A Quinoline‐Based Fluorescent Probe Based on a Novel Nitric Oxide‐Induced Cyclization‐Responsive Mechanism and Its Application in Bioimaging In Vitro and In Vivo

Nitric oxide (NO) plays pivotal roles in numerous physiological and pathological processes, making its real‐time detection in biological systems of paramount importance. Herein, a novel quinoline‐based fluorescent probe ( KL ) was developed for the sensitive and selective detection of NO in vitro and in vivo. The probe achieves NO sensing through a unique NO‐induced cyclization‐responsive mechanism. Upon reaction with NO, the thiocarbohydrazide moiety of KL undergoes specific cyclization to form a 1,2,3,4‐thiatriazole ring, leading to a distinct red shift in its UV–vis absorption spectrum and pronounced fluorescence quenching at 550 nm. Probe KL exhibits a rapid response time (40 s), a low detection limit (78 nM), excellent selectivity, and a large Stokes shift (150 nm). Benefiting from its favorable biocompatibility, probe KL has been successfully applied for the visualization of NO in living HeLa cells. Furthermore, probe KL was successfully extended to real‐time fluorescence imaging of NO in live nude mice. Consequently, the development of probe KL would provide a novel approach for further elucidating the physiological functions of NO in biological systems and a new cyclization reaction‐based responsive strategy for NO detection.