Label-free electrochemical immunoassay of carcinoembryonic antigen in human serum using magnetic nanorods as sensing probes

A new potentiometric immunoassay protocol for the determination of carcinoembryonic antigen (CEA) in human serum was designed by using a novel transparent immunoaffinity reactor. To construct such an affinity reactor, Fe3O4 nanorods with average diameter of 40 nm and length of 1.0 μm were initially synthesized through hydrolysis of FeCl3 and FeSO4 in the urea solution, and then the synthesized nanorods were used as the immobilized affinity support for the conjugation of anti-CEA antibodies (bionanorods). With an external magnet, the magnetic bionanorods were attached to the surface of a self-made carbon paste electrode. The performance and factors influencing the immunosensors were evaluated. Under optimal conditions, the binding of CEA in the samples onto the immobilized anti-CEA changed the potential response, a dynamic range from 1.5 to 80 ng·mL−1, and a detection limit of 0.9 ng·mL−1 CEA (at 3σ). The immunosensors show good precision, high sensitivity, acceptable stability and reproducibility. The CEA concentrations of the clinical serum specimens assayed by the immunosensor show consistent results in comparison with those obtained by commercially available enzyme-linked immunosorbent assay.