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)-Eu³⁺/Tb³⁺ (NPTTA-Eu³⁺/Tb³⁺), 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-Eu³⁺/Tb³⁺ moiety to 2,4-dinitrophenyl (DNP), the probe itself is weakly luminescent. In physiological pH aqueous media, the reaction of NPTTA-Eu³⁺/Tb³⁺ 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)-Eu³⁺/Tb³⁺ and terminates the PET process. Meanwhile, the intensity of Tb³⁺ emission at 540 nm is remarkably increased, while that of the Eu³⁺ emission at 610 nm is slightly decreased. After the reaction, the intensity ratio of Tb³⁺ emission to Eu³⁺ emission, <i>I</i>₅₄₀/<i>I</i>₆₁₀, was ∼220-fold increased, and the dose-dependent enhancement of <i>I</i>₅₄₀/<i>I</i>₆₁₀ showed a good linearity upon the increase of H₂S concentration with a detection limit of 3.5 nM. This unique luminescence response allowed NPTTA-Eu³⁺/Tb³⁺ to be conveniently used as a ratiometric probe for the time-gated luminescence detection of H₂S with <i>I</i>₅₄₀/<i>I</i>₆₁₀ 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