Rigidified DNA Triangle-Protected Molecular Beacon from Endogenous Nuclease Digestion for Monitoring microRNA Expression in Living Cells.

Utilizing the nucleic acid-based self-assembly technology, Y-shaped backbone-rigidified DNA triangles with substantially enhanced nuclease resistance are built by designing a Y-shaped backbone in the center of a planar DNA triangle. Along this line, we developed aptamer-targeted DNA triangle-based molecular beacon (Apt-Tri-MB) probes for monitoring the microRNA expression in living cells with high sensitivity and specificity. For the Apt-Tri-MB probe, the MB is protected by the DNA triangle from unwanted enzymatic digestion, and a targeting ligand aptamer is introduced to endow the MB with active tumor cell-targeting capability. Thus, the digestion-induced false-positive signal is avoided, and the background fluorescence, which originates from the passive cell uptake (e.g., transfection) of reporting probes, is substantially suppressed. The imaging capability of the Apt-Tri-MB is superior to the commercial transfection agent-based counterpart and exhibits good universality suitable for imaging different miRNAs by changing the recognition fragment of the MB. Meanwhile, the disadvantages are efficiently circumvented, including the susceptibility of nucleic acids to nuclease-mediated degradation, inability of MB probes to enter cells, lipofectamine-determined cellular cytotoxicity, and nontargeting cell uptake. Inspired by the Y-shaped backbone-rigidified Apt-Tri-MB, we also constructed X-shaped backbone-rigidified quadrangle-based probes (Apt-Qua-MB). The experimental results show that cell imaging and antidegradation capability of Apt-Qua-MB are comparable with Apt-Tri-MB. As a proof-of-concept study, the Apt-Tri-MB is expected to open an exciting avenue for the further application of nucleic acid probes in the cellular level research and clinical disease diagnosis.