Ultrathin Polyelectrolyte Multilayer Films with Silver Nanoparticles as a Potential Antibacterial Coating

Silver nanoparticles (AgNPs) are already used as antibacterial agents for medical devices and food packaging materials. However, concerns about its toxicity still exist. AgNPs can be incorporated into ultrathin polyelectrolyte multilayer (PEM) films to minimize this risk. With PEMs, full surface coverage can be achieved with minimal AgNPs, minimizing human exposure. In this study, a simple protocol to fabricate ultrathin PEM/AgNP films using sodium ascorbate as a reductant was developed. The effects of the number of bilayers and ionic strength (0.05 to 0.50 M) on film thickness and amount of AgNPs were investigated. UV/VIS spectra show that increasing the number of bilayers from 1 to 5 would lead to a corresponding increase in film thickness and amount of synthesized AgNPs. Thicker layers and more AgNPs were deposited when the films were fabricated under higher ionic strengths. Films with thicknesses ranging from 15.67 to 87.13 nm were fabricated. The sizes of the incorporated AgNPs were between 54.32 and 259.26 nm, as characterized by scanning electron microscopy. All films were stable when submerged in water for 240 h, suggesting the migration of Ag/Ag + from the films was minimal. The antibacterial efficacy of the films against Staphylococcus aureus was also assessed. Only the PEM/AgNP films fabricated with the highest salt concentration (0.50 M) showed antibacterial activity under resazurin assay. However, the Kirby Bauer method showed inhibition zones for all films fabricated under all salt concentrations, indicating antibacterial activity at the interface of the bacterial lawn and the films, even with the slow migration of Ag/Ag + . Thus, PEM/AgNP films have the potential to be used as an antibacterial coating.