A PNA-DNA2 Triple-Helix Molecular Switch-Based Colorimetric Sensor for Sensitive and Specific Detection of microRNAs from Cancer Cells.

Peptide nucleic acids (PNAs), the synthetic DNA mimics that can bind to oligonucleotides to form duplexes, triplexes, and quadruplexes, could be advantageous as probes for nucleic acid sequences owing to their unique physicochemical and biochemical properties. We have found that a homopurine PNA strand could bind to two homopyrimidine DNA strands to form a PNA-DNA2 triplex. Moreover, the cyanine dye DiSC2 (5) could bind with high affinity to this triplex and cause a noticeable color change. On the basis of this phenomenon, we have designed a label-free colorimetric sensing platform for miRNAs from cancer cells by using a PNA-DNA2 triple-helix molecular switch (THMS) and DiSC2 (5). This sensing platform can detect miRNA-21 specifically with a detection limit of 0.18 nM, which is comparable to that of the THMS-mediated fluorescence sensing platform. Moreover, this colorimetric platform does not involve any chemical modification or enzymatic signal amplification, which boosts its applicability and availability at the point of care in resource-limited settings. The universality of this approach can be simply achieved by altering the sequences of the probe DNA for specific targets.