Indole-based pH probe with ratiometric fluorescence behavior for intracellular imaging
Abstract
3-[3-(4-Fluorophenyl)-1-(1-methylethyl)-1H-indol-2-yl]-(E)-2-propenal (FMIP) was used as a ratiometric fluorescent pH probe with favorable optical properties for strong-acidity pH detection in living cells. The probe exhibits ratiometric fluorescence emission (I528 nm/I478 nm) characteristics with pKa 3.90 and linear response to strong-acidity range of 3.3–4.5. The major features of the probe include large Stokes shift (163 nm at pH 7.0 and 113 nm at pH 3.5), high selectivity and good photostability. More importantly, the probe has excellent cell membrane permeability and is further applied successfully to monitor pH in living cells.