A novel potentiometric immunosensor for the detection of diphtheria antigen (Diph) has been developed by means of self-assembly to covalently immobilized diphtheria antibody (anti-Diph) on a glassy carbon electrode. At first, the modification of glassy carbon electrode (GCE) with nano-gold (NG) by chemical adsorption of 2-aminoethane thoil (AET) was achieved, and then cysteine (Cys) molecules were adsorbed on the nano-gold surface. Finally, diphtheria antibodies were covalently immobilized on the electrode by glutaraldehyde (GA). The modification procedure was electrochemically monitored by characterization of the electrode surface. The performance and influencing factors of the resulting immunosensor were studied in detail. The resulting immunosensor exhibited fast potentiometric response to Diph and the detection limit of the immunosensor was from 24 ng·mL^-1 to 600 ng·mL^-1 with correlation coefficient of 0.9979 and a detection limit of 5.2 ng·mL^-1. More than 91.3% of the results of the bioproduced samples obtained by this method were in agreement with those by enzyme-linked immunosorbent assay (ELISA).

Key words: diphtheria, glassy carbon electrode, colloidal gold, potentiometric immunosensor