Bionic colorimetric sensing platform for indicating food freshness

Abstract

The invention provides a bionic colorimetric sensing platform for indicating food freshness. The bionic colorimetric sensing platform comprises a substrate and N preset gel columns arranged on the substrate, each gel column is divided into an adsorption layer and a sensing layer; the adsorption layer is used for adsorbing a target detection object so as to realize enrichment and diffusion of the target detection object; one surface of the sensing layer is directly combined with the substrate, and the other surface is combined with one surface, close to the substrate, of the adsorption layer; the sensing layer is used for receiving the target detection object diffused by the adsorption layer, the sensing layer is loaded with a dyeing substance, the dyeing substance and the target detection object are subjected to colorimetric reaction, and the existence and content of the target detection object are reflected through the optical signal change of the dyeing substance. According to the application, high-sensitivity detection of characteristic decay gas and food-borne pathogens is realized, the early decay of food can be effectively evaluated, and the application is simple and convenient.

Description

Technical Field

[0001] This application belongs to the field of food testing technology, specifically relating to a biomimetic colorimetric sensing platform for indicating food freshness. Background Technology

[0002] Currently, many technologies have been developed for the testing of refrigerated food quality. Traditional testing methods, such as microbial counting and physicochemical index detection, are highly accurate but suffer from problems such as complex operation, long processing time, and destructive effects on samples. Novel methods, such as fluorescence methods, enzyme detection based on biosensors, and gas-sensitive electrochemical sensors, have enabled the detection of metabolic markers such as volatile nitrogen compounds, sulfides, and organic acids produced during food spoilage.

[0003] Current methods for testing the quality of refrigerated food suffer from the following main drawbacks: Traditional chemical indicators (such as volatile basic nitrogen) often lag behind actual sensory deterioration of the food, failing to effectively assess early spoilage; many testing methods (such as high-performance liquid chromatography) are complex, time-consuming, and can damage samples. Emerging rapid and real-time detection technologies (such as mass spectrometry and smart tags) face challenges including high cost, operational complexity, insufficient portability, and potential reduction in stability and repeatability in complex real-world samples. Summary of the Invention

[0004] To address the aforementioned technical problems, this application proposes a biomimetic colorimetric sensing platform for indicating food freshness.

[0005] In a first aspect, this application proposes a biomimetic colorimetric sensing platform for indicating food freshness, including a substrate, and further including: N preset gel pillars disposed on the substrate; wherein each gel pillar is divided into an adsorption layer and a sensing layer;

[0006] The adsorption layer is used to adsorb the target analyte, so as to achieve the enrichment and diffusion of the target analyte;

[0007] One side of the sensing layer is directly bonded to the substrate, and the other side is bonded to the side of the adsorption layer closest to the substrate. The sensing layer is used to receive the target analyte diffused through the adsorption layer. The sensing layer is loaded with a dyeing substance, which reacts with the target analyte in a colorimetric manner. The presence and content of the target analyte are reflected by the change in the optical signal of the dyeing substance.

[0008] Optionally, the adsorption layer is made of a stimulus-responsive hydrogel; the sensing layer is made of a synthetic polymer-based dual-network hydrogel.

[0009] Optionally, the stimulus-responsive hydrogel is an agar hydrogel, and the polymer-based dual-network hydrogel is a polyvinyl alcohol and polyacrylamide dual-network hydrogel.

[0010] Optionally, the adsorption layer contains a nanoporous material; the nanoporous material is used to capture and selectively enrich the target analyte in a hydrated microenvironment composed of a stimulus-responsive hydrogel.

[0011] Optionally, the nanoporous material is ZIF-8 nanomaterial, and the ZIF-8 nanomaterial is etched into a hollow structure.

[0012] Optionally, the mass ratio of the ZIF-8 nanomaterial to the agar hydrogel is 1:5.

[0013] Optionally, the ratio of the average thickness of the agar hydrogel to the average thickness of the polyvinyl alcohol and polyacrylamide dual-network hydrogel is 1:4.

[0014] Optionally, the dyeing substance is a chemically responsive dye.

[0015] Optionally, the chemically responsive dye includes one or more of the following responsive dyes: 2,4-dinitrophenylhydrazine and sulfuric acid, zinc nitrate and bromophenol blue, p-roxaline, tetraphenylcobalt porphyrin(II), tetraphenylporphyrin zinc(II), tetrachlorop-benzoquinone, methyl orange, methyl red and bromothymol blue, and phenol red.

