Abstract: The invention relates to an electrochemical sensor with interdigital micro-electrodes (1) with structure widths in the sub-.mu.m range. With a twin or multi-pair array of the interdigital micro-electrodes on a substrate (8), the electrochemical detection of molecules with high sensitivity is made possible and further uses for the detection of chemical reaction cycles are made available. The electrodes may be arranged in a micro-channel applied to the substrate having a constant small volume of a few nanoliters. The electrochemical sensor of the invention is suitable for the multiple measurement of the same species of molecule or as a multi-sensitive sensor in chemical analysis and process control in various fields such as biotechnology, environmental protection or health.