Gold citrate-stabilized

In a recent report, new nanocomposites of Au NPs and poly(4-vinylpyridine) were obtained through surface-initiated atom-transfer radical polymerization (SI-ATRP). The citrate-stabilized gold nanoparticles were first modified by the disulfide initiator [BrC(CH3)2COO(CH2)iiS]2 for ATRP initiation, and the subsequent polymerization of 4-vinylpyridine occurred on the surface of the gold particles. The assembled Au PVP nanocomposites are pH-responsive because of the pyridyl groups, which are facially protonated and positively charged. The micrographs show Au N Ps of around 15 nm size [92] (Scheme 3.14). 

Controlled self-assembly allows exo-active surfaces to be viable supramolecular building blocks for constructing nanostructure assemblies. These nanostructure assemblies can be used to modify electrodes for sensing applications. Willner and coworkers have constructed nanostructure assemblies on electrodes through electrostatic cross-linking of citrate stabilized gold NPs and bipyridinium cyclophane (3,5-... 

Many different applications for gold cysteine nanoclusters have been proposed. One application is the use of citrate capped nanoparticles as sensors for the detection of thiol containing stractures. This application rehes on the fact that thiols can easily displace oxygen coordinated moieties. Zhong et al. have studied this process between cysteine and homocysteine to develop an assay for the homocysteine biomarker, a correlate to cardiovascular disease. When citrate stabilized particles of 13 run were incubated with either thiolate structure, the solution color changed from a dark red to a deep blue. The displacement of citrate by these moieties resulted... 

The use of nanoparticle arrays to generate surface-confined architectures has been extensively studied by Willner and co-workers [6]. The structural motif involves the sequential electrostatic assembly of nanoparticles and the desired molecules on planar electrodes. An ITO substrate is functionalized using an aminosilane molecule to yield a charged surface. Negatively charged citrate-stabilized gold... 

Figure 4. Electron micrograph of a 2D gold colloid monolayer prepared on carbon-coated copper grids (coating thickness 100 A) by electrophoresis of a 0.5 mM citrate stabilized Au sol at an applied positive voltage of 50 mV. Reprinted with permission from ref 27. Copyright 1993 American Chemical Society.

The interface between two immiscible electrolyte solutions offers the means to combine two-phase catalysis, colloid catalysts, and electrocatalysis. In the study of Lahtinen et al. [158] citrate-stabilized palladium and gold colloids were prepared by a traditional chemical reduction method. The voltammetric response of a system with an aqueous colloid and an electron donor in the organic phase revealed an irreversible voltammetric wave as the potential was swept positive. The response was detected only in the presence of both the colloid and the electron-donor DCMFc. The response was concluded to result from heterogeneous charging of the colloid with electrons from DCMFc. 

Figure 2. a) Schematic illustration of the e-beam conversion from a NO2 group in the SAMs of NPPTMS on an Si/SiO2 substrate to an NH2 group, b) The chemical pattern is subsequently capable of inducing the self-assembly of citrate-stabilized gold nanoparticles. 

FIGURE 51.4 Sketch of the surface reactions involved in the formation of a thin silica shell on citrate stabilized gold particles. 

A first attempt was made to measure the effect of temperature on the absorption spectra of citrate stabilized gold sols. However, at temperatures above about 40°C the stability of the dispersions was hindered, as observed by oscillations in the intensity of the measured spectra. This effect was not observed when silica coated particles were used. 

The samples were modified in direct (glow, diode) Ar plasma on Balzers SCD 050 device under the conditions presented in 2.3.1. Immediately after the plasma treatment the samples were inserted into water solution (2 wt. %) of 2-mercaptoethanol (ME), methanol solution (5.10 mol/dm ) of biphenyl-4,4 -dithiol (BPD) or into water solution (2 wt.%) of cysteamine (CYST) for 24 hours. To coat the polymers with the gold nanoobjects the plasma treated pol)rmers with grafted thiols were immersed for 24 hours into freshly prepared colloidal citrate stabilized solution of Au nanoparticles (AuNPs), [44,46] or Au nanorods (AuNR), 0.1 mol/dm water solution of cetyltrimethylammonium bromide). 

Good fits between experimental and theoretical amperometric responses at the tip were obtained for the composite films incorporating Pd nanoparticles to demonstrate that the generation of hydrogen peroxide (Equation 18.10) was accelerated from fe,=0.0014 cm/s to A ,=0.00534 cm/s as more Pd nanoparticles were loaded. By contrast, data for Pt composite films did not fit well with theory, which was ascribed to the formation of an oxide layer on Pt nanoparticles. In another study, LBL approach was employed to prepare the composite of gold nanoparticles, DNA, and polyethyleni-mine (PEI). Specifically, the SAM of 3-mercapto-l-propanesulfonic acid was formed on the gold electrode to deposit a cationic PEI film, which was followed by the deposition of double-stranded DNA or citrate-stabilized Au nanoparticles and PEL Approach curves were measured to demonstrate that 1 values for both FcMeOH and ferrocenecarboxyUc acid were highly dependent on the type of the outmost layer. 

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