The system concerns an electrode system for an electrochemical sensor, comprising, arranged on a conductive substrate (10), a plurality of micro-discs (22) electrically connected to the substrate and a generating electrode (20) insulated from the substrate by an insulating layer (14) and including a plurality of orifices (24) concentric with said micro-discs. A conductive layer (12) and connections (26, 28) enable to connect the electrodes to power sources. The generating electrode enables to modify locally, at the micro-discs, the concentrations of species present in solution opposite said electrodes.