Antibacterial efficacy of silver nanoparticles of different sizes, surface conditions and synthesis methods

Abstract

Silver nanoparticles (Ag-nps) are used as a natural biocide to prevent undesired bacterial growth in clothing and cosmetics. The objective of this study was to assess the antibacterial efficacy of Ag-nps of different sizes, surface conditions, and synthesis methods against Escherichia coli, Ag-resistant E. coli, Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), and Salmonella sp. Ag-nps samples were synthesized by: Base reduction with unmodified surfaces and used as synthesized (‘unwashed’; 20, 50 and 80 nm) or after 20 phosphate buffer washes (‘washed’; 20, 50 and 80 nm), or synthesized by laser ablation with carbon-stabilized surfaces (‘carbon-coated’; 25 and 35 nm). Unwashed Ag-nps were toxic to all bacterial strains at concentrations between 3.0–8.0 μg/ml. The washed Ag-nps and carbon-coated Ag-nps were toxic to all bacterial strains except Ag-resistant E. coli at concentrations between 64.0–1024.0 μg/ml. Ag-resistant E. coli died only when treated with unwashed Ag-nps or its supernatant, both of which contained formaldehyde.

Keywords::

• Silver
• nanoparticles
• nanotechnology
• nanotoxicity
• microbiology

Acknowledgements

This research was presented at the 49th annual meeting of the Society of Toxicology at Salt Lake City, Utah, on 10 March 2010. The authors would like to thank Dr Anne Summers of the University of Georgia for donation of Escherichia coli J53 and E. coli J53(pMG101), Megan Fauls of North Carolina State University for donation of Methicillin-Resistant Staphylococcus aureus and Salmonella sp., Mitsu Suyemoto of North Carolina State University for technical assistance and Dr Steven Oldenburg of NanoComposix for provision of Ag-nps.

Declaration of interest : This research was partially supported by the United States Air Force Office of Scientific Research (USAFOSR) grant no. FA 9950-08-1-0182. The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.