DISPERSIONS OF RHODAMINE-LABELED SILICA SPHERES - SYNTHESIS, CHARACTERIZATION, AND FLUORESCENCE CONFOCAL SCANNING LASER MICROSCOPY

Monodisperse colloidal silica spheres, with a total radius of 200 nm, labeled with the fluorescent dye rhodamine isothiocyanate (RITC) in a core of 100 nm radius have been synthesized. The particles were characterized by transmission electron microscopy and by static and dynamic light scattering. The fluorescence properties and dye concentration in the particles were measured with fluorescence and absorption spectroscopy. Stable dispersions of these hydrophilic, charge-stabilized silica spheres in polar solvents and of organophilic, sterically stabilized, 1-octadecanol-coated silica spheres in apolar solvents were studied with fluorescence confocal scanning laser microscopy (CSLM). The bleachability of these particles was determined with CSLM and compared with particles labeled with the dye fluorescein isothiocyanate (FITC). The possibilities and limitations of confocal microscopy to study individual fluorescent particles in the bulk of concentrated model dispersions are discussed and demonstrated with CSLM graphs of a time series showing colloidal crystallization (crystal growth rate approximately 4 mum/s), an equilibrium between a colloidal liquid and colloidal crystal interface, and a binary mixture of RITC- and FITC-labeled spheres. Further, the feasibility of using the RITC-labeled spheres with other techniques relying on fluorescence is discussed as well.