Bio-based gel bead for real-time freshness monitoring and preparation method of bio-based gel bead

Abstract

The invention belongs to the technical field of intelligent food monitoring and packaging, and discloses a bio-based gel bead for freshness real-time monitoring and a preparation method thereof.The preparation method comprises the steps that sulfur-doped graphene quantum dots are prepared, sulfur-doped graphene quantum dot / sodium alginate composite dispersion liquid is prepared based on the sulfur-doped graphene quantum dots, and the bio-based gel bead for freshness real-time monitoring is obtained. The preparation method comprises the following steps: preparing a sulfur-doped graphene quantum dot / sodium alginate composite dispersion liquid, preparing a sulfur-doped graphene quantum dot / sodium alginate composite dispersion liquid, preparing a reference-type poly (adipic acid) / butylene terephthalate spinning fiber, preparing a response-type cellulose nanofiber, and preparing bio-based gel beads based on the response-type cellulose nanofiber, the sulfur-doped graphene quantum dot / sodium alginate composite dispersion liquid and the reference-type poly (adipic acid) / butylene terephthalate spinning fiber; the three-in-one bio-based gel beads of detection, bacteriostasis and degradation can be formed, direct contact with food is not needed, ultra-fast response, high-sensitivity detection and full-life-cycle environmental protection of biogenic amine are achieved, the monitoring accuracy and reliability are remarkably improved, and the functions are comprehensive.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of intelligent monitoring packaging of food, in particular to a bio-based condensate bead for real-time freshness monitoring and a preparation method thereof. BACKGROUND

[0003] Currently, the freshness detection technology of high-protein food mainly focuses on three directions: electrochemical analysis, pH sensitive detection and traditional fluorescence detection, all of which have technical bottlenecks that are difficult to break through. For the freshness detection of high-protein food, the existing published patents mainly focus on the direction of membranes and gels. In recent years, condensate dosage forms have become a new carrier for food freshness monitoring due to their high efficiency in contacting target gases. However, the existing technology still has core shortcomings: low functional integration, existing condensate beads only have single detection function, cannot simultaneously inhibit microbial reproduction, are difficult to delay the food spoilage process, and cannot achieve "monitoring-preservation" synergy. At the same time, the preparation process is traditional, and the functional components (such as fluorescent probes and bacteriostatic agents) are prone to aggregation, resulting in low detection sensitivity, poor repeatability, and inability to meet the requirements of industrial application.

[0004] Therefore, there is an urgent need for a technology that can solve the problems of poor biodegradability, single function, response lag, and easy aggregation of existing monitoring materials, and the risk of food contamination. SUMMARY

[0005] The purpose of the present application is to provide a bio-based condensate bead for real-time freshness monitoring and a preparation method thereof to overcome the problems in the prior art. The present application can effectively solve the problems of easy aggregation and poor stability of quantum dots, ensure the sensitivity and rapid response of the monitoring signal, overcome the defects of traditional materials with response lag, and form a "detection-bacteriostatic-degradation" trinity bio-based condensate bead without direct contact with food, achieving ultra-fast response, high sensitivity detection, and full life cycle environmental protection of biological amines, adapting to multi-link monitoring of high-protein food, and significantly improving the accuracy and reliability of monitoring with comprehensive functions.

[0006] To achieve the above-mentioned purposes, the technical solutions adopted by the present application are as follows: In a first aspect, the present application provides a bio-based condensate bead preparation method for real-time freshness monitoring, comprising the following steps: Preparation of sulfur-doped graphene quantum dots; Preparation of sulfur-doped graphene quantum dots / sodium alginate composite dispersion based on sulfur-doped graphene quantum dots; Preparation of reference polybutylene terephthalate spinning fiber; Preparation of responsive cellulose nanofiber; Bio-based condensed beads are prepared based on a responsive cellulose nanofiber, a sulfur-doped graphene quantum dot / sodium alginate composite dispersion liquid and a reference polybutylene adipate terephthalate spinning fiber.

[0007] In some embodiments, the preparation of the sulfur-doped graphene quantum dot specifically comprises: After Soxhlet extraction of the sulfur-containing polymer and n-hexane, reflux and first vacuum drying are sequentially performed to obtain a sulfur-containing polymer with impurities removed, and the sulfur-containing polymer with impurities removed is subjected to first microwave pyrolysis to obtain a solid product and a pyrolysis oil, and the solid product is subjected to second microwave pyrolysis to obtain a pyrolysis graphite carbon; After the pyrolysis oil and the ethyl acetate-deionized water mixed solvent are mixed and subjected to oscillation extraction, the upper organic phase is collected, anhydrous sodium sulfate is added to the organic phase, and then standing drying and filtration are sequentially performed to obtain a filtrate, and the filtrate is subjected to rotary evaporation concentration to obtain a sulfur-containing small molecule carbon source; After the pyrolysis graphite carbon is ball milled and then sieved, an activated pyrolysis carbon is obtained, the sulfur-containing small molecule carbon source, the activated pyrolysis carbon and deionized water are mixed and then subjected to first ultrasonic dispersion, and then heating reaction and first centrifugation are sequentially performed to obtain a supernatant, and the supernatant is subjected to dialysis to obtain a dialysis product; The dialysis product is subjected to first freeze-drying to obtain a sulfur-doped graphene quantum dot.

[0008] In some embodiments, the sulfur-containing polymer includes waste tire rubber, vulcanized rubber product offcuts, sulfur-containing epoxy resin, thio-polyolefin or sulfur-containing plastic recyclate; The mass ratio of the sulfur-containing polymer to n-hexane is 10: (100-500); the temperature of the Soxhlet extraction is 80℃; the time of the reflux is 6-10 h; the temperature of the first vacuum drying is 60℃, and the time of the first vacuum drying is 12 h; The first microwave pyrolysis specifically comprises: heating at a temperature increasing rate of 250-400 ℃ / min to 450-800 ℃ under a power of 3000-5000 W, and holding for 10-30 min; The second microwave pyrolysis specifically comprises: heating at a temperature increasing rate of 5-20 ℃ / min to 1200-1500 ℃ under a power of 200-600 W, and holding for 5-10 h; The mass ratio of the pyrolysis oil, the ethyl acetate-deionized water mixed solvent and anhydrous sodium sulfate is 2:25:5, and in the ethyl acetate-deionized water mixed solvent, the volume ratio of ethyl acetate to deionized water is 8:2; The oscillation extraction is performed for 3-5 times, wherein the oscillation time of each oscillation extraction is 15-25 min, and the standing and layering time of each oscillation extraction is 10-20 min; The standing drying time is 2 h; the rotation speed of the rotary evaporation concentration is 100 rpm, the rotary evaporation concentration temperature is 45-55 ℃, and the rotary evaporation concentration vacuum degree is greater than 0.08 Mpa; The rotation speed of the ball milling is 300-500 rpm, and the ball milling time is 2-4 h; the screening standard is 300-400 mesh; The mass ratio of the sulfur small molecule carbon source, activated pyrolytic carbon and deionized water is (0.5-1):(0.1-0.2):(50-80); The first ultrasonic dispersion time is 15 min; the heating reaction temperature is 180-220 ℃, the heating reaction time is 12-24 h; the first centrifugation speed is 35000-55000 rpm, and the first centrifugation time is 2-4 h; the dialysis molecular weight cut-off is 500-1000 Da, the dialysis time is 48-72 h, and the dialysis liquid is replaced every 4-8 h during the dialysis; The first freeze-drying time is 48-60 h, and the first freeze-drying temperature is -50 ℃.

[0009] In some embodiments, the preparation of the sulfur-doped graphene quantum dot / sodium alginate composite dispersion based on the sulfur-doped graphene quantum dots specifically comprises: After dissolving the sodium alginate in deionized water, glycerol is added for the first stirring to obtain a sodium alginate solution; Sulfur-doped graphene quantum dots are added to the sodium alginate solution for the second ultrasonic dispersion to obtain a preliminary dispersion, and the preliminary dispersion is first adjusted in pH and then subjected to low-temperature shearing to obtain a sulfur-doped graphene quantum dot / sodium alginate composite dispersion; The mass ratio of the sodium alginate, deionized water, glycerol and sulfur-doped graphene quantum dots is 2:98:(0.005-0.01):(0.001-0.002); The first stirring temperature is 50 ℃, the first stirring time is 1 h, and the first stirring speed is 500 rpm; The second ultrasonic dispersion time is 30 min; the first pH adjustment specifically comprises adjusting the pH to 5.0-6.0 by hydrochloric acid; the low-temperature shearing temperature is 5-10 ℃, the low-temperature shearing speed is 5000-8000 rpm, and the low-temperature shearing time is 30-45 min.

[0010] In some embodiments, the preparation of the reference-type polybutylene adipate terephthalate spinning fiber specifically comprises: The red fluorescent substance is dissolved in N,N-dimethylformamide, then hexanediamine is added for second stirring, and the first precipitate is obtained by pouring into ice ethanol after the first precipitation, and the red fluorescent substance-hexanediamine grafting product is obtained by collecting the first precipitate through suction filtration; The polybutylene adipate terephthalate, the red fluorescent substance-hexanediamine grafting product, polyvinylpyrrolidone and antioxidant 1010 are high-speed mixed, and then the composite master batch is obtained by double-screw extrusion and pelletization at high temperature. The composite master batch is dissolved in a trichloromethane-N,N-dimethylformamide mixed solvent to obtain a spinning solution, and then the spinning solution is subjected to ultrasonic defoaming and electrospinning in sequence to obtain a spinning fiber membrane.

[0011] In some embodiments, the red fluorescent substance is one of sulforhodamine 640, sulforhodamine 101, and BODIPY 630 / 650-trisulfonic acid. The mass ratio of the red fluorescent substance, N,N-dimethylformamide, hexanediamine and ice ethanol is (1-5):200:1:1000; the temperature of the second stirring is 80 ℃, and the time of the second stirring is 6 h. The mass ratio of the polybutylene adipate terephthalate, the red fluorescent substance-hexanediamine grafting product, polyvinylpyrrolidone and antioxidant 1010 is 100:(0.5-1):(3-5):0.2; the K value of the polyvinylpyrrolidone is 30-60; the antioxidant 1010 is tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester; the rotation speed of the high-speed mixing is 1200 rpm, and the time of the high-speed mixing is 10 min; the temperature of the high temperature is 160-180 ℃. The mass ratio of the composite master batch and the trichloromethane-N,N-dimethylformamide mixed solvent is 20:(80-85); the volume ratio of trichloromethane to N,N-dimethylformamide in the trichloromethane-N,N-dimethylformamide mixed solvent is 3:1; the time of the ultrasonic defoaming is 20 min, and the frequency of the ultrasonic defoaming is 40 kHz; the voltage of the electrospinning is 18-22 kV, the receiving distance of the electrospinning is 15-20 cm, and the flow rate of the electrospinning is 0.5-1 mL / h. The temperature of the vacuum heat treatment is 80-100 ℃, and the time of the vacuum heat treatment is 30-60 min.

