A fresh-keeping film with near-infrared photodynamic sterilization activity and preparation method thereof

Abstract

The present invention provides a cling film with near-infrared photodynamic bactericidal activity and a preparation method thereof, belonging to the technical field of antibacterial cling film. Zinc oxide nanoparticles and H2O2 are used to jointly catalyze the rapid oxidative polymerization of polydopamine (PDA) to form zinc oxide nanoparticles encapsulating PDA. Combining zinc oxide nanoparticles with bactericidal activity with PDA can achieve synergistic bactericidal effects of metal ions and photothermal effects. At the same time, the photothermal conversion effect of PDA in near-infrared absorption can further stimulate zinc oxide nanoparticles to produce more reactive oxygen species (ROS), thereby achieving a long-lasting and efficient antibacterial effect. The PDA on the surface of ZnO NPs can improve the compatibility and binding force between ZnO NPs and biopolymers, thereby obtaining a cling film with near-infrared photodynamic bactericidal activity and excellent mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of antibacterial cling film, in particular to a cling film with near-infrared photodynamic sterilization activity and a preparation method thereof. Background Art

[0002] Contamination by foodborne microorganisms is a major factor leading to food spoilage and foodborne illness, and a key role of food packaging is to protect food from microbial contamination. However, most commonly used biopolymer materials currently lack strong antimicrobial activity or meet the requirements for food preservation. Therefore, the addition of antimicrobial agents to enhance the antimicrobial properties of biopolymers is an effective approach. Food wraps with antimicrobial properties can be achieved by incorporating antimicrobial agents internally or externally. However, conventional antimicrobial wraps generally lack satisfactory antimicrobial properties. Furthermore, the production and use of some non-degradable antimicrobial packaging materials are causing serious environmental pollution and health problems.

[0003] Sustainable cling film with antimicrobial activity is the future development direction of antimicrobial packaging. However, the current development of antimicrobial packaging is still limited by some bottleneck factors. For example, a large amount of plant-based antimicrobial agents usually need to be added to the packaging material to achieve a good antibacterial effect. Although some metal nanoparticles (gold, silver and copper, etc.) have good antibacterial effects, long-term use may pose a potential threat to human health and the environment. Photodynamic sterilization and photothermal sterilization are considered to be a natural sterilization strategy and a very promising method to replace traditional antimicrobial agents. Under normal circumstances, this physical sterilization does not lead to the development of microbial resistance. However, unfortunately, single photodynamic sterilization or photothermal sterilization also has the problem of insufficient sterilization power.

[0004] Zinc is an essential trace element for the human body. Zinc oxide, an oxidation product of zinc, exhibits excellent luminescence properties. Nano-zinc oxide (Nano-ZnO), in particular, not only exhibits excellent antibacterial activity but also possesses high chemical reactivity and excellent photocatalytic activity. Polydopamine (PDA) has attracted considerable attention due to its non-cytotoxicity, biodegradability, and remarkable photothermal conversion efficiency. The photothermal conversion efficiency of PDA nanoparticles is as high as 40%, exceeding that of gold nanorods. Therefore, the assembly of Nano-ZnO and PDA to prepare a nanomaterial with synergistic bactericidal properties to replace traditional antimicrobial agents has great development prospects and application value in the field of antimicrobial packaging. Summary of the Invention

[0005] The purpose of the present invention is to provide a cling film with near-infrared photodynamic bactericidal activity and a preparation method thereof, so as to solve the technical problems that the current antibacterial cling film has insufficient bactericidal power and pollutes the environment.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a fresh-keeping film having near-infrared photodynamic bactericidal activity, which is prepared from raw materials comprising the following parts by mass:

[0008]

[0009] 0.5 to 0.8 parts of polydopamine-wrapped zinc oxide nanoparticles PDA-ZnO NPs.

[0010] Furthermore, the method for preparing the polydopamine-encapsulated zinc oxide nanoparticles PDA-ZnO NPs comprises the following steps:

[0011] 1) mixing ammonium hydroxide, ethanol and water to obtain a mixed solution;

[0012] 2) adding dopamine hydrochloride, zinc oxide nanoparticles, and hydrogen peroxide to the mixed solution in sequence for reaction;

[0013] 3) The reaction precipitate obtained in step 2) is centrifuged and washed sequentially to obtain PDA-ZnO NPs.

[0014] Furthermore, in the step 1), the volume ratio of ammonium hydroxide, ethanol and water is 2-4:45-55:90-110, and the mixing is carried out under stirring at a stirring speed of 500-700 rpm and a stirring time of 20-30 min.

