Towards a "green" antimicrobial therapy: study of graphene nanosheets interaction with human pathogens

Graphene and its derivatives are versatile materials promising candidates for important biomedical applications. Graphene is composed of sp2-hybridized carbon atoms hexagonally arranged in a two-dimensional structure, resulting in a large surface area on both sides of the planar axis. Among the materials of the graphene family, graphene oxide (GO), because of the formation of hydrogen bonds between polar functional groups on its surface and water molecules, is stable in solution and has more advantages for potential biomedical applications. However studies concerning antimicrobial effects of GO evidenced contradictory results and toxic and nontoxic effects were simultaneously observed. Goal of this work is the precise analysis of size, buffer and concentration dependence of GO antimicrobial effects on important human pathogens, such as E.Coli, C.Albicans, E.Faecalis and S. Aureus. Different sizes of GO nanosheets have been produced by sonication and characterized by Dynamic Light Scattering and Atomic Force Microscopy. Subsequently GO sheets having size comprised between 1 µm and 50 nm have been incubated with pathogens in ddH20, saline solution or in LB Broth, i.e. in different ionic strength conditions, to follow the growth kinetics in presence of GO. We analysed in detail how the GO aggregation influences experimental results and optimized an experimental protocol and analysis method. Moreover, since high GO concentration caused the formation of complexes between pathogens and GO nanosheets, we characterized the surface covering of the bacteria and the leakage of genetic material, membrane damaging and biofilm formation. These results allow the optimization GO-based nanomaterial design for a new "green" antimicrobial therapy.