In vivo voltammetry for catecholamine analysis

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In vivo voltammetry for catecholamine
analysis

• Junfeng Xiao

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Outline of this talk

• Why in vivo voltammetry
• What is in vivo voltammetry
• Hows this technique been developed
• What can be achieved in future

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Why in vivo voltammetry

• Subjective reason
• People want to know more about brain
• by studying neurotransmitters.
• Objective realities
• a. neurotransmitters can be studied.
• b. in vivo voltammetry can study brain.

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Study in Brain chemistry
Jonathan A. Stamford, etal Analytical Chemistry
1996, (68) 359A-366A
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Structures of typical catecholamine compounds
dopamine epinephrine, norepinephrine
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Why in vivo voltammetry can study brain?

• 1. microelectrodes are small enough to access the
  brain.
• 2.carbon fiber electrodes are
• robust against surface degradation.
• 3.fast cyclic voltammetry can provide fast
  measurement in ms scale.

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What is in vivo voltammetry

• Basics in cyclic voltammetry(CV)
• Voltammetric analysis of cacholamines in brain.

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Basics in voltammetry
electron flow
How electrodes in electrochemical cell works
At the negative electrode, the cathode,
electrons are given off, and reduction takes
place. At the positive electrode, the
anode, the excess electrons are collected, and
oxidation occurs. This giving-and-taking of
electrons creates an electric current.
anode
cathode
http//nanonet.rice.edu/research/CVtutorial2/
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• How cyclic potential sweep applied
  in CV?

The system starts off with an initial potential
at which no redox can take place. At a critical
potential during the forward scan, the
electroactive species will begin to be
oxidized. After reversal of potential scan
direction and depletion of the oxidized species,
the reverse reduction reaction takes place.
http//www-biol.paisley.ac.uk/marco/Enzyme_Electro
de/Chapter1/Ferrocene_animated_CV1.htm
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Cyclic voltammogram
In CV, the current in the cell is measured
as a function of potential. The potential of an
electrode in solution is linearly cycled from a
starting potential to the final potential and
back to the starting potential. This process, in
turn, cycles the redox reaction. Multiple cycles
can take place. A plot of potential versus
current is then produced.
http//www-biol.paisley.ac.uk/marco/Enzyme_Electro
de/Chapter1/Ferrocene_animated_CV1.htm
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• CV can identify and quantify analytes

Kirk T. Kawagoe, etal Journal of Neuroscience
Methods, 48 (1993) 225-240
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Other voltammetry techniques
Robert D. ONeill, etal Analyst,
May 1994, Vol. 119. 767.
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Catecholamine analysis by in vivo CV

• How this experiment be carried out in brain?
• Special considerations for in vivo voltammetry
  compared with CV in beaker system.

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Experimental set up in vivo voltammetry
Jonathan A. Stamford, etal TINS, Vol. 12,
No. 10, 1989.
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Considerations to In Vivo CV

• In vivo working environment
• ECF (extracellular fluid)
• Requirements for electrodes
• a. minimum tissue damage
• b. stability
• Interferences in measurement
• a. ascorbic acid (AA vitamin C)
• b. DOPAC

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The big concern of in vivo voltammetry

• The Selectivity of catecholamine over
  interfering compounds MUST be guaranteed!

Kirk T. etal Journal of
Neuroscience Methods, 48 (1993) 225-240.
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Hows this technique been developed

• Improvements made based on
• High selectivity
• Good Sensitivity
• Less disturbance imposed on brain function
• Stability of electrodesless poisoning
• Three electrodes are developed carbon paste
  electrodes carbon epoxy electrodes carbon fibre
  electrodes.

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How high selectivity be achieved?

• Optimization of potential waveform

Crespi, F. etal. (1984) Brain Res. 322,
135-138.
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How high selectivity be achieved?

• Modification on electrodes
• a. coating the electrode surface with selectively
  permeable film or membrane.
• 1.enzyme coating
• 2.Nafion as coating is a breakthrough in
  selectivity
• b. electrochemical modification on working
  electrode
• applying high frequency triangular voltage
  waveform onto electrodes in vitro.
• c. adding chemicals to alter the composition of
  the electrode
• stearic acid modified carbon paste electrode

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How good sensitivity be made?

• Low sensitivity caused by biofoulingsuch as
  protein deposition on electrode, impeding
  electron transfer.
• Solution to circumvent this problem
• electrode surface coated with permselective
  coatings such as Nafion.

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Less disturbance and good stability of
electrodes

• Carbon fiber as starting materials for working
  electrodes.
• stable, strong and compatible with various
  modification.
• Fabrication of microelectrodes
• carbon fiber electrode with small size up to
  10-100µm.

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what else can be done by in vivo CV?

• Voltammetry with cells

• Voltammetry
• with brain slices

Jonathan A. Stamford, etal Analytical Chemistry
1996, (68) 359A-366A
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What can be done in future

• Smaller electrodes needed (submicrometer ) to
  study inferior structural and message
  transmission information in single cell.
• Development of integration and array of
  microelectrodes technology can facilitate the
  brain study in future.
• Electrode modification will be further developed
  in order to achieve better selectivity.

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We do help !!!