A lysosome-locating and acidic pH-activatable fluorescent probe for visualizing endogenous HO in lysosomes.

There is increasing evidence indicating that lysosomal HO is closely related to autophagy and apoptotic pathways under both physiological and pathological conditions. Therefore, fluorescent probes that can be exploited to visualize HO in lysosomes are potential tools for exploring diverse roles of HO in cells. However, functional exploration of lysosomal HO is limited by the lack of fluorescent probes capable of compatibly sensing HO under weak acidic conditions (pH = 4.5) of lysosomes. Lower spatial resolution of the fluorescent visualization of lysosomal HO might be caused by the interference of signals from cytosolic and mitochondrial HO, as well as the non-specific distribution of the probes in cells. In this work, we developed a lysosome-locating and acidic-pH-activatable fluorescent probe for the detection and visualization of HO in lysosomes, which consists of a HO-responsive boronate unit, a lysosome-locating morpholine group, and a pH-activatable benzorhodol fluorophore. The response of the fluorescent probe to HO is significantly more pronounced under acidic pH conditions than that under neutral pH conditions. Notably, the present probe enables the fluorescence sensing of endogenous lysosomal HO in living cells without external stimulations, with signal interference from the cytoplasm and other intracellular organelles being negligible.