Electrochemical ratiometric dual-signal immunoassay for accurate detection of carcinoembryonic antigen in clinical serum based on rGO-Pd@Au-Thi and Chi-Fc-Au

For prevention and early diagnosis of carcinoembryonic antigen (CEA), it is necessary to develop more accurate approaches for its detection. In this work, a new sensitive electrochemical ratiometric immunosensor for the determination of CEA was constructed on account of chitosan-ferrocenecarboxaldehyde-gold nanospheres (Chi-Fc-Au) and reduced graphene oxide-Pd@Au nanocomposits-thionine (rGO-Pd@Au-Thi) with dual-signal output. The immunosensor utilized Chi-Fc-Au as the substrate to anchor the primary antibody (Ab1) and rGO-Pd@Au-Thi as the secondary antibody (Ab2) label probe, generating two electrical signals (IFc and IThi) derived from Fc and Thi in the presence of CEA, respectively. With the increase of CEA concentration, the IFc and IThi showed opposite changes, so the peak current ratio of IThi/IFc was positively correlated with CEA concentration. In comparison with other immunosensors especially single-signal mode, the proposed immunosensor exhibited a wider linear range (10–4−200 ng mL−1) and a lower detection limit (14.9 fg mL−1), which could be applied in human serum samples for CEA measurement, and was comparable to commercial electrochemiluminescence (ECL) immunoassay. Given the significantly improved accuracy of the constructed sensor, it is expected to be applied in clinical diagnosis for other protein biomarkers determination.