A fluorescent probe for biothiols based on the conjugate addition of thiols to α,β-unsaturated ester

A sensitive fluorogenic probe 1 for biothiols was developed based on the Michael addition reaction. The probe 1 was readily synthesized via the reaction of 2-(4′-hydroxyphenyl) benzimidazole (HPBI) with acryloyl chloride and shows weak fluorescence emission. Upon mixing with biothiols, the fluorescence of 1 is significantly enhanced due to the conjugate addition of thiols to the α,β-unsaturated carbonyl moiety, thus eliminating the photoinduced electron transfer (PET) quenching of the fluorophore by the intramolecular carbon-carbon double bond. Cysteine (Cys) was selected as the representative thiol in the spectral experiment. A good linear relationship was obtained from 1.0 to 30.0 μmol L^-1 for Cys and the detection limit was 0.17 μmol L^-1. Furthermore, probe 1 was highly selective for biothiols without the interference of some biologically relevant analytes and has been applied to detecting biothiols in human urine samples.