Subcutaneous Glucose Electrode

Abstract

A small diameter flexible electrode designed for subcutaneous in vivo amperometric monitoring of glucose is described. The electrode is designed to allow “one-point” in vivo calibration, i.e., to have zero output current at zero glucose concentration, even in the presence of other electroreactive species of serum or blood. The electrode is preferably layered, with the layers serially deposited within a recess upon the tip of a polyamide insulated gold wire. A first glucose concentration-to-current transducing layer can be overcoated with an electrically insulating and glucose flux limiting layer (second layer) on which, optionally, an immobilized interference-eliminating horseradish peroxidase based film is deposited. An outer layer is preferably biocompatible.

1 .- 20 . (canceled) 
     
     
         21 . A method of calibrating an electrochemical sensor, the method comprising:
 implanting an electrochemical sensor subcutaneously into a subject;   obtaining an output signal from the electrochemical sensor to determine an analyte concentration;   withdrawing a single calibration sample from the subject;   determining an analyte concentration from the single calibration sample;   calibrating the output signal of the electrochemical sensor using the analyte concentration determined from the single calibration sample to provide a single point, in vivo calibration of the electrochemical sensor; and   allowing a predetermined period of time after implantation of the sensor before the output signal generated by the electrochemical sensor is used as an indicator of analyte concentration to the subject.   
     
     
         22 . The method according to  claim 21 , wherein the electrochemical sensor has a sensitivity from 10 pA/mg/dL to about 250 pA/mg/dL when implanted in subcutaneous tissue. 
     
     
         23 . The method according to  claim 21 , wherein at least 90% of analyte concentration values determined by the first electrochemical sensor are within 20% of the analyte concentration values as determined by blood. 
     
     
         24 . The method according to  claim 21 , wherein the analyte sensitivity is linear up to at least 20 mM. 
     
     
         25 . The method according to  claim 21 , wherein the in vivo sensitivity of the electrochemical sensor does not change by more than 5% for at least 72 hours of operation. 
     
     
         26 . The method according to  claim 21 , wherein the operating lifetime of the electrochemical sensor is at least 72 hours. 
     
     
         27 . The method according to  claim 21 , wherein the method further comprises:
 applying a first bias potential to the implanted electrochemical sensor for a first predetermined amount of time;   applying a second bias potential to the implanted electrochemical sensor for a second predetermined amount of time, wherein the first predetermined time is different from the second predetermined time.   
     
     
         28 . The method according to  claim 27 , wherein the first predetermined amount of time is 5 minutes or less. 
     
     
         29 . The method according to  claim 21 , wherein obtaining an output signal comprises applying a bias potential of 0.3V or less to a working electrode of the electrochemical sensor. 
     
     
         30 . The method according to  claim 21 , wherein the electrochemical sensor produces an in vivo baseline current of 5 nA or less. 
     
     
         31 . The method according to  claim 21 , wherein the electrochemical sensor produces an in vivo current output of 35 nA or less. 
     
     
         32 . The method according to  claim 21 , wherein the output signal from the electrochemical sensor is insensitive to oxygen. 
     
     
         33 . The method according to  claim 21 , wherein the electrochemical sensor is oxygen independent. 
     
     
         34 . The method according to  claim 21 , wherein the electrochemical sensor comprises:
 a working electrode; and   a multilayer membrane complex comprising:
 an analyte responsive sensing layer disposed on top and in electrical contact with the working electrode, the analyte responsive sensing layer comprising a glucose-specific enzyme, a mediator and a first polymer selected from the group consisting of poly(vinylimidazole), poly(vinylpyridine) and poly(acrylamide co-I-vinylimidazole), wherein at least one of the glucose-specific enzyme and the mediator is chemically bonded to the first polymer; and 
 a diffusion-limiting layer comprising a second polymer disposed on top and in contact with the analyte responsive sensing layer. 
   
     
     
         35 . The method according to  claim 34 , wherein the mediator is covalently bonded to the first polymer through a spacer moiety. 
     
     
         36 . The method according to  claim 34 , wherein the mediator is covalently bonded to the first polymer through a bidentate ligand. 
     
     
         37 . The method according to  34 , wherein the mediator is crosslinked with the first polymer through one or more crosslinking agent selected from the group consisting of substituted or unsubstituted epoxides, aldehydes, imidoesters, N-hydroxysuccinimide esters, carbodiimides, cyanuric chloride, tetrachlorobenzoquinone, benzoquinone and tetracyanoquinodimethane. 
     
     
         38 . The method according to  claim 21 , wherein the predetermined time period after implantation is 30 minutes or less. 
     
     
         39 . The method according to  claim 21 , wherein the output signal of the electrochemical sensor is calibrated using the withdrawn calibration sample as the only calibration sample. 
     
     
         40 . The method according to  claim 21 , wherein withdrawing a sample comprises obtaining a biological fluid sample from the subject from a location that is different from a site where the electrochemical sensor is implanted. 
     
     
         41 . A method of calibrating an electrochemical sensor, the method comprising:
 implanting an electrochemical sensor subcutaneously into a subject;   obtaining an output signal from the electrochemical sensor to determine an analyte concentration, wherein a predetermined period of time is allowed to lapse after implantation of the sensor before the output signal generated by the electrochemical sensor is used as an indicator of analyte concentration to the subject;   withdrawing a single calibration sample from the subject;   determining an analyte concentration from the single calibration sample; and   calibrating the output signal of the electrochemical sensor using the analyte concentration determined from the single calibration sample to provide a single point, in vivo calibration of the electrochemical sensor.