Hydrogel, and preparation method and application thereof

Abstract

The invention belongs to the technical field of food detection, and particularly relates to hydrogel and a preparation method and application thereof, the hydrogel comprises the following components: a hydrogel network, a solvent, a cross-linking agent and an initiator; wherein the hydrogel network comprises a first network and a second network; the second network is a rigid skeleton, and the space skeleton of the first network is filled with the second network; the first network is formed by copolymerization of a non-zwitterionic polyfunctional monomer and a zwitterionic monomer through free radical polymerization; the second network is constructed by cellulose derivatives through physical crosslinking; the molecular structure of the zwitterionic monomer simultaneously comprises a quaternary ammonium cation group and a sulfonic acid anion group; the solvent is water and / or a water-based solution; the initiator comprises an oxidizing agent and a catalyst. The hydrogel disclosed by the invention has a composite hydrogel network system which is stable in structure, has high response sensitivity and selectivity to volatile amine substances and can effectively inhibit pigment migration; and through color change observation, various decay indexes (volatile amine substances) in fresh food can be quickly and efficiently distinguished accurately, and the application prospect is wide.

Description

Technical Field

[0001] This invention belongs to the field of food testing technology, specifically relating to hydrogels, methods for preparing hydrogels, and their applications. Background Technology

[0002] Fresh foods such as shrimp are susceptible to spoilage due to physical, chemical, and biological factors during transportation, sales, and storage. This process is typically accompanied by the gradual release of volatile alkaline substances such as dimethylamine and ammonia, leading to an increase in pH levels. Rapid and accurate assessment of the freshness of fresh foods like shrimp is crucial for food safety and quality control. Currently, traditional methods for assessing freshness mainly include sensory evaluation, physicochemical index determination (volatile basic nitrogen (TVB-N) measurement, pH detection, etc.), and microbiological testing. Sensory evaluation relies on operator experience and subjective judgment, making it difficult to standardize and quantify results. Physicochemical index determination requires complex equipment and specialized operation, limiting its basic application. While microbiological testing can reflect the safety status of fresh foods, its long testing cycle makes it unsuitable for monitoring the freshness of such perishable foods.

[0003] Therefore, there is an urgent need to develop a simple, efficient, accurate, and repeatable method for detecting the freshness of fresh food. Summary of the Invention

[0004] This invention aims to at least partially solve one of the technical problems existing in the prior art. To this end, this invention provides a hydrogel, a method for preparing the hydrogel, and its applications. The hydrogel of this invention, by incorporating non-zwitterionic multifunctional monomers, zwitterionic monomers, and cellulose derivatives, and under the action of crosslinking agents and initiators, forms a structurally stable composite hydrogel network system with high responsiveness and selectivity to volatile amines and effective inhibition of pigment migration. Furthermore, when a colorimetric indicator is introduced into this hydrogel, it can utilize the carboxyl-rich functional groups and the charge regulation of the zwitterionic hydrogel to jointly construct multi-point sensitive units. Thus, by observing color changes, it can quickly and efficiently achieve accurate identification of multiple spoilage indicators (volatile amines) in fresh food, with broad application prospects.

[0005] In a first aspect, the present invention provides a hydrogel. According to an embodiment of the present invention, the hydrogel comprises the following components: a hydrogel network, a solvent, a crosslinking agent, and an initiator; wherein the hydrogel network comprises a first network and a second network; the second network is a rigid framework, and the second network fills the spatial framework of the first network; the first network is formed by free radical polymerization copolymerization of a non-zwitterionic multifunctional monomer and a zwitterionic monomer; the second network is formed by physical crosslinking of cellulose derivatives; the molecular structure of the zwitterionic monomer simultaneously contains quaternary ammonium cationic groups and sulfonic acid anionic groups; the solvent is water and / or an aqueous solution; the initiator comprises an oxidant and a catalyst. According to an embodiment of the present invention, the hydrogel network comprises a responsive network (first network) and a support network (second network). The support network is constructed by physical cross-linking of cellulose derivatives through hydrogen bonding, while the responsive network is formed by free radical polymerization of non-amphoteric multifunctional monomers and zwitterionic monomers. The responsive network fills the support network, thereby constituting a composite hydrogel network system. This unique dual-network structure design enables the hydrogel of the present invention to maintain its excellent mechanical properties and stability while exhibiting high sensitivity and selectivity to volatile amines, thus showing broad application prospects.

[0006] According to embodiments of the present invention, the hydrogel may further include the following technical features: According to embodiments of the present invention, the non-amphoteric multifunctional monomer includes one or more of acrylamide, divinylbenzene, ethylene glycol diacrylate, and trimethylolpropane triacrylate.

[0007] According to embodiments of the present invention, the zwitterionic monomer comprises one or more of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide, (3-(methacryloylamino)propyl)dimethyl(3-thiopropyl)ammonium hydroxide inner salt, and 3-(N,N-dimethyl-alkylantimony)propanesulfonate.

[0008] According to embodiments of the present invention, the cellulose derivative includes one or more of carboxylated cellulose nanofibers, carboxymethyl cellulose, and hydroxyethyl cellulose.

[0009] According to embodiments of the present invention, the crosslinking agent includes one or more of N-N'-methyleneacrylamide, ethylene glycol dimethacrylate, tetramethylene dimethacrylate, and N,N'-1,4-phenyldiacrylamide.

[0010] According to an embodiment of the present invention, the oxidant is persulfate.

[0011] According to an embodiment of the present invention, the catalyst is a tertiary amine compound.

[0012] According to embodiments of the present invention, the aqueous solution includes one or more of phosphate buffer solution, physiological saline and tris(hydroxymethyl)aminomethane hydrochloride buffer solution.

[0013] According to an embodiment of the present invention, the mass percentage of the non-zwitterionic multifunctional monomer: zwitterionic monomer: cellulose derivative: crosslinking agent: oxidant: catalyst: solvent is (9~18): (3~12): (1~5): (0.5~1): (0.03~0.05): (0.03~0.06): (64~87).

[0014] According to a preferred embodiment of the present invention, the non-amphoteric multifunctional monomer is acrylamide, the cellulose derivative is carboxylated cellulose nanofiber, the crosslinking agent is N-N'-methyleneacrylamide, the oxidant is potassium persulfate, the catalyst is tetramethylethylenediamine, and the solvent is water.

[0015] According to an embodiment of the present invention, the mass percentage of acrylamide: zwitterionic monomer: carboxylated cellulose nanofiber: N-N'-methyleneacrylamide: potassium persulfate: tetramethylethylenediamine: water is (9~18): (3~12): (1~5): (0.5~1): (0.03~0.05): (0.03~0.06): (64~87).

[0016] According to an embodiment of the present invention, the hydrogel further comprises: a colorimetric indicator; wherein the colorimetric indicator is an acid-base indicator and / or a pigment.

[0017] According to embodiments of the present invention, the pigment includes one or more of neutral red, alizarin, alizarin red, brilliant yellow, and purple sweet potato.

