Effect of silver nanoparticle and TiO2 coatings on biofilm formation on four types of modern glass

Four different types of modern glass were exposed to the open atmosphere for 5 months in São Paulo city. The effect of TiO2 (self-cleaning glass) and a silver nanoparticle polymeric coating on biofilm formation was evaluated under these conditions. Examination by various types of microscopy, standard microbiological sampling and culture methods, and estimation of transparency to light by measuring the current induced in an underlying photovoltaic cell showed that the self-cleaning glass did reduce biofilm formation very significantly as compared to other glass samples. The presence of the polymeric nanosilver coating on the glass surface increased the adhesion of microorganisms, except for self-cleaning glass. Both plating and direct microscope examination showed that the major colonizers were fungi, with few phototrophs (principally Chlorella) being detected. Approximately 80% of the fungi growing on plates were yeast-like, although substantial cover by fungal filaments was seen by direct microscopy of non-TiO2-coated glass. The results suggest that the TiO2 coating inhibits the formation of fungal filaments, hence reducing overall biofilm cover. Silver nanoparticles in a plastic film were not effective in reducing sub-aerial biofilm formation on non-TiO2-coated glass.