Light-independent redox reactions of graphene oxide in water: Electron transfer from NADH through graphene oxide to molecular oxygen, producing reactive oxygen species

Abstract

There is growing interest in finding industrial and commercial uses for graphene oxide (GO) because of its unique properties. As with other nanomaterials, increased production and use generally leads to increased environmental exposure. However, very limited information exists on how GO is further functionalized or mineralized in natural aquatic environments, or whether GO can participate in reactions involving other natural chemicals. In this research study, we hypothesized that reactive oxygen species (ROS) can be generated by electron transfer from a common biological electron donor (NADH) to GO, which then acts as an electron shuttle forming ROS from dissolved molecular oxygen in water. Indeed, aqueous suspensions of 5 mg/L GO were found to oxidize 0.2 mM β-nicotinamide adenine dinucleotide (NADH). Production of ▪ was shown to occur over a period of about 30 h, and by using another colorimetric assay, H2O2 was shown to accumulate. Hence, in the absence of light, GO can act as an electron shuttle, catalyzing the oxidation of NADH (i.e., transfer of electrons to GO) and then pass these electrons to molecular oxygen, forming ROS in water. Although hydroxyl radicals (OH) were not detected, pBR322 DNA plasmid was cleaved in GO suspension containing NADH and O2.