Optimization Of Enzyme-like Activities Of Pd-based Nanomaterials And Study Of Their Antibacterial Activities

Infection caused by drug-resistant bacteria is recognized to be one of the most urgent threats to public health in the world.Due to their unique properties,such as easily passing through the cell membrane,being difficultly expelled by the efflux pump,and so on,nanomaterials have been found to be less prone to induce bacterial resistance and provide a important chance to solve the problem of drug resistance.Previous studies have shown that nanomaterials with enzyme-like activity can selectively induce the generation of a large amount of reactive oxygen species and thus inhibiting the growth of bacteria and effectively killing them.However,compared with silver nanoparticles,the bactericidal activity of nanomaterials with enzyme-like activity still needs to be improved.Therefore,it is an important strategy to improve the antibacterial activity of nanomaterials through effectively enhancing their enzyme-like activities.Compared with their single-component counterparts,bimetallic core-shell structured nanoparticles can provide more attractive opportunities for marked enhancement in specific catalytic activity due to the synergistic effects between the core and the shell.Based on the above illustration,we focus on core-shell structured bimetallic nanomaterials and aim to optimize their bactericidal activity through tailoring the morphology of the core-shell nanostructures.First of all,the Pd cubes,Pd@Ir cubes and Pd@Ir octahedra were synthesized.The well-defined morphology and core-shell structure were confirmed using transmission electron microscopy and energy dispersive X-ray spectroscopy.Secondly,we evaluated the enenzyme-like activities(oxidase-like and peroxidase-like)of Pd-based nanomaterials with different morphologies and structures.The mechanism of enzyme-like activities of Pd-based nanomaterials was verified by measuring the consumption of substrates and the generation of products.According to the catalytic reaction kinetics experiment,the enzyme-like activities of Pd-based nanomaterials was found to be dependent on the morphology and structure as follows:Pd cubes<Pd@Ir cubes<Pd@Ir octahedra.The results showed that tuning the morphologies and structures of nanomaterials is an important approach to improve their enzyme-like activity.Thirdly,we investigated the antibacterial activity and action mechanism of Pd-based nanomaterials with different morphologies and structures.The antibacterial experiments showed that the order of antibacterial activity of nanomaterials was consistent with that of their enzyme-like activities,and the antibacterial mechanism was mainly related with the generation of reactive oxygen species.In the end,the effect of natural organic matter(NOM)on the antibacterial activity of Pd-based nanomaterials was also investigated.In the presence with NOM,the Pd@Ir nanostructures induced an elevated level of reactive oxygen species,resulting in significantly enhanced bactericidal activity of the nanostructures.Further mechanism analysis showed that the presence of HA efficiently enhances the oxidase-like activity of nanomaterials and promotes the cellular internalization of nanomaterials.