Ratiometric fluorescence probe for two-photon bioimaging of Cr3+ in living cells

We presented a ratiometric fluorescent probe dansylamide–rhodamine dyad (DANS–RB) for selectively detecting Cr3+ in semi-aqueous solution. The detection mechanism relies on the fluorescent resonance energy transfer (FRET) process from the dansylamide (energy donor) to the rhodamine (energy acceptor) after the addition of Cr3+. The cell-permeability of DANS–RB was confirmed by the two-photon fluorescence microscopy experiments, which demonstrated DANS–RB was a good candidate for monitoring the intracellular Cr3+ level with the ratiometric fluorescent method. Combining the excellent selectivity, the ratiometric quantitative detection, and the cell-permeability, DANS–RB may find a broad application in the investigation on biologically relevant species in living cells.