Photocatalytic antibacterial carbon dots, hydrogel containing carbon dots, and preparation method and application of hydrogel

Abstract

The invention discloses photocatalytic antibacterial carbon dots, hydrogel containing the carbon dots and a preparation method and application of the hydrogel, and belongs to the technical field of aquatic product preservation. The carbon dot is prepared by taking rose bengal and riboflavin as raw materials through a one-pot hydrothermal method. Wherein the mass ratio of rose bengal to riboflavin is 1: (0.5-2), and the mass ratio of rose bengal to riboflavin is 1: (0.5-2). Meanwhile, the invention also provides hydrogel containing the carbon dots, and preparation methods of the carbon dots and the hydrogel. The hydrogel prepared by using the photocatalytic antibacterial carbon dots has good antibacterial activity and oxidation resistance, also has good mechanical properties, and has a relatively wide application prospect in the fields of aquatic product preservation and antibiosis.

Description

Technical Field

[0001] The present invention belongs to the technical field of aquatic product preservation, and particularly relates to a photocatalytic antibacterial carbon dot, a hydrogel containing the carbon dot, and a preparation method and application thereof. Background Art

[0002] Aquatic products have a unique taste, high water content, and are rich in essential amino acids and polyunsaturated fatty acids, and are deeply favored by consumers. However, after aquatic products such as fish die, they are extremely prone to lipid oxidation and deterioration under the action of microorganisms, affecting subsequent storage, transportation and other processes, and thus losing their nutritional value and commercial value. In order to improve economic benefits, antibacterial methods such as antioxidants are usually used to extend the shelf life of aquatic products. Traditional antioxidants have the disadvantages of potential toxicity and non-biodegradability, thus greatly increasing the food safety and environmental pollution risks of fresh aquatic products. Therefore, intelligent packaging materials with high efficient preservation effects and biodegradable characteristics have received more and more attention.

[0003] As a natural polymer, polysaccharide-based hydrogels have been widely used in wound dressings, drug delivery and food packaging due to their unique three-dimensional network structure, a large number of water molecules enriched inside, and various physical and chemical properties of polysaccharides. The three-dimensional network structure endows the hydrogel with good drug loading performance, biocompatibility and antioxidant activity. Therefore, it is a good choice for intelligent packaging carriers. However, the cross-linking points in the hydrogel system of polysaccharides are irregularly distributed, making the gel system easy to be damaged and unable to meet the preservation requirements during the preservation process. Therefore, improving its mechanical properties is an urgent problem to be solved.

[0004] Polyvinyl alcohol (PVA) is a synthetic polymer, and its molecular weight varies depending on the length of the original vinyl acetate polymer. The hydroxyl groups of PVA generate intermolecular and intramolecular hydrogen bonds, which have a positive impact on the rheological and mechanical properties of the polymer, and the degree is determined by the density and spatial arrangement of the hydroxyl groups. Due to its non-toxicity, water solubility, non-carcinogenicity, good compatibility and biodegradability in human tissues and body fluids, PVA is one of the most commonly used polymers in the biomedical field.

[0005] Nanomaterials such as carbon dots (CDs) can improve bioavailability, enhance the interaction with bacteria, inhibit the development of bacterial drug resistance, and have small side effects. Therefore, carbon dots have been widely studied and concerned in the fields of disease treatment, especially tumor treatment, and food preservation. For example, Yue Juan used natural vitamin riboflavin as a raw material in "Construction of a Photo-responsive Nanoscale System and Research on Tumor Photo-synergistic Immunotherapy" (Ph.D. thesis of the University of Science and Technology of China) to prepare carbon dots with green fluorescence for the photodynamic therapy of tumors to solve problems such as poor targeting and water solubility of traditional photosensitizers.

[0006] Photoresponsive materials have the advantages of being easy to operate and not being affected by the surrounding environment (such as ionic strength, pH value, temperature, etc.), and have unique advantages in tumor treatment and food preservation. Among them, photocatalytic carbon dots can not only generate reactive oxygen species to kill bacteria, but also destroy essential structures for life maintenance such as bacterial nucleic acids and cell membranes, thereby enhancing their antibacterial activity. If the hydrogel for food preservation can simultaneously have antibacterial and antioxidant effects and have sufficient mechanical strength, it will undoubtedly be of great significance to food safety. However, although there have been many reports on carbon dot synthesis technology, there is still a large uncertainty about whether different raw materials can synthesize carbon dots and the categories and degrees of functional characteristics of the carbon dots. Therefore, how to develop a photocatalytic antibacterial carbon dot and a preservation hydrogel with the above characteristics is still an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0007] (I) Technical problems to be solved

[0008] The present invention aims to solve one of the following technical problems existing in the prior art or related technologies:

[0009] During the preservation of aquatic products such as fresh fish fillets, there are potential food safety and environmental pollution risks in the use of traditional antibacterial agents, the new intelligent packaging materials are lacking in mechanical properties, and they cannot have both antioxidant and antibacterial properties.

[0010] (II) Technical solutions

[0011] To solve the above technical problems, the present invention provides a photocatalytic antibacterial carbon dot, a hydrogel containing the carbon dot, and its preparation method and application. The specific technical solutions adopted are as follows:

[0012] A photocatalytic antibacterial carbon dot, which is prepared by a one-pot hydrothermal method using rose bengal and riboflavin as raw materials; the mass ratio of rose bengal to riboflavin is: rose bengal: riboflavin = 1: (0.5 - 2).

[0013] Preferably, the reaction temperature of the one-pot hydrothermal method is: 200 - 250 °C, and the reaction time is 6 - 10 h.

[0014] Another object of the present invention is to provide a preparation method of the above photocatalytic antibacterial carbon dot, which is characterized in that the steps are as follows:

[0015] (1) Dissolve rose bengal and riboflavin in water, and obtain a mixed solution after ultrasonic treatment;

[0016] (2) Transfer the mixed solution obtained in step (1) to a reaction kettle for reaction, and obtain a crude product of CDs after cooling after the reaction ends;

[0017] (3) Mix the crude CDs obtained in step (2) with water and perform ultrasonic treatment. After ultrasonic treatment, filter to retain the filtrate to obtain a CDs solution.

[0018] (4) Dialyze the CDs solution obtained in step (3) and then lyophilize it to obtain CDs powder.

