Antibacterial properties of green-synthesized noble metal nanoparticles

• Ag and Au nanoparticles were prepared by sputtering into propane-1,2,3-triol.
• Au nanoparticle size differed depending on the temperature of capturing media.
• Average Au nanoparticle diameter varied from 5 to 11 nm. Antibacterial properties of nanoparticles were tested against Escherichia coli and Staphylococcus epidermidis.
• Silver nanoparticles completely inhibited the growth of both pollutants.

We report on the antibacterial activity of noble metal nanoparticles prepared by direct sputtering into liquid medium (propane-1,2,3-triol). Silver and gold spherical nanoparticles with diameter of 4–6 nm (AgNP4–6, AuNP4–6) and gold spherical nanoparticles with diameter of 9–12 nm (AuNP8–12) were investigated. The possibility of managing nanoparticle diameter via controlling temperature of capturing media is also demonstrated. Nanoparticle size and shape were studied by transmission electron microscopy. Optical response of nanoparticle solutions was determined by UV–vis absorption spectroscopy. Antibacterial properties were tested against two common pollutants (Escherichia coli DBM 3138, a Gram-negative bacteria and Staphylococcus epidermidis DBM 3179, a Gram-positive bacteria). The cells (concentration of 11,000 cells ml−1) were incubated together with nanoparticles (concentration 0.8 mg ml−1). In the presence of silver nanoparticles the growth of E. coli and S. epidermidis was completely inhibited after 24 h. Any growth inhibition of E. coli was observed neither in the presence of smaller nor bigger gold nanoparticles during the whole experiment. Surprisingly, AuNP4–6, but not AuNP8–12 were able to inhibit the growth of S. epidermidis.