Intelligent hydrogel pH sensor based on fiber bragg grating and preparation method thereof

Abstract

The invention discloses an intelligent hydrogel pH sensor based on a fiber bragg grating and a preparation method of the intelligent hydrogel pH sensor, and belongs to the technical field of optical fiber sensing. The preparation method comprises the following steps: by taking acrylic acid as a monomer, hydroxyethyl methylacrylate as a comonomer, ethylene glycol methacrylate as a cross-linking agent and benzoin dimethyl ether as a photoinitiator, mixing citric acid and adding graphene, thereby obtaining the pH value sensitive hydrogel. The pH response sensitivity of the sensor can be greatly improved; meanwhile, by adding citric acid, the number of carboxyl groups is increased, the cross-linking speed is increased and enhanced, and the response range of the sensor to pH is enlarged. The intelligent hydrogel pH sensor adopts a fiber bragg grating sensing method, signal transmission of the intelligent hydrogel pH sensor is an optical signal, the intelligent hydrogel pH sensor is not easily interfered by a surrounding electromagnetic field, and due to the fact that circuit elements do not exist, the working stability can be shown under the special complex environments such as fishing-light complementation and the like.

Description

Technical Field

[0001] The invention relates to the field of optical fiber sensing technology, and more particularly to an intelligent hydrogel pH sensor based on optical fiber Bragg grating and a preparation method thereof. Background Art

[0002] In optical fiber sensing, fiber Bragg grating, as a representative of quasi-distributed optical fiber sensors, has been widely used in various application environments such as bridges, tunnels, and substations, and has achieved monitoring of various parameters such as temperature, stress, and vibration. Due to its high precision, anti-interference, and distributed characteristics, optical fiber sensing has become an important means of monitoring various infrastructure and environments, and has demonstrated good sensing performance.

[0003] Taking the monitoring of water bodies in fishery-photovoltaic complementarity as an example, in order to effectively ensure the feasibility of "fishing" in fishery-photovoltaic complementarity, pH value is an important parameter of the water environment. Appropriate pH promotes the growth of fish and shrimp, while inappropriate pH value will inhibit the growth of various microorganisms in the aquaculture water, which will in turn limit the integrity of the entire fish pond ecological chain. Therefore, the pH control level determines the quality of the water environment, and then determines the quality of aquatic product production and the overall quality of the fishery-photovoltaic complementarity project. Timely and accurate grasp and implementation of pH value adjustment is of great significance for the safe and efficient production of fishery-photovoltaic complementarity projects.

[0004] At present, the research on pH detection technology at home and abroad is mainly divided into two categories: one is electrical detection methods, such as hydrogen electrode, ion-sensitive field effect transistor (ISFET), potential electrode, current electrode, ion-sensitive selective electrode (ISE), etc.; the other is non-electrical detection methods, such as optical fiber method, colorimetry, near-infrared spectroscopy, optical scanning image sensing, etc. Considering the particularity of the aquaculture environment in fishery-light complementarity, special requirements are put forward for the precise control of pH, such as anti-interference ability, high humidity resistance, multi-point measurement, etc. Traditional pH sensors can no longer meet these detection requirements.

[0005] Therefore, how to propose an intelligent hydrogel pH sensor based on fiber Bragg grating and a preparation method thereof to achieve rapid and accurate online measurement of water pH in complex environments is a problem that technical personnel in this field urgently need to solve. Summary of the invention

[0006] In view of this, the present invention provides an intelligent hydrogel pH sensor based on fiber Bragg grating and a preparation method thereof, so as to realize rapid and accurate online measurement of water pH in complex environments.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] On the one hand, the present invention provides an intelligent hydrogel pH sensor based on a fiber Bragg grating, comprising a hydrogel pH sensitive coating and a fiber Bragg grating; the hydrogel pH sensitive coating is coated on the surface of the fiber Bragg grating;

[0009] The hydrogel pH sensitive coating is prepared by using acrylic acid as a monomer, hydroxyethyl methacrylate as a copolymer, ethylene glycol methacrylate as a crosslinker, benzoin dimethyl ether as a photoinitiator, mixing citric acid and adding graphene.

