Representative differential pulse voltammetric (DPV) curves of the AP-anti-IgG/AuNP-RGO/anti-NSE/NSE/GCE (A) and the alkaline phosphatase (AP)-anti-IgG/anti-NSE/NSE /GCE (B) obtained with NSE in a concentration of 0, 0.1, 1, 10, 100, 500, 1000, and 2000 ng/mL.