a working electrode, silver / silver chloride is used as a reference electrode, and a platinum wire is used as an auxiliary electrode. In a solution containing hydrochloric acid, a silver / silver chloride reference electrode is prepared using cyclic voltammetry; then, polyvinyl alcohol and potassium chloride are mixed, stirred, and drop-coated on the silver / silver chloride reference electrode, and the mixture is frozen to obtain a silver / silver chloride reference electrode covered with a gel electrolyte, and dried to obtain a pH reference electrode.

[0020] In one embodiment, the content of hydrochloric acid used in the preparation process of the pH reference electrode is 0.098 mol / L.

[0021] In one embodiment, during the preparation of the pH reference electrode, the reference electrode is commercial silver / silver chloride, silver / silver chloride, calomel electrode, mercury / mercuric oxide, or copper / copper sulfate.

[0022] In one embodiment, during the preparation of the pH reference electrode, the auxiliary electrode is platinum wire, nickel, tungsten, lead or glassy carbon.

[0023] In one embodiment, the cyclic voltammetry conditions are a voltage range of 0-0.2 V, a scan rate of 20-40 mV / s, and 2-4 cycles.

[0024] In one embodiment, the mass ratio of the polyvinyl alcohol to potassium chloride is 0.5-1.5:1.

[0025] In one embodiment, the stirring condition is stirring at 75-85° C. for 3-5 hours.

[0026] In one embodiment, the freezing is performed at -26 to -24°C for 4 to 6 hours to obtain a silver / silver chloride reference electrode covered with a gel electrolyte, and the drying is performed in an oven at 70°C.

[0027] The second object of the present invention is to provide a flexible pH sensor prepared by the above preparation method.

[0028] The third object of the present invention is to provide a flexible pH detection system, which comprises the above-mentioned flexible pH sensor, external circuit, program development and interface;

[0029] The external circuit connects the pH sensor and the analog-to-digital conversion module with an external wire, and the connection is fixed by spot welding. The analog-to-digital conversion module is connected to the development board through a wire, and the analog quantity is transmitted to the development board and converted into a data quantity;

[0030] The program development and interface is to process the data volume and output it as pH value, establish a connection with the mobile phone via Wi-Fi, and develop and design the mobile phone interface to display the pH value result.

[0031] A fourth object of the present invention is to provide a pH sensor paper, wherein the pH sensor paper is prepared based on the above-mentioned flexible pH sensor.

[0032] A fifth object of the present invention is to provide an application of the flexible pH sensor described above in detecting saliva pH to reflect oral health status and the freshness of fresh food.

[0033] The beneficial effects of the present invention are:

[0034] The present invention uses a composite conductive material composed of a material that does not react with the electrolyte and an insoluble, easily electrolyzed metal to print a pH-sensitive electrode substrate. This allows for the one-step synthesis of a metal-ion-doped polyaniline composite material via an electrochemical method. The metal content is controlled to vary the metal ion doping level in the polyaniline. During the electrochemical synthesis process, the composite conductive material mixed substrate serves as a working electrode, where an oxidation reaction occurs, converting aniline in the electrolyte solution into polyaniline. Simultaneously, the metal element in the mixed substrate is oxidized into metal ions that enter the electrolyte solution. During the polyaniline synthesis process, the metal ions are doped onto the imine nitrogen atoms of the polyaniline and deposited on the working electrode along with the polyaniline. Increasing the doped metal content increases the amount of oxidized metal, leading to an increase in the metal ion doping on the polyaniline, which in turn affects the pH sensing performance of the polyaniline. The addition of the metal increases the conductivity of the anode substrate, facilitating the deposition of the polyaniline. This one-step method for preparing the polyaniline composite material is simpler, more cost-effective, and pollution-free. The pH sensitivity of pure polyaniline is 52.47 mV / pH, and the reaction time from pH 4 to 8 is 41 seconds. The pH sensitivity can be effectively improved after doping with metal ions, and the reaction time is significantly reduced. Among them, the relative pH sensitivity after doping with silver ions is 130.2%, and the reaction time of pH 4-8 is 10s.

[0035] The material prepared by this invention was first applied to a pH sensor, achieving a wide pH detection range (2-12) and high bending stability. Finally, it was integrated into a fully solid-state pH sensor strip. Through signal processing and transmission circuitry, the pH data can be displayed on a mobile phone. It has also been successfully applied to saliva pH measurement to reflect oral health and to determine the freshness of fresh food. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0037] FIG1 is a flow chart of the preparation of the flexible pH sensor of the present invention.

[0038] FIG2 is a schematic diagram of the all-solid-state system of the present invention. DETAILED DESCRIPTION

[0039] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0040] The test methods involved in this application are as follows:

[0041] (1) Relative sensitivity:

[0042] The potential signal was collected by immersing the sensor in buffer solutions with pH values ​​of 2, 4, 6, 8, 10, and 12 respectively. The potential signal was obtained by measuring the potential difference between the working electrode and the reference electrode using an electrochemical workstation. The potential readings of the sensor at each pH value were recorded and linear fitting was performed. The slope of the straight line obtained was the sensitivity of the sensor, and the unit was mV / pH.

[0043] The sensitivity of the sensor prepared on the pure carbon substrate was taken as 100%, and the sensitivities of the sensors prepared in other examples were compared with it to obtain different percentages as relative sensitivity values.

