Direct detection of intracellular miRNA in living circulating tumor cells by tumor targeting nanoprobe in peripheral blood

Molecular analysis of circulating tumor cells (CTCs) is of critical significance for the non-invasive early detection of tumors. However, in situ detection of intracellular nucleic acids of CTCs in whole blood still remains challenge. By using a highly efficient tumor targeting nanoprobe, we realize in situ detection of microRNA-21 (miR-21) of living CTCs in unprocessed whole blood. In the nanoprobe, a catalytic hairpin assembly (CHA) system is complexed with protamine sulfate (PS), and then decorated by SYL3C conjugated hyaluronic acid (SHA) and hyaluronic acid (HA). The CHA system can be specifically delivered into living CTCs in whole blood, followed by hybridization between the CHA system and intracellular miR-21 in CTCs to induce strong fluorescence emission. After isolation of CTCs by membrane filtration, CTCs of cancer patients can be directly visualized by a fluorescence microscope for miR-21 detection at a single-cell level. Our study provides an efficient strategy to realize in situ genomic analysis of living CTCs in whole blood.