Biomineralized Metal–Organic Framework Nanoparticles Enable Enzymatic Rolling Circle Amplification in Living Cells for Ultrasensitive MicroRNA Imaging

The enzymatic amplification strategy in living cells faces challenges of highly efficient intracellular codelivery of amplification reagents including DNA polymerase. In this work, we develop biomineralized metal–organic framework nanoparticles (MOF NPs) as a carrier system for intracellular codelivery of ϕ29 DNA polymerase (ϕ29DP) and nucleic acid probes and realize a polymerization amplification reaction in living cells. A pH-sensitive biodegradable MOF NP of zeolitic imidazolate framework-8 (ZIF-8) is utilized to encapsulate ϕ29DP and adsorb nucleic acid probes. After uptake into cells, the encapsulated ϕ29DP and surface-adsorbed DNA probes are released and escaped from endolysosomes. In the presence of ϕ29DP and deoxyribonucleotide triphosphates (dNTPs), the intracellular miRNA-21 triggers a rolling circle amplification (RCA) reaction and the autonomous synthesized Mg2+-dependent DNAzyme cleaves the fluorogenic substrate, providing a readout fluorescence signal for the monitoring of miRNA-21. This is the first example of the intracellular RCA reaction in living cells. Therefore, the proposed method provides new opportunities for achieving enzymatic amplification reaction in living cells.