[0044] (2) pH detection range:

[0045] When the change in the measured potential value is linearly related to the change in the pH value, the pH value is considered to be within the measurable pH range of the sensor, and the maximum measurable range is considered to be the pH detection range.

[0046] (3) High bending stability:

[0047] Using a stepper motor, the sensor is attached to the center of a transparent film and driven by the motor for cyclic bending tests at a fixed bending angle. The sensor is bent a certain number of times at a specific angle on a constructed platform and then placed in buffer solutions of varying pH values. Potential measurements are performed to record the potential at each state. The bending stability of the sensor is evaluated by comparing the change in potential at different bending times and angles at the same pH.

[0048] (4) Response time:

[0049] The response time of a pH sensor is defined as the time it takes for the potential of the sensor to reach 90% of its equilibrium value after being immersed in buffer solutions of varying pH values. The test was conducted over a pH range of 4-8-4. The response time of pure polyaniline from pH 4 to 8 was 41 seconds, and from pH 8 to 4 was 48 seconds.

[0050] Example 1:

[0051] This embodiment provides a method for preparing a flexible pH sensor, which includes a pH sensitive electrode and a pH reference electrode. Referring to FIG1 , the method includes the following steps:

[0052] Step (1): printing electrodes;

[0053] As shown in Figure 1 (a), a composite slurry of silver paste doped with 10% (w / w) in carbon paste is printed as the first electrode, and then the silver paste is stirred and overprinted to form the second electrode. The printing substrate is a flexible PET film; that is, the first electrode is obtained by printing the composite slurry of carbon paste and silver paste on the flexible PET film, and the second electrode is obtained by printing with silver paste.

[0054] Step (2): preparing a pH sensitive electrode;

[0055] As shown in Figure 1 (b), 50 ml of an electrolyte solution containing 2.54 g of sulfuric acid and 1.17 g of aniline was prepared. In an electrochemical workstation, the first electrode prepared in step (1) was used as the working electrode, mercurous sulfate was used as the reference electrode, and a platinum wire was used as the auxiliary electrode. Cyclic voltammetry was used to prepare a polyaniline / silver ion composite material. The voltage range was set to -0.2-1.2 V, the scan rate was set to 40-80 mV / s, and the number of cycles was set to 6-12 times. The polyaniline / silver ion composite material was dried in an oven at 50-100°C to obtain a pH-sensitive electrode.

[0056] In this embodiment, multiple experiments were conducted with different values ​​for the scan rate, number of cycles, and subsequent oven temperature in the cyclic voltammetry during the preparation of the pH-sensitive electrode, and the average values ​​were finally taken as shown in Table 1.

[0057] During the experiment, it was found that the scan speed, cycle speed and subsequent oven temperature in cyclic voltammetry have little effect on the preparation of polyaniline / silver ion composite materials. Therefore, the scan speed can be set to 10-100 mV / s, the number of cycles can be greater than 4 times, and the subsequent oven temperature can be set to no higher than 150°C.

[0058] Step (3): preparing a pH reference electrode;

[0059] As shown in Figure 1 (c), the second electrode prepared in step (1) was used as the working electrode, commercial silver / silver chloride was used as the reference electrode, and platinum wire was used as the auxiliary electrode. In a 50 ml solution containing 0.48 g of hydrochloric acid, the voltage range was set to 0-0.2 V, the scan rate was 40 mV / s, and the cycle was repeated 4 times. As shown in Figure 1 (d), polyvinyl alcohol and potassium chloride were then mixed in a 1:1 (w / w) ratio, stirred at 80°C for 4 h, drop-coated on the reference electrode, and frozen at -26°C for 4 h to obtain a silver / silver chloride reference electrode covered with a gel electrolyte, which was then dried in an oven at 70°C to prepare a pH reference electrode.

[0060] A flexible pH sensor is prepared using the pH sensitive electrode obtained in step (2) and the pH reference electrode obtained in step (3).

[0061] Example 2:

[0062] This embodiment provides a method for preparing a flexible pH sensor, which includes a pH sensitive electrode and a pH reference electrode. Referring to FIG1 , the method includes the following steps:

[0063] Step (1): printing electrodes;

[0064] As shown in Figure 1 (a), a composite slurry of silver paste doped with 20% (w / w) in carbon paste is printed as the first electrode, and then the silver paste is stirred and overprinted to form the second electrode. The printing substrate is a flexible PET film; that is, the first electrode is obtained by printing the composite slurry of carbon paste and silver paste on the flexible PET film, and the second electrode is obtained by printing with silver paste.

[0065] Step (2): preparing a pH sensitive electrode;

[0066] As shown in FIG1 (b), 50 ml of an electrolyte solution containing 2.54 g of sulfuric acid and 1.17 g of aniline was prepared. In an electrochemical workstation, the first electrode prepared in step (1) was used as a working electrode, mercurous sulfate was used as a reference electrode, and a platinum wire was used as an auxiliary electrode. Cyclic voltammetry was used to prepare a polyaniline / silver ion composite material. The voltage range was set to -0.2-1.2 V, the scan rate was set to 40-80 mV / s, and the number of cycles was set to 6-12 times. The polyaniline / silver ion composite material was dried in an oven at 50-100°C to obtain a pH-sensitive electrode.

