2D analysis of polydisperse core–shell nanoparticles using analytical ultracentrifugation

Abstract

Accurate knowledge of size, density and composition of nanoparticles (NPs) is of major importance for their applications. In this work the hydrodynamic characterization of polydisperse core-shell NPs by means of analytical ultracentrifugation (AUC) is addressed. AUC is one of the most accurate techniques for the characterization of NPs in the liquid phase because it can resolve particle size distributions (PSDs) with unrivaled resolution and detail. Small NPs have to be considered as core-shell systems when dispersed in a liquid since a solvation layer and stabilizer shell will significantly contribute to the particle’s hydrodynamic diameter and effective density. AUC measures the sedimentation and diffusion transport of the analytes, which are affected by the core-shell compositional properties. This work demonstrates that polydisperse and thus widely distributed NPs pose significant challenges for current state-of-the-art data evaluation methods. Existing methods either have insufficient resolution or do not correctly reproduce the core-shell properties. First, we investigate the performance of different data evaluation models by means of simulated data. Then, we propose a new methodology to address the core-shell properties of NPs. This method is based on the parametrically constrained spectrum analysis and offers complete access to the size and effective density of polydisperse NPs. Our study is complemented using experimental data derived for ZnO and CuInS2 NPs, which do not have a monodisperse PSD. For the first time, the size and effective density of such structures can be resolved with high resolution by means of a two-dimensional AUC analysis approach.

Determination of the two-dimensional distributions of gold nanorods by multiwavelength analytical ultracentrifugation

“…In a prior study 51 , we presented a comparison of AUC measurements with SAXS/SANS measurements, wherein the results confirmed that the shell thickness around nanoparticles can reliably be determined by AUC. The results obtained for the gold nanorods are similar to values found in literature 21 , 52 – 54 .…”

“…However, this approach is extremely time-consuming since several thousand particles must be analyzed for proper statistical analysis. Among the few published data sets are mass-mobility diameter distributions measured by scanning mobility analysis 23 and in particular, data obtained from 2D AUC analysis for size and density 24 , 25 . In the recent past, analysis of sedimentation and optical properties using AUC equipped with multiwavelength detector has been successfully implemented for spherical nanoparticles 26 , 27 .…”

Practical Aspects of Multiwavelength Analytical Ultracentrifugation

“…The complexity of the hardware has limited the implementation of the instruments to a few laboratories. The details of results that may be achieved with MWL-AUC have been described previously for a diverse array of sample types and investigative questions [5][6][7]14,28,30,[33][34][35][36]. However, previous publications documenting the performance of MWL-AUC have provided only cursory descriptions of the requirements to build and operate a complete system.…”

“…The very low polydispersity, well-defined molecular weights, and good density estimation of proteins, allow precise extraction of additional molecular properties such oligomeric states, trace aggregates, or modeling interactions. Many types of nanoparticles, such as core-shell semiconductors, will sediment within a similar size regime, but will include a higher degree of polydispersity [7]. The choice of rotor speed must be carefully considered and can impose a large influence on the quality of the analysis.…”

“…This manuscript provides additional details that have not yet been described or were more recently adapted, but have proven essential to producing high quality measurements from the instrument. We hope to present a realistic portrayal of the challenges a researcher faces when considering implementing one of these systems in their own laboratory, in addition to many of the critical aspects of the installation that we have found necessary for successful instrument operation demonstrated in past publications [2,[6][7][8]. This includes a description of the necessary tools and expertise to build and install the detector, followed by a protocol for alignment and calibration.…”