Electrochemical sensor

In an electrochemical sensor for detecting the concentration of analyte in a fluid test sample comprising (1) a non-conductive base which provides a flow path for the fluid test sample which base has a front edge as well as a counter electrode and a working electrode on its upper surface which are in electrical communication with a detector of electrical current;

• (2) a reaction layer on at least the surface of the working electrode comprising an enzyme which reacts with the analyte to produce electrons which are transferred to the working electrode;
• and (3) a cover which when mated with the base forms a capillary space with an opening for the introduction of fluid test sample thereto which space contains the flow path for the fluid test sample in which the counter and working electrodes are situated so that the major portion of the counter electrode is located downstream of the opening from the working electrode with a sub-element of the reference electrode being upstream from the working electrode so that when electrochemical communication between only the sub-element of the counter electrode and the working electrode takes place, there is insufficient flow of electrical current through the detector to constitute a valid test for the concentration of analyte in the fluid test sample and the detector is pre-programmed to emit an error signal in the event of such insufficient flow of electrical current, the improvement which comprises placing the sub-element of the counter electrode on the upper surface of the base so that it is flush with the front edge of the base.