We report the in situ generation of aryl diazonium cations of Azure A, a redox-active phenothiazine dye, by reaction between the corresponding aromatic aminophenyl group and sodium nitrite in 0.1M HCl. The subsequent electrochemical reduction of these dye diazonium salts gives rise to conductive electrografted films onto screen-printed carbon (SPC) electrodes. The resulting Azure A films have a very stable and reversible electrochemical response and exhibit potent and persistent electrocatalytic behavior toward NADH oxidation. We have optimized the electrografting conditions in order to obtain SPC modified electrodes with high and stable electrocatalytic response. The kinetic of the reaction between the NADH and the redox active centers in the Azure A film has been characterized using cyclic voltammetry and single step chronoamperometry. The catalytic currents were proportional to the concentration of NADH giving rise to linear calibration plots up to a concentration of 0.5mM with a detection limit of 0.57±0.03μM and a sensitivity of 9.48Amolcm(-2)μM(-1). The precision of chronoamperometric determinations was found to be 2.3% for five replicate determinations of 3.95μM NADH. The great stability of such modified electrodes makes them ideal for their application in the development of biosensing platforms based on dehydrogenases.