Programmable Fluorescent RNA with a Catalytic Hairpin Assembly System Enables Label-Free Monitoring of MicroRNA in Living Cells

MicroRNA (miRNA), as a small noncoding RNA dysregulated in various cancers, can be considered an efficient biomarker for early diagnosis. Herein, we proposed a label-free fluorescent RNA-based catalytic hairpin assembly strategy to monitor miRNA in vivo and in vitro accurately with highly efficient performances. In the presence of target miRNA, it could activate the catalytic hairpin assembly (CHA) cycle by hybridizing with H1 and H2 to form an H1-H2 duplex complex and release target miRNA for cyclic amplification, while the H2 structure was induced into a fluorescence-active conformation in the H1-H2 duplex with a stable aptamer domain to react with a fluorescent molecule, generating a robust fluorescence response related with the concentration of target miRNA. Thus, the fluorescent RNA-based catalytic hairpin assembly system realizes the cyclic amplification with label-free fluorescent RNA (FLRNA), which produces simpler, efficient, and ultrahighly sensitive analytical capabilities, especially good linearity in the concentration range from 1 pM to 1 nM with a detection limit of 0.65 pM, opening a new door to monitor the expression levels of biomolecules for early diagnosis and prognostic assessment of a variety of diseases.