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Glucose Biosensors

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... Enzymatic Reactions for Glucose Analysis Thermometric Sensors Thermopile-based Enzyme Probe Optical Sensors Electrochemical Sensors So Why Is This Useful? – PowerPoint PPT presentation

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Title: Glucose Biosensors


1
Glucose Biosensors
Presented by
Jay Leitch
2
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
  • Low cost
  • Can be scaled down

3
Biosensor Components
  • Membranes
  • Used to protect immobilized GOD electrodes from
    high metabolite concentration. Extends linearity
    of sensor by limiting glucose, but not O2
    diffusion
  • 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

4
Enzymatic Reactions for Glucose Analysis
?H
glucose oxidase
  • Glucose O2 Gluconic acid H2O2 19 kcal
  • H2O2 ½ O2 H2O 24 kcal
  • Total Reaction
  • Glucose ½ O2 Gluconic acid H2O 43 kcal
  • Glucose oxidase (GOD) is commonly used since it
    fairly stable requires no cofactors or
    coenzymes

catalase
GOD
catalase
5
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

6
Thermopile-based Enzyme Probe
7
Optical Sensors
  • Can measure aqueous glucose concentrations by
    optical emissions by using fluorescence,
    chemiluminescence and optical rotation of
    molecules
  • Advantages
  • Electrical isolation from patient
  • Eliminates electrical interference
  • No need for a reference electrode
  • 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
2.8-22 mM. Response time 5-7 min.
8
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

9
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

10
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
  • plane-geometry see figure below

11
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
  • 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

12
References
  1. Cunningham, A. Introduction to bioanalytical
    sensors. New York John Wiley Sons, Inc.
    1998, pp.159-62
  2. Turner,A. Advances in Biosensors. Vol.1 England
    Jai Press Ltd. 1991, pp.67-72.
  3. Ward, W. et. al. A new amperometric glucose
    microsensor in vitro and short-term in vivo
    evaluation. Elsevier Science. Biosensors
    Bioelectronics 17 (2002) 181-189.
  4. Wilson, G. et. al. Biosensors Fundamentals and
    Applications. New York Oxford University Press,
    1989, pp.390-405.
  5. Wise, L. Bioinstrumentation and Biosensors. New
    York Marcel Dekker, Inc., 1991, pp.229-45.
  6. Wise, L. Applied Biosensors. Boston
    Butterworth Publishers, 1989, pp.227-44.
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