Silver nanoparticles: partial oxidation and antibacterial activities

Abstract

The physical and chemical properties of silver nanoparticles that are responsible for their antimicrobial activities have been studied with spherical silver nanoparticles (average diameter approximately 9 nm) synthesized by the borohydride reduction of Ag+ ions, in relation to their sensitivity to oxidation, activities towards silver-resistant bacteria, size-dependent activities, and dispersal in electrolytic solutions. Partially (surface) oxidized silver nanoparticles have antibacterial activities, but zero-valent nanoparticles do not. The levels of chemisorbed Ag+ that form on the particle's surface, as revealed by changes in the surface plasmon resonance absorption during oxidation and reduction, correlate well with the observed antibacterial activities. Silver nanoparticles, like Ag+ in the form of AgNO3 solution, are tolerated by the bacteria strains resistant to Ag+. The antibacterial activities of silver nanoparticles are related to their size, with the smaller particles having higher activities on the basis of equivalent silver mass content. The silver nanoparticles aggregate in media with a high electrolyte content, resulting in a loss of antibacterial activities. However, complexation with albumin can stabilize the silver nanoparticles against aggregation, leading to a retention of the antibacterial activities. Taken together, the results show that the antibacterial activities of silver nanoparticles are dependent on chemisorbed Ag+, which is readily formed owing to extreme sensitivity to oxygen. The antibacterial activities of silver nanoparticles are dependent on optimally displayed oxidized surfaces, which are present in well-dispersed suspensions.

Binding of Silver Nanoparticles to Bacterial Proteins Depends on Surface Modifications and Inhibits Enzymatic Activity

“…This hypothesis has been corroborated by the observations that factors influencing nanoparticle surface reactivity, including size (9,14) and shape (15), influence AgNP toxicity. One proposed mechanism to explain how the AgNP surface can be seemingly more toxic than free Ag + ions is that large amounts of surfaceassociated Ag 0 are oxidized after attachment of AgNPs to biomolecules on the cell, which induces AgNP dissolution (12,14). Because of the targeted delivery of Ag + ions in close proximity to, and possibly inside, the cell, the bulk silver concentration needed to exceed the lethal limit is significantly lower in the case of AgNPs (11).…”

Silver Release from Silver Nanoparticles in Natural Waters

“…In most cases, we observed a rapid loss of Ag at the first time point after deployment, which suggests a rapid initial loss rate (Figures 1−3). We explored two hypotheses to account for that initial loss: (1) an oxidative dissolution process with O 2 as the oxidant as described by Liu et al 12 or (2) the release of chemisorbed Ag + as described by Lok et al 5 The first hypothesis was explored by carrying out Ag release experiments with gel pucks embedded with 5 and 50 nm PVPcoated AgNPs in oxic or anoxic 0.22 μm prefiltered R1 water. After 5 min of exposure, approximately 30% of Ag is lost from 5 nm AgNP gel pucks regardless of the oxygen content of the solution ( Figure 5).…”

Scalable and Environmentally Benign Process for Smart Textile Nanofinishing

“…Both enhanced adhesion and a large exposed surface can thus be achieved by making the particles small. 54 Deposition of NPs deeper within the textiles, which should also reduce their release during mechanical washing, can be achieved by simply increasing the quenching gas flow rate Q q as indicated by equation (1) (cf. Figure S5).…”