Aptamer-based label-free detection of PDGF using ruthenium(II) complex as luminescent probe

We report a simple, cost-effective, and label-free detection method, consisting of a platelet-derived growth factor (PDGF) binding aptamer and hydrophobic Ru(II) complex as a sensor system for PDGF. The binding of PDGF with the aptamer results in the weakening of the aptamer–Ru(II) complex, monitored by luminescence signal. A substantial enhancement in the luminescence intensity of Ru(II) complex is observed in the presence of aptamer due to the hydrophobic interaction. Upon addition of PDGF, the luminescence intensity is decreased, due to the stronger interaction between the aptamer and PDGF resulting in the displacement of Ru(II) complex to the aqueous solution. Our assay can detect a target specifically in a complex medium such as the mixture of proteins, at a concentration of 0.8 pM.

A new spirobifluorene-bridged bipolar system for a nitric oxide turn-on fluorescent probe

A new spirobifluorene-bridged bipolar molecule (EDADO) as a nitric oxide (NO) turn-on fluorescent probe was designed and synthesized. The fluorescence of EDADO is strongly quenched by photoinduced electron transfer (PET) from the electron-donating o-phenylenediamine-containing biphenyl branch to the orthogonally arranged electron-accepting 1,3,4-oxadiazole-containing conjugated oligoaryl system. Upon reacting with NO, EDADO is converted to EDADO-T, which exhibits strong fluorescence due to the suppression of PET.     

Conjugated metallopolymers for fluorescent turn-on detection of nitric oxide

A series of eight pi-conjugated polymers (CPs) composed of phenylenevinylene, phenyleneethynylene, fluorene, and thiophene derivatives have been prepared with bipyridyl or terpyridyl substituents within the pi-conjugated backbone or at side-chain positions. These ligand-modified CPs serve as macromolecular scaffolds for conducting metallopolymers. The optical and photoluminescent properties of the polymers and corresponding copper(II) metallopolymers were investigated. Copper(II) is a highly efficient quencher of CP emission (75-100% quenching). CPs featuring bipyridyl units within the CP backbone are quenched more efficiently than those with terpyridyl units. The copper(II) metallopolymer undergoes reduction to the corresponding copper(I) species upon reaction with nitric oxide, with concomitant changes in integrated emission ranging from a 50% decrease to a 320% increase. The positive emission response is largest when Cu(II) was bound to the CP through bipyridyl units within the backbone, making these materials the best candidates for NO sensing by a turn-on emission mechanism.     

Photoluminescent and electrochemiluminescent dual-signaling probe for bio-thiols based on a ruthenium(II) complex

Photoluminescence (PL) and electrochemiluminescence (ECL) detection techniques are highly sensitive and widely used methods for clinical diagnostics and analytical biotechnology. In this work, a unique ruthenium(II) complex, [Ru(bpy)₂(DNBSO-bpy)](PF₆)₂ (bpy: 2,2′-bipyridine; DNBSO-bpy: 2,4-dinitrobenzenesulfonate of 4-(4-hydroxyphenyl)-2,2′-bipyridine), has been designed and synthesized as a highly sensitive and selective PL and ECL dual-signaling probe for the recognition and detection of bio-thiols in aqueous media. As a thiol-responsive probe, the complex can specifically and rapidly react with bio-thiols in aqueous solutions to yield a bipyridine-Ru(II) complex derivative, [Ru(bpy)₂(HP-bpy)]²⁺ (HP-bpy: 4-(4-hydroxyphenyl)-2,2′-bipyridine), accompanied by the remarkable PL and ECL enhancements. The complex was used as a probe for the PL and ECL detections of cysteine (Cys) and glutathione (GSH) in aqueous solutions. The dose-dependent PL and ECL enhancements showed good linear relationships against the Cys/GSH concentrations with the detection limits at nano-molar concentration level. Moreover, the complex-loaded HeLa cells were prepared for PL imaging of the endogenous intracellular thiols. The results demonstrated the practical utility of the complex as a cell-membrane permeable probe for PL imaging detection of bio-thiols in living cells.     

