Cytotoxicity of Ultra-pure TiO2 and ZnO Nanoparticles Generated by Laser Ablation

This paper aims to address the cellular toxicity of ultra-pure titanium dioxide (TiO2) and zinc oxide (ZnO) nanoparticles (NPs) frequently employed in sunscreens as inorganic physical sun blockers to provide protection against adverse effects of ultraviolet (UV) radiation including UVB (290-320 nm) and UVA (320-400 nm). In consideration that the production and the use of inorganic NPs have aroused many concerns and controversies regarding their safety and toxicity and that microsized TiO2 and ZnO have been increasingly replaced by TiO2 and ZnO NPs (< 100 nm), it is very important to directly investigate a main problem related to the intrinsic/inherent toxicity of these NPs and/or their incompatibility with biological objects. In the present study, we took advantage of the laser-assisted method called laser ablation for generation of TiO2 and ZnO NPs. NPs were prepared through a physical process of irradiating solid targets in liquid phase, enabling verification of the toxicity of ultra-pure NPs with nascent surfaces free from any contamination. Our results show that TiO2 NPs are essentially non-poisonous and ZnO NPs are more toxic than TiO2 NPs based on the cell viability assays.