[0016] Beneficial effects

[0017] 1. This application achieves highly sensitive detection of characteristic putrefactive gases and foodborne pathogens;

[0018] 2. This application has a detection limit of 0.02 ppm for trimethylamine, and can rapidly identify and detect volatile spoilage markers such as 2-nonanone, glutaraldehyde, and trimethylamine;

[0019] 3. This application can effectively detect a variety of common foodborne pathogens, including Staphylococcus aureus, enterohemorrhagic Escherichia coli (EHEC), Listeria monocytogenes and Salmonella. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of the biomimetic colorimetric sensing platform for indicating food freshness according to an embodiment of this application.

[0021] Figure 2 This is a flowchart illustrating the preparation process of the hollow ZIT-8 nanomaterial according to an embodiment of this application.

[0022] Among them, 1 is the biomimetic colorimetric sensing platform, 2 is the adsorption layer, 3 is the sensing layer, 4 is the nanoporous material, 5 is the chemically responsive dye, 6 is the dyeing product, 7 is the substrate, and 8 is the gel column. Detailed Implementation

[0023] The terms "first," "second," "third," "fourth," etc. (if present) in the specification and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus. The technical solutions of the embodiments of this application will now be clearly and completely described in conjunction with the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them.

[0024] Example

[0025] To address the issues in the background technology, this application designs and fabricates a biomimetic colorimetric sensing platform for indicating food freshness based on the multi-level layered structure of the human olfactory mucosa.

[0026] Analysis of the olfactory mucosa reveals that its core functional layers are: the upper mucus layer is responsible for "dynamically capturing, dissolving, and initially screening" odor molecules; the lower epithelial tissue is responsible for "stable sensing, conversion, and transmission" of bioelectrical signals. This is an efficient system model that separates "dynamic interface" from "homeostatic basis".

[0027] Reproducing this model in an artificial system presents the following fundamental contradiction: no single material can simultaneously optimize the two conflicting performances of "efficient capture" and "stable sensing / support"; this application proposes the design concept of "using two materials with very different properties for functional division".

[0028] To achieve "efficient capture" functionality, those skilled in the art typically focus on chemically responsive materials. This application, based on the physical properties of biological mucus's "fluidity" and "renewability," seeks materials with controllable physical phase transition characteristics—thermally reversible agar hydrogels. The "heat-liquefaction-cooling-gelling" physical property of agar hydrogels represents the most direct and gentle engineering approach to achieving a similar "flushing-regeneration" cycle to biological mucus. Those skilled in the art will understand that hydrogel materials possessing similar properties to those used in the sensing platform based on the principles of this application also fall within the scope of this technology.

[0029] Considering the need for periodic phase transitions (heating / cooling) in the upper layer, the lower layer must be able to withstand the resulting thermal stress and mechanical disturbances. Therefore, the lower layer material needs to possess extremely high toughness, fatigue resistance, and stable electrical properties. PVA / PAM (polyvinyl alcohol and polyacrylamide) dual-network hydrogels are the preferred hydrogel material in this application due to their classic high strength, high toughness, and good ionic conductivity. This achieves the function of "stable conduction."

[0030] In specific implementation, a biomimetic colorimetric sensing platform 1 for indicating food freshness includes a substrate 7, such as... Figure 1 As shown, it also includes: N gel pillars 8 sequentially disposed on the substrate 7; wherein each gel pillar 8 is divided into an adsorption layer 2 and a sensing layer 3;

[0031] The adsorption layer 2 is used to specifically adsorb the target analyte and to achieve the enrichment and diffusion of the target analyte.

[0032] One side of the sensing layer 3 is directly bonded to the substrate 7, and the other side is bonded to the side of the adsorption layer 2 that is close to the substrate 7. The sensing layer 3 is used to receive the target analyte diffused by the adsorption layer 2 and to produce a specific colorimetric reaction. The presence and content of the target analyte are reflected by the change in the optical signal of the dyeing substance it carries.

[0033] It is understandable that the above reaction is a synergistic effect of adsorption layer 2 and sensing layer 3. The diffusion efficiency of the target analyte in adsorption layer 2 is matched with the colorimetric reaction sensitivity of the dyeing substance, so as to achieve accurate and rapid colorimetric detection of the target analyte.

