A hemicyanine fluorescent probe with intramolecular charge transfer (ICT) mechanism for highly sensitive and selective detection of acidic pH and its application in living cells

Intracellular pH (pHi) plays an essential role in organelles . Fluorescent probe combined with fluorescence imaging analytical approach has been used for detection pH fluctuation due to high sensitivity and good photostability. Herein, a benzoindole-based colorimetric and naked-eye hemicyanine fluorescent probe 2,3-trimethy-3-[2,4-(dihyoxyl-4-yl)vinyl]-3 H -benzo[e]indole ( BiDD ) was developed in one step. Upon the decreasing of pH, BiDD exhibited strong a pH-dependent characteristic with p K a 4.98 and responded linearly within the pH range of 4.4–6.2. BiDD also showed high sensitivity and selectivity , colorimetric and fluorometric dual-modal response, high photostability, low cytotoxicity as well as good cell membrane permeability. More importantly, the probe was applied to sense and visualize the pH fluctuations in HeLa cells successfully by the fluorescence confocal microscope .