Hazard assessment of polymer-capped CuO and ZnO nanocolloids: A contribution to the safe-by-design implementation of biocidal agents

The antibacterial activity of metal oxide (MeO) nanoparticles (NPs) has been extensively reported. Nevertheless, there is a general concern about MeO NPs toxicity, and much efforts are being devoted to improve a safe employment of these nanomaterials by surface functionalization. In this work, we propose to investigate if the coating of copper and zinc oxides (CuO and ZnO) NPs with the polymers poly(ethylene imine) (PEI) or poly(ethylene glycol) (PEG) is able protect non-target cells and organisms from the toxicity of antibacterial MeOs NPs. The overall results obtained exposing lung cells and Xenopus laevis embryos to CuO-PEG, CuO-PEI, ZnO-PEG and ZnO-PEI, indicate that PEG, but not PEI coating, is able to exert a protective function against MeOs toxicity. The ability of PEG shell to reduce the adverse impact of MeOs NPs is in part associated to a protection from the oxidative stress, even if in vitro results indicate that peghylation is not able to prevent pro-inflammatory responses. We suggest that the different intracellular availability of the metal oxides upon capping with PEG or PEI, together with the involvement of multiple mechanisms of action, may be responsible for the different toxicological outcome on lung cells viability and Xenopus mortality and malformations.