[0019] Preferably, the mass ratio of rose bengal, riboflavin and water in step (1) is: rose bengal: riboflavin: water = 1: (0.5 - 2): (5 - 10); the ultrasonic frequency of the ultrasonic treatment in steps (1) and (3) is 40 - 60 KHz, and the ultrasonic time is 10 - 30 min.

[0020] Preferably, the temperature of the reaction kettle in step (2) is 200 - 250 °C, and the reaction time is 6 - 10 h; the mass ratio of the crude CDs and water in step (3) is: 1: (1 - 2.5); the molecular weight cut-off of the dialysis bag used in step (4) for dialysis is 2000 - 5000 Da, and the dialysis time is 18 - 24 h.

[0021] The third object of the present invention is to provide a hydrogel containing the above-mentioned photocatalytic antibacterial carbon dots, and the hydrogel comprises the following raw materials in parts by weight:

[0022] 0.1 - 0.5 g of photocatalytic antibacterial carbon dots; 2.5 - 10 g of polyvinyl alcohol; 2.5 - 7.5 g of konjac glucomannan; 2.5 - 7.5 g of locust bean gum; 0.5 - 1.5 g of citric acid.

[0023] The fourth object of the present invention is to provide a preparation method of the above-mentioned hydrogel, which is characterized in that the steps are as follows:

[0024] (1) Weigh each raw material component according to the parts by weight of the raw materials.

[0025] (2) Dissolve polyvinyl alcohol in water and mix evenly to obtain a polyvinyl alcohol solution; dissolve konjac glucomannan and locust bean gum in boiling distilled water to obtain a polysaccharide solution; then mix the obtained polyvinyl alcohol solution and polysaccharide solution evenly to obtain a polyvinyl alcohol-polysaccharide solution.

[0026] (3) Add citric acid to the polyvinyl alcohol-polysaccharide solution obtained in step (2), mix evenly and cool to room temperature, then add photocatalytic carbon dots, and perform ultrasonic treatment to obtain a precursor solution of the hydrogel.

[0027] (4) Place the precursor solution of the hydrogel obtained in step (3) in a refrigerator for freezing, and then thaw it to room temperature. Repeat the freezing-thawing three times to obtain a fresh-keeping hydrogel.

[0028] Preferably, in step (2), the concentration of the polyvinyl alcohol solution is 50 - 200 g / L, the concentration of the konjac glucomannan (KGM) solution is 40 - 60 g / L, and the concentration of the locust bean gum (LBG) solution is 40 - 60 g / L; in step (3), the citric acid is added to a concentration of 5 - 15 g / L, and the photocatalytic antibacterial carbon dots are added to a concentration of 0.5 - 1.5 g / L.

[0029] Preferably, the mixing in steps (2) and (3) is uniform. Using a magnetic stirrer at a rate of 800 r / min, stir for 1 h, and the stirring temperature is 85°C; in step (3), the ultrasonic frequency is 40 - 60 KHz, the ultrasonic time is 10 min, and the ultrasonic temperature is 25°C; in step (4), the refrigeration in the refrigerator is at -20°C for 12 h; the thawing is at 25°C for 12 h.

[0030] The photocatalytic antibacterial carbon dots provided by the present invention, and the hydrogel containing such carbon dots can be applied to the preservation of aquatic products.

[0031] More preferably, the above-mentioned photocatalytic antibacterial carbon dots, and the hydrogel containing such carbon dots are specifically applied to the preservation of fish such as salmon and tuna.

[0032] (III) Beneficial effects

[0033] Compared with the prior art, the beneficial effects obtained by the present invention are as follows:

[0034] First, the photocatalytic antibacterial CDs prepared by the present invention have the ability to generate reactive oxygen species such as superoxide anion, singlet oxygen, and hydroxyl radical, and have good in vitro antibacterial effects against various aquatic spoilage bacteria and pathogenic bacteria such as Pseudomonas fluorescens, Listeria monocytogenes, and Hafnia alvei.

[0035] Second, the antioxidant - type preservative hydrogel KLP / CDs containing photocatalytic antibacterial CDs prepared by the present invention, by constructing a three - dimensional network structure, efficiently loads the active substance of photocatalytic CDs, has good antibacterial and antioxidant properties, can well maintain the freshness of aquatic products, and has good biocompatibility, effectively extending the shelf life of salmon. At the same time, this preservative hydrogel is made of photo - responsive antibacterial CDs, and has the characteristics of being easy to control and not being affected by environmental factors such as ionic strength, pH value, temperature, etc., facilitating its application in a wider range of antibacterial preservation scenarios.

[0036] III. Aiming at the problems of toxicity, peculiar smell, and unstable active ingredients in the preparation process of traditional fresh-keeping films, the present invention first obtains photocatalytically active CDs through a one-step hydrothermal method, and then loads the photocatalytic CDs into the hydrogel KLP / CDs with mechanical strength constructed, preparing a fresh-keeping hydrogel KLP / CDs with good advantages in inhibiting spoilage bacteria and lipid spoilage of aquatic products, being easy to peel off without residue, and integrating antibacterial and antioxidant functions. The hydrogel KLP / CDs of the present invention can be directly used as a packaging material to wrap salmon, can exert the antibacterial activity of photocatalytic CDs, avoid the spoilage of aquatic products caused by lipid oxidation, can be completely peeled off from the surface of aquatic products, is safe and non-toxic, solves the problems of poor mechanical properties, poor application stability, and residue of fresh-keeping films, and can inhibit microbial spoilage and lipid oxidation. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0038] Figure 1 It is a transmission electron microscope (TEM) image of the photocatalytic antibacterial carbon dots prepared in Example 1.

[0039] Figure 2 It is a Fourier transform infrared spectroscopy (FT-IR) image of the photocatalytic antibacterial carbon dots prepared in Example 1.

[0040] Figure 3 It is the minimum inhibitory concentration (MIC) of the photocatalytic antibacterial carbon dots prepared in Example 1 against Escherichia coli, Staphylococcus aureus, Pseudomonas fluorescens, Aeromonas sobria, Hafnia alvei, Listeria monocytogenes, and Serratia marcescens.

[0041] Figure 4 It is the antibacterial effect diagram of the carbon dots prepared in Example 3 against Escherichia coli and Staphylococcus aureus.

