Search results for: Colloidal Gold Sol Size 40 nm
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2018/01/15
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Carbon Monoxide Oxidation by Polyoxometalate-Supported Gold Nanoparticulate Catalysts: Activity, Stability, and Temperature- Dependent Activation Properties.
Nanoparticulate gold supported on a Keggin-type polyoxometalate (POM), Cs [α-SiW O ]⋅n H O, was prepared by the sol immobilization method. The size of the gold nanoparticles (NPs) was approximately 2 nm, which was almost the same as the size of the gold colloid precursor. Deposition of gold NPs smaller than 2 nm onto POM (Au/POM) was essential for a high catalytic activity for CO oxidation. The temperature for 50 % CO conversion was -67 °C. The catalyst showed extremely high stability for at least one month at 0 °C with full conversion. The catalytic activity and the reaction mechanism drastically changed at temperatures higher than 40 °C, showing a unique behavior called a U-shaped curve. It was revealed by IR measurement that Au was a CO adsorption site and that adsorbed water promoted CO oxidation for the Au/POM catalyst. This is the first report on CO oxidation utilizing Au/POMs catalysts, and there is a potential for expansion to various gas-phase reactions.Takuya Yoshida, Toru Murayama, Norihito Sakaguchi, Mitsutaka Okumura, Tamao Ishida, Masatake Haruta
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Light-scattering submicroscopic particles as highly fluorescent analogs and their use as tracer labels in clinical and biological applications.
Submicroscopic gold particle suspensions scatter colored light when illuminated with white light, and we have observed that a light-scattering gold particle suspension has the same appearance as a fluorescing solution. Thus, when illuminated by a narrow beam of white light, a 40-nm gold sol displays a clear (not cloudy), green scattered light (Tyndall) beam and has the same appearance as a fluorescing fluorescein solution. These, as well as other, observations have suggested to us that, in general, light-scattering particles can be treated as fluorescent analogs and used as fluorescent analog tracers in immuno- and DNA probe assays as well as in cell and molecular biology studies. Light-scattering particles are advantageous in these applications because particles such as gold and silver have very high light-scattering powers, which allows these particles to be easily detected, by light-scattering, at particle concentrations as low as 10(-16) M. The scattered light can be detected by the unaided eye for qualitative measurements or with a simple light-sensitive detector for quantitative measurements. Moreover, individual particles can be easily detected by eye or a video camera using a simple light microscope with a proper illuminating system. In addition, submicroscopic particles which scatter blue, green, yellow, orange, or red light can be readily synthesized. Antibodies, DNA probes, and other tracer substances can be readily attached to gold and other particles without altering their light-scattering properties. In this article we present the theory which allows one to predict the light-scattering properties of particles of different sizes and compositions and identify those particle sizes and compositions which appear most adequate for particular applications. Furthermore, we calculate molar extinction coefficients and emission efficiencies for particles of different sizes and compositions which allows us to compare the light-producing powers of these particles with those of well known fluorescent tracers. A 60-nm gold particle, for example, is equivalent to about 3 x 10(5) fluorescein molecules. Very simple, easy to use, low-cost, ultrasensitive immuno- and DNA probe assays can be developed using light-scattering particles as fluorescent analog tracers. Single particles can be detected on cell surfaces and inside cells using light microscopy techniques with proper illumination as described in the article. At high particle densities, particle-labeled cells have the same appearance as fluorescent cells.J Yguerabide, E E Yguerabide