As a typical reactive nitrogen species(RNS),peroxynitrite(ONOO-) plays an important role in physiological and pathological processes.In the past few years,a number of fluorescent probes have been reported in ONOO- detection.However,most of probes suffer from delayed response time,low selectivity and sensitivity,which greatly limits the real time,in situ detection of ONOO- in living organisms.Besides,some probes need complicated synthetic and purification procedures,which restricts their promotion and application.In this work,a novel benzothiazole-based fluorescent probe(E)-2-(benzo［d］thiazol-2-yl)-6-((2,2-dimethylhydrazono)-methyl)-4-methylphenol(BD) for ONOO- detection was prepared through the condensation reaction of 2-(2′-hydroxy-3′-aldehyde-5′-methylphenyl)benzothiazole and 1,1 dimethylhydrazine.The free probe showed weak fluorescence due to the nonradiative deactivation induced by the rotation of N—N single bond.Upon treatment with ONOO-,the hydrazone in the probe BD was hydrolyzed into aldehyde group,and thus the N—N single bond was removed,which resulted in a dramatic fluorescence enhancement with naked eye colorimetric and fluorescence color changes.The sensing mechanism of probe BD for ONOO- was verified by high resolution mass spectrometry.In PBS buffer solution(DMSO∶H2O=2∶8,by volume,pH 7.4),the probe exhibited many advantages,including rapid response(25 s),low detection limit(7 nmol/L),high selectivity to ONOO- over other biological related species and tolerance of a wide range of pH values including physiological pH.More importantly,this probe was successfully applied to the fluorescence imaging of ONOO- in HepG2 cells with excellent cell-membrane permeability.Therefore,it could be used as a potential analytical tool to reveal the role of ONOO- in living cells.