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Negligible Particle-Specific Antibacterial Activity of Silver Nanoparticles
Link to Journal 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 ìg/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.
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+).
Peer Reviewed Journal Article
Exposure Or Hazard Target
Method Of Study
Risk Exposure Group
Nano Letters, 2012, 12(8): 4271-4275
Xiu ZM, Zhang QB, Puppala HL, Colvin VL, Alvarez PJJ
Last updated on October 29, 2012
This work is supported in part by the Nanoscale Science and Engineering Initiative of the National Science Foundation
under NSF Award Number EEC-0118007.
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