Antibacterial Toxicity of Photochemically Transformed Graphene Oxide

Abstract

Two-dimensional carbon-based nanomaterials including graphene and graphene oxide (GO) have attracted great research interests for their potential applications in biomedical electronics energy and materials areas Ecological impacts of these materials must be properly evaluated prior to their widespread use Previous research has shown that GO can be phototransformed under simulated sunlight exposure forming products with progressively reduced sizes and oxygen-containing functionalities The aim of this work was to examine the antibacterial toxicity of GO before and after photoreactions Photoproducts generated by direct photolysis and indirect photolysis in which hydroxyl radical was involved were examined We found that Gram negative Escherichia coli (E coli) had a minimum inhibitory concentration (MIC) of 5 mg/L and a half maximal inhibitory concentration (IC50) of 5 03 ± 1 75 mg/L for parent GO Interestingly GO derivatives produced by direct photoreduction exhibited stronger antibacterial effects than parent GO while GO samples after indirect photoreaction showed opposite results (i e reduced toxicity) The enhanced toxicity correlates with the reduced functional groups and/or sizes after direct photolysis while the reduced toxicity may be mainly attributed to the significantly decreased mass concentration after indirect photolysis Another part of this research was to evaluate the potential mechanisms behind the observed antibacterial toxicity The whole cell and membrane integrities the depletion of glutathione (GSH) an intracellular antioxidant and reactive oxygen species (ROS) formation were examined We found that the cell deformation occurred upon exposure to GO samples irradiated for a longer time period under direct photolysis conditions and that bacterial cells strongly aggregated in the presence of GO The increased cell membrane permeability was observed after exposure to GO Increased irradiation time period under direct photolysis conditions resulted in intermediate products with greater capabilities in GSH depletion and ROS　formation Taken together the results point to the oxidative stress-mediated antibacterial toxicity Overall the findings of this work indicate that phototransformed GO exhibits different antibacterial toxicity from parent GO

Date of Award	2015 Aug 31
Original language	English
Supervisor	Wen-Che Hou (Supervisor)