[0018] In a second aspect, the present invention provides a method for preparing the hydrogel described in the first aspect. According to an embodiment of the present invention, the method includes: S1: in the solvent, subjecting the non-amphoteric multifunctional monomer, the zwitterionic monomer, the crosslinking agent, and the oxidant to a first mixing treatment to obtain a hydrogel precursor solution; S2: subjecting the hydrogel precursor solution and the cellulose derivative solution to a second mixing treatment, and then adding the catalyst to simultaneously carry out free radical polymerization and physical crosslinking to obtain the hydrogel. According to the method of the embodiments of the present invention, through stepwise mixing and free radical polymerization, the formation process of the hydrogel network can be precisely controlled, thereby obtaining a structurally stable hydrogel with high responsiveness and selectivity to volatile amines and effective inhibition of pigment migration. This method has advantages such as simple operation, mild conditions, and ease of large-scale production, and has broad application prospects.

[0019] According to embodiments of the present invention, the method may further include the following technical features: According to an embodiment of the present invention, the method further includes: dispersing the cellulose derivative to obtain a cellulose derivative solution.

[0020] According to an embodiment of the present invention, the method further includes: contacting the hydrogel obtained in step S2 with a colorimetric indicator.

[0021] According to an embodiment of the present invention, the temperature of the free radical polymerization reaction and the physical crosslinking are 60~70°C, and the time is 30~60 min.

[0022] According to an embodiment of the present invention, the stirring time of the first mixing treatment is 30~120 min, and the stirring speed is 45~60 rpm.

[0023] According to an embodiment of the present invention, the stirring time for the second mixing process is 15-30 min, and the stirring speed is 45-60 rpm.

[0024] According to an embodiment of the present invention, the contact treatment time is 10 to 30 minutes.

[0025] In a third aspect, the present invention provides a method for detecting the freshness of a sample to be tested. According to an embodiment of the present invention, the method includes: exposing the sample to be tested and the hydrogel described in the first aspect to the same sealed environment, allowing volatile substances released by the sample to contact the hydrogel, and determining the freshness of the sample based on color changes; wherein the hydrogel contains a colorimetric indicator; and the sample to be tested is food or a food sample. The method according to the embodiments of the present invention utilizes the color change of the aforementioned hydrogel to achieve rapid and accurate detection of the freshness of the sample to be tested. This method has the advantages of being simple and fast to operate, highly sensitive, and selective.

[0026] In a fourth aspect of the invention, the invention proposes the application of the hydrogel described in the first aspect and the method described in the second aspect in the detection of food or food samples.

[0027] Those skilled in the art will understand that the features and advantages described above for hydrogels and methods for detecting the freshness of test samples are also applicable to this application, and will not be repeated here.

[0028] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0029] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 The following are the pH sensitivity test results of candidate dyes in the colorimetric sensor array in Example 1 of the present invention: (a) is the pH sensitivity test result of the colorimetric sensor array for alizarin red pigment, (b) is the pH sensitivity test result of the colorimetric sensor array for sweet potato pigment, (c) is the pH sensitivity test result of the colorimetric sensor array for neutral red pigment, and (d) is the pH sensitivity test result of the colorimetric sensor array for brilliant yellow pigment. Figure 2 The graph shows the test results of ED values ​​and mechanical properties of colorimetric sensor array hydrogels I to VI in Example 8 of this invention. Figure 3 This is a graph showing the detection results of the colorimetric sensor array hydrogel II for different amine substances in Example 9 of the present invention; Figure 4 The image shows the infrared spectral analysis results of samples such as colorimetric sensor array hydrogel in Example 9 of this invention. Figure 5 The diagram shows the monitoring device for the freshness of prawns in Embodiment 9 of the present invention, wherein (1) is a 2D schematic diagram of the monitoring device for the freshness of prawns, and (3) is a 3D schematic diagram of the monitoring device for the freshness of prawns. Figure 6 The following are the results of monitoring the freshness of prawns using colorimetric sensor array hydrogel II in Example 9 of this invention: (a) shows the TVB-N content detection results of prawns from 1 to 8 days using colorimetric sensor array hydrogel II (storage temperature 4℃); (b) shows the TVB-N content detection results of prawns from 0 to 36 hours using colorimetric sensor array hydrogel II (storage temperature 25℃); (c) shows the pH value detection results of prawns from 1 to 8 days using colorimetric sensor array hydrogel II (storage temperature 4℃); and (d) shows the pH value detection results of prawns from 0 to 36 hours using colorimetric sensor array hydrogel II (storage temperature 25℃). Figure 7 This is a graph showing the response sensitivity detection results of different colorimetric sensor array hydrogels in Example 10 of the present invention. Detailed Implementation

[0030] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0031] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0032] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0033] In this document, the terms “comprising” or “including” are open-ended expressions, meaning that they include the contents specified in this invention, but do not exclude other aspects.

[0034] In this document, the terms “optionally,” “optionally,” or “optionally” generally refer to an event or condition that may, but may not, occur, and the description includes both cases in which the event or condition occurs and cases in which the event or condition does not occur.

[0035] hydrogel This invention proposes a hydrogel. According to an embodiment of the invention, the hydrogel comprises the following components: a hydrogel network, a solvent, a crosslinking agent, and an initiator; wherein, the hydrogel network comprises a first network and a second network; the second network is a rigid framework, and the second network fills the spatial framework of the first network; the first network is formed by free radical polymerization copolymerization of non-amphoteric multifunctional monomers and zwitterionic monomers; the second network is formed by physical crosslinking of cellulose derivatives; the molecular structure of the zwitterionic monomers simultaneously contains quaternary ammonium cationic groups and sulfonic acid anionic groups; the initiator includes an oxidant and a catalyst. According to an embodiment of the invention, the hydrogel network comprises a responsive network (first network) and a supporting network (second network), wherein the supporting network is obtained by physical crosslinking of cellulose derivatives through hydrogen bonding, and the responsive network is formed by free radical polymerization of non-amphoteric multifunctional monomers and zwitterionic monomers. The responsive network fills the supporting network, thereby constituting a composite hydrogel network system. This unique dual-network structure design enables the hydrogel of this invention to maintain its excellent mechanical properties and stability while exhibiting high sensitivity and selectivity to volatile amines, thus showing broad application prospects.

[0036] In this paper, the term "non-zwitterionic multifunctional monomer" refers to a monomer that does not contain groups that are simultaneously positively and negatively charged, but has multiple active groups that can participate in polymerization reactions.

[0037] In this paper, the term "response network" refers to the network structure (i.e., the first network, also known as the flexible network) formed by free radical polymerization of non-zwitterionic multifunctional monomers and zwitterionic monomers. This part of the network can produce a highly sensitive and selective response to volatile amines and intuitively reflect the changes in pH of the surrounding environment through color changes, thereby achieving rapid and accurate detection of the freshness of food or food samples.

