MicroRNA Triggered DNA "Nano Wheel" for Visualizing Intracellular microRNA via Localized DNA Cascade Reaction

There is intense interest in visualizing intracellular microRNA (miRNA) in situ due to its valuable diagnostic and prognostic function and expressional heterogeneity. The direct monitoring of intracellular miRNA expressional level with a wide concentration range and in ultralow amount remains a key challenge. Herein, we report a responsive DNA "nano wheel" (DNW) by hybridization of modified six DNA hairpin structures to a programmed DNA nanowire for highly efficient and fast miRNA imaging in living cells. We demonstrate that one target miRNA is able to trigger the nearby DNA hairpins sequential hybridization through accelerated localized DNA cascade reaction (LDCR) along the DNA nanowire and open of the self-quenched hairpins to assemble six-arm branched junction "nano wheel" structure lighted with three fluorescence dye. Notably, the recycled miRNA target further acts as an catalyst to generate multiple lighted "nano wheel" structures, thus one target miRNA enable to trigger strong and amplified fluorescence signal for intracellular sensitive imaging. Meanwhile, the LDCR endows the system with fast reaction kinetics owing to the high local concentration. It outperforms the "one-to-one" conventional molecular beacon (MB) and intermolecular hybridization-based six-arm branched junction in sensitivity and reaction kinetics for intracellular miRNA imaging verified using MCF-7, A549, Hela, and NHDF cells. The programmed DNW provides a useful and valuable tool for rapid and highly efficient visualization of low-abundance miRNA in living cells, which is beneficial to understand the miRNA function and exploration of its biomedical application.