Enhanced antibacterial activity of bimetallic gold-silver core-shell nanoparticles at low silver concentrationElectronic supplementary information (ESI) available. See DOI: 10.1039/c1nr10703h

Herein we report the development of bimetallic Au@Ag core-shell nanoparticles (NPs) where gold nanoparticles (Au NPs) served as the seeds for continuous deposition of silver atoms on its surface. The core-shell structure and morphology were examined by UV-Vis spectroscopy, transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis and X-ray diffraction (XRD). The core-shell NPs showed antibacterial activity against both Gram negative ( Escherichia coli and Pseudomonas aeruginosa ) and Gram positive ( Enterococcus faecalis and Pediococcus acidilactici ) bacteria at low concentration of silver present in the shell, with more efficacy against Gram negative bacteria. TEM and flow cytometric studies showed that the core-shell NPs attached to the bacterial surface and caused membrane damage leading to cell death. The enhanced antibacterial properties of Au@Ag core-shell NPs was possibly due to the more active silver atoms in the shell surrounding gold core due to high surface free energy of the surface Ag atoms owing to shell thinness in the bimetallic NP structure. Au@Ag core-shell nanoparticles annihilate bacteria more efficiently than Ag nanoparticles for the same amount of silver.