Fig. 8. (A) CVs of 50 μM DA and 200 μM UA at the PTPCNs/GCE in 0.1 M PBS of pH 7.0 at different scan rates (a–f): 50, 100, 200, 300, 400, 500 mV s⁻¹. The relationship between the oxidation peak current densities (B) and reduction peak current densities (C) of DA and UA with the square root of the scan rates.