[0038] In this paper, the term "support network" refers to the rigid framework structure (i.e., the second network, also known as the rigid network) formed by physical cross-linking of cellulose derivatives. This part of the network provides physical support for the response network, further enhancing the overall mechanical properties and stability of the hydrogel of the present invention. In the hydrogel of the present invention, the main function of the support network is to fill the framework of the response network, forming a stable three-dimensional structure, ensuring the durability and reliability of the hydrogel in practical applications, and effectively inhibiting the migration and diffusion of colorimetric indicator dye molecules, thereby improving the service life of the hydrogel.

[0039] In this article, the term "freshness" refers to the degree to which a product (food / food sample) retains its original quality, function, and safety under specific conditions.

[0040] According to embodiments of the present invention, the molecular structure of the zwitterionic monomer simultaneously contains quaternary ammonium cation groups and sulfonic acid anion groups, endowing the hydrogel of the present invention with an electrically neutral but highly polar ionic environment. This environment enables electrostatic adsorption and ion-dipole interactions with charged groups (such as phenolic hydroxyl groups, carboxyl groups, etc.) of colorimetric indicator dye molecules, effectively enhancing its affinity for colorimetric indicator dye molecules and significantly improving the structural stability and pigment fixation of the sensing system. Furthermore, the cellulose derivative provides a rigid framework for the hydrogel. For example, the surface of carboxylated cellulose nanofibers is rich in polar groups such as -COOH and -OH, possessing high specific surface area and good dispersibility. It can form stable multi-point connections with hydroxyl groups, carboxyl groups, phenolic hydroxyl groups, etc. in colorimetric indicator dye molecules through hydrogen bonding. Further, the cellulose derivative also undergoes hydrogen bonding entanglement and network intercalation with the zwitterionic monomer segments, constructing a dense and stable three-dimensional gel network, thereby forming a "spatial confinement microenvironment" for colorimetric indicator dye molecules, effectively inhibiting their migration and diffusion. Therefore, by adding non-zwitterionic multifunctional monomers, zwitterionic monomers, and cellulose derivatives, and with the help of crosslinking agents and initiators, a composite hydrogel network system with stable structure, high responsiveness and selectivity to volatile amines, and effective inhibition of pigment migration is formed. This hydrogel system constructs a colorimetric sensor array through multi-site, multi-color response, thereby enabling rapid response to changes in environmental pH caused by volatile alkaline amines (such as trimethylamine and ammonia) during the spoilage of fresh food (such as shrimp), achieving multi-dimensional color feature recognition, and further improving the accuracy and sensitivity of freshness judgment.

[0041] According to embodiments of the present invention, the non-zwitterionic multifunctional monomer includes one or more of acrylamide, divinylbenzene, ethylene glycol diacrylate, and trimethylolpropane triacrylate. Therefore, the hydrogel of the present invention is applicable to a variety of non-zwitterionic multifunctional monomers, and can be selected and adjusted according to specific application requirements.

[0042] According to embodiments of the present invention, the zwitterionic monomer includes one or more of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide, (3-(methacryloylamino)propyl)dimethyl(3-thiopropyl)ammonium hydroxide inner salt, and 3-(N,N-dimethyl-alkylantimony)propanesulfonate. Therefore, the hydrogel of the present invention is applicable to a variety of zwitterionic monomers and can be selected and adjusted according to specific application requirements.

[0043] It should be noted that the zwitterionic monomers are not limited to those specifically listed above. Any zwitterionic monomer whose molecular structure simultaneously contains a quaternary ammonium cation group and a sulfonic acid anion group, such as [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl)ammonium chloride, [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl)ammonium sulfate, and [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl)ammonium phosphate, are all within the scope of protection of this invention.

[0044] According to embodiments of the present invention, the cellulose derivative includes one or more of carboxylated cellulose nanofibers, carboxymethyl cellulose, and hydroxyethyl cellulose. Therefore, the hydrogel of the present invention is applicable to a variety of cellulose derivatives, and can be selected and adjusted according to specific application requirements.

[0045] In this document, the term "cellulose derivative" refers to materials that modify natural cellulose through chemical or physical methods to impart specific functions. These materials typically contain abundant carboxyl, hydroxyl, or other functional groups. Cellulose derivatives play a key role in enhancing the mechanical properties and stability of the hydrogel network of this invention. Common cellulose derivatives include carboxylated cellulose nanofibers (C-CNF), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), carboxylated cellulose microfibers, sodium carboxymethyl cellulose (CMC-Na), hydroxypropyl cellulose (HPC), methyl cellulose (MC), ethyl cellulose (EC), hydroxyethyl methyl cellulose (HEMC), and hydroxypropyl methyl cellulose (HPMC), etc.

[0046] It should be noted that the cellulose derivatives are not limited to the types specifically listed above. Any cellulose modified by chemical or physical methods, such as carboxylated cellulose microfibers, sodium carboxymethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, etc., as long as they can form a stable second network (i.e., a rigid skeleton network) through physical cross-linking and can enhance the mechanical properties and stability of the hydrogel, are all within the scope of protection of this invention.

[0047] According to embodiments of the present invention, the crosslinking agent includes one or more of N-N'-methyleneacrylamide, ethylene glycol dimethacrylate, tetramethylene dimethacrylate, and N,N'-1,4-phenyldiacrylamide. Thus, the crosslinking agent promotes the formation of a stable three-dimensional network structure hydrogel system from the raw materials. The hydrogel of the present invention is suitable for crosslinking agents, which can be selected and adjusted according to specific application requirements.

[0048] It should be noted that the crosslinking agent is not limited to the types specifically listed above. Any compound that can effectively promote crosslinking polymerization between monomers (such as non-zwitterionic multifunctional monomers and zwitterionic monomers), such as trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, dipentaerythritol hexaacrylate, N,N'-methylenebisacrylamide, etc., are all within the scope of protection of this invention.

[0049] According to an embodiment of the present invention, the oxidant is persulfate. Thus, persulfate decomposes in water or an aqueous solution to generate free radicals, which can initiate cross-linking polymerization reactions, thereby forming a stable hydrogel network and further improving the uniformity and stability of the hydrogel of the present invention.

[0050] It should be noted that the oxidant used in the hydrogel of this invention is not limited to potassium persulfate specifically used in the examples, but also includes ammonium persulfate, sodium persulfate, lithium persulfate, magnesium persulfate and other persulfates. Any tertiary amine compound that acts as an oxidant and synergistic catalyst is within the scope of protection of this invention.

[0051] According to an embodiment of the present invention, the catalyst is a tertiary amine compound. Thus, through the synergistic effect of the tertiary amine compound and persulfate, more free radicals are generated, thereby accelerating the cross-linking polymerization reaction and forming a stable hydrogel network, further improving the uniformity and stability of the hydrogel of the present invention.

