Oxidative and membrane stress-mediated antibacterial activity of WS2 and rGO-WS2 nanosheets

Abstract

Graphene-based materials have strong cytotoxic attributes against bacteria due to their unique physicochemical properties. We examined the antibacterial activities of nanosheets of the graphene analogue tungsten disulphide (WS₂) and a composite of reduced graphene oxide-tungsten disulphide (rGO-WS₂), comparing them with reduced graphene oxide (rGO) by a time and concentration dependent viability assay and growth curve studies against four bacterial strains: Gram negative Escherichia coli (E. coli) and Salmonella typhimurium (S. typhimurium), and Gram positive Bacillus subtilis (B. subtilis) and Staphylococcus epidermidis (S. epidermidis). The nanosheets of the rGO-WS₂ composite caused a more significant retardation in bacterial growth and inhibitory effect on the tested bacterial strains than WS₂, followed by rGO. The tested E. coli and B. subtilis strains were more susceptible than the other strains. A mechanistic study revealed that rGO and WS₂ did not produce the superoxide anion (O₂^˙−) or reactive oxygen species (ROS), but the nanocomposite of rGO-WS₂ did produce both. However, all these materials did oxidize glutathione, which serves as a redox state mediator in bacteria. We conclude that the antimicrobial mechanism is due to the combined effect of initial cell deposition on the rGO-WS₂ materials, the membrane stress due to direct contact with the nanosheets, and the produced superoxide anion-independent oxidation mechanisms. The beneficial aspects of the physicochemical properties of rGO-WS₂, such as its size and conductivity, can be precisely customized to reduce its health and environmental risk factors.