FSCV for Neurotransmitter Study: Waveform Optimization

See Part 1 here, or Part 2 here.

The work described in this paper aims to develop a fast-scan cyclic voltammety (FSCV) procedure to identify octopamine and tyramine while minimizing the polymerization that leads to fouling of the electrode. The optimal waveform is said to be from 0.1 to 1.3 V and back at 600 v/s, every 100 ms.

Cyclic voltammograms and corresponding color plots from detection of 1 uM tyramine and octopamine samples using specified waveform. Main tyramine oxidation peak at 0.92V; main octopamine peak at 0.98 V. Peaks higher than 1.1 V.
represent switching error. Injection between 5 and 10 seconds, CVs taken at 7.5 seconds.

The oxidation peak for tyramine is typically around 0.9 V, while that of octopamine is about 1.1 V. Each phenolamine produces a characteristic shape on the CV; deviations from this shape indicate the presence of another compound or some other experimental error. Even at this optimized waveform however, there is still a problem with passivation. After 10 to 15 tests with 1 uM analyte concentrations, the signal are typically too weak to clearly read.

There has been some indication that Nafion coated electrodes show increased sensitivity to catecholamines, as well as a reduced tendency to cause electrode fouling. Nafion-coated microelectrodes were prepared to test for octopamine and tyramine in homogenized larval fruit fly brains. These tests are performed with disk electrodes, which have a very small surface area compared with cylindrical electrodes. To compensate, a larger diameter carbon fiber is used to increase the disk electrode surface area. Otherwise, the resultant surface area from smaller electrodes can be too small to generate a coherent signal, unless very high gain can be achieved .