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

Abstract

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.

A ruthenium(II) complex-based lysosome-targetable multisignal chemosensor for in vivo detection of hypochlorous acid

“…MitoTracker ® Green FM, ER-Tracker™ Green, LysoSensor™ Green, LysoTracker ® Blue, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), Roswell Park Memorial Institute's Medium (RPMI-1640), Dulbecco's Modified Eagle Medium (DMEM), fetal bovine serum (FBS), L-glutamine, penicillin, and streptomycin sulfate were purchased from Life Technologies (Australia). 4-Carboxylic acid-4 0 -methyl-2,2 0 -bipyridine [22,41], cis-Ru(bpy) 2 Cl 2 $2H 2 O [17,42], [Ru(bpy) 2 (COOH-bpy)] 2þ [22] and 1-hydroxy-2-oxo-3-(3-aminopropyl)-3-methyl-1-triazene (NOC-13, an NO donor) [40] were synthesized by using the literature methods. Cultured D. magna and zebrafish were obtained from Professor Jingwen Chen's group at School of Environmental Science and Technology, Dalian University of Technology.…”

“…In previous work, although we have demonstrated the applicability of ruthenium(II) complexes as luminescent chemosensors for the detection of HOCl in live cells [22,41], the more reliable method that can be used for multisignal detection of HOCl is unexplored. In addition, the distribution of ruthenium(II) complexes in live cells and pathways for cellular uptake of these complexes are unclear [19,44,48].…”

“…As shown in Scheme 1, the new chemosensor, Ru-Fc, was designed according to the "PL and ECL reporter-reactive linkerquencher" sandwich approach [41]: a bipyridine-ruthenium(II) complex core was used as a PL and ECL reporter, a ferrocenyl moiety as signal quencher [62,63], and a hydrazine as the reactive linker. The choice of bipyridine-ruthenium(II) complex as a signal reporter is due to its rich PL and ECL properties reported in literature [12,27], and the choice of ferrocenyl moiety as a signal quencher is based on the consideration that ferrocenyl derivatives can effectively quench the luminescence through the PET process to corrupt the excited state of a luminophore [63].…”

“…In previous works, we identified that the MLCT excited state of ruthenium(II) complexes could be corrupted by the intramolecular photoinduced electron transfer (PET) process when an electron donor or acceptor was attached to polypyridyl ligands, and the elimination of PET by the analyte-triggered reaction could restore the MLCT state to switch on the luminescence of the complexes [40e42]. Using this strategy, our group has developed a series of polypyridyl-ruthenium(II) complex-based luminescent chemosensors/probes for reactive oxygen/nitrogen species (ROS/RNS) [22,28,40,41,43], highly active amino acids [14,17,30] and ions [42], and successfully demonstrated their applicability for biosensing and bioimaging [17,22,40,41]. Nevertheless, mechanisms for cellular uptake and distribution of ruthenium(II) complexes in live cells remained ill-defined [16,44e48].…”

“…The endogenous HOCl is an essential molecule in immune defense against microorganisms. However, excessive or misplaced HOCl could induce apoptosis of cells through the rupture of lysosomes [22,41]. In this regard, the development of accurate and reliable detection methods for HOCl in lysosome is fundamentally important to understand its physiological functions in living organisms.…”