An unexpected fluorescent probe for G-quadruplex DNA based on a nitro-substituted ruthenium (II) complex

The detection of G-quadruplex is of major interest. Nitro-substituted ruthenium (II) complexes have attracted much attention due to fluorescent sensitivity to environment change. We report here a new nitro-substituted ruthenium (II) complex, [Ru (phen)₂(hnoip)]²⁺ ( 1) (hnoip = 2-(2-hydroxyl-5-nitrophenyl)imidazo[4,5-f][1,10-phenanthroline]), which displays distinct fluorescent properties in aqueous solution and non-aqueous solvents. This complex exhibits large fluorescence enhancement after binding with G-quadruplex DNA, and displays good fluorescent selectivity over other DNAs. The limit of detection is 6 nm for 22AG in Na⁺ and 43 nm for 22AG in K⁺, respectively. The results demonstrated that nitro-substituted ruthenium (II) complexes can be utilized to design as G-quadruplex fluorescent probes by protection of the nitro group on the complex from water.     

A 1,8-naphthalimide-derived turn-on fluorescent probe for imaging lysosomal nitric oxide in living cells

Nitric oxide has played an important role in many physiological and pathological processes as a kind of important gas signal molecules. In this work, a new fluorescent probe LysoNO-Naph for detecting NO in lysosomes based on 1,8-naphthalimide was reported. LysoNO-Naph has sub-groups of o-phenylenediamine as a NO reaction site and 4-(2-aminoethyl)-morpholine as a lysosome-targetable group. This probe exhibited good selectivity and high sensitivity (4.57 μmol/L) toward NO in a wide pH range from 4 to 12. Furthermore, LysoNO-Naph can be used for imaging NO in lysosomes in living cells.     

Visible light induced reversible extrusion of nitric oxide from a ruthenium(II) nitrosyl complex: a facile delivery of nitric oxide

The new ruthenium compound [Ru(NO)(pysiS4)]Br (3) (pysiS4 = 2,6-bis(3-triphenylsilyl-2-sulfanylphenylthiomethyl)pyridine), containing sterically bulky SiPh3 groups ortho to the thiolate donors, has been synthesized. In solution, 3 releases NO efficiently on exposure to visible light (lambda >/= 455 nm) at room temperature to afford [Ru(Br)(pysiS4)] (4). Treatment of 4 with NO yielded exclusively 3 without any metal-bound side reaction.     

A fluorescence turn-on sensor for iodide based on a thymine-Hg(II)-thymine complex

Iodide plays a vital role in many biological processes, including neurological activity and thyroid function. Due to its physiological relevance, a method for the rapid, sensitive, and selective detection of iodide in food, pharmaceutical products, and biological samples such as urine is of great importance. Herein, we demonstrate a novel and facile strategy for constructing a fluorescence turn-on sensor for iodide based on a T-Hg(II)-T complex (T=thymine). A fluorescent anthracene-thymine dyad (An-T) was synthesized, the binding of which to a mercury(II) ion lead to the formation of a An-T-Hg(II)-T-An complex, thereby quenching the fluorescent emission of this dyad. In this respect, the dyad An-T constituted a fluorescence turn-off sensor for mercury(II) ions in aqueous media. More importantly, it was found that upon addition of iodide, the mercury(II) ion was extracted from the complex due to the even stronger binding between mercury(II) ions and iodide, leading to the release of the free dyad and restoration of the fluorescence. By virtue of this fluorescence quenching and recovery process, the An-T-Hg(II)-T-An complex constitutes a fluorescence turn-on sensor for iodide with a detection limit of 126 nM. Moreover, this sensor is highly selective for iodide over other common anions, and can be used in the determination of iodide in drinking water and biological samples such as urine. This strategy may provide a new approach for sensing some other anions.     

Determination of diphenhydramine by capillary electrophoresis with tris(2,2'-bipyridyl)ruthenium(II) electrochemiluminescence detection

Tris(2,2′-bipyridyl)ruthenium(II) electrochemiluminescence detection in a capillary electrophoresis separation system was used for the determination of diphenhydramine. In this study, platinum disk electrode (300 μm in diameter) was used as a working electrode and the influence of applied potential and buffer conditions were investigated. Under optimal conditions: 1.2 V applied potential, pH 8.50, 15 kV separation voltage and 10 mmol l⁻¹ running buffer, the calibration curve of diphenhydramine was linear over the range of 4×10⁻⁸ to 1×10⁻⁵ mol l⁻¹. This technique gave satisfactory precision, and relative standard deviations of migration times and chemiluminescence peak intensities were less than 1 and 6%, respectively. The technique was applied to animal studies for determination of diphenhydramine extracted from rabbit plasma and urine samples, and the extraction efficiency were between 92 and 98.5%.     