[0012] In some embodiments, the preparation of the responsive cellulose nanofiber specifically comprises: adding a green fluorescent substance solution to the chitosan solution in acetic acid solution, stirring in the dark, then adjusting the pH for the second time and centrifuging for the second time in sequence, collecting the second precipitate, and performing second freeze-drying on the second precipitate to obtain a green fluorescent substance-chitosan graft product; dispersing the cellulose nanofiber uniformly in deionized water, then uniformly coating the cellulose nanofiber on a polytetrafluoroethylene substrate to perform second vacuum drying, and forming a cellulose nanofiber dry film; placing the cellulose nanofiber dry film into an atmosphere of argon and oxygen to perform etching, dispersing the cellulose nanofiber dry film in deionized water after etching to obtain a cellulose nanofiber suspension; adding the green fluorescent substance-chitosan graft product and N,N-methylene bisacrylamide to the cellulose nanofiber suspension, then performing ultrasonic treatment and third centrifugation in sequence, collecting the third precipitate, and performing third vacuum drying on the third precipitate to obtain responsive cellulose nanofiber.

[0013] In some embodiments, the mass ratio of the chitosan, the acetic acid solution, and the green fluorescent substance solution is 1:50:(0.1-0.2); the degree of deacetylation of the chitosan is greater than or equal to 90%; the mass concentration of the acetic acid solution is 1 wt%; and the green fluorescent substance solution is one of 5-carboxyfluorescein, fluorescein sodium, and fluorescein isothiocyanate dissolved in N,N-dimethylformamide; The temperature of the light-shielded stirring is 30°C, and the time of the light-shielded stirring is 12 h; the second adjustment of the pH is specifically adjusting the pH to 7.0 by sodium hydroxide; the speed of the second centrifugation is 10,000 rpm, and the time of the second centrifugation is 15 min; the temperature of the second freeze-drying is -70°C, and the time of the second freeze-drying is 24 h; The mass ratio of the cellulose nanofiber and the deionized water is 5:(95-100); the temperature of the second vacuum drying is 40-60°C, and the time of the second vacuum drying is 6 h; The volume ratio of the argon and the oxygen is 4:1; the power of the etching is 300-400 W, and the temperature of the etching is 10-15 min; and the mass concentration of the cellulose nanofiber suspension is 1 wt%; The mass ratio of the cellulose nanofiber suspension, the green fluorescent substance-chitosan graft product, and N,N-methylene bisacrylamide is 100:(0.1-0.2):0.05; and the mass ratio of the green fluorescent substance and N,N-dimethylformamide is 1:10; The frequency of the ultrasonic treatment is 40 kHz, the time of the ultrasonic treatment is 20-30 min; the speed of the third centrifugation is 8000-12000 rpm, the time of the third centrifugation is 10-20 min; the temperature of the third vacuum drying is 40-50 ℃, the time of the third vacuum drying is 6-10 h.

[0014] In some embodiments, the bio-based coacervate is prepared based on the responsive cellulose nanofiber, the sulfur-doped graphene quantum dot / sodium alginate composite dispersion and the reference polybutylene adipate terephthalate spinning fiber, and specifically comprises: The responsive cellulose nanofiber is uniformly dispersed in deionized water to obtain a responsive cellulose nanofiber suspension; The sulfur-doped graphene quantum dot / sodium alginate composite dispersion, the reference polybutylene adipate terephthalate spinning fiber and the responsive cellulose nanofiber suspension are mixed and then subjected to a third stirring to obtain a paste-like gel, vitamin E is added to the paste-like gel and subjected to a fourth stirring, and then the paste-like gel is injected into an inner phase reservoir of a microfluidic device, and then the droplets flowing out of the inner phase reservoir of the microfluidic device are dropped into a first cross-linking liquid to form a coacervate precursor; The coacervate precursor is transferred to a second cross-linking liquid and then subjected to washing and constant-temperature drying in sequence to obtain the bio-based coacervate; The mass concentration of the responsive cellulose nanofiber suspension is 1 wt%; the mass ratio of the sulfur-doped graphene quantum dot / sodium alginate composite dispersion, the reference polybutylene adipate terephthalate spinning fiber, the responsive cellulose nanofiber suspension and vitamin E is 100: (5-10): (3-5): (0.1-0.2); The temperature of the third stirring is 25 ℃, the speed of the third stirring is 800 rpm, and the time of the third stirring is 20 min; the temperature of the fourth stirring is 25 ℃, the speed of the fourth stirring is 800 rpm, and the time of the fourth stirring is 10 min; The inner phase reservoir of the microfluidic device, wherein the outer phase is paraffin oil containing 1-2 wt% of Span 80, the Span 80 is sorbitan fatty acid ester, the flow rate of the outer phase is 5-8 mL / h, and the flow rate of the inner phase is 0.5-1 mL / h; The concentration of the first cross-linking liquid is 3 wt%, the temperature of the first cross-linking liquid is 30 ℃, and the time of the first cross-linking liquid is 10-15 min; The mass ratio of the bead coagulation precursor to the second cross-linking liquid is (10-20):(100-200); the initial mass concentration of the second cross-linking liquid is 3 wt%, and is reduced by 0.5 wt% every 30 min until the mass concentration of the second cross-linking liquid is 0.5 wt%; the first cross-linking liquid and the second cross-linking liquid are both calcium chloride-magnesium chloride composite cross-linking agent solutions, wherein the molar ratio of calcium ions to magnesium ions is 2:1; The temperature of the constant temperature drying is 25-30 DEG C, and the time of the constant temperature drying is 5-15 min.

[0015] In a second aspect, the present application provides a bio-based bead coagulum for real-time freshness monitoring, which is based on a bio-based bead coagulum preparation method for real-time freshness monitoring.

[0016] The above technical solution has the following advantages or beneficial effects: In a first aspect, the present application provides a bio-based bead coagulum preparation method for real-time freshness monitoring, which effectively solves the problems of easy agglomeration and poor stability of quantum dots by constructing a sulfur-doped graphene quantum dot / sodium alginate composite system, ensures the sensitivity and rapid response of the monitoring signal (such as fluorescence intensity), and overcomes the defects of traditional material response lag; at the same time, the bead coagulum is entirely made of bio-based materials such as sodium alginate and cellulose, which ensures that the material is biodegradable and has no toxic substance residue, and fundamentally eliminates the risk of food contamination; in addition, the unique response type and reference type fiber are cooperatively designed to realize self-calibration and visual monitoring of pH or biological amine and other spoilage markers, forming a "detection-antibacterial-degradation" three-in-one bio-based bead coagulum, which does not need to directly contact food, realizes ultra-fast response, high sensitivity detection, and full life cycle environmental protection of biological amine, and is suitable for multi-link monitoring of high-protein food, significantly improves the accuracy and reliability of monitoring, and has comprehensive functions.

[0017] In some embodiments, the preparation of sulfur-doped graphene quantum dots adopts a "top-down" step-by-step strategy: first, the sulfur-containing polymer is converted into pyrolysis oil and pyrolysis graphite carbon by microwave pyrolysis, and then the selective extraction principle of ethyl acetate-deionized water mixed solvent is used to realize the accurate separation of sulfur-containing small molecule carbon source; Specifically, ethyl acetate can efficiently dissolve the target sulfur-containing small molecules, while deionized water can remove acid alcohol impurities, and non-polar impurities can be separated by layering; In the hydrothermal synthesis of sulfur-doped graphene quantum dots, the high-temperature and high-pressure environment promotes the in-situ doping and carbonization reaction of sulfur-containing small molecule carbon source and activated pyrolysis carbon, in which the sulfur atom forms a stable C-S bond by replacing the carbon site in the carbon lattice, and the size uniformity of the quantum dots is greatly improved by the synergistic control of reaction temperature and time, and the closed system of the hydrothermal environment also avoids the oxidation side reaction; Then, through the operation of ultracentrifugation and dialysis purification, the unreacted precursors and impurities are removed, and finally the sulfur-doped graphene quantum dots with high fluorescence quantum yield and good dispersion uniformity are obtained; Sulfur doping not only enhances the fluorescence emission performance of graphene quantum dots by introducing sulfur-related defect states into the carbon lattice of graphene quantum dots, but also the thiol groups present on the surface of the modified sulfur-doped graphene quantum dots can specifically bind with the amino groups of biological amine molecules, thereby significantly improving the detection sensitivity; The hydrothermal method converts industrial solid waste into fluorescent functional materials, and sulfur doping not only enhances the fluorescence performance of quantum dots, but also endows them with antibacterial function; Finally, the preparation of sulfur-doped graphene quantum dot / sodium alginate composite dispersion liquid makes the surface of sulfur-doped graphene quantum dots weakly negatively charged through pH regulation, and forms an "electrostatic repulsion-hydrogen bond synergy" with the carboxyl group of sodium alginate, then combined with low-temperature shearing to realize the uniform dispersion of quantum dots, avoid the fluorescence quenching caused by agglomeration, and at the same time, glycerol as a plasticizer can weaken the hydrogen bonds between the molecular chains of sodium alginate, greatly improving the flexibility of the beads.

[0018] In some embodiments, for the preparation of reference-type polybutylene adipate terephthalate spinning fibers, first, the red fluorescent substance is grafted and modified by hexanediamine, which greatly enhances its hydrophilicity, thereby forming a stable dispersion system in the organic solvent spinning solution; The spinning solution uses a mixture of chloroform and N,N-dimethylformamide, in which chloroform mainly dissolves hydrophobic polybutylene adipate terephthalate, and N,N-dimethylformamide assists in dissolving the hydrophilic graft product; The electrospinning process can prepare nanofibers with high specific surface area, providing a rapid mass transfer channel for biological amines; The red fluorescent signal as an internal reference can effectively correct the errors caused by environmental temperature and humidity fluctuations, greatly improving the detection reliability.

[0019] In some embodiments, the responsive cellulose nanofiber realizes functional enhancement through multiple modifications. First, chitosan is combined with a green fluorescent substance to form a grafted product, which can greatly improve the solubility and dispersion uniformity of the fluorescent substance, and the amino group of chitosan can enhance the capture ability of the fluorescent substance to biological amines. Second, in the preparation of the responsive cellulose nanofiber, an argon-oxygen mixed gas is used in the low-temperature plasma etching process to activate the surface. High-energy electrons in the plasma collide with gas molecules to produce active species such as ·O and ·OH, which attack the C-H bonds on the surface of the cellulose nanofiber through a free radical reaction mechanism, oxidizing them to carboxyl and hydroxyl groups, greatly increasing the surface functional group density. At the same time, the etching process forms a large number of nanoscale pits and grooves on the surface of the cellulose nanofiber, which can further increase its specific surface area and provide more active sites for biological amine adsorption. In addition, the plasma bombardment can effectively remove the lignin residues and organic impurities on the surface of the cellulose, eliminating the fluorescence quenching phenomenon caused by the π-π stacking effect, and greatly improving the fluorescence intensity stability of the subsequently modified green fluorescent substance. Finally, N,N-methylenebisacrylamide is used as a crosslinking agent to form a three-dimensional network with the cellulose carboxyl and chitosan amino groups, greatly improving the mechanical properties and anti-swelling properties of the responsive cellulose nanofiber.

