Synthesis and time-resolved fluorimetric application of a europium chelate-based phosphorescence probe specific for singlet oxygen

Abstract

A new europium chelate, [4′-(9-anthryl)-2,2′:6′,2′′-terpyridine-6,6′′-diyl]bis(methylenenitrilo) tetrakis(acetate)-Eu³⁺ (ATTA-Eu³⁺), has been designed and synthesized as a highly sensitive and selective time-resolved phosphorescence probe for singlet oxygen (¹O₂). The probe can specifically react with ¹O₂ to yield its endoperoxide (EP-ATTA-Eu³⁺) with a great increase of the luminescence quantum yield and a long phosphorescence lifetime of 1.21 ms, which renders the probe favorable to be used for highly sensitive time-resolved luminescence detection of ¹O₂. The new phosphorescence probe is highly water soluble with a large stability constant of ∼10²⁰ and a wide available pH range at pH > 3. Upon reactions with some reactive oxygen species including hydrogen peroxide, superoxide, hydroxyl radical and ¹O₂, the probe shows high specificity for ¹O₂. The probe was used for quantitative detection of ¹O₂ generated from a MoO₄²⁻–H₂O₂ system to give a detection limit of 2.8 nM. Furthermore, the good applicability of the probe was demonstrated by the real-time monitoring of the kinetic process of ¹O₂ generation in a horseradish peroxidase (HRP) catalyzed oxidation system of indole-3-acetic acid (IAA) in a weakly acidic buffer and in a photosensitization system of 5,10,15,20-tetrakis(N-methyl-4-pyridyl)-21H,23H-porphine (TMPyP) in a neutral buffer.