Direct tris(2,2'-bipyridyl)ruthenium (II) electrochemiluminescence detection of polyamines separated by capillary electrophoresis

Capillary electrophoresis (CE) with tris(2,2'-bipyridyl) ruthenium (II) (Ru(bpy)3(2+)) electrochemiluminescence (ECL) detection technique was developed for the analysis of four polyamines (putrescine (Put), cadaverine (Cad), spermidine (Spd), and spermine (Spm)) analysis. The four polyamines contain different amine groups, which have different ECL activity. There are several parameters which influence the resolution and ECL peak intensities, including the buffer pH and concentrations, separation voltage, sample injection, electrode materials, and Ru(bpy)3(2+) concentrations. Polyamines are separated by capillary zone electrophoresis in an uncoated fused-silica capillary (50 cmx25 micro m (ID) filled with acidic phosphate buffer (200 mmol/L phosphate, pH 2.0) - 1mol/L phosphoric acid (9:1 v/v) and a separation voltage of 5 kV (25 micro A), with end-column Ru(bpy)3(2+) ECL detection. A 5 mmol/L Ru(bpy)3(2+) solution plus 200 mmol/L phosphate buffer (pH 11.0) is added into the reagent reservoir. The calibration curve is linear over a concentration range of two or three orders of magnitude for the polyamines. The analysis time is less than 25 min. Detection limits for Put and Cad are 1.9x10(-7) mol/L and 7.6x10(-9) mol/L for Spd and Spm, respectively. Intraday and interday relative standard deviations of ECL peak intensities are less than 8%. The main advantages of this CE-ECL detection technique for polyamines analysis presented herein are the omission of chemical derivatization of the analytes and the high selectivity.     

Comparative study of ruthenium(II) tris(bipyridine) derivatives for electrochemiluminescence application

Several [Ru(bpy)3]2+ (bpy = 2,2'-bipyridine and its derivatives) complexes were synthesized and compared electrochemically and spectroscopically in the search for better luminophores for electrochemiluminescence (ECL)-based analytical applications. ECL measurement in [Ru(bpy)3]2+/tripropylamine (TPA) aqueous buffer solutions has led to a conclusion that due to the complexity of the ECL generation process, the photoluminescence efficiency cannot be used to predict ECL intensity and there is no obvious relationship between the photoluminescence quantum yield and the ECL intensity. Under the present experimental condition, when compared with the pristine [Ru(bpy)3]2+, the ethoxycarbonyl-substituted derivative, [Ru(bpy-COOEt)3]2+, one of the most efficient luminophores under photoexcitation, did not generate reasonably intense ECL, whereas luminophores with lower photoluminescence quantum yields demonstrated higher ECL. These findings are useful for further efforts in the search for more efficient ECL luminophores.     

A heterobimetallic ruthenium(II)-copper(II) donor-acceptor complex as a chemodosimetric ensemble for selective cyanide detection

A trinuclear heterobimetallic Ru(II)-Cu(II) donor-acceptor complex, [Ru(II)((t)Bubpy)(CN)(4)-[Cu(II)(dien)](2)](ClO(4))(2) ((t)Bubpy = 4,4'-di-tert-butyl-2,2'-bipyridine; dien = diethylenetriamine) (1), has been synthesized and successfully used as an chemodosimetric ensemble for the specific detection of cyanide in aqueous DMF. X-ray crystallography, solid and solution IR spectroscopy, and conductivity measurements reveal that complex 1 is a one-dimensional polymer in the crystalline state and dissociates into its [Ru(II)((t)Bubpy)(CN)(2)[(CN)Cu(II)(dien)L](2)](2+) (L = solvent) monomeric units in polar solvents. The MLCT transition and luminescence properties of the solvatochromic [Ru(II)((t)Bubpy)(CN)(4)](2)(-) donor are perturbed by the coordination of two Cu(II) acceptors but restored in the presence of CN(-). Spectroscopic and mass spectrometric studies confirm the cleavage of the cyano bridge between Ru(II) and Cu(II) of the chemodosimetric ensemble after the binding of cyanide to the Cu(II) centers. The overall binding constant, K(B), between 1 and CN(-) is measured to be (7.39 +/- 0.23) x 10(6) M(-2). A detection limit of 1.2 microM (0.03 ppm) of CN(-) in aqueous DMF (pH 7.4) is achievable. Thermodynamic evaluation shows that the analyte specificity of chemodosimeter 1 is attributable to the relative stability of the donor-acceptor complex to that of adducts formed between the acceptor metal center and the analytes.     

