(380y) Characterization of Nanoparticle Size Distributions and Aspect Ratio through Single-Particle Tracking and Analytical Ultracentrifugation

Colloidal dispersions of nanoparticles have been a focus of recent study due to their unique properties and potential applications. However, a varying degree of polydispersity is inevitable in most non-ideal systems where the nanoparticles are derived from natural sources or top-down methods. Combined with the fact that colloidal dispersions are inherently unstable and are also sensitive to environmental influences, the characterization these materials with respect to the evolution of their size distributions should be routine for their biological applications.

The most commonly employed methods in the literature, such as dynamic light scattering, only estimate the first or second moment of narrow distributions. In this contribution, we leverage single-particle tracking (SPT) to evaluate the sample preparation and purification of single-walled carbon nanotubes (SWCNT) and graphene oxide (GOx). Noncovalent conjugations of SWCNT with DNA and sodium dodecyl sulfate (SDS) were studied due to their differences in surface coverage and dispersion protocol. Changes in particle hydrodynamic size distribution with varying degrees of centrifugation were monitored. The SPT data collection and processing were optimized for adequate sampling and noise cutoff. Comparison of samples of increasing centrifugation duration show overall left shift of distribution toward smaller sizes. Analytical ultracentrifugation (AUC) on a similar set of samples show a corresponding decrease in particles of large sedimentation coefficients.

The two analytical techniques provide independent sets of information including the aspect ratio of the particles via the frictional coefficient, which for SWCNT and GOx can be modeled as simple geometric shapes with two dimensional parameters. Thus, for the highly centrifuged relatively monodisperse samples, we were able extract additional information through the combination of the AUC and SPT to provide reasonable estimates of particle hydrodynamic dimensions.