Control of Nanosilver Toxicity

G.A. Sotiriou, K. Fujiwara, S.E. Pratsinis
Harvard University, US

Keywords: silver nanoparticles, antibacterial activity, Ag+ ion release

Summary:

Nanosilver is considered the most commonly used engineered nanomaterial in antibacterial textiles, polymer films for food packaging, pigments, filters for water or air treatment etc. Concerns however about released Ag+ ions during dispersion of nanosilver in liquids have limited its broad use. Here nanosilver supported on nanostructured silica is made with controlled Ag size both by dry (flame aerosol) and wet chemistry (impregnation) processes without, however, any surface functionalization that could interfere with its ion release. The dispersion method of nanosilver in solutions affects its dissolution rate but not the final Ag+ ion concentration. By systematically comparing nanosilver size distributions to their equilibrium Ag+ ion concentrations, it is revealed, that the latter correspond precisely to dissolution of one to two surface silver oxide monolayers, depending on particle diameter. When, however, nanosilver is selectively conditioned by washing, the oxide layers are removed minimizing Ag+ ion leaching and its toxicity. That way the bactericidal activity of nanosilver is confined to contact with its surface rather than to rampant ions. This leads to nanosilver with antibacterial properties that are essential for medical tools and hospital applications. Complete cure of nano-Ag toxicity is achieved by its hermetic coating by nanothin inert silica films.