Triplex-Functionalized DNA Tetrahedral Nanoprobe for Imaging of Intracellular pH and Tumor-Related Messenger RNA

A new triplex-functionalized DNA tetrahedral nanoprobe is proposed herein for monitoring pH and messenger RNA (mRNA) in living cells. Different from traditional DNA tetrahedron-based nanoprobes, DNA triplex was employed to serve as important conformational conversion elements. Inspired by the low extracellular pH in tumor cells, the mRNA-targeted H1 and H2 were stably assembled on the extended short hairpin probes of DNA tetrahedron via Hoogsteen bonding to form DNA triplex. Due to the high intracellular pH and presence of target mRNA, hybridization chain reaction (HCR) was triggered between H1 and H2 which were released from the dissociation of DNA triplex, and the generated long double-stranded DNA activated a Föster resonance energy transfer (FRET) signal indicating target mRNA expression even at very low contents. By combining the distinguishing feature of DNA triplex structure (pH-responsive) and HCR (signal amplification), sensitive imaging of intracellular pH and tumor-related mRNA can be realized. As a further application, dynamic imaging of intracellular pH and mRNA during "mitochondria-dependent" pathway apoptosis was successfully achieved in human breast cancer cells, which indicated huge potential of our proposed nanoprobe in early diagnosis and treatment of diseases.