[0042] Figure 5 It is the antibacterial effect diagram of the carbon dots prepared in Example 4 against Escherichia coli and Staphylococcus aureus.

[0043] Figure 6 It is the SEM micrograph of the cross-section of the hydrogels prepared in Examples 5, 6, 7, and 8. Among them, a is the hydrogel prepared in Example 8; b is the hydrogel prepared in Example 5; c is the hydrogel prepared in Example 6; d is the hydrogel prepared in Example 7.

[0044] Figure 7 It is the measurement result of the elongation performance of the hydrogels containing photocatalytic carbon dots prepared in Examples 5, 6, 7, and 8.

[0045] Figure 8 Pictures of the tensile properties of the hydrogels containing photocatalytic carbon dots prepared for Examples 7 and 8. Among them, A is the hydrogel prepared in Example 8; B is the hydrogel prepared in Example 7.

[0046] Figure 9 Fourier transform infrared spectroscopy (FT-IR) diagrams of the hydrogels KLP / CDs containing photocatalytic carbon dots prepared for Examples 5, 6, and 7. Among them, PVA: polyvinyl alcohol; KGM: konjac glucomannan; LBG: locust bean gum.

[0047] Figure 10 Bacteriostatic effect diagrams of the hydrogels KLP / CDs containing photocatalytic carbon dots prepared for Examples 5, 6, and 7.

[0048] Figure 11 Antioxidant activity diagrams of the hydrogels KLP / CDs containing photocatalytic carbon dots prepared for Examples 5, 6, and 7. Among them, a is the inhibition rate of the hydrogel on DPPH; b is the inhibition rate of the hydrogel on ABTS.

[0049] Figure 12 Physical pictures of the hydrogels KLP / CDs containing photocatalytic carbon dots prepared for Example 7 at different storage days (0, 3, 6, 9, 12, 15 days) of salmon blocks.

[0050] Figure 13 Determination results of the influence of the hydrogels KLP / CDs containing photocatalytic carbon dots prepared for Example 7 on the total number of colonies (TVC) in the salmon preservation experiment.

[0051] Figure 14 Cytotoxicity test results of the hydrogels KLP / CDs containing photocatalytic carbon dots prepared for Examples 5, 6, and 7. Detailed implementation manners

[0052] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be specifically described below through specific examples. It should be noted here that the following examples are only used to further illustrate the present invention and should not be construed as limiting the protection scope of the present invention. The present invention will be further elaborated below in conjunction with the accompanying drawings and specific examples, and the present invention is not limited thereto.

[0053] The reagents, materials, instruments, and methods described in the following examples are all conventional reagents, materials, instruments, and methods in the art unless otherwise specified, and ordinary technical personnel in the art can obtain them through commercial channels.

[0054] In the following examples, the purity of the polyvinyl alcohol used was ≥98%, the purity of the locust bean gum used was ≥99%, the purity of the citric acid was ≥99.5%, and the viscosity of the konjac glucomannan used was ≥915000 mPa·sA.

[0055] In the following examples, the morphological characterization (TEM) of the photocatalytic CDs, the morphological characterization (FT-IR) of the photocatalytic CDs, the antibacterial performance test (MIC) of the photocatalytic CDs, the total viable count (TVC) of the hydrogel samples, and the biocompatibility of the hydrogel were referred to the methods of Cui et al. (F. Cui, X. Wang, D. Wang, L. Ren, Y. Meng, R. Ma, S. Wang, Z. Liu, Y. Jiang, Y. Lu, Multifunctional visible light photocatalytic carbon dots synergize with reactive oxygen species for anti-quorum sensing and anti-bacteria for salmon preservation, Chemical Engineering Journal 499 (2024) 156546.).

[0056] The test of the microstructure of the hydrogel (SEM), the determination of the mechanical properties of the hydrogel, the Fourier transform infrared spectroscopy test of the hydrogel, and the antibacterial and antioxidant properties of the hydrogel against Escherichia coli and Staphylococcus aureus were referred to the methods of Wang et al. (Z. Wang, P. Zhang, C. Yin, Y. Li, Z. Liao, C. Yang, H. Liu, W. Wang, C. Fan, D. Sun, Antibiotic-Derived Carbon-Nanodot-Decorated Hydrogel for Reactive Oxygen Species-Enhanced Anti-Infection Through Biofilm Damage, Advanced Functional Materials 33(29)(2023)2300341.).

[0057] The DPPH radical scavenging rate and ABTS radical scavenging rate of the hydrogel were determined according to the method of Hu et al. (B. Hu, Y. Ouyang, T. Zhao, Z. Wang, Q. Yan, Q. Qian, W. Wang, S. Wang, Antioxidant Hydrogels: Antioxidant Mechanisms, Design Strategies, and Applications in the Treatment of Oxidative Stress-Related Diseases, Advanced healthcare materials 13(11)(2024)2303817.).

[0058] Example 1

[0059] This example provides a photocatalytic antibacterial carbon dot and a preparation method thereof. The specific steps are as follows:

[0060] (1) Dissolve 0.25 g of rose bengal and 0.25 g of riboflavin in 2.5 g of ultrapure water. Then, under an ultrasonic frequency of 50 KHz, ultrasonically treat for 10 min to obtain a mixed solution;

[0061] (2) Transfer the mixed solution obtained in step (1) to a 40 mL reaction kettle for reaction. Heat-treat at 200 °C for 6 h. After the reaction is completed, let it stand and cool to room temperature to obtain the crude product of photocatalytic antibacterial carbon dots CDs;

[0062] (3) Add the CDs crude product obtained in step (2) to 2.5 g of ultrapure water and mix. Then, under an ultrasonic frequency of 50 KHz, ultrasonically treat for 10 min. Subsequently, filter using a 0.22 μm aqueous filter membrane to obtain a CDs solution;

[0063] (4) Transfer the CDs solution obtained in step (3) to a dialysis bag with a molecular cut-off of 2000 Da and dialyze for 24 h. After dialysis, lyophilize to obtain CDs powder.