[0020] In some embodiments, for the preparation of bio-based beads, a performance breakthrough is achieved through microfluidic-gradient crosslinking technology. First, the microfluidic device can control the preparation of beads with uniform particle size, making the spherical structure have a larger specific surface area than thin film materials. Then, the gradient crosslinking strategy forms a hierarchical structure with a dense outer layer and a porous inner layer, ensuring mechanical strength and facilitating biological amine diffusion. The liquid water in the beads can quickly adsorb gaseous biological amines, making them evenly distributed inside the beads. Combined with the fluorescence resonance energy transfer mechanism, the beads can achieve rapid response. Sulfur-doped graphene quantum dots serve as the fluorescence resonance energy transfer donor, green fluorescent substances serve as the energy acceptor and response signal, and red fluorescent substances serve as the reference signal, together forming a ratio fluorescence detection system. Compared to traditional membrane materials, which have long mass transfer paths and are prone to swelling, the bead dosage form has extremely significant advantages in detection sensitivity, response speed, and stability.

[0021] In the second aspect, the application provides a bio-based bead for real-time freshness monitoring. Through material design, process innovation, and dosage form optimization, a "detection-bacteriostasis-degradation" trinity bio-based bead system is constructed. The innovation lies in: waste resource utilization (waste tires to sulfur-doped graphene quantum dots), improving detection sensitivity through fluorescence resonance energy transfer mechanism, optimizing mass transfer efficiency through bead dosage form, and improving anti-interference ability through reference-response dual signal system, providing a new solution for high-protein food freshness monitoring. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 Flow chart of a process for the preparation of a bio-based coagulation bead for real-time freshness monitoring according to some embodiments of the present specification; Figure 2 Schematic representation of a box containing live shrimp in Example 1 at 20 °C for 1 day; Figure 3 Schematic representation of a box containing live shrimp in Example 1 at 20 °C for 15 days; Figure 4 Schematic representation of a box containing live pork in Example 5 at 25 °C for 48 h. DETAILED DESCRIPTION

[0023] Hereinafter, only certain exemplary embodiments are described simply. As can be recognized by those skilled in the art, the described embodiments can be modified in various different ways without departing from the spirit or scope of the present invention. Therefore, the drawings and the description are to be considered exemplary in nature rather than limiting.

[0024] Furthermore, the terms "first", "second", etc. are used only for the purpose of description and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Thus, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0025] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0026] ​​Currently, the freshness detection technology of high-protein food mainly focuses on three directions: electrochemical analysis, pH-sensitive detection and traditional fluorescence detection. However, there are technical bottlenecks that are difficult to break through: first, although electrochemical detection technology has high precision, it relies on expensive instruments such as high-performance liquid chromatography-mass spectrometry, and requires professional personnel to spend a lot of time for sample pretreatment, which cannot meet the real-time monitoring needs of the whole chain of food production, transportation and sales; second, pH-sensitive detection materials (such as phenolphthalein and bromocresol green composite film) can determine freshness by color change, but are significantly disturbed by pH fluctuations of food juice, with high detection error rate, and some synthetic pigments have migration pollution risk, which does not meet the safety standards (GB 4806.1-2016) of food contact materials; third, traditional fluorescence detection technology is mostly based on a single light source (such as fluorescein and rhodamine dyes), and the fluorescence intensity is easily affected by temperature, humidity and instrument sensitivity, and the mainstream film dosage form has small contact area with biological amines, with response lag, making it difficult to capture early spoilage signals of high-protein food. In addition, the carrier form of fluorescence detection is generally film or gel. For example, the patent "Ratio-type fluorescent biological base indicator film for freshness detection of high-protein food and preparation method thereof" discloses a ratio-type fluorescent indicator film for detecting biological amines, which is mainly composed of gel nanocellulose, red fluorescent lignin and green fluorescent cellulose acetate; the patent "Regenerated cellulose fluorescent sensing film material, preparation method and application thereof" discloses a fluorescent sensing film material mainly composed of regenerated cellulose and vinyl COFs; the patent "Intelligent gel label for freshness monitoring and preservation integration, and preparation method and application thereof" discloses an intelligent gel label mainly composed of polyacrylic acid-carboxymethyl cellulose-polyvinyl alcohol porous gel substrate, eugenol and aggregation-induced emission copper nanoclusters.

[0027] For the freshness detection of high-protein food, the existing public patents mainly focus on the film and gel directions. In recent years, the bead type has become a new carrier for food freshness monitoring due to its high efficiency in contacting target gas. However, the existing technology still has three major shortcomings: first, the substrate selection is not environmentally friendly, and petroleum-based polymers such as polyethylene and polypropylene are often used, which have a natural degradation period of more than 500 years; second, the functional integration is low, and the existing beads only have a single detection function, cannot simultaneously inhibit microbial reproduction, are difficult to delay the food spoilage process, and cannot realize the "monitoring-preservation" synergy; third, the preparation process is traditional, and the functional components (such as fluorescent probes and bacteriostatic agents) are prone to aggregation, resulting in low detection sensitivity and poor repeatability, which cannot meet the requirements of industrial application. In addition, the existing technology lacks systematic consideration of "biomass resource high-value utilization-multicomponent collaborative functional design-advanced preparation process integration", and there is no technical solution to organically combine sulfur-doped carbon nanomaterials, biodegradable polymers and nanocellulose, which is difficult to balance detection accuracy, environmental friendliness and practical application adaptability. Therefore, developing a biological-based bead with "detection-bacteriostatic-degradation" three-in-one function and adapting to real-time monitoring of the whole chain is a key direction to break through the bottleneck of high-protein food freshness monitoring technology, ensure food safety and promote the upgrading of green packaging industry.

[0028] The present application can effectively solve the problems of easy aggregation and poor stability of quantum dots, ensure the sensitivity and rapid response of the monitoring signal, and overcome the defects of response lag of traditional materials. At the same time, the "detection-bacteriostatic-degradation" three-in-one biological-based bead is formed, which does not need to directly contact food, realizes ultra-fast response, high sensitivity detection and full life cycle environmental protection of biological amines, adapts to multi-link monitoring of high-protein food, significantly improves the accuracy and reliability of monitoring, and has comprehensive functions.

[0029] Example 1 Figure 1 is a flowchart of a biological-based bead preparation method for real-time freshness monitoring according to some embodiments of the present specification, comprising the following steps: Step one, preparation of sulfur-doped graphene quantum dots: Take 10 g of 100-125 mesh waste tire rubber, and use 500 mL of n-hexane as a solvent to perform Soxhlet extraction at 80 ℃ for 10 h to remove impurities, and then vacuum dry at 60 ℃ for 12 h to obtain the impurity-removed sulfur-containing polymer; under the condition of nitrogen atmosphere and microwave power of 3000 W, the first microwave pyrolysis of the impurity-removed sulfur-containing polymer is performed, first with a heating rate of 250 ℃ / min to 450 ℃, and then heat preservation for 30 min, and then the liquid product pyrolysis oil is collected; then the second microwave pyrolysis is performed, the microwave power is reduced to 200 W, and the low-speed heating is performed at a rate of 5 ℃ / min until 1200 ℃, and heat preservation for 10 h, to obtain the solid product pyrolysis graphite carbon; Take 2 mL of pyrolysis oil, add 25 mL of ethyl acetate-deionized water mixed solvent with a volume ratio of 8:2, shake and extract at room temperature for 3 times (each time for 25 min, and stand for 20 min), and collect the upper organic phase; add 5 g of anhydrous sodium sulfate to the organic phase, stand for 2 h, and then filter to remove the drying agent, to obtain the filtrate, and then concentrate the filtrate by rotary evaporation at a rotation speed of 100 rpm under the condition of 45 ℃ and vacuum degree of 0.085 MPa, to obtain the sulfur-containing small molecule carbon source; Mill the pyrolysis graphite carbon at a rotation speed of 300 rpm for 4 h, sieve through a 300-mesh standard sieve, collect the particles passing through the sieve, and obtain the activated pyrolysis carbon; take 0.5 g of the sulfur-containing small molecule carbon source, 0.1 g of the activated pyrolysis carbon, and 50 mL of deionized water, and ultrasonically disperse for 15 min; then transfer to a high-pressure reaction kettle, and react at 180 ℃ for 24 h; after the reaction is completed, cool to 25 ℃, and ultracentrifuge at 35000 rpm for 4 h, collect the supernatant, and place it in a dialysis bag with a molecular weight cut-off of 500 Da for dialysis for 72 h, and replace the dialysate every 8 h during the period; finally, freeze-dry the product in the dialysis bag at -50 ℃ for 48 h, to obtain the sulfur-doped graphene quantum dots.

[0030] Step two, preparation of sulfur-doped graphene quantum dot / sodium alginate composite dispersion based on sulfur-doped graphene quantum dots: Dissolve 2 g of sodium alginate in 98 mL of deionized water, add 0.005 mL of glycerol, and stir at 500 rpm for 1 h at 50 ℃ to prepare a sodium alginate solution; then add 0.001 g of sulfur-doped graphene quantum dots, and ultrasonically disperse for 30 min to obtain a preliminary dispersion; adjust the pH of the preliminary dispersion to 5.0 with 0.1 mol / L hydrochloric acid, and then shear at 5000 rpm for 45 min at 5 ℃ to obtain the sulfur-doped graphene quantum dot / sodium alginate composite dispersion.

[0031] Step three, preparation of reference type polybutylene adipate / terephthalate spinning fiber: Sulfo-rhodamine 640 was dissolved in 200 mL of N,N-dimethylformamide, 1 mL of hexanediamine was added, and the reaction was stirred at 80 °C for 6 h under nitrogen protection to obtain a reaction solution. The reaction solution was cooled to 25 °C and then slowly poured into 1000 mL of ice ethanol under stirring to precipitate a precipitate, which was collected by suction filtration to obtain a sulfo-rhodamine 640-hexanediamine grafted product; 100 g of polybutylene adipate / terephthalate, 0.5 g of sulfo-rhodamine 640-hexanediamine grafted product, 3 g of polyvinylpyrrolidone with a K value of 30, and 0.2 g of tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester were mixed at 1200 rpm for 10 min, and then pelletized by double screw extrusion at a temperature of 160 °C to obtain a composite master batch; 20 g of the composite master batch was dissolved in 80 mL of a mixed solvent of chloroform-N,N-dimethylformamide with a volume ratio of 3:1 to obtain a spinning solution. Then, 100 mL of the spinning solution was ultrasonically degassed at 40 kHz for 20 min, and electrospun under the conditions of a voltage of 18 kV, a receiving distance of 15 cm, and a flow rate of 0.5 mL / h to obtain a spinning fiber membrane. 5 g of the spinning fiber membrane was vacuum heat-treated at 80 °C for 60 min, and then cooled to room temperature to obtain a reference polybutylene adipate / terephthalate spinning fiber.

