Antibacterial activity of photocatalytic titanium dioxide (TiO ₂ ) thin films for <i>Listeria monocytogenes</i> biofilms disinfection

The presence of microbial biofilms on equipment surfaces is a recurrent problem in the food industry. To reduce the risk of biofilm development, a preventive method based on photoactive antibacterial surfaces is proposed. In the present study, crystalline rutile form titanium dioxide (TiO₂) thin layers are deposited on stainless steel substrates by RF sputtering under reactive plasma. Such layers are assessed for their bactericidal activity on two strains of Listeria monocytogenes. After 1 h of irradiation under UV-A at 365 nm, a decrease of 2 log of the number of adherent Listeria cells is observed. Analysis with scanning electron microscopy suggests damages to the bacterial walls. Moreover, the peroxidation of the membrane lipids of L. monocytogenes by the radical species formed by photocatalysis is confirmed since malondialdehyde was detected after irradiation. Furthermore, the present work investigates the role of the redox species generated by photocatalysis. Indeed, experiments carried out in the presence of scavenger molecules (DMSO, EDTA-2Na, superoxide dismutase) show that holes are the main redox species involved in the antibacterial activity of the deposited layers. These results allow a better understanding of the role of the redox species generated by the photocatalytic activity of the rutile TiO₂ thin layers.