[0015] Furthermore, the usage ratio of ammonium hydroxide, dopamine hydrochloride, zinc oxide nanoparticles and hydrogen peroxide is 2-4 mL: 1-2 g: 5-10 g: 0.3-0.8 g.

[0016] Furthermore, in the step 2), the reaction temperature is 20-30° C., and the reaction time is 5-6 h.

[0017] Furthermore, in the step 3), the centrifugal speed is 6000-8000 rpm, and the centrifugal time is 3-5 min.

[0018] The present invention provides a method for preparing a fresh-keeping film having near-infrared photodynamic bactericidal activity, comprising the following steps:

[0019] a. Add aloe vera gel and polyvinyl alcohol into water respectively, and heat until dissolved to obtain aloe vera gel solution and polyvinyl alcohol solution;

[0020] b. mixing the aloe vera gel solution, the polyvinyl alcohol solution and glycerin to obtain a mixed solution;

[0021] c. Zinc oxide nanoparticles (PDA-ZnO NPs) coated with polydopamine and Span 80 were added to the mixture, and the obtained plastic wrap solution was cast on an acrylic plate to form a film, thereby obtaining a plastic wrap with near-infrared photodynamic bactericidal activity.

[0022] Furthermore, in step a, the heating temperature is independently 70-90°C.

[0023] Furthermore, the usage ratio of the aloe vera gel to water is 55-70:1200, and the usage ratio of polyvinyl alcohol to water is 25-35:1200.

[0024] Beneficial effects of the present invention:

[0025] (1) Combining ZnO NPs with bactericidal activity with PDA can achieve synergistic bactericidal effects of metal nanoparticles and photothermal effects. At the same time, the photothermal conversion effect of PDA in the near-infrared absorption can further stimulate ZnO NPs to produce more reactive oxygen species (ROS), thereby achieving a highly efficient and long-lasting antibacterial effect.

[0026] (2) PDA not only has outstanding adhesion but also contains a large number of functional groups such as amino, hydroxyl and imine groups on its surface. Using it to modify ZnO NPs can give them surface functional properties, allowing them to undergo Michael addition or Schiff reaction with the polysaccharides and proteins contained in aloe vera gel, which can significantly improve the physicochemical stability of ZnO NPs in plastic wrap and the mechanical properties of the film.

[0027] (3) The method of the present invention effectively combines photodynamic sterilization, photothermal sterilization and metal ion sterilization, and can effectively solve the problem of low antibacterial efficiency commonly found in traditional antibacterial cling films through a multi-pathway synergistic sterilization effect.

[0028] (4) The present invention provides a production process for a green and sustainable antibacterial film with simple preparation process, no harmful substances and high efficiency and long-lasting bactericidal activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a transmission electron microscopy (TEM) image of PDA-ZnO NPs prepared in Example 1 of the present invention;

[0030] Figure 2 This is a comparison chart of the transparency and tensile strength of the cling film prepared in Comparative Example 1 and Example 2 without adding PDA-ZnO NPs;

[0031] Figure 3 This is a comparison chart of the antibacterial activity of the fresh-keeping film prepared in the present invention under light and dark conditions;

[0032] Figure 4This is a diagram showing the preservation effect of commercially available PE cling film and the cling film prepared in Example 2 on mangoes under near-infrared long-wavelength light;

[0033] Figure 5 The diagram shows the preservation effects of commercially available PE cling film and the cling film prepared in Example 2 on grapes under natural light conditions. DETAILED DESCRIPTION

[0034] The present invention provides a fresh-keeping film having near-infrared photodynamic bactericidal activity, which is prepared from raw materials comprising the following parts by mass:

[0035]

[0036] 0.5 to 0.8 parts of polydopamine-wrapped zinc oxide nanoparticles PDA-ZnO NPs.

[0037] In the present invention, the content of the aloe vera gel is preferably 60 to 68 parts by mass, and more preferably 62 to 64 parts by mass.

[0038] In the present invention, the content of the polyvinyl alcohol is preferably 28 to 32 parts by mass, more preferably 30 parts by mass.

[0039] In the present invention, the content of glycerol is preferably 0.9 to 1.1 parts by mass, more preferably 1.0 part by mass.

[0040] In the present invention, the content of Span 80 is preferably 0.5 to 0.7 parts by mass, more preferably 0.6 parts by mass.

