The electro-reduction of nitrate ions in artificial sea water was investigated at a gold substrate (E_Au) functionalized by silver nanoparticles (AgNPs). These AgNPs were generated in situ on the gold substrate by the direct decomposition of the metalorganic N,N′-diisopropylacetamidinate silver precursor [Ag(Amd)] in the liquid phase. Very small and well dispersed AgNPs were deposited on the gold electrode and then used as working electrode (E_Au/AgNPs). Square wave voltammetry (SWV) was successfully employed to detect nitrate ions (NO₃⁻) with a detection limit (LOD) of 0.9 nmol∙L⁻¹ in artificial sea water (pH = 6.0) without pre-concentration or pH adjustment.