Impact of Sulfidation of Silver Nanoparticles on Established P. aeruginosa Biofilm

Silver nanoparticles (Ag-NPs), one of the most common types of nanomaterials in medical fields and consumer products, are known to have antimicrobial effects; these materials also undergo a series of chemical and biological transformations in the environment. Although the pristine form of silver nanoparticles has been studied, less is known about the impacts of the transformed Ag-NPs on biological systems. This knowledge gap hinders the progress of effectively assessing the impacts of Ag-NPs on the environment and human health. In this study, we demonstrate that the most common form of transformed Ag-NPs, sulfidized silver nano-particles (Ag2S-NPs), show less damage on established Pseudomonas aeruginosa GFP (ATCC® 10145 GFP™) biofilm than the pristine form of the nanoparticle. At a dosage of 0.625 mg/L, the total biomass in the biofilm decreased 64% after being exposed to Ag-NPs and 44% after exposure to Ag2S-NPs. Live biofilms were also interrogated. We observed high reduction in live population for biofilm exposed to Ag-NPs and relatively low reduction by Ag2S-NPs at exposure concentrations higher than 0.625 mg/L. Compared with Ag-NPs, the lower solubility of Ag2S-NPs results in less Ag+ diffusion into established biofilms. Our results suggest that the sulfidation of Ag-NPs reduces their impacts on established biofilms, indicating that the transformed Ag-NPs may have less environmental or human health risks.