Fluorescent imaging of acidic compartments in living cells with a high selective novel one-photon ratiometric and two-photon acidic pH probe

Fluorescent imaging of acidic compartments in living cells was carried out successfully by a novel molecule (CAE) that contained a pyridine unit and a carbazole core. As the protonation of the pyridine N atom of CAE, pH-dependent absorption and fluorescence properties were shown with a pKa of 5.47 which matches the pH range of intracellular acidic compartments. Moreover, a large Stokes shift, a significant enhancement in ratios of I544 nm/I460 nm and a distinct two-photon turn-on character were exhibited in spectral analysis. Meanwhile, direct intracellular imaging and standard double-staining experiments of CAE and LTR (co-localization coefficient: 0.83) revealed that CAE is an effective one-photon ratiometric and two-photon acidic pH probe for imaging intracellular acidic compartments. The pH distribution pattern of intracellular acidic compartments can be obtained facilely by CAE. In especial, CAE possessed well membrane-permeability, brilliant selectivity among various bioanalyte and excellent counterstain compatibility with Hoechst 33342, MTR and LTR.