A combination of sputtering and colloidal chemistry is employed to prepare [Co/Al2O3//Ru nanoparticles//Al2O3/Co] junctions (see figure). These junctions are applied as variable capacitors relying on Coulomb blockades in a 2D assembly of nanoparticles. AC measurements show a significant capacitance variation as a function of applied DC voltage with a maximum of relative variation value that is proportional to the particle density embedded in the dielectric layer and is in good agreement with the theoretical model.