Simulations of morphological transformation in silver nanoparticles as a tool for assessing their reactivity and potential toxicity

Concerns about the safety of engineered nanomaterials have not yet been addressed in a systematic way, despite many years of nanotoxicology research. Here we present a computational approach that allows predictions of nanomaterial reactivity as an indicator for toxicity; the approach is powerful, as it is based on fundamental structural criteria, but we also demonstrate that predictions from the simulations fit well with experimentally observed nanoparticle behaviour. Using molecular dynamic simulations, the study predicts surface structures and energetics of silver nanoparticles (AgNPs), which enable an assessment of the impact of water molecules on the surface transformation of AgNPs; the latter controls their behaviour in aqueous media and ultimately their transport, fate, and toxicity. The work shows that size exerts an important control on reactivity and likely also toxicity, a concept proposed at the start of the nanotoxicology debate, but never demonstrated at the smaller end of the nanoscale, or at a systematically resolved range of sizes. A key observation is that experimentally imperceptible differences in size may stabilise structures with hugely different reactivities. We build our framework using AgNPs, but stipulate this can be easily extended to other NP structures and chemistries and expanded to include interactions with biomolecules.