A pH-switchable azo-based fluorescence reporter for lysosome-confined visualization of hypoxia status.

Lysosomes, important acidic organelles, under hypoxia status are closely associated with many diseases. The development of a molecular tool for the precise monitoring of lysosomal hypoxia is of great significance but remains challenging. Herein, we present a novel fluorescence probe HPFR, which is consisted of anthocyanidin fluorophore incorporated with quenching and hypoxia-sensitive azobenzene group, pH-switchable spirolactam moiety, and morpholine as lysosome targetable unit. Due to its hypoxia and acid dual-activatable characteristics, the proposed probe displays a highly sensitive and selective fluorescence response to azoreductase under a lysosomal pH environment but remains silent under neutral or alkaline conditions. Furthermore, it is confirmed to be biocompatible and could be employed to accurately visualize the hypoxia level of acidic lysosomes, offering a promising imaging tool for investigating hypoxic lysosome-related physiopathology. • A hypoxia-sensitive and pH-switchable fluorescence probe was developed. • The probe can specifically detect hypoxia-related azoreductase under acidic solution. • The probe enables to precisely monitor lysosome-confined hypoxia level. [ABSTRACT FROM AUTHOR]