A dual-mode biosensor for microRNA detection based on DNA tetrahedron-gated nanochannels

A biosensor based on solid-state nanochannels of anodic aluminum oxide (AAO) membrane for both electrochemical and naked-eye detection of microRNA-31 (MiR-31) is proposed. For this purpose, MoS₂ nanosheets, which possess different adsorption capabilities to single-stranded and double-stranded nucleic acids, are deposited onto the top surface of the AAO membrane. Moreover, multi-functional DNA nanostructure have been designed by linking a G-rich sequence for folding to a G-quadruplex at three vertices and a complementary sequence of MiR-31 at the other one vertex of a DNA tetrahedron. In the absence of MiR-31, the tetrahedron DNAzyme probe formed after the addition of hemin can mediate the deposition of insoluble on MoS₂/AAO, which not only enables the color change of the membrane but also gates the transport of K₃[Fe(CN)₆] across the nanochannels. Therefore, the detection of MiR-31 is realized by both visual observation of the brown color and measuring the electrochemical redox current of [Fe(CN)₆]^3-. Using this biosensor, a detection limit as low as 0.06 fM is achieved. The dual-mode detection method also exhibits good specificity, reproducibility, and stability, demonstrating potential application in the diagnosis of oral squamous cell carcinoma and other related biological purposes.