A novel and photostable pH probe for selectively staining nuclei in living cells.

A novel pH probe based on hemi-cyanine was synthesized, which displays extremely large Stokes shift (122 nm) and good photostability. The probe responds to basic pH (pKa 8.32) with a colorimetric and fluorescence turn-on signal. Interestingly, the probe has good cell membrane permeability and could selectively stain nuclei in living cells.