Gas-Phase Ion-Mobility Characterization of SAM-Functionalized Au Nanoparticles

Abstract

We present results of a systematic examination of functionalized gold nanoparticles (Au-NPs) by electrospray-differential mobility analysis (ES-DMA). Commercially available, citrate-stabilized Au colloid solutions (10-60 nm) were sized using ES-DMA, from which changes in particle size of less than 0.3 nm were readily discerned. It was found that the formation of salt particles and the coating of Au-NPs by salt during the electrospray process can interfere with the mobility analysis, which required the development of sample preparation and data correction protocols to extract correct values for the Au-NP size. Formation of self-assembled monolayers (SAMs) of alkanethiol molecules on the Au-NP surface was detected from a change in particle mobility, which could be modeled to extract the surface packing density of SAMs. A gas-phase temperature-programmed desorption (TPD) kinetic study of SAMs on Au-NPs found the data to be consistent with a second-order Arrhenius-based rate law, yielding an Arrhenius factor of 1.0 x 10 (11) s (-1) and an activation energy approximately 105 kJ/mol. For the size range of SAM-modified Au-NP we considered, the effect of surface curvature on the energetics of binding of carboxylic acid terminated SAMs is evidently negligible, with binding energies determined by TPD agreeing with those reported for the same SAMs on planar surfaces. This study suggests that the ES-DMA can be added to the tool set of characterization methods used to study the structure and properties of coated nanoparticles.

Electrospray–differential mobility analysis of bionanoparticles

“…and quantify surface coverage of single strand DNA molecules on 10 nm gold nanoparticles [65]. Similar studies have been reported for self-assembled alkane thiol monolayers (SAMs) on 10 and 60 nm AuNPs [15]. This study found that the coverage of SAMs was independent of the size of the AuNPs.…”

“…This work was followed over the next decade by several reports from Allmaier et al [11], Wick et al [12] and de la Mora et al [13] related to characterization of several other proteins, viruses and polymers. Starting in 2006 as seen in Figures 1.3A and 1.3B a dramatic increase in the number of publications and citations related to ES-DMA occurred with contributions from Biswas et al [14], Zachariah et al [15], Loo et al [16], Hogan et al [17], Pergantis et al [18], Pease et al [19] and Hackley et al [20]. Although developed primarily for size determination, with an increasing pool of users, several orthogonal utilities have been found for this technique a detailed discussion of which will be appear later in Chapter 3.…”

“…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.…”

“…One approach for quantification is based on the increase in projected surface area due to adsorption of ligand [15,20,65] …”

Hygroscopic Growth and Deliquescence of NaCl Nanoparticles Coated with Surfactant AOT

“…Tsai et al 59 showed that gold nanoparticles (10-60 nm) coated with self-assembled monolayers (SAMs) of alkanethiols appeared to have a "soft" organic coating. The SAM/Au particle size deduced from the mobility measurements was smaller than the size expected from purely geometric considerations.…”