[0067] In this embodiment, multiple experiments were conducted with different values ​​for the scan rate, number of cycles, and subsequent oven temperature in the cyclic voltammetry during the preparation of the pH-sensitive electrode, and the average values ​​were finally taken as shown in Table 1.

[0068] Step (3): preparing a pH reference electrode;

[0069] As shown in Figure 1 (c), the second electrode prepared in step (1) was used as the working electrode, commercial silver / silver chloride was used as the reference electrode, and platinum wire was used as the auxiliary electrode. In a 50ml solution containing 0.48g of hydrochloric acid, the voltage range was set to 0-0.2V, the scanning speed was 40mV / s, and the cycle was repeated 4 times; as shown in Figure 1 (d), polyvinyl alcohol and potassium chloride were then mixed in a 1:1 (w / w) ratio, stirred at 80℃ for 4h, drop-coated on the reference electrode, and frozen at -24℃ for 6h to obtain a silver / silver chloride reference electrode covered with gel electrolyte, which was then dried in an oven at 70℃ to prepare a pH reference electrode.

[0070] A flexible pH sensor is prepared using the pH sensitive electrode obtained in step (2) and the pH reference electrode obtained in step (3).

[0071] Example 3:

[0072] This embodiment provides a method for preparing a flexible pH sensor, which includes a pH sensitive electrode and a pH reference electrode. Referring to FIG1 , the method includes the following steps:

[0073] Step (1): printing electrodes;

[0074] As shown in Figure 1 (a), a composite slurry of silver paste doped with 10% (w / w) in carbon paste is printed as the first electrode, and then the silver paste is stirred and overprinted to form the second electrode. The printing substrate is a flexible PET film; that is, the first electrode is obtained by printing the composite slurry of carbon paste and silver paste on the flexible PET film, and the second electrode is obtained by printing with silver paste.

[0075] Step (2): preparing a pH sensitive electrode;

[0076] As shown in FIG1 (b), 50 ml of an electrolyte solution containing 0.74 g of sulfuric acid and 0.71 g of aniline was prepared. In an electrochemical workstation, the first electrode prepared in step (1) was used as a working electrode, mercurous sulfate was used as a reference electrode, and a platinum wire was used as an auxiliary electrode. Cyclic voltammetry was used to prepare a polyaniline / silver ion composite material. The voltage range was set to -0.2-1.2 V, the scan rate was set to 40-80 mV / s, and the number of cycles was set to 6-12 times. The polyaniline / silver ion composite material was dried in an oven at 50-100°C to obtain a pH-sensitive electrode.

[0077] In this embodiment, multiple experiments were conducted with different values ​​for the scan rate, number of cycles, and subsequent oven temperature in the cyclic voltammetry during the preparation of the pH-sensitive electrode, and the average values ​​were finally taken as shown in Table 1.

[0078] Step (3): preparing a pH reference electrode;

[0079] As shown in Figure 1 (c), the second electrode prepared in step (1) was used as the working electrode, commercial silver / silver chloride was used as the reference electrode, and platinum wire was used as the auxiliary electrode. In a 50ml solution containing 0.48g of hydrochloric acid, the voltage range was set to 0-0.2V, the scanning speed was 40mV / s, and the cycle was repeated 4 times; as shown in Figure 1 (d), polyvinyl alcohol and potassium chloride were then mixed in a 1:1 (w / w) ratio, stirred at 80℃ for 4h, drop-coated on the reference electrode, and frozen at -24℃ for 6h to obtain a silver / silver chloride reference electrode covered with gel electrolyte, which was then dried in an oven at 70℃ to prepare a pH reference electrode.

[0080] A flexible pH sensor is prepared using the pH sensitive electrode obtained in step (2) and the pH reference electrode obtained in step (3).

[0081] Example 4:

[0082] This embodiment provides a method for preparing a flexible pH sensor, which includes a pH sensitive electrode and a pH reference electrode. Referring to FIG1 , the method includes the following steps:

[0083] Step (1): printing electrodes;

[0084] As shown in Figure 1 (a), 10% (w / w) tungsten powder is doped into carbon paste and printed as the first electrode, and then silver paste is stirred and overprinted to form the second electrode. The printing substrate is a flexible PET film; that is, the first electrode is obtained by printing a composite paste of carbon paste and tungsten powder on the flexible PET film, and the second electrode is obtained by printing with silver paste.

[0085] Step (2): preparing a pH sensitive electrode;

[0086] As shown in FIG1 (b), 50 ml of an electrolyte solution containing 1.27 g of sulfuric acid and 2.33 g of aniline was prepared. In an electrochemical workstation, the first electrode prepared in step (1) was used as a working electrode, mercurous sulfate was used as a reference electrode, and a platinum wire was used as an auxiliary electrode. Cyclic voltammetry was used to prepare a polyaniline / tungsten ion composite material. The voltage range was set to -0.2-1.2 V, the scan rate was set to 40-80 mV / s, and the number of cycles was set to 6-12 times. The polyaniline / tungsten ion composite material was dried in an oven at 50-100°C to obtain a pH-sensitive electrode.

[0087] In this embodiment, multiple experiments were conducted with different values ​​for the scan rate, number of cycles, and subsequent oven temperature in the cyclic voltammetry during the preparation of the pH-sensitive electrode, and the average values ​​were finally taken as shown in Table 1.

