Photoinactivation of S. aureus biofilms using porphyrin conjugates with green-synthesized TiO2 immobilized on waste polystyrene

Waterborne infections remain a global concern, exacerbated by biofilms in water storage systems that resist chlorine disinfection. In this study, antimicrobial photodynamic inactivation was investigated using novel porphyrin-TiO ₂ nanoconjugates prepared from green-derived TiO ₂ nanoparticles using Citrus sinensis extracts and immobilized on waste polystyrene (PS) for the first time. Metal-free 5,10,15-tris(4-bromophenyl)-20-(4-carboxyphenyl)porphyrin (1) and its ClIn(iii) derivative (2) were conjugated to TiO ₂, then immobilized on PS. Characterization by FTIR, EDX, TGA, SEM, TEM, and UV-vis confirmed successful formation of thermally stable and spherical nanostructures. Moreover, photophysical studies showed that metalation reduced fluorescence quantum yield (Φ _F) from 0.01 (1) to <0.01 (2) due to heavy atom effect) while boosting singlet oxygen yield ((Φ _Δ) from 0.68 (1) to 0.85 (2)–0.90 (2-TP). Free 2-TP achieved 0.0006% S. aureus survival percentage while PS-immobilized versions reached 2.5% under 30 minutes visible light exposure. These sustainable, high-efficiency materials advance biofilm-resistant water treatment for resource-limited settings.