[0064] Example 2

[0065] This example provides a photocatalytic antibacterial carbon dot and a preparation method thereof. The specific steps are as follows:

[0066] (1) Dissolve 0.25 g of rose bengal and 0.5 g of riboflavin in 2.5 g of ultrapure water. Then, under an ultrasonic frequency of 50 KHz, ultrasonically treat for 10 min to obtain a mixed solution;

[0067] (2) Transfer the mixed solution obtained in step (1) to a 40 mL reactor for reaction, heat-treat it at 250 °C for 10 h, and after the reaction is completed, let it stand and cool to room temperature to obtain the crude product of photocatalytic antibacterial carbon dots CDs;

[0068] (3) Add the crude CDs product obtained in step (2) to 2.5 g of ultrapure water and mix, then ultrasonically treat it at an ultrasonic frequency of 50 KHz for 10 min, and then filter it using a 0.22 μm aqueous filter membrane to obtain a CDs solution;

[0069] (4) Transfer the CDs solution obtained in step (3) to a dialysis bag with a molecular cut-off of 2000 Da for dialysis for 24 h, and after dialysis, lyophilize it to obtain CDs powder.

[0070] Example 3

[0071] During the selection process of carbon dot raw materials, curcumin and lysine were also selected as raw materials to prepare carbon dots, and the specific steps of its preparation method are as follows:

[0072] (1) Dissolve 0.25 g of curcumin and 0.5 g of lysine in 2.5 g of ultrapure water, and then ultrasonically treat it at an ultrasonic frequency of 50 KHz for 10 min to obtain a mixed solution;

[0073] (2) Transfer the mixed solution obtained in step (1) to a 40 mL reactor for reaction, heat-treat it at 250 °C for 10 h, and after the reaction is completed, let it stand and cool to room temperature to obtain the crude product of photocatalytic antibacterial carbon dots CDs;

[0074] (3) Add the crude CDs product obtained in step (2) to 2.5 g of ultrapure water and mix, then ultrasonically treat it at an ultrasonic frequency of 50 KHz for 10 min, and then filter it using a 0.22 μm aqueous filter membrane to obtain a CDs solution;

[0075] (4) Transfer the CDs solution obtained in step (3) to a dialysis bag with a molecular cut-off of 2000 Da for dialysis for 24 h, and after dialysis, lyophilize it to obtain CDs powder.

[0076] Example 4

[0077] During the selection process of carbon dot raw materials, histidine and theanine were also selected as raw materials to prepare carbon dots, and the specific steps of its preparation method are as follows:

[0078] (1) Dissolve 0.25 g of histidine and 0.5 g of theanine in 2.5 g of ultrapure water, and then ultrasonically treat it at an ultrasonic frequency of 50 KHz for 10 min to obtain a mixed solution;

[0079] (2) Transfer the mixed solution obtained in step (1) to a 40 mL reaction kettle for reaction, heat-treat at 250 °C for 10 h, and after the reaction is completed, let it stand and cool to room temperature to obtain a crude product of photocatalytic antibacterial carbon dots CDs;

[0080] (3) Add the crude CDs obtained in step (2) to 2.5 g of ultrapure water and mix, ultrasonically treat at an ultrasonic frequency of 50 KHz for 10 min, and then filter using a 0.22 μm aqueous filter membrane to obtain a CDs solution;

[0081] (4) Transfer the CDs solution obtained in step (3) to a dialysis bag with a molecular cut-off of 2000 Da for dialysis for 24 h, and after dialysis, lyophilize to obtain CDs powder.

[0082] Example 5

[0083] This example provides an antioxidant preservative hydrogel containing the photocatalytic antibacterial carbon dots prepared in Example 1, and a preparation method of the hydrogel. The specific steps are as follows:

[0084] (1) Weigh the main raw materials required for preparing the hydrogel according to the following parts by weight:

[0085] Photocatalytic antibacterial carbon dots 0.1 g; polyvinyl alcohol 2.5 g; konjac glucomannan 2.5 g; locust bean gum 2.5 g; citric acid 1 g;

[0086] (2) Dissolve 2.5 g of polyvinyl alcohol in 50 mL of ultrapure water, magnetically stir at 800 r / min and 85 °C for 1 h to obtain a polyvinyl alcohol solution; then dissolve 2.5 g of konjac glucomannan and 2.5 g of locust bean gum in 50 mL of boiling distilled water, and also magnetically stir at 800 r / min and 85 °C for 1 h to obtain a polysaccharide solution; finally, mix the polyvinyl alcohol solution and the polysaccharide solution, and magnetically stir at 800 r / min and 85 °C for 1 h to obtain a polyvinyl alcohol-polysaccharide solution;

[0087] (3) Add 1 g of citric acid to the polyvinyl alcohol-polysaccharide solution obtained in step (2), and at 800 r / min,

[0088] Magnetically stir at 85 °C for 1 h, and after stirring, cool to room temperature; then, add the photocatalytic antibacterial carbon dots prepared in Example 1 according to the usage amount of 0.1 g, and ultrasonically treat at a frequency of 50 KHz for 10 min to obtain a precursor solution of the hydrogel;

[0089] (4) Place the precursor solution of the hydrogel prepared in step (3) in a refrigerator and freeze at -20 °C for 12 h, then thaw at 25 °C for 12 h, and repeat three times to obtain the preservative hydrogel KLP / CDs-1.

[0090] Example 6

[0091] This example provides an antioxidant fresh-keeping hydrogel containing the photocatalytic antibacterial carbon dots prepared in Example 1, and a preparation method of the hydrogel. The specific steps are as follows:

[0092] (1) Weigh the main raw materials required for preparing the hydrogel according to the following weight parts:

[0093] 0.1 g of photocatalytic antibacterial carbon dots; 5 g of polyvinyl alcohol; 2.5 g of konjac glucomannan; 2.5 g of locust bean gum; 1 g of citric acid;

[0094] (2) Dissolve 5 g of polyvinyl alcohol in 50 mL of ultrapure water, and magnetically stir at 800 r / min and 85 °C for 1 h to obtain a polyvinyl alcohol solution; then dissolve 2.5 g of konjac glucomannan and 2.5 g of locust bean gum in 50 mL of boiling distilled water, and also magnetically stir at 800 r / min and 85 °C for 1 h to obtain a polysaccharide solution; finally, mix the polyvinyl alcohol solution and the polysaccharide solution, and magnetically stir at 800 r / min and 85 °C for 1 h to obtain a polyvinyl alcohol-polysaccharide solution;

[0095] (3) Add 1 g of citric acid to the polyvinyl alcohol-polysaccharide solution obtained in step (2), and magnetically stir at 800 r / min and 85 °C for 1 h. After the stirring is completed, cool to room temperature; then, add the photocatalytic antibacterial carbon dots prepared in Example 1 according to the usage amount of 0.1 g, and ultrasonically treat at a frequency of 50 KHz for 10 min to obtain a hydrogel precursor solution;

[0096] (4) Place the hydrogel precursor solution prepared in step (3) in a refrigerator and freeze it at -20 °C for 12 h, then thaw it at 25 °C for 12 h, and repeat three times to obtain the fresh-keeping hydrogel KLP / CDs-2.

