Salt-Mediated Self-Assembly of Thioctic Acid on Gold Nanoparticles

Abstract

Self-assembled monolayer (SAM) modification is a widely used method to improve the functionality and stability of bulk and nanoscale materials. For instance, the chemical compatibility and utility of solution-phase nanoparticles are often improved using covalently bound SAMs. Herein, solution-phase gold nanoparticles are modified with thioctic acid SAMs in the presence and absence of salt. Molecular packing density on the nanoparticle surfaces is estimated using X-ray photoelectron spectroscopy and increases by ~20% when molecular self-assembly occurs in the presence vs. the absence of salt. We hypothesize that as the ionic strength of the solution increases, pinhole and collapsed-site defects in the SAM are more easily accessible as the electrostatic interaction energy between adjacent molecules decreases thereby facilitating the subsequent assembly of additional thioctic acid molecules. Significantly, increased SAM packing densities increase the stability of functionalized gold nanoparticles by a factor of two relative to nanoparticles functionalized in the absence of salt. These results are expected to improve the reproducible functionalization of solution-phase nanomaterials for various applications.

Preparation and Characterization of Gold Nanoparticles with Amino Acids, Examination of Their Stability

“…The gold nanoparticles capped and stabilized with thiol-derivative monolayers are dispersed in organic solvents [7,10]. Since then enormous researches have been performed on modifying the surface of gold colloids through changing the molecular structures of the thiolates on the particle surface [11][12][13][14][15][16][17]. The protection capping agent (thiols) is chemically bound to the surface of gold nanoparticles [7].…”

Modulating the catalytic activity of enzyme-like nanoparticles through their surface functionalization

“…Under low ionic strength conditions, the monolayer of our NP scaffolds should acquire a lower compaction degree. 20,21 All NPs scaffolds displayed increased substrate adsorption capacity in deionized water than PBS (see ESI-4). These results suggest that the more expanded the monolayer of our NPs the greater their capacity to associate substrates (see ESI-5).…”

Soft Ultraviolet (UV) Photopatterning and Metallization of Self-Assembled Monolayers (SAMs) Formed from the Lipoic Acid Ester of α-Hydroxy-1-acetylpyrene: The Generality of Acid-Catalyzed Removal of Thiol-on-Gold SAMs using Soft UV Light

“…1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 reconciled with the results of XPS studies of lipoic acid based SAMs which almost always show both 'bound' (Au?S) and 'unbound' (S?H or S?S) sulfur. 31,32 The source and nature of the 'unbound' sulfur revealed by these XPS studies remains unclear. It has been suggested that, for lipoic acid itself, it relates to an ionically bound or hydrogen bonded ad?layer on top of the lipoic acid SAM.…”