Wrapping Bacteria by Graphene Nanosheets for Isolation from Environment, Reactivation by Sonication, and Inactivation by Near-Infrared Irradiation

Bioactivity of Escherichia coli bacteria (as a simple model for microorganisms) and interaction of them with the environment were controlled by their capturing within aggregated graphene nanosheets. The oxygen-containing functional groups of chemically exfoliated single-layer graphene oxide nanosheets were reduced by melatonin as a biocompatible antioxidant. While each one of the graphene (oxide) suspension and melatonin solution did not separately show any considerable inactivation effects on the bacteria, aggregation of the sheets in the melatonin–bacterial suspension resulted in trapping the bacteria within the aggregated sheets, i.e., a kind of inactivation. The bacteria trapped within the aggregated sheets were biologically disconnected from their environment, because they could not proliferate in a culture medium and consume the glucose of their environment. However, after removing the sheets from the surface of the microorganisms by using sonication, they could again interact with their environment. The reactivated bacteria consumed glucose and could be proliferated; i.e., they were alive within the aggregated graphene sheets (here, at least for 24 h). The trapped alive bacteria could be photothermally inactivated forever by near-infrared irradiation at 808 nm. These results suggest that graphene nanosheets may potentially serve as an encapsulating material for delivery of such microorganisms and as an effective photothermal agent for inactivation of the graphene-wrapped microorganisms.