[0032] Step four, preparation of responsive cellulose nanofiber: 1 g of chitosan with a degree of deacetylation of 90% was dissolved in 50 mL of an acetic acid solution with a mass concentration of 1 wt%, 0.1 mL of 5-carboxyfluorescein solution dissolved in N,N-dimethylformamide (mass ratio of 5-carboxyfluorescein to N,N-dimethylformamide was 1:10) was added, and the mixture was stirred at 30 °C in the dark for 12 h. Then, the pH was adjusted to 7.0 with 1 mol / L sodium hydroxide, and the precipitate was collected by centrifugation at 10000 rpm for 15 min. The precipitate was freeze-dried at -70 °C for 24 h to obtain a 5-carboxyfluorescein-chitosan grafted product; 5 g of cellulose nanofiber was uniformly dispersed in 95 mL of deionized water, and then uniformly coated on a polytetrafluoroethylene substrate and dried in a vacuum drying oven at 40 °C for 6 h to form a cellulose nanofiber dry film. The cellulose nanofiber dry film was placed in an atmosphere with a volume ratio of argon to oxygen of 4:1 and subjected to low-temperature plasma etching at a power of 300 W for 15 min. After etching, the cellulose nanofiber dry film was dispersed in deionized water to form a cellulose nanofiber suspension with a mass concentration of 1 wt%; To 100 mL of cellulose nanofiber suspension, 0.1 g of 5-carboxyfluorescein-chitosan graft product and 0.05 g of N,N-methylenebisacrylamide were added, and after ultrasonic treatment at 40 kHz for 20 min, reaction was carried out at 60 °C for 4 h in a nitrogen atmosphere, followed by centrifugation at 8000 rpm for 20 min to collect the precipitate, and finally the precipitate was vacuum dried at 40 °C for 10 h to obtain responsive cellulose nanofiber.

[0033] Step five, preparation of bio-based coacervate based on responsive cellulose nanofiber, sulfur-doped graphene quantum dot / sodium alginate composite dispersion and reference polybutylene adipate terephthalate spinning fiber: 1 g of responsive cellulose nanofiber was uniformly dispersed in deionized water to prepare a 1 wt% responsive cellulose nanofiber suspension; 100 mL of sulfur-doped graphene quantum dot / sodium alginate composite dispersion, 5 g of reference polybutylene adipate terephthalate spinning fiber, 3 mL of responsive cellulose nanofiber suspension were stirred at 25 °C and 800 rpm for 20 min to prepare a paste-like gel, and 0.1 mL of vitamin E was added and stirred for another 10 min; then the paste-like gel was injected into the microfluidic device, the outer phase was paraffin oil containing 1 wt% sorbitan fatty acid ester, the flow rate of the outer phase was set to 5 mL / h and the flow rate of the inner phase was set to 0.5 mL / h, the liquid droplets flowing out were dropped into a 3 wt% calcium chloride-magnesium chloride composite crosslinking agent solution with a calcium ion to magnesium ion molar ratio of 2:1, and crosslinked at 30 °C for 10 min to form coacervate precursors; 10 g of coacervate precursors were transferred into 100 mL of calcium chloride-magnesium chloride composite crosslinking agent solution with a calcium ion to magnesium ion molar ratio of 2:1 (initial mass concentration of 3 wt%, reduced by 0.5 wt% every 30 min until the mass concentration of the crosslinking solution was 0.5 wt%), and then placed at 25 °C for 2 h, washed with deionized water, and finally dried at 25 °C for 15 min to remove surface moisture to obtain bio-based coacervate.

[0034] The prepared bio-based coacervate was placed on the non-woven fabric and attached to the inside of the lid of the box containing live shrimp, and then the box was placed at 20 °C for 1 day, as shown in FIG. 1, the color of the bio-based coacervate was still red under ultraviolet lamp irradiation, proving that the live shrimp remained fresh, and after another 14 days, as shown in FIG. 2, the color of the bio-based coacervate changed from red to yellow, proving that the freshness of the live shrimp decreased to a slightly deteriorated state. Figure 2 Figure 3

[0035] Example 2: Figure 1 ​​is a flowchart of a bio-based bead preparation method for real-time freshness monitoring according to some embodiments shown in the specification, comprising the following steps: Step one, preparation of sulfur-doped graphene quantum dots: Take 10 g of 175-200 mesh sulfurized rubber product offcuts, perform Soxhlet extraction at 80°C with 100 mL of n-hexane as solvent, reflux for 6 h to remove impurities, and then vacuum dry at 60°C for 12 h to obtain the impurity-removed sulfur-containing polymer; perform the first microwave pyrolysis of the impurity-removed sulfur-containing polymer in a nitrogen atmosphere at a microwave power of 5000 W, first increase the temperature to 800°C at a rate of 400°C / min, and then collect the liquid product pyrolysis oil; then perform the second microwave pyrolysis, reduce the microwave power to 600 W, and perform low-speed heating at a rate of 20°C / min until 1500°C, and then heat for 5 h to obtain the solid product pyrolysis graphite carbon; Take 2 mL of pyrolysis oil, add 25 mL of a mixture of ethyl acetate and deionized water in a volume ratio of 8:2, shake and extract at room temperature for 5 times (each time for 15 min, and stand for 10 min), and collect the upper organic phase; add 5 g of anhydrous sodium sulfate to the organic phase, stand for 2 h, then filter to remove the drying agent, obtain the filtrate, and concentrate the filtrate by rotary evaporation at 55°C, a vacuum degree of 0.098 MPa and a rotation speed of 100 rpm, to obtain a sulfur-containing small molecule carbon source; Ball mill the pyrolysis graphite carbon at a rotation speed of 500 rpm for 2 h, sieve through a 400 mesh standard sieve, collect the particles passing through the sieve, and obtain activated pyrolysis carbon; take 1 g of the sulfur-containing small molecule carbon source, 0.2 g of the activated pyrolysis carbon, and 80 mL of deionized water, and ultrasonically disperse for 15 min; then transfer to a high-pressure reaction kettle, and react at 220°C for 12 h; after the reaction is completed, cool to 25°C, and ultracentrifuge at 55000 rpm for 2 h; collect the supernatant and place it in a dialysis bag with a molecular weight cutoff of 1000 Da, dialyze for 48 h, and change the dialysate every 4 h during the dialysis; finally, freeze-dry the product in the dialysis bag at -50°C for 60 h to obtain sulfur-doped graphene quantum dots.

[0036] Step two, preparation of sulfur-doped graphene quantum dot / sodium alginate composite dispersion based on sulfur-doped graphene quantum dots: Sodium alginate solution was prepared by dissolving 2 g of sodium alginate in 98 mL of deionized water, adding 0.01 mL of glycerol, and stirring at 500 rpm for 1 h at 50°C; then 0.002 g of sulfur-doped graphene quantum dots were added, and ultrasonic dispersion was performed for 30 min to obtain a preliminary dispersion liquid; the pH of the preliminary dispersion liquid was adjusted to 6.0 with 0.1 mol / L hydrochloric acid, and then shearing was performed at 10°C and 8000 rpm for 30 min to obtain a sulfur-doped graphene quantum dot / sodium alginate composite dispersion liquid.

[0037] Step three, preparation of reference polybutylene adipate terephthalate spinning fiber: Sulfonated rhodamine 101-hexanediamine grafting product was obtained by dissolving 5 g of sulfonated rhodamine 101 in 200 mL of N,N-dimethylformamide, adding 1 mL of hexanediamine, stirring at 80°C under nitrogen protection for 6 h, and then slowly pouring the reaction liquid into 1000 mL of ice ethanol under stirring to precipitate the product, which was collected by suction filtration. 100 g of polybutylene adipate terephthalate, 1 g of sulfonated rhodamine 101-hexanediamine grafting product, 5 g of polyvinylpyrrolidone with a K value of 60, and 0.2 g of tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester were mixed at 1200 rpm for 10 min, and then the composite master batch was obtained by twin-screw extrusion and pelletization at a temperature of 180°C. A spinning solution was prepared by dissolving 20 g of the composite master batch in 85 mL of a mixed solvent of chloroform and N,N-dimethylformamide in a volume ratio of 3:1, and then the 100 mL spinning solution was ultrasonically degassed at 40 kHz for 20 min, and then electrospinning was performed at a voltage of 22 kV, a receiving distance of 20 cm, and a flow rate of 1 mL / h to obtain a spinning fiber membrane; 10 g of the spinning fiber membrane was vacuum heat-treated at 100°C for 30 min, and then cooled to room temperature to obtain a reference polybutylene adipate terephthalate spinning fiber.

[0038] Step four, preparation of responsive cellulose nanofiber: Chitosan with a degree of deacetylation of 95% was dissolved in 50 mL of an acetic acid solution with a mass concentration of 1 wt%, 0.2 mL of a fluorescein sodium solution dissolved in N,N-dimethylformamide (fluorescein sodium and N,N-dimethylformamide in a mass ratio of 1:10) was added, and stirring was performed at 30°C in the dark for 12 h; then the pH was adjusted to 7.0 with 1 mol / L sodium hydroxide, and the precipitate was collected by centrifugation at 10000 rpm for 15 min; the precipitate was freeze-dried at -70°C for 24 h to obtain a fluorescein sodium-chitosan grafting product; 5 g of cellulose nanofiber was uniformly dispersed in 100 mL of deionized water, then uniformly coated on a polytetrafluoroethylene substrate, and placed in a vacuum drying oven at 60 ℃ for 6 h to form a cellulose nanofiber dry film; the cellulose nanofiber dry film was placed in an atmosphere with an argon to oxygen volume ratio of 4:1, and low-temperature plasma etching was carried out at a power of 400 W for 10 min; after etching, the cellulose nanofiber dry film was dispersed in deionized water to form a cellulose nanofiber suspension with a mass concentration of 1 wt%; 0.2 g of fluorescein sodium-chitosan graft product and 0.05 g of N,N-methylene bisacrylamide were added to 100 mL of cellulose nanofiber suspension, ultrasonically treated at 40 kHz for 30 min, then reacted at 60 ℃ in a nitrogen atmosphere for 4 h, then centrifuged at 12000 rpm for 10 min to collect the precipitate, and finally the precipitate was vacuum dried at 50 ℃ for 6 h to obtain responsive cellulose nanofiber.

