Nucleic Acid‐to‐Small Molecule Converter through Amplified Hairpin DNA Circuits

Many microRNAs (miRNAs) are characteristically found in cancer cells, making miRNAs promising marker biomolecules for cancer diagnosis and therapeutics. However, it is challenging to use miRNA as a cancer signature because it is difficult to convert the nucleic acid sequence information into molecular functionality. To address this challenge, we realize nucleic acid‐to‐small molecule converters using hairpin DNA circuits. Harnessing a Staudinger reduction as a trigger for the conversion, we constructed hybridization chain reaction (HCR) and catalytic hairpin assembly (CHA) circuits that respond to oncogenic miR‐21. Fluorophore and dye molecules were released in response to miR‐21 through the HCR, providing fluorogenic and chromogenic readouts. Selective cytotoxicity in miR‐21‐abundant cells was realized by the CHA to release the anticancer drug SN‐38. This would be the first example of selective activation of a small‐molecule prodrug triggered by oncogenic miRNA in human living cells.