THE PROBE

A carbon fiber thinner than a hair

Size A carbon-fiber microelectrode is about 5 to 7 micrometers wide, roughly a tenth of a human hair

Why it is good Small enough to cause little damage and to sense a tiny region

Reference A silver/silver chloride electrode completes the circuit

Small probes disturb the tissue less.

THE SCAN

A voltage that sweeps

The voltage ramps up and back down in under 10 milliseconds, then rests, and repeats about ten times a second.

Each scan is one tiny snapshot of what is at the electrode.

THE CHEMISTRY

Dopamine gives up electrons

dopamine → dopamine-o-quinone + 2 e⁻

As the voltage passes about +0.6 V, dopamine at the surface is oxidized and releases two electrons. The current from those electrons is proportional to how much dopamine is there. This is the same idea as the current in a glucose sensor, applied at much higher speed.

More dopamine means more current.

READING THE SIGNAL

Subtract the background

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Background

Charging the electrode's surface produces a current much larger than the dopamine signal, so it is subtracted

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Fingerprint

The shape of the remaining current against voltage identifies the molecule

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Concentration

A calibration converts current to concentration

Subtraction removes the electrode's own response, leaving the chemistry.

STRENGTHS AND LIMITS

Fast and sensitive, but picky about what it sees

Strengths Sub-second resolution, nanomolar sensitivity, and a tiny footprint

Limit 1 Only molecules that react at the electrode, such as dopamine, norepinephrine, and serotonin, are detected. Glutamate and GABA are not

Limit 2 Surfaces can foul, and results are best for changes rather than absolute baseline levels

Voltammetry is the fastest electrochemical tool, for molecules that oxidize.

UNIT 16 STUDY COMPLETE

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Ready for the Fab Challenge?

You've seen how a swept voltage lets a tiny carbon fiber pick out dopamine in under a second.