[0039] Step five, preparation of bio-based coagulation beads based on responsive cellulose nanofiber, sulfur-doped graphene quantum dot / sodium alginate composite dispersion and reference polybutylene adipate terephthalate spinning fiber: 1 g of responsive cellulose nanofiber was uniformly dispersed in deionized water to obtain a responsive cellulose nanofiber suspension with a mass concentration of 1 wt%; 100 mL of sulfur-doped graphene quantum dot / sodium alginate composite dispersion, 10 g of reference polybutylene adipate terephthalate spinning fiber, and 5 mL of responsive cellulose nanofiber suspension were stirred at 25 ℃ and 800 rpm for 20 min to form a paste-like gel, and 0.2 mL of vitamin E was added and stirred for another 10 min; then the paste-like gel was injected into the microfluidic device, the outer phase was paraffin oil containing 2 wt% sorbitan fatty acid ester, the flow rate of the outer phase was set to 8 mL / h, and the flow rate of the inner phase was set to 1 mL / h, the liquid droplets flowed out were dropped into a calcium chloride-magnesium chloride composite crosslinking agent solution with a mass concentration of 3 wt% and a molar ratio of calcium ions to magnesium ions of 2:1, and crosslinked at 30 ℃ for 15 min to form a coagulation bead precursor; 20 g of the coagulation bead precursor was transferred into 200 mL of calcium chloride-magnesium chloride composite crosslinking agent solution with a molar ratio of calcium ions to magnesium ions of 2:1 (initial mass concentration of 3 wt%, reduced by 0.5 wt% every 30 min until the mass concentration of the crosslinking solution was 0.5 wt%), and then placed at 25 ℃ for 2 h, washed with deionized water, and finally dried at 30 ℃ for 5 min to remove surface moisture, to obtain bio-based coagulation beads.

[0040] The prepared bio-based coagulation beads were placed on the non-woven fabric and attached to the inside of the lid of the box containing the small yellow croakers, and then the box was placed at -4℃ for 24 h. Under the irradiation of ultraviolet lamp, the color of the bio-based coagulation beads changed from red to orange, proving that the freshness of the small yellow croakers decreased to a relatively fresh state. After being placed for another 60 h, the color of the bio-based coagulation beads changed from orange to green, proving that the small yellow croakers had become deteriorated.

[0041] Example 3: Figure 1 is a flowchart of a bio-based coagulation bead preparation method for real-time freshness monitoring according to some embodiments of the present specification, comprising the following steps: Step 1, preparation of sulfur-doped graphene quantum dots: Take 10 g of sulfur-containing epoxy resin with a particle size of 125-150, and perform Soxhlet extraction at 80℃ with 400 mL of n-hexane as the solvent, reflux for 9 h to remove impurities, and then vacuum dry at 60℃ for 12 h to obtain the impurity-removed sulfur-containing polymer. Perform the first microwave pyrolysis of the impurity-removed sulfur-containing polymer in a nitrogen atmosphere at a microwave power of 3500 W, first increase the temperature to 600℃ at a rate of 300℃ / min, and then collect the liquid product pyrolysis oil after holding for 25 min. Then perform the second microwave pyrolysis, reduce the microwave power to 300 W, and perform low-speed heating at a rate of 10℃ / min until 1300℃, and hold for 9 h to obtain the solid product pyrolysis graphite carbon; Take 2 mL of pyrolysis oil, add 25 mL of ethyl acetate-deionized water mixed solvent with a volume ratio of 8:2, and shake extract at room temperature for 4 times (each time for 20 min, and stand for 15 min for layering), and collect the upper organic phase. Add 5 g of anhydrous sodium sulfate to the organic phase, stand for 2 h, and then filter to remove the drying agent to obtain the filtrate. Concentrate the filtrate by rotary evaporation at 52℃, a vacuum degree of 0.092 MPa, and a rotation speed of 100 rpm to obtain a sulfur-containing small molecule carbon source. Milling the pyrolysis graphite carbon at a rotation speed of 350 rpm for 2.5 h, sieving through a 350 mesh standard sieve, and collecting the particles passing through the sieve to obtain activated pyrolysis carbon. Take 0.6 g of the sulfur-containing small molecule carbon source, 0.12 g of the activated pyrolysis carbon, and 60 mL of deionized water, and perform first ultrasonic dispersion for 15 min. Then transfer to a high-pressure reaction kettle and react at 190℃ for 14 h. After the reaction is completed, cool to 25℃, and perform ultracentrifugation at 40000 rpm for 3.5 h. Collect the supernatant and place it in a dialysis bag with a molecular weight cutoff of 600 Da for dialysis for 68 h, replacing the dialysate every 7 h during the period. Finally, freeze-dry the product in the dialysis bag at -50℃ for 55 h to obtain sulfur-doped graphene quantum dots.

[0042] Step two, preparation of sulfur-doped graphene quantum dot / sodium alginate composite dispersion based on sulfur-doped graphene quantum dots: Sodium alginate solution was prepared by dissolving 2 g of sodium alginate in 98 mL of deionized water, adding 0.006 mL of glycerol, and stirring at 500 rpm for 1 h at 50°C; then 0.0012 g of sulfur-doped graphene quantum dots was added, and ultrasonic dispersion was performed for 30 min to obtain a preliminary dispersion; the preliminary dispersion was adjusted to pH 5.5 with 0.1 mol / L hydrochloric acid, and then sheared at 6000 rpm for 35 min at 6°C to obtain a sulfur-doped graphene quantum dot / sodium alginate composite dispersion.

[0043] Step three, preparation of reference polybutylene adipate terephthalate spinning fiber: BODIPY630 / 650-trisulfonic acid-hexanediamine graft product was obtained by dissolving 2 g of BODIPY630 / 650-trisulfonic acid in 200 mL of N,N-dimethylformamide, adding 1 mL of hexanediamine, and stirring at 80°C under nitrogen protection for 6 h; the reaction solution was cooled to 25°C, and then slowly poured into 1000 mL of ice ethanol under stirring to precipitate the product, which was collected by suction filtration; 100 g of polybutylene adipate terephthalate, 0.6 g of BODIPY630 / 650-trisulfonic acid-hexanediamine graft product, 3.5 g of polyvinylpyrrolidone with a K value of 40, and 0.2 g of tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol were mixed at 1200 rpm for 10 min; then, the composite master batch was obtained by twin-screw extrusion and pelletization at a temperature of 165°C; 20 g of the composite master batch was dissolved in 82 mL of a mixture of chloroform and N,N-dimethylformamide in a volume ratio of 3:1 to obtain a spinning solution; then, 100 mL of the spinning solution was ultrasonically degassed at 40 kHz for 20 min, and electrospinning was performed at a voltage of 19 kV, a receiving distance of 16 cm, and a flow rate of 0.6 mL / h to obtain a spinning fiber membrane; 6 g of the spinning fiber membrane was vacuum heat-treated at 85°C for 35 min, and then cooled to room temperature to obtain the reference polybutylene adipate terephthalate spinning fiber.

[0044] Step four, preparation of responsive cellulose nanofiber: 1 g of chitosan with a deacetylation degree of 90% was dissolved in 50 mL of an acetic acid solution with a mass concentration of 1 wt%, 0.12 mL of a fluorescein isothiocyanate solution dissolved in N,N-dimethylformamide (the mass ratio of fluorescein isothiocyanate to N,N-dimethylformamide was 1:10) was added, stirring was performed at 30°C for 12 h in the dark, then the pH was adjusted to 7.0 with 1 mol / L sodium hydroxide, and the precipitate was collected by centrifugation at 10,000 rpm for 15 min. The precipitate was freeze-dried at -70°C for 24 h to obtain a fluorescein isothiocyanate-chitosan grafting product; 5 g of cellulose nanofibers were uniformly dispersed in 96 mL of deionized water, then uniformly coated on a polytetrafluoroethylene substrate, and placed in a vacuum drying oven at 45°C for drying for 6 h to form a cellulose nanofiber dry film. The cellulose nanofiber dry film was placed in an atmosphere with an argon / oxygen volume ratio of 4:1, and low-temperature plasma etching was performed at a power of 325 W for 14 min. After etching, the cellulose nanofiber dry film was dispersed in deionized water to form a cellulose nanofiber suspension with a mass concentration of 1 wt%; 0.12 g of the fluorescein isothiocyanate-chitosan grafting product and 0.05 g of N,N-methylenebisacrylamide were added to 100 mL of the cellulose nanofiber suspension, ultrasonic treatment was performed at 40 kHz for 22 min, then reaction was performed at 60°C in a nitrogen atmosphere for 4 h, then the precipitate was collected by centrifugation at 9,000 rpm for 18 min, and finally the precipitate was vacuum dried at 42°C for 9 h to obtain responsive cellulose nanofibers.

[0045] Step five, preparation of bio-based coagulation beads based on responsive cellulose nanofibers, sulfur-doped graphene quantum dot / sodium alginate composite dispersion, and reference polybutylene adipate terephthalate spinning fibers: 1 g of responsive cellulose nanofiber was uniformly dispersed in deionized water to prepare a 1 wt% responsive cellulose nanofiber suspension; 100 mL of sulfur-doped graphene quantum dot / sodium alginate composite dispersion, 6 g of reference polybutylene adipate terephthalate spinning fiber, 3.5 mL of responsive cellulose nanofiber suspension were stirred at 25°C and 800 rpm for 20 min to prepare a paste-like gel, and 0.12 mL of vitamin E was added and stirred for another 10 min; then the paste-like gel was injected into the microfluidic device, the outer phase was paraffin oil containing 1.2 wt% sorbitan fatty acid ester, the flow rate of the outer phase was set to 6 mL / h and the flow rate of the inner phase was set to 0.6 mL / h, the liquid droplets were dropped into a 3 wt% calcium chloride-magnesium chloride composite crosslinking agent solution with a calcium ion to magnesium ion molar ratio of 2:1, and the liquid droplets were crosslinked at 30°C for 12 min to form a bead precursor; 12 g of the bead precursor was transferred into 120 mL of a calcium chloride-magnesium chloride composite crosslinking agent solution with a calcium ion to magnesium ion molar ratio of 2:1 (initial mass concentration of 3 wt%, reduced by 0.5 wt% every 30 min until the mass concentration of the crosslinking solution was 0.5 wt%), and the solution was allowed to stand at 25°C for 2 h. After washing with deionized water, the surface moisture was removed by constant temperature drying at 26°C for 13 min to obtain the bio-based beads.

[0046] The prepared bio-based beads were placed on the non-woven fabric and attached to the inside of the box cover containing the large yellow croaker, and then the box was placed at 4°C for 96 h. Under the irradiation of ultraviolet lamp, it was observed that the color of the bio-based beads changed from red to dark green, proving that the large yellow croaker had been severely deteriorated.

