Rational design of Red fluorescent and selective G-quadruplex DNA sensing probes: The study of interaction signaling and the molecular structural relationship achieving high specificity

Red fluorescent G-quadruplex DNA selective organic binding probe is relatively underdeveloped. In the present study, we designed a series of new fluorescent probes that exhibit large Stokes shift (112−131 nm), high quantum yield (up to 0.56), robust against photo-bleaching and high selectivity towards quadruplex structures of c-MYC and telomere DNA with strong binding affinity. The discrimination ability of the probes towards G-quadruplex structures against single-/double-stranded DNA or RNA was investigated by analyzing their structural property with respect to their binding specificity. From the sensing application of the probe targeting pu27, an excellent linear relationship (R² = 0.9997) with respect to the pu27-A3 interaction signal was observed. The LOD was found down to 4.0 nM, which is superior to thiazole orange dye. The probe is able to realize real-time fluorescence visualization in aqueous, PAGE staining and live cell imaging. In addition, from the immunofluorescence analysis using the probe and BG4 antibody, the A3 foci and BG4 staining co-localized well in PC3 cells, which suggest that the probe is G-quadruplex selective and is useful for visualizing G-quadruplex DNA structures in live cells. Cytotoxicity assays also demonstrated that the probe has low cytotoxicity against both PC3 cancer cells and 16HBE normal cells.