A pH-activated fluorescent probe via transformation of azo and hydrazone forms for lysosomal pH imaging.

We developed a fluorescent probe Sth-NH by introducing a 6-hydroxypyridone skeleton. The presence of an active proton enables the probe to transform from a deprotonated azo form to a hydrazone form in a strongly acidic environment to realize fluorescence light-up behavior, thus monitoring the lower lysosomal pH of cancer cells and distinguishing them from normal cells.