Synthesis of Nano-Silver Colloids and Their Anti- Microbial Effects

The antimicrobial effects of silver nanoparticles were studied. Silver nanoparticles were synthesized through wet chemistry method, and were dispersed in an aqueous suspension. With nanoscale silica particles serving as heterogeneous nucleation sites, silver nanoparticles were formed on the silica surface. Suspensions were found to be stable at high silver concentrations as well as over a broad pH range. By varying the processing conditions, the diameter of the silver nanoparticles could be controlled between ~2 nm to ~25 nm. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to reveal the formation and the corresponding morphology of the silver-silica coupling nanoparticles. Ultra-violet visible (UV-vis) scanning spectrophotoscopy was used to detect the distinct absorption spectrum of silver nanoparticles. The antimicrobial activities of these silver-silica coupling nanoparticles were investigated. E. coli and S aureus were used as representatives of Gram-negative and Gram-positive bacteria, respectively. Bacteriological tests showed either bacterial growth inhibition or cell death occurred, depending on the concentration of silver nanoparticles and the type of bacteria. Fluorescent microscopic images were also obtained to confirm the bacterial toxicity after exposure for several hours to silver nanoparticles.