Ratiometric time-gated luminescence probe for hydrogen sulfide based on lanthanide complexes

Developments of ratiometric bioprobes are highly appealing due to the superiority of their self-calibration capability for the quantitative biotracking. In this work, we designed and synthesized a novel lanthanide complex-based ratiometric luminescence probe, [4'-(2,4-dinitrophenyloxy)-2,2':6',2″-terpyridine-6,6″-diyl]bis(methylenenitrilo) tetrakis(acetate)-Eu(3+)/Tb(3+) (NPTTA-Eu(3+)/Tb(3+)), for the specific recognition and quantitative time-gated luminescence detection of hydrogen sulfide (H2S) in aqueous and living cell samples. Due to the presence of the photoinduced electron transfer (PET) process from the terpyridine-Eu(3+)/Tb(3+) moiety to 2,4-dinitrophenyl (DNP), the probe itself is weakly luminescent. In physiological pH aqueous media, the reaction of NPTTA-Eu(3+)/Tb(3+) with H2S leads to the cleavage of DNP moiety from the probe molecule, which affords the deprotonated (4'-hydroxy-2,2':6',2″-terpyridine-6,6″-diyl)bis(methylenenitrilo) tetrakis(acetate)-Eu(3+)/Tb(3+) and terminates the PET process. Meanwhile, the intensity of Tb(3+) emission at 540 nm is remarkably increased, while that of the Eu(3+) emission at 610 nm is slightly decreased. After the reaction, the intensity ratio of Tb(3+) emission to Eu(3+) emission, I540/I610, was ∼220-fold increased, and the dose-dependent enhancement of I540/I610 showed a good linearity upon the increase of H2S concentration with a detection limit of 3.5 nM. This unique luminescence response allowed NPTTA-Eu(3+)/Tb(3+) to be conveniently used as a ratiometric probe for the time-gated luminescence detection of H2S with I540/I610 as a signal. In addition, the applicability of the probe for the quantitative time-gated luminescence imaging of intracellular H2S in living cells was investigated. The results demonstrated the efficacy and advantage of the new probe for the time-gated luminescence cell imaging application.