[0047] Example 4: Figure 1 is a flowchart of a bio-based bead preparation method for real-time freshness monitoring according to some embodiments of the present specification, comprising the following steps: Step 1, preparation of sulfur-doped graphene quantum dots: 10 parts by mass of 150-175 mesh sulfur-containing polyolefin was subjected to Soxhlet extraction at 80°C with 300 mL of n-hexane as the solvent, and the extraction was carried out under reflux for 7 h to remove impurities, and then the sulfur-containing polymer was vacuum dried at 60°C for 12 h to obtain the sulfur-containing polymer; the sulfur-containing polymer was subjected to first microwave pyrolysis under a nitrogen atmosphere at a microwave power of 4000 W, first heated to 700°C at a heating rate of 350°C / min, and then the liquid product pyrolysis oil was collected; then the second microwave pyrolysis was carried out, the microwave power was reduced to 400 W, and the low-speed heating was carried out at a rate of 15°C / min until 1400°C, and the solid product pyrolysis graphite carbon was obtained; Take 2 mL of pyrolysis oil, add 25 mL of ethyl acetate-deionized water mixed solvent with a volume ratio of 8:2, shake extraction at room temperature for 4 times (each time for 25 min, stand for 10 min), collect the upper organic phase; add 5 g of anhydrous sodium sulfate to the organic phase, stand for 2 h, then filter to remove the drying agent, obtain the filtrate, and concentrate the filtrate at 48 ℃, vacuum degree 0.096 MPa, and rotation speed 100 rpm, to obtain a sulfur-containing small molecule carbon source; The pyrolytic graphite carbon is ball milled at a rotation speed of 400 rpm for 3.5 h, and after sieving through a 375 mesh standard sieve, the particles passing through the sieve are collected to obtain activated pyrolytic carbon; take 0.8 g of the sulfur-containing small molecule carbon source, 0.18 g of the activated pyrolytic carbon, and 70 mL of deionized water, and ultrasonically disperse them for 15 min; then transfer them to a high-pressure reaction kettle, and react at 200 ℃ for 18 h; after the reaction is completed, cool to 25 ℃, and ultracentrifuge at 45000 rpm for 2.5 h; collect the supernatant and place it in a dialysis bag with a molecular weight cutoff of 800 Da, and dialyze for 52 h, replacing the dialysate every 5 h; finally, freeze-dry the product in the dialysis bag at -50 ℃ for 50 h to obtain sulfur-doped graphene quantum dots.

[0048] Step two, preparation of sulfur-doped graphene quantum dot / sodium alginate composite dispersion based on sulfur-doped graphene quantum dots: Dissolve 2 g of sodium alginate in 98 mL of deionized water, add 0.009 mL of glycerol, and stir at 500 rpm for 1 h at 50 ℃ to prepare a sodium alginate solution; then add 0.0018 g of sulfur-doped graphene quantum dots, and ultrasonically disperse for 30 min to obtain a preliminary dispersion; adjust the pH of the preliminary dispersion to 5.8 with 0.1 mol / L hydrochloric acid, and then shear at 7000 rpm for 40 min at 9 ℃ to obtain a sulfur-doped graphene quantum dot / sodium alginate composite dispersion.

[0049] Step three, preparation of reference type polybutylene adipate / terephthalate spinning fiber: Dissolve 4 g of sulfo-rhodamine 640 in 200 mL of N,N-dimethylformamide, add 1 mL of hexanediamine, and stir at 80 ℃ under nitrogen protection for 6 h to obtain a reaction solution; cool the reaction solution to 25 ℃, and slowly pour it into 1000 mL of ice ethanol under stirring to precipitate a precipitate, which is collected by suction filtration to obtain a sulfo-rhodamine 640-hexanediamine grafted product; Take 100 g of polybutylene adipate terephthalate, 0.9 g of sulfonated rhodamine 640-hexanediamine graft product, 4.5 g of polyvinylpyrrolidone, and 0.2 g of tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester at 1200 rpm for 10 min, wherein the K value of the polyvinylpyrrolidone is 50; then granulate by double screw extrusion at a temperature of 175°C to obtain a composite master batch; Dissolve 20 g of the composite master batch in 84 mL of a mixture of chloroform-N,N-dimethylformamide with a volume ratio of 3:1 to obtain a spinning solution, then ultrasonic defoaming for 20 min at 40 kHz, and electrospinning under the conditions of voltage 21 kV, receiving distance 19 cm, and flow rate 0.9 mL / h to obtain a spinning fiber membrane. Heat-treat 9 g of the spinning fiber membrane at 95°C for 55 min under vacuum, and then cool to room temperature to obtain a reference polybutylene adipate terephthalate spinning fiber.

[0050] Step four, preparation of responsive cellulose nanofiber: Dissolve 1 g of chitosan with a degree of deacetylation of 90% in 50 mL of an acetic acid solution with a mass concentration of 1 wt%, add 0.18 mL of 5-carboxyfluorescein solution dissolved in N,N-dimethylformamide (mass ratio of 5-carboxyfluorescein to N,N-dimethylformamide is 1:10), stir at 30°C in the dark for 12 h, then adjust the pH to 7.0 with 1 mol / L sodium hydroxide, and centrifuge at 10000 rpm for 15 min to collect the precipitate. Freeze-dry the precipitate at -70°C for 24 h to obtain a 5-carboxyfluorescein-chitosan graft product. Disperse 5 g of cellulose nanofiber uniformly in 98 mL of deionized water, and then uniformly coat on a polytetrafluoroethylene substrate. Place the substrate in a vacuum drying oven and dry at 55°C for 6 h to form a cellulose nanofiber dry film. Perform low-temperature plasma etching on the cellulose nanofiber dry film in an atmosphere with a volume ratio of argon to oxygen of 4:1 at a power of 375 W for 12 min. After etching, disperse the cellulose nanofiber dry film in deionized water to obtain a cellulose nanofiber suspension with a mass concentration of 1 wt%. Add 0.18 g of 5-carboxyfluorescein-chitosan graft product and 0.05 g of N,N-methylenebisacrylamide to 100 mL of cellulose nanofiber suspension. Ultrasonic treatment at 40 kHz for 28 min, then reaction at 60°C under nitrogen atmosphere for 4 h. Then centrifuge at 11000 rpm for 12 min to collect the precipitate. Finally, vacuum dry the precipitate at 48°C for 7 h to obtain responsive cellulose nanofiber.

[0051] Step five, preparation of bio-based coacervate based on responsive cellulose nanofiber, sulfur-doped graphene quantum dots / sodium alginate composite dispersion and reference poly(butylene adipate-co-terephthalate)spun fiber: 1 g of responsive cellulose nanofiber was uniformly dispersed in deionized water to prepare a 1 wt% responsive cellulose nanofiber suspension; 100 mL of sulfur-doped graphene quantum dots / sodium alginate composite dispersion, 9 g of reference poly(butylene adipate-co-terephthalate)spun fiber, 4.5 mL of responsive cellulose nanofiber suspension were stirred at 25°C and 800 rpm for 20 min to prepare a paste-like gel, and 0.18 mL of vitamin E was added and stirred for another 10 min; then the paste-like gel was injected into the microfluidic device, the outer phase was paraffin oil containing 1.8 wt% sorbitan fatty acid ester, the flow rate of the outer phase was set to 7 mL / h and the flow rate of the inner phase was set to 0.9 mL / h, the liquid droplets flowed out were dropped into a 3 wt% calcium chloride-magnesium chloride composite crosslinking agent solution with a calcium ion to magnesium ion molar ratio of 2:1, and the coacervate precursor was formed by crosslinking at 30°C for 14 min; 18 g of the coacervate precursor was transferred into 180 mL of a calcium chloride-magnesium chloride composite crosslinking agent solution with a calcium ion to magnesium ion molar ratio of 2:1 (initial mass concentration of 3 wt%, reduced by 0.5 wt% every 30 min until the crosslinking liquid mass concentration was 0.5 wt%), and the mixture was placed at 25°C for 2 h, then washed with deionized water, and finally dried at 29°C for 8 min to remove the surface water, thereby obtaining the bio-based coacervate.

[0052] The prepared bio-based coacervate was placed on the non-woven fabric and attached to the inside of the lid of the box containing the live crabs, and then the box was placed at 16°C for 36 h. Under the irradiation of the ultraviolet lamp, it was observed that the color of the bio-based coacervate changed from red to yellow, indicating that the freshness of the live crabs decreased to a slightly deteriorated state. After another 64 h, it was observed that the color of the bio-based coacervate changed from yellow to dark green, indicating that the live crabs had already deteriorated to a serious state.

[0053] Example 5: Figure 1 is a flowchart of a bio-based coacervate preparation method for real-time freshness monitoring according to some embodiments of the present specification, which comprises the following steps: Step one, preparation of sulfur-doped graphene quantum dots: Take 10 parts by mass of 140-165 mesh sulfur-containing plastic recyclates, and perform Soxhlet extraction at 80°C for 8 hours with 375 mL of n-hexane as the solvent to remove impurities, and then vacuum dry at 60°C for 12 hours to obtain the impurity-removed sulfur-containing polymer; under the condition of nitrogen atmosphere and microwave power of 3750 W, the first microwave pyrolysis of the impurity-removed sulfur-containing polymer is performed, first increasing the temperature to 650°C at a rate of 325°C / min, and then holding for 20 min, and then collecting the liquid product pyrolysis oil; then the second microwave pyrolysis is performed, the microwave power is reduced to 350 W, and the low-speed heating is performed at a rate of 12°C / min until 1350°C, and then holding for 8 hours to obtain the solid product pyrolysis graphite carbon; Take 2 mL of pyrolysis oil, add 25 mL of ethyl acetate-deionized water mixed solvent with a volume ratio of 8:2, shake and extract at room temperature for 3 times (each time for 20 min, and stand for 15 min), and collect the upper organic phase; add 5 g of anhydrous sodium sulfate to the organic phase, stand for 2 hours to dry, and then filter to remove the drying agent; concentrate the filtrate by rotary evaporation at 50°C, 0.094 MPa vacuum, and 100 rpm rotation speed to obtain a sulfur-containing small molecule carbon source; Milling the pyrolysis graphite carbon at a rotation speed of 375 rpm for 3 hours, sieving through a 360 mesh standard sieve, collecting the particles passing through the sieve to obtain activated pyrolysis carbon; take 0.7 g of the sulfur-containing small molecule carbon source, 0.16 g of the activated pyrolysis carbon, and 65 mL of deionized water, and ultrasonically disperse for 15 min; then transfer to a high-pressure reaction kettle, and react at 195°C for 16 hours; after the reaction is completed, cool to 25°C, and ultracentrifuge at 42500 rpm for 3 hours; collect the supernatant and place it in a dialysis bag with a molecular weight cutoff of 700 Da for dialysis for 60 hours, replacing the dialysate every 6 hours during the period; finally, freeze-dry the product in the dialysis bag at -50°C for 52 hours to obtain sulfur-doped graphene quantum dots.

[0054] Step two, preparation of sulfur-doped graphene quantum dot / sodium alginate composite dispersion based on sulfur-doped graphene quantum dots: Dissolve 2 g of sodium alginate in 98 mL of deionized water, add 0.008 mL of glycerol, and stir at 500 rpm for 1 hour at 50°C to prepare a sodium alginate solution; then add 0.0015 g of sulfur-doped graphene quantum dots, and ultrasonically disperse for 30 min to obtain a preliminary dispersion; adjust the pH of the preliminary dispersion to 5.6 with 0.1 mol / L hydrochloric acid, and then shear at 8°C and 6500 rpm for 38 min to obtain a sulfur-doped graphene quantum dot / sodium alginate composite dispersion.