[0097] Example 7

[0098] This example provides an antioxidant fresh-keeping hydrogel containing the photocatalytic antibacterial carbon dots prepared in Example 1, and a preparation method of the hydrogel. The specific steps are as follows:

[0099] (1) Weigh the main raw materials required for preparing the hydrogel according to the following weight parts:

[0100] 0.1 g of photocatalytic antibacterial carbon dots; 10 g of polyvinyl alcohol; 2.5 g of konjac glucomannan; 2.5 g of locust bean gum; 1 g of citric acid;

[0101] (2) Dissolve 10 g of polyvinyl alcohol in 50 mL of ultrapure water, and magnetically stir at 800 r / min and 85 °C for 1 h to obtain a polyvinyl alcohol solution; then dissolve 2.5 g of konjac glucomannan and 2.5 g of locust bean gum in 50 mL of boiling distilled water, and also magnetically stir at 800 r / min and 85 °C for 1 h to obtain a polysaccharide solution; finally, mix the polyvinyl alcohol solution and the polysaccharide solution, and magnetically stir at 800 r / min and 85 °C for 1 h to obtain a polyvinyl alcohol-polysaccharide solution;

[0102] (3) Add 1 g of citric acid to the polyvinyl alcohol-polysaccharide solution obtained in step (2), and magnetically stir at 800 r / min and 85 °C for 1 h. After stirring, cool to room temperature; then, add the photocatalytic antibacterial carbon dots prepared in Example 1 in an amount of 0.1 g, and ultrasonically treat for 10 min at a frequency of 50 KHz to obtain a hydrogel precursor solution;

[0103] (4) Place the hydrogel precursor solution prepared in step (3) in a refrigerator and freeze at -20 °C for 12 h, then thaw at 25 °C for 12 h. Repeat three times to obtain the fresh-keeping hydrogel KLP / CDs-3.

[0104] Example 8

[0105] This example provides an antioxidant fresh-keeping hydrogel containing the photocatalytic antibacterial carbon dots prepared in Example 1, and a preparation method of the hydrogel. The specific steps are as follows:

[0106] (1) Weigh the main raw materials required for preparing the hydrogel according to the following weight parts:

[0107] Photocatalytic antibacterial carbon dots 0.1 g; Konjac glucomannan 2.5 g; Locust bean gum 2.5 g; Citric acid 1 g;

[0108] (2) Dissolve 2.5 g of konjac glucomannan and 2.5 g of locust bean gum in 100 mL of boiling distilled water, and also magnetically stir at 800 r / min and 85 °C for 1 h to obtain a polysaccharide solution;

[0109] (3) Add 1 g of citric acid to the polysaccharide solution obtained in step (2), and magnetically stir at 800 r / min and 85 °C for 1 h. After stirring, cool to room temperature; then, add the photocatalytic antibacterial carbon dots prepared in Example 1 in an amount of 0.1 g, and ultrasonically treat for 10 min at a frequency of 50 KHz to obtain a hydrogel precursor solution;

[0110] (4) Place the hydrogel precursor solution prepared in step (3) in a refrigerator and freeze at -20 °C for 12 h, then thaw at 25 °C for 12 h. Repeat three times to obtain the fresh-keeping hydrogel KL / CDs.

[0111] Example 9

[0112] This example is for the morphological characterization of photocatalytic CDs to prove the successful synthesis of photocatalytic CDs.

[0113] Referring to the method of Cui et al., TEM was used to characterize the morphology of the photocatalytic CDs synthesized in Example 1. The TEM image is as Figure 1 shown. The structure shows that RR-CDs exhibit an obvious spherical shape with an average size of 3.1 ± 0.83 nm. In addition, the HRTEM of RR-CDs proves that it has an obvious lattice with a lattice fringe spacing of 0.19 nm, indicating the successful synthesis of CDs.

[0114] Example 10

[0115] This example is for the structural characterization of photocatalytic CDs to prove that the surface of photocatalytic CDs contains various functional groups.

[0116] Referring to the method of Cui et al., Fourier transform infrared spectroscopy (FT-IR) was used to characterize the functional groups of the photocatalytic CDs synthesized in Example 1. The FT-IR image is as Figure 2 shown. The peaks at 3000 - 2850 cm -1 may represent the stretching vibration of alkyl C-H and the stretching absorption of carboxyl O-H respectively, while the peaks at 1440 - 1340 cm -1 represent the bending vibration of alkyl C-H. In addition, the peaks at 1772, 1320 - 1210 and 937 cm -1 represent the C=O stretching absorption, C-O stretching vibration and out-of-plane bending vibration of the O-H bond respectively, confirming the presence of carboxylic acid in RR-CDs. The peak at 3388 cm -1 may represent the intermolecular hydroxyl and amino NH stretching vibration. The peaks at 769–659 cm -1 represent the out-of-plane bending of the hydroxyl group, confirming the presence of hydroxyl groups in RR-CDs.

[0117] The peaks at 1640 - 1560 and 900 - 650 cm -1 represent the deformation vibration and out-of-plane bending oscillation of N-H respectively, indicating the presence of amino groups. The peaks at 645 and 600 - 500 cm -1 are attributed to the C-Cl and C-I bonds in RR-CDs respectively; the Cl and I elements come from Rose Bengal.

[0118] Example 11

[0119] This example is for the performance test of photocatalytic CDs to prove that it is an effective antibacterial material.

