Development of an engineered carbazole/thiazole orange conjugating probe for G-quadruplexes

Abstract The development of selective and sensitive probes for sensing G-quadruplexes either in vitro or in cellulo has been the focus of investigation for a long time. Of those investigated, 3,6-bis(1-methyl-4-vinylpyridinium) carbazole diiodide (BMVC) is a promising fluorescent probe utilized in many studies investigating G-quadruplex structures. However, its shortcomings, including similar fluorescence responses for G-quadruplex and duplex DNA and green but not red fluorescent emission, might restrict the further application of BMVC. In this study, in order to improve the selectivity and optical properties of BMVC, we engineered a new probe ( TO-CZ ) by incorporating thiazole orange (TO) into the structure of BMVC. We next found that TO-CZ can act as a colorimetric and red-emitting fluorescent dual probe selective for G-quadruplexes without affecting the G-quadruplex topology. Further experiments showed that a 2:1 binding model involving the external binding of TO-CZ to both ends of the G-quadruplex is the most possible binding mode. Furthermore, we applied TO-CZ in sensing G-quadruplexes both in vitro and in cellulo , and found that TO-CZ can selectively and sensitively visualize G-quadruplexes. Notably, TO-CZ might be used to map DNA and RNA G-quadruplexes in cellulo , showing its great potential in investigating intracellular G-quadruplex structures.