[0088] Step (3): preparing a pH reference electrode;

[0089] As shown in Figure 1 (c), the second electrode prepared in step (1) was used as the working electrode, commercial silver / silver chloride was used as the reference electrode, and platinum wire was used as the auxiliary electrode. In a 50ml solution containing 0.48g of hydrochloric acid, the voltage range was set to 0-0.2V, the scanning speed was 20mV / s, and the cycle was repeated twice; as shown in Figure 1 (d), polyvinyl alcohol and potassium chloride were then mixed in a 1:1 (w / w) ratio, stirred at 80°C for 4h, drop-coated on the reference electrode, and frozen at -26°C for 4h to obtain a silver / silver chloride reference electrode covered with a gel electrolyte, which was then dried in an oven at 70°C to prepare a pH reference electrode.

[0090] A flexible pH sensor is prepared using the pH sensitive electrode obtained in step (2) and the pH reference electrode obtained in step (3).

[0091] Example 5:

[0092] This embodiment provides a method for preparing a flexible pH sensor, which includes a pH sensitive electrode and a pH reference electrode. Referring to FIG1 , the method includes the following steps:

[0093] Step (1): printing electrodes;

[0094] As shown in Figure 1 (a), 10% (w / w) zinc powder doped in carbon paste is printed as the first electrode, and then silver paste is stirred and overprinted to form the second electrode. The printing substrate is a flexible PET film; that is, the first electrode is obtained by printing a composite slurry of carbon paste and zinc powder on the flexible PET film, and the second electrode is obtained by printing with silver paste.

[0095] Step (2): preparing a pH sensitive electrode;

[0096] As shown in FIG1 (b), 50 ml of an electrolyte solution containing 1.27 g of sulfuric acid and 2.33 g of aniline was prepared. In an electrochemical workstation, the first electrode prepared in step (1) was used as a working electrode, mercurous sulfate was used as a reference electrode, and a platinum wire was used as an auxiliary electrode. Cyclic voltammetry was used to prepare a polyaniline / zinc ion composite material. The voltage range was set to -0.2-1.2 V, the scan rate was set to 40-80 mV / s, and the number of cycles was set to 6-12 times. The polyaniline / zinc ion composite material was dried in an oven at 50-100°C to obtain a pH-sensitive electrode.

[0097] In this embodiment, multiple experiments were conducted with different values ​​for the scan rate, number of cycles, and subsequent oven temperature in the cyclic voltammetry during the preparation of the pH-sensitive electrode, and the average values ​​were finally taken as shown in Table 1.

[0098] Step (3): preparing a pH reference electrode;

[0099] As shown in Figure 1 (c), the second electrode prepared in step (1) was used as the working electrode, commercial silver / silver chloride was used as the reference electrode, and platinum wire was used as the auxiliary electrode. In a 50ml solution containing 0.48g of hydrochloric acid, the voltage range was set to 0-0.2V, the scanning speed was 20mV / s, and the cycle was repeated twice; as shown in Figure 1 (d), polyvinyl alcohol and potassium chloride were then mixed in a 1:1 (w / w) ratio, stirred at 80°C for 4h, drop-coated on the reference electrode, and frozen at -26°C for 4h to obtain a silver / silver chloride reference electrode covered with a gel electrolyte, which was then dried in an oven at 70°C to prepare a pH reference electrode.

[0100] A flexible pH sensor is prepared using the pH sensitive electrode obtained in step (2) and the pH reference electrode obtained in step (3).

[0101] Example 6:

[0102] This embodiment provides a method for preparing a flexible pH sensor, which includes a pH sensitive electrode and a pH reference electrode. Referring to FIG1 , the method includes the following steps:

[0103] Step (1): printing electrodes;

[0104] As shown in Figure 1 (a), carbon paste is printed as the first electrode, and then silver paste is stirred and overprinted to form the second electrode. The printing substrate is a flexible PET film; that is, the first electrode is obtained by printing carbon paste on the flexible PET film, and the second electrode is obtained by printing silver paste.

[0105] Step (2): preparing a pH sensitive electrode;

[0106] As shown in FIG1 (b), a 50 ml electrolyte solution containing 1.27 g sulfuric acid, 2.33 g aniline and 0.56 g calcium chloride was prepared. In an electrochemical workstation, the first electrode prepared in step (1) was used as the working electrode, mercurous sulfate was used as the reference electrode, and platinum wire was used as the auxiliary electrode. Cyclic voltammetry was used to prepare the polyaniline / calcium ion composite material. The voltage range was set to -0.2-1.2 V, the scan rate was set to 40-80 mV / s, and the number of cycles was set to 6-12 times. The polyaniline / calcium ion composite material was dried in an oven at 50-100°C to obtain a pH sensitive electrode.

[0107] In this embodiment, multiple experiments were conducted with different values ​​for the scan rate, number of cycles, and subsequent oven temperature in the cyclic voltammetry during the preparation of the pH-sensitive electrode, and the average values ​​were finally taken as shown in Table 1.

[0108] Step (3): preparing a pH reference electrode;

[0109] As shown in Figure 1 (c), the second electrode prepared in step (1) was used as the working electrode, commercial silver / silver chloride was used as the reference electrode, and platinum wire was used as the auxiliary electrode. In a 50ml solution containing 0.48g of hydrochloric acid, the voltage range was set to 0-0.2V, the scanning speed was 20mV / s, and the cycle was repeated twice; as shown in Figure 1 (d), polyvinyl alcohol and potassium chloride were then mixed in a 1:1 (w / w) ratio, stirred at 80°C for 4h, drop-coated on the reference electrode, and frozen at -26°C for 4h to obtain a silver / silver chloride reference electrode covered with a gel electrolyte, which was then dried in an oven at 70°C to prepare a pH reference electrode.

