Suspensions of polyaniline-coated latex particles 13 pm in diameter showed the integer-fold voltammetric currents at the microelectrode of which size was similar to the diameter of the particles. The currents did not vary with concentrations of polyaniline particles but varied accidentally with each voltammetric run. They were caused by the reduction of a few polyaniline particles adsorbed on the electrode rather than diffusion of polyaniline particles in the suspension. The voltammetric behavior was almost the same as at the large electrode except for the integer-fold currents. The particle was a nearly mono-dispersed sphere, and was composed of a polystyrene core and a polyaniline shell. The particles were dispersed in acidic aqueous solution to form a colloidal suspension. The redox charge per particle was 9.5 G redox electrons, one-third of which participated in the voltammetric reduction current. (c) 2005 Elsevier B.V. All rights reserved.