Sequentially amplified integration of catalytic DNA circuits for high-performance intracellular imaging of miRNA and interpretation of mRNA-miRNA signalling pathway

The cascaded catalytic circuits are viable tools for improving the signal gain of biosensors, yet their sensing performance is still limited by the signal leakage from complex biological environment and unsatisfying reaction efficiency from inter-reactants steric hindrance. Herein, we proposed a catalytically localized DNA (CLD) circuit for the accurate and high-efficiency imaging of microRNA (miRNA) in living cells by virtue of the sequentially and successively amplified integration of catalytic DNA circuits. The compact CLD circuit was constructed by integrating two elemental catalytic circuits, cell-responsive EDR module and analyte-sensing CHA module, where CHA module was initially caged in EDR module for eliminating the unwanted off-site and off-target signal leakage. Only by cell-specific messenger RNA (mRNA)-activated EDR operation then the elemental CHA circuit could be successively connected to facilitate the highly efficient intramolecular reaction with low steric hindrance, thus leading to accelerated reaction efficiency for miRNA analyte. The multiple molecular recognition and the spatial self-confinement of the smart CLD circuit enable the accurate and high-efficiency imaging of intracellular miRNA. The interaction network of mRNA and miRNA was then investigated in situ through our CLD circuit, which provides a powerful tool for discovering the underlying signal pathways between these different RNAs in living cells.