[0041] In the present invention, the content of the polydopamine-encapsulated zinc oxide nanoparticles PDA-ZnONPs is preferably 0.6 to 0.7 parts by mass, and more preferably 0.65 parts by mass.

[0042] In the present invention, the method for preparing the polydopamine-encapsulated zinc oxide nanoparticles PDA-ZnO NPs comprises the following steps:

[0043] 1) mixing ammonium hydroxide, ethanol and water to obtain a mixed solution;

[0044] 2) adding dopamine hydrochloride, zinc oxide nanoparticles, and hydrogen peroxide to the mixed solution in sequence for reaction;

[0045] 3) The reaction precipitate obtained in step 2) is centrifuged and washed sequentially to obtain PDA-ZnO NPs.

[0046] In the present invention, in step 1), the volume ratio of ammonium hydroxide, ethanol and water is 2-4:45-55:90-110, preferably 3:50:100.

[0047] In the present invention, in step 1), the mixing is carried out under stirring, the stirring speed is 500-700 rpm, preferably 600 rpm; the stirring time is 20-30 min, preferably 22-28 min, more preferably 25 min.

[0048] In the present invention, the usage ratio of ammonium hydroxide, dopamine hydrochloride, zinc oxide nanoparticles and hydrogen peroxide is 2-4 mL: 1-2 g: 5-10 g: 0.3-0.8 g, preferably 3 mL: 1.5 g: 6-8 g: 0.4-0.6 g, and more preferably 3 mL: 1.5 g: 7 g: 0.5 g.

[0049] In the present invention, in step 2), the reaction temperature is 20-30° C., preferably 25° C.; the reaction time is 5-6 h, preferably 5 h.

[0050] In the present invention, in step 3), the centrifugal speed is 6000-8000 rpm, preferably 7000 rpm; the centrifugal time is 3-5 min, preferably 4 min.

[0051] In the present invention, the particle size of the zinc oxide nanoparticles is 140 to 190 nm, preferably 150 to 180 nm, and more preferably 160 to 170 nm.

[0052] The present invention provides a method for preparing a fresh-keeping film having near-infrared photodynamic bactericidal activity, comprising the following steps:

[0053] a. Add aloe vera gel and polyvinyl alcohol into water respectively, and heat until dissolved to obtain aloe vera gel solution and polyvinyl alcohol solution;

[0054] b. mixing the aloe vera gel solution, the polyvinyl alcohol solution and glycerin to obtain a mixed solution;

[0055] c. Zinc oxide nanoparticles (PDA-ZnO NPs) coated with polydopamine and Span 80 were added to the mixture, and the obtained plastic wrap solution was cast on an acrylic plate to form a film, thereby obtaining a plastic wrap with near-infrared photodynamic bactericidal activity.

[0056] In the present invention, in step a, the heating temperature is independently 70-90°C, preferably 80°C.

[0057] In the present invention, the usage ratio of the aloe vera gel to water is 55-70:1200, preferably 65:1200; the usage ratio of polyvinyl alcohol to water is 25-35:1200, preferably 35:1200.

[0058] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0059] Example 1

[0060] (1) 3 mL of ammonium hydroxide (NH4OH), 50 mL of ethanol, and 100 mL of ultrapure water were stirred at 500 rpm for 20 min at 25°C to obtain a mixed solution.

[0061] (2) Add 1 g of dopamine hydrochloride (DA) and 5 g of zinc oxide nanoparticles (ZnONPs) to the mixed solution prepared in step (1) and stir at the same speed for 5 min. Then, add 0.3 g of H2O2 dropwise and continue stirring at 900 rpm for 5 h.

[0062] (3) The reaction mixture obtained in step (2) was centrifuged at 6000 rpm for 3 min, and the resulting precipitate was washed three times with ultrapure water to obtain PDA-ZnO NPs.

[0063] (4) Weigh 65 parts of aloe vera gel and 35 parts of polyvinyl alcohol, add them into 1200 parts of distilled water, and heat them in a water bath at 80°C until they are completely dissolved.

[0064] (5) The dissolved aloe vera gel and polyvinyl alcohol solution were mixed at a ratio of 1:1 (v / v), 0.8 parts of glycerol was added, and the mixture was stirred at 80°C for 1 h.

[0065] (6) After the mixed solution in step (5) is cooled to 40°C, 0.5 parts of PDA-ZnO NPs and 0.4 parts of Span 80 are added and stirred for 30 minutes to obtain a plastic wrap solution with near-infrared photodynamic bactericidal activity. The solution is cast on an acrylic plate to form a film and dried for later use.

