Studies on polymer-coated zinc oxide nanoparticles: UV-blocking efficacy and in vivo toxicity

Zinc oxide (ZnO) is explicitly used in sunscreens and cosmetic products; however, its effect in vivo is toxic in some cases. The UV blocking efficacy of ZnO nanoparticles is lost due to photocatalysis. To isolate a lower toxic species of sunblockers, ZnO nanoparticles were synthesized and coated with chitosan - a natural polymer (ZnO-CTS) and polyethylene glycol (PEG) - a synthetic polymer (ZnO-PEG). Coating with CTS and PEG circumvented the photocatalytic activity, increased the stability and improved the UV absorption efficacy. The effect of ZnO, ZnO-CTS and ZnO-PEG nanoparticles in vivo on zebrafish embryo revealed lower deposition of ZnO-CTS and ZnO-PEG nanoparticles atop the eggs compared to ZnO. The survival of zebrafish embryos was always found to be higher in case of ZnO-CTS with respect to ZnO-treated ones. PEG coating exhibited better UV attenuation, but, in vivo it induced delayed hatching. Thus, one of the reasons for better survival could be attributed to lower aggregation of ZnO-CTS nanoparticles atop eggs thereby facilitating the breathing of embryos.