Synthesis of colloidal silver nanoparticles and their bactericidal effects on E. coli, S. epidermidis and oral plaque

Silver nanoparticles have been obtained by colloidal synthesis using two different reducing agents: ascorbic acid and ethylene glycol. The colloids have been characterized by UV-Vis Spectroscopy, atomic absorption and transmission electron microscopy (TEM). The UV-visible spectra show the typical peak with a maximum ranging between 390-420 nm, due to the plasmon resonance of spherical silver nanoparticles. TEM micrographs show non-aggregated spherical silver nanoparticles whit diameters between 30 and 50 nm. The antibacterial effect was tested in three different bacteria cultures: Escherichia coli (gram negative), Staphylococcus epidermidis (gram positive) and dental plaque, which were grown in Mueller-Hinton agar. For comparative purposes the bactericidal effect of silver nitrate was also evaluated. Inhibition index (IIC) was calculated, obtaining satisfactory results for the three kinds of microorganism when silver nanoparticles are used.