Ultrasound-triggered reactive oxygen species production and antibacterial activity by thulium oxide nanoparticles

Sonodynamic therapy (SDT), due to its non-invasive nature, high tissue penetration, and lack of drug resistance, has shown significant application prospects in the field of clinical antibacterial treatment. However, existing studies often require high ultrasonic energy, long ultrasonic exposure time, and high concentrations of sonosensitizer materials because the production of reactive oxygen species (ROS) by the sonosensitizers is typically insufficient. In this study, we showed that thulium oxide nanoparticles (Tm₂O₃ NPs) could be a candidate sonosensitizer exhibiting superior ROS production. We adjusted the ratio of surfactants in the synthesis system, tested the production of various types of ROS under ultrasonic irradiation, and studied the antibacterial activity of thulium oxide nanoparticles against gram-negative Escherichia coli (E. coli) and gram-positive Staphylococcus aureus (S. aureus). Under ultrasonic action, thulium oxide nanoparticles can produce singlet oxygen (¹O₂) and hydroxyl radicals (·OH), with type I ROS (radical type) being the primary form of ROS produced. We demonstrated that the thulium oxide nanoparticles exhibited apparent antibacterial activity against E. coli and S. aureus under ultrasonic irradiation and promoted the healing of bacterial-infected wounds. This study suggested a novel rare-earth nanomaterial sonosensitizer with outstanding ROS yield and clinical practicality, providing an energy-efficient and material-saving alternative to classical sonodynamic and photodynamic therapies.