An iminofluorescein-Cu²⁺ ensemble probe for selective detection of thiols

An iminofluorescein-Cu²⁺ ensemble probe was prepared for the detection of thiols in aqueous solution. In HEPES buffer, among various amino acids, only cysteine (Cys) induced fluorescence enhancement of Cu²⁺ ensemble. The mechanism was proposed that addition of Cys induced decomplexation of Cu2+ from weak-fluorescent ensemble, followed by hydrolytic cleavage of the resulted Schiff base to give a strongly fluorescent fluoresceinaldehyde. By fluorescence titration using 2 μM iminofluorescein-Cu2+ ensemble probe, the detection limit for Cys was evaluated to be 9 μM with a signal-to-noise ratio of 3. Furthermore, the confocal microscopy experiments demonstrated that this sensor was potential for the imaging of thiols in living cells.