Synthesis, Characterization of Dihydrolipoic Acid Capped Gold Nanoparticles, and Functionalization by the Electroluminescent Luminol

Abstract

The use of gold nanoparticles as biological probes requires the improvement of colloidal stability. Dihydrolipoic acid (DHLA), a dithiol obtained by the reduction of thioctic acid, appears therefore very attractive for the stabilization and the further functionalization of gold nanoparticles because DHLA is characterized by a carboxylic acid group and two thiol functions. The ionizable carboxylic acid groups ensure, for pH > or = 8, the water solubility of DHLA-capped gold (Au@DHLA) nanoparticles, prepared by the Brust protocol, and the stability of the resulting colloid by electrostatic repulsions. Moreover almost all DHLA, adsorbed onto gold, adopts a conformation allowing their immobilization by both sulfur ends. It is proved by sulfur K-edge X-ray absorption near edge structure spectroscopy, which appears as an appropriate tool for determining the chemical form of sulfur atoms present in the organic monolayer. Such a grafting renders the DHLA monolayers more resistant to displacement by dithiothreitol than mercaptoundecanoic acid monolayers. The presence of DHLA on gold particles allows their functionalization by the electroluminescent luminol through amine coupling reactions assisted by 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide. As a luminol-functionalized particle is nine times as bright as a single luminol molecule, the use of the particles as a biological probe with a lower threshold of detection is envisaged.

Synthesis and characterization of photolabile aminoterpolymers for covalent attachment onto gold substrates

“…3, top). Due to the anchoring capacity onto gold of molecules containing lipoic units, as widely demonstrated in the attachment of small molecules in SAMs [29 -31] or in the stabilization of gold nanoparticles [27], this moiety was selected to be included in the objective monomers for the covalent attachment of our polymers to gold surfaces. There is a strong preference of the disulfide group to attach to the gold surface relative to a wide variety of polar and non polar groups, as hydroxyl, amino, carbonyl, chloro, alkyl, phenyl, nitro, or even other sulfur-containing functional groups such as thiols and sulfides, those being also less competitive in the absorption process rate relative to disulfides [32 -34].…”

“…Although the nature of the bonding of the thiol group on the gold nanoparticle surface is not fully understood, the interaction between gold and sulfur atoms is sufficiently strong to allow immobilization of thiolated species. Among the molecules that can be grafted to gold by several sulfur ends, lipoic acid (LA) and its reduced form, dihydrolipoic acid (DHLA), appear as specially interesting candidates [27]. LA is commonly used for electrochemical studies of biomolecules or for the elaboration of biological sensors because the carboxylic acid group allows the immobilization of a biomolecule on an electrode surface.…”

The fabrication and surface functionalization of porous metal frameworks – a review

“…Therefore, general pathways for pure metal functionalization may lead to unstable bonds that can be impaired through the input of thermal, chemical or electrical energy 221,222 . Pure metal nanoparticles have been successfully functionalized with thiols 204,223,224 , di-sulfides 200 , amines 223,[225][226][227] , nitriles, carboxylic acids and phosphines 225,226,228 . Selected examples will be presented in the following sections.…”

Apolipoprotein E3-mediated cellular uptake of reconstituted high-density lipoprotein bearing core 3, 10, or 17 nm hydrophobic gold nanoparticles

“…[1][2][3] Depending on the intended application, AuNPs can be functionalized with various bioconjugates, namely proteins and peptides, 4 nucleic acids, 5 and other biologically relevant molecules. 6,7 Typically, AuNP bioconjugation involves several strategies 8 such as covalent coupling to the surface ligand using reagents such as 1-ethyl-3-(3-dimethylaminopropyl)carboiimide and N-hydroxysuccinimide with biomolecules 7,9,10 or direct conjugation of biomolecules to the Au surface, often achieved by introducing reactive functional groups such as sulfhydryl groups on the side chains of the peptide and allowing the high-affinity Au-S bonding to take place. 11 In addition, conjugation may also involve an initial chemisorption of thiol ligands onto the Au surface, forming a self-assembled monolayer coating of Au thiolates, followed by self-assembly of biomolecules onto the ligands through electrostatic interactions.…”