[0052] It should be noted that the catalyst used in the hydrogel of this invention is not limited to tetramethylethylenediamine specifically used in the examples, but also includes various tertiary amine compounds such as triethylamine, tripropylamine, tributylamine, trimethylamine, dimethylethylamine, and diethylmethylamine. Any catalyst that works in conjunction with the oxidant persulfate to play a corresponding role is within the scope of protection of this invention.

[0053] According to embodiments of the present invention, the aqueous solution includes one or more of phosphate buffer solution, physiological saline, and tris(hydroxymethyl)aminomethane hydrochloride buffer. Therefore, the hydrogel of the present invention is applicable to a variety of aqueous solutions and can be selected and adjusted according to specific application requirements to ensure its stability and responsiveness under different conditions.

[0054] According to an embodiment of the present invention, the mass percentage of the non-zwitterionic multifunctional monomer: zwitterionic monomer: cellulose derivative: crosslinking agent: oxidant: catalyst: solvent is (9~18): (3~12): (1~5): (0.5~1): (0.03~0.05): (0.03~0.06): (64~87). Therefore, by optimizing and controlling the proportions of each component, the performance of the hydrogel can be further optimized, ensuring an optimal balance between mechanical strength, responsiveness, and stability. For example, the mass percentages of the non-amphoteric multifunctional monomer:amphoteric monomer:cellulose derivative:crosslinking agent:oxidant:catalyst:solvent are 9:3:1:0.5:0.03:0.03:64, 10:3:1:0.5:0.03:0.03:64, 11:3:1:0.5:0.03:0.03:64, 12:3:1:0.5:0.03:0.03:64, and 13:3:1:0.5:0. 03:0.03:64, 14:3:1:0.5:0.03:0.03:64, 15:3:1:0.5:0.03:0.03:64, 16:3:1:0.5:0.03:0.03:64, 17:3:1:0.5:0.03:0.03:64, 18:3:1:0.5:0.03:0.03:64, 9:4:1:0.5:0.03:0.03:64, 9:5:1:0.5:0.03:0.03:64, 9:6:1:0.5:0.03:0.03:64, 9:7:1:0.5:0.03:0.0 3:64, 9:8:1:0.5:0.03:0.03:64, 9:9:1:0.5:0.03:0.03:64, 9:10:1:0.5:0.03:0.03:64, 9:11:1:0.5:0.03:0.03:64, 9:12:1:0.5:0.03:0.03:64, 9:3:2:0.5:0.03:0.03:64, 9:3:3:0.5:0.03:0.03:64, 9:3:4:0.5:0.03:0.03:64, 9:3:5:0.5:0.03:0.03:64, 9:3 :1:0.6:0.03:0.03:64、9:3:1:0.7:0.03:0.03:64、9:3:1:0.8:0.03:0.03:64、9:3:1:0.9:0.03:0.03:64、9:3:1:1:0.03:0.03:64、9:3:1:0.5:0.04:0.03:64、9:3:1:0.5:0.05:0.03:64、9:3:1:0.5:0.03:0.04:64、9:3:1:0.5:0.03:0.05:64、9:3:1:0.5:0.03:0.06:64, 9:3:1:0.5:0.03:0.03:66, 9:3:1:0.5:0.03:0.03:68, 9:3:1:0.5:0.03:0.03:70, 9:3:1:0.5:0.03:0.03:72, 9:3:1:0.5:0.03:0.03:74, 9:3:1:0.5:0.03:0.03:75, 9:3:1 The preferred ratio is (12~18):(6~12):(1~3):(0.5~0.8):(0.03~0.04):(0.03~0.05):(66~85), and the more preferred ratio is (16~18):(6~9):(1~2):(0.5~0.6):(0.03~0.035):(0.03~0.04):(70~76).

[0055] According to a preferred embodiment of the present invention, the non-amphoteric multifunctional monomer is acrylamide, the cellulose derivative is carboxylated cellulose nanofibers, the crosslinking agent is N-N'-methyleneacrylamide, the oxidant is potassium persulfate, the catalyst is tetramethylethylenediamine, and the solvent is water. This further optimizes the combination and matching of the components, thereby further optimizing the various properties of the hydrogel.

[0056] According to an embodiment of the present invention, the mass percentage of acrylamide: zwitterionic monomer: carboxylated cellulose nanofiber: N-N'-methyleneacrylamide: potassium persulfate: tetramethylethylenediamine: water is (9~18): (3~12): (1~5): (0.5~1): (0.03~0.05): (0.03~0.06): (64~87). Therefore, by optimizing the combination and proportion of each component, the performance of the hydrogel can be further optimized to ensure an optimal balance between mechanical strength, response sensitivity, and stability. For example, the mass percentages of acrylamide: zwitterionic monomer: carboxylated cellulose nanofibers: N-N'-methyleneacrylamide: potassium persulfate: tetramethylethylenediamine: water are 9:3:1:0.5:0.03:0.03:64, 10:3:1:0.5:0.03:0.03:64, 11:3:1:0.5:0.03:0.03:64, and 12:3:1:0.5:0.03:0. 03:64, 13:3:1:0.5:0.03:0.03:64, 14:3:1:0.5:0.03:0.03:64, 15:3:1:0.5:0.03:0.03:64, 16:3:1:0.5:0.03:0.03:64, 17:3:1:0.5:0.03:0.03:64, 18:3:1:0.5:0.03:0.03:64, 9:4:1:0.5:0.03:0.03:64, 9:5:1:0.5:0.03:0.03:64, 9:6:1:0.5:0.03:0.03:6 4. 9:7:1:0.5:0.03:0.03:64, 9:8:1:0.5:0.03:0.03:64, 9:9:1:0.5:0.03:0.03:64, 9:10:1:0.5:0.03:0.03:64, 9:11:1:0.5:0.03:0.03:64, 9:12:1:0.5:0.03:0.03:64, 9:3:2:0.5:0.03:0.03:64, 9:3:3:0.5:0.03:0.03:64, 9:3:4:0.5:0.03:0.03:64, 9:3:5 :0.5:0.03:0.03:64、9:3:1:0.6:0.03:0.03:64、9:3:1:0.7:0.03:0.03:64、9:3:1:0.8:0.03:0.03:64、9:3:1:0.9:0.03:0.03:64、9:3:1:1:0.03:0.03:64、9:3:1:0.5:0.04:0.03:64、9:3:1:0.5:0.05:0.03:64、9:3:1:0.5:0.03:0.04:64、9:3:1:0.5:0.03:0.05:64, 9:3:1:0.5:0.03:0.06:64, 9:3:1:0.5:0.03:0.03:66, 9:3:1:0.5:0.03:0.03:68, 9:3:1:0.5:0.03:0.03:70, 9:3:1:0.5:0.03:0.03:72, 9:3:1:0.5:0.03:0.03:74, 9:3:1:0.5:0.03:0 0.03:75, 9:3:1:0.5:0.03:0.03:77, preferably (12~18):(6~12):(1~3):(0.5~0.8):(0.03~0.04):(0.03~0.05):(66~85), more preferably (16~18):(6~9):(1~2):(0.5~0.6):(0.03~0.035):(0.03~0.04):(70~76).

