Photokilling of Malignant Cells with Ultrafine TiO2 Powder

Abstract Photo-irradiated TiO2 particles drive various chemical reactions due to their strong oxidation and reduction ability. This effect is applied in order to kill malignant HeLa cells with TiO2 particles. During 10-min UV irradiation periods, HeLa cells were completely killed in the presence of TiO2 (100 μg cm−3). However, without irradiation these particles showed little cytotoxicity up to 360 μg cm−3. It is concluded that the cells were killed by hydroxyl (OH·) and perhydroxyl (HO2·) radicals produced from water by the irradiated TiO2 particles, and also that the cells were directly oxidized by photogenerated holes in TiO2. The distribution of TiO2 powders in the cells was observed using a transmission electron microscope. The TiO2 powder existed not only on the cell membrane, but also in the cytoplasm. Thus, the cells were damaged by photoexcited TiO2 not only from the cell membrane, but also from the inside of cytoplasm. Finally, the application of this malignant cell photokilling effect to photodynamic therapy is discussed.