Various amounts of silver nano-clusters were introduced into the core of poly(2-vinyl pyridine) core-polystyrene shell type polymer microspheres. The density of the microsphere increased linearly from 1.08 to 1.44 with increasing feed amounts of silver ions. The diffusibility and diffusion coefficients of the microspheres in a good solvent for polystyrene were measured by dynamic light scattering. (C) 1997 Elsevier Science Ltd.