A. Differential pulse voltammograms of an iodine-coated platinum electrode in 0.1 M PBS (pH 7) containing different concentrations of dopamine. scan rate: 5 mV s-1, modulation amplitude = 50 mV. pulse repeat time: 1 s. B. A plot of the concentration of dopamine vs. the peak currents extracted from the corresponding voltammograms (in Fig. 4A).