A ratiometric lysosomal pH probe based on the naphthalimide–rhodamine system

The ratiometric pH probe RNL was constructed by integrating the naphthalimide moiety as an FRET donor into the rhodamine moiety as an FRET acceptor. The probe with a pK_a of 4.82 could detect pH in the range of 4.50–5.50, selectively stain lysosome and detect lysosomal pH changes.