[0034] In this embodiment, N takes the value of any positive integer greater than or equal to 1; N is not a fixed value. The selection of the number of sensing layers (one sensing layer for each gel column) that function as dye dots depends on whether they can produce a specific response to the target analyte. When the sensing platform needs to perform response analysis on multiple target analytes, multiple dye dots need to be selected to form a response pattern, thereby achieving specific identification of different target analytes. Therefore, the value of N depends on whether the number of gel columns in the sensing platform loaded with gel columns reaches a suitable number, such that this suitable number can provide a pattern response to the target analyte.

[0035] The sensing layer is bonded to the substrate mainly by directly laminating hydrogel onto the substrate surface and fixing it by interfacial adsorption force; the gel column can be cylindrical or other shapes, which is not limited here; in this embodiment, a cylindrical gel column is selected.

[0036] In one feasible implementation, the material of the adsorption layer is selected as a stimulus-responsive hydrogel; the material of the sensing layer is selected as a synthetic polymer-based dual-network hydrogel.

[0037] In one alternative embodiment, the adsorption layer 2 further comprises a nanoporous material 4; the nanoporous material 4 is used for rapid capture and selective enrichment of target analytes in a hydrated microenvironment composed of a stimulus-responsive hydrogel.

[0038] In one feasible embodiment, the stimulus-responsive hydrogel is an agar hydrogel, and the polymer-based dual-network hydrogel is a polyvinyl alcohol and polyacrylamide dual-network hydrogel. It is understood that the stimulus-responsive hydrogel can also be a similar type of natural polysaccharide-based stimulus-responsive hydrogel, such as carrageenan or gellan gum hydrogel.

[0039] It is generally believed in the art that due to different gelation mechanisms, it is difficult to achieve seamless integration of bilayer hydrogel interfaces, and delamination is prone to occur. This embodiment addresses this problem through the following strategy: at the interface between the adsorption layer and the sensing layer, a permeable interlocking structure is formed by molecular chain entanglement; simultaneously, during the ultraviolet (UV) curing process of the sensing layer, an in-situ network generation reaction is induced at the interface. Thus, the upper agar hydrogel and the lower polyvinyl alcohol / polyacrylamide bilayer hydrogel form a continuous bond at the interface, significantly improving the anti-peeling ability under wet cycling conditions. Furthermore, this embodiment uses a UV-cured polyvinyl alcohol / polyacrylamide bilayer hydrogel as a constraint layer to suppress in-plane deformation. This constraint layer ensures that the upper agar hydrogel maintains a stable bond state and maintains an effective diffusion contact area, thereby avoiding performance fluctuations caused by swelling mismatch. This design overcomes the common swelling mismatch problem in traditional bilayer hydrogel sensors—that is, warping, wrinkling, and interface bond damage caused by swelling differences.

[0040] To improve gas adsorption efficiency, in one feasible implementation, in a design that mimics the olfactory system of mammals, ZIF-8 nanomaterial is selected as the nanoporous material. ZIF-8 is etched into a hollow structure and combined with the hydrogel in the adsorption layer 2 to construct a highly efficient adsorption layer.

[0041] First, traditional olfactory biomimetic materials face an inherent contradiction between "high adsorption capacity" and "rapid response / desorption." While dense nanomaterials possess high specific surface area, the slow diffusion of molecules within deep pores leads to sluggish response and difficulty in refreshing. Ordinary hydrogels exhibit good biocompatibility, but their adsorption selectivity and capacity are limited. Etching ZIF-8 into a hollow structure (HollowZIF-8, HZIF-8) goes beyond simply increasing specific surface area; it aims to create a "molecular trapping and pre-enrichment chamber." This hollow cavity, acting as a giant nanoscale gas storage unit, can rapidly capture and initially enrich specific odor molecules through its porous outer shell, allowing the molecules to quickly reach an equilibrium concentration within the cavity.

[0042] The hollow ZIF-8 is not used in isolated powder form. This application further combines the hollow ZIF-8 with a hydrogel system to construct a gas adsorption layer, structurally achieving a "layered synergistic" function similar to the olfactory mucosa of mammals: the hydrogel provides a continuous flexible matrix and a stable hydration microenvironment, which can simulate the dissolution, enrichment, and interfacial diffusion of odor molecules by the surface mucus layer of the olfactory system, while confining and fixing the particles to prevent powder migration, aggregation, or shedding; the hollow ZIF-8 forms a highly efficient and regenerable adsorption-enrichment unit in the hydrogel network, undertaking the rapid capture and selective enrichment of volatile molecules. After the two are coupled, the adsorption layer is no longer a simple superposition of "hydrogel + filler", but forms a biomimetic structure with a synergistic mechanism of interfacial capture / enrichment, rapid internal mass transfer, and reversible release. Thus, while maintaining soft adhesion and environmental stability, it can achieve high-throughput adsorption and dynamic response performance that is difficult to achieve with traditional single-layer hydrogels or solid particle-filled systems.

