Self-Powered Biosensor Based on DNA Walkers for Ultrasensitive MicroRNA Detection

A novel self-powered biosensor is fabricated for ultrasensitive microRNA-21 (miRNA-21) detection, which includes an enzymatic biofuel cell (EBFC), DNA walkers, a digital multimeter (DMM), and a capacitor. As a novel strategy for signal amplification, DNA walkers are designed in the cathode, while the capacitor stores electrochemical energy from the EBFC to further boost the instantaneous current displayed by the DMM. When miRNA-21 is present, the DNA walkers are provoked to walk from as-opened hairpin structures to other hairpin structures, generating double-strand DNA structures, which stimulate [Ru(NH₃)₆]³⁺ to be adsorbed on the cathode surface by electrostatic interaction. Afterward, [Ru(NH₃)₆]³⁺ is reduced to [Ru(NH₃)₆]²⁺, and the open circuit voltage (E^OCV) is significantly increased. Depending on the approach of signal amplification from DNA walkers, this biosensor displays an ultrasensitive assay toward miRNA-21 in the range of 0.5 to 10⁴ fM, with a detection limit of 0.15 fM. In addition, this self-powered biosensor displays high selectivity for miRNA-21 assay in human serum samples.