Silver Nanoparticle−Reactive Oxygen Species Interactions: Application of a Charging−Discharging Model

Abstract

The silver-nanoparticle-catalyzed decomposition of hydrogen peroxide (H2O2) in pH 9.5 bicarbonate buffer is investigated here with attention given to (i) the mechanism of decomposition, (ii) the role of superoxide in mediating silver nanoparticle re-formation, and (iii) the effect of nanoparticle size on decomposition rate. Silver nanoparticles (AgNPs) of average size between 25.0 and 69.4 nm were synthesized via the reduction of Ag+ [the dominant Ag(I) species present] by photochemically produced superoxide at pH 9.5 and characterized by UV−visible spectroscopy and dynamic light scattering. The ability of these particles to catalytically decompose H2O2 was examined by measuring the decay of H2O2 and the approach to steady state in AgNP and Ag+ concentrations. Additionally, the generation of superoxide on reaction of AgNPs with H2O2 was monitored using a chemiluminescence-based method. The second-order rate constants for reaction between AgNPs and H2O2 correlated linearly with their average particle size ranging from 35.0 to 3.0 × 102 M−1 s−1 for average sizes between 69.4 and 25.0 nm. A sensitive trap-and-trigger chemiluminescence-based method for hydroxyl radical detection showed no evidence for the presence of hydroxyl radicals, though an inhibitory effect of tert-butyl alcohol suggested the presence of a strongly oxidizing species. A process involving the superoxide-mediated charging of silver nanoparticles with subsequent discharge by reaction with oxygen and Ag+ leading to regeneration of Ag0 and superoxide is proposed to account for the results obtained.

Hierarchical nanostructures of Au@ZnO: antibacterial and antibiofilm agent

“…Most of the Gram-negative organisms, including E. coli, possess an extra outermost layer made up of lipopolysaccharide and thus may restrict the damage to cell membrane of organisms (Wagh et al 2013). The antibacterial action of Au@ZnO nanostructures can be explained in the light of following four most common reported mechanisms: (1) the uptake of free Ag ions followed by the disruption of ATP production and DNA replication (Chernousova and Epple 2013), (2) the charging-discharging model for superoxide-mediated generation of reactive oxygen species (ROS) (He et al 2011), (3) the Ag NPs and Ag ions generation of ROS (Xu et al 2012), and (4) the Ag nanoparticles direct damage to the cell membranes (Gholap et al 2013;Panmand et al 2014). In our previous study (Patil et al 2015;Patil et al 2014), we have shown that ZnO nanostructures act on microbial cells by generating ROS on cellular membrane, which virtually oxidizes every cellular components and thus ruptures the cell wall.…”

Kinetic Modeling of the Electro-Fenton Process: Quantification of Reactive Oxygen Species Generation

“…The fluorescence of the sample was measured in a Cary Eclipse spectrophotometer using settings described previously [28,29]. For H 2 O 2 quantification, a calibration curve encompassing H 2 O 2 concentrations over the range of 75-600 nM was obtained.…”

Transport of silver nanoparticles in intact columns of calcareous soils: The role of flow conditions and soil texture

“…Discharged nanoparticles (NPs) find their way into the soils during their manufacturing, transportation, application, and disposal (Pachapur et al, 2016), and soils and aquifers act as primary filter systems to remove particulate materials from percolating water and protect water resources (Kasel et al, 2013a;Liang et al, 2013a). Many previous studies have shown the negative effects of AgNPs on human health and the environment (e.g., He et al, 2011;Carbone et al, 2014). Hence, a detailed understanding of the processes governing the transport and retention of AgNPs in soil is required to accurately assess the fate and distribution of AgNPs and to design effective strategies for reducing their toxicity in the environment.…”