Disposable biosensor based on cathodic electrochemiluminescence of tris(2,2-bipyridine)ruthenium(II) for uric acid determination

A new method for uric acid (UA) determination based on the quenching of the cathodic ECL of the tris(2,2-bipyridine)ruthenium(II)–uricase system is described. The biosensor is based on a double-layer design containing first tris(2,2-bipyridine)ruthenium(II) (Ru(bpy)₃²⁺) electrochemically immobilized on graphite screen-printed cells and uricase in chitosan as a second layer. The uric acid biosensing is based on the ECL quenching produced by uric acid over the cathodic ECL caused by immobilized Ru(bpy)₃²⁺ in the presence of uricase. The use of a −1.1 V pulse for 1 s with a dwelling time of 10 s makes it possible to estimate the initial enzymatic rate, which is used as the analytical signal. The Stern–Volmer type calibration function shows a dynamic range from 1.0 × 10⁻⁵ to 1.0 × 10⁻³ M with a limit of detection of 3.1 × 10⁻⁶ M and an accuracy of 13.6% (1.0 × 10⁻⁴ M, n = 5) as relative standard deviation. Satisfactory results were obtained for urine samples, creating an affordable alternative for uric acid determination.     

A dinuclear ruthenium(II) complex as an inducer and potential luminescent switch-on probe for G-quadruplex DNA

Given that recognition and regulation of G-quadruplex nucleic acid structures is an important goal for the development of chemical tools and medicinal agents, a dinuclear ruthenium complex [Ru₂(bpy)₄(bip-phenol)](ClO₄)₄ {bpy?=?2,2′-bipyridine, bip-phenol?=?2,4-bis(1H-imidazo[4,5-f] [1,10] phenanthroline-2-yl)phenol} has been synthesized and characterized, and its interactions with telomeric G-quadruplex DNA have been explored by photophysical and biophysical methods. This complex can induce and stabilize the formation of an antiparallel G-quadruplex of telomeric DNA in the absence of salt, or in the presence of K⁺/Na⁺-containing buffer. The complex binds strongly to the telomeric G-quadruplex, with a binding constant K_b?>?10⁶ and a 2:1 [complex]/[quadruplex] binding ratio. Fluorescence titrations revealed that the complex behaves as a promising photophysical “light switch” for G-quadruplex DNA, with 8.6- and 8.4-fold fluorescence enhancements in Na⁺ and K⁺ buffers, respectively.     

A fluorescent "turn-on" probe for the dual-channel detection of Hg(II) and Mg(II) and its application of imaging in living cells

A novel rhodamine-based fluorescent chemosensor (RND) was synthesized that contains two independent fluorophores and acts as a very sensitive, selective and reversible off-on probe for Hg(II). Importantly, this newly developed sensing system exhibited different fluorescent responses toward Hg(II) and Mg(II) at 589 nm and 523 nm, respectively. RND also displayed detectable color change upon treatment with Hg(II). Results from confocal laser scanning microscopy experiments demonstrated that this chemosensor is cell permeable and can be used as a fluorescent probe for monitoring Hg(II) or Mg(II) in living cells. This probe can also indirectly detect glutathione (GSH) and cysteine (Cys) with good linear relationships.     

Enhancing the electrochemiluminescence of tris(2,2'-bipyridyl)ruthenium(II) by ionic surfactants

The dependence of the electrochemiluminescence of Ru(bpy)3(2+) (bpy = 2,2'-bipyridine) with tri-n-propylamine as co-reactant on the anionic surfactant SDS (sodium dodecyl sulfate) and the cationic surfactants CTAX (CTA = cetyltrimethylammonium cation, X = bromide, chloride and hydrogensulfate) was studied. Both SDS and CTAX, at low surfactant concentrations below the critical micelle concentrations, enhance the electrochemiluminescence at a platinum working electrode. A further enhancement of the light emission intensity by bromide ions was observed when CTAB (B = bromide) was used-an overall 30-fold increase in electrochemiluminescence efficiency was obtained at a CTAB concentration of 0.08 mM. Voltammetric data support adsorption of surfactant molecules on the electrode surface as the cause of the enhancement of electrochemiluminescence by ionic surfactants.     

Electrochemical behavior of complex based on ruthenium(II) phthalocyaninate

The electrochemical reactions of ruthenium(II) bis(triethylenediamine)tetra-tret-butyl-phthalocyaninate in dimethylformamide are studied. Two reversible redox reactions on the platinum amalgam electrode are revealed at the potentials of ?0.73 and ?1.16 V (Ag/AgCl). Similarly to several other phthalocyanines, these redox reactions correspond to the successive transfer of two electrons to phthalocyanine ring. A new phenomenon, which has not been reported in the literature for phthalocyanines, namely, the cathodic polymerization, is discovered. Thus formed polymer is redox-active, and only one cathodic reaction at the potentials from ?0.78 to ?0.84 V (a shift in the cathodic direction takes place as the film thickness increases) is observed in the polymer. In addition, the polymer exhibits also considerable electron conductivity that enables one to perform various electrochemical reactions in a wide potential range on the electrode modified with the polymer.     

