Eradicating fungal biofilm-based infections by ultrasound-assisted semiconductor sensitized upconversion photodynamic therapy

Fungal biofilms, as self-produced extracellular polymeric substances that resist antifungal agents and immune defense, represent a major cause of treatment failure and recurrent infections. Therefore, it is of great importance to eradicate fungal biofilms to achieve efficient therapy. This study develops a synergistic reactive oxygen species (ROS)-enhanced strategy to eradicate Candida albicans biofilms by designing ultrasound-light dual-responsive nanohybrids (UCNP@CR). The system integrates thulium-doped upconversion nanoparticles (UCNPs) with carbon nitride-coated surfaces (g-C₃N₄) and polypyridine ruthenium complex (Ru) photosensitizers. In treatment, the dense fungal biofilm can be effectively loosened under ultrasound stimulation while ultrasound simultaneously triggers ROS production of UCNP@CR, collectively promoting irreversible destruction of biofilm and inward penetration of photosensitizer. Moreover, UCNP@CR exhibits strong fungal adhesion, while its g-C₃N₄-mediated enhanced metal-to-ligand charge transfer (MLCT) process of Ru under near-infrared light irradiation amplifies ROS generation, which leads to efficient eradication of fungal biofilms. As in vivo experimental evidence, UCNP@CR exhibits excellent antifungal efficacy in treating fungal biofilm-infected wounds in immunosuppressed male mice under ultrasound-light stimulation. These findings establish the ultrasound-assisted, ROS-enhanced synergistic strategy as a promising approach against fungal biofilm infections and provide diverse perspective for managing other biofilm-related infectious diseases.