A facile method has been developed to prepare aqueous dispersions of encapsulated conjugated polymer nanoparticlesexhibiting high fluorescence brightness. Salient features of the nanoparticles include their small diameter and sphericalmorphology. Encapsulation of the nanoparticles with a silica shell reduces the rate of photooxidation and allows facileattachment of functional groups for subsequent bioconjugation and nanoparticle assembly. Functionalization of thenanoparticle with amine groups followed by the addition of Au nanoparticles resulted in the formation of nanoparticleassemblies, as evidenced by the efficient quenching of the conjugated polymer fluorescence by the Au nanoparticles.