A highly sensitive ratiometric fluorescent probe with a large emission shift for imaging endogenous cysteine in living cells

•A strategy to construct ratiometric probe with a large emission shift is developed.•A selective and sensitive visual and fluorescent probe for Cys is synthesized.•The probe detects Cys by ratiometric fluorescent spectra with a 117 nm red-shift.•The probe can monitor the changes of endogenous Cys level in living cells.

A new design strategy for the construction of ratiometric fluorescent probe with a large emission shift was developed. Based on this strategy, a highly selective and sensitive colorimetric and ratiometic fluorescent probe for cysteine (Cys) with a 117 nm red-shifted emission was synthesized and applied to the ratiometric imaging of endogenous Cys in living cells.