(190p) Nanosilver: Exposed Surface Area and Antibacterial Activity

Nanosilver is one of the first nanomaterials to be closely monitored by regulatory agencies worldwide. Here, nanosilver was immobilized on nanostructured silica particles upon its flame synthesis. These stable Ag/SiO₂ nanoparticles had closely controlled Ag-content and size and were free from artifacts arising typically from flocculation in bacterial suspensions. The nanosilver toxicity against the Gram negative bacteria Escherichia coli was investigated by monitoring their recombinantly synthesized green fluorescent protein. Suspensions with identical Ag mass concentration exhibited drastically different antibacterial activity. It is discovered, for the first time to our knowledge, that over a wide range of particle sizes, concentrations and Ag contents, the antibacterial activity of nanosilver is determined by its exposed surface area concentration (as determined by O₂ chemisorption) rather than its mass or molar concentration. It is shown that this holds also for a number of literature studies when their Ag mass concentration is converted to surface area concentration.