[0055] Step three, preparation of reference type polybutylene adipate terephthalate spinning fiber: Sulfo-rhodamine 101 was dissolved in 200 mL of N,N-dimethylformamide, 1 mL of hexanediamine was added, and the reaction was stirred at 80°C for 6 h under nitrogen protection to obtain a reaction solution. The reaction solution was cooled to 25°C and then slowly poured into 1000 mL of ice ethanol under stirring to precipitate a sediment. The grafted product of sulfo-rhodamine 101-hexanediamine was collected by suction filtration. 100 g of polybutylene adipate terephthalate, 0.8 g of the grafted product of sulfo-rhodamine 101-hexanediamine, 4 g of polyvinylpyrrolidone with a K value of 45, and 0.2 g of tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester were mixed at 1200 rpm for 10 min. Then, the composite master batch was obtained by twin-screw extrusion and pelletization at a temperature of 170°C. 20 g of the composite master batch was dissolved in 83 mL of a mixed solvent of chloroform-N,N-dimethylformamide with a volume ratio of 3:1 to obtain a spinning solution. Then, 100 mL of the spinning solution was ultrasonically degassed at 40 kHz for 20 min, and electrospinning was performed at a voltage of 20 kV, a receiving distance of 18 cm, and a flow rate of 0.8 mL / h to obtain a spinning fiber membrane. The spinning fiber membrane was vacuum heat-treated at 90°C for 40 min, and then cooled to room temperature to obtain a reference polybutylene adipate terephthalate spinning fiber.

[0056] Step four, preparation of responsive cellulose nanofiber: 1 g of chitosan with a degree of deacetylation of 90% was dissolved in 50 mL of an acetic acid solution with a mass concentration of 1 wt%, 0.15 mL of a fluorescein sodium solution dissolved in N,N-dimethylformamide (fluorescein sodium and N,N-dimethylformamide had a mass ratio of 1:10) was added, and the mixture was stirred at 30°C in the dark for 12 h. Then, the pH was adjusted to 7.0 with 1 mol / L sodium hydroxide, and the precipitate was collected by centrifugation at 10000 rpm for 15 min. The precipitate was freeze-dried at -70°C for 24 h to obtain the grafted product of fluorescein sodium-chitosan. 5 g of cellulose nanofiber was uniformly dispersed in 97 mL of deionized water, and then uniformly coated on a polytetrafluoroethylene substrate. The substrate was placed in a vacuum drying oven and dried at 50°C for 6 h to form a cellulose nanofiber dry film. The cellulose nanofiber dry film was placed in an atmosphere with a volume ratio of argon to oxygen of 4:1, and subjected to low-temperature plasma etching at a power of 350 W for 13 min. After etching, the cellulose nanofiber dry film was dispersed in deionized water to form a cellulose nanofiber suspension with a mass concentration of 1 wt%. To 100 mL of cellulose nanofiber suspension, 0.15 g of fluorescein sodium-chitosan graft product and 0.05 g of N,N-methylene bisacrylamide were added, and after ultrasonic treatment at 40 kHz for 25 min, reaction was carried out at 60℃ under nitrogen atmosphere for 4 h, followed by centrifugation at 10000 rpm for 15 min to collect the precipitate, and finally the precipitate was vacuum dried at 45℃ for 8 h to obtain responsive cellulose nanofiber.

[0057] Step five, preparation of bio-based coagulation beads based on responsive cellulose nanofiber, sulfur-doped graphene quantum dot / sodium alginate composite dispersion and reference polybutylene adipate terephthalate spinning fiber: 1 g of responsive cellulose nanofiber was uniformly dispersed in deionized water to obtain a 1 wt% responsive cellulose nanofiber suspension; 100 mL of sulfur-doped graphene quantum dot / sodium alginate composite dispersion, 8 g of reference polybutylene adipate terephthalate spinning fiber, 4 mL of responsive cellulose nanofiber suspension were stirred at 25℃ and 800 rpm for 20 min to prepare a paste-like gel, and 0.15 mL of vitamin E was added and stirred for another 10 min; then the paste-like gel was injected into the microfluidic device, the outer phase was paraffin oil containing 1.5 wt% sorbitan fatty acid ester, the flow rate of the outer phase was set to 6.5 mL / h and the flow rate of the inner phase was set to 0.8 mL / h, the liquid droplets flowing out were dropped into a 3 wt% calcium chloride-magnesium chloride composite crosslinking agent solution with a calcium ion to magnesium ion molar ratio of 2:1, and the coagulation bead precursor was formed by crosslinking at 30℃ for 13 min; 15 g of the coagulation bead precursor was transferred into 150 mL of calcium chloride-magnesium chloride composite crosslinking agent solution with a calcium ion to magnesium ion molar ratio of 2:1 (initial mass concentration 3 wt%, reduced by 0.5 wt% every 30 min until the crosslinking liquid mass concentration was 0.5 wt%), and then the mixture was placed at 25℃ for 2 h, washed with deionized water, and finally dried at 28℃ for 10 min to remove surface moisture, thereby obtaining bio-based coagulation beads.

[0058] The prepared bio-based coagulation beads were placed on a non-woven fabric and attached to the inside of the lid of a box containing raw pork, and then the box was placed at 25℃ for 48 h, as shown in Figure 4 Under the irradiation of ultraviolet lamp, the color of the bio-based coagulation beads changed from red to green, proving that the raw pork had become spoiled.

[0059] The relationship between the color change of the bio-based coagulation beads and the freshness of the food is shown in the following table: Table 1 Relationship between color change of bio-based coagulation beads and freshness of food

[0060] The purpose of the present application is to provide a bio-based condensate preparation method for real-time monitoring of the freshness of high-protein food, which addresses the problems of poor biodegradability of existing monitoring materials (mostly petroleum-based, causing environmental burden when discarded), single function (only detecting without antibiosis), response lag (low contact efficiency with biological amines), and traditional preparation prone to agglomeration and food contamination risk, etc. By drawing on the concept of high-value utilization of biomass-based materials, the sulfur-doped graphene quantum dots, reference polybutylene adipate / terephthalate spinning fibers, responsive cellulose nanofibers, and sodium alginate are organically integrated through a multi-step technical solution to prepare a "detection-antibiosis-degradation" trinity bio-based condensate, which does not require direct contact with food, realizes ultra-fast response, high sensitivity detection of biological amines, and environmental protection throughout the life cycle, and is suitable for multi-link monitoring of high-protein food.

[0061] The present application realizes the triple breakthroughs of resource recycling, detection sensitivity improvement and dosage form optimization through systematic technical innovation: in terms of resource recycling, the monitoring system is constructed by using sulfur-containing polymer waste such as waste tire rubber as raw material, combined with bio-based materials such as polybutylene adipate / terephthalate and cellulose nanofiber; in terms of sensitivity, the detection limit is greatly improved through fluorescence resonance energy transfer mechanism, and the detection effect is much better than that of traditional methods; in terms of dosage form design, the condensate dosage form developed breaks through the limitations of traditional membrane or gel materials, has the advantages of large specific surface area and high mass transfer efficiency, and solves the problem of low contact efficiency with biological amines.

[0062] The above shows and describes the basic principles and main features of the present application and the advantages of the present application, and it is obvious to those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and the present application can be realized in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting, and the scope of the present application is defined by the appended claims rather than the above description, and therefore all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application. Any reference signs in the claims should not be considered as limiting the claims involved.

[0063] In addition, it should be understood that although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the description of the specification is only for the sake of clarity, and those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that those skilled in the art can understand. The above is only to illustrate the technical idea of the present application, and cannot limit the protection scope of the present application, and any modification made on the basis of the technical solutions according to the present application falls within the protection scope of the claims of the present application.

Claims

1. A bio-based bead preparation method for freshness real-time monitoring, characterized by, The method comprises the following steps: Preparation of sulfur-doped graphene quantum dots; Preparation of sulfur-doped graphene quantum dots / sodium alginate composite dispersion based on sulfur-doped graphene quantum dots; Preparation of reference polybutylene adipate terephthalate spinning fibers; Preparation of responsive cellulose nanofibers; Preparation of bio-based condensed beads based on responsive cellulose nanofibers, sulfur-doped graphene quantum dots / sodium alginate composite dispersion and reference polybutylene adipate terephthalate spinning fibers.

2. A bio-based bead preparation method for real-time freshness monitoring according to claim 1, characterized in that, The preparation of sulfur-doped graphene quantum dots specifically comprises: After Soxhlet extraction of sulfur-containing polymers and n-hexane, reflux and first vacuum drying are sequentially performed to obtain impurity-removed sulfur-containing polymers, and the impurity-removed sulfur-containing polymers are subjected to first microwave pyrolysis to obtain solid products and pyrolysis oil, and the solid products are subjected to second microwave pyrolysis to obtain pyrolysis graphite carbon; After the pyrolysis oil and the ethyl acetate-deionized water mixed solvent are mixed and subjected to oscillation extraction, the upper organic phase is collected, anhydrous sodium sulfate is added to the organic phase, and then standing drying and filtration are sequentially performed to obtain a filtrate, and the filtrate is subjected to rotary evaporation concentration to obtain a sulfur-containing small molecule carbon source; After the pyrolysis graphite carbon is ball milled and then subjected to screening, activated pyrolysis carbon is obtained, the sulfur-containing small molecule carbon source, the activated pyrolysis carbon and deionized water are mixed and subjected to first ultrasonic dispersion, and then heating reaction and first centrifugation are sequentially performed to obtain supernatant, and the supernatant is subjected to dialysis to obtain a dialysis product. The dialysis product is subjected to first freeze-drying to obtain sulfur-doped graphene quantum dots.

