A novel modified electrode was designed and fabricated by linking L-Leucine capped gold nanopartides to 1,3-propanedithiol self-assembled monolayer (SAM), on gold substrate. Using UV-Vis and FT-IR spectroscopy, we have shown that L-Leucine molecules functionalize the gold nanoparticles. Morphological characteristics of capped nanoparticles before and after linking to SAM were evidenced by TEM and tapping (TM) mode AFM. The properties of the nanostructured assembly were tested for detection of Cu(II) ions, by employing cyclic voltammetry as investigation techniques. A detection limit of 5.4 x 10(-7) M was obtained in this case. The results were compared with those obtained for bare gold electrode or modified by citrate-capped gold nanoparticles. Additionally, Electrochemical Impedance Spectroscopy was used to further characterize the electrode modified with L-Leucine capped gold nanoparticles. An equivalent electrical circuit was developed to interpret and fit the experimental EIS data. The circuit contains the solution resistance (R-5), the charge-transfer resistance (R-ct), the Warburg impedance (Z(Wt) - transmissive boundary) and a constant phase element (CPE) that models the behavior of the double-layer capacitance. The charge-transfer resistance was found to vary with Cu(II) concentration within 10(-5) to 10(-3) M concentration range; a saturation tendency was observed at higher concentrations. (C) 2012 Elsevier Ltd. All rights reserved.