[0120] The antibacterial performance of the photocatalytic CDs synthesized in Example 1 was characterized by the minimum inhibitory concentration (MIC) using the method of Cui et al. The samples (photocatalytic CDs) were mixed with Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), Pseudomonas fluorescens (P. fluorescens), Aeromonas sobria (A. sobria), Hafnia alvei (H. alvei), Listeria monocytogenes (L. monocytogenes), and Serratia marcescens (S. marcescens) that had been activated overnight. After 1 h of illumination, 100 μL of the mixed solution was taken and placed on a solid agar culture dish, and cultured overnight. Whether colonies grew on the solid agar culture dish was observed. The MIC was the lowest concentration at which no bacterial growth was observed.

[0121] The MIC images are as Figure 3 shown. The results show that the MIC of the photocatalytic CDs against Pseudomonas fluorescens is 50 μg / mL, the MIC against Escherichia coli and Staphylococcus aureus is 100 μg / mL, and the MIC against Aeromonas sobria, Hafnia alvei, Listeria monocytogenes, and Serratia marcescens is 200 μg / mL. It is worth noting that the antibacterial effect of RR-CDs combined with illumination is the best among all treatment groups, and the number of colonies decreased significantly. Especially when treated with 200 μg / mL RR-CDs under illumination conditions, almost no colonies visible to the naked eye formed on the surface of the culture medium. However, it was found that the bacteria grew normally in the treatment group with only RR-CDs added without illumination treatment, indicating that RR-CDs only have antibacterial activity after illumination and have photocatalytic antibacterial ability.

[0122] Example 12

[0123] The antibacterial performance of the CDs synthesized in Example 3 was characterized by referring to the method of Cui et al. The samples (CDs) were mixed with Escherichia coli and Staphylococcus aureus that had been activated overnight. After 1 h of illumination, 100 μL of the mixed solution was taken and placed on a solid agar culture dish, and cultured overnight. Whether colonies grew on the solid agar culture dish was observed. Among them, the concentrations of Escherichia coli and Staphylococcus aureus were 100 μg / mL. At the same time, a dark group without illumination and a control group without adding samples were set up.

[0124] The MIC images are as Figure 4 shown. The results show that the CDs have no antibacterial effect on Escherichia coli and Staphylococcus aureus under both dark and illumination conditions. It shows that the carbon dots synthesized in Example 3 do not have antibacterial properties at 100 μg / mL and do not have photocatalytic characteristics either.

[0125] Example 13

[0126] The antibacterial performance of the CDs synthesized in Example 4 was characterized by referring to the method of Cui et al. The sample (CDs) was mixed with Escherichia coli and Staphylococcus aureus that had been activated overnight. After 1 h of light irradiation, 100 μL of the mixed solution was taken and placed in a solid agar culture dish, and cultured overnight. Whether colonies grew on the solid agar culture dish was observed. Among them, the concentrations of Escherichia coli and Staphylococcus aureus were 100 μg / mL. At the same time, a dark group without light irradiation and a control group without adding the sample were set up.

[0127] The MIC images are as Figure 5 shown. The results show that the CDs have no antibacterial effect on Escherichia coli and Staphylococcus aureus under dark and light conditions. It shows that the carbon dots synthesized in Example 4 do not have antibacterial properties at 100 μg / mL, and there is also no photocatalytic property.

[0128] Example 14

[0129] In order to verify the microstructure of the prepared antioxidant fresh-keeping hydrogel containing photocatalytic antibacterial CDs, SEM tests were carried out on the hydrogels KLP / CDs-1, KLP / CDs-2, KLP / CDs-3 and KL / CDs prepared in Examples 5-8. The specific steps are as follows:

[0130] The prepared hydrogel was freeze-dried by referring to the method of Wang et al. The hydrogel sample was placed at -80 °C overnight, and the water in it was removed by freeze-drying for 48 h using a freeze-dryer. The freeze-dried hydrogel was cut and torn, and the cross-section of the hydrogel was observed by SEM.

[0131] The measurement results are as Figure 6 shown. Although the hydrogel without adding polyvinyl alcohol also has a three-dimensional network structure, the structure is loose and the pores are very large. With the addition of polyvinyl alcohol, the cross-linking between polyvinyl alcohol and the polysaccharide solution forms a reticular porous structure, and SEM shows that the pores of the gel are larger. With the increase of polyvinyl alcohol, the hydrogel binds more tightly under the microscope, indicating that polyvinyl alcohol endows the hydrogel with better mechanical properties.

[0132] Example 15

[0133] In order to verify the change in the mechanical properties of the prepared antioxidant fresh-keeping hydrogel containing photocatalytic antibacterial CDs, SEM tests were carried out on the hydrogels KLP / CDs-3 and KL / CDs prepared in Examples 5 and 8. The specific steps are as follows:

[0134] The prepared hydrogel was cut into strips of 2 cm × 6 cm × 0.5 cm by referring to the method of Wang et al. The two ends were clamped with a fixing device, the maximum stretching was set to 50 cm, and the stretching speed was 3 mm / s.

[0135] The measurement results are as Figure 7 andFigure 8 As shown, before adding polyvinyl alcohol, the maximum tensile strength of the hydrogel did not reach 50 g and it was prone to breakage. As the amount of polyvinyl alcohol increased, the force that the hydrogel could withstand became greater and greater, reaching up to 300 g at most, which was more than 6 times that of the hydrogel without polyvinyl alcohol.

[0136] Example 16

[0137] In order to verify the functional group structures of the prepared antioxidant preservative hydrogels KLP / CDs-1, KLP / CDs-2, and KLP / CDs-3 containing photocatalytic antibacterial CDs, Fourier transform infrared spectroscopy tests were carried out on the hydrogels prepared in Examples 5-7. The specific operation steps are as follows:

[0138] Refer to the method of Wang et al. Grind the hydrogel sample finely in an agate mortar, mix it with KBr in a ratio of 1:100, transfer it to a tablet die after grinding and mixing evenly, and complete sample preparation by evacuating and pressurizing. Measure at a wavelength of 500 - 4000 cm -1

[0139] The measurement results are as Figure 9 shown. A broad absorption peak was observed at 3500 - 3100 cm -1 corresponding to the stretching vibration of -OH within and between molecules, indicating that hydrogen bonds were formed between the polysaccharide and PVA. After adding citric acid, different -OH and CO peaks of the carboxyl group were observed at 1404, 1100 - 1000 cm -1 respectively. In addition, the C-O and C-O-C peaks of the ester bond were observed at 1670 - 1723 and 1144 cm -1 indicating that citric acid promoted the crosslinking of the polysaccharide and PVA. As the amount of PVA increased, the peak at 1723 cm -1 gradually increased, which was due to the increased opportunity for the carboxyl group to combine with the hydroxyl group, resulting in a tighter connection of the hydrogel.

