Photocatalytic and phototoxic properties of TiO2-based nanofilaments: ESR and AFM assays

There is uncertainty in understanding of the relationship between physico-chemical parameters of nanosized titanium dioxide (nano-TiO2) and its toxicity when brought into contact with living cells. This study provides a multidisciplinary experimental insight into the toxicity and phototoxicity of the custom-made TiO2-based nanowires (TiO2-NWs). We employed electron spin resonance (ESR) to detect reactive oxygen species (ROS) generated in aqueous suspensions of TiO2-NWs and combined these results with atomic force microscopy (AFM) to trace the onset of toxic effects towards human melanoma cells. The cells were treated with low concentrations (similar to 2.5 mu g/ml) of TiO2-NWs and Degussa P25. High-resolution AFM surface topography and cell elasticity measurements revealed toxic effects both in cells incubated with TiO2-NWs in the dark and exposed to the photo-oxidative stress under UVA radiation. In contrast to ROS generation efficacy in the absence of cells in vitro, no direct correlation was found between the physical parameters of nano-TiO2 and cell toxicity.