[0057] According to an embodiment of the present invention, the hydrogel further comprises: a colorimetric indicator; wherein the colorimetric indicator is an acid-base indicator and / or a pigment. Thus, the introduction of the colorimetric indicator enables the hydrogel of the present invention to intuitively reflect changes in the pH of the surrounding environment through color changes, thereby achieving highly sensitive, rapid, and accurate detection of the freshness of foods such as fresh produce.

[0058] According to embodiments of the present invention, the pigment includes one or more of neutral red, alizarin, alizarin red, brilliant yellow, and purple sweet potato. Thus, the pigment is pH sensitive, reflecting pH changes in the environment surrounding the hydrogel through color variations. By selecting a preferred pigment combination, multi-color response and multi-dimensional identification can be achieved, further improving the accuracy and resolution of the judgment. For example, a preferred pigment combination may include alizarin red, purple sweet potato, neutral red, and brilliant yellow.

[0059] It should be noted that the colorimetric indicator is not limited to the types of colorimetric indicators specifically listed above, such as phenolphthalein, methyl orange, bromophenol blue, bromocresol green, bromocresol purple, thymol blue, phenol red, etc. Any compound that can reflect changes in the pH of the surrounding environment through color changes and can be used as a colorimetric indicator falls within the protection scope of this invention.

[0060] For example, the hydrogel may exist in the form of a colorimetric sensor array, that is, a combination of hydrogels containing a variety of different pigments, and the size of the colorimetric sensor array may be 2 cm × 2 cm, 3 cm × 3 cm, 4 cm × 4 cm, etc.

[0061] Preparation method This invention proposes a method for preparing the aforementioned hydrogel. According to an embodiment of the invention, the method includes: S1: in the solvent, a first mixing treatment is performed on the non-amphoteric multifunctional monomer, the zwitterionic monomer, the crosslinking agent, and the oxidant to obtain a hydrogel precursor solution; S2: the hydrogel precursor solution and the cellulose derivative solution are secondly mixed, and then the catalyst is added to carry out a free radical polymerization reaction to obtain the hydrogel. According to the method of this invention, through stepwise mixing and free radical polymerization, the formation process of the hydrogel network can be precisely controlled, thereby obtaining a structurally stable hydrogel with high responsiveness and selectivity to volatile amines and effective inhibition of pigment migration. This method has the advantages of simple operation, mild conditions, and ease of large-scale production, and has broad application prospects.

[0062] According to an embodiment of the present invention, the method further includes: dispersing the cellulose derivative to obtain a cellulose derivative solution. Thus, by uniformly distributing the cellulose derivative in a solvent to form a stable cellulose derivative solution, it can be fully mixed with other components in the hydrogel precursor solution in subsequent operations, thereby further improving the mechanical properties and stability of the prepared hydrogel.

[0063] According to an embodiment of the present invention, the method further includes: contacting the hydrogel obtained in step S2 with a colorimetric indicator. Thus, by contacting the hydrogel with the colorimetric indicator, the colorimetric indicator can be uniformly loaded into the hydrogel, thereby preparing a hydrogel containing a colorimetric sensor array, which can be applied to the freshness detection of food or food samples.

[0064] According to an embodiment of the present invention, the temperature of the free radical polymerization reaction is 60-70°C, and the time is 30-60 min. Thus, by optimizing and controlling the temperature and time of the free radical polymerization reaction, the degree of crosslinking and network structure of the prepared hydrogel can be precisely controlled. Exemplarily, the temperature of the free radical polymerization reaction is 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C, or 70°C, preferably 60-65°C, more preferably 63-65°C; the time of the free radical polymerization reaction is 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, or 60 min, preferably 30-45 min, more preferably 35-45 min.

[0065] According to an embodiment of the present invention, the stirring time for the first mixing treatment is 30-120 min, and the stirring speed is 45-60 rpm. Thus, by optimizing and controlling the stirring time and speed of the first mixing treatment, the non-amphoteric multifunctional monomer, the amphoteric monomer, the crosslinking agent, and the oxidant are ensured to be fully mixed to form a homogeneous hydrogel precursor solution, thereby enabling the preparation of hydrogels with better performance. Exemplarily, the stirring time for the first mixing treatment is 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, or 120 min, preferably 60-80 min, more preferably 60-70 min; the stirring speed for the first mixing treatment is 45 rpm, 47 rpm, 49 rpm, 50 rpm, 51 rpm, 53 rpm, 55 rpm, 57 rpm, 59 rpm, or 60 rpm, preferably 50-60 rpm, more preferably 57-60 rpm.

[0066] According to an embodiment of the present invention, the stirring time for the second mixing treatment is 15-30 min, and the stirring speed is 45-60 rpm. Thus, by optimizing and controlling the stirring time and speed of the second mixing treatment, it is ensured that the hydrogel precursor solution and the cellulose derivative solution are fully mixed to form a homogeneous mixed solution, thereby providing better conditions for the subsequent free radical polymerization reaction. Exemplarily, the stirring time for the second mixing treatment is 15 min, 17 min, 19 min, 20 min, 21 min, 23 min, 25 min, 27 min, 29 min, or 30 min, preferably 25-30 min, more preferably 27-30 min; the stirring speed for the second mixing treatment is 45 rpm, 47 rpm, 49 rpm, 50 rpm, 51 rpm, 53 rpm, 55 rpm, 57 rpm, 59 rpm, or 60 rpm, preferably 55-60 rpm, more preferably 57-60 rpm.

[0067] According to an embodiment of the present invention, the contact treatment time is 10-30 min. Thus, by optimizing the control of the contact treatment time between the colorimetric indicator and the hydrogel, it is ensured that the colorimetric indicator can be uniformly loaded in the hydrogel, forming a more stable colorimetric hydrogel sensor array; exemplaryly, the contact treatment time is 10 min, 15 min, 20 min, 25 min, or 30 min, preferably 15-25 min, and more preferably 20-25 min.

[0068] It should be noted that the colorimetric hydrogel sensor array prepared by this invention can be directly attached to the inside of the packaging. Users can judge the freshness of food or food samples (such as shrimp meat) by observing the color change with the naked eye. No professional instruments or complicated operations are required, making it particularly suitable for real-time monitoring in various scenarios such as food distribution, retail and home.

[0069] Methods for detecting the freshness of a sample This invention proposes a method for detecting the freshness of a test sample. According to an embodiment of the invention, the method includes: exposing the test sample and a aforementioned hydrogel to the same sealed environment, allowing volatile substances released from the test sample to contact the hydrogel, and determining the freshness of the test sample based on color changes; wherein the hydrogel contains a colorimetric indicator; and the test sample is food or a food sample. The method according to this invention utilizes the color change of the aforementioned hydrogel to achieve rapid and accurate detection of the freshness of the test sample. This method has the advantages of being simple and fast to operate, highly sensitive, and selective.

