Electrochemical Transduction in Chemical Sensors

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Electrochemical Transductionin Chemical Sensors

• Brent Lutz
• BioMEMS Microfluidics Lab
• IMG Brown Bag Lectures
• November 18, 2004

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Outline

• Aims
• Introduction to Chemical and Biological Sensors.
• Fundamentals of Electrochemical Transduction.
• Brief Introduction to BioMEMS Microfluidics Lab.

• Overview
• What are chem/biosensors?
• What are their important performance
  characteristics?
• How are they structured and classified?
• How do they work by electrochemical transduction?
• Example of an electrochemical biosensor.

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Definitions

• Physical Sensors Track STATE VARIABLES and
  GENERAL PROPERTIES of a system (T, P, R, I, r, Q,
  etc....)
• Chemical Sensors Track MOLECULAR COMPOSITION.
• Recognition element physical sensor
• DEFINING PERFORMANCE FACTOR Selectivity
• pH meter, MOS gas sensors

• SEMANTICS Is gas chromatography a chemical
  sensor?

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Definitions

• Biological Sensors Chemical sensors containing
  and/or tracking BIOMOLECULES
• AKA Biosensors
• DNA, RNA, proteins, enzymes, antibodies,
  metabolites, etc....
• Superior SELECTIVITY (for now)
• glucose monitors, breathalyzers
• mainly in the development phase
• SEMANTICS Are EEG MRI biosensors?

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In the BioMEMS Lab

• Building mTAS chips that function as biosensors
• DNA protein sensors for
• medical research diagnosis
• biowarfare
• Gas-phase biosensors for detection of H2

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Outline

• Overview
• What are chem/biosensors?
• What are their important performance
  characteristics?
• How are they structured and classified?
• How do they work by electrochemical transduction?
• Example of an electrochemical biosensor.

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Performance Factors

• Selectivity How much signal does an interfering
  molecule cause, relative to the TARGET ANALYTE?
• e.g., for potentiometric chemical sensors

• kt,i selectivity coefficient for specific
  interferent
• 0 ? ideal
• 0.1 ? moderate interference
• 1.0 ? complete interference
• Biosensors Working lifetime durability

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Outline

• Overview
• What are chem/biosensors?
• What are their important performance
  characteristics?
• How are they structured and classified?
• How do they work by electrochemical transduction?
• Example of an electrochemical biosensor.

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Chemical Sensor Structure

• Recognition Element

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Classification

• Recognition Element
• Selective membranes
• Electromagnetic energy
• Chemical reaction
• Biological reaction

• Transducer
• Electrochemical
• Optical
• Calorimetric
• Gravimetric Resonance

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Outline

• Overview
• What are chem/biosensors?
• What are their important performance
  characteristics?
• How are they structured and classified?
• How do they work by electrochemical transduction?
• Example of an electrochemical biosensor.

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Electrochemical Transduction

• Theory Behind of Electrochemical Analysis
• The Half-Cell Red-Ox Reaction
• (R) (O)
• The Nernst Equation

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Electrochemical Transduction

• The Electroanalytical Cell

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Electrochemical Transduction

• Accomplishing Detection
• Chronoamperometry - Set potential measure
  current (vs. time)
• Voltammetry - Measure current vs. potential
• Potentiometry - Zero current measure potential
  

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Electrochemical Transduction

• Accomplishing Detection Chronoamperometry
• Disturb system
• Starting with a finite aR and negligible aO
• Enforce a DE, such that aR ? 0
• Creates concentration gradient (dCR/dx) from
  working electrode surface to bulk solution
• Measure response of system
• Ficks 1st Faradays laws show current is
  proportional to dC/dx

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Electrochemical Transduction

• Accomplishing Detection Chronoamperometry
• Ficks 2nd law tell us that current will decrease
  with time

0 M 10 mM 20 mM
(Cottrell equation, planar electrode)
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Electrochemical Transduction

• Main Advantages
• Simple integration with electronics
• Compatibility with biochemical systems
• Disadvantages
• Requires presence of electroactive species
• Electrode degradation (fouling)
• Some Design Considerations
• Electrochemical species environment
• Electrode size, shape, material orientation
• Potentiostat circuitry Dynamic Range vs.
  Sensitivity

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Outline

• Overview
• What are chem/biosensors?
• What are their important performance
  characteristics?
• How are they structured and classified?
• How do they work by electrochemical transduction?
• Example of an electrochemical biosensor.

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H2 Biosensor

• Objectives
• H2 gas leak detection
• Overcome limitations of current technology
• Selectivity stability
• High temperature requirements
• Utilize microfluidic and bioMEMS technology
• Enzyme-based selectivity
• Miniaturized sampling, sample preparation and
  detection components

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H2 Biosensor

• Recognition Element Enzymatic Reaction
• Transduction Chronoamperometry

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H2 Biosensor

• Phase I Bench-top testing

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H2 Biosensor

• Phase I Bench-top testing

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H2 Biosensor

• Phase II Microfluidic Implementation

micro-electrodes
gas injection
waste collection
liquid injection
to potentiostat
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Useful References

• Chemical Sensors
• Eggins, BR (2002). Chemical Sensors and
  Biosensors. New York, NY, John Wiley Sons, Inc.
  
• Cattrall, RW (1997). Chemical Sensors. New York,
  NY, Oxford University Press Inc.
• Electrochemical Transduction
• Kissinger, T (1996). Laboratory Techniques in
  Electroanalytical Chemistry, 2nd edition. New
  York, NY, Marcel Dekker, Inc.