Antibacterial Activity of Nanosilver Ions and Particles

The antibacterial activity of nanosilver against Gram negative Escherichia coli bacteria is investigated by immobilizing nanosilver on nanostructured silica particles and closely controlling Ag content and size. These Ag/SiO2 nanoparticles were characterized by S/TEM, EDX spectroscopy, X-ray diffraction the exposed Ag surface area was measured qualitatively by O2 chemisorption. Furthermore, the fraction of dissolved nanosilver was determined by measuring the released (leached) Ag+ ion concentration in aqueous suspensions of such Ag/SiO2 particles. The antibacterial effect of Ag+ ions was distinguished from that of nanosilver particles by monitoring the growth of E. coli populations in the presence and absence of Ag/SiO2 particles. The antibacterial activity of nanosilver was dominated by Ag+ ions when fine Ag nanoparticles (less than about 10 nm in average diameter) were employed that release high concentrations of Ag+ ions. In contrast, when relatively larger Ag nanoparticles were used, the concentration of the released Ag+ ions was lower. Then the antibacterial activity of the released Ag+ ions and nanosilver particles was comparable.