Investigation of the Photoinduced Antimicrobial Properties of N-Doped TiO2 Nanoparticles under Visible-Light Irradiation on Salmonella Typhimurium Biofilm

The aim of the present study was to investigate the photoinduced properties of nitrogen-doped titanium dioxide (N-TiO2) against the Salmonella ser. Typhimurium bacterial biofilm, under visible-light irradiation. The capability of N-TiO2 nanoparticles working as multipurpose materials with antimicrobial applications, as well as environmental ones, was therefore investigated. The sol–gel method was used to synthesize N-TiO2 particles, which were then characterized by Fourier-transform infrared (FTIR) spectroscopy, dynamic light scattering (DLS), Brunauer–Emmett–Teller (BET) analysis of surface area, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS), and transmission electron microscopy (TEM). The results showed that the particles formed were nano-sized and had the expected Ti-O bonds and the presence of elemental N. The as-produced N-TiO2 nanoparticles (NPs) were tested for their antimicrobial activity. The antibacterial photocatalytic testing was performed under visible-light irradiation, on Salmonella Typhimurium biofilm. To form the biofilm, stainless steel (ss) coupons were incubated with three different strains of Salmonella Typhimurium bacteria for 48 h at 15 °C in tryptone soy broth (TSB). After the biofilm’s formation, the coupons were placed on a horizontal, rectangular, batch, equipped with a vis-LED irradiation source reactor in the presence of N-TiO2 NPs. After 1, 2, and 3 h of irradiation, sampling of the bacterial population was assessed. The results showed an evident inhibition of proliferation under light irradiation when the N-TiO2 was present, compared to the non-irradiated NPs. It is noteworthy that, during the first 2 h, the TiO2 NPs specimens tended to attract more bacteria on their surface then the control specimens, due to their higher available surface area, which worked as a shelter. There were ~6% viable (remaining) Salmonella cells after the first hour of visible-light irradiation with N-TiO2 NPs.