Herein, an electrochemiluminescence (ECL) and electrochemical (EC) dual-mode biosensor platform with a self-powered DNAzyme walking machine was established for accurate and sensitive detection of miRNA-21. By employing a magnesium ion (Mn²⁺)-dependent DNAzyme cleavage cycling reaction, the walking machine was built by assembling DNAzyme walking strands and ferrocene (Fc)-labeled substrate strands on the Au nanoparticles and graphitic carbon nitride nanosheet (g-C₃N₄ NS)-covered electrode. The DNAzyme walking strand was first prohibited by a blocker strand. After the addition of target miRNA-21 and Mn²⁺, the DNAzyme walker could be activated and produce autonomous movements along the electrode track fueled by Mn²⁺-dependent DNAzyme-catalyzed substrate cleavage without additional energy supply. Notably, each walking step resulted in the cleavage of a substrate strand and the release of a Fc-labeled DNA strand fragment, allowing us to acquire an extreme ECL signal recovery of g-C₃N₄ inhibited by Fc. Meanwhile, numerous Fc-labeled DNA fragments escaped from the surface of the electrode, directly producing an obvious decrease in the square wave voltammetry (SWV) signal from Fc on the same sensing platform. This work not only avoided difficultly assembling various signal indicators but also significantly improved the sensitivity through using self-powered DNAzyme-walker amplification. Moreover, the proposed design employed the same reaction to produce two signal output modes, which could eliminate the interference from diverse reactive pathways on the outcome to mutually improve the accuracy. Therefore, the dual-mode miRNA-21 biosensor exhibited wide detection ranges of 100 aM to 100 nM with low detection limits of 54.3 and 78.6 aM by ECL and SWV modes, respectively, which provided an efficient and universal biosensing approach with extensive applications in early disease diagnosis and bioanalysis.

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