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Graphene, a Dirac material, permits the free flow of electrons on its surface. The interface of graphene with different bio-materials is the emerging interest. In this paper, we describe interfaces of graphene variants and two photosynthetic species (belonging to the class of alpha-proteobacteria), Rhodobacter spand Rhodopseudomonas sp, both using photon capture in their respective electron transport process. When grown on graphene oxide (or its exfoliated forms obtained after microwave treatment) the bacterial species show differential pigment excretion patterns, which is a measure of their photon driven electron-transport-chain activity. The responses are measured by hydrodynamic diameters of pigment clusters and steady-state quantum yield and time-dependent fluorescent emission patterns. The responses carry fingerprints of graphene-specific effects on the respective microbes. Interestingly, there is a reciprocal relationship between the size of the pigment cluster formed in the presence of graphene (which varies for the two microbes) and the rate of fluorescence emission change. The report opens up the possibility of developing photo-sensing and light-harvesting devices exploiting the richness and diversity of this interface of the free-flowing electrons of this 2D-material (graphene) and these cells, undergoing graphene-specific dynamics of pigmentation.

A simple and green chemistry approach for the preparation of reduced graphene oxide nanosheets was successfully demonstrated through the reduction of graphene oxide (GO) to obtain greenly-reduced graphene oxide (GRGO) using various green reagents. Without using toxic and harmful chemicals, this method is environmentally-friendly and suitable for the large-scale production of graphene. The prepared GO and GRGO were characterized by UV–Visible, X-ray diffraction, and Fourier transform infra-red spectroscopic analysis which showed a clear indication of the removal of oxygen-containing groups from the GO and the formation of GRGO. The morphology of the GRGO samples was characterized by transmission electron microscopy. Dynamic light scattering was used to measure the size of the GRGO particles along with zeta potential measurements. Electrical conductivity measurement was used to check the extent of reduction of GO to GRGO samples. The electrochemical properties of these carbonaceous materials were determined by cyclic voltammetry. The methods employed can lead to the preparation of GRGO can be effectively used in sensors and various electronic device fabrications.