One arrow two eagle: Multifunctional Nb5+-doped TiO2 nanoparticles for tumor photothermal-sonodynamic therapy

Titanium dioxide nanoparticles (TiO₂) have been widely used as biocompatible sonosensitizers, but their wide bandgap (3.0-3.2 eV) and rapid carrier recombination result in poor sonodynamic therapy efficacy. In order to expand the biological applications of nano-TiO₂, this work prepared Nb-doped TiO₂ nanoparticles (Nb:TiO₂) via a simple thermal decomposition method. The optical absorption of Nb:TiO₂ extended from the ultraviolet absorption edge (∼380 nm) of pure TiO₂ to near-infrared (NIR) absorption (>1100 nm). Under 1064 nm light irradiation, Nb:TiO₂ nanoparticles efficiently convert NIR light energy into heat, with a photothermal conversion efficiency of 39.1 %, demonstrating their potential as excellent nano-photothermal agents. Under ultrasound excitation, the singlet oxygen (¹O₂) generation rate of Nb:TiO₂ was 1.51 times higher than that of undoped TiO₂, making it a more effective inorganic nano-sonosensitizer. Under combined light-ultrasound conditions, the cell survival rate was reduced to just 8.3 % after 8 min, indicating that the synergistic treatment of PTT-SDT effectively kills tumor cells. Therefore, this doping strategy provides new insights for expanding the biological applications of other TiO₂-based semiconductors.