A ratiometric lysosomal pH probe based on the coumarin–rhodamine FRET system

The ratiometric pH probe RC1 was constructed by integrating a coumarin moiety as a FRET donor into a rhodamine moiety as a FRET acceptor. The probe with a pK_a of 4.98 could detect pH in the range of 4.20–6.00 and selectively stain lysosomes.