Presented by:

Jay Leitch

What are Glucose Biosensor?What are Glucose Biosensor? Immobilized biological components fixed

on ordinary analytical detectors

Selectively detects and quantifies the analyte in a natural matrix without requiring any separation

Ideal Sensor:Ideal Sensor: Highly SpecificHighly Specific

Linearity in signal responseLinearity in signal response

Independent of hydrodynamicsIndependent of hydrodynamics

Independent of co-substratesIndependent of co-substrates

Requires minimal calibrationRequires minimal calibration

• BiocompatibleBiocompatible

• Long lifespanLong lifespan

• Low costLow cost

• Can be scaled downCan be scaled down

BiosensorBiosensor ComponentsComponents Membranes:Membranes:

• Used to protect immobilized GOD electrodes from Used to protect immobilized GOD electrodes from high metabolite concentration. Extends linearity of high metabolite concentration. Extends linearity of sensor by limiting glucose, but not Osensor by limiting glucose, but not O22 diffusion diffusion

• E.g. Polyurethane (PU), Perforated, PolycarbonateE.g. Polyurethane (PU), Perforated, Polycarbonate

Transducers:Transducers: ThermometricThermometric Optical – fluorescence, chemiluminescence, optical Optical – fluorescence, chemiluminescence, optical

rotationrotation Electrochemical – potentiometric, voltammetric, Electrochemical – potentiometric, voltammetric,

amperometricamperometric Biological Component:Biological Component:

• Biocatalytic Mediator: enzyme/antibody etc. that Biocatalytic Mediator: enzyme/antibody etc. that interacts with the desired analyteinteracts with the desired analyte

Enzymatic Reactions for Glucose Enzymatic Reactions for Glucose AnalysisAnalysis

Glucose + OGlucose + O22 Gluconic acid + HGluconic acid + H22OO2 2 19 kcal19 kcal

HH22OO22 ½ O ½ O22 + H + H22OO 24 kcal24 kcal

Total Reaction:Total Reaction:

Glucose + ½ OGlucose + ½ O22 Gluconic acid + HGluconic acid + H22O O 43 kcal43 kcal

* Glucose oxidase (GOD) is commonly used since it fairly stable & requires no cofactors or coenzymes

*glucose oxidase

catalase

ΔΔHH

GOD +

catalase

Thermometric SensorsThermometric Sensors Measures heat changes caused by Measures heat changes caused by

enzymatic reactionsenzymatic reactions Limited to in vitro analysisLimited to in vitro analysis Transducers:Transducers:

ThermistorThermistor – very sensitive, but excitation – very sensitive, but excitation electricity causes a raise in thermister electricity causes a raise in thermister

temperature, thus strict control over temperature, thus strict control over ambient ambient temperatures is neededtemperatures is needed

ThermocoupleThermocouple – no excitation electricity, – no excitation electricity, but low sensitivitybut low sensitivityThermopileThermopile – Antimony and Bismuth – Antimony and Bismuth

evaporated in thin film creating a series evaporated in thin film creating a series array of array of thermocouple thermocouple junctions. Sensitivity junctions. Sensitivity increases with the number of junctions. Do increases with the number of junctions. Do not require excitation electricitynot require excitation electricity

Thermopile-based Enzyme ProbeThermopile-based Enzyme Probe

Optical SensorsOptical Sensors Can measure aqueous glucose concentrations by Can measure aqueous glucose concentrations by

optical emissions by using fluorescence, optical emissions by using fluorescence, chemiluminescence and optical rotation of moleculeschemiluminescence and optical rotation of molecules

Advantages:Advantages:• Electrical isolation from patientElectrical isolation from patient• Eliminates electrical interferenceEliminates electrical interference• No need for a reference electrodeNo need for a reference electrode• Easily miniaturized due to advances in fiber opticsEasily miniaturized due to advances in fiber optics

Bioaffinity glucose sensor: glucose binds to con A (concanavalin A) releasing a fluoroesceinated dextran. Range of measureable glucose levels 2.8-22 mM. Response time 5-7 min.

