Interfacial Mass Flux at 11-Mercaptoundecanoic Acid Linked Nanoparticle Assembly on Electrodes

Abstract

Thin films derived from nanocrystal cores and functionalized linkers provide a large surface area-to-volume ratio and three-dimensional ligand framework. This paper describes the results of an investigation of the interfacial mass flux and binding properties of such thin films using an electrochemical quartz crystal nanobalance technique. The hydrogen-bonding assembly from gold nanocrystals and 11-mercaptoundecanoic acid was studied as a model system. The results reveal four distinctive mass response characteristics upon pH tuning or metal ion binding. First, the protonation-deprotonation characteristic of the carboxylic acid groups in the nanostructured framework is dependent on particle core size and film thickness. Second, the pHtunable cationic redox reaction across the electrode|film|electrolyte interface is accompanied by a large cationic electrolyte mass flux. Third, the spontaneous complexation to copper ions by the nanostructured carboxylate framework is reflected by a mass increase of the film. Fourth, the redox reaction of copper loaded in the nanostructured film is accompanied by fluxes of electrolyte cations across the electrode|film|electrolyte interface which compensate electrostatically the fixed negative charges. On the basis of the mass change detected in the presence of a series of electrolyte cations, a linear relationship was determined between the mass increase and the atomic mass of the cation, and a concurrent flux of solvent molecules was also revealed. Implications of the findings to the delineation of the design parameters of the nanostructured ligand framework for controlled release and environmental monitoring or removal of metals are also discussed.

Resonance elastic light scattering (RELS) spectroscopy of fast non-Langmuirian ligand-exchange in glutathione-induced gold nanoparticle assembly

“…The solution pH was 3.24 ± 0.03 which is within the range of predominantly neutral (zwitterionic) form of GSH (pH = 2.04-3.4; pK a values for GSH are: pK 1 = 2.04 (glutamate -COOH), pK 2 = 3.4 (glycine -COOH), pK 3 = 8.72 (-SH group), pK 4 = 9.49 (-NH 2 group)). Note that surface pK a values may shift for surface-confined GSH similar to other molecules with pH-sensitive pendant groups ( [75][76][77][78][79][80][81]), hence, these values are used only as guidelines. However, the strong RELS increase in pH range close to 3.2 confirms that zwitterionic form of GSH is in relative predominance in the AuNP shells, otherwise the assembly and strong scattering would not be observed.…”

Thin Film Assemblies of Molecularly-Linked Metal Nanoparticles and Multifunctional Properties

“…pH-tuned structural and morphological properties: ( A ) IRS spectra and peak areas (obtained by spectral deconvolution) vs pH for each of the ν CO (CO 2 H) bands, 1 , 2 , 4 , and the ν a (CO 2 − ) band, as well as the total ( 1 + 2 + 4 ), for a MUA-Au 5nm film (ref ). (B) Mass change vs pH in 0.5 M KCl for MUA-Au 2nm films with different thicknesses (number of equivalent layers): 302 (a), 193 (b), and 68 (c) (ref ). (C) Topographical images of MUA-Au 5nm film on an ODT-MHA patterned surface (MHA, squares) under different pHs (ref ).…”

Specific pH effect for selective colorimetric assay of glutathione using anti-aggregation of label-free gold nanoparticles

“…[37][38][39] The pH values of the resulting solutions were 5.8 AE 0.1 for Cys/AuNPs. 31 For GSH, the pK a of GSH can be slightly shied to a higher value in the presence of AuNPs [40][41][42] and the color of the solution changed from red to blue. AuNPs aggregated instantly and the solution has a nal pH of 3.7.…”