Effect of Size and Surface Ligands of Silver (Ag) Nanoparticles on Waterborne Bacteria

Clean drinking water is a matter of concern for all countries, more so for many developing countries and consequently various methods of producing clean drinking water are being practiced for provision of such water to the consumers. At the same time an attempt is always made to adopt any new technique or technology to use it for commercially feasible production of such water. In recent years, with the advent of fast developing technologies, nanotechnology has also come into operation for economic and commercial production of clean drinking water. With a view to produce clean drinking water free from pathogens by the use of nanotechnology, we have investigated the antibacterial properties of silver (Ag) nanoparticles against waterborne bacteria in the public water supply sources in Islamabad, the capital of Pakistan. Water samples from over 50 water supply sources were collected and bacterial strains were identified by API20E method. Different silver nanoparticles were tested against 8 different bacterial isolates at concentrations varying from 26 to about 77 μg/mL. Nanoparticles of size ranging from 3-8 nm prepared by casein stabilization method showed the best activity against all isolated strains, E. coli being the most effectively inhibited with an average 14.9 mm zone of inhibition. C. sakazakii (12.6 mm) was most sensitive to citrate stabilized particles, followed by E. coli (12.3 mm), K. pneumoniae (12 mm) and P. aeruginosa (11.6 mm). These results provide a useful picture for the development of water filters incorporated with silver nanoparticles. We believe that this study is important for the public, particularly in the developing countries and also for others working in the area of antibacterial effects of nanoparticles.