Triblock polyadenine-based electrochemical aptasensor for ultra-sensitive detection of carcinoembryonic antigen via exonuclease III-assisted target recycling and hybridization chain reaction.

Carcinoembryonic antigen (CEA), a key colon biomarker, demands a precise detection method for cancer diagnosis and prognosis. This study introduces a novel electrochemical aptasensor using a triblock polyadenine probe for ultra-sensitive detection of CEA. The method leverages Exonuclease III (Exo III)-assisted target recycling and hybridization chain reaction. The triblock polyadenine probe self-assembles on the bare gold electrode through the strong affinity between adenine and gold electrode, blocking CEA diffusion and providing a large immobilization surface. CEA binding to hairpin probe 1 (HP1), followed by the hybridization between HP1 and hairpin probe 2 (HP2), triggers DNA cleavage by Exo III, amplifying the signal via a hybridization chain reaction and producing numerous dsDNA walkers that generates a dramatic electrochemical impedance signal. Under optimized conditions, the aptasensor achieved two ultra-low detection limits: 0.39 ag∙mL within the concentration range of 5 ag∙mL to 5 × 10 ag∙mL, and 1.5 ag∙mL within the concentration range of 5 × 10 ag∙mL to 1 × 10 ag∙mL. Its performance in human serum samples meets the practical standards, offering a promising new tool for ultrasensitive tumor marker detection, potentially revolutionizing early cancer diagnosis.