[0140] The doublet peaks at 1280 and 1306 cm -1 , the peak at 650 - 550 cm -1 and the peak at 830 - 600 cm -1 are the characteristic peaks of CDs, corresponding to the C-N stretching, C-I, and C-Cl peaks respectively, indicating the successful introduction of CDs. The peak at 1579 - 1566 cm -1 is the in-plane deformation vibration of the amide bond N-H, indicating that CDs were bound to the inside of the hydrogel by binding to the surface amino group of the carboxyl group of citric acid. The above results show that the hydrogel molecules are mainly connected by hydrogen bonds and ester bonds, and CDs are stably bound inside the hydrogel.

[0141] Example 17

[0142] ​To verify the antibacterial properties of the prepared antioxidant preservative hydrogels KLP / CDs-1, KLP / CDs-2, and KLP / CDs-3 containing photocatalytic antibacterial CDs, antibacterial experiments were conducted on the hydrogels prepared in Examples 5-7 against Escherichia coli and Staphylococcus aureus. The specific operation steps are as follows:

[0143] Refer to the method of Wang et al. Take 0.5 g of hydrogel (containing 100 μg / mL CDs) and mix it with 0.5 mL of Escherichia coli and Staphylococcus aureus bacterial solutions respectively. Place the mixed solution under a xenon lamp for irradiation for 1 h, and the control group is cultured in the dark for 1 h. After the culture is completed, take 100 μL of the bacterial solution for plate coating, and then observe the colony growth after culturing in a constant temperature incubator for 12 h.

[0144] The measurement results are as Figure 10 shown. The surface of the solid medium cultured in the dark is covered with bacteria, while after light treatment, there is no obvious bacterial growth on the medium. This is because the CDs in the hydrogel generate reactive oxygen species (ROS) after light treatment. ROS can damage the structure of bacteria, leading to an imbalance in the redox state within the bacteria, thereby killing the bacteria.

[0145] Example 18

[0146] To verify the antioxidant properties of the prepared antioxidant preservative hydrogels KLP / CDs-1, KLP / CDs-2, and KLP / CDs-3 containing photocatalytic antibacterial CDs, antioxidant experiments against DPPH and ABTS were conducted on the hydrogels prepared in Examples 5-7. The specific operation steps are as follows:

[0147] Refer to the method of Wang et al. Take 0.5 g of hydrogel and mix it with 0.5 mL of Escherichia coli and Staphylococcus aureus bacterial solutions respectively. Place the mixed solution under a xenon lamp for irradiation for 1 h, and the control group is cultured in the dark for 1 h. After the culture is completed, take 100 μL of the bacterial solution for plate coating, and then observe the colony growth after culturing in a constant temperature incubator for 12 h.

[0148] Refer to the method of Hu et al. Take 0.5 g of hydrogel and add it to 4 mL of 0.1 mmol / L DPPH solution (dissolved in 95% ethanol). After reacting in the dark for 30 min, measure the absorbance value (A1) at 517 nm. Use 95% absolute ethanol to replace the DPPH solution and measure the absorbance value (A2) at 517 nm. Use distilled water to replace R-CDs and measure the absorbance value (A0) at 517 nm. The DPPH radical scavenging rate is calculated according to formula 1.

[0149]

[0150] Refer to the method of Hu et al. An aqueous solution of ABTS at 7 mmol / L was mixed with a solution of potassium persulfate at 2.45 mmol / L in a ratio of 1:1 and left to stand in the dark at room temperature for 12 h to generate ABTS⁺. It was diluted with PBS buffer until the absorbance dropped to about 0.7 to obtain the working solution. 0.5 g of the hydrogel was respectively mixed with the working solution and PBS in a ratio of 1:10, and after standing in the dark for 6 minutes, the absorbance was measured at 734 nm and recorded as A1 and A2 respectively. 0.5 mL of PBS was mixed with ABTS in a ratio of 1:10, and the absorbance measured under the same conditions was recorded as A0. The ABTS radical scavenging rate was calculated according to Equation 2.

[0151]

[0152] The antioxidant assay results are as Figure 11 shown. With the addition of polyvinyl alcohol, the inhibition rates of the hydrogel against DPPH and ABTS gradually decreased. This is because at the same weight, the higher the content of polysaccharides with antioxidant activity, the higher the antioxidant activity. However, generally, the antioxidant ability of the hydrogel against DPPH and ABTS > 60%, indicating that the hydrogel can reduce the oxidation of fish fillets to a certain extent.

[0153] Example 19

[0154] To verify the practicality of the prepared antioxidant preservative hydrogel containing photocatalytic antibacterial CDs in the preservation of aquatic products, the hydrogel prepared in Example 7 was used with fresh salmon meat as the sample for a preservation experiment. During the preservation process, the fresh salmon meat blocks were completely wrapped with the transparent hydrogel and placed in a freezer at 4°C for storage. At the same time, the total viable count (TVC) of the samples during preservation was measured. The specific steps are as follows:

[0155] Refer to the method of Cui et al. Prepare 10 g of minced fish, TCA solution (26.315 g of trichloroacetic acid dissolved in a 500 mL volumetric flask), and TBA solution (0.02 mol / L): Accurately weigh 0.288 g (accurate to 0.001 g) of thiobarbituric acid, dissolve it in water, and dilute it to 100 mL. Add 10 g of minced fish to 50 mL of TCA and homogenize. After homogenization, let it stand for 30 min and filter. Pipette 5 mL of the supernatant from the filtrate into a stoppered test tube, add 5 mL of TBA to it, place the stoppered test tube in a constant temperature water bath at 80°C for 40 min, and after cooling to room temperature (put an ice bag in a washbasin), measure the absorbance of the mixed solution at 532 nm. Control: 5 mL of TCA + 5 mL of TBA.

