Electrochemical sensor with thin film guard electrode

There is presented an electrochemical sensor (100) for sensing an analyte in an associated volume (106), the sensor comprising a first solid element and a second solid element being joined to the first solid element, a chamber (110) being placed at least partially between the first solid element and the second solid element, said chamber comprising a reaction region (130), and a reservoir region (132) being connected with the reaction region, wherein an one or more analyte permeable openings (122) connect the reaction region (130) with the associated volume (106), and wherein the electrochemical sensor (100) further comprises an analyte permeable membrane (124) in said one or more analyte permeable openings, a working electrode (104) a reference electrode (108), and a guard electrode (109) arranged so as to enable reduction or oxidation of at least some reactants from at least a part of the reservoir region.