Insights Into The Mechanism On Photodynamic Sterilization Of Foodborne Pathogens By Development Of Novel Two-dimensional Materials

Food poisoning caused by foodborne pathogens accounted for the highest proportion in food safety incidents,and it is becoming the primary problem in food safety of China.Traditional sterilization methods are mostly physicochemical sterilization methods such as ultraviolet sterilization or chlorine-containing fungicides.The former is simple and reliable,but the equipment requirements are too high and affect the practical application.The latter is easy to react with organic substances to form chloride residues,which may cause potential hazards to the human body.Therefore,it is of great significance to develop a new sterilization technology that is efficient,fast,and non-toxic.In recent years,photodynamic sterilization technology with semiconductor materials as an ideal energy utilization and new sterilization method has great application prospect in the field of microorganism control.Compared with traditional sterilization technology,photodynamic sterilization technology has the advantages of high efficiency,energy saving and environmental protection.Therefore,the development of photocatalysts with high efficiency,broad-spectrum sterilization performance and no secondary pollution is of great value for ensuring food safety in killing foodborne pathogens.In this paper,we designed three nano-antibacterial agents and explored their photodynamic sterilization mechanism for rapid killing foodborne pathogens of Salmonella,Staphylococcus aureus,methicillin-resistant Staphylococcus aureus and multidrug resistant Salmonella based on graphitic carbon nitride of the highly efficient absorption of sunlight.The main research contents and results are as follows:1.Preparation of vanadate quantum dots/ graphitic carbon nitride antibacterial agent and study of its photodynamic sterilization performance for Salmonella.The vanadate quantum dots/graphitic carbon nitride(vanadate QDs/g-C3N4)nano-antibacterial agent was synthesized by microwave ultrasonic method.Detailed characterization through SEM-EDS,TEM,XRD,FT-IR and XPS confirmed the successful synthesis of vanadate QDs/g-C3N4.The bactericidal efficiency of nano-antibacterial agent against food-borne Salmonella was then investigated using standard plate counting methods.Tests have shown that bactericidal efficiency of Ag VO3/g-C3N4 could reach 96.4% toward Salmonella in a concentration of 0.75 mg/m L under visible-light irradiation.SEM technique,fluorescent-based cell live/dead test and BCA protein assay showed that vanadate QDs/g-C3N4 nano antibacterial agents could produce a large amount of active oxygen under visible-light irradiation,and then rapidly attack bacterial cell membrane and lead the leakage of cell contents.The leakage of the contents finally destroys the metabolism of the bacteria,and ultimately killing the bacteria.The development of vanadate QDs/g-C3N4 nano-antibacterial agent confirmed the high efficient sterilization performance of graphitic carbon nitride-based nanomaterials against Salmonella,laying a foundation for the subsequent development of new nano-antibacterial agents and research on photodynamic sterilization mechanism.2.Preparation of multifunctional nitrogen-rich carbon-coated bismuth/cobalt antibacterial agent and study of its photodynamic sterilization performance for Staphylococcus aureus.A multifunctional nitrogen-rich carbon-coated bismuth/cobalt nano antibacterial agent(Bi@Co@CN)with a foam-like structure was synthesized by a simple two-step method.The results show that Bi@Co@CN can extend the spectral range of graphitic carbon nitride from visible light to near-infrared light.Within 20 min irradiation,the Bi@Co@CN nano antibacterial agent showed good light conversion and produced a large amount of reactive oxygen species and heat,which could effectively kill 7-log of Staphylococcus aureus.In addition,Bi@Co@CN has good antibacterial activity against both Escherichia coli and Salmonella,showing broad-spectrum sterilization performance.In vitro experiments show that reactive oxygen species and photothermal conversion can seriously damage the bacterial cell membrane,and inhibit the virulence factors produced by bacterial metabolism,and ultimately lead to the death of Staphylococcus aureus.The photodynamic sterilization of Staphylococcus aureus in milk shows that Bi@Co@CN could separate the materials from the milk after killing the bacteria and cause no harms to human body,showing excellent practical application.3.Preparation of vertical molybdenum disulfide/carbon nitride antibacterial agent and study of its photodynamic sterilization performance for multidrug-resistant bacteria.In this study,vertical molybdenum disulfide/carbon nitride(Mo S2/CN)nano antibacterial agent was synthesized by urea-derived g-C3N4 and doped heterogeneous element Mo S2.Detailed characterization through SEM,TEM and XRD confirmed the successful synthesis of Mo S2/CN nano antibacterial agent.Photodynamic sterilization test of methicillin-resistant Staphylococcus aureus(MRSA)and multidrug resistant Salmonella(MDR-Salmonella)showed that Mo S2/CN exhibited excellent bactericidal efficiency toward the two resistant bacteria during photodynamic sterilization process.TEM technology,intracellular ATP concentration determination and potassium ion concentration measurement showed that Mo S2/CN produced a large amount of active oxygen species after irradiation treatment,which destroyed the permeability of bacterial cell membrane and lead to the leakage of MRSA cell contents.The anti-biofilm test confirmed that the formation of bacterial biofilm was inhibited during the sterilization process,indicating that photodynamic sterilization caused severe damage to the MRSA biofilm structure.The total enterotoxin assay showed that the Mo S2/CN nano antibacterial agent can inhibit the expression of MRSA enterotoxin to a certain degree.The development of Mo S2/CN nano antibacterial agent can not only effectively kill the resistant bacteria,but also solve the antibiotic resistance problem to a certain extent,and provide new ideas and technology for food safety.4.Mechanism of photodynamic sterilization for the treatment of wound healing cousued by foodborne pathogens.Based on the previous photodynamic sterilization of carbon nitride nano antibacterial agent,a photodynamic sterilization treatment system based on multifunctional nitrogen-rich carbon-coated bismuth/cobalt nano-antibacterial agent was established.In this treatment system,Bi@Co@CN can rapidly generate active oxygen species and heat under visible light and near-infrared light,which could effectively control the growth of MRSA on the surface of the skin,and accelerate the wound healing of skin.H&E staining and immunofluorescence analysis of mouse wound tissue confirmed that Bi@Co@CN nano antibacterial agent can promote the wound healing by participating in stimulation to affect cell behavior.In addition,the MTT in vitro test and the in vivo toxicity evaluation of mouse showed that Bi@Co@CN nano antibacterial agent not only exhibit excellent bactericidal efficiency,but also has good biocompatibility.In a word,Bi@Co@CN has great potential as a safe antibacterial agent in photodynamic sterilization treatment system,and is of great value for clinical rapid sterilization and wound healing treatment.