Highly selective and sensitive pH-responsive fluorescent probe in living Hela and HUVEC cells

A new fluorescent probe has been synthesized, characterized and evaluated in living cells as an intracellular pH indicator. The probe is designed based on the fluorescence switching character of rhodamine B dye. The probe exhibits highly selective and sensitive response to acidic pH. The fluorescence intensity of the probe gradually increases about 46-fold from pH 6.7 to 4.4 with a pKa value of 5.05 which is suitable for studying acidic organelles in living cells. Moreover, the fluorescence intensity of the probe is linearly proportional (R = 0.98809) to pH values in the range of 4.7–5.7. The probe can monitor intracellular pH in living Hela and HUVEC cells. The fluorescence of the probe in cells weakened as the addition of bafilomycin A1 or chloroquine that could induce pH value increase in lysosomes. The results demonstrate that the probe can selectively mark lysosomes and is valuable to monitor intracellular pH in living cells.