Electrochemical Glucometers
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
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
Management of Diabetes
• Diet• Exercise• Oral Medication
• Insulin Therapy: injection of exogenous insulin analogs when blood glucose levels are high
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
Type I check 4 times/day Type II check 2 times/day
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-
Ag+
GOD(red) + 2Fecp2R+ GOD(ox) + 2Fecp2R + 2H+
2Fecp2R 2Fecp2R + 2e-
Chemical ReactionsOXIDATION OF GLUCOSE BY ENZYME
REDUCTION OF ENZYME BY MEDIATOR
Glucose Oxidase (GOD) is an enzyme directly oxides Glucose
Mediator transports electrons to working electrodeFerrocene monocarboxylic acid (Fecp2R)
glucose + GOD(ox) gluconolactone + GOD(red)
glucose gluconolactone + 2e-
2e- + GOD(ox) GOD(red) D-glucose
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
Amperometric Analysis
• Current measured 5-15 seconds after blood is drawn
• Current levels directly proportional to glucose levels
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.
AdvantagesFast
Disposable StripNo Instrument Contamination
Disadvantages
Discomfort of pricking fingerNon-continuous measurement
Implantable Glucose Sensor
• Advantage: continuous glucose monitoring – Could be coupled with continuous subcutaneous
insulin infusions• Problems:– Sensor stability– Calibration– Biocompatibility
Recent Study
Designed Implantable sensor recorded glucose values every 128 sLongest sensor (of 5 subjects) lasted 103 days in vivo!
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