Fig 3. Toxicity and phototoxicity of TiO₂-NTs.

MCF-7 cells were grown during the first day, exposed to 1000 μg/mL of nanotubes during the second day and incubated in dark or under UV irradiation (1.6 W/m², wavelength 356 nm, every 3 h for 15 min in a period of 24 h) during the third day. Control experiment were performed without the appropriate stressor (nanotubes during the second day or UV irradiation during the third day). On the fourth day: (A) optical density of samples was measured by MTS assay, (B) cells were trypsinized and counted manually using Trypan Blue, (C) the same number of MCF-7 cell were seeded in pools to grow for additional 14 days and colonies were counted. Survival factor (SF) was calculated as percentage of plating efficiency (PE) of the treated cells over PE of the untreated cells. Since normality test (Shapiro-Wilk) failed, we used Mann-Whitney U statistics instead. ** denotes the significant difference in the median values at P = <0.001.