Preparation Of Cu-based Ternary Chalcogenide Nanozymes And Their Antibacterial Applications

Various natural enzymes can catalyze the generation of reactive oxygen species(ROS)to kill bacteria by damaging bacteria membrane and proteins in the host defense.However,natural enzymes have the disadvantages of high cost and easy inactivation in the applications.To overcome the shortcomings of natural enzymes,the researchers have developed many artificial enzymes(nanozymes)based on the biomimetic strategy.Nanozymes is a kind of nanomaterials with enzyme-like catalytic activity,they can catalyze the generation of ROS for bacteria killing.Recently,nanozymes including unary noble metals,carbon-based materials,and binary metal chalcogenides have been used in the filed of antibacterial treatment,but the current research on nanozymes is still in the preliminary stage,and these nanozymes show limited antibacterial performance.Therefore,it is very important to develop new nanozymes with high antibacterial activity.Compared with the above compounds,due to the unique physicochemical properties and adjustable composition of ternary metal chalcogenides,they have attracted the attention of researchers.Thus,it is very significant to explore the enzyme-like catalytic perporties,antibacterial performance,and mechanisms of ternary metal chalcogenides.Cu₂MS₄(M=W,Mo)is a Cu-based ternary chalcogenide with two crystal structures(P phase and I phase),unique optical properties and excellent catalytic performance,which is mainly used in electrochemical catalysis and photocatalysis.However,the enzyme-like activity and antibacterial properties of Cu₂MS₄nanomaterials have never been fully studied until now.In this paper,the enzyme-like activity,antibacterial property and antibacterial mechanism of Cu₂MS₄ nanomaterials will be explored,and the following three parts of work were carried out.1.Efficient bacteria killing by Cu₂MS₄ nanozymes with bacteria-binding abilityDue to the short half-life and limited diffusion distance of ROS,the nanozymes lacking bacteria-binding ability show low antibacterial activity.Therefore,it is very important to develop antibacterial nanozymes with bacteria-binding ability.Here,Cu₂WS₄ nanocrystals(CWS NCs,?20nm)are prepared by using a microve-assisted method.In vitro antibacterial experiments show that CWS NCs achieve 5 log(>99.999%)inactivation efficiencies of both Escherichia coli(E.coli,Gram-negative)and Staphylococcus aureus(S.aureus,Gram-positive)at very low concentration(<2?g/m L)whether in the dark or under ambient light,which is at least 2 log higher than typical antibacterial nanomaterials(unary Ag nanoparticles and binary TiO₂ nanoparticles)and antibiotics(vancomycin and daptomycin)at the same concentration.Mechanism studies reveal that CWS NCs have oxidase-like and peroxidase-like properties and can generate ROS(H₂O₂ and·OH)to kill the bacteria.More importantly,CWS NCs can efficiently attach to the surface of bacteria through the interaction of cooper atoms from CWS NCs and amino groups from peptidoglycan in bacteria cell wall.Hence,the ROS produced by CWS NCs can kill the bacteria in situ,which significantly improves the antibacterial efficiency and reduces the possible collateral damage to normal mamalian cells.CWS NCs exhibit both excellent antibacterial activity and good biocompatibility during in vitro and in vivo experiments.Animal study showed that CWS NCs have better therapeutic efficacy for the methicillin-resistant S.aureus(MRSA)infected wounds in mice compared with vancomycin,suggesting their potential medical use.2.P-Cu₂MoS₄ nanoparticles with enzyme-like activity for antibacterial applicationDue to Cu₂MoS₄(CMS)nanomaterials with excellent catalytic activity,they have attracted more and more attention in the fields of photocatalysis and electrocatalysis.CMS usually has two crystal structures of P phase and I phase.I-and P-CMS have the same chemical formula and atomic arrangement,but they are stacked in different ways,thus they show different physical and chemical properties.Here,the enzyme-like properties and antibacterial activity of P-CMS nanomaterials are firstly studied.The ultrasmall P-CMS NPs(?4 nm)are prepared by using a microwave-assisted method.P-CMS NPs show p H-dependent peroxidase-like activity and can catalyze H₂O₂ to produce highly active·OH under p H<5.5.However,P-CMS NPs have not peroxidase-like activity under p H>5.5.Toxicity study shows that P-CMS NPs have no obvious toxicity in vitro and in vivo.In vitro antibacterial experiments prove P-CMS NPs without obvious antibacterial activity,but they can co-incubate with exogenous H₂O₂ to produce·OH for destroying the integrity of bacteria,and then cause bacterial death.Results indicates that P-CMS NPs can kill 62% of MRSA.Animal experiments show that the combination of P-CMS NPs with H₂O₂ can treat MRSA infected wounds.3.NIR-II light responsive I-Cu₂MoS₄ nanoplates for enhanced antibacterial treatmentThe low catalytic activity of nanozymes significantly limits their antibacterial efficiency.Therefore,the nanozymes with high antibacterial activity are developed.Here,I-CMS nanoplates(I-CMS NPs)are prepared by using a ball-milling method.I-CMS NPs have both excellent oxidase/peroxidase-like catalytic activity and high NIR-II photothermal conversion efficiency(37.8%,1064 nm).The bacterial inactivation efficiency of CMS NPs(40?g/m L)is 8 log for MDR E.coli and 6 log for MDR S.aureus in 10 min under NIR-II light irradiation(1064 nm,1 W/cm²).Moreover,antibacterial mechanism study reveals that the excellent antibacterial activity of CMS NPs under NIR-II light irradiation can be ascribed to the localized photothermal effect enhanced catalytic generation of H₂O₂ and·OH,which further results in significantly improved intracellular ROS level of the bacteria,and causes bacterial death.In vivo study demonstrated that CMS NPs can effectively treat MRSA infections in mice under NIR-II light irradiation and the bacterial inactivation efficiency was up to 6 log.In conclusion,these works find CWS nanozyme with bacteria-binding ability.CWS nanozyme can effectively bind on the surface of bacteria,improve the antibacterial efficiency of ROS,and its antibacterial performance is higher than the common unary metals,binary chalcogenide nanomaterials,and antibiotics.Secondly,P-CMS nanoparticles show p H-dependent peroxidase-like catalytic activity and can catalyze exogenous H₂O₂ produce·OH for bacteria killing.However,I-CMS nanozyme has excellent double enzyme-like activities and NIR-II light enhanced catalytic activity.Compared with P-CMS nanozyme,I-CMS nanozyme exhibits higher antibacterial properties,thus the phase can affect the catalytic activity of CMS nanozyme.Based on these studies,it is expected to promote the development of novel ternary antibacterial nanozymes.