Development of a Ruthenium(II) Complex-Based Luminescent Probe for Hypochlorous Acid in Living Cells

A novel Ru­(II) complex, [Ru­(bpy)₂(DNPS-bpy)]­(PF₆)₂ (bpy: 2,2′-bipyridine, DNPS-bpy: 4-(2,4-dinitrophenylthio)­methylene-4′-methyl-2,2′-bipyridine), has been designed and synthesized as a highly sensitive and selective luminescence probe for the recognition and detection of hypochlorous acid (HOCl) in living cells by exploiting a “signaling moiety-recognition linker-quencher” sandwich approach. The complex possesses large stokes shift (170 nm), long emission wavelength (626 nm), and low cytotoxicity. Owing to the effective photoinduced electron transfer (PET) from Ru­(II) center to the electron acceptor, 2,4-dinitrophenyl (DNP), the red-emission of bipyridine-Ru­(II) complex was completely withheld. In aqueous media, HOCl can trigger an oxidation reaction to cleave the DNP moiety from the Ru­(II) complex, which results in the formation of a highly luminescent bipyridine-Ru­(II) complex derivative, [Ru­(bpy)₂(COOH-bpy)]­(PF₆)₂ (COOH-bpy: 4′-methyl-2,2′-bipyridyl-4-carboxylic acid), accompanied by a 190-fold luminescence enhancement. Cell imaging experimental results demonstrated that [Ru­(bpy)₂(DNPS-bpy)]­(PF₆)₂ is membrane permeable, and can be applied for capturing and visualizing the exogenous/endogenous HOCl molecules in living cell samples. The development of this Ru­(II) complex probe not only provides a useful tool for monitoring HOCl in living systems, but also strengthens the application of transition metal complex-based luminescent probes for bioimaging