Ultrasensitive Electrochemiluminescence Biosensor for MicroRNA Detection by 3D DNA Walking Machine Based Target Conversion and Distance-Controllable Signal Quenching and Enhancing

In this study, an electrochemiluminescence (ECL) regenerated biosensor was reported to sensitively detect microRNA through 3D DNA walking machine and "on–off–super on" strategy. First, 3D DNA walking machine with higher efficiency of payload releasing and superior signal amplification than those of the traditional DNA walking machine was initially introduced in the ECL system for converting target microRNA to intermediate DNA and achieving significant signal amplification. Second, the distance between CdS:Mn quantum dots and Au nanoparticles was increased with the hybridization of intermediate DNA and Au nanoparticles modified S2, which weakened the energy transfer for ECL signal recovering and excited the surface plasma resonance for further enhancing the signal to construct the on–off–super on biosensor. Such an on–off–super on strategy not only reduced the ECL background signal but also increased the detection sensitivity. Impressively, the elaborately designed biosensor could be regenerated by Lambda exonuclease hydrolyzing the intermediate DNA to make Au nanoparticles modified S2 recover to their original hairpin structure. With the amazing signal amplification of 3D DNA walking machine and sensitive distance control of the on–off–super on strategy, the biosensor showed excellent performance for microRNA-141 detection with a low detection limit of 3.3 fM and could be applied to human prostate cancer cells analysis. Furthermore, this work established a foundation to apply 3D walker in ECL methodology and provided an effective way for analysis of other microRNA or cancer cells.