A two-photon metal-organic framework nanoprobe with catalytic hairpin assembly for amplified MicroRNA imaging in living cells and tissues

Monitoring miRNAs can provide critical information for the generation and progress of various cancers. However, the existing DNA amplification strategies-based fluorescent nanoprobes for intracellular miRNAs imaging are often confronted with problems such as shallow light-penetration depth, enzymatic degradation, and low DNA loading efficiency. Herein, we developed a new two-photon nanoprobe (TP-CHA-MOFs) by using MOF as the nanocarrier and hairpins as a two-photon fluorescence signal amplifier for intracellular miRNA imaging. After cell penetration, intracellular phosphate could coordinate with Zr atoms in the MOFs, leading to the release of hairpins from the surfaces of TP-CHA-MOFs. The intracellular miRNA could trigger the formation of the H1-H2 duplex, which led to a turn-on TP fluorescence signal, realizing amplified detection of target miRNA. TP-CHA-MOFs nanoprobe showed high loading capacity of nucleic acid molecules, high biostability toward enzyme, and good biocompatibility. Because of the employment of TP fluorophore, TP-CHA-MOFs achieved sensitive imaging of intracellular miRNA and differentiated tumor cells with different miRNA levels. Moreover, sensitive imaging of miRNA in deep tumor tissues was realized with a penetration depth of 160 µm. The TP-CHA-MOFs nanoprobe is highly promising for future application in medical diagnostics.