The surface of a screen-printed carbon electrode (SPCE) was modified by using amorphous carbon nitride (a-CNx) thin film deposited by reactive magnetron sputtering. Scanning electron microscopy and photoelectron spectroscopy measurements were used to characterise respectively the morphology and the chemical structure of the a-CNx modified electrodes. The incorporation of nitrogen in the amorphous carbon network was demonstrated by X ray photoelectron spectroscopy. The a-CNx layers were deposited on both carbon screen-printed electrode (SPCE) and silicon (Si) substrates. A comparative study showed that the nature of substrate, i.e. SPCE and Si, has a significant effect on both the surface morphology of deposited a-CNx film and their electrochemical properties. The improvement of the electrochemical reactivity of SPCE after a-CNx film deposition was highlighted both by comparing the shapes of voltammograms and calculating the apparent heterogeneous electron transfer rate constant. (c) 2007 Elsevier Ltd. All rights reserved.