Gold surfaces were modified with an electrochemically deposited layer of non-stoichiometric molybdenum oxides. At these surfaces, trans-[Ru(III)(NH3)(4)(SO4)4pic](+) complex was incorporated in a controlled way by cycling the potential consecutively in the range +0.50 to -0.25 V at pH 2.6. Very reproducible voltammetric curves corresponding to the electrochemical process of the ruthenium complex were obtained, confirming the immobilisation of the material into the molybdenum oxide film. The anodic oxidation of nitric oxide (NO) at pH 7.4 was investigated at the modified electrode containing the molybdenum oxide+trans-[Ru(III)(NH3)(4)(SO4)4pic](+) complex and an enhancement in the current response was observed compared with the signal at a bare electrode. The rate for NO electrochemical oxidation was dependent on the amount of catalytic ruthenium sites dispersed into the molybdenum oxide film. A linear relationship between current signals measured by square wave voltammetry and NO concentration was obtained in the 0-10 muM range. The applicability of the modified electrode as a sensor for real-time NO monitoring was also demonstrated. (C) 2003 Elsevier Science B.V. All rights reserved.