Electrochemical sensor

Abstract

Disclosed is an improved electrochemical sensor for the detection of an analyte in a fluid test sample. The electrochemical sensor is of the type in which the fluid test sample is drawn into a capillary space and the improvement to the sensor involves an arrangement where a portion of the sensor's counter electrode is placed on the edge of the capillary space in a relationship to the sensor's working electrode such that if the capillary space is not completely filled there will be generated only a very weak current. When the sensor is connected to a properly programmed current detector, the weak current caused by the underfilling of the capillary space will be detected as an error and will notify the user of the sensor that the test should not be continued.

1 . 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.  
     
     
         2 . The electrochemical sensor of  claim 1  which is connected to a current detector which is programmed to give an error signal when the current it receives is below a predetermined level.  
     
     
         3 . The electrochemical sensor of  claim 1  wherein there is a dielectric layer over the working and counter electrode having openings to expose these electrodes to a reaction layer on top of the dielectric layer and the area of the sub-element of the counter electrode which is exposed is 2% to 7% of the area of the working electrode which is exposed.  
     
     
         4 . The electrochemical sensor of  claim 3  wherein the sub-element of the counter electrode is not in contact with the reaction layer.  
     
     
         5 . The electrochemical sensor of  claim 1  wherein the sub-element is physically disconnected from the rest of the counter electrode and is provided with its own connector from contact with a current detector.  
     
     
         6 . The electrochemical sensor of  claim 1  wherein the cover has a concave portion; so that the concave portion forms the capillary space when the cover is mated with the base.  
     
     
         7 . The electrochemical sensor of  claim 1  which has a spacer element with a U shaped indentation so that the U shaped indentation forms the capillary space when it is inserted between the cover and the base.  
     
     
         8 . A method for the electrochemical determination of an analyte in a fluid test sample which comprises connecting the electrochemical sensor of  claim 1  to a current detector which is programmed to detect a current which is weaker than a predetermined current level and introducing the fluid test sample into the capillary space of the sensor.  
     
     
         9 . The method of  claim 8  wherein the current detector is programmed to provide an error signal when the current is weaker than the predetermined current level.  
     
     
         10 . The method of  claim 8  wherein the fluid test sample is blood and the analyte is glucose.  
     
     
         11 . A method for the production of a base member for an electrochemical sensor for detecting the concentration of an analyte in a fluid test sample which comprises the steps of: 
 a) providing an insulating base material in the form of a sheet from which a plurality of bases for the sensor can be punched out to form a base having a front edge;    b) screen printing an electrically conductive pattern on to the insulating base material;    c) screen printing a working electrode and a counter electrode onto the conductive pattern so that the main portion of the counter electrode lies further from the front edge of the base than the working electrode and a sub-element of the counter electrode overlaps the base's front edge; and    d) punching the base from the sheet of insulating base material in a pattern such that the sub-element of the counter electrode is flush with the front edge of the base.    
     
     
         12 . A method for the production of an electrochemical sensor which comprises the steps of: 
 a) providing the base member prepared as in claim  11 ;    b) screen printing a dielectric layer onto the working and control electrodes in a pattern which leaves predetermined portions of these electrodes exposed;    c) screen printing a reaction layer over the dielectric layer; and    d) applying a cover member to the base member to form a capillary space into which the fluid test sample can flow;    wherein steps a, b, c and d are carried out before the base member is punched from the sheet of insulating base member material.