[0010] Preferably, the fiber Bragg grating is obtained based on an optical fiber, and the optical fiber is a quartz single-mode germanium-doped optical fiber, comprising an optical fiber cladding, an optical fiber core and a fiber Bragg grating;

[0011] The optical fiber core is covered with an optical fiber cladding, and the optical fiber Bragg grating is embedded in the optical fiber core.

[0012] Preferably, the central wavelength of the fiber Bragg grating is 1550 nm.

[0013] Preferably, the graphene is a graphene microsheet layer, the sheet diameter of the graphene microsheet layer is 100 to 300 nm, and the mass ratio is 0.5% to 1.0%.

[0014] Preferably, the intelligent hydrogel pH sensor is used to construct a pH value experimental testing platform;

[0015] The pH value experimental testing platform comprises a computer, an optical fiber demodulator, and an intelligent hydrogel pH sensor which are connected in sequence. The intelligent hydrogel pH sensor is placed in a pH value testing solution device.

[0016] On the other hand, the present invention also provides a method for preparing an intelligent hydrogel pH sensor based on a fiber Bragg grating, which is used to prepare the intelligent hydrogel pH sensor based on a fiber Bragg grating, and the method comprises the following steps:

[0017] S1: hydrogen loading treatment is performed on the optical fiber, and then the optical fiber cladding in the optical fiber is removed to obtain a fiber Bragg grating;

[0018] S2: preparing a hydrogel pH sensitive coating, wherein the hydrogel pH sensitive coating is composed of a pH sensitive hydrogel, using an electronic balance to weigh hydroxyethyl methacrylate, acrylic acid, ethylene glycol methacrylate, benzoin dimethyl ether, and citric acid in a ratio of 79:11:1:3:4, and weighing graphene in a ratio of acrylic acid:graphene=100:1; then pouring the weighed hydroxyethyl methacrylate, acrylic acid, ethylene glycol methacrylate, benzoin dimethyl ether, citric acid, and graphene into a glass beaker and mixing to obtain a mixed solution; ultrasonically mixing the mixed solution with the aid of an ultrasonic cleaner to obtain a pH sensitive hydrogel; and storing the pH sensitive hydrogel at low temperature to obtain a pH sensitive hydrogel solution;

[0019] S3: irradiating the pH-sensitive hydrogel solution with an ultraviolet light source to obtain a viscous hydrogel;

[0020] S4. Fix the fiber Bragg grating on the bracket and make the fiber Bragg grating in a natural vertical state;

[0021] S5. Coat the viscous hydrogel on the surface of the fiber Bragg grating and wash it with deionized water to obtain an intelligent hydrogel pH sensor.

[0022] Preferably, in S1, chemical etching is used to remove the optical fiber cladding.

[0023] Preferably, in S2, the glass beaker is pre-cleaned with deionized water and wrapped with tin foil.

[0024] It can be known from the above technical scheme that compared with the prior art, the present invention discloses an intelligent hydrogel pH sensor based on fiber Bragg grating and a preparation method thereof, with pH-sensitive hydrogel as the sensitive material, the sensitive material is prepared by mixing acrylic acid as a monomer, hydroxyethyl methacrylate as a copolymer, ethylene glycol methacrylate as a crosslinker, and benzoin dimethyl ether as a photoinitiator, with citric acid and adding graphene. Since graphene has excellent mechanical properties, it can greatly improve the pH response sensitivity of the sensor; at the same time, by adding citric acid to increase the number of carboxyl groups, increase the crosslinking speed, and increase the sensor's responsive range to pH. The intelligent hydrogel pH sensor in the present invention adopts a fiber Bragg grating sensing method, and its signal transmission is an optical signal, which is not easily interfered by the surrounding electromagnetic field, and since there are no circuit elements, the working stability can be demonstrated in special complex environments such as fish-light complementarity. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0026] Figure 1 A structural diagram of the intelligent hydrogel pH sensor provided by the present invention;

[0027] Figure 2 It is a schematic diagram of the pH value experimental testing platform provided by the present invention;

[0028] Figure 3 The present invention provides a flow chart of the preparation and testing of a smart hydrogel pH sensor. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] On the one hand, the embodiment of the present invention provides an intelligent hydrogel pH sensor based on fiber Bragg grating, such as Figure 1 As shown, the intelligent hydrogel pH sensor includes a hydrogel pH sensitive coating and a fiber Bragg grating; the hydrogel pH sensitive coating is coated on the surface of the fiber Bragg grating.