[0043] The hollow ZIF-8 nanomaterial in this application, such as Figure 2 As shown, ZIF-8 particles were prepared using the following method: ZIF-8 particles were synthesized via a classical hydrothermal method. 5 mL of a 0.27 M zinc acetate solution was mixed with 6.4 mL of a 2.72 M 2-methylimidazole solution and stirred at room temperature for 10 minutes until the mixture changed from transparent to milky white. Subsequently, the raw ZIF-8 nanomaterials (40 mg) were mixed with a tannic acid solution (20 mL, 2.5 g / L) and then sonicated together with the zinc acetate and 2-methylimidazole mixture for 10 minutes. Finally, the mixture was collected by centrifugation, washed with water and methanol, and dried to obtain the final hollow ZIF-8 nanomaterials.

[0044] In this application, the adsorption layer hydrogel uses agar as raw material, and hollow ZIF-8 nanomaterials are added at a preferred doping ratio of 20%. It can be understood that the hollow ZIF-8 nanomaterials and agar hydrogels are mixed at a mass ratio of 1:5.

[0045] In one feasible implementation, the biomimetic colorimetric sensing platform further includes: N chemically responsive dyes 5; the chemically responsive dyes 5 are respectively injected into polyvinyl alcohol and polyacrylamide dual-network hydrogel.

[0046] It is understandable that the sensing layer 3 receives the target analyte diffused through the adsorption layer 2 and undergoes a specific colorimetric reaction, which is mainly a chemical reaction between the chemically responsive dye 5 and the corresponding target analyte to form a staining product 6.

[0047] Specifically, in this embodiment, the number of gel columns N is set to 9, and each sensing layer is loaded with a chemically responsive dye; the preferred ratio of the average thickness of the adsorption layer hydrogel to the sensing layer hydrogel in dry or wet state is 1:4, where the dry state is the test state and the wet state is the use state; the two hydrogels are combined in this ratio to prepare a biomimetic colorimetric sensing platform for indicating food freshness.

[0048] Accordingly, in the specific implementation process, nine chemically responsive dyes were selected. These nine chemically responsive dyes were selected for the target analyte. This screening was to achieve accurate detection of the target analyte.

[0049] Specifically, the chemically responsive dyes are: 2,4-dinitrophenylhydrazine and sulfuric acid (H2SO4), zinc nitrate (Zn(NO3)2) and bromophenol blue, pararosaniline, tetraphenylcobalt(II) (CoTPP), tetraphenylporphyrin(II) (ZnTPP), tetrachloro-p-benzoquinone (Chloranil), methyl orange, methyl red, bromothymol blue, and phenol red. The target volatile organic compounds corresponding to the above dyes are detailed in Table 1, and their specific compositions are detailed in Table 2.

[0050] Table 1:

[0051] Target VOCs (volatile organic compounds) Dye Composition(s) Aldehydes (aldehydes), ketones (ketones) <![CDATA[2,4-dinitrophenylhydrazine + H2SO4]]> Aldehydes (aldehydes), ketones (ketones) <![CDATA[Zn (NO3)2+ bromophenol blue]]> Ketones Pararosaniline Amines CoTPP Amines ZnTPP Sulfur compounds Chloranil рH Methyl orange рH Methyl red + Bromothymol blue рH Phenol red

[0052] Table 2:

[0053] Serial Number Dye Composition(s) Preparation 1 <![CDATA[2,4-dinitrophenylhydrazine + H2SO4]]> <![CDATA[1 mg / mL 2,4-dinitrophenylhydrazine in MOE (ethylene glycol monomethyl ether) + 1 M H2SO4; 80:1 v / v]]> 2 <![CDATA[Zn (NO3)2+bromophenol blue]]> <![CDATA[18 mg / mL Zn (NO3)2 + 4 mg / mL bromophenol blue + MOE 1:1 v / v]]> 3 Pararosaniline <![CDATA[1 mg / mL pararosaniline in MOE + 1 MH2SO4]]> 4 CoTPP 6 mg / mL in MOE 5 ZnTPP 6 mg / mL in MOE 6 Chloranil 0.25 g tetra-chloro-benzoquinone + 100 mL N,N-dimethylformamide 7 Methyl orange 0.3% methyl orange in ethanol 8 Methyl red + bromothymol blue 0.3% (w / v) methyl red in aqueous ethanol (1:1 v / v) + 0.3% (w / v) bromothymol blue inaqueous ethanol (1:1 v / v); 3:2 v / v 9 Phenol red 50 mg phenol red + 1.34 mL tetrabutylammonium hydroxide

