Run Zhang

Turn-on Luminescent Probe for Cysteine/Homocysteine Based on a Ruthenium(II) Complex

A unique ruthenium(II) complex, tris(4-methyl-2,2-bipyridyl-4-carboxaldehyde)Ru(II) hexafluorophosphate [Ru(CHO-bpy)(3)](PF(6))(2), has been designed and synthesized as a highly sensitive and selective luminescence probe for the recognition and detection of cysteine (Cys) and homocysteine (Hcy). The almost non-luminescent probe can rapidly react with Cys and Hcy to yield the corresponding thiazolidine and thiazinane derivatives, accompanied by the remarkable luminescence enhancement and a large blue-shift of the maximum emission wavelength from 720 to 635 nm. The dose-dependent luminescence enhancement of the probe shows a good linearity in the Cys/Hcy concentration range of 15 to 180 microM with the detection limits of 1.41 microM and 1.19 microM for Cys and Hcy, respectively. Furthermore, the luminescence response of the probe is highly specific to Cys/Hcy only even in the presence of various amino acids, protein, and DNA. The results of this work not only demonstrate the efficacy and advantages of the Ru(II) complex-based luminescence probe for the sensitive and selective detection of Cys/Hcy but also provide a useful strategy for the rational design of Ru(II) complex-based luminescence probes for various biological molecules.

Development of a heterobimetallic Ru(II)–Cu(II) complex for highly selective and sensitive luminescence sensing of sulfide anions

A heterobimetallic ruthenium(II)-copper(II) complex-based luminescent chemosensor, [Ru(bpy)(2)(bpy-DPA)Cu](4+) (bpy: 2,2-bipyridine; bpy-DAP: 4-methyl-4-[N,N-bis(2-picolyl)amino-methylene]-2,2-bipydine), has been designed and synthesized for the highly selective and sensitive recognition and detection of sulfide anions in 100% aqueous solutions. Owing to the high affinity of sulfide to Cu(II), the non-luminescent chemosensor can specifically and rapidly react with sulfide to yield the corresponding ruthenium(II) complex, [Ru(bpy)(2)(bpy-DPA)](2+), accompanied by the remarkable luminescence enhancement. The dose-dependent luminescence enhancement of the sensor shows a good linearity with a detection limit of 20.7 nM for sulfide anions. The novel luminescence sensor has a widely available pH range from 4.5 to 10 and an excellent response selectivity to sulfide only even in the presence of various other anions. Based on this chemosensor, a rapid, selective and sensitive luminescence method for the detection of sulfide anions in wastewater samples was established. The coefficient variations (CVs) of the method are less than 3.1%, and the recoveries are in the range of 90.9-108.5%.

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-Tb(3+) {ANMTTA, [4-(4-amino-3-nitrophenoxy)methylene-2,2:6,2-terpyridine-6,6-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-Ln(3+) 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-Eu(3+) and HTTA-Tb(3+) {HTTA, (4-hydroxymethyl-2,2:6,2-terpyridine-6,6-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-Eu(3+) and ANMTTA-Tb(3+), respectively. In addition, the luminescence responses of ANMTTA-Eu(3+) and ANMTTA-Tb(3+) to HOCl are pH-independent with excellent selectivity to distinguish HOCl from other reactive oxygen/nitrogen species (ROS/RNS). The ANMTTA-Ln(3+)-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.

Development of a Ruthenium(II) Complex Based Luminescent Probe for Imaging Nitric Oxide Production in Living Cells

A unique ruthenium(II) complex, bis(2,2-bipyridine)(4-(3,4-diaminophenoxy)-2,2-bipyridine)ruthenium(II) hexafluorophosphate ([(Ru(bpy)(2)(dabpy)][PF(6)](2)), has been designed and synthesized as a highly sensitive and selective luminescence probe for the imaging of nitric oxide (NO) production in living cells. The complex can specifically react with NO in aqueous buffers under aerobic conditions to yield its triazole derivative with a high reaction rate constant at the 10(10) M(-1) s(-1) level; this reaction is accompanied by a remarkable increase of the luminescence quantum yield from 0.13 to 2.2 %. Compared with organic probes, the new Ru(II) complex probe shows the advantages of a large Stokes shift (>150 nm), water solubility, and a wide pH-availability range (pH independent at pH>5). In addition, it was found that the new probe could be easily transferred into both living animal cells and plant cells by the coincubation method, whereas the triazole derivative was cell-membrane impermeable. The probe was successfully used for luminescence-imaging detection of the exogenous NO in mouse macrophage cells and endogenous NO in gardenia cells. The results demonstrated the efficacy and advantages of the new probe for NO detection in living cells.

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.

A Lanthanide Complex-Based Ratiometric Luminescence Probe for Time-Gated Luminescence Detection of Intracellular Thiols

A lanthanide complex-based ratiometric luminescence probe, [4-(2,4-dinitrobenzenesulfonyloxy)-2,2:6,2-terpyridine-6,6-diyl] bis(methylenenitrilo) tetrakis(acetate)-Eu(3+)/Tb(3+) (NSTTA-Eu(3+)/Tb(3+)), has been designed and synthesized for the specific recognition and time-gated luminescence detection of biothiols in physiological pH aqueous media. The probe itself is almost nonluminescent due to the presence of photoinduced electron transfer (PET) from the terpyridine-Ln(3+) moiety to the 2,4-dinitrobenzenesulfonyl (DNBS) moiety. In the presence of biothiols, the reaction of NSTTA-Eu(3+)/Tb(3+) with biothiols results in the cleavage of DNBS to afford the deprotonated (4-hydroxy-2,2:6,2-terpyridine-6,6-diyl) bis(methylenenitrilo) tetrakis(acetate)-Eu(3+)/Tb(3+) (HTTA-Eu(3+)/Tb(3+)), which terminates the PET process. After the reaction, the intensity of Eu(3+) emission at 610 nm is unchanged, while that of Tb(3+) emission at 540 nm is remarkably increased, which provides a ~36-fold enhanced intensity ratio of Tb(3+) emission to Eu(3+) emission (I540/I610). This unique luminescence response allows NSTTA-Eu(3+)/Tb(3+) to be used as a ratiometric probe for the time-gated luminescence detection of biothiols, using the intensity ratio of I540/I610 as a signal. Thus, based on the probe NSTTA-Eu(3+)/Tb(3+), a ratiometric time-gated luminescence detection method for biothiols was established and successfully used for the quantitative detection of the total biothiols in several living cell samples.

