Sensitive immunosensing of the carcinoembryonic antigen utilizing aptamer-based in-situ formation of a redox-active heteropolyacid and rolling circle amplification

A highly sensitive electrochemical scheme for the detection of the cancer biomarker carcinoembryonic antigen (CEA) is reported. An aptamer-based formation of redox-active molybdophosphate is combined with rolling circle amplification (RCA). Gold nanoparticles (AuNPs) were utilized as supporting matrix for the aptamer and the primer to increase the primer/aptamer loading. The formation of a sandwich structure of anti-CEA/CEA/AuNP − aptamer-primer onto a glassy carbon electrode surface enabled an effective RCA reaction. Square wave voltammetry was applied to record the current signal at a peak potential of 0.18 V vs. Ag/AgCl. Compared to the immunosensor without RCA, the sensitivity of the immunosensor with RCA is increased by about a factor of 6. In the latter case, a wider linear range was obtained for the determination of CEA (from 0.5 pg mL−1 to 1 ng mL−1) with a detection limit as low as 0.1 pg mL−1. The practical applicability of the method was studied by analyzing CEA in human serum samples. The results were found to be in good agreement with those obtained by a reference method. Conceivably, the method can be applied to other DNA amplifications and therefore has the potential of finding wide applications.