A novel pH fluorescent probe based on indocyanine for imaging of living cells

• Fluorescent pH probe based on indole derivatives and pyridine was constructed.
• Probe exhibits sensitive pH responded linearly within the range of 3.0–4.6.
• Probe has good cell membrane permeability and monitor pH fluctuations in live cells.

In this paper, we report a novel pH fluorescent probe, 1,1-dimethyl-2-((E)-2-(pyridin-4-yl)vinyl)-1H-benzo[e]indole (PVBI), for imaging in living cells via ethylene bridging of indole derivatives and pyridine. The pH titration indicated that the probe exhibits sensitive pH-dependent behavior with pKa 3.87 and responded linearly and rapidly to minor pH fluctuations within the range of 3.0–4.6 (linear coefficient of 0.9968). Thus PVBI could be potentially useful for quantitative determination of pH within the acidic window. Also, PVBI displays a notably large Stokes shift of 93 nm which could effectively reduce the excitation interference. Moreover, PVBI possesses highly selective response to H+ over various metal ions, good photostability and excellent reversibility. The confocal laser scanning microscope images for PVBI diffusing into cells in real-time and detection of pH in living cells were achieved successfully, suggesting the probe has excellent cell membrane permeability and could be applied to monitor pH fluctuations in living cells.

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