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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 .

17The interaction of metallic nanoparticles with light excites a local surface plasmon resonance 18 (LSPR). This phenomenon enables the transfer of hot electrons to substrates that release 19 Reactive Oxygen Species (ROS). In this context, the present study was aimed at enhancing 20 the antibacterial effect of citrate-covered silver nanoparticles (AgNPs), which already possess 21 excellent antimicrobial properties, via LSPR excitation with visible LED 22 against Pseudomonas aeruginosa, one of the most refractory organisms to antibiotic 23 treatment. The Minimum Inhibitory Concentration (MIC) of AgNPs was 10 μg/ml under dark 24 conditions and 5 μg/ml under light conditions. The combination of light and AgNPs led to 25 100% cell death after 60 minutes. Quantification of ROS via flow cytometry showed that 26 LSPR stimulated AgNPs increased intracellular ROS concentration by 4.8-fold, suggesting 27 that light-exposed AgNPs caused cell death via ROS production. Light exposition caused a 28 small release of silver ions (0.4%) reaching a maximum after 6 hours. This indicates that 29 silver ions play at most a secondary role in P. aeruginosa death. Overall, the results presented 30 here show that LSPR generation from AgNPs by visible light enhances the antimicrobial 31 activity of silver nanoparticles and can be an alternative for the treatment of topic infections 32 caused by antibiotic-resistant bacteria such as P. aeruginosa. 33 34 36 37 Running title: Light-enhanced Ag nanoparticles against P. aeruginosa 38 39 40 42 ability of fine tuning their composition, structure and shape (1). The desired electronic, 43 optical and chemical properties of nanoparticles can be obtained through modern synthetic 44 techniques devised in the past decades (2). Even small variations in one of these parameters 45 may result in new properties that are absent in the analogous bulk material. Due to its high 46 range of controllable features, metallic nanoparticles are now used in many processes, such as 47 48others. 49Silver nanoparticles (AgNPs)(2), exhibit a great potential of use in many areas, due to their 50 relative easy and controlled synthesis (8), ranging from small and simple spheroidal AgNPs 51 (9) to more complex geometries (10, 11) and even asymmetric shapes (12-14) with solid or 52 hollow interiors (15-17). Historrically, silver has been extensively used as an antimicrobial 53 agent. Many different commercial products relying on silver biocidal properties have been 54 produced, most of them in the last 10 years (18, 19). The wide variety of AgNPs as well as 55 the intrinsic properties of metallic silver in relation to biological system and biomolecules 56 (20) fostered the extensive use of AgNPs in medical applications, such as cancer treatment 57 (21-23), drug delivery (24, 25), imaging (26, 27) and antimicrobial treatment (28, 29). 58 P. aeruginosa is a ubiquitous Gram-negative γ-proteobacterium and an opportunistic 59 pathogen associated with nosocomial infections. It also affects patients afflicted by chronic 60 res...

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