Effects of Surface Chemistry on Cytotoxicity, Genotoxicity, and the Generation of Reactive Oxygen Species Induced by ZnO Nanoparticles

The relationship between the toxicity of zinc oxide (ZnO) nanoparticles (NPs) and their surface chemistry was investigated. Cytotoxicity, genotoxicity, and the ability to generate reactive oxygen species (ROS) were assessed for well-characterized ZnO NPs whose surface chemistry was varied from its pristine state by coating with oleic acid (OA), poly(methacrylic acid) (PMAA), or components adsorbed from cell culture medium (medium-soaked). It was found that uncoated NPs showed ROS accumulation and diminished cell viability whereas all tested surface coatings assisted in reducing ROS production and cytotoxicity. The ability of coatings to reduce the cytotoxicity of ZnO NPs was ranked in the following order: medium-soaked ≈ PMAA > OA. However, PMAA-coated ZnO had significant genotoxicity compared to uncoated ZnO and the other coated NPs, highlighting the need to investigate thoroughly the effects of NP surface modification on both cytotoxicity and genotoxicity assays. The lowest toxicity was achieved with a surface coating of components from a cell culture medium.