A label-free fluorescent probe for accurate mitochondrial G-quadruplex structures tracking via assembly hindered rotation induced emission

Inspired by the mechanism of aggregation induced emission, two derivatives of thiazole orange (TPE-mTO and Ph-TO) were rationally designed and prepared in this work. Their selectivity and sensitivity towards G-quadruplex were studied by fluorescence titration, gel analysis, and circular dichroism (CD) experiments. TPE-mTO could selectively lights-up G-quadruplex DNA structures with no conformational transition, while Ph-mTO could not distinguish the G-quadruplex DNA structure from other nucleic acid, which probably owing to the pocket size and shape of the G-quadruplex DNA only could hinder the rotation of TPE moiety. Then the speculation was verified by molecular docking, TPE-mTO could adopt an appropriate pose in 3 ' and 5 ' binding pockets of CM22 (G-quadruplex), the multiple interaction between TPE-mTO and CM22 do hinder the rotation of TPE moiety and lead to strong fluorescence. In addition, the detection limit (DL) of TPE-mTO towards CM22 (prefolded Gquadruplex) was found as low as 4.1 nM. With the help of TPE-mTO, the G-quadruplex DNA structures in mitochondrion can be easily and quickly tracked without further washing operations. Overall, the probe we developed (TPE-mTO) was a simple but powerful tool for studying G-quadruplex structures.