Tailored TiO ₂ Nanoparticles for Broad-Spectrum Antibiofilm Applications: A Systematic Comparison of Structural and Functional Properties of Carbon- and Nitrogen-Doped TiO ₂ Nanoparticles

Nonmetal doping extends the photocatalytic response of TiO₂ nanoparticles (NPs) into the visible light region; however, systematic evaluations of how specific dopants influence their antimicrobial performance remain limited. In this study, we present a direct comparison of carbon-doped TiO₂ (C-TiO₂) and nitrogen-doped TiO₂ (N-TiO₂) NPs synthesized via a sol-gel method. Structural and optoelectronic properties were characterized by powder X-ray diffraction (p-XRD), transmission electron microscopy (TEM), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), and X-ray photoelectron spectroscopy (XPS), confirming dopant incorporation and band gap narrowing. Carbon doping resulted in a more pronounced band gap reduction (2.66 eV compared with 3.09 eV for N-TiO₂), which correlated with stronger visible light absorption and increased reactive oxygen species (ROS) generation. Under visible light irradiation, C-TiO₂ NPs achieved 80% eradication of <i>Staphylococcus aureus</i> biofilms and 69% eradication of <i>Escherichia coli</i> biofilms, corresponding to a ∼1.5-fold higher antibiofilm activity relative to N-TiO₂ NPs. Differences in bacterial susceptibility were associated with cell envelope architecture, in which the outer phospholipid membrane of Gram-negative <i>Escherichia coli</i> likely limited ROS penetration and contributed to lower eradication efficiency compared with Gram-positive <i>Staphylococcus aureus</i>. These findings demonstrate that dopant selection directly modulates photocatalytic functionality and identify C-TiO₂ NPs as a broad-spectrum antimicrobial material. The results have implications for the rational design of TiO₂-based nanomaterials in antimicrobial photodynamic therapy (aPDT), indoor building environments where pathogen control is essential, environmental remediation, and the development of next-generation self-disinfecting surfaces.