Alternating polyelectrolyte "layer-by-layer" deposition has been used to create emissive thin films of a weakly anionic, nonaggregating poly(phenylene ethynylene) on silica microspheres. The resulting particles are smooth and emit fluorescence solely from the outside polymer-coated surface. Suspensions of the coated microspheres show similar fluorescence properties to polymers in solution, but with enhanced sensitivity (up to 200-fold) to nitroaromatic quenchers. These enhancements are attributed to a combination of surface and electronic effects.