(458f) Universal Correlation and Mechanism for the Antibacterial Activity of Ag Nanoparticles

Uncoated and SiO₂-coated Ag/SiO₂ nanoparticles were made by flame spray pyrolysis (FSP) of a Ag nitrate and hexamethyldisiloxane (HMDSO) containing solution. The product particles were characterized by STEM/TEM, EDX spectroscopy, X-ray diffraction, N₂ absorption (BET) and O₂ chemisorption. The Ag clusters exhibited a bimodal distribution as determined by microscopy and XRD. The conductivity of aqueous solutions containing the uncoated Ag/SiO₂ nanoparticles was measured as well as their antibacterial activity against the Gram negative bacterium Escherichia coli. Low Ag-content particles had more exposed Ag surface area. The antibacterial performance of Ag/SiO₂ nanoparticles was determined solely by the exposed Ag surface area in the solution over a wide range of particle concentrations and Ag-content. Additionally, by hermetically coating the Ag nanoparticles by a SiO₂ layer, inhibition of the antibacterial activity can be established. Finally, Ag ions rather than Ag nanoparticles determine the antibacterial performance of the Ag/SiO₂ nanoparticles, as it was shown by monitoring bacterial growths in solutions containing similar Ag⁺ ions concentrations, in the presence and absence of Ag nanoparticles.