A red-emitting water-soluble fluorescent probe for biothiol detection with a large Stokes shift

In this work, we presented a fluorescent probe (MCQ-DNBS) for selective and sensitive detection of biothiols based on a methylated chromenoquinoline (MCQ) derivative. Probe MCQ-DNBS was constructed by masking the OH group in MCQ with a common sensing unit, 2,4-dinitrobezensulfonate group (DNBS) for biothiols. Due to the photo-induced electron transfer (PET) process between MCQ and DNBS, this probe was weekly fluorescent. Upon the addition of biothiols (Cys, Hcy and GSH), this probe emitted a strong red fluorescence (λem max = 613 nm) with a large Stokes shift (115 nm). In addition, fluorescence imaging of biothiols in living cells was successfully realized using MCQ-DNBS as a detector.