Colloidal gold, formation

Non-Aqueous Colloidal Metal Solutions. It has been difficult to prepare colloidal gold in non-aqueous media due to limitations in preparative methods (low salt solubilities, solvent reactivity, etc.), and the fact that the low dielectric constant of organic solvents has hindered stabilization of the particles. In aqueous solution the gold particles are stabilized by adsorption of innocent ions, such as chloride, and thus stabilized toward flocculation by the formation of a charged double layer, which is dependent on a solvent of high dielectric constant. Thus, it seemed that such electronic stabilization would be poor in organic media. 

A report of a particle-based FPIA<56) details improvement in the limit of detection by two orders of magnitude over a conventional FPIA format for rabbit IgG, to 10 ° M. Goat anti-rabbit capture antibody (binder) is immobilized on polystyrene microspheres or colloidal gold particles, and the sample competes with a fluorescein-labeled rabbit IgG probe. The observed increase in sensitivity is apparently due to the large increase in effective mass of the binding complex. The polarization range is rather limited, though, reportedly due to low concentrations of immobilized antibodies. 

One of the approaches is to use colloidal gold as label [29] in electrochemical immunoassay. In addition to standard stages of the immune complex formation, oxidative release of gold and removal of excessive bromine are included into the analysis procedure. 

A similar process for preparing functional cyclodextrin nanospheres has been reported by the Harada group [25], )-Cyclodextrins were exhaustively thiolated at the lower rim and assembled around colloidal gold nanoparticles. Following assembly around the gold template the cyclodextrins were linked through the formation... 

When stannous chloride is added to solutions of platinum salts a red coloration is produced, which is due to the formation of so-called red colloidal platinum, which is kept in a fine state of division by the colloidal products of hydrolysis of the stannous chloride.7 In the absence of a protective colloid the red platinum changes to brown colloidal platinum. An interesting analogy may be traced between this red. colloidal metal and the better-known colloidal gold, termed purple of Cassius. ... 

Sunlight greatly facilitates the formation of colloidal gold, but the light of a mercury lamp is less energetic.24 Certain soaps are said to... 

A in particle size distribution curves. Colloidal gold, silver, platinum and platinized cadmium sulfide were generated in Aerosol-OT reversed micelles or in microemulsions by in situ photolysis of the appropriate ions (Figure 3.15). Under suitable conditions, each assembly contained approximately eight Au " ions, which firstly led to the formation of Aug clusters. ... 

Tsunoyama, H., Sakurai, H., Ichikuni, N., Negishi, Y. and Tsukuda, T. (2004) Colloidal gold nanoparticles as catalyst for carbon-carbon bond Formation Application to aerobic homocoupling of phenylboronic acid in water. Langmuir, 20, 11293-11296. 

The study of colloidal crystals was initiated as part of research into the determination of phase diagrams for colloids, which itself was perceived as a means to model phase behaviour in molecular systems [22]. Extensive literature is available on the dynamics of colloidal crystal formation, as a function of several parameters, such as the nature of the solvent, surface charge, particle size and concentration. The results described here refer to the formation of colloidal crystals from dispersions of silica-coated gold nanoparticles in ethanol, after silica surface functionalization with 3-(trimethoxysilyl)propyl methacrylate (TPM). Earlier studies by Philipse and Vrij [23] showed that TPM adsorption leads to a reduction in surface charge, so that the particles are stable in organic solvents with low polarity, such as ethanol, toluene or DMF. This means that the particle be-... 

Transient bivalent gold ions and two unidentified species, possibly Au°, were prepared and stiuded in different aqueous matrices by pulse radiolysis. Their absorption spectra and rate constants of formation and decay are reported. Bivalent gold was prepared by the oxidation of Au(CN)2 in neutral chloride solutions of N20, and also by the reduction of AuClf in the presence of CH3OH. The kinetics of its decay indicates disproportionation. The reduced species of Au(CN)2 from H atoms is different from that obtained with e aq, the latter being attributed to an electron adduct. Both of these species decay, forming colloidal gold. 

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