Bacterial inactivation on sputtered TiOMoN and TiOMoN-Ag thin films under solar simulated light

Abstract

The bacterial inactivation kinetics of Escherichia coli (E. coli) by innovative sputtered TiMoON and TiMoON-Ag films under simulated solar light irradiation is accounted for in a detailed, comprehensive and systematic form. This study presents the evidence that normal E. coli degrades faster compared to genetically modified porinless E. coli due to Ag+-ions transfer occurring from the beginning of the bacterial inactivation process. The Ag-films were deposited by RF-reactive sputtering and presented a high hydrophobic character, which facilitated their contact/interaction with the bacteria cell wall. To reach homogeneous distribution of Ag in the films, annealing under vacuum at 400 °C was required. The films were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron microscopy (XPS), X-ray fluorescence (XRF) and contact angle (CA) measurements. TiMoON-Ag films led to the formation of highly reactive oxidative radicals (ROS) under solar irradiation. The nature of these species was specifically identified. The formation of TiN and TiO-sites on the film surface was detected by XPS. TiMoON-Ag films with 6.7 and 7.4 at. % Ag led to E. coli inactivation ∼ 90 min under solar simulated light (50 mW/cm2, 320–800 nm). The later films present a practical potential for the disinfection of medical surfaces and devices under solar light due to the narrow film ban-gap of 2.10 eV.