Lanthanide complex-based luminescent probes for highly sensitive time-gated luminescence detection of hypochlorous acid

Two novel lanthanide complex-based luminescent probes, ANMTTA-Eu ³⁺ and ANMTTA-Tb³⁺ {ANMTTA, [4′-(4-amino-3- nitrophenoxy)methylene-2,2′:6′,2â-terpyridine-6,6â-diyl] bis(methylenenitrilo) tetrakis(acetic acid)}, have been designed and synthesized for the highly sensitive and selective time-gated luminescence detection of hypochlorous acid (HOCl) in aqueous media. The probes are almost nonluminescent due to the photoinduced electron transfer (PET) process from the 4-amino-3-nitrophenyl moiety to the terpyridine-Ln³⁺ moiety, which quenches the lanthanide luminescence effectively. Upon reaction with HOCl, the 4-amino-3-nitrophenyl moiety is rapidly cleaved from the probe complexes, which affords strongly luminescent lanthanide complexes HTTA-Eu³⁺ and HTTA-Tb³⁺ {HTTA, (4′-hydroxymethyl-2,2′:6′, 2â-terpyridine-6,6â-diyl) bis(methylenenitrilo) tetrakis(acetic acid)}, accompanied by the remarkable luminescence enhancements. The dose-dependent luminescence enhancements show good linearity with detection limits of 1.3 nM and 0.64 nM for HOCl with ANMTTA-Eu³⁺ and ANMTTA-Tb³⁺, respectively. In addition, the luminescence responses of ANMTTA-Eu³⁺ and ANMTTA-Tb³⁺ to HOCl are pH-independent with excellent selectivity to distinguish HOCl from other reactive oxygen/nitrogen species (ROS/RNS). The ANMTTA-Ln³⁺-loaded HeLa and RAW 264.7 macrophage cells were prepared, and then the exogenous HOCl in HeLa cells and endogenous HOCl in macrophage cells were successfully imaged with time-gated luminescence mode. The results demonstrated the practical applicability of the probes for the cell imaging application.