Aggregation Kinetics of Colloidal Particles Measured by Gas-Phase Differential Mobility Analysis

Abstract

We demonstrate the utility of electrospray gas-phase ion-mobility analysis as a new method to investigate nanoparticle flocculation, or aggregation. Au nanoparticle (Au-NP) solutions were sampled via electrospray (ES), followed by differential ion-mobility analysis (DMA) to determine the particle mobility distribution. Multimodal size distributions obtained with ES-DMA indicated the presence of single Au-NPs (monomer) as well as larger Au-NP clusters such as dimers, trimers, and tetramers under specific solution conditions. The fraction of each aggregate species as a function of time was quantitatively characterized, from which the degree of aggregation, aggregation rate, and stability ratio at different ionic strengths were determined. The latter enabled the extraction of a surface potential (or surface charge density) of 64 +/- 2 mV for 10 nm Au-NPs, which is in good agreement with values obtained from other methods, thus validating our approach. Our results show that ES-DMA is a valuable tool for quantitatively probing the early stages of colloidal aggregation or as a preparatory tool for the size election of aggregates.

Electrospray–differential mobility analysis of bionanoparticles

“…This investigation suggested that both volume based and area based approaches are not accurate as ligands can change conformation and adsorb in multiple layers on different bionanoparticles. [15,143]. In addition, viruses can be identified based on particle size, thereby ruling out contaminating adventitious agents unless they are of the same size.…”

“…Proteins could be desorbing either as monomers or aggregates such as dimers, trimers etc., and could be desorbing in their native form or in denatured state [129,130,162]. Careful analysis of the mobility spectra between the desorption and adsorption experiments for all proteins indicate no significant mobility size change in the monomers or dimers indicating that at least to the level of the instrument resolution, 0.3 nm in mobility diameter [15,143], there is no discernable changes in protein onformation. Further the desorbing species were primarily monomers.…”

“…This is not surprising since the dimer would have nominally twice as many antigen binding sites, b) the monomer and dimer mobilities sizes obtained during desorption are invariant of the two surfaces which may either imply that the two surfaces do not cause a significant change in the protein at least within the uncertainty of the instrument which in this regard is about ~ 0.3 nm [15,143], or that once the proteins desorb from the surfaces they return to their native state and c) the total protein eluting out is the same irrespective of the surface. The third similarity has an important consequence as discussed here.…”

“…Gold nanoparticles (Ted Pella) prepared in ammonium acetate buffer or 60 nm polystyrene latex particles (NIST SRM ® 1963) were used as system suitability standards to confirm operation of the instrumentation [15,78,143].…”

Establishing SI-Traceability of Nanoparticle Enumeration Techniques: A Case Study on Electrospray Differential Mobility Analysis

“…In the case of nano-bio-objects, and more specifically nanobioparticles, ES-DMA has already proven its added value and has been used to characterize a wide variety of nano-bioparticles: proteins [12,13], protein aggregates [14,15], viruses [16,17], supramolecular complexes [18] or lipoproteins [19] [12,13]. Similarly, Caulfield et al reported the use of ES-DMA as a tool to directly measure lipoprotein particle number concentrations in biological samples using direct calculations [20].…”