[0110] A flexible pH sensor is prepared using the pH sensitive electrode obtained in step (2) and the pH reference electrode obtained in step (3).

[0111] Example 7:

[0112] This embodiment provides a method for preparing a flexible pH sensor, which includes a pH sensitive electrode and a pH reference electrode. Referring to FIG1 , the method includes the following steps:

[0113] Step (1): printing electrodes;

[0114] A 100nm gold film was evaporated on a PET substrate as the first electrode, and then a silver paste was stirred and overprinted to form the second electrode. The printing substrate was a flexible PET film.

[0115] Step (2): preparing a pH sensitive electrode;

[0116] As shown in FIG1 (b), 50 ml of an electrolyte solution containing 2.45 g of sulfuric acid and 2.35 g of aniline was prepared. In an electrochemical workstation, the first electrode prepared in step (1) was used as the working electrode, mercurous sulfate was used as the reference electrode, and a platinum wire was used as the auxiliary electrode. Cyclic voltammetry was used to prepare polyaniline. The voltage range was set to -0.2-1.2 V, the scan rate was set to 40-80 mV / s, and the number of cycles was set to 6-12 times. The polyaniline was dried in an oven at 50-100°C to obtain a pH-sensitive electrode.

[0117] In this embodiment, multiple experiments were conducted with different values ​​for the scan rate, number of cycles, and subsequent oven temperature in the cyclic voltammetry during the preparation of the pH-sensitive electrode, and the average values ​​were finally taken as shown in Table 1.

[0118] Step (3): preparing a pH reference electrode;

[0119] As shown in Figure 1 (c), the second electrode prepared in step (1) was used as the working electrode, commercial silver / silver chloride was used as the reference electrode, and platinum wire was used as the auxiliary electrode. In a 50ml solution containing 0.48g of hydrochloric acid, the voltage range was set to 0-0.2V, the scanning speed was 40mV / s, and the cycle was repeated 4 times; as shown in Figure 1 (d), polyvinyl alcohol and potassium chloride were then mixed in a 1:1 (w / w) ratio, stirred at 80℃ for 4h, drop-coated on the reference electrode, and frozen at -24℃ for 6h to obtain a silver / silver chloride reference electrode covered with gel electrolyte, which was then dried in an oven at 70℃ to prepare a pH reference electrode.

[0120] A flexible pH sensor is prepared using the pH sensitive electrode obtained in step (2) and the pH reference electrode obtained in step (3).

[0121] Example 8:

[0122] This embodiment provides a method for preparing a flexible pH sensor, which includes a pH sensitive electrode and a pH reference electrode. Referring to FIG1 , the method includes the following steps:

[0123] Step (1): printing electrodes;

[0124] A 100nm silver film was evaporated on a PET substrate, and a 100nm gold film was evaporated on the original base as the first electrode. Then, the silver paste was stirred and overprinted as the second electrode. The printing substrate was a flexible PET film.

[0125] Step (2): preparing a pH sensitive electrode;

[0126] As shown in FIG1 (b), 50 ml of an electrolyte solution containing 2.45 g of sulfuric acid and 2.35 g of aniline was prepared. In an electrochemical workstation, the first electrode prepared in step (1) was used as a working electrode, mercurous sulfate was used as a reference electrode, and a platinum wire was used as an auxiliary electrode. Cyclic voltammetry was used to prepare a polyaniline / silver ion composite material. The voltage range was set to -0.2-1.2 V, the scan rate was set to 40-80 mV / s, and the number of cycles was set to 6-12 times. The polyaniline / silver ion composite material was dried in an oven at 50-100°C to obtain a pH-sensitive electrode.

[0127] In this embodiment, multiple experiments were conducted with different values ​​for the scan rate, number of cycles, and subsequent oven temperature in the cyclic voltammetry during the preparation of the pH-sensitive electrode, and the average values ​​were finally taken as shown in Table 1.

[0128] Step (3): preparing a pH reference electrode;

[0129] As shown in Figure 1 (c), the second electrode prepared in step (1) was used as the working electrode, commercial silver / silver chloride was used as the reference electrode, and platinum wire was used as the auxiliary electrode. In a 50ml solution containing 0.48g of hydrochloric acid, the voltage range was set to 0-0.2V, the scanning speed was 40mV / s, and the cycle was repeated 4 times; as shown in Figure 1 (d), polyvinyl alcohol and potassium chloride were then mixed in a 1:1 (w / w) ratio, stirred at 80℃ for 4h, drop-coated on the reference electrode, and frozen at -24℃ for 6h to obtain a silver / silver chloride reference electrode covered with gel electrolyte, which was then dried in an oven at 70℃ to prepare a pH reference electrode.

[0130] A flexible pH sensor is prepared using the pH sensitive electrode obtained in step (2) and the pH reference electrode obtained in step (3).

