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

) of the probe changed significantly within the pH range from 4.50 to 5.50. The probe showed excellent selectivity among various metal cations, amino acids and ATP. Moreover, RNL has been successfully applied in HeLa cells, and the results demonstrated that it could be used to detect lysosomal pH changes. The probe could also selectively stain lysosome in HeLa cells. Besides, the probe exhibited low cytotoxicity and satisfactory photostability in living HeLa cells.