Cascade OFF-ON-OFF fluorescent probe: Dual detection of Fe³⁺ ions and thiols

A new novel Rhodamine B-based fluorescent probe was synthesized for the selective cascade signaling of Fe³⁺ and thiols (glutathione, homo-cysteine, cysteine). Non-fluorescent rhodamine derivatives can selectively detect Fe³⁺ over some other metal ions in ethanol-water (4/1, v/v, pH 7.0) media, leading to prominent fluorescence OFF-ON switching. The obtained LDF-Fe³⁺ ensemble can subsequently serve as a sensitive and selective chemosensor for thiols, exhibiting complete signal quenching (fluorescence ON-OFF switching). The practical use of its Fe³⁺ ions ensemble was demonstrated by its application to the detection of thiols in the living cells.