(485b) Origin, Cure and Control of Nanosilver Toxicity

Nanosilver is considered the most commonly used engineered nanomaterial, for example, in antibacterial textiles, polymer films for food packaging, paints and pigments, filters for water or air treatment to name a few applications (1).  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 closely 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 (2). 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 either washing or H₂ reduction, the oxide layers are removed, drastically minimizing Ag⁺ ion leaching and its antibacterial activity against E. coli. That way the bactericidal activity of nanosilver is confined to contact with its surface rather than to rampant ions. This leads to silver nanoparticles 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.

1. G.A. Sotiriou, S.E. Pratsinis, “Engineering nanosilver as an antibacterial, biosensor and bioimaging material”, Curr. Opinion Chem. Eng. 1, 3-10 (2011)

2. G.A. Sotiriou, A. Meyer, J.T.N. Knijnenburg S. Panke, S.E. Pratsinis, “Quantifying the origin of nanosilver ions and their antibacterial activity”, Langmuir, 28, 15929–15936 (2012).