Probing metal nanoparticles and assemblies with analytical ultracentrifugation

Abstract

Analytical Ultracentrifugation (AUC) is a powerful tool to obtain statistically relevant size and shape measurements for macromolecular systems. Metal nanoparticles coated by a ligand shell of thiolated molecules provide diverse functionality, from targeted cellular delivery to the formation of complex assemblies. Here I show that AUC can be used to determine particle size distribution, ligand shell density, shape, and hydrodynamic radius. It can also be used to probe complex mixtures of nanoparticle assemblies, from 2D dimers and chains, to 3D trimers, tetramers, and higher order assemblies, from a consideration of their hydrodynamic shape factor and its relation to the sedimentation coefficient. With AUC, the ease of sample preparation, ligand shell information, and dramatic increase in sample size are improvements compared with electron microscopy, and the ability to probe multiple, discrete absorbing wavelengths and globally analyze with interference information offers a measured improvement compared with dynamic light scattering (DLS). This work describes multiple calibrations and considerations as well as theoretical contributions concerning the application of AUC to nanoparticle systems