Core-shell nanoparticles are emerging advanced materials for developing novel electroanalytical platforms, This paper describes the results of an investigation of the electroactivity of Cu2+ ions on electrodes coated with thin films assembled from thiolate-encapsulated gold nanoparticles of 2 nm core size (Au2-nm) and a carboxylic functionalized alkyl thiol linker, i.e. 11-mercaptoundecanoic acid (MUA). The high surface-to-volume ratio and the 3-D ligand network properties are potentially useful as sensitive and selective nanomaterials for the monitoring and removal of environmental heavy metals. The nanostructured MUA-Au2-nm film is sensitive to Cu2+ below 1 ppm. The selectivity of the electroactivity is also probed using mixed-metal systems such as Cu2+ and Fe3+ and Cu2+ and Zn2+. Issues related to the electrochemical activity of these metal ions are also discussed.