Mitigation in the toxicity of graphene oxide nanosheets towards Escherichia coli in the presence of humic acid

Abstract

GO nanosheets have been reported to show strong cytotoxicity towards Escherichia coli (E. coli) in aqueous solution. Natural organic matters (NOMs) in water may probably coat on the surface of GO nanosheets, which possibly influence its cytotoxicity. In this study, we illustrated how humic acid (HA), a ubiquitous NOM, mitigated the toxicity of GO nanosheets towards E. coli based on the cytotoxicity mechanism of GO nanosheets. Adsorption and cell viability tests proved that HA was adsorbed by GO nanosheets and decreased the toxicity of GO nanosheets towards E. coli. It was found that HA was adsorbed on the surface of GO nanosheets by polar groups, which prevented E. coli from contacting with GO nanosheets and weakened the toxicity of GO nanosheets. Besides, HA exerted an antioxidant role in maintaining the activity of the antioxidant enzyme and decreasing the ROS generation according to the results of oxidative stress experiments. The work revealed that HA relieved the toxicity of GO nanosheets and decreased the ecological risks induced by GO nanosheets.