Microfluidic Systems For Electrochemical Transdermal Analyte Sensing Using a Capillary-Located Electrode

Abstract

A sensing device, designed to be used in contact with the skin, contains a plurality of individually controllable sites for electrochemically monitoring an analyte, such as glucose, in interstitial fluid of a user. The device includes at least a hydrophobic layer designed to contact the skin; a capillary channel providing an opening adjacent the skin; a metal electrode layer having a sensor layer applied to an edge portion thereof such that it is exposed to the interior of said capillary channel, the sensing layer being effective to measure the analyte.

1 . A sensing device comprising a plurality of individually controllable detection sites for electrochemically monitoring an analyte in interstitial fluid of a user, each individually controllable detection site comprising:
 a dual opening capillary channel traversing multiple layers and having one of the dual openings located adjacent to the skin of the user, the multiple layers including at least a hydrophobic layer, designed to contact the skin, and a metal electrode layer, wherein the metal electrode layer is discontinuous at a circumference of the capillary channel, such that two non-contiguous edge portions of the metal electrode layer are present within the circumference of said channel; and   a first non-contiguous edge portion of the metal electrode layer including a sensing layer applied thereto and being exposed to an interior of the capillary channel, wherein the sensing layer is effective to measure the analyte within interstitial fluid of the user entering the capillary channel and contacting the first non-contiguous edge portion including the sensing layer.   
     
     
         2 . The sensing device of  claim 1 , further comprising: a microheater located adjacent said hydrophobic layer, the microheater being effective to produce heat when a sufficient voltage is applied thereto to ablate the stratum corneum of the underlying skin and access the interstitial fluid containing the analyte. 
     
     
         3 . The sensing device of  claim 1 , wherein the hydrophobic layer is silicone. 
     
     
         4 . The sensing device of  claim 1 , wherein the first structural layer is selected from the group consisting of glass and a ceramic-like material. 
     
     
         5 . The sensing device of  claim 1 , wherein the metal electrode layer is selected from the group consisting of gold and platinum. 
     
     
         6 . The sensing device of  claim 5 , wherein the sensing layer is a conducting polymer. 
     
     
         7 . The sensing device of  claim 6 , wherein the conducting polymer is polypyrrole (PPy). 
     
     
         8 . The sensing device of  claim 7 , wherein the polypyrrole (PPy) is modified with glucose oxidase (GOx). 
     
     
         9 . The sensing device of  claim 8 , wherein the polypyrrole (PPy) is modified with glucose oxidase (GOx) is co-deposited on the edge of the metal electrode layer with a mediator. 
     
     
         10 . The sensing device of  claim 9 , wherein the mediator is ferricyanide. 
     
     
         11 . A method for electrochemically monitoring an analyte in interstitial fluid of a user, the method comprising:
 contacting the user's skin with a monitoring device, the monitoring device including a plurality of individually controllable detection sites for electrochemically monitoring the analyte in interstitial fluid of a user;   controlling at least a first of the individually controlled detection sites to apply a first voltage to a microheater located adjacent to the user's skin at the first of the individually controlled detection sites, wherein the microheater produces heat responsive to the applied first voltage, the heat being sufficient to ablate the stratum corneum of the underlying skin and access the interstitial fluid of the user containing the analyte;   receiving the accessed interstitial fluid at a first opening of a dual opening capillary channel of the first of the individually controlled detection sites, wherein the accessed interstitial fluid rises through the capillary channel, traversing multiple material layers including at least a hydrophobic layer contacting the user's skin, first structural layer and a metal electrode layer that is discontinuous at a circumference of the capillary channel, such that two non-contiguous edge portions of the metal electrode layer are present within the circumference of said capillary channel, a first non-contiguous edge portion of the metal electrode layer including a sensing layer applied thereto and being exposed to an interior of the capillary channel;   applying a second voltage between the two non-contiguous edge portions of the metal electrode layer when the interstitial fluid passes thereby within the capillary channel; and   electronically detecting the analyte in the interstitial fluid using the sensing layer responsive to the application of the second voltage.   
     
     
         12 . The method of  claim 11 , further comprising applying the first voltage for approximately 30 msec. 
     
     
         13 . The method of  claim 12 , wherein the first voltage is about 3V. 
     
     
         14 . The method of  claim 11 , wherein the second voltage is about 0.2 to 0.4 V. 
     
     
         15 . The method of  claim 11 , wherein the hydrophobic layer is silicone. 
     
     
         16 . The method of  claim 11 , wherein the first structural layer is selected from the group consisting of glass and a ceramic-like material. 
     
     
         17 . The method of  claim 11 , wherein the metal electrode layer is selected from the group consisting of gold and platinum. 
     
     
         18 . The method of  claim 17 , wherein the sensing layer is a conducting polymer. 
     
     
         19 . The method of  claim 18 , wherein the conducting polymer is polypyrrole (PPy). 
     
     
         20 . The method of  claim 19 , wherein the polypyrrole (PPy) is modified with glucose oxidase (GOx).