1. Electrochemical Glucometers

2. Diabetes
Diabetes affects 17 million Americans and 171 million people worldwide.
Two Major Types
Type I: Pancreas produces very little or no insulin; affects younger patients
Type II: Pancreas does not produce enough insulin or does not use produced insulin effectively (insulin resistant); affect middle-aged to older patients
Other Types: Gestational Diabetes during pregnancy 1.
Heller, A. and B. Feldman. Chemical Reviews. (2008)108:
Electrochemical Glucose Sensors and Their Applications in Diabetes Management

3. Blood Glucose
Insulin
hormone that circulates in the blood
helps body use and store glucose
Low levels of insulin: body cannot store glucose
After eating, blood glucose rises as food is broken down
High blood glucose levels damage the eyes, kidneys, nerves, and heart over time
Normal glucose levels: 82 to 110 mg/dL 1.

4. Management of Diabetes
Diet
Exercise
Oral Medication
Insulin Therapy: injection of exogenous insulin analogs when blood glucose levels are high
Image: public domain

5. Electrochemical Glucometers
Measure glucose in blood
At home testing requires minimal amounts of blood
Utilizes disposable electrochemical cell
electrical current is created from the oxidation of glucose 1.
Type I check 4 times/day
Type II check 2 times/day

6. Traditional Electrochemistry
Components
Working electrode: Silver electrode
Where reaction of interest takes place
Reference electrode: Standard hydrogen electrode
Measure current flowing between electrodes
H2 gas
Cl-
Leary and Skoog. Principles of Instrumental Analysis. Orlando: Sauders College Publishing (1992).
Ag+

7. Chemical Reactions Oxidation of Glucose by Enzyme
glucose + GOD(ox)  gluconolactone + GOD(red)
glucose  gluconolactone + 2e-
2e- + GOD(ox)  GOD(red)
D-glucose
Glucose Oxidase (GOD) is an enzyme directly oxides Glucose
Cass, Anthony E. G. Analytical Chemistry. (1984)56:
Ferrocene-mediated enzyme electrode for amperometric determination of glucose
Reduction of Enzyme by Mediator
GOD(red) + 2Fecp2R+  GOD(ox) + 2Fecp2R + 2H+
2Fecp2R Fecp2R + 2e-
Ferrocene monocarboxylic acid (Fecp2R)
Mediator transports electrons to working electrode

8. Test Strips
When blood added, glucose is oxidized by enzyme coated on working electrode
Voltage applied between working and reference electrode
Measure current between working and reference electrode 1.

9. Amperometric Analysis
Current measured 5-15 seconds after blood is drawn
Current levels directly proportional to glucose levels 1.
Cass, Anthony E. G. Analytical Chemistry. (1984)56:
Ferrocene-mediated enzyme electrode for amperometric determination of glucose
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 OC.

10. Advantages Disadvantages
Fast Disposable Strip No Instrument Contamination
Disadvantages
1. Newman, Jeffery D. And Anthony P.F. Turner. Biosensors and Bioelectronics. (2005)20:
Home blood glucose biosensors: a commercial perspective
Discomfort of pricking finger
Non-continuous measurement

11. Implantable Glucose Sensor
Advantage: continuous glucose monitoring
Could be coupled with continuous subcutaneous insulin infusions
Problems:
Sensor stability
Calibration
Biocompatibility
1. Newman, Jeffery D. And Anthony P.F. Turner. Biosensors and Bioelectronics. (2005)20:
Home blood glucose biosensors: a commercial perspective

12. Recent Study
1. Gilligan, Barbara J. et. Al. Diabete Technology & Therapeutics. (2004)6:
Feasibility of Continuous Long-Term Glucose Monitoring from a Subcutaneous Glucose Sensor in Human
Designed Implantable sensor recorded glucose values every 128 s
Longest sensor (of 5 subjects) lasted 103 days in vivo!