[0031] Among them, the hydrogel pH sensitive coating, that is, the pH sensitive smart hydrogel uses acrylic acid as a monomer, hydroxyethyl methacrylate as a copolymer, ethylene glycol methacrylate as a cross-linking agent, benzoin dimethyl ether as a photoinitiator, mixed citric acid to provide more carboxyl groups, and graphene is doped. The diameter of the graphene microsheet layer is 100 to 300 nm, and the mass ratio is 0.5% to 1.0%.

[0032] In this embodiment, the graphene microsheet layer is graphene. The graphene microsheet layer can be coated on the surface of the hydrogel, has excellent conductivity, mechanical strength and surface hydrophilicity, and can significantly enhance the conductivity, mechanical properties and responsiveness of the hydrogel after being combined with the hydrogel material. In addition to excellent conductivity, the graphene microsheet has a high specific surface area, and after being coated on the surface of the hydrogel, it can improve the charge conduction ability of the hydrogel, thereby enhancing the response of the hydrogel to pH changes.

[0033] Specifically, the fiber Bragg grating is obtained based on an optical fiber, and the optical fiber is a quartz single-mode germanium-doped optical fiber, including an optical fiber cladding, an optical fiber core and a fiber Bragg grating; the optical fiber core is covered with the optical fiber cladding, and the fiber Bragg grating is embedded in the optical fiber core.

[0034] Furthermore, the fiber core is located at the center of the fiber and is mainly responsible for the transmission of light. The fiber cladding surrounds the outside of the core and is made of pure quartz material. Its main function is to confine the light beam in the core through total internal reflection. The fiber Bragg grating is a periodic refractive index modulation structure formed in the core by ultraviolet light irradiation. It is usually located at a specific position in the core and is used to select or reflect light of a specific wavelength.

[0035] In this embodiment, the grating region length of the fiber Bragg grating is 2 cm, and the central wavelength is 1550 nm.

[0036] Furthermore, the smart hydrogel pH sensor is used to construct a pH value experimental test platform, referring to Figure 2 The pH value experimental test platform includes a computer, an optical fiber demodulator, and an intelligent hydrogel pH sensor which are connected in sequence. The intelligent hydrogel pH sensor is placed in a pH value test solution device.

[0037] On the other hand, the present invention also proposes a method for preparing an intelligent hydrogel pH sensor based on a fiber Bragg grating, which is used to prepare the intelligent hydrogel pH sensor based on a fiber Bragg grating. Figure 3 , the preparation method comprises the following steps:

[0038] S1: hydrogen loading treatment is performed on the optical fiber, and then the optical fiber cladding is removed to obtain a fiber Bragg grating. In this step, a chemical etching method is used to remove the optical fiber cladding.

[0039] S2: Preparation of hydrogel pH sensitive coating.

[0040] Taking the preparation of 10ml pH-sensitive hydrogel as an example, 7.9 grams of hydroxyethyl methacrylate, 1.1 grams of acrylic acid, 0.1 grams of ethylene glycol methacrylate and 0.3 grams of benzoin dimethyl ether, 0.4 grams of citric acid, and a certain amount of graphene (acrylic acid: graphene mass ratio is 100: 1) are weighed out using an electronic balance. All chemical raw materials used are produced by Guangzhou Suhao Chemical Co., Ltd., and the electronic balance model is ME204. Then the weighed hydroxyethyl methacrylate, acrylic acid, ethylene glycol methacrylate, benzoin dimethyl ether, citric acid, and graphene are poured into a 25ml glass beaker for mixing. In order not to introduce impurities into the mixed solution and to prevent the mixed solution from being irradiated by external ultraviolet light, the glass beaker needs to be cleaned with deionized water in advance and wrapped with tin foil. Finally, the beaker containing the mixed solution is placed on an ultrasonic cleaning instrument, and the mixed solution is ultrasonically mixed with the help of an ultrasonic cleaning instrument. The ultrasonic mixing time is 20 minutes, and the ultrasonic cleaning instrument model is ElmasonicP30H. After 20 minutes of ultrasonic mixing, the mixed liquid in the beaker was prepared into the pH-sensitive hydrogel required for making the sensor, and was placed in a refrigerator for low-temperature storage to obtain a pH-sensitive hydrogel solution.

