Enhancement by Nanogold of the Efficacy of a Light-Activated Antimicrobial Coating

Reducing the microbial load on environmental surfaces is an important means of preventing hospital cross-infection and there is great interest in developing self-disinfecting surface coatings for this purpose. The aims of this study were to produce a coating containing a light-activated antimicrobial agent (LAAA) that could exert an antimicrobial effect when illuminated with white light and to ascertain whether the antimicrobial activity could be enhanced by the presence of gold nanoparticles. Silicone polymers that contained either the LAAA methylene blue (MB) or MB together with 2 nm gold nanoparticles were produced. A suspension of Staphylococcus aureus was placed on the surface of the polymers which were exposed to white light for various periods of time and the number of viable organisms remaining were determined. Polymers containing MB or MB plus nanogold achieved a light dose-dependent killing of the test organism. In the case of the polymers exposed to the lowest light dose (a 4 hour exposure time) the kills attained by the MB-containing polymers were significantly greater when nanogold was present. These findings suggest that polymers containing MB and nanogold could provide a coating that would exert an antimicrobial effect at the low light intensities encountered in many hospital environments.