Imaging of lysosomal pH changes with a fluorescent sensor containing a novel lysosome-locating group.

Rlyso, a highly selective and sensitive pH sensor, can stain lysosomes with a novel lysosome-locating group, methylcarbitol. Rlyso was successfully used to detect lysosomal pH changes during apoptosis or induced by chloroquine while avoiding the "alkalizing effect" on lysosomes of current lysosomal probes with nitrogen-containing sidechains.