Quantitative determination of OH radical generation and its cytotoxicity induced by TiO 2–UVA treatment

Abstract

Titanium dioxide (TiO 2) has been reported to produce OH radical under ultraviolet-A (UVA) irradiation and to induce cytotoxicity. Various crystal forms and sizes of TiO 2 with UVA irradiation from OH radical generation was analysed spin trapping-X band (electron-spin resonance (ESR) spectroscopy. The amount of OH radical was determined with ESR signal intensity of the adducts in which OH radical was trapped with the spin-trapping reagent dimethyl pyrroline- N-oxide (DMPO). The formation of OH radicals varied in both crystal size and form of TiO 2. Irradiation of the anatase form of TiO 2 produced large numbers of OH radical in TiO 2 and UVA in a dose-dependent manner, but rutil form (90 nm in size) showed less OH radical generation. The crystal size had large influence on OH radical generation, but the optimum size for the OH radical generation was different between both forms. The UVA absorption spectrum of TiO 2 differed in regard to crystal size and form of TiO 2, but no relation was observed between UVA absorbency and OH radical formation. The cytotoxicity of TiO 2–UVA irradiation was determined against Chinese hamster ovary (CHO) cells and a significant relationship was obtained between the cytotoxicity and the OH generation. Measurement of the amount of OH radical production by UVA irradiation with ESR is needed to clarify the effect of crystal form or sizes of TiO 2 on OH radical production and cytotoxicity.