Controlled Release of Biologically Active Silver from Nanosilver Surfaces

Abstract

Major pathways in the antibacterial activity and eukaryotic toxicity of nano-silver involve the silver cation and its soluble complexes, which are well established thiol toxicants. Through these pathways, nano-silver behaves in analogy to a drug delivery system, in which the particle contains a concentrated inventory of an active species, the ion, which is transported to and released near biological target sites. Although the importance of silver ion in the biological response to nano-silver is widely recognized, the drug delivery paradigm has not been well developed for this system, and there is significant potential to improve nano-silver technologies through controlled release formulations. This article applies elements of the drug delivery paradigm to nano-silver dissolution and presents a systematic study of chemical concepts for controlled release. After presenting thermodynamic calculations of silver species partitioning in biological media, the rates of oxidative silver dissolution are measured for nanoparticles and macroscopic foils and used to derive unified area-based release kinetics. A variety of competing chemical approaches are demonstrated for controlling the ion release rate over four orders of magnitude. Release can be systematically slowed by thiol and citrate ligand binding, formation of sulfidic coatings, or the scavenging of peroxy-intermediates. Release can be accelerated by pre-oxidation or particle size reduction, while polymer coatings with complexation sites alter the release profile by storing and release inventories of surface-bound silver. Finally, the ability to tune biological activity is demonstrated through bacterial inhibition zone assay carried out on selected formulations of controlled release nano-silver.

Silver Release from Silver Nanoparticles in Natural Waters

“…This finding suggests a dominant effect of SA in determining Ag loss and confirms findings by other studies. 34 The permutation in the order of maximum Ag release as compared to the expected order (smaller particles release more) suggests that other unidentified factors could also play a role.…”

Antibacterial activity of silver nanoparticles: A surface science insight

“…For similar reasons, aggregated NPs expose less surface to the solvent than separated NPs, and thus possess a lower antibacterial impact [64]. While size of the NPs is a crucial parameter to determine their proper activity per unit of mass (or mole), it has been recently demonstrated by Liu et al [65] that the released Ag + scaled well if the sample were normalized by their exposed surface. Afterwards, Xiu et al [21] showed in 2012 that the significant parameters to evaluate the activity of silver nanoparticles were the silver released as Ag + and not the amount of elemental silver introduced as nanoparticle (Fig.…”

“…(ii) The second lever of control consists in improving the availability of the silver antibacterial species, by tuning the dissolution of the NPs. This aspect involves a control of the Ag NPs size, shape and coating [65]. It is also preferable to avoid surface passivation, formation of insoluble precipitates or aggregation of the NPs.…”

Screening Small Metabolites from Cells as Multifunctional Coatings Simultaneously Improves Nanomaterial Biocompatibility and Functionality

“…The zeta potential of nAg‐sorbitol (−28.2 ± 2.1 mV) was lower than that of nAg (−22.1 ± 1.5 mV) in a neutral environment (Figure 6b). The decrease in zeta potential suggested an increase in electronegative groups,35 that is, the coating of hydroxyls from d ‐sorbitol. In contrast, the presence of H + shielded the electronegativity of the hydroxyls, as shown by the higher zeta potential in an acid environment (−26.4 ± 0.5 mV) than in a neutral environment (−28.2 ± 2.1 mV).…”