Visible Light Plasmon Excitation of Silver Nanoparticles Against Antibiotic-ResistantPseudomonas aeruginosa

Abstract

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...

Biomedical Applications of Reactive Oxygen Species Generation by Metal Nanoparticles

“…Regarding their antibacterial role, once the AgNPs are in contact with bacteria, the free radical-mediated pore generation into the cell wall is the leading mechanism of bacterial cell death. Therefore, some authors have investigated how to improve the AgNPs’ antimicrobial activity via localized surface plasmon resonance (LSPR) to increase the ROS generation by exposure to visible light [ 80 ].…”

“…The main objective of this study was to increase the antibacterial activity of AgNPs by exploiting the capability of LSPR to influence the electronic state of the particles and increase the number of silver ions (Ag + ) which ultimately are responsible for the antimicrobial effect. Recently, research from da Silva and colleagues [ 80 ] has shown a link among AgNPs, LSPR, ROS and the AgNPs’ antimicrobial activity. The authors claim that, even if some studies support the idea that Ag + plays a main role in antibacterial activity [ 83 ], together with the capability of AgNPs to introduce nicks in the cytoplasmic membrane [ 84 ], AgNPs and Ag + can also induce ROS formation, which damages the cell cytoskeleton, oxidizing nucleic acids and proteins, leading to potential chromosomal aberrations and cell death [ 85 ].…”

Antibacterial and antibiofilm potential of silver nanoparticles against antibiotic-sensitive and multidrug-resistant Pseudomonas aeruginosa strains

“…Antibacterial activity of AgNPs against Pseudomonas aeruginosa National Institute of Quality Control in Health isolates of P. aeruginosa. Silva et al[71] performed chemical synthesis of AgNPs covered with sodium citrate. The nanoparticles exhibit size of 20 ± 3 nm and spherical format.…”

An Updated Review on Silver Nanoparticles in Biomedicine

“…However, the ROS-mediated cytotoxicity was more evident in the case of Gram-negative bacterium [ 181 ]. Light-irradiated enhanced bactericidal effects were also reported for P. aeruginosa treated with citrate-coated nanoparticles [ 182 ].…”