Electrochemical sensor with dual purpose electrode

Abstract

The present invention provides an electrode assembly for use in a transdermal analyte sensor operating in an alternating polarity mode in which a single electrode element provides both the counter electrode and iontophoretic electrode functions. By combining both the functions of the iontophoretic and counter electrode, the surface area of the electrode with respect to each function may be made larger. In turn this increases the ability of the electrode to deliver the required electrical field over a larger area when operating in the iontophoretic mode as well as increasing the ability of the counter electrode to compensate for the larger sensing electrode facilitated by this new design.

We claim:  
     
         1 . An electrode assembly for use in a trancutaneous reverse-ionotophoresis diagnostic system wherein said assembly comprises: 
 (a) a first and second bi-modal electrodes;    (b) a first and second sensing electrodes;    (c) a substrate; wherein the bi-modal electrodes and sensing electrodes are substantially co-planar.    
     
     
         2 . The electrode assembly of  claim 1 , wherein the catalytic face of each sensing electrode comprises a platinum catalytic surface and the bi-modal electrodes are comprised of Ag/AgCl  
     
     
         3 . The electrode assembly of  claim 2  further characterized by a flat configuration and having a thickness in a range of about 0.25 μm to 250 μm.  
     
     
         4 . The electrode assembly of  claim 3  further characterized by a surface area in the range of about 0.1 cm 2  to about 8 cm 2 .  
     
     
         5 . The electrode assembly of  claim 4 , further comprising a reference electrode wherein said reference electrode is substantially the same plane as the bi-modal and sensing electrodes.  
     
     
         6 . The electrode assembly of  claim 5 , wherein the sensing electrode operates at a current level in the range of 1 nanoamp to 1 milliamp and the bi-modal electrode operates at a current level in the range of 1 nanoamp to 5 milliamps.  
     
     
         7 . The electrode assembly of  claim 6  wherein the said electrode assembly is supported on a ceramic, plastic or polyethylene film substrate.  
     
     
         8 . The electrode assembly of  claim 6 , further comprising a hydrogel patch, the patch having a surface in contact with a surface of the bi-modal, sensing and reference electrodes.  
     
     
         9 . The electrode assembly of  claim 6  further comprising a monitoring device.  
     
     
         10 . A method of determining the concentration of an analyte in a mammalian subject using a trancutaneous reverse-ionotophoresis diagnostic system, said method comprising the steps of: 
 (a) contacting a first surface of an ionically conductive hydrogel comprising water, electrolyte and an enzyme with skin of the mammalian subject and contacting a bi-modal electrode assembly to a second surface of the hydrogel, the assembly comprising a first and second bi-modal electrodes, a first and second sensing electrodes and a first and second reference electrodes;    (b) for a fixed period of time, providing a current to the first bi-modal electrode in an amount sufficient to effect the reverse-iontophoretic extraction of a chemical signal through the mammalian subject's skin, through the hydrogel and to the catalytic surface of the first sensing electrode;    (c) for a second period of time, providing a potential to the first sensing electrode in an amount sufficient to drive electrochemical conversion of chemical signal while utilizing the second bi-modal electrode as a counter electrode with respect to the first sensing electrode;    (d) measuring the electrical current generated by the electrochemical conversion at the electrode; and    (e) correlating the measured current to a concentration of chemical signal in the mammalian subject.    
     
     
         11 . The method of  claim 10 , wherein the catalytic face of each sensing electrode comprises a platinum catalytic surface and the bi-modal electrodes are comprised of Ag/AgCl.  
     
     
         12 . The method of  claim 11 , wherein the sensing electrode operates at a current level in the range of 1 nanoamp to 1 milliamp and the bi-modal electrode operates at a current level in the range of 1 nanoamp to 5 milliamps. and reference electrodes.  
     
     
         13 . The method of  claim 12  wherein the chemical signal is glucose and the enzyme if glucose oxidase.  
     
     
         14 . The method of  claim 13  wherein said transcutaneous reverse-iontophoresis diagnostic system is operated in an alternating polarity mode.