Sputter-Deposition of Silver Nanoparticles into Ionic Liquid as a Sacrificial Reservoir in Antimicrobial Organosilicate Nanocomposite Coatings

We present a new approach for fabricating robust, regenerable antimicrobial coatings containing an ionic liquid (IL) phase incorporating silver nanoparticles (AgNPs) as a reservoir for Ag0/Ag+ species within sol–gel-derived nanocomposite films integrating organosilicate nanoparticles. The IL serves as an ultralow volatility (vacuum-compatible) liquid target, allowing for the direct deposition and dispersion of a high-density AgNP “ionosol” following conventional sputtering techniques. Two like-anion ILs were investigated in this work: methyltrioctylammonium bis­(trifluoromethylsulfonyl)­imide, [N8881]­[Tf2N], and 1-ethyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide, [emim]­[Tf2N]. Silver ionosols derived from these two ILs were incorporated into silica-based sol–gel films and the resultant antimicrobial activity evaluated against Pseudomonas aeruginosa bacteria. Imaging of the surface morphologies of the as-prepared films established a link between an open macroporous film architecture and the observation of high activity. Nanocomposites based on [N8881]­[Tf2N] displayed excellent antimicrobial activity against P. aeruginosa over multiple cycles, reducing cell viability by 6 log units within 4 h of contact. Surprisingly, similar films prepared from [emim]­[Tf2N] presented negligible antimicrobial activity, an observation we attribute to the differing abilities of these IL cations to infiltrate the cell wall, regulating the influx of silver ions to the bacterium’s interior.