A regioisomer of thiazole orange derivate for selective G-Quadruplex DNA detection and in vivo tumor imaging.

G-Quadruplex (G4) DNA structures play a crucial role in regulating various biological processes, rendering them attractive targets for diagnostic and therapeutic applications. The development of G4-targeted fluorescent probes will significantly enhance our understanding of G4 DNA biology in vivo and improve the precision of diagnosing and treating genetic diseases. Herein, we report on a regioisomer of a thiazole orange derivative (SQ2) as a promising fluorescent dye for G4 DNA structures and demonstrate its application in both cell and tumor tissue imaging. Spectral analysis reveals that SQ2 exhibits minimal background fluorescence in solution and displays distinct fluorescent signal discrimination towards G4 DNAs compared to ssDNA, dsDNA, RNA, and other biological species. Importantly, this G4-activated fluorescent response is unaffected by environmental factors such as viscosity and polarity. Furthermore, SQ2's remarkable optical changes upon binding to G4 DNA structures facilitated the development of a label-free binary INHIBIT gate. This gate serves as a proof-of-principle for the future design of molecular logic circuits. Imaging experiments demonstrate that SQ2 exhibits remarkable spatiotemporal specificity for nuclear G4s and enables specific tumor tissue imaging in vivo, highlighting its tumor diagnostic potential.