Highly Porous Inorganic Thin Films Formed Using Polymer Microsphere Templates
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ment. In the case of metal–polymer core–shell structures, the fluorescence of the organic dye may be quenched because of complex interactions with the metal core. To study the effect of separation distance on fluorescence quenching, G. Schneider and G. Decher of Institut Charles Sadron and Université Louis Pasteur, along with N. Nerambourg, R. Praho, M. Werts, and M. Blanchard-Desce of Université de Rennes, have described an approach in which up to 20 polyelectrolyte layers (the last layer being fluorescently labeled) were coated on gold nanoparticles. The core–shell distance was altered by tailoring the thickness of adsorbed, nonfluorescent polymers, which were used as spacer layers in the core–shell structure. As reported in the March 8 issue of Nano Letters (10.1021/ nl052441s; p. 530), gold particles (diameter, 13 nm) were synthesized by the reduction of tetrachloroauric acid with trisodium citrate. Spacer layers of polyallylamine hydrochloride (PAH) and polystyrene sulfonate (PSS) were adsorbed consecutively using electrostatic layer-by-layer assembly to obtain gold nanoparticles coated with 2, 10, and 20 layers of Au(PAH/PSS) n. Fluorescein
Fluorescence quenching is distance-dependent and remained significant 8 nm from the metal core. The fluorescence quenching seems to be caused by a decrease in radiative transition probabilities induced by the gold core. The researchers said that despite quenching, dye fluorescence remains sufficiently bright for diagnostic and sensing applications. JEREMIAH T. ABIADE
isothiocyanate (FITC) and lissamine rhodamine B sulfonyl chloride (LISS) were covalently attached to PAH to obtain PAH-FITC and PAH-LISS, which were then adsorbed onto the Au(PAH/PSS)n core–shell particles, followed by the adsorption of a final PSS layer. After each coating step, the particles were washed thoroughly by successive centrifugation/ re-suspension cycles. Transmission electron microscopy and in situ UV–visible absorption spectra were used to characterize the structural and photophysical properties of the nanoparticle dispersions. The researchers said that the addition of dye-functionalized polyelectrolytes does not perturb layer growth or the aggregation state of the solution. For n > 5 layers, the surface plasmon resonance from the gold particles reaches a fixed position and intensity, 534 nm in the case of PAH-FITC and 533 nm for PAH-LISS, and obscures the dye-related absorption bands. The surface-plasmon band was removed by slow dissolution of the gold core by adding cyanide ions to the solution. Dissolution of the gold core is accompanied by a strong increase in fluorescence, and reveals the weak dye-related absorption band.
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Trace and Ultra Trace Elemental Analysis Laboratory
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Bulk, Near Surface and Depth Profile Elemental Evaluation
Highly Porous Inorganic Thin Films Formed Using Polymer Microsphere Templates The use of colloidal templates as selfassembled building blocks for fabricating ordered submicrometer structures of various materials has been explored in recent years. These te
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