Green synthesis of colloidal silver nanoparticles through electrochemical method and their antibacterial activity

•Colloidal AgNPs were greenly synthesized at room temperature, in a single process.•The size of AgNPs was 19.7 ± 4.3 nm with nearly spherical shape and high purity.•AgNPs had high antibacterial activity against Gram-positive and -negative bacteria.•The materials, power and cost were inexpensive.

This paper presents a facile, and ecofriendly method to prepare colloidal silver nanoparticles (AgNPs) at room temperature using bulk silver bars, bi-distilled water, trisodium citrate, and a direct-current voltage source. AgNP formation was confirmed and characterized by ultraviolet–visible spectroscopy, transmission electron microscopy and X-ray diffraction. Their antibacterial activity was examined by disc diffusion and minimum inhibitory concentration (MIC) techniques against three bacterial strains, including the Gram-positive bacteria Staphylococcus aureus and the Gram-negative bacteria Escherichia coli and Pseudomonas aeruginosa. Results showed that the size of AgNPs formed was about 19.7±4.3 nm with nearly spherical shape and high purity. The antibacterial activity of as-prepared AgNPs was determined through zones of inhibition against the growth of three bacterial strains on agar. MIC analysis showed that S. aureus had resistance to AgNPs that was about 2–3 times higher than those of E. coli and P. aeruginosa, and that resistance ability depended on the bacterial concentrations inoculated. This work revealed the effective method of synthesizing a large quantity of colloidal AgNPs with high antibacterial effectiveness and potential application in different fields.