Effect of the spectral properties of TiO2, Cu, TiO2/Cu sputtered films on the bacterial inactivation under low intensity actinic light

Bacterial inactivation by TiO2, Cu and TiO2/Cu DC-magnetron sputtered thin films was systematically investigated in the dark and under low intensity visible/actinic light. Low intensity actinic light led to a fast 6 log10 (complete) bacterial inactivation within the minute range. The TiO2/Cu bifunctional composite films led to the fastest bacterial inactivation. The Cu sputtered on the TiO2 enabled the absorption of visible light by the supported film and triggered a photo-induced IFCT effect from TiO2 to the Cu/Cu-ions. Evidence for a direct relation between the films optical absorption obtained by diffuse reflection spectroscopy (DRS) and the bacterial inactivation kinetics (CFU) is presented. The film microstructure was characterized by X-ray fluorescence (XRF) and X-ray photoelectron spectroscopy (XPS). The Ti- and Cu-ions in solution were followed by inductive coupled plasma spectroscopy (ICPS). The small amount of Cu-ions determined by ICPS provide the evidence for an oligodynamic effect during bacterial inactivation. The Cu-redox changes and the ratio of the oxidized C/reduced C species were determined by XPS within the bacterial inactivation time.