An efficient circularly polarized luminescence probe base on anthryl-modified Eu(III)-helicates for the detection and imaging singlet oxygen in living cells

Abstract

Singlet oxygen (¹O₂) is the main active ingredient in photodynamic therapy (PDT). However, an excess ¹O₂ can cause unnecessary toxicity. Therefore, it is of great importance to develop reliable and sensitive methods or probes for detecting ¹O₂ in biological systems. In this study, a pair of anthryl-modified Eu(III) binaphthol-bis-β-diketones helicates, (NEt₄)₂[Eu₂(L^R/S)₄] are designed, synthesized and characterized. Initially, the complexes display faint luminescence. Upon reacting with ¹O₂ to create endoperoxides of the anthracene framework, the long-lived luminescence of the Eu(III) complexes is activated. Notably, the high luminescence dissymmetry factor, g_lum of the ⁵D₀ → ⁷F₁ transition (595 nm) shows an obvious increase from −1.21 to −1.29 before and after oxidation. The complex exhibits a highly selective luminescent response to the ¹O₂ generated by 5-aminolevulinic acid (ALA) loaded 4 T1 cells during photodynamic processes. To the best of we knowledge, this is the first example of ¹O₂ detection based on circularly polarized luminescence (CPL) probe. The design of the lanthanide CPL probe provides a practical way for the sensitive detection of ¹O₂ in the future.