[0131] Comparative Example 1:

[0132] This comparative example provides a method for preparing a flexible pH sensor, which includes a pH sensitive electrode and a pH reference electrode. Referring to FIG1 , the method includes the following steps:

[0133] Step (1): printing electrodes;

[0134] First, a layer of silver paste is printed, and after drying, a layer of carbon paste is printed. The double-layer substrate is used as the first electrode. Then, the silver paste is stirred and overprinted to form the second electrode. The printing substrate is a flexible PET film.

[0135] Step (2): preparing a pH sensitive electrode;

[0136] As shown in FIG1 (b), 50 ml of an electrolyte solution containing 1.27 g of sulfuric acid and 2.33 g of aniline was prepared. In an electrochemical workstation, the first electrode prepared in step (1) was used as a working electrode, mercurous sulfate was used as a reference electrode, and a platinum wire was used as an auxiliary electrode. Cyclic voltammetry was used to prepare a polyaniline / silver ion composite material. The voltage range was set to -0.2-1.2 V, the scan rate was set to 40-80 mV / s, and the number of cycles was set to 6-12 times. The polyaniline / silver ion composite material was dried in an oven at 50-100°C to obtain a pH-sensitive electrode.

[0137] In this embodiment, multiple experiments were conducted with different values ​​for the scan rate, number of cycles, and subsequent oven temperature in the cyclic voltammetry during the preparation of the pH-sensitive electrode, and the average values ​​were finally taken as shown in Table 1.

[0138] Step (3): preparing a pH reference electrode;

[0139] As shown in Figure 1 (c), the second electrode prepared in step (1) was used as the working electrode, commercial silver / silver chloride was used as the reference electrode, and platinum wire was used as the auxiliary electrode. In a 50ml solution containing 0.48g of hydrochloric acid, the voltage range was set to 0-0.2V, the scanning speed was 20mV / s, and the cycle was repeated twice; as shown in Figure 1 (d), polyvinyl alcohol and potassium chloride were then mixed in a 1:1 (w / w) ratio, stirred at 80°C for 4h, drop-coated on the reference electrode, and frozen at -26°C for 4h to obtain a silver / silver chloride reference electrode covered with a gel electrolyte, which was then dried in an oven at 70°C to prepare a pH reference electrode.

[0140] A flexible pH sensor is prepared using the pH sensitive electrode obtained in step (2) and the pH reference electrode obtained in step (3).

[0141] Comparative Example 2:

[0142] This comparative example provides a method for preparing a flexible pH sensor, which includes a pH sensitive electrode and a pH reference electrode. Referring to FIG1 , the method includes the following steps:

[0143] Step (1): printing electrodes;

[0144] As shown in Figure 1 (a), a copper paste composite paste doped with 10% (w / w) in carbon paste was printed as the first electrode, and then silver paste was stirred and overprinted as the second electrode. The printing substrate was a flexible PET film.

[0145] Step (2): preparing a pH sensitive electrode;

[0146] As shown in Figure 1 (b), 50 ml of an electrolyte solution containing 1.27 g of sulfuric acid and 2.33 g of aniline was prepared. In an electrochemical workstation, the first electrode prepared in step (1) was used as the working electrode, mercurous sulfate was used as the reference electrode, and a platinum wire was used as the auxiliary electrode. Cyclic voltammetry was used to prepare a polyaniline / copper ion composite material. The voltage range was set to -0.2-1.2 V, the scan rate was set to 40-80 mV / s, and the number of cycles was set to 6-12 times. The polyaniline / copper ion composite material was dried in an oven at 50-100°C to obtain a pH-sensitive electrode.

[0147] In this embodiment, multiple experiments were conducted with different values ​​for the scan rate, number of cycles, and subsequent oven temperature in the cyclic voltammetry during the preparation of the pH-sensitive electrode, and the average values ​​were finally taken as shown in Table 1.

[0148] Step (3): preparing a pH reference electrode;

[0149] As shown in Figure 1 (c), the second electrode prepared in step (1) was used as the working electrode, commercial silver / silver chloride was used as the reference electrode, and platinum wire was used as the auxiliary electrode. In a 50ml solution containing 0.48g of hydrochloric acid, the voltage range was set to 0-0.2V, the scanning speed was 20mV / s, and the cycle was repeated twice; as shown in Figure 1 (d), polyvinyl alcohol and potassium chloride were then mixed in a 1:1 (w / w) ratio, stirred at 80°C for 4h, drop-coated on the reference electrode, and frozen at -26°C for 4h to obtain a silver / silver chloride reference electrode covered with a gel electrolyte, which was then dried in an oven at 70°C to prepare a pH reference electrode.

[0150] A flexible pH sensor is prepared using the pH sensitive electrode obtained in step (2) and the pH reference electrode obtained in step (3).

[0151] Comparative Example 3:

[0152] This comparative example provides a method for preparing a flexible pH sensor, which includes a pH sensitive electrode and a pH reference electrode. Referring to FIG1 , the method includes the following steps:

[0153] Step (1): printing electrodes;

[0154] As shown in Figure 1 (a), carbon paste is printed as the first electrode, and then silver paste is stirred and overprinted as the second electrode. The printing substrate is a flexible PET film.