Fiber-optic fluorescence sensor for dissolved oxygen detection based on fluorinated xerogel immobilized with ruthenium (II) complex

A fiber-optic sensor based on fluorescence quenching was designed for dissolved oxygen (DO) detection. The fluorinated xerogel-based sensing film of the present sensor was prepared from 3, 3, 3-trifluoropropyltrimethoxysilane (TFP–TriMOS). Oxygen-sensitive fluorophores of tris (2, 2′- bipyridine) ruthenium (II) (Ru(bpy)₃²⁺) were immobilized in the sensing film and the emission fluorescence was quenched by dissolved oxygen. In the sensor fabrication, a two-fiber probe was employed to obtain the best fluorescence collection efficiency and the sensing film was attached to the probe end. Scanning electron microscope (SEM), UV–Vis absorption spectroscopy (UV–Vis) and fourier transform infrared spectroscopy (FTIR) measurements have been used to characterize the sensing film. The sensor sensitivity is quantified by I _deoxy/I _oxy, where I _deoxy and I _oxy represented the detected fluorescence intensities in fully deoxygenated and fully oxygenated environments, respectively. Compared with tetramethoxysilane (TMOS) and methyltriethoxysilane (MTMS)-derived sensing films, TFP–TriMOS-based sensor exhibited excellent performances in dissolved oxygen detection with short response time of 4 s, low limit of detection (LOD) of 0.04 ppm (R.S.D. = 2.5%), linear Stern–Volmer calibration plot from 0 to 40 ppm and long-term stability during the past 10 months. The reasons for the preferable performances of TFP–TriMOS-based sensing film were discussed.     

One-step immobilization of tris(2,2'-bipyridyl)ruthenium(II) via vapor-surface sol-gel deposition towards solid-state electrochemiluminescence detection

A novel method for immobilization of tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃Cl₂) on electrode surfaces based on the vapor-surface sol-gel deposition strategy is first demonstrated in this paper. Ru(bpy)₃Cl₂ immobilized sol-gel (Ru(bpy)₃Cl₂/sol-gel) films were characterized by UV-vis spectroscopy and field-emitted scanning electron microscopy (FE-SEM). These results showed that Ru(bpy)₃Cl₂ was successfully incorporated into the silica sol-gel film. It was found that many irregular Ru(bpy)₃Cl₂/sol-gel clusters were formed on surfaces through one deposition and thick sol-gel films were observed after further deposition. Electrochemical properties and electrochemiluminescence (ECL) behaviors of Ru(bpy)₃Cl₂/sol-gel films could be easily adjusted by deposition numbers and time. At last, the Ru(bpy)₃Cl₂/sol-gel film modified electrode was used for solid-state ECL detection of tripropylamine. The linear range was from 5.8 × 10⁻⁸ to 2.4 × 10⁻⁴ M with the detection limit of 5 nM, which was three orders of magnitude lower than that from pure Nafion-modified electrodes. The ECL sensor also exhibited high stability, and still remained 92% response after being stored in air for 35 days. This method for immobilization of Ru(bpy)₃Cl₂ is simple, convenient and low-cost relative to others, so it shows promising applications in solid-state ECL detection.     

Silver(I) ions-enhanced electrochemiluminescence of tris(2,2-bipyridyl)ruthenium(II)

In this paper, we demonstrate an electrochemiluminescence (ECL) enhancement of tris(2,2-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) by the addition of silver(I) ions. The maximum enhancement factor of about 5 was obtained on a glassy carbon electrode in the absence of co-reactant. The enhancement of ECL intensity was possibly attributed to the unique catalytic activity of Ag⁺ for reactions between Ru(bpy)₃³⁺ with OH. The higher enhancement was observed in phosphate buffer solutions compared with that from borate buffer solutions. This resulted from the fact that formation of nanoparticles with large surface area in the phosphate buffer solution exhibited high catalytic activity. The amount of Ag⁺, solution pH and working electrode materials played important roles for the ECL enhancement. We also studied the effects of Ag⁺ on Ru(bpy)₃²⁺/tripropylamine and Ru(bpy)₃²⁺/C₂O₄²⁻ ECL systems.