Monodisperse ruthenium nanoparticles functionalized by electroactive oligothiophenes have been prepared and characterized. Using TEM, UV-visible and FTIR we established that the organization of these nanoparticles into nanospheres call be directly controlled via modulation of the, pi-pi interaction between the organic components adsorbed oil the surface. This finding also shows that the self-assembled nanoheterostructures may be switched from monodisperse nanoparticles to ordered nanospheres by lulling the pH. (c) 2005 Elsevier Inc. All rights reserved.