[0066] The PDA-ZnO NPs obtained in Example 1 were added to the conductive resin and photographed using TEM. Figure 1 It can be seen that most of the prepared PDA-ZnO NPs are approximately spherical particles with a size of about 140 to 190 nm.

[0067] Example 2

[0068] (1) 3 mL of ammonium hydroxide (NH4OH), 50 mL of ethanol, and 100 mL of ultrapure water were stirred at 700 rpm for 30 min at 25°C to obtain a mixed solution.

[0069] (2) Add 2 g of dopamine hydrochloride (DA) and 10 g of zinc oxide nanoparticles (ZnO NPs) to the mixed solution prepared in step (1), stir at the same speed for 10 min, then add 0.8 g of H2O2 dropwise, and continue stirring at a speed of 1200 rpm for 6 h.

[0070] (3) The reaction mixture obtained in step (2) was centrifuged at 8000 rpm for 3 min, and the resulting precipitate was washed three times with ultrapure water to obtain PDA-ZnO NPs.

[0071] (4) Weigh 70 parts of aloe vera gel and 30 parts of polyvinyl alcohol, add them into 1200 parts of distilled water, and heat them in a water bath at 80°C until they are completely dissolved.

[0072] (5) The dissolved aloe vera gel and polyvinyl alcohol solution were mixed at a ratio of 1:1 (v / v), 1.2 parts of glycerol were added, and the mixture was stirred at 80°C for 2 h.

[0073] (6) After the mixed solution in step (5) is cooled to 50°C, 0.8 parts of PDA-ZnO NPs and 0.8 parts of Span 80 are added and stirred for 30 minutes to obtain a plastic wrap solution with near-infrared photodynamic bactericidal activity. The solution is cast on an acrylic plate to form a film and dried for later use.

[0074] Comparative Example 1

[0075] (1) Weigh 70 parts of aloe vera gel and 30 parts of polyvinyl alcohol, add them into 1200 parts of distilled water, and heat them in a water bath at 80°C until they are completely dissolved.

[0076] (2) The dissolved aloe vera gel and polyvinyl alcohol solution were mixed at a ratio of 1:1 (v / v), 1.2 parts of glycerol were added, and the mixture was stirred at 80°C for 2 h.

[0077] (3) After the mixed solution in step (2) is cooled to 50°C, 0.8 parts of Span 80 is added and stirred for 30 minutes to obtain a preservative film solution, which is cast on an acrylic plate and dried for later use.

[0078] Figure 2 A is the transparency of the plastic wrap of Comparative Example 1 without adding PDA-ZnO NPs, Figure 2 B is the transparency of the fresh-keeping film prepared in Example 2 of the present invention. Figure 2As can be seen in A and 2B, the addition of PDA-ZnO NPs has no significant effect on the transparency of the plastic wrap. Figure 2 C is the tensile strength of the plastic wrap of Comparative Example 1 without adding PDA-ZnO NPs, Figure 2 D is the tensile strength of the fresh-keeping film prepared in Example 2 of the present invention. Figure 2 As can be seen in C and 2D, the addition of PDA-ZnO NPs has no significant effect on the tensile strength of the plastic wrap.

[0079] Comparative Example 2

[0080] (1) 3 mL of ammonium hydroxide (NH4OH), 50 mL of ethanol, and 100 mL of ultrapure water were stirred at 700 rpm for 30 min at 25°C to obtain a mixed solution.

[0081] (2) Add 10 g of zinc oxide nanoparticles (ZnO NPs) to the mixed solution prepared in step (1) and stir at the same speed for 10 min. Then, add 0.8 g of H2O2 dropwise and continue stirring at a speed of 1200 rpm for 6 h.

[0082] (3) The reaction mixture obtained in step (2) was centrifuged at 8000 rpm for 3 min, and the resulting precipitate was washed three times with ultrapure water for later use.

[0083] (4) Weigh 70 parts of aloe vera gel and 30 parts of polyvinyl alcohol, add them into 1200 parts of distilled water, and heat them in a water bath at 80°C until they are completely dissolved.

[0084] (5) The dissolved aloe vera gel and polyvinyl alcohol solution were mixed at a ratio of 1:1 (v / v), 1.2 parts of glycerol were added, and the mixture was stirred at 80°C for 2 h.

[0085] (6) After the mixed solution in step (5) is cooled to 50°C, 0.8 parts of ZnO NPs prepared in step (3) and 0.8 parts of Span 80 are added and stirred for 30 minutes to obtain a preservative film solution, which is cast on an acrylic plate and dried for later use.