[0054] This application's sensing platform, referencing the structure and functional characteristics of the natural olfactory system, employs a bilayer hydrogel design to simulate the olfactory mucosa with physical adsorption and diffusion functions of odor substances. Agar hydrogel is introduced as the adsorption layer, providing a micro-liquid environment for the target microparticles, enabling the adsorption and diffusion of odor molecules. To simulate odor-binding proteins, specific colorimetric reagents are embedded in the lower sensing layer hydrogel as basic recognition units. To simulate olfactory receptors that generate olfactory signals through conformational changes, the characteristic color changes generated by the reaction are considered as "olfactory signals." The adsorption layer in this application's sensing platform contains hollow ZIF-8 nanomaterials. The open structure of the hollow cavity expands the charge interaction range, improving molecular capture efficiency and enabling it to function as an effective molecular concentrator, maintaining a high analyte concentration and extending the residence time at the hydrogel interface.

[0055] 1. Conventional olfactory bionics research usually focuses on optimizing a single material (such as improving the porosity or sensitivity of a hydrogel) or simply stacking different functional materials. This application aims to solve a neglected but crucial system-level contradiction through a bilayer gel composite design: how to simultaneously achieve a "dynamic and open molecular interaction environment" and a "stable and faithful biological signal generation / transmission environment" on a single interface.

[0056] 2. Multilayer structures: Because the interlayer interface increases diffusion resistance, it is generally believed in the art that the interlayer interface will inevitably reduce mass transfer efficiency. However, this application achieves higher dynamic adsorption efficiency than single-layer structures by constructing a continuous network and gradient channels.

[0057] 3. It is generally believed in the art that improving stability (anti-swelling / high strength) inevitably sacrifices wettability and mass transfer. This application delegates "stability" to the lower layer and "wetting and mass transfer" to the upper layer, no longer requiring a material to bear all the indicators at the same time.

[0058] It is understood that the bilayer gel system of this application is not a conventional stacked structure in the art, but rather a functional division structure proposed to address the contradictory requirements of biomimetic olfactory interfaces that need to simultaneously meet the requirements of "high hydration and rapid mass transfer" and "long-term steady-state support": the upper agar hydrogel simulates the olfactory mucus layer to provide an interface for rapid capture and diffusion of volatiles; the lower layer uses UV-cured PVA / PAM gel to construct a highly stable support layer to suppress swelling deformation and performance drift. This structure unexpectedly solves the problems of response hysteresis, memory effect, baseline drift, and contamination-triggered failure that are prone to occur in single-layer high-wetting systems, while overcoming the bonding barriers between thermogels and UV-cured gels in terms of interface compatibility, swelling mismatch, and wet cycle peeling, and breaking through the technical difficulties of "layering increasing resistance and agar being unsuitable for engineered interface layers".

[0059] To better understand the actual performance of this application, here is an example of its application in pathogen detection and food freshness indication:

[0060] 1. Materials

[0061] 1.1 Drugs: boric acid, hydrochloric acid, potassium carbonate, gum arabic, glycerin, methyl red, bromocresol green, 95% ethanol.

[0062] 1.2 The salmon was sourced from a local supermarket.

