Functional DNA hexahedron for real-time detection of multiple microRNAs in living cells.

Intracellular microRNA (miRNA) analysis in single cell is highly informative and offers valuable insights to its physiological and pathological state, but it must confront the pivotal challenge of gene probe delivery and conditional release. Herein, we report an assembled DNA mini-hexahedron (DMH) that can selectively package and protect miRNA probe, target-cell-specific delivery and release it based on the target sequence recognition for intracellular miRNA detection. In brief, the DMH is self-assembled from six single-stranded oligonucleotide strands through rational design, one of which containing AS1411 sequence for specific uptake. Two fluorescent dye labeled recognition strands are inserted into two DMH edges with quencher groups through partially complementary hybridization. We find that this DMH possesses great biocompatibility, good trans-membrane ability and are able to protect the gene cargo against enzymatic degradation and protein binding. Fluorescence restoration caused by the target-mediated competitive chain replacement reaction allows to simultaneous detection of two cancer-related intracellular miRNAs with little false-positive signal, providing a powerful tool to discriminate healthy normal cell and cancerous cell. Thus, the construct opens a new avenue to circumvent the challenges in gene delivery, specific delivery and intrinsic interferences resistance.