Endogenous Glutathione-Activated Nucleic Acid Molecular Circuitry for Cell-Specific MicroRNA Imaging.

Sensitive and reliable microRNA imaging in living cells has significant implications for clinical diagnosis and monitoring. Catalytic DNA circuits have emerged as potent tools for tracking these intracellular biomarkers and probing the corresponding biochemical processes. However, their utility is hindered by the low resistance to external interference, leading to undesired off-site activation and consequent signal leakage. Therefore, achieving the endogenous control of the DNA circuit's activation is preferable to the reliable target analysis in living cells. In this study, we attempted to address this challenge by engineering a simple yet effective endogenous glutathione (GSH)-regulated hybridization chain reaction (HCR) circuit for acquiring high-contrast miRNA imaging. Initially, the HCR hairpin reactants were blocked by the engineered disulfide-integrated DNA duplex, thus effectively passivating their sensing function. And the precaged HCR hairpin was liberated by the cell-specific GSH molecule, thus initiating the HCR system for selectively amplified detection of microRNA-21 (miR-21). This approach prevented unwanted signal leakage before exposure into target cells, thus ensuring robust miR-21 imaging with high accuracy and reliability in specific tumor cells. Moreover, the endogenously responsive HCR circuit established a link between the small regulatory factors and miRNA, thereby enhancing the signal gain. In summary, the endogenously activatable DNA circuit represents a versatile toolbox for robust bioanalysis and exploration of potential signaling pathways in living cells.