Sensitive detection of miR-122 via toehold-promoted strand displacement reaction and enzyme-assisted cycle amplification

It is of great significance to develop a sensitive detection platform for miRNA, a non-invasive biological indicator for the diagnosis, treatment and prognosis monitoring of tumors. In this paper, we design an electrochemical DNA sensor to detect miR-122, based on toehold promoted strand displacement reaction, combined with enzyme assisted cycle amplification. In this strategy, when miR-122 and Exonuclease III (Exo III) coexist in the detection system, the toehold promotes the chain replacement reaction, and the miR-122 hybridizes with a stem-loop DNA, HC-DNA. Simultaneously, Exo III hydrolyzes part of HC-DNA and releases miR-122 and sign-DNA. Then, after multiple enzymatic cyclic amplification reactions (N Cycle), a large amount of Sign-DNA was released. Methylene blue (MB), as the signal molecule, is attached to sign-DNA, close to the surface of the electrode, and resulting in a increased electrochemical signal. Using this method, we can qualitatively analyze the concentration of miR-122 by the amplified electrochemical signals. The detection limit of miR-122 is 0.304 pM, lower than that of the many common large-scale instrumental analysis. Further, the method has good selectivity and anti-interference performance in complex environments. This electrochemical DNA biosensor has potential applications in highly sensitive detection of target molecules even concluding viruses.