Presented by: Jay Leitch

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:  Highly Specific  Linearity in signal response  Independent of hydrodynamics  Independent of co-substrates  Requires minimal calibration Biocompatible Long lifespan Long lifespan Low cost Low cost Can be scaled down Can be scaled down

Biosensor Components  Membranes: Used to protect immobilized GOD electrodes from high metabolite concentration. Extends linearity of sensor by limiting glucose, but not O 2 diffusion Used to protect immobilized GOD electrodes from high metabolite concentration. Extends linearity of sensor by limiting glucose, but not O 2 diffusion E.g. Polyurethane (PU), Perforated, Polycarbonate E.g. Polyurethane (PU), Perforated, Polycarbonate  Transducers:  Thermometric  Optical – fluorescence, chemiluminescence, optical rotation  Electrochemical – potentiometric, voltammetric, amperometric  Biological Component: Biocatalytic Mediator: enzyme/antibody etc. that interacts with the desired analyte Biocatalytic Mediator: enzyme/antibody etc. that interacts with the desired analyte

Enzymatic Reactions for Glucose Analysis Glucose + O 2 Gluconic acid + H 2 O 2 19 kcal H 2 O 2 ½ O 2 + H 2 O 24 kcal Total Reaction: Glucose + ½ O 2 Gluconic acid + H 2 O 43 kcal * Glucose oxidase (GOD) is commonly used since it fairly stable & requires no cofactors or coenzymes *glucose oxidase catalase ΔHΔHΔHΔH GOD + catalase

Thermometric Sensors  Measures heat changes caused by enzymatic reactions  Limited to in vitro analysis  Transducers: Thermistor – very sensitive, but excitation electricity causes a raise in thermister temperature, thus strict control over ambient temperatures is needed Thermocouple – no excitation electricity, but low sensitivity Thermopile – Antimony and Bismuth evaporated in thin film creating a series array of thermocouple junctions. Sensitivity increases with the number of junctions. Do not require excitation electricity

Thermopile-based Enzyme Probe

Optical Sensors  Can measure aqueous glucose concentrations by optical emissions by using fluorescence, chemiluminescence and optical rotation of molecules  Advantages: Electrical isolation from patient Electrical isolation from patient Eliminates electrical interference Eliminates electrical interference No need for a reference electrode No need for a reference electrode Easily miniaturized due to advances in fiber optics Easily 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 mM. Response time 5-7 min.

Electrochemical Sensors  commonly measured by amperometric or potentiometric methods  composed of electrode with enzyme, such as GOD immobilized and surrounded by PU membrane  can monitor glucose levels by examining reaction substrates or products  can be miniaturized easily and produce effective signals

So Why Is This Useful?  Many individuals in the world are diagnosed with Diabetes Mellitus  Diabetes mellitus is a disease that affects the production or release of insulin  Chronic elevations of blood glucose can lead to renal, retinal and neural complications  Traditionally glucose levels could be monitored using capillary blood from finger prick and using GOD/peroxidase dry reagent strips and insulin injections  Implantable glucose sensors could be a solution to prevent insulin shock and diabetic coma

Implantable Glucose Sensors  Continuous monitoring of analyte concentration  Sensor signal coupled to an infusion pump for a closed-loop insulin delivery (i.e. forming an artificial pancrease)  Usually implanted in subcutaneous tissue  Based on electrochemical or optical techniques  3 Basic Designs: vessel-shaped – blood flows through it needle type – injected by needle needle type – injected by needle plane-geometry – see figure below plane-geometry – see figure below

Glucose Sensor Implant Results  Implant showed a linear trend between sensor output and glucose concentration  95% accurate  Only a slight lag (60 secs.) between increased glucose and signal  Fairly Sensitive  Showed no effects in the presence of inhibitors Problems : Short lifespan – performance impaired in 3-7 days and need replacing after 4 weeks Short lifespan – performance impaired in 3-7 days and need replacing after 4 weeks Eliminating lag would be ideal since high glucose levels for even one minute good potentially cause damage Eliminating lag would be ideal since high glucose levels for even one minute good potentially cause damage Glucose concentration is lower in subcutaneous interstitial fluids than in bloodstream Glucose concentration is lower in subcutaneous interstitial fluids than in bloodstream

References 1. Cunningham, A. Introduction to bioanalytical sensors. New York: John Wiley & Sons, Inc. 1998, pp Turner,A. Advances in Biosensors. Vol.1 England: Jai Press Ltd. 1991, pp Ward, W. et. al. A new amperometric glucose microsensor: in vitro and short-term in vivo evaluation. Elsevier Science. Biosensors & Bioelectronics 17 (2002) Wilson, G. et. al. Biosensors: Fundamentals and Applications. New York: Oxford University Press, 1989, pp Wise, L. Bioinstrumentation and Biosensors. New York: Marcel Dekker, Inc., 1991, pp Wise, L. Applied Biosensors. Boston: Butterworth Publishers, 1989, pp