[0070] For example, the types of food or food samples can be seafood products (such as squid, octopus, shellfish, crab, shrimp), processed meats (such as sausage, ham, bacon, cured meat), ready-to-eat foods (such as salads, sandwiches, sushi, bento boxes), frozen foods (such as frozen shrimp, frozen fish), etc. Any sample that deteriorates and metabolizes to produce volatile amines (such as trimethylamine, ammonia, dimethylamine, etc.) can be rapidly and accurately detected using the method of the present invention for detecting the freshness of the sample.

[0071] application This invention proposes the application of the aforementioned hydrogel and the aforementioned method in the detection of food or food samples.

[0072] Those skilled in the art will understand that the features and advantages described above for hydrogels and methods for detecting the freshness of test samples are also applicable to this application, and will not be repeated here.

[0073] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0074] Example 1: pH sensitivity test of candidate dyes using a colorimetric sensor array 1. Preparation of the test pigment solution First, buffer solutions with different pH values ​​of pH=1, pH=2, pH=3, pH=4, pH=5, pH=6, pH=7, pH=8, pH=9, pH=10, pH=11, and pH=12 were prepared.

[0075] Then, 0.5 mg of Alizarin Red (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., catalog number A100195), purple sweet potato (purchased from Yunnan Tonghai Yangshi Natural Products Co., Ltd., catalog number YSPSPC-90), Neutral Red (purchased from Sinopharm Chemical Reagent Co., Ltd., catalog number C71028144), and Brilliant Yellow (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., catalog number B109621) were dissolved in 20 mL of the aforementioned buffer solutions with different pH values ​​to obtain the test pigment solutions.

[0076] 2. Ultraviolet spectroscopy analysis The color changes of different pigments at different pH values ​​were captured by a camera, and the ultraviolet-visible spectrophotometer was used to scan the pigment solutions obtained in step 1 and record their ultraviolet absorption spectra at different pH values.

[0077] The pH sensitivity test results of the candidate dyes for the colorimetric sensor array are shown in the figure. Figure 1 .

[0078] The results showed that the positions and absorption intensities of the UV absorption peaks of each pigment exhibited significant changes with pH, ​​reflecting the protonation and deprotonation processes of functional groups in the dye molecules. Specifically, Alizarin Red and Neutral Red showed that the absorbance of their absorption peaks increased with increasing pH, and the peak shapes remained relatively stable, indicating that their structures were relatively stable in the neutral-to-acidic to neutral-to-alkaline range. Sweet potato purple dye exhibited strong absorbance under acidic conditions, but its absorbance decreased significantly under alkaline conditions, showing its dependence on acidity and sensitivity to alkalinity. Brilliant Yellow pigment reached its peak absorbance under neutral and slightly alkaline conditions, and the absorption intensity weakened beyond a certain alkalinity, suggesting that its structure underwent some changes under alkaline conditions.

[0079] The above results indicate that alizarin red, sweet potato purple, neutral red, and brilliant yellow all exhibit significant pH response characteristics, and their color changes have good visual recognition effects.

[0080] Example 2: Preparation of colorimetric sensor array hydrogel I 1. Preparation of Cellulose Derivative Solution I 0.5 wt% of carboxylated cellulose nanofibers (C-CNF, purchased from Shanghai Maclean Biochemical Technology Co., Ltd., catalog number C875077) (based on solvent mass) were mixed with deionized water by magnetic stirring at 50 rpm for 60 min until homogeneous, to obtain 0.5 wt% cellulose derivative solution I.

[0081] 2. Preparation of hydrogel precursor solution I 18 wt% acrylamide (purchased from Shanghai Titan Technology Co., Ltd., catalog number G83627C) was dissolved in deionized water along with 3 wt% [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide (SBMA, CAS No. 3637-26-1, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., catalog number M164461), 0.3 wt% potassium persulfate (purchased from Sinopharm Chemical Reagent Co., Ltd., catalog number P816371), and 0.03 wt% N-N'-methyleneacrylamide (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., catalog number M104022) (all mass fractions are based on solvent mass). The mixture was magnetically stirred at 50 rpm for 30 min until homogeneous, yielding hydrogel precursor solution I.

[0082] 3. Preparation of hydrogel I The 0.5 wt% cellulose derivative solution I obtained in step 1 and the hydrogel precursor solution I obtained in step 2 were mixed at a ratio of 3:5 (v / v) and magnetically stirred at 50 rpm for 20 min until homogeneous. Then, 0.06 wt% tetramethylethylenediamine (purchased from Sinopharm Chemical Reagent Co., Ltd., catalog number N818999) was added and stirred until homogeneous. The resulting solution was poured into a glass mold containing a 0.1 mm gasket and placed in a 65℃ oven for free radical polymerization for 30 min to obtain hydrogel I.

[0083] 4. Preparation of colorimetric sensor array hydrogel I The hydrogel I obtained in step 3 was cut into circular molds with a diameter of 1 cm and then immersed in four pigment solutions: neutral red, alizarin red, purple sweet potato, and brilliant yellow. The solution was immersed for 15 min by solvent displacement to obtain hydrogel I loaded with different pigments. Then, the hydrogel I loaded with different pigments was placed on a square PET film with a length of 3 cm to prepare a 2×2 colorimetric sensor array hydrogel I.

[0084] Example 3: Preparation of colorimetric sensor array hydrogel II 1. Preparation of Cellulose Derivative Solution II The preparation steps of cellulose derivative solution II are the same as step 1 in Example 2, to obtain cellulose derivative solution II.

[0085] 2. Preparation of hydrogel precursor solution II 30 wt% acrylamide, 6 wt% [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, 0.3 wt% potassium persulfate, and 0.03 wt% N-N'-methyleneacrylamide were dissolved in deionized water (all mass fractions are based on solvent mass). The mixture was magnetically stirred at 50 rpm for 30 min until homogeneous, thus obtaining hydrogel precursor solution II.

[0086] 3. Preparation of Hydrogel II The preparation steps for hydrogel II are the same as step 3 in Example 2, to obtain hydrogel II.

[0087] 4. Preparation of colorimetric sensor array hydrogel II The preparation steps of colorimetric sensor array hydrogel II are the same as step 4 in Example 2, and colorimetric sensor array hydrogel II is obtained.

[0088] Example 4: Preparation of Colorimetric Sensor Array Hydrogel III 1. Preparation of Cellulose Derivative Solution III The preparation steps of cellulose derivative solution III are the same as step 1 in Example 2, to obtain cellulose derivative solution III.

[0089] 2. Preparation of hydrogel precursor solution III 30 wt% acrylamide, 9 wt% [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, 0.3 wt% potassium persulfate, and 0.03 wt% N-N'-methyleneacrylamide were dissolved in deionized water (all mass fractions are based on solvent mass). The mixture was magnetically stirred at 50 rpm for 30 min until homogeneous, thus obtaining hydrogel precursor solution III.