[0041] S3: Using an ultraviolet light source to irradiate the pH-sensitive hydrogel solution to obtain a viscous hydrogel.

[0042] The production of the smart hydrogel pH sensor mainly involves coating the prepared pH-sensitive hydrogel on the prepared fiber Bragg grating. Since the hydrogel is bound by its own viscosity and is not easy to be evenly coated, and the fiber Bragg grating is also easy to bend when coated because it is relatively light and thin, it brings certain difficulties to the production of the pH sensor. And the hydrogel changes from the newly prepared "sample gel" (i.e., the pH-sensitive hydrogel solution obtained in S2) to the "gel film" coated on the FBG (fiber Bragg grating) in a process from liquid to viscous state and then to crystal colloidal state. The newly prepared hydrogel "sample gel" is in liquid state, and the hydrogel solution in this physical state is difficult to be evenly coated and fixed on the FBG. Therefore, an ultraviolet light source is needed in the experiment to change the state of the hydrogel. In order to make it easier for the hydrogel to be coated on the FBG, the hydrogel is irradiated with an ultraviolet light source, and the hydrogel is adjusted to a certain degree of viscosity before the hydrogel is coated on the FBG.

[0043] S4: Fix the fiber Bragg grating on the bracket and make the fiber Bragg grating in a natural vertical state.

[0044] Regarding the fixed direction of the fiber Bragg grating, attempts were made during the experiment to coat the hydrogel by fixing the fiber Bragg grating in the horizontal and vertical directions. The experiment proved that coating the fiber Bragg grating in a natural vertical state with hydrogel can better avoid the bending of the fiber Bragg grating and is also more conducive to increasing the coating thickness of the hydrogel.

[0045] S5: Coat the viscous hydrogel on the surface of the fiber Bragg grating and wash it with deionized water to obtain an intelligent hydrogel pH sensor.

[0046] Use a micro spoon to fill a spoonful of viscous hydrogel, and then slowly sweep the micro spoon along the axial direction of the fiber grating. In this process, the micro spoon should be used to coat from different sides of the FBG to ensure the "circumferential symmetry" of the hydrogel on the FBG. In this way, after the micro spoon is swept several times, you can see that the surface of the FBG is coated with a thin layer of viscous hydrogel. Finally, use deionized water to wash and remove the unreacted reactants to complete the preparation of the pH hydrogel sensitive coating. In this embodiment, its thickness is 560um, and an intelligent hydrogel pH sensor is also obtained.

[0047] The prepared intelligent hydrogel pH sensor based on fiber Bragg grating, fiber demodulator, computer, pH value test solution device are connected to the optical fiber through a network cable to obtain a pH value experimental test platform.

[0048] Use a network cable to connect the computer and the fiber Bragg grating signal processing test program used with the fiber demodulator. After the intelligent hydrogel pH sensor, fiber demodulator, and computer are connected, open the fiber Bragg grating signal processor test program, place the intelligent hydrogel pH sensor in a standard buffer solution with 10 integer points of pH value from 3 to 12, and record the wavelength when the sensor response is stable.

[0049] The sensor was placed in standard buffer solutions with 10 integer points of pH value from 3 to 12 for calibration and recording wavelength. The center wavelength increment of pH sensitive element in different standard buffer solutions was recorded. The obtained data was processed and plotted with pH value as the horizontal axis and Bragg center wavelength as the vertical axis. Linear fitting was performed according to the sensor center wavelength function equation, and the formula is: Y = A*X + B; in the above formula, Y represents the center wavelength of the fiber Bragg pH sensor, X represents the standard buffer solution with different pH values, and B represents the intercept of the fitting equation. The slope A of the equation is the pH sensitivity coefficient of the sensor.

