Bi-directionally amplified ratiometric electrochemical aptasensor for the ultrasensitive detection of alpha-fetoprotein

Alpha-fetoprotein (AFP) is always employed as a biomarker for liver cancer. The detection of AFP with high sensitivity and good anti-interference property is extremely imperative for clinical cancer diagnosis and effective treatment. In this work, a novel bi-directionally amplified ratiometric electrochemical aptasensor based on exonuclease-assisted target recycling and bioconjugate probe was developed for the ultrasensitive detection of AFP. The aptasensor was fabricated by attaching ferrocene-labeled capture probe (Fc-CP) onto electrode surface through the hybridization with thiolated DNA(1). The recognition of AFP caused the disassociation of Fc-CP from the DNA(1)/Fc-CP duplex, and further triggered the cleavage process of RecJ(f) exonuclease and recycling of AFP. As a result, numerous Fc labels were released, accompanied by plenty exposed DNA(1) on the electrode surface for the hybridization with bioconjugate probe containing vast methylene blue (MB) molecules. This strategy significantly amplified the decrease of Fc signal and the increase of MB signal, finally achieving a wide detection range of seven orders of magnitude and an ultralow AFP detection limit down to 269.4 ag/mL. The anti-interference property of the aptasensor was verified by analyzing clinical human serum samples. This aptasensor is promising for the development of reliable electrochemical devices for point-of-care diagnosis.