Reversible FRET Fluorescent Probe for Ratiometric Tracking of Endogenous Fe³⁺ in Ferroptosis

A reversible fluorescent probe DRhFe is devised by linking spirolactam rhodamine and dansylamide through an Fe³⁺ ionophore N²-hydroxyethyldiethylenetriamine, where Fe³⁺ chelation generating rhodamine B can switch intramolecular fluorescence resonance energy transfer for ratiometric Fe³⁺ sensing. Probe DRhFe exhibits an Fe³⁺-specific emission shift from 483 to 576 nm, and this ratiometric response has been successfully applied to monitor labile Fe³⁺ fluctuations in cells undergoing ferroptosis.