Light-triggered simultaneous release of reactive oxygen species and thymol from mesoporous organosilica particles with potential application in deep tissue

Antibiotic resistance in bacterial pathogens is a global health problem requiring enormous research into alternative, easily accessible antibacterial substances and treatments to replace antibiotics. Components of essential oils (EOs) that possess broad-spectrum antibacterial properties are promising candidates. However, due to their high volatility and low solubility, their administration remains difficult. A promising method is to load materials with the active component and design a triggered release system to avoid rapid exhaustion of the carried material. If such a drug-release system would additionally exhibit antibacterial properties itself, it could significantly advance combatting bacterial infections. Therefore, in the present study, we combine the light-triggered and simultaneous release of the antimicrobial substance thymol with antibacterial photodynamic therapy (aPDT) within one nanoparticle. The irradiation of an immobilized photosensitizer produces reactive oxygen species (ROS) that oxidatively cleave a linker and ultimately releases thymol detected by GC-MS. Antibacterial properties towards Staphylococcus aureus biofilm formation were verified by ATP-based viability assay. To improve the application for deep tissue delivery, we also take into account the low transmittance of visible light. A highly developed trifunctional material enables 2-photon excitation via Förster resonance energy transfer (FRET) and thus shifts the wavelength into the biological window. The release of the third functionality can be monitored in situ by fluorescence microscopy. This model system lays the foundation for future antibacterial materials