Preparation And Antibacterial Effect Of MnO₂ Nanosheets And Ag₂S NCs

Salmonella is a kind of foodborne pathogen that can cause zoonosis.It has a wide range of hosts and a high incidence.According to statistics,about 93.8 million people around the world are infected with Salmonella every year,which can lead to 155000 deaths.Because of the serious harm caused by Salmonella,Salmonella has been listed as an important detection object in the detection of pathogenic microorganisms all over the world.However,the unreasonable use of antibiotics in clinic leads to the gradual evolution of pathogens into drug-resistant strains,and the increasing number of drug-resistant bacteria makes antibiotics lose their excellent therapeutic effect.In order to overcome the problem of antibiotic resistance,it is an urgent problem to develop a new type of antibacterial material with high efficiency,low toxicity,long-lasting effect and no drug resistance.Nanomaterials have their unique physical and chemical properties and their inherent or highly effective bactericidal activity obtained through functional modification,which is considered as the most promising strategy to overcome the problem of drug resistance of pathogens and have a broad application prospect.This paper is mainly based on the study of the antibacterial activity of MnO2 nanosheets and Ag2S NCs against Salmonella,and discusses the antibacterial mechanism of the two materials by physiological and biochemical means.The main work of this paper is as follows:1.A novel,low toxicity two-dimensional sheet material MnO2 nanosheets was synthesized by one-step method.The morphology,structure,surface composition,functional groups and valence states of the compounds were characterized and analyzed by means of TEM,UV-Vis,XRD,XPS and FT-IR.Then the antibacterial activity of the product was analyzed,including plate count,the minimum inhibitory concentration and the bacterial growth curve.The results showed that the inhibition rate was 91.1%when the concentration of MnO2 nanosheets was 313 ?g/mL.Through TEM,SEM and fluorescence microscopy,it was found that MnO2 nanosheets could directly damage the cell membrane through sharp edges,which led to the rupture of the membrane structure of bacteria and the death of a large number of bacteria.At the same time,it can cause the increase of ROS,the change of zeta potential on the surface,the leakage of protein,the decrease of ATPase activity and the increase of electric conductivity of bacterial solution.2.GSH capped Ag2S NCs with good water solubility and biocompatibility were prepared by one pot method.TEM,UV-Vis,XRD,XPS and FT-IR were used to characterize and analyze the system.Through plate count,minimum inhibitory concentration and bacterial growth curve,when the concentration of Ag2S NCs was 750?g/mL,the inhibition rate was as high as 95%,and the minimum inhibitory concentration of Ag2S NCs was 187.5 ?g/mL.Finally,the antibacterial mechanism of Ag2S NCs was investigated.The results showed that Ag2S NCs and bacteria co-incubation will release Ag+continuously.The released Ag+ interfered with the enzyme activity of bacteria and increased the ROS in bacteria,and caused oxidative stress damage to bacteria,resulting in a large number of bacterial deaths.3.The cytotoxicity of two kinds of antibacterial nanomaterials was analyzed by Vero model.When 625 ?g/mL MnO2 nanosheets were cultured with Vero cells for 24 hours,the cell survival rate was still above 90%;when 750 ?g/mL Ag2S NCs were cultured with Vero cells for 24 hours,the cell survival rate was 92.8%.Two kinds of antibacterial nanomaterials not only have high antibacterial effect,but also have good biocompatibility and low toxicity to mammalian cells.In summary,the research and development of these two new antibacterial nanomaterials provide new ideas and technical means for the efficient removal of Salmonella contamination in food and the protection of food safety.