A novel potentiometric immunosensor for detection of hepatitis B surface antigen (HBsAg) has been developed by means of self-assembly (SA) and opposite-charged adsorption (OCA) techniques to immobilize hepatitis B surface antibody (HBsAb) on a platinum electrode. A cleaned platinum electrode was first pretreated in the presence of 10% HNO3 and 2.5% K2CrO4 solution and held at -1.5 V (vs SCE) for 1 min to make it negatively charged and then immersed in a mixing solution containing hepatitis B surface antibody, colloidal gold (An), and polyvinyl butyral (PVB). Finally, HBsAb was successfully immobilized onto the surface of the negatively charged platinum electrode modified nanosized gold and PVB sol-gel matrixes. The modified procedure was characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The immobilized hepatitis B surface antibody exhibited direct electrochemical behavior toward hepatitis B surface antigen (HBsAg). The performance and factors influencing the performance of the resulting immunosensor were studied in detail. More than 95.7% of the results of the human serum samples obtained by this method were in agreement with those obtained by enzyme-linked immunosorbent assays (ELISAs). The resulting immunosensor exhibited fast potentiometric response (< 3 min) to HBsAg. The detection limit of the immunosensor was 2.3 ng(.)mL(-1), and the linear range was from 8 to 1280 ng(.)mL(-1). Moreover, the studied immunosensor exhibited high sensitivity, good reproducibility, and long-term stability (> 6 months).