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!