A disposable ratiometric electrochemical aptasensor with exonuclease I-powered target recycling amplification for highly sensitive detection of aflatoxin B1

A disposable ratiometric electrochemical aptasensor has been constructed for highly sensitive detection of aflatoxin B1 (AFB1) with exonuclease I (Exo I)-powered cascade amplification. Specifically, the in-situ growth of Au nanoflowers (AuNFs) on indium tin oxide (ITO) surface was used to anchor methylene blue (MB) labeled the complementary DNA of aptamer. Ferrocene (Fc) labeled aptamer was then hybrid with cDNA(MB) to produce a duplex structure. Due to the rigid structure of the duplex structure, Fc molecules were close to the electrode surface while MB molecules were far away, which respectively produced a faded external response signal and an enhanced internal reference signal. When AFB1 was present in sample, the aptamers specifically bond with the targets and then detached from electrode surface, which resulted a signal-off for Fc indicators. Meanwhile, more MB molecules were close to the electrode surface owing to an increasing target concentration, which caused a signal-on for MB indicators. On this basis, the ratiometric electrochemical detection of AFB1 was achieved employing the peak current intensity ratio (IMB/IFc) as signal transducer. Moreover, Exo I was introduced to digest the detached aptamer, and the released AFB1 entered the next round of circulation which formed the target recycling and realized the signal amplification. This aptasensor exhibited a wide detection range (0.1–1000 pg mL−1) and a low detection limit (0.032 pg mL−1). We anticipate this method may find good utility in food quality control and further facilitate the development of aptasensor for other targets.