(627d) Leaching Rate of Silver Ions from Engineered Nanosilver

Nanosilver is the third largest nanomaterial today and is used extensively into consumer products, including socks, food containers, bandages, and cosmetics. In addition, it exhibits remarkable antibacterial activity and strong plasmonic performance. Yet, there are growing concerns about the adverse effects of nanosilver on human health and the environment. Even though silver metal is not soluble in water, nanosilver particles of less than 10 nm release silver ions from the particle (leaching) into aquatic environments. This silver ion leaching is associated with nanosilver toxicity. However, the precise effect of nanosilver characteristics on silver leaching and the underlying mechanisms for toxicity are poorly understood.

Here, the mechanisms of silver ion release from nanosilver particles and their leaching rate is studied by reactive Molecular Dynamics simulations. Specifically, the effect of particle characteristics (size, crystallinity, specific surface area) and environmental conditions (temperature, concentration) on the leaching rate of nanosilver is quantified. Figure 1 shows the fraction of silver ions in nanosilver particles as function of particle size obtained by reactive molecular dynamics simulations (circles). The results are in excellent agreement with experiments of flame- and wet-made nanosilver (triangles) in aqueous suspensions. For comparison, the estimated silver ion fractions assuming one (squares) and two (diamonds) silver oxide layers are shown.Small nanosilver particles (with diameter of 3 – 4 nm) exhibit a large fraction of silver ions, present in the form of silver oxide at the particle surface. This fraction corresponds to a double layer of silver oxide. In contrast, larger nanosilver (7 – 8 nm) exhibit a smaller fraction of silver ions (corresponding to a single layer), consistent with experiments (Sotiriou et al., 2012).

The employed reactive molecular dynamics simulations are used, for the first time, to quantify the nanosilver oxidation rate and ion release rate from the particle surface in aqueous solutions that are responsible for the nanosilver toxic manifestations. Understanding the mechanism of silver ion release rate from nanosilver particles will determine their environmental fate and adverse effects on human health. Minimising these release rates will also enable the expanded use of silver nanoparticles and their nanocomposites as bioimaging materials or plasmonic biosensors.

References

Sotiriou, G. A., Meyer, A., Knijnenburg, J. T., Panke, S., & Pratsinis, S. E. (2012). Quantifying the origin of released Ag+ ions from nanosilver. Langmuir, 28(45), 15929-15936.