Escherichia coli bacteria reduce graphene oxide to bactericidal graphene in a self-limiting manner

Interactions of chemically exfoliated graphene oxide (GO) nanosheets and Escherichia coli bacteria living in mixed-acid fermentation with an anaerobic condition were investigated for different exposure times. X-ray photoelectron spectroscopy showed that as the exposure time increased (from 0 to 48 h), the oxygen-containing functional groups of the GO decreased by similar to 60%, indicating a relative chemical reduction of the sheets by interaction with the bacteria. Raman spectroscopy and current-voltage measurement confirmed the reduction of the GO exposed to the bacteria. The reduction was believed to be due to the metabolic activity of the surviving bacteria through their glycolysis process. It was found that the GO sheets could act as biocompatible sites for adsorption and proliferation of the bacteria on their surfaces, while the bacterially-reduced GO (BRGO) sheets showed an inhibition for proliferation of the bacteria on their surfaces. It was shown that the slight antibacterial property of the BRGO sheets and the detaching of the already proliferated bacteria from the surface of these sheets contributed to the growth inhibition of the bacteria on the surface of the reduced sheets. (C) 2011 Elsevier Ltd. All rights reserved.