Poly(o-phenylenediamine) nanosphere-conjugated capture antibody immobilized on a glassy carbon electrode for electrochemical immunoassay of carcinoembryonic antigen

We report on a new electrochemical immunosensor for the carcinoembryonic antigen (CEA; a model analyte). First, poly(o-phenylenediamine) nanospheres (PPDNSs) were synthesized by using a wet-chemistry method. The nanospheres were utilized as the support for immobilizing horseradish peroxidase-labeled polyclonal rabbit anti-human CEA antibody (HRP-anti-CEA) on a pretreated glassy carbon electrode (GCE) using glutaraldehyde as a crosslinker. In the presence of target CEA, an antigen-antibody immunocomplex formed on the electrode. This results in a partial inhibition of the active center of HRP and decreases the activity of HRP in terms of H2O2 reduction. The performance and factors influencing the performance of the immunoelectrode were studied. Under optimal conditions, the reduction current obtained from the anti-CEA-conjugated HRP (best at a working voltage of -265 mV vs. Ag/AgCl) is proportional to the CEA concentration in the 0.01 to 60 ng mL(-1) range, with a detection limit of 3.2 pg mL(-1). Non-specific adsorption was not observed. Relative standard deviations for intra-assay and inter-assay are < 8.3 % and < 9.7 %, respectively. The method was applied to the analysis of nine human serum samples, and a good relationship was found between the electrochemical immunoassay and the commercialized ELISA kit for human CEA.