Innovative TiO2/Cu Nanosurfaces Inactivating Bacteria in the Minute Range under Low-Intensity Actinic Light

The bacterial inactivation of E. coli by cotton TiO2/Cu DC-magnetron sputtered thin films was investigated in the dark and under low-intensity actinic light. The TiO2/Cu sputtered layers revealed to be sensitive to actinic light showing the spectral characteristics of Cu/CuO. This indicates that Cu does not substitute Ti4+ in the crystal lattice. Under diffuse actinic light (4 mW/cm(2)), the hybrid composite TiO2/Cu sample lead to fast bacterial inactivation times <5 min. This study presents evidence for a direct relation between the film optical absorption obtained by diffuse reflectance spectroscopy (DRS) and the bacterial inactivation kinetics by the TiO2/Cu samples. The Cu-ions inactivating the bacteria were followed in solution by inductively plasma coupled spectroscopy (ICPS). The amounts of Cu-ions detected by ICPS provide the evidence for an oligodynamic antibacterial effect. The changes in the oxidation state of Cu during bacterial inactivation were followed by XPS. The E. coli cell viability was detected by standard coliform counting CFU methods. The TiO2/Cu thickness layer was determined by profilometry and the film microstructure by XPS, TEM, AFM, XRD, XRF and contact angle (CA). A mechanism of bacterial inactivation by TiO2/Cu samples is suggested in terms of interfacial charge transfer (IFCT) involving charge transfer between TiO2 and Cu.