[0156] The physical picture (after removing the hydrogel) of the actual preservation effect of the fresh salmon meat blocks using the hydrogel prepared in Example 7 is as Figure 12 shown. FromFigure 12 It can be seen that the salmon meat blocks preserved with hydrogel maintained a fresher color for a longer time. In the control group and the carbon dot group, the surface color of the meat blocks changed significantly on the 6th day, while the hydrogel preservation group could still maintain a relatively fresh color on the 12th day. TVC measurement results Figure 13 As shown, after treatment with CDs and hydrogel, the microbial growth rate on the surface of the fish fillets was significantly lower than that of the untreated salmon fillets. On the 6th day, the microorganisms on the surface of the salmon fillets in the blank group were near the limit, and on the 9th day, they far exceeded the limit. The microorganisms on the surface of the salmon fillets treated with CDs exceeded the limit on the 9th day. Although the microorganisms on the surface of the salmon fillets treated with hydrogel also increased over time, the growth rate was the slowest, and spoilage did not occur until about the 15th day. The results of the total number of colonies indicated that the hydrogel had good antibacterial properties.

[0157] Example 20

[0158] To verify the practicability of the prepared antioxidant preservation hydrogels KLP / CDs-1, KLP / CDs-2, and KLP / CDs-3 containing photocatalytic antibacterial CDs in the preservation process of aquatic products, the biocompatibility of the hydrogels prepared in Examples 5-7 was determined. The specific experiment was a cytotoxicity test, and the specific experimental steps were as follows:

[0159] The cytotoxicity referred to the method of Cui et al.: The CCK-8 was used to test the proliferation rate of cells. 100 μL of HepG-2 cell suspension was added to a 96-well cell culture plate, and the cell culture plate was placed in an incubator at 37 °C and 5% CO2 for overnight culture. Subsequently, 0.5 g of hydrogel was added to each well. After culturing for 24 h, the supernatant was discarded, CCK-8 staining was performed, and after culturing for 1 h, the OD value was measured at 450 nm. The cell proliferation rate was calculated by the following formula.

[0160] Cell proliferation rate % = OD experimental group / OD control group × 100% Formula (3)

[0161] The results of the cytotoxicity measurement are as Figure 14 shown. The cell compatibility of the hydrogel was close to 100%, indicating that the hydrogel had good biocompatibility and could be further used in the food field.

[0162] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A photocatalytic antibacterial carbon dot, characterized in that: The method is prepared by a one-pot hydrothermal method using Bengal rose red and riboflavin as raw materials; the mass ratio of Bengal rose red to riboflavin is: Bengal rose red: riboflavin = 1: (0.5～2)。 2. The photocatalytic antibacterial carbon dots according to claim 1, characterized in that: The reaction temperature of the one-pot hydrothermal method is 200-250° C., and the reaction time is 6-10 hours.

3. A method for preparing the photocatalytic antibacterial carbon dots according to any one of claims 1 or 2, characterized in that: Here are the steps: (1) dissolving Rose Bengal and riboflavin in water, and obtaining a mixed solution after ultrasonic treatment; (2) transferring the mixed solution obtained in step (1) to a reactor for reaction, and cooling after the reaction to obtain a crude CDs product; (3) adding water to the crude CDs obtained in step (2), mixing the mixture and ultrasonically treating the mixture, filtering the mixture after the ultrasonic treatment to obtain a CDs solution; (4) The CDs solution obtained in step (3) is dialyzed and then freeze-dried to obtain CDs powder.

4. The preparation method according to claim 3, characterized in that: The mass ratio of Bengal rose red, riboflavin and water in step (1) is: Bengal rose red: riboflavin: water = 1: (0.5-2): (5-10); the ultrasonic frequency of the ultrasonic treatment in step (1) and step (3) is 40-60 KHz, and the ultrasonic time is 10-30 min.

5. The preparation method according to claim 3, characterized in that: In step (2), the temperature of the reactor is 200-250° C., and the reaction time is 6-10 h. In step (3), the mass ratio of the crude CDs product to water is 1:(1-2.5). In step (4), the molecular weight cutoff of the dialysis bag for dialysis is 2000-5000 Da, and the dialysis time is 18-24 h.

6. A hydrogel containing the photocatalytic antibacterial carbon dots according to claim 1 or 2, characterized in that: The invention comprises the following raw materials in parts by weight: 0.1-0.5 parts of photocatalytic antibacterial carbon dots; 2.5-10 parts of polyvinyl alcohol; 2.5-7.5 parts of konjac glucomannan; 2.5-7.5 parts of locust bean gum; and 0.5-1.5 parts of citric acid.

7. A method for preparing the hydrogel according to claim 6, characterized in that: Here are the steps: (1) Weigh each raw material component according to its weight; (2) dissolving polyvinyl alcohol in water and mixing to obtain a polyvinyl alcohol solution; dissolving konjac glucomannan and locust bean gum in boiling distilled water to obtain a polysaccharide solution; and then mixing the obtained polyvinyl alcohol solution and the polysaccharide solution to obtain a polyvinyl alcohol-polysaccharide solution; (3) adding citric acid to the polyvinyl alcohol-polysaccharide solution obtained in step (2), mixing evenly and cooling to room temperature, adding photocatalytic carbon dots, and obtaining a hydrogel precursor liquid after ultrasonic treatment; (4) The hydrogel precursor liquid obtained in step (3) is placed in a refrigerator for freezing, and then thawed to room temperature. The freezing-thawing process is repeated three times to obtain a fresh hydrogel.

8. The preparation method according to claim 7, characterized in that: In step (2), the concentration of the polyvinyl alcohol solution is 50-200 g / L, the concentration of konjac glucomannan in the polysaccharide solution is 40-60 g / L, and the concentration of locust bean gum is 40-60 g / L; in step (3), the citric acid is added to a concentration of 5-15 g / L, and the photocatalytic antibacterial carbon dots are added to a concentration of 0.5-1.5 g / L.

9. The preparation method according to claim 7, characterized in that: The mixing of steps (2) and (3) is uniform, and the stirring is carried out at a rate of 800 r / min for 1 hour using a magnetic stirrer, and the stirring temperature is 85° C.; in step (3), the ultrasonic frequency is 40-60 kHz, the ultrasonic time is 10 min, and the ultrasonic temperature is 25° C.; in step (4), the refrigerator freezing is carried out at -20° C. for 12 hours; and the thawing is carried out at 20-25° C. for 12 hours.

10. Use of the photocatalytic carbon dots according to claim 1 or 2 in the preservation of aquatic products.

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