Caged rhodamine-based fluorescent probe for biothiol: Selective detection of cysteine over homocysteine and glutathione in water

We report a rhodamine-based fluorescent probe (1) for cysteine (Cys). Masked with a para-hydroxybenzyl alcohol (HBA) unit, the probe's initial weak fluorescence is converted to strong fluorescence through a series of reactions of Michael addition and intramolecular cyclization of Cys, followed by deprotection of HBA. The caged probe (1) exhibits a selective and sensitive response toward Cys over homocysteine (Hcy) and glutathione (GSH) in HEPES buffer.