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Title:

Negligible Particle-Specific Antibacterial Activity of Silver Nanoparticles

Date:

8/2012

Link to Journal Abstract

Abstract:

For nearly a decade, researchers have debated the mechanisms by which AgNPs exert toxicity to bacteria and other organisms. The most elusive question has been whether the AgNPs exert direct �particle-specific� effects beyond the known antimicrobial activity of released silver ions (Ag+). Here, we infer that Ag+ is the definitive molecular toxicant. We rule out direct particle-specific biological effects by showing the lack of toxicity of AgNPs when synthesized and tested under strictly anaerobic conditions that preclude Ag(0) oxidation and Ag+ release. Furthermore, we demonstrate that the toxicity of various AgNPs (PEG- or PVP- coated, of three different sizes each) accurately follows the dose�response pattern of E. coli exposed to Ag+ (added as AgNO3). Surprisingly, E. coli survival was stimulated by relatively low (sublethal) concentration of all tested AgNPs and AgNO3 (at 3�8 �g/L Ag+, or 12�31% of the minimum lethal concentration (MLC)), suggesting a hormetic response that would be counterproductive to antimicrobial applications. Overall, this work suggests that AgNP morphological properties known to affect antimicrobial activity are indirect effectors that primarily influence Ag+ release. Accordingly, antibacterial activity could be controlled (and environmental impacts could be mitigated) by modulating Ag+ release, possibly through manipulation of oxygen availability, particle size, shape, and/or type of coating.

Non-technical Summary:

This study determines the toxicity of silver nanoparticles (AgNPs) when synthesized and tested under strictly anaerobic conditions that preclude Ag(0) oxidation and Ag+ release to evaluate if AgNPs exert direct �particle-specific� effects beyond the known antimicrobial activity of released silver ions (Ag+).

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Peer Reviewed Journal Article

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