[0086] Comparative Example 3

[0087] (1) 3 mL of ammonium hydroxide (NH4OH), 50 mL of ethanol, and 100 mL of ultrapure water were stirred at 700 rpm for 30 min at 25°C to obtain a mixed solution.

[0088] (2) Add 2 g of dopamine hydrochloride (DA) to the mixed solution prepared in step (1) and stir at the same speed for 10 min, then add 0.8 g of H2O2 dropwise and continue stirring at a speed of 1200 rpm for 6 h.

[0089] (3) The reaction mixture obtained in step (2) was centrifuged at 8000 rpm for 3 min, and the resulting precipitate was washed three times with ultrapure water to obtain PDA.

[0090] (4) Weigh 70 parts of aloe vera gel and 30 parts of polyvinyl alcohol, add them into 1200 parts of distilled water, and heat them in a water bath at 80°C until they are completely dissolved.

[0091] (5) The dissolved aloe vera gel and polyvinyl alcohol solution were mixed at a ratio of 1:1 (v / v), 1.2 parts of glycerol were added, and the mixture was stirred at 80°C for 2 h.

[0092] (6) After the mixed solution in step (5) is cooled to 50°C, 0.8 parts of PDA and 0.8 parts of Span 80 are added and stirred for 30 minutes to obtain a preservative film solution, which is cast on an acrylic plate and dried for later use.

[0093] The cling film prepared in Comparative Examples 1 to 3 and the cling film prepared in Example 2 were cut into circles with a diameter of 0.6 cm, and then the cling films were placed on a plate coated with a suspension of Botrytis cinerea and Colletotrichum gloeosporioides (10 5 The culture dishes were placed at 28°C in a near-infrared long wavelength 1400nm (power: 2W / cm 2 ) and cultured in a dark environment for 72 hours, and the antibacterial effect of the membrane was observed. Figure 3 It can be clearly seen that under near-infrared light conditions, the cling films prepared in Comparative Examples 1 and 3 did not show an inhibition zone, and the cling film prepared in Comparative Example 2 showed a slight inhibition zone. However, it can be clearly seen from the figure that the nano cling film prepared in Example 2 has a good inhibitory effect on both Penicillium roqueforti and Aspergillus niger, showing a larger inhibition zone. This shows that compared with the cling films to which ZnO NPs are added alone and PDA is added alone, the nano cling film prepared in Example 2 has a synergistic antibacterial effect. Although the inhibitory effect of the nano cling film prepared in Example 2 on these two fungi under dark conditions is not as significant as under near-infrared light conditions, it also has a certain inhibitory effect.

[0094] Under the storage condition of 30℃, the degradable nano plastic wrap prepared in Example 2 and the commercially available PE plastic wrap were placed in a near infrared long wavelength 1400nm (power: 2W / cm 2 ) Comparative experiment under lighting conditions. Figure 4The results clearly show that mangoes packaged with commercially available PE plastic wrap (A1) at 30°C showed obvious black plaque and rot on the sixth day, while mangoes packaged with the degradable nano plastic wrap prepared in Example 2 of the present invention (A2) showed no signs of black plaque or rot on the sixth day. Only on the eighth day of storage did slight mold plaques appear on the mangoes. This demonstrates that the degradable nano plastic wrap prepared in the present invention provides excellent protection for mangoes under near-infrared long-wavelength conditions.

[0095] In order to further verify whether the degradable nano plastic wrap prepared by the present invention also has the same preservation effect under natural light, we used the degradable nano plastic wrap to pack grapes and found that ( Figure 5 Grapes packaged with PE plastic wrap (B1) at 30°C showed mild mold spots on the sixth day, which became more pronounced on the ninth day. However, grapes packaged with the degradable nano plastic wrap prepared in Example 2 of the present invention (B2) showed no mold spots on the ninth day, and only showed mild mold spots on the tenth day. This demonstrates that the degradable nano plastic wrap prepared in the present invention also provides good protection for grapes under natural light.

