A cell-penetrating ratiometric probe for simultaneous measurement of lysosomal and cytosolic pH change.

A new ratiometric fluorescent probe based on cell-penetrating peptides (CPPs) was constructed for whole-cell pH mapping and simultaneous measurement of pH changes in the cytoplasm and lysosomes. The arginine-rich CPP, RK worked as linker, carrier and part of the fluorophore. Benefiting from RK, the fluorescent probe is completely water soluble, membrane permeable and well biocompatible. It shows high selectivity, sensitivity and reversibility to pH fluctuations. The ratio of fluorescence intensities F/F increased from 0.2 to 9.2 over the pH range from 3.3 to 8.1. Intracellular pH mapping was successfully realized owing to the wide distribution of the probe in live cells (even in nucleus). Moreover, cytosolic and lysosomal pH change caused by the stimuli can be simultaneously detected. Compared to other ratiometric pH probes, RhB-RK-FITC can provide more precise information about H redistribution between different cellular compartments.