Fig. 6

DPVs of different concentrations of 4-AP (0.8–22.0 µM) and PAR (2.0–55.0 µM) in 0.1 M PBS, pH 6.0, and its corresponding calibrating plot (a,b), DPVs of different concentrations of 4-NP (0.1–250.0 µM) in 0.1 M PBS, pH 6.0, and its corresponding calibrating plot (c,d).