Fluorescence Resonance Energy Transfer-Based DNA Tetrahedron Nanotweezer for Highly Reliable Detection of Tumor-Related mRNA in Living Cells.

Accurate detection and imaging of tumor-related mRNA in living cells hold great promise for early cancer detection. However, currently, most probes designed to image intracellular mRNA confront intrinsic interferences arising from complex biological matrices and resulting in inevitable false-positive signals. To circumvent this problem, an intracellular DNA nanoprobe, termed DNA tetrahedron nanotweezer (DTNT), was developed to reliably image tumor-related mRNA in living cells based on the FRET (fluorescence resonance energy transfer) "off" to "on" signal readout mode. DTNT was self-assembled from four single-stranded DNAs. In the absence of target mRNA, the respectively labeled donor and acceptor fluorophores are separated, thus inducing low FRET efficiency. However, in the presence of target mRNA, DTNT alters its structure from the open to closed state, thus bringing the dual fluorophores into close proximity for high FRET efficiency. The DTNT exhibited high cellular permeability, fast response and excellent biocompatibility. Moreover, intracellular imaging experiments showed that DTNT could effectively distinguish cancer cells from normal cells and, moreover, distinguish among changes of mRNA expression levels in living cells. The DTNT nanoprobe also exhibits minimal effect of probe concentration, distribution and laser power as other ratiometric probe. More importantly, as a result of the FRET "off" to "on" signal readout mode, the DTNT nanoprobe almost entirely avoids false-positive signals due to intrinsic interferences, such as nuclease digestion, protein binding and thermodynamic fluctuations in complex biological matrices. This design blueprint can be applied to the development of powerful DNA nanomachines for biomedical research and clinical early diagnosis.