[0090] 3. Preparation of Hydrogel III The preparation steps for hydrogel III are the same as in step 3 of Example 2, to obtain hydrogel III.

[0091] 4. Preparation of colorimetric sensor array hydrogel III The preparation steps of colorimetric sensor array hydrogel III are the same as step 4 in Example 2, and colorimetric sensor array hydrogel III is obtained.

[0092] Example 5: Preparation of colorimetric sensor array hydrogel IV 1. Preparation of Cellulose Derivative Solution IV The preparation steps of cellulose derivative solution IV are the same as step 1 in Example 2, to obtain cellulose derivative solution IV.

[0093] 2. Preparation of hydrogel precursor solution IV 30 wt% acrylamide, 12 wt% [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, 0.3 wt% potassium persulfate, and 0.03 wt% N-N'-methyleneacrylamide were dissolved in deionized water (all mass fractions are based on solvent mass). The mixture was magnetically stirred at 50 rpm for 30 min until homogeneous, thus obtaining hydrogel precursor solution III.

[0094] 3. Preparation of Hydrogel IV The preparation steps of hydrogel IV are the same as step 3 in Example 2, to obtain hydrogel IV.

[0095] 4. Preparation of colorimetric sensor array hydrogel IV The preparation steps of the colorimetric sensor array hydrogel IV are the same as step 4 in Example 2, and the colorimetric sensor array hydrogel IV is obtained.

[0096] Example 6: Preparation of colorimetric sensor array hydrogel V The preparation steps of the colorimetric sensor array hydrogel V are the same as in Example 3, except that [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide is replaced with (3-(methacryloylamino)propyl)dimethyl(3-thiopropyl)ammonium hydroxide inner salt (SPP, CAS No. 5205-95-8, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., catalog number M303877), thereby obtaining the colorimetric sensor array hydrogel V.

[0097] Example 7: Preparation of colorimetric sensor array hydrogel VI The preparation steps of the colorimetric sensor array hydrogel VI are the same as in Example 3, except that [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propionic acid)ammonium hydroxide is replaced with 3-(N,N-dimethyl-alkylantimony)propanesulfonate (SB3-12, CAS No. 14933-08-5, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., catalog number N755589), thereby obtaining the colorimetric sensor array hydrogel VI.

[0098] Example 8: Preliminary performance tests of colorimetric sensor array hydrogels I-IV The colorimetric sensor array hydrogels I-IV prepared in Examples 2-5 were placed in a trimethylamine atmosphere of the same concentration (30 ppm), and compared using ED value, PCA score, and mechanical properties as indicators.

[0099] The ED values ​​and mechanical property test results of colorimetric sensor array hydrogels I-VI are shown in the figure. Figure 2 .

[0100] The results showed that hydrogel II had the highest PCA1 score and a wide data distribution, indicating that it had the best overall performance and a large range of variation. Furthermore, from the mechanical property graph, hydrogel II exhibited lower stress but greater strain extensibility (the curve extends further to the right), indicating that it was more flexible and extensible. Therefore, the colorimetric sensor array hydrogel II achieved a good balance between performance and mechanical flexibility by adjusting the dosage.

[0101] Example 9: Performance Testing of Colorimetric Sensor Array Hydrogel II Further performance testing was conducted on colorimetric sensor array hydrogel II, which showed the best performance among the colorimetric sensor array hydrogels I-IV prepared in Examples 2-5. The specific steps are as follows: 1. Detection of color response effects of different amine substances First, solutions of different volatile amines with a concentration of 30 ppm were prepared, including ammonia (NH3), dimethylamine (DMA), trimethylamine (TMA), triethylamine (TEA), tyramine (Ty), spermine (SPM), putrescine (PUT), and tryptamine (Tr). Then, the colorimetric sensor array hydrogel II was exposed to the vapors of the aforementioned solutions of different volatile amines, and the color changes were captured by a camera.

[0102] The results of the colorimetric sensor array hydrogel II's color response to different amines are shown in the figure. Figure 3 .

[0103] The results showed that the colorimetric sensor array hydrogel II prepared in Example 3 could distinguish between simple amines (such as NH3) and various substituent amines (DMA, TMA, TEA), as well as polyamines (Ty, SPM, PUT, Tr), with clear color differences. This indicates that the hydrogel is highly sensitive to the spatial structure and functional groups of amine molecules. Among them, TMA, NH3 and DMA have moderate molecular size, strong polarity and hydrogen bond donor ability, and can effectively form stable interactions with the hydrogel, thereby driving significant color changes.

[0104] 2. Infrared spectroscopy analysis Carboxylated cellulose nanofibers, zwitterionic monomers ([2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide), acrylamide, and colorimetric sensor array hydrogel II prepared in Example 3 were taken respectively, and their infrared spectral characteristics were recorded by Fourier transform infrared spectroscopy (FTIR).

[0105] Infrared spectral analysis results of samples such as colorimetric sensor array hydrogel II are shown in the figure. Figure 4 .

[0106] The result showed: 1038cm -1 The characteristic peak at 1716 cm⁻¹ is the S═O sulfur stretching vibration band of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide. -1 The peak at 1636 cm⁻¹ originates from the C=O stretching vibration of the ester bond in [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide. -1 The peak at 1455 cm⁻¹ can be considered as the C=C double bond peak (with a relatively long wavelength) in acrylamide and [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide. -1 The peak at 3358 cm⁻¹ is attributed to the methyl bending vibration on the quaternary ammonium salt; -1 The characteristic peak at 1674 cm⁻¹ is related to the NH stretching vibration of acrylamide. -1 The peak at 3422 cm⁻¹ is attributed to the C=O stretching vibration of acrylamide. -1 The peak at 2913 cm⁻¹ is attributed to the OH stretching characteristic peak of carboxylated cellulose nanofibers. -1 The -COOH symmetric stretching vibrations of carboxylated cellulose nanofibers shift to 1038 cm⁻¹ in the hydrogel. -1 The C=O stretching vibration shifted to 1653 cm. -1 The presence of hydrogen bonds and electrostatic interactions is indicated by the significant reduction in the double bond absorption peak of the hydrogel. The remaining small peak may originate from [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide, indicating successful monomer polymerization. Therefore, intermolecular interactions exist in the colorimetric sensor array hydrogel II.

[0107] 3. Practice in monitoring the freshness of prawns The colorimetric sensor array hydrogel II prepared in Example 3 was used to monitor the freshness of prawns. The specific steps are as follows: Take 50 g of whole prawn samples and place them in a round glass preservation box. Fix the 2×2 colorimetric sensor array hydrogel II prepared in Example 3 to the inner surface of the preservation film with medical tape and filter paper. Then seal the preservation box with the preservation film. Then place the whole prawn samples in environments of 4℃ and 25℃ respectively for freshness monitoring. The detection indicators are the content of volatile basic nitrogen (TVB-N) and pH value in the prawn samples.

