Accu-Chek Advantage: Electrochemistry for Diabetes …

1 DiabetesElectrochemistry Basic PrinciplesWhen the body no longer produces insulin, or has a reducedsensitivity to it, Diabetes is the result. In Indiana, over 338,000people ( of the population) have been diagnosed, andanother 182,000 are thought to have unidentified is, roughly one in twelve Hoosiers has Diabetes . Thechronic elevated blood sugar which results from this conditioncauses long-term damage to numerous tissues and medical and financial costs to our state, summarized ina recent State Department of Health report (1), are staggering:Much of this burden may be reduced or eliminated by earlydetection and improved self-care.

2 The Diabetes Control andComplications Trial (DCCT) (2), a 10-year nationwide studyof 1,441 diabetics, conclusively demonstrated that improvedcontrol of blood sugar delayed or prevented many of thesecomplications at least 50% better than with poorly-controlledsubjects. Subsequent studies have corroborated thisconclusion. This good control is enabled by frequent,consistent and accurate self-testing of blood glucose tooptimize are several essential elements in a medical devicedesigned for patient self-monitoring.

3 Because these systemsare medical devices, used to make medical decisions or avoidpotentially life-threatening incidents every day, they must beof very high quality, and the information displayed must beaccurate. The sensors must be easily manipulated by sight-impaired users, and the system must be very user-friendly toencourage more frequent testing for better control. In thehospital or physician s office there are additional qualityrequirements, and the possibility of multiple sample types( , capillary, arterial, venous and neonatal blood).

4 Accu-Chek advantage meets these needs by providingaccurate and dependable glucose measurement using a tinydrop of blood, for all blood sample types (capillary, arterial,venous and neonatal) over a wide range of hematocrit. Itdelivers this performanceattemperatures from 57 to 104 F, and at altitudes to above10,000 feet. More patients and hospitals worldwide rely onAccu- chek advantage than any other glucose advantage technology uses two components:Let s begin with basic electrical definitions and concepts andassemble them into adescription of themeasurement method.

5 """" Diabetes has caused nearly 40% of end-stage renaldisease in has blinded 22,000 Hoosiers over age 40 andcauses over 1,700 non-traumatic amputations each year roughly doubles a patient s risk of death andcontributes to over 5,000 deaths in Indiana each cost Indiana almost $ billion in patient simply inserts a biosensor into the meter andapplies a small drop of AdvantageHow Does the Hand-heldElectrochemical System Work?simplifiedin a matter of secondsBrian Hill, ,Roche Diagnostics, 9115 Hague Road, Indianapolis, Indiana 46256 advantage .

6 Electrochemistry for Diabetes Management This article discusses the electrochemical principles behind the Accu-Chek glucose SeparationsElectronic Meter(measurement, storage andcommunication device)"""Applies potentialdifferences in aprogrammed sequenceto the sensorCollects biamperometriccurrent dataRecords and displaysresultsDisposable Biosensor(sample measurement reaction site)"""Collects the blood sampleSample undergoes anenzymatic chemicalreaction followed by:An electrochemicalreaction""""""""Current: Theof electron movement or chargetransfer. This is analogous to water flow in a pipe ( ,gallons per hour for water,for current).

7 Potential: If current is, potential is( , pounds per square inch for water,forpotential). A potential difference represents a differencein theat two ll limit this discussion to particularchemical and electrical interactions between two phases:a chemically inert, electrical conductor () and aliquid ionic conductor (or) wherechemical reactions electron energy in ions or moleculesis determined by chemical structure, the energy ofelectrons in an electrode may be easily changed byadjusting the electrode potential. There are two commonmethods for controlling:Blood is a complex fluid and glucose levels vary widelyover time in a single factors besides glucose vary in blood from healthypatients (, hematocrit, oxygen levels, metabolicbyproducts,).

8 Patients with Diabetes may have a wide range of othermedical problems creating even greater variation in permit chemical reactions to occur at muchfaster rates without requiring major modifications to thebiological sample (, increased temperature orpressure, dramatic pH changes, addition of highlyreactive chemicals,).rateamperesflow ratepressurevoltsaverage electron energyelectrodeelectrolytesampleelectrod e as water will flow if a pressure difference exists betweentwo points in a pipe,will flow if aexists between two points in a conductor. Similarly, as flowincreases with pressure in a pipe, current increases in aconductor as the potential difference is Electronically using a meter Chemically.

9 If an electrode can match its electronenergy with ions in solution, those ions may define theelectrode potential. Thedefines the(electron addition) of potassiumferricyanide (M ) to potassium ferrocyanide (M). This is asimple:Fe(CN)+ eFe(CN)M+ e MSince Mand Meach have different electron energies, weuse the Nernst equation to define the solution potential (theaverage energy of electrons in the solution):E=Enzymes are protein catalysts which accelerate specificchemical reactions. In the plumbing metaphor, enzymesincrease pipe diameter by removing a blockage; instead ofwater trickling past the blockage, it may now flow are often highly specific, and this specificityenables organisms to manage a single type of molecule amongtens of thousands within a cell or organ.

10 Enzymes offerpowerful advantages for biological , enzymes rarely exchange electrons directlywith electrodes. The same is true for many other biologicalmolecules, such as glucose. An electrochemical measurementoften requires a substance to facilitate (or mediate) thistransfer, and such reagents are well-known mediator is potassium ferricyanide. Thereaction process is:a) Glucose first reacts with the enzyme g. Glucose is oxidized to gluconic acidand the enzyme is temporarily reduced by twoelectrons transferred from glucose to the ) The reduced enzyme next reacts with M , transferringa single electron to each of two mediator ions.