A chronoamperometric assay for vanadium ions, based on the inhibition of the enzyme alkaline phosphatase, is reported. Screen-printed carbon electrodes modified with gold nanoparticles were used as transducers for the immobilization of the enzyme. The enzymatic activity over riboflavin-5-monophosphate sodium salt is affected by vanadium ions, which results in a decrease in the chronoamperometric current registered. The assay has a detection limit of 3.9 +/- 0.4 mu M, a repeatability of 7.6% (n = 4) and a reproducibility of 11.6% (n = 4). A study of the possible interferences shows that the presence of Mo (VI) may affect vanadium determination. The method was successfully applied to the determination of vanadium in tap water. (C) 2013 Elsevier B.V. All rights reserved.