SYNTHESIS AND CHARACTERIZATION OF COLLOIDAL DISPERSIONS OF FLUORESCENT, MONODISPERSE SILICA SPHERES

Stable dispersions of monodisperse colloidal silica spheres containing a dye or fluorophore have been synthesized according to a general procedure and dispersed in polar and apolar liquids. The procedure consists of the coupling of the dye to a silane coupling agent, (3-aminopropyl)triethoxysilane, and the controllable incorporation of the reaction product into the silica sphere. The silica spheres are prepared from tetraethoxysilane in mixtures of ammonia, water, and ethanol. The composition of the silica spheres can be controlled in such a way that the organic groups can be placed on the surface, in a thin shell inside the particle or distributed through the volume of an inner core. Fluorescein isothiocyanate was used to make easily bleachable, fluorescent silica spheres. Hydrophilic charge stabilized and organophilic sterically stabilized 1-octadecanol-coated dyed silica systems were synthesized and dispersed in several solvents. All the particles were characterized after the several reaction steps by static and dynamic light scattering and transmission electron microscopy. The fluorescent spheres were further characterized by fluorescence spectroscopy and confocal scanning laser fluorescence microscopy. Great effort was taken to prepare monodisperse dispersions free of clusters of particles. Such model dispersions are required for (scattering) studies of interparticle interactions in (concentrated) systems. Therefore, the several steps of the synthesis and optical characterization are described in detail.