One-step synthesis and size control of dendrimer-protected gold nanoparticles: A heat-treatment-based strategy

Dendrimer-protected gold nanoparticles have been facilely obtained by heating an aqueous solution containing third generation poly(propyleneimine) dendrimers and HAuCl4 without the additional step of introducing other reducing agents. Transmission electron microscopy (TEM) and UV vis data indicate the size the nucleation and growth kinetics of gold nanoparticles thus formed which can be tuned by changing the initial molar ratio of dendrimer to gold.

Gold nanoparticles as fine tuners of electrochemical properties of the electrode/solution interface

Recently, a novel approach for preparing SERS and SPR substrates was developed, which indicates a potential application in tailoring the interfacial structure of an electrode surface. In this study, (3-mercaptopropyl)trimethoxysilane (MPTMS) was selected as a polymeric adhesive layer, and a low concentration of colloid Au solution was used to achieve a more accurate control over interface morphology at nanoscale dimensions due to slow self-assembling kinetics of gold nanoparticle's. Subsequent seeding growth of these MPTMS-supported submonolayers of gold nanoparticles in Au3+/NH2OH aqueous solution enlarges particle size and eventually results in the generation of conductive gold films (similar to previous (3-aminopropyl)trimethoxysilane-supported gold films). Such tunable interface structure was evaluated by atomic force microscopy (AFM). Also, ac impedance spectroscopy (ACIS) and cyclic voltammograms were performed to evaluate electrochemical properties of the as-prepared interfaces by using Fe(CN)(6) (3-/4-) couples as a probe. Furthermore, relevant theories of microarray electrodes were introduced into this study to explain the highly tunable electrochemical properties of the as-prepared interfaces. As a result, it is concluded that the electrochemical properties toward Fe(CN)(6) (3-/4-) couples are highly dependent on the active nanoelectrode (nanoparticles) area fraction and nanoparticles are fine-tuners of interfacial properties because the number density. (numbers/unit area) and size of nanoparticles are highly tunable by self-assembling and seeding growth time scale control. This is in agreement with the theoretical expectations for a microarray electrode if a single nanoparticle tethered to a blocking SAM is taken as a nanoelectrode and 2-D nanoparticle assemblies are taken as nanoelectrode arrays.

Direct electron transfer between hemoglobin and a glassy carbon electrode facilitated by lipid-protected gold nanoparticles

We synthesized a kind of gold nanoparticle protected by a synthetic lipid (didodecyidimethylammonium bromide, DDAB). With the help of these gold nanoparticles, hemoglobin can exhibit a direct electron transfer (DET) reaction. The formal potential locates at -169 mV vs. Ag/AgCl. Spectral data indicated the hemoglobin on the electrode was not denatured. The lipid-protected gold nanoparticles were very stable (for at least 8 months). Their average diameter is 6.42 nm. It is the first time to use monolayer-protected nanoparticles to realize the direct electrochemistry of protein.

Investigation of electrochemical charging behaviors of "naked" gold nanoparticles ensembles in aqueous media

Gold nanopartides were Immobilized onto the electrode surface by simple self-assembly technique. Interestingly, the ensembles of these nanopartides exhibit quantized charging behaviors in aqueous solution. Possible mechanism for such behaviors was proposed.

A method to construct a third-generation horseradish peroxidase biosensor: Self-assembling gold nanoparticles to three-dimensional sol-gel network

A novel method for fabrication of horseradish peroxidase biosensor has been developed by self-assembling gold nanoparticles to a thiol-containing sol-gel network. A cleaned gold electrode was first immersed in a hydrolyzed (3-mercaptopropyl)-trimethoxysilane (MPS) sol-gel solution to assemble three-dimensional silica gel, and then gold nanoparticles were chemisorbed onto the thiol groups of the sol-gel network. Finally, horseradish peroxidase (HRP) was adsorbed onto the surface of the gold nanoparticles. The distribution of gold nanoparticles and HRP was examined by atomic force microscopy (AFM). The immobilized horseradish peroxidase exhibited direct electrochemical behavior toward the reduction of hydrogen peroxide. The performance and factors influencing the performance of the resulting biosensor were studied in detail. The resulting biosensor exhibited fast amperometric response (2.5 s) to H2O2. The detection limit of the biosensor was 2.0 mumol L-1, and the linear range was from 5.0 mumol L-1 to 10.0 mmol L-1. Moreover, the studied biosensor exhibited high sensitivity, good reproducibility, and long-term stability.