[0108] The practical device for monitoring the freshness of prawns is shown in [link / reference]. Figure 5 The results of the practical test for monitoring the freshness of prawns using a colorimetric sensor array hydrogel II are shown below. Figure 6 .

[0109] The results showed that as the storage time of the shrimp samples increased, the colorimetric sensor array hydrogel II prepared in Example 3 underwent significant color changes.

[0110] The above results demonstrate that the colorimetric sensor array hydrogel II prepared in Example 3 has a very good indication effect on the freshness of shrimp samples.

[0111] Example 10: Performance Testing of Hydrogels II, V, and VI for Colorimetric Sensor Arrays 1. Response sensitivity detection First, trimethylamine solutions with concentrations of 0.2 ppm, 0.4 ppm, 0.5 ppm, 1 ppm, 2 ppm, 4 ppm, 5 ppm, 10 ppm, 20 ppm, and 40 ppm were prepared. Then, the colorimetric sensor array hydrogel II prepared in Example 3, the colorimetric sensor array hydrogel V prepared in Example 6, and the colorimetric sensor array hydrogel VI prepared in Example 7 were exposed to the aforementioned trimethylamine solutions of different concentrations, and their response sensitivity to pH changes was tested.

[0112] The detection results of the response sensitivity of different colorimetric sensor array hydrogels are shown in the figure. Figure 7 .

[0113] The results showed that the colorimetric sensor array hydrogel II prepared in Example 3 exhibited the most stable and increasing response, with a relatively high overall Euclidean distance, especially at concentrations of 10 ppm and above, demonstrating strong sensitivity. The colorimetric sensor array hydrogel V prepared in Example 6 showed a faster response increase than that of colorimetric sensor array hydrogel VI, but was slightly lower than that of colorimetric sensor array hydrogel II around 10 ppm, and slightly better than that of colorimetric sensor array hydrogel VI at 20 ppm. The colorimetric sensor array hydrogel VI prepared in Example 7 showed a relatively flat response before 20 ppm, but a significant jump occurred at 40 ppm, with a rapid increase in response.

[0114] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0115] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A hydrogel, characterized in that, The hydrogel comprises the following components: Hydrogel networks, solvents, crosslinking agents, and initiators; The hydrogel network includes a first network and a second network; The second network is a rigid skeleton, and the second network fills the spatial skeleton of the first network; The first network is formed by free radical polymerization copolymerization of non-zwitterionic multifunctional monomers and zwitterionic monomers. The second network is formed by physically cross-linking cellulose derivatives; The molecular structure of the zwitterionic monomer contains both quaternary ammonium cationic groups and sulfonic acid anionic groups. The solvent is water and / or an aqueous solution; The initiator includes an oxidant and a catalyst.

2. The hydrogel according to claim 1, characterized in that, The non-zwitterionic multifunctional monomers include one or more of acrylamide, divinylbenzene, ethylene glycol diacrylate, and trimethylolpropane triacrylate; Optionally, the zwitterionic monomer comprises one or more of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide, (3-(methacryloylamino)propyl)dimethyl(3-thiopropyl)ammonium hydroxide inner salt, and 3-(N,N-dimethyl-alkylantimony)propanesulfonate; Optionally, the cellulose derivative includes one or more of carboxylated cellulose nanofibers, carboxymethyl cellulose, and hydroxyethyl cellulose; Optionally, the crosslinking agent includes one or more of N-N'-methyleneacrylamide, ethylene glycol dimethacrylate, tetramethylene dimethacrylate, and N,N'-1,4-phenyldiacrylamide; Optionally, the oxidant is a persulfate; Optionally, the catalyst is a tertiary amine compound; Optionally, the aqueous solution includes one or more of phosphate buffer, physiological saline, and tris(hydroxymethyl)aminomethane hydrochloride buffer.

3. The hydrogel according to claim 1, characterized in that, The mass percentages of the non-zwitterionic multifunctional monomer, zwitterionic monomer, cellulose derivative, crosslinking agent, oxidant, catalyst, and solvent are (9~18): (3~12): (1~5): (0.5~1): (0.03~0.05): (0.03~0.06): (64~87).

4. The hydrogel according to claim 3, characterized in that, The non-zwitterionic multifunctional monomer is acrylamide, the cellulose derivative is carboxylated cellulose nanofibers, the crosslinking agent is N-N'-methyleneacrylamide, the oxidant is potassium persulfate, the catalyst is tetramethylethylenediamine, and the solvent is water. Optionally, the mass percentage of acrylamide: zwitterionic monomer: carboxylated cellulose nanofiber: N-N'-methyleneacrylamide: potassium persulfate: tetramethylethylenediamine: water is (9~18): (3~12): (1~5): (0.5~1): (0.03~0.05): (0.03~0.06): (64~87).

5. The hydrogel according to claim 1, characterized in that, The hydrogel further comprises: Colorimetric indicators; The colorimetric indicator is an acid-base indicator and / or a pigment.

6. The hydrogel according to claim 5, characterized in that, The pigments include one or more of neutral red, alizarin, alizarin red, brilliant yellow, and purple sweet potato.

7. A method for preparing the hydrogel according to any one of claims 1 to 6, characterized in that, The method includes: S1: In the solvent, the non-zwitterionic multifunctional monomer, the zwitterionic monomer, the crosslinking agent and the oxidant are subjected to a first mixing treatment to obtain a hydrogel precursor solution; S2: The hydrogel precursor solution and the cellulose derivative solution are mixed and treated for the second time, and then the catalyst is added to simultaneously carry out free radical polymerization and physical crosslinking to obtain the hydrogel.

8. The method according to claim 7, characterized in that, The method further includes: The cellulose derivative is dispersed to obtain a cellulose derivative solution; Optionally, the method further includes: The hydrogel obtained in step S2 is subjected to contact treatment with a colorimetric indicator.

9. The method according to claim 7 or 8, characterized in that, The free radical polymerization reaction and physical crosslinking are carried out at a temperature of 60~70℃ for a time of 30~60 min. Optionally, the stirring time for the first mixing treatment is 30 to 120 minutes, and the stirring speed is 45 to 60 rpm; Optionally, the stirring time for the second mixing treatment is 15-30 min, and the stirring speed is 45-60 rpm; Optionally, the contact treatment time is 10 to 30 minutes.

10. A method for detecting the freshness of a sample to be tested, characterized in that, The method includes: The sample to be tested is exposed to the hydrogel of any one of claims 1 to 6 in the same closed environment, so that the volatile substances released by the sample to be tested come into contact with the hydrogel of any one of claims 1 to 6, and the freshness of the sample to be tested is determined according to the color. The hydrogel contains a colorimetric indicator; The sample to be tested is food or a food sample.

11. The application of the hydrogel according to any one of claims 1 to 6, or the method according to claim 10, in the detection of food or food samples.

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