Tetrahedral DNA-guided catalytic hairpin assembly for reference-calibrated intracellular microRNA imaging and sensing.

We report a tetrahedral DNA platform that positions a catalytic hairpin assembly within an optimal spatial confinement window, thereby maximizing target-triggered amplification relative to background leakage. AS1411-mediated targeting and a β-actin reference channel further enable selective, internally calibrated imaging and sensing of intracellular microRNA-21.