Sulfidation of Silver Nanoparticles Decreases Escherichia coli Growth Inhibition

Abstract

Sulfidation of metallic nanoparticles such as silver nanoparticles (AgNPs) released to the environment may be an important detoxification mechanism. Two types of AgNPs-an engineered polydisperse and aggregated AgNP powder, and a laboratory-synthesized, relatively monodisperse AgNP aqueous dispersion-were studied. The particles were sulfidized to varying degrees and characterized to determine the effect of initial AgNP polydispersity and aggregation state on AgNP sulfidation, and then exposed to Escherichia coli to determine if the degree of sulfidation of pristine AgNPs affects growth inhibition of bacteria. The extent of sulfidation was found to depend on the HS(-)/Ag ratio. However, for the same reaction times, the more monodisperse particles were fully transformed to Ag(2)S, and the polydisperse, aggregated particles were not fully sulfidized, thus preserving the toxic potential of Ag(0) in the aggregates. A higher Ag(2)S:Ag(0) ratio in the sulfidized nanoparticles resulted in less growth inhibition of E. coli over 6 h of exposure. These results suggest that the initial properties of AgNPs can affect sulfidation products, which in turn affect microbial growth inhibition, and that these properties should be considered in assessing the environmental impact of AgNPs.

Rethinking Stability of Silver Sulfide Nanoparticles (Ag2S-NPs) in the Aquatic Environment: Photoinduced Transformation of Ag2S-NPs in the Presence of Fe(III)

“…Also, DOM and DO showed negligible effects on the stability of Ag 2 S-NPs in the light or dark ( Figure S1b of the Supporting Information and Figure 1c). All of these evidently suggest that Ag 2 S-NPs are relatively stable in the aquatic environment, being well consistent with the findings in previous studies, which presented negligible dissolution of Ag 2 S-NPs in either bacteria culture media (5 mM bicarbonate, with pH adjusted to 7 by HCl) within 6 h or 10 mM NaNO 3 aqueous solution at pH 7 within 720 h. 18,25 However, significant changes in dissolution of Ag 2 S-NPs were observed in the presence of Fe 3+ under the light condition ( Figure S1d of the Supporting Information). This finding indicates that stability of Ag 2 S-NPs in aqueous solution may be overestimated in past studies, suggesting that light and Fe 3+ may be key factors to influence the Ag 2 S-NP stability in an aqueous system.…”

“…18 In brief, at each time interval (0, 4,8,18,28,48,72, and 96 h), 4 mL of aqueous sample was taken from each quartz glass bottle. Every 4 mL of solution was then divided into two subsamples: one group of subsamples (1 mL) was characterized by DLS and TEM or HRTEM−EDX.…”

Antibacterial activity of silver nanoparticles: A surface science insight

“…The toxicity reduction has thus been associated to the formation of an insoluble precipitate that scavenges most of the Ag + ions from the solution and hence lowers their availability and action. Presence of sulfides is one of the most notable cases, due to the very low solubility of Ag 2 S. Several studies showed that presence of traces of this ion almost suppressed the biocidal activity of silver containing-systems, as seen in Fig. 2A [57][58][59]. Furthermore, both Reinsch et al [58] and Levard et al [59] showed an inhibition of the effect for S 2− /Ag molar ratio below 0.5 (which corresponds to the stoichiometric conditions).…”

“…Presence of sulfides is one of the most notable cases, due to the very low solubility of Ag 2 S. Several studies showed that presence of traces of this ion almost suppressed the biocidal activity of silver containing-systems, as seen in Fig. 2A [57][58][59]. Furthermore, both Reinsch et al [58] and Levard et al [59] showed an inhibition of the effect for S 2− /Ag molar ratio below 0.5 (which corresponds to the stoichiometric conditions). This was explained by the formation of an insoluble Ag 2 S layer around the Ag NPs, preventing further dissolution and hence activity.…”

Magnetic sulfide-modified nanoscale zerovalent iron (S-nZVI) for dissolved metal ion removal

“…Sulfidation may decrease the toxicity of nZVI as seen in other nanoparticles (e.g. silver, (Reinsch et al, 2012)). Also, Kim et al find nZVI coated with CdS exhibits limited toxicity to Escherichia coli.…”