Size-selective silver nanoparticles: future of biomedical devices with enhanced bactericidal properties

Silver nanoparticles (AgNPs) are attracting attention due to their bactericidal activity and consequent possible biomedical applications. The key to their broad-acting and potent biocidal property seems to be based on the size-related mechanism by which AgNPs act on different bacteria strains. Here, we report the synthesis and successful size-selective fractionation of AgNPs obtained through chemical reduction of silver nitrate in ethylene glycol using polyvinylpyrrolidone as a protective agent. A combination of characterization techniques (UV-vis spectroscopy, transmission electron microscopy and small-angle X-ray scattering) is employed to differentiate the two size-fractionated samples. From the analyses, it is evidenced that AgNPs are mainly spherical and have their radius centered at similar to 8.5 and similar to 11.0 nm. The nanoparticles bactericidal efficacy is investigated using the disk diffusion test against Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis and Micrococcus lysodeikticus. Although both fractionated samples present bactericidal activity against all four tested bacteria (one Gram negative and three Gram positives), those presenting smaller size own enhanced antibacterial properties.