A DNAzyme-cleavage-activated turn-on fluorescence sensing platform for sensitive miRNA detection and in situ intracellular imaging.

MicroRNAs (miRNAs) are crucial regulators in tumor development, so accurately detecting and imaging them in living cells is vital for early cancer diagnosis. However, their low levels inside cells and the complex cellular environment make traditional detection methods challenging. We developed a fluorescent sensing platform, ZIF-8@SA@reporter, which combines DNAzyme catalytic cleavage with ZIF-8-mediated fluorescence quenching for sensitive detection and imaging of miRNA-21. ZIF-8 acts as a nanocarrier to efficiently load and deliver fluorophore-labeled substrates while quenching fluorescence to minimize background signals. When miRNA-21 is present, the DNAzyme is activated by Mg2+, cleaving the substrate and releasing the fluorophore, restoring fluorescence. This sensor has a linear detection range from 1 μmol L-1 to 10 pmol L-1, with the lowest experimentally detectable concentration of 1 pmol L-1. Live-cell imaging showed clear green fluorescence in MCF-7 and MKN-45 tumor cells, with stronger signals in MKN-45 cells due to higher miRNA-21 levels. This approach offers a reliable tool for early cancer diagnosis and monitoring of miRNA-related diseases.