Figure 2. Exocytotic event recorded by fast-scan cyclic voltammetry.

The false-color plot (a) was constructed based on the oxidation and reduction current (encoded by color) recorded at the carbon-fiber microelectrode when its potential was rapidly ramped from −0.4 V to 1 V and back to −0.4 V at 2000 V s⁻¹ every 2 ms. Each vertical 2 ms “slice” and the full 2D representation are a single scan and a stack of consecutive single scans, respectively. The second event at ~1.3 s displays a small current (white arrow, termed foot feature) prior to the major current feature. The reconstructed amperometric response using the oxidation peak current value (at ~0.6 V) obtained on each consecutive scan and the cyclic voltammograms using two single scans obtained from the foot feature and the major current spike are plotted in panel b. The cyclic voltammograms (solid line, insets in b) show identical oxidation(~0.6 V)/reduction (~−0.4 V, partially shown) peak locations and peak separation compared to those obtained from a standard serotonin solution (dotted line) and thus, confirm the secreted molecules as serotonin during both the foot and full fusion events.