Antibacterial Properties of TiO<sub>2</sub> Layers Formed by Au-Sputtering and Thermal Oxidation of Titanium under Visible Light

To prevent infection in dental implants using photocatalytic activity under visible-light irradiation, the fabrication of Au-added TiO2 layers on Ti substrates and their antibacterial properties were studied. Pure Au and Ti-(60, 40) mol％Au alloy films with thicknesses of 10-47 nm were sputtered onto Ti, followed by thermal oxidation in air at 873 K for 1.8 ks to form TiO2 layers. The antibacterial properties against Escherichia coli, cytotoxicity, and bonding strength to Ti substrates were evaluated. The highest antibacterial activity under visible-light irradiation was obtained when the sputtered film was pure Au and its thickness was 38 nm. Compared with as-polished commercially pure Ti, the number of viable mouse osteoblast-like cells and human gingival fibroblasts on Au-added TiO2 layers increased after placement in the dark but decreased after visible-light irradiation. The best antibacterial property-bonding strength balance was achieved when the Ti-40 mol％Au sputtered film with a thickness of 42 nm was formed on Ti. To the best of our knowledge, this study is the first to report the formation of TiO2 layers with antibacterial activity under visible-light irradiation by combining Au-sputtering and thermal oxidation of Ti.