Plasma-Mediated Nanosilver-Organosilicon Composite Films Deposited on Stainless Steel: Synthesis, Surface Characterization, and Evaluation of Anti-Adhesive and Anti-Microbial Properties on the Model Yeast Saccharomyces cerevisiae

A series of plasma-mediated thin films (175?nm), containing silver nanoparticles embedded in an organosilicon matrix with controllable properties (silver content, nanoparticle size, matrix composition), were deposited onto stainless steel and chemically and structurally characterized, using a large set of analytical techniques. The process originality relies on a dual strategy, associating silver sputtering, and simultaneous plasma enhanced chemical vapor deposition, in an argon-hexamethyldisiloxane plasma, using an asymmetrical radiofrequency discharge at 13.56?MHz. X-ray photoelectron spectroscopy, FTIR spectroscopy, and Raman spectroscopy demonstrated the inclusion of metallic silver nanoparticles within the organosilicon-like matrix. Silver content was directly related to the plasma process conditions. TOF-SIMS analysis revealed that the film composition was homogeneous in depth. SEM and TEM observations confirmed the nanoparticle-based morphology of the coatings, dependent on the silver content. The film anti-adhesive potentialities were evaluated in vitro toward the model yeast Saccharomyces cerevisiae by performing shear-flow induced detachment experiments, under well-controlled hydrodynamic, and physico-chemical conditions. The maximal effect was achieved for the organosilicon matrix alone. When silver nanoparticles were incorporated, yeast detachment was lower, probably due to the strong affinity of embedded silver for biological components of the cell wall surface. The presence of methyl groups in the matrix network could also promote enhanced hydrophobic yeast/coating interactions. An anti-microbial action of silver (conjugated effect of nanoparticles and chemisorbed Ag+ ions and complexes released through nanoparticle oxidation) at the immediate vicinity of the coating surface occurred, depending on the silver content. In the conditions under study, a maximal 1.9 log reduction in viable counts was observed, compared to control conditions with bare stainless steel. Based on NanoSIMS50 elemental mapping, various characteristic cell sub-structures and inclusions were detected, such as cell wall and nucleus. After yeast exposure to nanosilver-containing films, a quite homogeneous distribution of released silver all over the cell was observed, overlapping with sulfur and phosphorous signals.