Investigation of antibacterial photodynamic inactivation in urea-doped TiO2 sensitized with porphyrin photocatalysis

Choosing the right photosensitizers (PSs) as well as the right light source is very critical in antimicrobial photodynamic therapy (aPDT). Some light sources, such as ultraviolet, have high cytotoxicity and poor penetration and some PSs are hydrophobic with low solubility in water, and easy aggregation. To address these issues, we modified TiO2 nanoparticles with urea and TCPP (TCPP=tetra(4-carboxyphenyl) porphyrin) as a PS and prepared N-doped-TiO2 (NT), TCPP/TiO2 (PT), and TCPP/N-doped-TiO2 (PNT). Urea is a safe compound used here as a source of nitrogen (N). Nitrogen doping produces a localized N state within the TiO2 bandgap which broadens the absorption in the visible light region. Both urea and TCPP shifted the bandgap of TiO2 to the visible area and enabled the photodegradation of methylene blue after 30 min of aging under visible light. O-1(2) production was monitored by the rapid and irreversible conversion of anthracene to its corresponding endoperoxide. Meanwhile, different scavengers such as p-benzoquinone (p-BQ) and tert-butanol (t-BuOH) were employed in a photocatalytic process to specify the existence of superoxide and hydroxyl radical species, respectively. PNT showed a promising photobactericidal activity and reached 100% of inhibition activity against both types of bacteria after 120 and 180 min, respectively under LED lamp (15 W) irradiation. The interaction between PNT and bacteria was also examined by FESEM.