[0096] As can be seen from the above embodiments, the present invention provides a fresh-keeping film with near-infrared photodynamic bactericidal activity and a preparation method thereof. The present invention utilizes zinc oxide nanoparticles (ZnO NPs) and H2O2 to jointly catalyze the rapid oxidative polymerization of polydopamine (PDA) to form zinc oxide nanoparticles (PDA-ZnO NPs) wrapped with PDA. Combining zinc oxide nanoparticles with bactericidal activity with PDA can achieve synergistic bactericidal effects of metal ions and photothermal effects. At the same time, the photothermal conversion effect of PDA in near-infrared absorption can further excite zinc oxide nanoparticles to produce more reactive oxygen species (ROS), thereby achieving a long-lasting and efficient antibacterial effect. In addition, the PDA on the surface of ZnO NPs can improve the compatibility and binding force of ZnO NPs with biopolymers. PDA-ZnO NPs are added as fillers to a film mixture consisting of aloe vera gel and polyvinyl alcohol to prepare a fresh-keeping film with near-infrared photodynamic bactericidal activity having excellent mechanical properties. The method of the present invention effectively combines photothermal sterilization, photodynamic sterilization and metal ion sterilization, and realizes a "triple" synergistic bactericidal effect through multiple pathways, effectively solving the bottleneck problem of the short antibacterial action time of the antibacterial film. At the same time, it solves the defect that the mechanical properties of the film are affected by adding excessive antibacterial agents to the film matrix. The cling film with near-infrared photodynamic bactericidal activity prepared by the present invention not only has efficient "triple" synergistic bactericidal efficacy and excellent mechanical properties, but also has a simple preparation process and does not produce harmful substances. It is a green and sustainable antibacterial film production process. Compared with PE cling film, it can effectively extend the shelf life of mangoes and grapes by 2 to 4 days. The cling film has a very broad application prospect in the field of fruit and vegetable preservation.

[0097] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A fresh-keeping film with near-infrared photodynamic bactericidal activity, characterized in that: Prepared from the following raw materials in parts by weight: 55-70 parts of aloe vera gel; 25-35 parts of polyvinyl alcohol; 0.8~1.2 parts of glycerin; Span 80 0.4~0.8 parts; 0.5~0.8 parts of zinc oxide nanoparticles PDA-ZnO NPs wrapped with polydopamine; The method for preparing the polydopamine-encapsulated zinc oxide nanoparticles PDA-ZnO NPs comprises the following steps: 1) mixing ammonium hydroxide, ethanol and water to obtain a mixed solution; 2) adding dopamine hydrochloride, zinc oxide nanoparticles, and hydrogen peroxide to the mixed solution in sequence for reaction; 3) The reaction precipitate obtained in step 2) is centrifuged and washed sequentially to obtain PDA-ZnO NPs.

2. The fresh-keeping film having near-infrared photodynamic bactericidal activity according to claim 1, characterized in that: In step 1), the volume ratio of ammonium hydroxide, ethanol and water is 2-4:45-55:90-110, and the mixing is carried out under stirring at a stirring speed of 500-700 rpm for 20-30 minutes.

3. The fresh-keeping film having near-infrared photodynamic bactericidal activity according to claim 2, characterized in that: The usage ratio of the ammonium hydroxide, dopamine hydrochloride, zinc oxide nanoparticles and hydrogen peroxide is 2-4 mL: 1-2 g: 5-10 g: 0.3-0.8 g.

4. The fresh-keeping film having near-infrared photodynamic bactericidal activity according to claim 3, characterized in that: In the step 2), the reaction temperature is 20-30° C., and the reaction time is 5-6 hours.

5. The fresh-keeping film having near-infrared photodynamic bactericidal activity according to claim 2 or 3, characterized in that: In step 3), the centrifugal speed is 6000-8000 rpm, and the centrifugal time is 3-5 minutes.

6. The method for preparing a fresh-keeping film having near-infrared photodynamic bactericidal activity according to any one of claims 1 to 5, characterized in that: The following steps are involved: a. Add aloe vera gel and polyvinyl alcohol into water respectively, and heat until dissolved to obtain aloe vera gel solution and polyvinyl alcohol solution; b. mixing the aloe vera gel solution, the polyvinyl alcohol solution and glycerin to obtain a mixed solution; c. Zinc oxide nanoparticles (PDA-ZnO NPs) coated with polydopamine and Span 80 were added to the mixture, and the obtained plastic wrap solution was cast on an acrylic plate to form a film, thereby obtaining a plastic wrap with near-infrared photodynamic bactericidal activity.

7. The method for preparing a fresh-keeping film having near-infrared photodynamic bactericidal activity according to claim 6, characterized in that: In the step a, the heating temperature is independently 70-90°C.

8. The method for preparing a fresh-keeping film having near-infrared photodynamic bactericidal activity according to claim 7, characterized in that: The usage ratio of the aloe vera gel to water is 55-70:1200, and the usage ratio of the polyvinyl alcohol to water is 25-35:1200.

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