Anionic Functionalized Gold Nanoparticle Continuous Full Filling Separations: Importance of Sample Concentration

Abstract

Electrically driven separations which contain nanoparticles offer detection and separation advantages but are often difficult to reproduce. To address possible sources of separation inconsistencies, anionic functionalized gold nanoparticles are thoroughly characterized and subsequently included in continuous full filling capillary electrophoresis separations of varying concentrations of three small molecules. Citrate stabilized gold nanospheres are functionalized with 11-mercaptoundecanoic acid, 6-mercaptohexanoic acid, or thioctic acid self-assembled monolayers (SAMs) and characterized using dynamic light scattering, extinction spectroscopy, zeta potential, and X-ray photoelectron spectroscopy prior to use in capillary electrophoresis. Several important trends are noted. First, the stability of these anionic nanoparticles in the capillary improves with increased ligand packing density as indicated by a ratio of absorbance collected at 520 to 600 nm. Second, increasing nanoparticle concentration from 0 to 2 nM (0-0.002(5)%, w/w) minimally impacts analyte migration times; however, when higher nanoparticle concentrations are included within the capillary, nanoparticle aggregation occurs which induces separation inconsistencies. Third, analyte peak areas are most significantly impacted as their concentration decreases. These trends are attributed to both sample enrichment and electrostatic interactions between the anionic carboxylic acid functionalized gold nanoparticles and sample. These important findings suggest that sample concentration-induced conductivity differences between the sample matrix and separation buffer as well as SAM packing density are important parameters to both characterize and consider when nanoparticles are used during continuous full filling separations and their subsequent use to enhance spectroscopic signals to improve in-capillary analyte detection limits.

How to accurately predict solution-phase gold nanostar stability

“…To quantify differences in flocculation (i.e., both agglomeration and aggregation), relative changes in integrated area ((t i −t 0 )/t 0 , %) are calculated from LSPR spectra [54]. Once again, interesting trends are noted.…”

Selective and colorimetric detection of Ba2+ ions in aqueous solutions using 11-mercaptoundecylphosphonic acid functionalized gold nanoparticles

“…40,41 Data from complementary techniques such as XPS and NMR suitable for study the binding sites of phosphonic and thiol ligands to AuNPs, compare favorably with our results. [42][43][44]…”

Improved theoretical prediction of nanoparticle stability and the synthesis, characterization, and application of gold nanopartticles of various morphology in surface-enhanced infrared spectroscopy

“…The overall objective of this study is the development of a model system for solutionphase SE-2D IR spectroscopy. Three specific objectives, namely;(1)…”

“…nanoparticles were then functionalized with thioctic acid (TA) (pKa (COOH) = 4.75-5.301 ), 6-mercaptohexanoic acid (MHA) (pKa (COOH) = 4.8 1 ), or 11-mercaptoundecanoic acid (MUA) (pKa (COOH) = 4.6-5.0 1 ) (Sigma Aldrich). For each self-assembled monolayer, 1 mL of 10 mM ligand (TA, MHA, or MUA) in ethanol was added to 10 mL of a 10 nM nanoparticle solution and stirred at 500 RPM for at least 60 hours at room temperature.…”

“…1,102 Under these conditions, use of ζ values leads to a significant underestimation of Vele.To avoid the underestimation of electrostatic interactions between nanostructures, we calculate the surface potential by solving the Poisson-Boltzmann equation for a distribution of point charges that decay as a function of radial distance from the charged nanoparticle surface. The surface potential is then expressed as…”