A novel ratiometric electrochemical aptasensor for highly sensitive detection of carcinoembryonic antigen.

A novel ratiometric electrochemical aptasensor was proposed for carcinoembryonic antigen (CEA) detection based on exonuclease III (Exo III)-assisted recycling and rolling circle amplification (RCA) strategies. A thiolated ferrocene-labeled hairpin probe 2 (Fc-HP2) was fixed on the gold nanoparticles (AuNPs)-modified gold electrode (AuE) surface through Au-S bonds. The presence of CEA led to the release of trigger, which hybridized with the 3'-protruding of hairpin probe 1 (HP1) and triggered the Exo III cleavage reaction, accompanied by the releasing of trigger and generation of new DNA fragment which was used for the successive hybridization with Fc-HP2. After the Exo III cleavage process, the remaining Fc-HP2 fragments hybridized as primers with the RCA template to initiate the RCA process, and long single-stranded polynucleotides were produced for methylene blue (MB) binding. Such changes resulted in the signal of Fc (IFc) decreased and that of MB (IMB) increased, achieving a linear relationship between IMB/IFc and logarithm of CEA concentrations ranging from 1.0 pg mL-1 to 100.0 ng mL-1 with a detection limit of 0.59 pg mL-1. Additionally, the developed aptasensor had been successfully applied to detect CEA in human serum samples. Therefore, the proposed strategy might provide a new platform for clinical detections of CEA.

Ratiometric electrochemical aptasensor for the sensitive detection of carcinoembryonic antigen based on a hairpin DNA probe and exonuclease I-assisted target recycling.

A novel ratiometric electrochemical aptasensor was constructed for the detection of carcinoembryonic antigen (CEA) based on a hairpin DNA (hpDNA) probe and exonuclease Ⅰ (Exo Ⅰ)-assisted target recycling amplification strategy. A thiolated methylene blue (MB)-labeled hpDNA as the internal control element was fixed on the surface of the gold nanoparticles (AuNPs)-modified gold electrode (AuE) through Au-S bonds. A ferrocene (Fc)-modified aptamer DNA (Fc-Apt) was partially hybridized with hpDNA to form a Fc-Apt/hpDNA duplex. Due to the specific recognition of Fc-Apt to CEA, the presence of CEA caused dissociation of Fc-Apt from the duplex, and further triggered the degradation process of Exo Ⅰ and recycling of CEA. Hence, the Fc tags were released from the electrode surface and the oxidation peak current of Fc (IFc) decreased while that of MB (IMB) remained stable owing to the distance between MB tags and the electrode unchanged. A linear relationship was observed between IFc/IMB and the logarithm of CEA concentration from 10 pg mL-1 to 100 ng mL-1 with a detection limit of 1.9 pg mL-1. Moreover, the developed aptasensor had been applied to detect CEA in diluted human serum with satisfactory results, indicating its great potential in practical applications.