A Ratiometric Electrochemical Aptasensor with Exonuclease I-assisted Target Recycling Amplification for Highly Sensitive Detection of Carcinoembryonic Antigen

In this study, a ratiometric electrochemical aptasensor was proposed for the highly sensitive detection of carcinoembryonic antigen (CEA) with exonuclease I (Exo I)-assisted target recycling amplification. The thiolated methylene blue (MB)-labelled hairpin capture probe (MB-HP) was immobilized on the surface of gold nanoparticles (AuNPs) modified gold electrode (AuE) via Au-S bonding, and the hybridization between MB-HP and ferrocene (Fc)-labelled aptamer (Fc-Apt) formed a duplex structure, leading to Fc molecules approaching to the electrode surface while MB molecules were far away. In the presence of CEA, its specific recognition with the aptamer caused the release of Fc-Apt from the electrode surface and subsequently the formation of a hairpin structure for MB-HP, resulting in both “signal-on” of MB (IMB) and “signal-off” of Fc (IFc). To improve the sensitivity of the aptasensor, an Exo I-assisted target recycling amplification strategy was designed to achieve an amplified ratiometric signal. Under the optimal conditions, the proposed aptasensor showed a linear detection range from 10 pg mL-1 to 100 ng mL-1 with a detection limit of 4.1 pg mL-1. Furthermore, the stability, reproducibility, selectively and real sample detection ability of the aptasensor were investigated and satisfactory results were obtained.