On the long term antibacterial features of silver-doped diamondlike carbon coatings deposited via a hybrid plasma process.

Environmental surfaces are increasingly recognized as important sources of transmission of hospital-acquired infections. The use of antibacterial surface coatings may constitute an effective solution to reduce the spread of contamination in healthcare settings, provided that they exhibit sufficient stability and a long-term antibacterial effect. In this study, silver-incorporated diamondlike carbon films (Ag-DLC) were prepared in a continuous, single-step plasma process using a hybrid, inductively coupled plasma reactor combined with a very-low-frequency sputtering setup. The average Ag concentration in the films, ranging from 0 to 2.4 at. %, was controlled by varying the sputtering bias on the silver target. The authors found that the activity of Escherichia coli was reduced by 2.5 orders of magnitude, compared with the control surface, after a 4-h contact with a 2.4 at. % Ag-DLC coating. The coatings displayed slow release kinetics, with a total silver ion release in the sub-ppb range after 4 h in solution, as measured by graphite furnace-atomic absorption spectroscopy. This was confirmed by Kirby-Bauer diffusion tests, which showed limited diffusion of biocidal silver with a localized antibacterial effect. As a slow and continuous release is mandatory to ensure a lasting antibacterial effect, the newly developed Ag-DLC coatings appears as promising materials for environmental hospital surfaces.