Discriminating the states of matter in metallic nanoparticle transformations: What are we missing?
John M. Pettibone, Julien C. Gigault, Vincent A. Hackley
A limiting factor in assessing the risk of current and emerging nanomaterials in biological and environmental systems is the ability to accurately detect and characterize their size, shape and composition in broad distributions and complex media. Asymmetric flow field-flow fractionation (A4F) is capable of softer separation without stationary phase interactions or large applied forces, but metallic nanoparticle separation below 10 nm was thought to be intractable with A4F. We demonstrate that metallic nanoclusters with core diameters near 1 nm can be selectively separated with high resolution. We apply the current methods to compare and characterize the products in a model system, poly(N-vinyl-2-pyrrolidone)-protected, silver nanoparticles and excess glutathione a ubiquitous tripeptide. Monitoring the temporal evolution, we observed the formation and persistence of a continuum of matter states (e.g., Ag+, nanoclusters and nanoparticles). The data suggest the current methodology provides an opportunity to reassess a broad range of metal nanoparticle transformations, including rates of processing, in more relevant biological and environmental systems.