Antibacterial mechanisms of nanocrystalline diamond film and graphene sheet

Abstract

Abstract In this study, we investigated the antibacterial activities of a nanocrystalline diamond (NCD) thin film and graphene sheet. In addition, we functionalized the surfaces of the NCD film and graphene sheet with fluorine by plasma treatments to increase their antibacterial activities. The antibacterial activities of the NCD film and graphene sheet were confirmed by both colony forming unit (CFU) counting and adenosine triphosphate (ATP) bioluminescence assay based on the drop-test method. The CFU counting showed that the ratios of surviving bacteria on the NCD film and graphene sheet were 27.5% and 13.9%, respectively. The ratios of surviving bacteria on the fluorinated NCD (F-NCD) film and fluorinated graphene (F-graphene) sheet were decreased to 15.2% and 9.3%, respectively, which indicated that the antibacterial activities of the F-NCD film and F-graphene sheet increased upon fluorine functionalization. In addition, an ATP bioluminescence assay was employed based on the concentration of ATP released from cultured Escherichia coli (E. coli), which confirmed that the fluorinated surface had high antibacterial activity. The ratios of metabolism-cultured E. coli on the F-NCD film and F-graphene sheet were 15.0% and 7.4%, respectively. Furthermore, we observed the morphologies of E. coli cultured on the NCD film and graphene sheet. The antibacterial activity was attributed to the destruction of the E. coli membranes. These results show that the antibacterial activities of the NCD film and graphene sheet depend on their surface functional groups and conductivities.