[0050] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0051] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An intelligent hydrogel pH sensor based on fiber Bragg grating, characterized in that: It includes a hydrogel pH sensitive coating and a fiber Bragg grating; the hydrogel pH sensitive coating is coated on the surface of the fiber Bragg grating; The hydrogel pH sensitive coating is prepared by using acrylic acid as a monomer, hydroxyethyl methacrylate as a copolymer, ethylene glycol methacrylate as a crosslinker, benzoin dimethyl ether as a photoinitiator, mixing citric acid and adding graphene.

2. The intelligent hydrogel pH sensor based on fiber Bragg grating according to claim 1, characterized in that: The fiber Bragg grating is obtained based on an optical fiber, and the optical fiber is a quartz single-mode germanium-doped optical fiber, comprising an optical fiber cladding, an optical fiber core and a fiber Bragg grating; The optical fiber core is covered with an optical fiber cladding, and the optical fiber Bragg grating is embedded in the optical fiber core.

3. The intelligent hydrogel pH sensor based on fiber Bragg grating according to claim 1, characterized in that: The central wavelength of the fiber Bragg grating is 1550 nm.

4. The intelligent hydrogel pH sensor based on fiber Bragg grating according to claim 1, characterized in that: The graphene is a graphene micro-sheet layer, the sheet diameter of the graphene micro-sheet layer is 100-300nm, and the mass ratio is 0.5%-1.0%.

5. The intelligent hydrogel pH sensor based on fiber Bragg grating according to claim 1, characterized in that: The intelligent hydrogel pH sensor is used to construct a pH value experimental testing platform; The pH value experimental testing platform comprises a computer, an optical fiber demodulator, and an intelligent hydrogel pH sensor which are connected in sequence. The intelligent hydrogel pH sensor is placed in a pH value testing solution device.

6. A method for preparing an intelligent hydrogel pH sensor based on a fiber Bragg grating, used for preparing an intelligent hydrogel pH sensor based on a fiber Bragg grating as claimed in any one of claims 1 to 5, characterized in that: The following steps are involved: S1: hydrogen loading treatment is performed on the optical fiber, and then the optical fiber cladding in the optical fiber is removed to obtain a fiber Bragg grating; S2: preparing a hydrogel pH sensitive coating, wherein the hydrogel pH sensitive coating is composed of a pH sensitive hydrogel, using an electronic balance to weigh hydroxyethyl methacrylate, acrylic acid, ethylene glycol methacrylate, benzoin dimethyl ether, and citric acid in a ratio of 79:11:1:3:4, and weighing graphene in a ratio of acrylic acid:graphene=100:1; then pouring the weighed hydroxyethyl methacrylate, acrylic acid, ethylene glycol methacrylate, benzoin dimethyl ether, citric acid, and graphene into a glass beaker and mixing to obtain a mixed solution; ultrasonically mixing the mixed solution with the aid of an ultrasonic cleaner to obtain a pH sensitive hydrogel; and storing the pH sensitive hydrogel at low temperature to obtain a pH sensitive hydrogel solution; S3: irradiating the pH-sensitive hydrogel solution with an ultraviolet light source to obtain a viscous hydrogel; S4. Fix the fiber Bragg grating on the bracket and make the fiber Bragg grating in a natural vertical state; S5. Coat the viscous hydrogel on the surface of the fiber Bragg grating and wash it with deionized water to obtain an intelligent hydrogel pH sensor.

7. The method for preparing a fiber Bragg grating-based intelligent hydrogel pH sensor according to claim 6, characterized in that: In S1, the optical fiber cladding is removed by chemical etching.

8. The method for preparing a fiber Bragg grating-based intelligent hydrogel pH sensor according to claim 6, characterized in that: In S2, the glass beaker is pre-washed with deionized water and wrapped with tin foil.

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