Stable ruthenium nanoparticles were synthesized in a biphasic system with a protecting monolayer of dithiocarbarnate derivatives. The core size of the resulting Ru particles was found to vary with the initial ligand-metal feed ratio. UV-vis spectroscopic measurements showed a Mie scattering profile, with no obvious surface-plasmon resonance. The size and crystal structures of the particles were characterized by transmission electron microscopic (TEM) measurements. A significant fraction of the nanoparticles was found within the size range of 2-4 mn in diameter and of spherical shape from the TEM measurements. Clear lattice fringes could be observed in high-resolution TEM images with the fringe spacing consistent with the Ru(1 0 1) lattice planes. Electrochemical studies of Ru particles with different core size exhibited the solution-phase quantized charging of the particle double layers, analogous to those reported for gold and other transition-metal particles. The potential spacing between adjacent quantized charging peaks was found to vary with the particle core size, corresponding to the variation of the particle molecular capacitance. These charge-transfer properties were very consistent with the STM measurements of isolated nanoparticles which exhibit clear Coulomb blockade and staircase features. (c) 2007 Published by Elsevier Ltd.