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

Although considerable efforts have been made for the development of ruthenium(II) complex-based chemosensors and bioimaging reagents, the multisignal chemosensor using ruthenium(II) complexes as the reporter is scarce. In addition, the mechanisms of cellular uptake of ruthenium(II)-based chemosensors and their intracellular distribution are ill-defined. Herein, a new ruthenium(II) complex-based multisignal chemosensor, Ru-Fc, is reported for the highly sensitive and selective detection of lysosomal hypochlorous acid (HOCl). Ru-Fc is weakly luminescent because the MLCT (metal-to-ligand charge transfer) state is corrupted by the efficient PET (photoinduced electron transfer) process from Fc (ferrocene) moiety to Ru(II) center. The cleavage of Fc moiety by a HOCl-induced specific reaction leads to elimination of PET, which re-establishes the MLCT state of the Ru(II) complex, accompanied by remarkable photoluminescence (PL) and electrochemiluminescence (ECL) enhancements. The result of MTT assay showed that the proposed chemosensor, Ru-Fc, was low cytotoxicity. The applicability of Ru-Fc for the quantitative detection of HOCl in live cells was demonstrated by the confocal microscopy imaging and flow cytometry analysis. Dye colocalization studies confirmed very precise distribution of the Ru(II) complex in lysosomes, and inhibition studies revealed that the caveolae-mediated endocytosis played an important role during the cellular internalization of Ru-Fc. By using Ru-Fc as a chemosensor, the imaging of the endogenous HOCl generated in live macrophage cells during the stimulation was achieved. Furthermore, the practical applicability of Ru-Fc was demonstrated by the visualizing of HOCl in laboratory model animals, Daphnia magna and zebrafish.

Developing red-emissive ruthenium(II) complex-based luminescent probes for cellular imaging.

Ruthenium(II) complexes have rich photophysical attributes, which enable novel design of responsive luminescence probes to selectively quantify biochemical analytes. In this work, we developed a systematic series of Ru(II)-bipyrindine complex derivatives, [Ru(bpy)(3-n)(DNP-bpy)(n)](PF(6))(2) (n = 1, 2, 3; bpy, 2,2-bipyridine; DNP-bpy, 4-(4-(2,4-dinitrophenoxy)phenyl)-2,2-bipyridine), as luminescent probes for highly selective and sensitive detection of thiophenol in aqueous solutions. The specific reaction between the probes and thiophenol triggers the cleavage of the electron acceptor group, 2,4-dinitrophenyl, eliminating the photoinduced electron transfer (PET) process, so that the luminescence of on-state complexes, [Ru(bpy)(3-n)(HP-bpy)(n)](2+) (n = 1, 2, 3; HP-bpy, 4-(4-hydroxyphenyl)-2,2-bipyridine), is turned on. We found that the complex [Ru(bpy)(DNP-bpy)(2)](2+) remarkably enhanced the on-to-off contrast ratio compared to the other two (37.8 compared to 21 and 18.7). This reveals a new strategy to obtain the best Ru(II) complex luminescence probe via the most asymmetric structure. Moreover, we demonstrated the practical utility of the complex as a cell-membrane permeable probe for quantitative luminescence imaging of the dynamic intracellular process of thiophenol in living cells. The results suggest that the new probe could be a very useful tool for luminescence imaging analysis of the toxic thiophenol in intact cells.

A cell-membrane-permeable europium complex as an efficient luminescent probe for singlet oxygen

A unique cell-membrane-permeable europium complex has been developed as a probe for time-gated luminescence detection of singlet oxygen (1O2). Combined with the time-gated luminescence imaging technique, the probe was successfully used for investigating the time-dependent generation and distribution of 1O2 induced by the clinical drugs of photodynamic therapy in cancer cells.

A highly selective and sensitive ON-OFF-ON fluorescence chemosensor for cysteine detection in endoplasmic reticulum.

A new complex between coumarin-based ligand (CL) and copper ion has been prepared and applied to be an ON-OFF-ON reversible fluorescence chemosensor for the detection of Cys with high sensitivity and specificity. In HEPES buffer, CL displayed high affinity towards Cu(2+) ion over other physiological and environmental metal ions, accompanied with a 98.4% of fluorescence quenching. In the presence of Cys, the detachment of Cu(2+) ion of CL-Cu(2+) ensemble led to the liberation of the fluorophore, CL, and thus fluorescence was recovered. The results of absorption and emission spectroscopy analyses confirmed that the fluorescence turn ON response of CL-Cu(2+) ensemble was selective towards Cys only with high sensitivity (detection of limit, 7.2×10(-7) M). Confocal microscopy studies indicated that the lipophilic CL targets the endoplasmic reticulum (ER) of live cells, where it could be functioned as a fluorescent chemosensor for visualization of Cys in this organelle. Quantitative fluorescence detection of Cys in ER was successfully realized by flow cytometry analysis. The developed chemosensor was further applied to detect Cys in real urine samples with great recoveries ranges from 95.41% to 107.40%.