ElectrochemicalElectrochemical Sensors Sensors commonly measured by commonly measured by

amperometric or potentiometric amperometric or potentiometric methodsmethods

composed of electrode with composed of electrode with enzyme, such as GOD immobilized enzyme, such as GOD immobilized and surrounded by PU membraneand surrounded by PU membrane

can monitor glucose levels by can monitor glucose levels by examining reaction substrates or examining reaction substrates or productsproducts

can be miniaturized easily and can be miniaturized easily and produce effective signalsproduce effective signals

So Why Is This Useful?So Why Is This Useful? Many individuals in the world are diagnosed with Many individuals in the world are diagnosed with

Diabetes MellitusDiabetes Mellitus

Diabetes mellitus is a disease that affects the Diabetes mellitus is a disease that affects the production or release of insulinproduction or release of insulin

Chronic elevations of blood glucose can lead to Chronic elevations of blood glucose can lead to renal, retinal and neural complicationsrenal, retinal and neural complications

Traditionally glucose levels could be monitored Traditionally glucose levels could be monitored using capillary blood from finger prick and using using capillary blood from finger prick and using GOD/peroxidase dry reagent strips and insulin GOD/peroxidase dry reagent strips and insulin injectionsinjections

Implantable glucose sensors could be a solution Implantable glucose sensors could be a solution to prevent insulin shock and diabetic comato prevent insulin shock and diabetic coma

Implantable Glucose SensorsImplantable Glucose Sensors Continuous monitoring of analyte concentrationContinuous monitoring of analyte concentration Sensor signal coupled to an infusion pump for a Sensor signal coupled to an infusion pump for a

closed-loop insulin delivery (i.e. forming an artificial closed-loop insulin delivery (i.e. forming an artificial pancrease)pancrease)

Usually implanted in subcutaneous tissueUsually implanted in subcutaneous tissue Based on electrochemical or optical techniquesBased on electrochemical or optical techniques 3 Basic Designs:3 Basic Designs: vessel-shaped – blood flows through itvessel-shaped – blood flows through it

needle type – injected needle type – injected by needleby needle

plane-geometry – see plane-geometry – see figure belowfigure below

Glucose Sensor Implant ResultsGlucose Sensor Implant Results Implant showed a linear trend Implant showed a linear trend

between sensor output and between sensor output and glucose concentrationglucose concentration

95% accurate95% accurate Only a slight lag (60 secs.) Only a slight lag (60 secs.)

between increased glucose and between increased glucose and signalsignal

Fairly Sensitive Fairly Sensitive Showed no effects in the Showed no effects in the

presence of inhibitorspresence of inhibitors

ProblemsProblems::

• Short lifespan – performance impaired in 3-7 days and need Short lifespan – performance impaired in 3-7 days and need replacing after 4 weeksreplacing after 4 weeks

• Eliminating lag would be ideal since high glucose levels for even Eliminating lag would be ideal since high glucose levels for even one minute good potentially cause damage one minute good potentially cause damage

• Glucose concentration is lower in subcutaneous interstitial fluids Glucose concentration is lower in subcutaneous interstitial fluids than in bloodstreamthan in bloodstream

ReferencesReferences1.1. Cunningham, A. Cunningham, A. Introduction to bioanalytical sensors. Introduction to bioanalytical sensors. New New

York: John Wiley & Sons, Inc. 1998, pp.159-62York: John Wiley & Sons, Inc. 1998, pp.159-62

2.2. Turner,A. Turner,A. Advances in BiosensorsAdvances in Biosensors. Vol.1 England: Jai Press . Vol.1 England: Jai Press Ltd. 1991, pp.67-72.Ltd. 1991, pp.67-72.

3.3. Ward, W. et. al. Ward, W. et. al. A new amperometric glucose microsensor: in A new amperometric glucose microsensor: in vitro and short-term in vivo evaluation. vitro and short-term in vivo evaluation. Elsevier Science. Elsevier Science. Biosensors & Bioelectronics 17 (2002) 181-189. Biosensors & Bioelectronics 17 (2002) 181-189.

4.4. Wilson, G. et. al. Wilson, G. et. al. Biosensors: Fundamentals and Applications.Biosensors: Fundamentals and Applications. New York: Oxford University Press, 1989, pp.390-405. New York: Oxford University Press, 1989, pp.390-405.

5.5. Wise, L. Wise, L. Bioinstrumentation and Biosensors.Bioinstrumentation and Biosensors. New York: New York: Marcel Dekker, Inc., 1991, pp.229-45.Marcel Dekker, Inc., 1991, pp.229-45.

6.6. Wise, L. Wise, L. Applied Biosensors. Applied Biosensors. Boston: Butterworth Publishers, Boston: Butterworth Publishers, 1989, pp.227-44.1989, pp.227-44.