PLASMONIC SILVER NANOPRISMS TO IMPROVE ANTIMICROBIAL PHOTODYNAMIC INACTIVATION

Photodynamic inactivation has proven to be a viable therapeutic modality to fight bacterial and fungal infections and to overcome microbial resistance. It effectively annihilates the biological probe by coupling the fluorescence of dyes with light irradiation and molecular oxygen to generate highly reactive oxygen species (ROS). The enhancement of photodynamic efficiency has long been a key objective for researchers, particularly in tumor therapy and antimicrobial photodynamic inactivation (aPDI). In this regard, the application of the plasmonic effect due the coupling of the dyes to nanostructured noble metals in order to enhance photosensitizer response has been studied since the first observations in the late 1990s. While the controlled implementation of this effect still requires a thorough investigation, numerous successful examples have been documented in the literature. Here we show that by coupling morphologically engineered silver nanostructures into prismatic nanoplatelets (AgNPs), we adjusted their plasmonic resonance in the region that overlaps spectrally with the absorption profile of methylene blue, a  known PS, and showed the overall enhancement of the photodynamic action. Two in vitro aPDI applications of these systems will be emphasized at this moment: targeting multidrug-resistant Staphylococcus aureus and Candida albicans cells. It was observed that the application of AgNPs reduced the light dose required for complete eradication of microorganisms. We propose that the enhancement is primarily attributed to the plasmonic surface resonance effect resulting from optical coupling, in combination with the proximity of the negatively charged AgNP surface and the cationic methylene blue molecules, which collectively contribute to the observed increase in efficacy.