Electrochemical Glucometers

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Diabetes



Glucometers
            Electrochemical glucometer                      
Example home glucometer




  • At home glucometers allow diabetic patients to monitor their blood glucose levels with a minimal amount of sample blood. 
  • Glucometers utilize disposable electrochemical cells. 
  • Type I diabetics check their blood glucose levels about 4 times a day. 
  • Type II diabetics check their blood glucose levels about 2 times a day. 




Traditional Electrochemistry


Components of a typical galvanic electrochemical cell:
  • Working electrode: reaction of interest takes place
    • example: silver electrode
  • Reference electrode: standard hydrogen electrode
Current flowing between electrodes can be measured using a voltmeter. 
example cell
Traditional Electrochemical Cell
composing of working electrod,
reference electrode, and ions. 

Chemical Reactions

Step 1: Oxidation of Glucose by Enzyme
Glocuse Oxidase (GOD) is an enzyme that directly oxides glucose


Step 2: Reduction of enzyme by Mediator

Mediator transports electrons to working electrode. 


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An example of a mediator is ferrocene monocarboxylic acid. 





Testing Strips


  • When blood added, glucose is oxidized by enzyme coated on the working electrode
  • Voltage applied between working and reference electrode
  • Measure current between working and reference electrode












Example Testing Strip (left) composing of all necessary components. 



Amperometric Analysis

  • Current measured across the test strip 5-15 seconds after blood is drawn
  • As seen on the calibration curve to the right, current levels directly proportional to glucose levels.







Ampometric Analysis Output (left) Calibration curve for glucose enzyme electrode in (*) argon, (0) air, and (+) oxygen-saturated buffer. Steady-state current was measured at 160 mV vs. SCE, pH 7.0, and 25 degrees Celcius. (Cass 1984)



Advantages
  • Fast
  • Disposable Strip
  • No Instrument Contamination
Disadvantages
  • Discomfort of pricking finger
  • Non-continuous measurement


Further Advancements: Implantable Electrochemical Glucometers





  • In a recent study by Barbara Gillian et. al. was able to construct an implantable electrochemical glucosensor that lasted over 100 days in vivo. 
  • In this study, the designed glucosensor was able to record blood glucose levels every 128 seconds and were highly corelated with lab monitors and two common glucose monitors (see left). 
  • While implantable glucosensors show promise, problems arise with:
  • Sensor stability
  • Calibration
  • Biocompatability (rejection): Immunoresponse from the body can destroy implanted sensors.  
 
References
Cass, Anthony E. G. "Ferrocene-mediated enzyme electrode for amperometric determination of glucose." Analytical Chemistry.  (1984)56:667-671

Heller, A. and B. Feldman. "Electrochemical glucose sensors and their applications in diabetes management."  Chemical Reviews.  (2008)108: 2482-2505

Gilligan, Barbara J. et. al. "Feasibility of Continuous Long-Term Glucose Monitoring from a Subcutaneous Glucose Sensor in Humans"  Diabete Technology & Therapeutics.  (2004)6:378-388. 

Leary and Skoog.  Principles of Instrumental Analysis.  Orlando: Sauders College Publishing (1992)

Newman, Jeffery D.  and Anthony P.F. Turner.  "Home blood glucose biosensors: a commercial perspective."  Biosensors and Bioelectronics.  (2005)20:2435-2453.