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 Ag(0)/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, [N(8881)][Tf(2)N], and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [emim][Tf(2)N]. 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 [N(8881)][Tf(2)N] 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][Tf(2)N] 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.

Electrochemical Properties of Carbon Nanoparticles Entrapped in Silica Matrix.

Carbon-based electrode materials have been widely used for many years for electrochemical charge storage, energy generation, and catalysis. We have developed an electrode material with high specific capacitance by entrapping graphite nanoparticles into a sol-gel network. Films from the resulting colloidal suspensions were highly porous due to the removal of the entrapped organic solvents from sol-gel matrix giving rise to high Brunauer-Emmett-Teller (BET) specific surface areas (654 m(2)/g) and a high capacitance density ( approximately 37 F/g). An exponential increase of capacitance was observed with decreasing scan rates in cyclic voltammetry studies on these films suggesting the presence of pores ranging from micro (< 2 nm) to mesopores. BET surface analysis and scanning electron microscope images of these films also confirmed the presence of the micropores as well as mesopores. A steep drop in the double layer capacitance with polar electrolytes was observed when the films were rendered hydrophilic upon exposure to a mild oxygen plasma. We propose a model whereby the microporous hydrophobic sol-gel matrix perturbs the hydration of ions which moves ions closer to the graphite nanoparticles and consequently increase the capacitance of the film.