The presence of a Nafion membrane significantly affects sensitivity to L-DOPA, DA, and AA. Upper panel shows representative cyclic voltammograms for bare (black) and Nafion-coated (gray) electrodes for L-DOPA (1 µM), DA (500 nM), and AA (200 µM). Lower panel: A summary of the entire data set. The values are averages ± SEM. (n = 3–9 electrodes per group, unpaired t-test, **p <0.01, *p <0.05).