Evennett, P. J. and Hammond, C.
Microscopy overview.  Encyclopedia of Analytical Science: 32-41 (2005).

Carbon and ceramic electrodes have been used for quantitative and qualitative recordings of the neurotransmitters dopamine (DA), 5-hydroxytryptamine (5-HT), and their metabolites 3,4-dihydroxyphenylacetic acid (DOPAC), 5-hydroxyindoleacetic acid (5-HIAA), and L-glutamate. Nitric oxide can also be recorded. In this case the carbon surface of the electrode is covered with a p-type semiconducting polymeric porphyrin that acts as a catalyst for the oxidation of nitric oxide. Nitric oxide is responsible for the activity of the endothelium-derived relaxing factor associated with hypertension, diabetes, ischemia, and arteriosclerosis.