Carbon Dots–TiO2 Hybrid Nanomaterials with Enhanced Photochemical Properties and Photodynamic Therapy Activity

Photodynamic therapy (PDT) is a promising cancer treatment employing photo-induced reactive oxygen species (ROS) generation by a photosensitizer (PS). Titanium dioxide (TiO2) is a potential PS due to its superb photocatalytic features and biocompatibility. However, its clinical potential is restricted by its predominant ultraviolet (UV) absorption. To address this limitation, this work introduces TiO2/carbon dots (CDs) nanohybrid materials for improving the photophysical properties of TiO2 and its photodynamic performance. TiO2 and CDs were synthesized through wet chemical and hydrothermal techniques, and subsequently combined via a facile ex situ solvothermal process to produce hybrid materials containing 1–50% w/w CDs. The materials were characterized using XRD, Raman, TEM, FT-IR, zeta potential, TGA, UV-Vis and PL. PDT studies on A431 skin cancer cells indicated improved photosensitizing ability of TiO2/CDs, with TiO2/CDs (10%) inducing 47% cell toxicity, versus 20% for TiO2 after 10 min of red-light irradiation (661 nm, 18 mW/cm2, 12.96 J/cm2). Intracellular localization studies revealed enhanced cellular uptake of TiO2/CDs (10%), compared with TiO2. In vitro studies on 3T3 healthy fibroblasts confirmed PSs’ safety both with and without light. Overall, this study elucidates the key role of CDs in the photophysical and photodynamic behavior of TiO2-based systems, providing design guidelines for the next-generation inorganic PSs.