Cyclic Voltammetry for the
Detection of Dopamine in vivo
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Structure of Dopamine.
- small molecule chemical messenger
- Important for motor and cognitive functions
- Deficts in dopamine levels cause Parkinson Disease
- Regulates reward
- Dopamine increases after drugs of abuse like cocaine
- Dopamine is synthesized in
dopaminergic neurons and packaged into membrane bound vesicles.
- Electrical action potential initiates the release of
- Dopamine vesicles undergo exocytosis.
- Spills out into the extracellular space
- Can be detected
The dompaminergic neuron
can release dopamine into the extracellular space where its contents
can be detected by target neurons. (Venton
& Wightman 2003)
- Exocytosis of dopamine from vesicle occurs on a millisecond time
- Sensor must be fast, sensitive, and selective since dopamine
concentrations are low
- Fast scan cyclic voltametry is the dominant electrochemical
- Electrochemical technique in which the current (I) is measured as
function of voltage (Eapp)
There are several kinds:
- Linear ccan voltametry (Polarography)
- Differential pulse polarography
- Square-wave voltametry
- Cyclic voltametry
- A potential is applied between the reference electrode and the
- The electrode potential ramps linearly at the experimental scan
- The current is measured between the working electrode and
- Data is plotted as Current (I) vs. Potential(E).
- Forward scan
produces a current peak for the analystes that have been reduced in
scanned potential range.
- The direction of the potential is reversed at the end of the each
in cyclic voltametry
- Current increases as the potential reached the reduction
- Current decreases as the analyte is depleted in the redox
|Carbon Fiber Microelectrodes
(CFME) are electrodes in which a carbon fibers serve as the
- Carbon fibers are biological compatible to cells
- Small size (less than 10um in diameters) allows for
- Commonly used with cyclic voltametry
Scan electrode from a holding potential to a switching potential and
back at a
high scan rate. Repeat these scans every 100 ms.
As potential is ramped up, dopamine is oxidized to dopamine-o-quinone.
As potential is ramped down, dopamine-o-quinone reduced back to
Fast scan rate cause a large background
charging current due to charging
the double layer.
When dopamine is added (red line),
the differences are small.
cyclic voltammogram of dopamine
The background current is stable and can
be subtracted out to obtain a background-
subtracted cyclic voltammogram for dopamine.
The position of the peaks help identify the
molecule being detected.
Data can also be depicted as a color plot to show many CVs over time.
Current is in color and shows when dopamine is present.
Electrically-Stimulated release in a
(Addy, et al. 2010)
- Carbon-fiber microelectrode implanted in nucleus accumbens
- Nucleus accumbens regulates reward
- Electrically stimulate cell bodies in ventral tegmental area
Spontaneous dopamine transients in a
Spontaneous dopamine transients in a
rat after cocaine
- Size of dopamine evoked depends on frequency of stimulation
- Color plots look like dopamine
Cocaine increases the concentration and the length of time for dopamine
signaling (Aragona et. al. 2008).
- Allows for the product of the electron transfer reaction that
in the forward scan to be probed again in the reverse scan
- Can be used to determine of formal redox potentials, detect of
reactions that occur before or after a electrochemical reaction, and
evaluate electron transfer kinetics
and Venton, B.J.
applications." Analyst (2009): 18-24.
B. J. and Wightman, M. R. "Psychoanalytical
Chemistry: Dopamine and Behavior." Analytical
Chemistry (2003): 414-421.