A new ratiometric electrochemical aptasensor for the sensitive detection of carcinoembryonic antigen based on exonuclease I-assisted target recycling and hybridization chain reaction amplification strategy

In this work, a novel ratiometric electrochemical aptasensor was designed on the basis of dual-amplification mechanism by using exonuclease I (Exo I)-assisted target recycling and hybridization chain reaction (HCR). The thiol-modified capture DNA (Cp-DNA) was fixed on the surface of the gold electrode (AuE) modified with gold nanoparticles (AuNPs) through Au-S bonds. The ferrocene (Fc)-labeled DNA (Fc-DNA) hybridized with Cp-DNA to form Fc-DNA/Cp-DNA duplex. The presence of carcinoembryonic antigen (CEA) led to the dissociation of Fc-DNA from Fc-DNA/Cp-DNA duplex and initiated Exo Ⅰ-assisted target recycling to digest Fc-DNA, so numerous Fc left away from the electrode surface and resulting in the “signal off” of Fc. Moreover, Cp-DNA was exposed to bind trigger DNA and initiate HCR with the presence of H1 and H2 probes, resulting in the intercalating of numerous methylene blue (MB) molecules and the “signal-on” of MB. This dual signal strategy significantly amplified the decrease of Fc signal and the increase of MB signal, achieving a linear range of 1 pg mL−1 to 100 ng mL−1 with a detection limit of 0.479 pg mL−1 (S/N = 3). Besides, the developed aptasensor exhibited high specificity, good stability and reproducibility. More importantly, the aptasensor had been applied in detection of CEA in diluted human serum and displayed satisfactory anti-interference property. By changing the corresponding aptamer sequences, the designed strategy can be employed to detect other targets, which holds promising application in clinical diagnosis.