Antibacterial Activity of Light-Activated Silicone Containing Methylene Blue and Gold Nanoparticles of Different Sizes

Methylene Blue and methylene blue-gold nanoparticle mixtures were encapsulated in a silicone polymer using a swell-encapsulation-shrink technique. The antibacterial properties of the materials, when tested against Escherichia coli and Staphylococcus epidermidis, and exposed to laser light (660 nm), were significantly affected by both the presence and size of Au nanoparticles. Bacterial inactivation data were analysed using the Weibull inactivation model. For both E. coli and S. epidermidis the value of the parameter, indicating the time required to achieve the first log(10) reduction in the viable count, decreased when Au nanopartidies of ca 2 nm diameter were present. Larger Au nanoparticles (diameters of 5 and 20 nm) in combination with methylene blue were also embedded in silicone. The values of these materials increased with nanoparticle diameter, indicating a reduction in antibacterial activity. In all cases E. coli had higher values than S. epidermidis.