Influence of capping ligands on the self-organizations of gold nanoparticles into superlattice from CTAB reverse micelles

Gold nanoparticles with size 3-10 nm (diameter) were prepared by the reduction of HAuCl4 in a CTAB/octane + 1-butanol/H2O reverse micelle system using NaBH4 as the reducing agent. The as-formed gold nanoparticle colloid was characterized by UV/vis absorption spectrum and transmission electron microscopy(TEM). Various capping ligands, such as alkylthiols with different chain length and shape, trioctylphosphine (TOP), and pyridine are used to passivate the gold nanoparticles for the purpose of self-organization into superstructures. It is shown that the ligands have a great influence on the self-organization of gold nanoparticles into superlattices, and dodecanethiol C12H25SH is confirmed to be the best ligand for the self-organization. Self-organization of C12H25SH-capped gold nanoparticles into 1D, 2D and 3D superlattices has been observed on the carbon-coated copper grid by TEM without using any selective precipitation process.

Self-assembled multilayers of alternating gold nanoparticles and dithiols: approaching to superlattice

The preparation of self-assembled multilayers of alternating gold nanoparticles and dithiols on Si or SiO2 substrates coated with (3-aminopropyl) trimethoxysilane are reported. The superlattice structure of these self-assembled multilayers was demonstrated by the results of UV-Vis spectrometry, AFM and X-ray diffraction measurements. The multilayer assembled by small-size gold particles has good periodic structure. (C) 2000 Elsevier Science B.V. All rights reserved.

Formation of ordered arrays of gold nanoparticles from CTAB reverse micelles

In this presentation, a reverse micelle technique was described to create colloid gold nanoparticles and their self-organization into superlattices. Gold nanoparticles were prepared by the reduction of HAuCL4 in CTAB/octane + 1-butanol/H2O reverse micelle system using NaBH4 as reducing agent. Dodecanethiol (C12H25SH) was used to passivate the gold nanoparticles immediately after formation of the gold colloid. After re-dispersing in toluene under ultrasonication, a supernatant containing nearly monodispersed dodecanethiol-capped gold nanoparticles was obtained. Self-organization of the gold nanoparticles into 1D, 2D and 3D superlattices was observed on the carbon-coated copper grid by TEM. UV-vis absorption spectra were also used to characterize the gold colloids with and without dodecanethiol capping. (C) 2001 Elsevier Science B.V. All rights reserved.

Controlled nucleation and growth of surface-confined gold nanoparticles on a (3-aminopropyl)trimethoxysilane-modified class slide: A strategy for SPR substrates

The thickness of the gold film and its morphology, including the surface roughness, are very important for getting a good, reproducible response in the SPR technique. Here, we report a novel alternative approach for preparing SPR-active substrates that is completely solution-based. Our strategy is based on self-assembly of the gold colloid monolayer on a (3-aminopropyl)trimethoxysilane-modified glass slide, followed by electroless gold plating. Using this method, the thickness of films can be easily controlled at the nanometer scale by setting the plating time in the same conditions. Surface roughness and morphology of gold films can be modified by both tuning the size of gold nanoparticles and agitation during the plating. Surface evolution of the Au film was followed in real time by UV-vis spectroscopy and in situ SPRS. To assess the surface roughness and electrochemical stability of the Au films, atomic force microscopy and cyclic voltammetry were used. In addition, the stability of the gold adhesion is demonstrated by three methods. The as-prepared Au films on substrates are reproducible and stable, which allows them to be used as electrodes for electrochemical experiments and as platforms for studying SAMs.

Superlattice structure of gold nanoparticles film deposited by Langmuir-Blodgett technique

Dodecanethiol-capped gold nanoparticles could spread on water subphase and be transferred by LB technique. The superlattice structure of gold nanoparticles multilayer was discussed.

Functionalization of lamellar molybdenum disulphide nanocomposite with gold nanoparticles

This work explores the functionalization of an organic-inorganic MoS2 lamellar compound, prepared by a Chemical Liquid Deposition Method (CLD), that has an interlamellar distance of ~5.2 nm, using clusters of gold nanoparticles. The gold nanoparticles have a mean diameter of 1.2 nm, a stability of ~85 days, and a zeta potential measured to be ζ = -6.8 mV (solid). The nanoparticles are localized in the hydrophilic zones, defined by the presence of amine groups of the surfactant between the lamella of MoS2. SEM, TEM, EDAX and electron diffraction provide conclusive evidence of the interlamellar insertion of the gold nanoparticles in the MoS2.

Recent advances in understanding CO oxidation on gold nanoparticles using density functional theory

Since the discovery of a series of Au-based catalysts by Haruta et al. considerable progress has been made in understanding the active role of Au in CO oxidation catalysis. This review provides a summary of recent theoretical work performed in this field; in particular it addresses DFT studies of CO oxidation catalysis over free and supported gold nanoparticles. Several properties of the Au particles have been found to contribute to their unique catalytic activity. Of these properties, the low-coordination state of the Au atoms is arguably the most pertinent, although other properties of the Au cluster atoms, such as electronic charge, cannot be ignored. The current consensuses regarding the mechanism for CO oxidation over Au-based catalysts is also discussed. Finally, water-enhanced catalysis of CO oxidation on Au clusters is summarized.