[0155] Step (2): preparing a pH sensitive electrode;

[0156] As shown in FIG1 (b), 50 ml of an electrolyte solution containing 1.27 g of sulfuric acid and 2.33 g of aniline was prepared. In an electrochemical workstation, the first electrode prepared in step (1) was used as the working electrode, mercurous sulfate was used as the reference electrode, and a platinum wire was used as the auxiliary electrode. Cyclic voltammetry was used to prepare the polyaniline material. The voltage range was set to -0.2-1.2 V, the scan rate was set to 40-80 mV / s, and the number of cycles was set to 6-12 times. The polyaniline material was dried in an oven at 50-100°C to obtain a pH-sensitive electrode.

[0157] In this embodiment, multiple experiments were conducted with different values ​​for the scan rate, number of cycles, and subsequent oven temperature in the cyclic voltammetry during the preparation of the pH-sensitive electrode, and the average values ​​were finally taken as shown in Table 1.

[0158] Step (3): preparing a pH reference electrode;

[0159] As shown in Figure 1 (c), the second electrode prepared in step (1) was used as the working electrode, commercial silver / silver chloride was used as the reference electrode, and platinum wire was used as the auxiliary electrode. In a 50ml solution containing 0.48g of hydrochloric acid, the voltage range was set to 0-0.2V, the scanning speed was 20mV / s, and the cycle was repeated twice; as shown in Figure 1 (d), polyvinyl alcohol and potassium chloride were then mixed in a 1:1 (w / w) ratio, stirred at 80°C for 4h, drop-coated on the reference electrode, and frozen at -26°C for 4h to obtain a silver / silver chloride reference electrode covered with a gel electrolyte, which was then dried in an oven at 70°C to prepare a pH reference electrode.

[0160] A flexible pH sensor is prepared using the pH sensitive electrode obtained in step (2) and the pH reference electrode obtained in step (3).

[0161] Comparative Example 4:

[0162] This comparative example provides a method for preparing a flexible pH sensor, which includes a pH sensitive electrode and a pH reference electrode. Referring to FIG1 , the method includes the following steps:

[0163] Step (1): printing electrodes;

[0164] As shown in Figure 1 (a), carbon paste is printed as the first electrode, and then silver paste is stirred and overprinted as the second electrode. The printing substrate is a flexible PET film.

[0165] Step (2): preparing a pH sensitive electrode;

[0166] As shown in FIG1 (b), a 50 ml electrolyte solution containing 1.27 g sulfuric acid, 2.33 g aniline and 0.43 g silver nitrate was prepared. In an electrochemical workstation, the first electrode prepared in step (1) was used as the working electrode, mercurous sulfate was used as the reference electrode, and platinum wire was used as the auxiliary electrode. Cyclic voltammetry was used to prepare the polyaniline / silver ion composite material. The voltage range was set to -0.2-1.2 V, the scan rate was set to 40-80 mV / s, and the number of cycles was set to 6-12 times. The polyaniline / silver ion composite material was dried in an oven at 50-100°C to obtain a pH sensitive electrode.

[0167] In this embodiment, multiple experiments were conducted with different values ​​for the scan rate, number of cycles, and subsequent oven temperature in the cyclic voltammetry during the preparation of the pH-sensitive electrode, and the average values ​​were finally taken as shown in Table 1.

[0168] Step (3): preparing a pH reference electrode;

[0169] As shown in Figure 1 (c), the second electrode prepared in step (1) was used as the working electrode, commercial silver / silver chloride was used as the reference electrode, and platinum wire was used as the auxiliary electrode. In a 50ml solution containing 0.48g of hydrochloric acid, the voltage range was set to 0-0.2V, the scanning speed was 20mV / s, and the cycle was repeated twice; as shown in Figure 1 (d), polyvinyl alcohol and potassium chloride were then mixed in a 1:1 (w / w) ratio, stirred at 80°C for 4h, drop-coated on the reference electrode, and frozen at -26°C for 4h to obtain a silver / silver chloride reference electrode covered with a gel electrolyte, which was then dried in an oven at 70°C to prepare a pH reference electrode.

[0170] A flexible pH sensor is prepared using the pH sensitive electrode obtained in step (2) and the pH reference electrode obtained in step (3).

[0171] Test example:

[0172] The flexible pH sensors prepared in each embodiment and each comparative example were tested for sensitivity, pH detection range, and high bending stability. The test results are shown in Table 1:

[0173] The sensitivity of the sensor prepared on the pure carbon substrate in Comparative Example 3 was taken as 100%, and the sensitivities of the sensors prepared in other examples were compared with it to obtain different percentages as relative sensitivity values.

[0174] Table 1

[0175] Relative sensitivity pH detection range high bending stability response time Example 1130.2% 2-12 good 8s Example 2128.3% 2-12 good 10s Example 3108.3% 2-12 good 33s Example 4109.0% 2-12 good 30s Example 5105.5% 2-12 good 47s Example 6101.2% 2-12 good 3s Example 7111.2% 2-12 good 13s Example 8120.7% 2-12 good 4s Comparative Example 1115.1% 2-12 good 11s Comparative Example 262.7% 2-12 good 23s Comparative Example 3100.0% 2-12 good 41s Comparative Example 4115.4% 2-12 good 14s

[0176] As can be seen from Table 1, the pH sensors prepared in each embodiment have good high bending stability (good is defined as the polyaniline does not fall off after bending, and the change after bending is within 10%), the pH detection range can reach 2-12, and the sensitivity and response time are improved compared to those without metal ion doping. Among them, the relative pH sensitivity after silver ion doping is 130.2%, and the reaction time for pH 4-8 is 10 seconds, which is very effective.

