A Lanthanide Complex-Based Ratiometric Luminescence Probe for Time-Gated Luminescence Detection of Intracellular Thiols

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A lanthanide complex-based ratiometric luminescence probe, [4'-(2,4-dinitrobenzenesulfonyloxy)-2,2':6',2''-terpyridine-6,6''-diyl] bis(methylenenitrilo) tetrakis(acetate)-Eu(3+)/Tb(3+) (NSTTA-Eu(3+)/Tb(3+)), has been designed and synthesized for the specific recognition and time-gated luminescence detection of biothiols in physiological pH aqueous media. The probe itself is almost nonluminescent due to the presence of photoinduced electron transfer (PET) from the terpyridine-Ln(3+) moiety to the 2,4-dinitrobenzenesulfonyl (DNBS) moiety. In the presence of biothiols, the reaction of NSTTA-Eu(3+)/Tb(3+) with biothiols results in the cleavage of DNBS to afford the deprotonated (4'-hydroxy-2,2':6',2''-terpyridine-6,6''-diyl) bis(methylenenitrilo) tetrakis(acetate)-Eu(3+)/Tb(3+) (HTTA-Eu(3+)/Tb(3+)), which terminates the PET process. After the reaction, the intensity of Eu(3+) emission at 610 nm is unchanged, while that of Tb(3+) emission at 540 nm is remarkably increased, which provides a ~36-fold enhanced intensity ratio of Tb(3+) emission to Eu(3+) emission (I540/I610). This unique luminescence response allows NSTTA-Eu(3+)/Tb(3+) to be used as a ratiometric probe for the time-gated luminescence detection of biothiols, using the intensity ratio of I540/I610 as a signal. Thus, based on the probe NSTTA-Eu(3+)/Tb(3+), a ratiometric time-gated luminescence detection method for biothiols was established and successfully used for the quantitative detection of the total biothiols in several living cell samples.