Quantifying the Origin of Nanosilver Ions and Their Antibacterial Activity

Nanosilver is one of the most prominent components in several nanotechnology products, primarily for its bactericidal and plasmonic properties [1,2]. Its use, however, is questioned as U.S. EPA has been petitioned to label it as pesticide. To better understand its antibacterial activity, nanosilver with closely controlled size immobilized on nanostructured silica is generated by flame aerosol technology [3]. The antibacterial activity of small (<10 nm) nanosilver particles is attributed mostly to released Ag⁺ ions from their surface upon contact with water [1]. The origin of these ions is explored systematically now by conditioning the surface of various nanosilver particles (4-9 nm) immobilized on nanostructured silica by wet-impregnation and dry flame-spray pyrolysis. Silica prevents nanosilver flocculation without the need of any surface functionalization (e.g. citrate) that would compromise the Ag⁺ ion release kinetics. Washing or reducing the Ag/SiO₂ nanoparticles removes the oxide layer from the nanosilver surface minimizing their ion leaching. The amount of leached Ag⁺ ions corresponds to the dissolution of one or two silver oxide monolayers. Finally, the antibacterial activity of small (< 10 nm) nanosilver particles that have their surface oxide layer removed or reduced is significantly lower than the freshly prepared ones by either wet or dry methods.

1. Sotiriou, G. A.; Pratsinis, S. E., Antibacterial activity of nanosilver ions and particles. Environ. Sci. Technol. 2010, 44, 5649.

2. Sotiriou, G. A.; Sannomiya, T.; Teleki, A.; Krumeich, F.; Vörös, J.; Pratsinis, S. E., Non-Toxic Dry-Coated Nanosilver for Plasmonic Biosensors. Adv. Funct. Mater. 2010, 20, 4250.

3. Sotiriou, G. A.; Teleki, A.; Camenzind, A.; Krumeich, F.; Meyer, A.; Panke, S.; Pratsinis, S. E. Nanosilver on nanostructured silica: Antibacterial activity and Ag surface area. Chem. Eng. J. 2011, 170, 547.