[0177] Application examples:

[0178] This application example provides a flexible pH detection system, which includes the above-mentioned flexible pH sensor, external circuit, program development and interface; the external circuit uses external wires to connect the pH sensor and the analog-to-digital conversion module, and the connection is fixed by spot welding. The analog-to-digital conversion module is connected to the analog channel of the development board through wires, and the received pH sensor signal is transmitted to the development board through the analog channel. The data received by the development board is processed and output as a pH value. After being processed by operational amplifier and filtering, the signal is denoised, cached and forwarded through the Wi-Fi module, and finally received by the mobile phone. The pH value result is displayed through the mobile phone interface, as shown in Figure 2.

[0179] During use, the flexible pH sensor is placed in a saliva sample or a fresh food packaging box to obtain the pH value of the sample in real time.

[0180] The program development and interface mainly use some data boxes and curve graphs to display the changes in pH and voltage in real time. At the same time, the operation interface can also provide the response of the pH value in the corresponding scenario and corresponding suggestions. For example, when used to detect the pH value of saliva samples, the operation interface provides the current dental health status and suggestions for different health conditions; when used to detect the pH value of fresh food samples, the operation interface provides the freshness of fresh food at different pH values. At the same time, Wi-Fi transmission can maintain the same communication effect while significantly reducing power consumption and cost compared to Bluetooth transmission. When the test equipment and the mobile phone are in the same wireless local area network, the MQTT protocol is used to connect to the cloud server, and both parties upload data to the cloud server for data communication. The resulting device has a sensitivity of 110.3%, a response time of 10s, and good flexibility and reusability.

[0181] Some steps in the embodiments of the present invention may be implemented using software, and the corresponding software program may be stored in a readable storage medium, such as a CD or a hard disk.

[0182] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a flexible pH sensor, characterized in that: The flexible pH sensor comprises a pH sensitive electrode and a pH reference electrode; wherein the preparation of the pH sensitive electrode comprises: Step (1): preparing a first electrode using a composite conductive material as a conductive layer and a flexible film as a substrate, wherein the composite conductive material is composed of two conductive materials, which are respectively denoted as conductive material A and conductive material B; Step (2): prepare an electrolyte solution containing acid and aniline, use the first electrode prepared in step (1) as a working electrode, combine with a reference electrode and an auxiliary electrode, use cyclic voltammetry to prepare a polyaniline / cation composite material, and dry it to obtain a pH sensitive electrode.

2. The preparation method according to claim 1, characterized in that: The conductive material A is a material that does not react with the electrolyte and serves as a growth substrate for polyaniline; the conductive material B is an insoluble and easily electrolyzed material that is oxidized after voltage is applied and provides cations for polyaniline.

3. The preparation method according to claim 2, characterized in that: The material that does not react with the electrolyte includes carbon, FTO, platinum and gold.

4. The preparation method according to claim 2, characterized in that: The insoluble and easily electrolytic material includes one or more of silver, aluminum, iron, tungsten, zinc and calcium.

5. The preparation method according to claim 2, characterized in that: In the composite conductive material, the mass ratio of the material that does not react with the electrolyte to the insoluble and easily electrolyzed material is 3-20:

1.

6. The preparation method according to claim 1, characterized in that: The acid in step (2) is one of sulfuric acid, hydrochloric acid, phosphoric acid, oxalic acid, dodecylbenzenesulfonic acid and salicylic acid.

7. The preparation method according to claim 1, characterized in that: The conditions of the cyclic voltammetry in step (2) are as follows: a voltage range of -0.2-1.2 V, a scan rate of 10-100 mV / s, and a cycle number of more than 4 times.

8. The preparation method according to claim 1, characterized in that: The drying condition in step (2) is drying in an oven at a temperature less than 150°C.

9. The preparation method according to claim 1, characterized in that: The preparation process of the pH reference electrode is to use a flexible film as a substrate and prepare a second electrode in combination with silver / silver chloride; The silver / silver chloride reference electrode is prepared by cyclic voltammetry in a solution containing hydrochloric acid, using the second electrode as the working electrode, silver / silver chloride as the reference electrode, and platinum wire as the auxiliary electrode; polyvinyl alcohol and potassium chloride are then mixed, stirred, and drop-coated on the silver / silver chloride reference electrode, and the silver / silver chloride reference electrode covered with a gel electrolyte is obtained by freezing, and then dried to obtain a pH reference electrode.

10. A flexible pH sensor, characterized in that: The flexible pH sensor is prepared according to the preparation method according to claims 1 to 9.

11. The flexible pH sensor according to claim 10, characterized in that: The flexible pH sensor can be used for saliva pH detection and freshness detection of fresh food.

12. A flexible pH detection system, characterized in that: The flexible pH detection system comprises the flexible pH sensor of claim 10 and is connected to an external circuit.

13. The system according to claim 12, characterized in that The external circuit includes an analog-to-digital conversion module and a communication module. The flexible sensor is connected to the analog-to-digital conversion module via a wire. The analog-to-digital conversion module is used to convert the data measured by the flexible sensor into a pH value and transmit it to the display terminal via the communication module.

14. The system according to claim 13, characterized in that The communication modules are Wi-Fi communication modules and mobile communication modules.

15. The system according to claim 14, characterized in that The display terminal includes a mobile phone.

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