Dual-color polystyrene microspheres by two-stage dispersion copolymerization

Dual-color monodisperse polystyrene microspheres have been prepared by two-stage dispersion polymerization, whose addition of the dye-comonomer was deferred until the nucleation stage was complete. Two dyes were covalently incorporated into microspheres by copolymerization without disturbing the final particle size and size distribution. No dye leakage occurs for the microsphere suspension because of covalent bonding of dye molecules. By varying the dye concentrations in microspheres, we obtained fluorescent microspheres with two distinguishing parts of fluorescence and varied fluorescent intensity ratios under a single-wavelength excitation. The microspheres present intense fluorescence for the large amount of encapsulated dye molecules.