Electrical sensor

Abstract

Disclosed is an electrochemical sensor for the determination of analytes in body fluids, e.g. glucose in blood. The sensor involves a non-conductive base which provides a flow path for the body fluid with the base having a working and counter electrode on its surface which are in electrical communication with a detector of current. The base and a cover therefore provide a capillary space containing the electrodes into which the body fluid is drawn by capillary action. The counter electrode has a sub-element which contains an electroactive material and is configured in the system (sensor and meter) to provide an error signal when insufficient body fluid is drawn into the capillary.

What is claimed is:  
     
         1 . In an electrochemical sensor for determining the concentration of an analyte in a fluid test sample comprising 1) a non-conductive base which provides a flow path for the fluid test sample and has 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 the upper surface of the working electrode comprising an enzyme and mediator which reacts with the analyte to cause electrons to be transferred between the analyte and 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 working and counter 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 counter electrode being upstream from the working electrode, so that when electrical 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 upon the application of between the working electrode and the sub-element, the improvement which comprises employing a sub-element of the counter electrode which comprises an electroactive material capable of allowing oxidation to occur at the surface of the working electrode under the applied potential and is present in an amount which is insufficient to maintain the flow of electric current through the detector to constitute a valid determination of analyte concentration.  
     
     
         2 . The sensor of  claim 1  which comprises an insulating base, an electrical conductor pattern, an electrode pattern comprising a working electrode and a counter electrode, a sub-element of the counter electrode, an insulating layer partially covering the electrodes, and a reaction layer.  
     
     
         3 . The sensor of  claim 2  wherein the reaction layer comprises poly(ethylene oxide), an enzyme and a ferricyanide salt.  
     
     
         4 . The sensor of  claim 3  wherein the enzyme is glucose oxidase.  
     
     
         5 . The sensor of  claim 1  wherein the electroactive material is an oxide of Ag, Cu, Mn, Pb, Hg, Ni, Co, Bi, Re, or Te.  
     
     
         6 . The sensor of  claim 1  wherein the electroactive material is AgO.  
     
     
         7 . The sensor of  claim 1  wherein silver has been deposited on the surface of the sub-element of the counter electrode and oxidized in place to form silver oxide.  
     
     
         8 . The sensor of  claim 1  wherein the electroactive material is a metal halide.  
     
     
         9 . The sensor of  claim 1  wherein the sub-element of the counter electrode is physically disconnected from the main body of the counter electrode and provided with its own connection to the detector through the main body of the counter electrode.  
     
     
         10 . The sensor of  claim 2  wherein there is no reagent in contact with the sub-element of the counter electrode.