3. A bio-based bead preparation method for real-time freshness monitoring according to claim 2, characterized in that, The sulfur-containing polymers include waste tire rubber, vulcanized rubber product offcuts, sulfur-containing epoxy resin, thio-polyolefin or sulfur-containing plastic recyclates; The mass ratio of the sulfur-containing polymers to n-hexane is 10:(100-500), the temperature of the Soxhlet extraction is 80℃, the time of the reflux is 6-10 h, the temperature of the first vacuum drying is 60℃, and the time of the first vacuum drying is 12 h; The first microwave pyrolysis specifically comprises: heating at a temperature increasing rate of 250-400℃ / min to 450-800℃ under a power of 3000-5000 W, and maintaining the temperature for 10-30 min; The second microwave pyrolysis specifically comprises: heating at a temperature increasing rate of 5-20℃ / min to 1200-1500℃ under a power of 200-600 W, and maintaining the temperature for 5-10 h; The mass ratio of the pyrolysis oil, the ethyl acetate-deionized water mixed solvent and anhydrous sodium sulfate is 2:25:5, in the ethyl acetate-deionized water mixed solvent, the volume ratio of ethyl acetate to deionized water is 8:2; The oscillation extraction is performed for 3-5 times, wherein the oscillation time of each oscillation extraction is 15-25 min, and the standing and layering time of each oscillation extraction is 10-20 min; The time of the standing drying is 2 h, the rotation speed of the rotary evaporation concentration is 100 rpm, the temperature of the rotary evaporation concentration is 45-55℃, and the vacuum degree of the rotary evaporation concentration is greater than 0.08 Mpa; The rotation speed of the ball milling is 300-500 rpm, and the ball milling time is 2-4 h; the screening standard is 300-400 mesh; The mass ratio of the sulfur small molecule carbon source, activated pyrolysis carbon and deionized water is (0.5-1):(0.1-0.2):(50-80); The ultrasonic dispersion time is 15 min; the heating reaction temperature is 180-220 ℃, the heating reaction time is 12-24 h; the first centrifugation speed is 35000-55000 rpm, and the first centrifugation time is 2-4 h; the dialysis molecular weight cut-off is 500-1000 Da, the dialysis time is 48-72 h, and the dialysis liquid is replaced every 4-8 h during the dialysis; The first freeze-drying time is 48-60 h, and the first freeze-drying temperature is-50 ℃.

4. The bio-based bead preparation method for real-time freshness monitoring according to claim 1, wherein, The preparation of the sulfur-doped graphene quantum dot / sodium alginate composite dispersion based on the sulfur-doped graphene quantum dots specifically includes: The sodium alginate is dissolved in deionized water, glycerol is added, and the first stirring is performed to obtain a sodium alginate solution; The sulfur-doped graphene quantum dots are added to the sodium alginate solution, and the second ultrasonic dispersion is performed to obtain a preliminary dispersion, the pH of the preliminary dispersion is adjusted for the first time, and low-temperature shearing is performed to obtain a sulfur-doped graphene quantum dot / sodium alginate composite dispersion; The mass ratio of the sodium alginate, deionized water, glycerol and sulfur-doped graphene quantum dots is 2:98:(0.005-0.01):(0.001-0.002); The first stirring temperature is 50 ℃, the first stirring time is 1 h, and the first stirring speed is 500 rpm; The second ultrasonic dispersion time is 30 min; the first pH adjustment specifically includes adjusting the pH to 5.0-6.0 by using hydrochloric acid; the low-temperature shearing temperature is 5-10 ℃, the low-temperature shearing speed is 5000-8000 rpm, and the low-temperature shearing time is 30-45 min.

5. The bio-based bead preparation method for real-time freshness monitoring according to claim 1, wherein, The preparation of the reference-type polybutylene adipate terephthalate spinning fiber specifically includes: The red fluorescent substance is dissolved in N,N-dimethylformamide, hexanediamine is added, and the second stirring is performed, and the first precipitation is obtained after pouring into ice ethanol, the first precipitation is collected by suction filtration, and a red fluorescent substance-hexanediamine graft product is obtained; The polybutylene adipate terephthalate, the red fluorescent substance-hexanediamine graft product, polyvinylpyrrolidone and antioxidant 1010 are high-speed mixed, and then the double-screw extrusion is performed at high temperature to obtain a composite master batch; The composite master batch is dissolved in a trichloromethane-N,N-dimethylformamide mixed solvent to obtain a spinning solution, and then the spinning solution is subjected to ultrasonic defoaming and electrospinning in sequence to obtain a spinning fiber membrane, and the spinning fiber membrane is subjected to vacuum heat treatment to obtain a reference-type polybutylene adipate terephthalate spinning fiber.

6. A bio-based bead preparation method for real-time freshness monitoring according to claim 5, characterized in that, The red fluorescent substance is one of sulforhodamine 640, sulforhodamine 101 and BODIPY 630 / 650-trisulfonic acid. The mass ratio of the red fluorescent substance, N,N-dimethylformamide, and hexanediamine to ice ethanol is (1-5):200:1:1000; the temperature of the second stirring is 80 ℃, and the time of the second stirring is 6 h; The mass ratio of the polybutylene adipate terephthalate, red fluorescent substance-hexanediamine graft product, polyvinylpyrrolidone, and antioxidant 1010 is 100:(0.5-1):(3-5):0.2; the K value of the polyvinylpyrrolidone is 30-60; the antioxidant 1010 is tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester; the rotating speed of the high-speed mixing is 1200 rpm, and the time of the high-speed mixing is 10 min; the temperature of the high temperature is 160-180 ℃; The mass ratio of the composite master batch to the trichloromethane-N,N-dimethylformamide mixed solvent is 20:(80-85); the volume ratio of trichloromethane to N,N-dimethylformamide in the trichloromethane-N,N-dimethylformamide mixed solvent is 3:1; the time of the ultrasonic defoaming is 20 min, and the frequency of the ultrasonic defoaming is 40 kHz; the voltage of the electrospinning is 18-22 kV, the receiving distance of the electrospinning is 15-20 cm, and the flow rate of the electrospinning is 0.5-1 mL / h; The temperature of the vacuum heat treatment is 80-100 ℃, and the time of the vacuum heat treatment is 30-60 min.

7. The bio-based bead preparation method for real-time freshness monitoring according to claim 1, wherein, The preparation of the responsive cellulose nanofiber specifically comprises: The chitosan is dissolved in an acetic acid solution, then a green fluorescent substance solution is added, and the mixture is stirred in the dark, then the pH is adjusted for the second time, and the second centrifugation is performed, the second precipitate is collected, the second precipitate is freeze-dried for the second time, and a green fluorescent substance-chitosan graft product is obtained; The cellulose nanofiber is uniformly dispersed in deionized water, then is uniformly coated on a polytetrafluoroethylene substrate, and is subjected to second vacuum drying to form a cellulose nanofiber dry film; The cellulose nanofiber dry film is placed in an atmosphere of argon and oxygen for etching, and then the cellulose nanofiber dry film is dispersed in deionized water to obtain a cellulose nanofiber suspension; The green fluorescent substance-chitosan graft product and N,N-methylenebisacrylamide are added to the cellulose nanofiber suspension, and then ultrasonic treatment and third centrifugation are performed in sequence, the third precipitate is collected, and the third precipitate is vacuum dried for the third time to obtain a responsive cellulose nanofiber.

8. The bio-based bead preparation method for real-time freshness monitoring according to claim 7, characterized in that, The mass ratio of the chitosan, acetic acid solution, and green fluorescent substance solution is 1:50:(0.1-0.2); the degree of deacetylation of the chitosan is ≥90%; the mass concentration of the acetic acid solution is 1 wt%; and the green fluorescent substance solution is one of 5-carboxyfluorescein, fluorescein sodium, and fluorescein isothiocyanate dissolved in N,N-dimethylformamide. The light-shielded stirring temperature is 30 DEG C, the light-shielded stirring time is 12 h; the second pH adjustment is adjusting the pH to 7.0 by sodium hydroxide; the second centrifugation speed is 10000 rpm, the second centrifugation time is 15 min; the second freeze-drying temperature is -70 DEG C, the second freeze-drying time is 24 h; The cellulose nanofiber and deionized water mass ratio is 5: (95-100); the second vacuum drying temperature is 40-60 DEG C, the second vacuum drying time is 6 h; The argon and oxygen gas volume ratio is 4:1; the etching power is 300-400 W, the etching temperature is 10-15 min; the cellulose nanofiber suspension mass concentration is 1 wt%; The cellulose nanofiber suspension, green fluorescent substance-chitosan graft product and N, N-methylene bisacrylamide mass ratio is 100: (0.1-0.2): 0.05; the green fluorescent substance and N, N-dimethylformamide mass ratio is 1:10; The ultrasonic treatment frequency is 40 kHz, the ultrasonic treatment time is 20-30 min; the third centrifugation speed is 8000-12000 rpm, the third centrifugation time is 10-20 min; the third vacuum drying temperature is 40-50 DEG C, the third vacuum drying time is 6-10 h.

9. The bio-based bead preparation method for real-time freshness monitoring according to claim 1, wherein, The preparation of the bio-based condensate beads based on the responsive cellulose nanofiber, sulfur-doped graphene quantum dot / sodium alginate composite dispersion and reference polybutylene adipate terephthalate spinning fiber specifically comprises: The responsive cellulose nanofiber is uniformly dispersed in deionized water to obtain a responsive cellulose nanofiber suspension; The sulfur-doped graphene quantum dot / sodium alginate composite dispersion, reference polybutylene adipate terephthalate spinning fiber and responsive cellulose nanofiber suspension are mixed and then subjected to third stirring to obtain a paste-shaped gel, vitamin E is added to the paste-shaped gel and subjected to fourth stirring, and then the paste-shaped gel is injected into an internal phase reservoir of a microfluidic device, and then the droplets flowing out of the internal phase reservoir of the microfluidic device fall into a first crosslinking liquid to perform crosslinking, forming a condensate bead precursor; The condensate bead precursor is transferred to a second crosslinking liquid and then subjected to washing and constant-temperature drying in sequence to obtain bio-based condensate beads; The responsive cellulose nanofiber suspension mass concentration is 1 wt%; the sulfur-doped graphene quantum dot / sodium alginate composite dispersion, reference polybutylene adipate terephthalate spinning fiber, responsive cellulose nanofiber suspension and vitamin E mass ratio is 100: (5-10): (3-5): (0.1-0.2); The third stirring temperature is 25 DEG C, the third stirring speed is 800 rpm, the third stirring time is 20 min; the fourth stirring temperature is 25 DEG C, the fourth stirring speed is 800 rpm, the fourth stirring time is 10 min; An inner phase reservoir in the microfluidic device, wherein the outer phase is paraffin oil containing 1-2 wt% Span 80, the Span 80 is sorbitan fatty acid ester, the flow rate of the outer phase is 5-8 mL / h, and the flow rate of the inner phase is 0.5-1 mL / h; The concentration of the first cross-linking liquid is 3 wt%, the temperature of the first cross-linking liquid is 30 ℃, and the time of the first cross-linking liquid is 10-15 min; The mass ratio of the bead precursor to the second cross-linking liquid is (10-20):(100-200); the initial mass concentration of the second cross-linking liquid is 3 wt%, which is reduced by 0.5 wt% every 30 min until the mass concentration of the second cross-linking liquid is 0.5 wt%; the first cross-linking liquid and the second cross-linking liquid are both calcium chloride-magnesium chloride composite cross-linking agent solutions, wherein the molar ratio of calcium ions to magnesium ions is 2:1; The temperature of the constant temperature drying is 25-30 ℃, and the time of the constant temperature drying is 5-15 min.

10. A bio-based coagulum bead for freshness real-time monitoring, characterized in that, A biological-based bead preparation method for real-time freshness monitoring according to any one of claims 1-9 is obtained.

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