Intracellular pH sensing and targeted imaging of lysosome by a galactosyl naphthalimide-piperazine probe

A series of galactosyl naphthalimide-piperazine derivatives have been synthesized as intracellular pH and lysosome-targeting imaging probes for live human hepatoma cells. The probes show good sensitivity in both aqueous buffer and intracellular environments. Incorporation of the galactose moiety with the pH probes facilitates their specific endocytosis and, thus targeted trafficking to lysosome, by the asialoglycoprotein receptor of human hepatoma cells. The acidic intracellular pH of live human hepatoma cells gives rise to a fluorescence turn-on signal of the probes probably via a modulation of the photo induced electron transfer (PET) mechanism. Additionally, galactosylation of the probes enhances their selective accumulation in lysosome and decreases the cytotoxicity. (C) 2016 Elsevier Ltd. All rights reserved.