Study of the Effect of Anisotropic Gold Nanoparticles on Plasmonic Coupling with a Photosensitizer for Antimicrobial Film

Development of antimicrobial surfaces for sterilization is much needed to avoid the spreading of drug resistant bacteria. Light can activate antimicrobial surfaces by an interaction between nanoparticles and a photosensitizer dye to produce a steady and efficient killing of bacteria. The film studied in this work contains gold nanorods (AuNRs) of 32 nm length and 16 nm diameter and gold nanostars (AuNSs) of 50 nm of diameter, in combination with crystal violet (CV) dye. The surface plasmon resonance (SPR) of the nanoparticles used in the film was mathematically simulated and characterized to understand different SPR between the particles. Their effects on plasmonic coupling with the dye, and thus the production of reactive oxygen species (ROS) and consequently the activity of the film against bacteria, were studied. The films showed great antimicrobial activity against Gram-negative bacteria (E. coli) in 4 h of light exposure; when modified with AuNSs, it could kill E. coli with 5 orders of magnitude (5-log), and the one modified with AuNRs could kill with 4 order of magnitude (4-log), while maintaining partial activity against Gram-positive bacteria (S. aureus), i.e. being able to kill with 2.5 orders of magnitude by the film containing AuNSs and 3 orders of magnitude by those containing AuNRs. The differential response of Gram-negative and Gram-positive bacteria to the ROS generated by the films would allow a more targeted approach for specific bacterial species, for example, surfaces of bedpans or common contact surfaces (handles, handrails, etc.) that are contaminated principally by Gram-negative or Gram-positive bacteria, respectively.