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BioMed Research International
Volume 2013 (2013), Article ID 819252, 9 pages
http://dx.doi.org/10.1155/2013/819252
Research Article

Dissolution of Silver Nanowires and Nanospheres Dictates Their Toxicity to Escherichia coli

1Institute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia
2Estonian Nanotechnology Competence Center, Riia 142, 51014 Tartu, Estonia
3Laboratory of Environmental Toxicology, National Institute of Chemical Physics and Biophysics, Akadeemia 23, 12618 Tallinn, Estonia
4Department of Chemistry, Tallinn University of Technology, Akadeemia 15, 12618 Tallinn, Estonia

Received 30 April 2013; Revised 1 July 2013; Accepted 8 July 2013

Academic Editor: Muthuswamy Sathishkumar

Copyright © 2013 Meeri Visnapuu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Silver nanoparticles are extensively used in antibacterial applications. However, the mechanisms of their antibacterial action are not yet fully explored. We studied the solubility-driven toxicity of  nm (mean primary diameter × length) silver nanowires (NWs) to recombinant bioluminescent Escherichia coli as a target representative of enteric pathogens. The bacteria were exposed to silver nanostructures in water to exclude the speciation-driven alterations. Spherical silver nanoparticles (83 nm mean primary size) were used as a control for the effect of NPs shape. Toxicity of both Ag NWs and spheres to E. coli was observed at similar nominal concentrations: the 4h EC50 values, calculated on the basis of inhibition of bacterial bioluminescence, were 0.42 ± 0.06 and 0.68 ± 0.01 mg Ag/L, respectively. Dissolution and bioavailability of Ag from NWs and nanospheres, analyzed with AAS or Ag-sensor bacteria, respectively, suggested that the toxic effects were caused by solubilized Ag+ ions. Moreover, the antibacterial activities of Ag NWs suspension and its ultracentrifuged particle-free supernatant were equal. The latter indicated that the toxic effects of ~80–100 nm Ag nanostructures to Escherichia coli were solely dependent on their dissolution and no shape-induced/related effects were observed. Yet, additional nanospecific effects could come into play in case of smaller nanosilver particles.