The electrochemical determination of Hg(II) at trace level using gold nanoparticles-modified glassy carbon (AuNPs-GC) electrodes is described. Starting from HAuCl4 in NaNO3, gold nanoparticles (AuNPs) were deposited onto Glassy Carbon (GC) electrodes using Cyclic Voltammetry (CV). Different deposits were obtained by varying the global charge consumed during the whole electroreduction step, depending on the number of cyclic potential scans (N). AuNPs were characterized as a function of the charge using both CV in H2SO4 and Field Emission Gun Scanning Electron Microscopy (FEG-SEM). The AuNPs-GC electrodes were then applied to determine low Hg(II) concentrations using Square Wave Anodic Stripping Voltammetry (SWASV). The AuNPs-GC electrodes provided significantly improved performances in Hg(II) determination compared to unmodified GC and bare Au electrodes. It was shown that the physico-chemical properties of the deposits are correlated to the performances of the AuNPs-GC electrode with respect to Hg(II) assay. The best results were obtained for four electrodeposition cyclic scans, where small-sized particles (36 +/- 13 rim) with high density (73 particles mu m(-2)) were obtained. Under these conditions, a linearity range from 0.64 to 4.00 nM and a limit of detection of 0.42 nM were obtained. (C) 2011 Elsevier B.V. All rights reserved.