[0063] 2. Methods and Results

[0064] 2.1 Indications for the freshness of fish products

[0065] According to the TVB-N detection limit specified in the Chinese standard (GB 2733–2015 "Fresh and Frozen Aquatic Animal Products"), salmon is inedible when TVB-N exceeds 20 mg / 100g. TVB-N was determined using the method specified in GB 5009.228-2016. Fish with TVB-N values ​​between 15 and 20 mg N / 100g were classified as partially fresh, while those exceeding 20 mg N / 100g were classified as spoiled. The TVB-N level of salmon continuously increased during storage. It transitioned from fresh to partially fresh between days 3 and 4, and became completely spoiled after 5 to 6 days. Simultaneously, we used another widely used indicator in food testing, TVC, to jointly determine freshness along with TVB-N, thereby establishing the correlation between colorimetric changes and the actual freshness of the samples. TVC was measured using the method in GB 4789.2-2022. When TVC reached ~log 6 CFU / g, it was considered near spoilage (sub-fresh); when it exceeded ~log 7 CFU / g, it was considered inedible. With increasing storage time, the TVC of salmon during low-temperature storage showed a similar trend to TVB-N, gradually increasing. Similarly, during days 3-4, the TVC level increased to ~6 log CFU / mL, entering the sub-fresh stage. On days 5-6, the TVC level increased to ~log 7 CFU / mL, entering the complete spoilage stage. Correspondingly, the composite hydrogel colorimetric sensor array (i.e., the sensing platform in this embodiment) exhibited significant color changes. The Euclidean distance (ED) generated by each staining point (corresponding to the sensing layer of each gel column) changed with storage time in a trend basically consistent with that of TVB-N and TVC, indicating that the sensing platform of this invention can achieve accurate monitoring of freshness changes in fish products during the storage period.

[0066] Further correlation analysis was conducted on the ED value and TVB-N content of meat samples during storage. The results showed that under different temperature conditions, storage time, TVB-N content, and TVC were all highly linearly correlated with the ED value in response to salmon, with correlation coefficients exceeding 0.96, a value generally considered to indicate a strong correlation. Therefore, this application can serve as a novel and convenient method for assessing meat freshness, achieving highly sensitive detection of food freshness.

[0067] The scope of protection of this application is not limited to the embodiments described above. Obviously, those skilled in the art can make various modifications and variations to this disclosure without departing from the scope and spirit of this disclosure. If such modifications and variations fall within the scope of the technology disclosed herein and its equivalents, then the intent of this disclosure also includes such modifications and variations.

Claims

1. A biomimetic colorimetric sensing platform for indicating food freshness, comprising a substrate, characterized in that, Also includes: N gel pillars are disposed on the substrate; wherein each gel pillar is divided into an adsorption layer and a sensing layer; The adsorption layer is used to adsorb the target analyte, so as to achieve the enrichment and diffusion of the target analyte; One side of the sensing layer is directly bonded to the substrate, and the other side is bonded to the side of the adsorption layer closest to the substrate. The sensing layer is used to receive the target analyte diffused through the adsorption layer. The sensing layer is loaded with a dyeing substance, which reacts with the target analyte in a colorimetric manner. The presence and content of the target analyte are reflected by the change in the optical signal of the dyeing substance.

2. The biomimetic colorimetric sensing platform for indicating food freshness according to claim 1, characterized in that, The adsorption layer is made of a stimulus-responsive hydrogel; the sensing layer is made of a synthetic polymer-based dual-network hydrogel.

3. The biomimetic colorimetric sensing platform for indicating food freshness according to claim 2, characterized in that, The stimulus-responsive hydrogel is an agar hydrogel, and the polymer-based dual-network hydrogel is a polyvinyl alcohol and polyacrylamide dual-network hydrogel.

4. The biomimetic colorimetric sensing platform for indicating food freshness according to claim 2, characterized in that, The adsorption layer contains nanoporous materials; the nanoporous materials are used to capture and selectively enrich target analytes in a hydrated microenvironment composed of a stimulus-responsive hydrogel.

5. The biomimetic colorimetric sensing platform for indicating food freshness according to claim 4, characterized in that, The nanoporous material is ZIF-8 nanomaterial, which is etched into a hollow structure.

6. The biomimetic colorimetric sensing platform for indicating food freshness according to claim 5, characterized in that, The mass ratio of the ZIF-8 nanomaterial to the agar hydrogel is 1:

5.

7. The biomimetic colorimetric sensing platform for indicating food freshness according to claim 3, characterized in that, The average thickness of the agar hydrogel is in a ratio of 1:4 to the average thickness of the polyvinyl alcohol and polyacrylamide dual-network hydrogel.

8. The biomimetic colorimetric sensing platform for indicating food freshness according to claim 1, characterized in that, The dyeing substance is a chemically responsive dye.

9. The biomimetic colorimetric sensing platform for indicating food freshness according to claim 8, characterized in that, The chemically responsive dyes include one or more of the following responsive dyes: 2,4-dinitrophenylhydrazine and sulfuric acid, zinc nitrate and bromophenol blue, p-roxaline, tetraphenylcobalt porphyrin(II), tetraphenylporphyrin zinc(II), tetrachlorop-benzoquinone, methyl orange, methyl red and bromothymol blue, and phenol red.

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