An instantaneous near-infrared trimethyl lock based fluorescent probe for biothiols with a large Stokes shift

Using trimethyl lock as a useful mean, a selective and sensitive fluorescent probe was developed for the detection of biothiols with an emission in near infrared spectral region (694 nm) and a large Stokes shift (129 nm). The inserted trimethyl lock between the fluorophore and the sensing group, 2, 4-dinitrobenzensulfonate, highly improved the response rate of this probe toward GSH because the unfavorable steric interactions between three methyl groups resulted in an extremely rapid intramolecular lactonization reaction to form a hydrocoumarin. This probe displayed an instantaneous response (within seconds) to GSH at a very low concentration in aqueous medium and the detection limit was as low as 2.5 nM based on S/N = 3. The fluorescence intensity of the solution of probe 1 at 694 nm displayed a good linearity (R = 0.9917) with the concentration of GSH in a range of 0.0-5.0 μM. Importantly, this probe exhibited a good performance in detecting biothiols in serum samples, living cells and organism.