Visible Light Plasmon Excitation of Silver Nanoparticles Against Antibiotic-Resistant Pseudomonas aeruginosa

The interaction of metallic nanoparticles with light excites a local surface plasmon resonance (LSPR). This phenomenon enables the transfer of hot electrons to substrates that release Reactive Oxygen Species (ROS). In this context, the present study was aimed at enhancing the antibacterial effect of citrate-covered silver nanoparticles (AgNPs), which already possess excellent antimicrobial properties, via LSPR excitation with visible LED against Pseudomonas aeruginosa, one of the most refractory organisms to antibiotic treatment. The Minimum Inhibitory Concentration (MIC) of AgNPs was 10 g/ml under dark conditions and 5 g/ml under light conditions. The combination of light and AgNPs led to 100% cell death after 60 minutes. Quantification of ROS via flow cytometry showed that LSPR stimulated AgNPs increased intracellular ROS concentration by 4.8-fold, suggesting that light-exposed AgNPs caused cell death via ROS production. Light exposition caused a small release of silver ions (0.4%) reaching a maximum after 6 hours. This indicates that silver ions play at most a secondary role in P. aeruginosa death. Overall, the results presented here show that LSPR generation from AgNPs by visible light enhances the antimicrobial activity of silver nanoparticles and can be an alternative for the treatment of topic infections caused by antibiotic-resistant bacteria such as P. aeruginosa.