A bacteria-activated photodynamic nanosystem based on polyelectrolyte-coated silica nanoparticles.

In this study, we present a novel and robust strategy to develop a bacteria-activated photodynamic nanosystem based on polyelectrolyte-coated silica nanoparticles modified with chlorin e6 photosensitizer. Due to the aggregation of chlorin e6 on silica nanoparticles to induce excited-state quenching, the fluorescence and singlet oxygen generation of the obtained nanosystem are quenched. We demonstrate that polyelectrolyte-chlorin e6 complexes can be effectively extracted, by bacteria, from silica nanoparticles and form stable binding on the bacterial surface, changing the aggregation state of chlorin e6 and leading to the recovery of fluorescence and singlet oxygen generation. Based on this activatable photodynamic nanosystem, complete elimination of methicillin-resistant Staphylococcus aureus (MRSA) is achieved via a mechanism involving cell wall and membrane disruption, showing great potential to combat drug-resistant bacterial infections in clinical settings. Different from the bacterial enzyme-activated photodynamic systems responsive to specific bacterial strains, our activatable nanosystem exerts a broad-spectrum bacteria-triggered photodynamic effect by exploiting the unique charge characteristics of the cell envelope structure of bacteria. More importantly, we believe that the mechanism of bacteria-triggered polyelectrolyte dissociation from nanoparticles proposed in this work could be further used as a general strategy for the fabrication of bacteria-responsive multifunctional nanomaterials.