Novel tris(2,2'-bipyridine)ruthenium(II) cathodic electrochemiluminescence in aqueous solution at a glassy carbon electrode

A novel approach of generating cathodic electrochemiluminescence of Ru(bpy)3(2+) at -0.4 V triggered by reactive oxygen species is reported for detecting alkylamines and some organic acids.     

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.     

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.     

Aryl-diamide bridged binuclear ruthenium (II) tris(bipyridine) complexes: Synthesis, photophysical, electrochemical and electrochemiluminescence properties

Several new symmetrical aromatic hydrocarbon bridged bipyridine ligands and their binuclear Ru (II) complexes have been designed, synthesized and characterized on the basis of ¹H NMR, MS and HRMS. Their absorption and emission properties, electrochemical behaviors and electrochemical luminescence were investigated. All ruthenium complexes show characteristic MLCT absorption and similar redox potential. Among the three complexes reported, 4c has the best electrochemical luminescence property.     

Nitrate enhanced electrochemiluminescence determination of tris(2,3-dibromopropyl) isocyanurate with a gold nanoparticles-modified gold electrode

Tris(2,3-dibromopropyl) isocyanurate (TBC) is a heterocyclic hexabrominated flame retardant, which cannot be degraded even over a long time and may be a potential environmental pollutant. In this paper, TBC is for the first time as far as we know determined by silver nitrate-enhanced electrochemiluminescence (ECL) using a gold nanoparticles (AuNPs)-modified gold electrode. In our experiments, TBC was found to have the characteristics of increasing the ECL intensity of Ru(bpy)(3)(2+), and the ECL signal was proportional to the concentration of TBC. Based on this, we have successfully developed a novel, fast and sensitive method for the analysis of TBC. The main influencing factors including the volume ratio of acetonitrile and water, and the concentration of Ru(bpy)(3)(2+) were investigated in detail. Compared with using a bare gold electrode in MeCN without AgNO(3), the limit of detection is remarkably lowered by 20 times and the linear range is expanded by 5 times by using the AuNPs-modified gold electrode and AgNO(3). Under the optimal conditions, a limit of detection of 5.0 × 10(-8) M (S/N = 3) is achieved with a linear range of 1.0 × 10(-7) to 5.0 × 10(-5) M. The mechanism of the ECL enhancement of the system is also investigated.     

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.     

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.     

Efficiency of polymer sensitizer in photosensitized reaction of tris(bipyridine)ruthenium(II) complex-containing polymer

Photochemical properties of Ru(bpy)₂(poly-4-methyl-4′-vinyl-2,2′-bipyridine)Cl₂ ( 2 ) were studied and compared with that of Ru(bpy)₃Cl₂. Continuous irradiation of a solution, which contains polymer 2 as a photosensitizer, methylviologen (MV²⁺) or 4,4′-bipyridinium-1,1′-bis(trimethylenesulfonate) (SPV) as an electron acceptor and triethanolamine (TEOA) as a sacrificial donor, resulted in the formation of viologen radical ion (MV⁺ or SPV^?). The rate of formation of MV⁺ or SPV^? for the polymer 2 system was smaller than that for the Ru(bpy)₃ Cl₂ systems. The reason for this fact was kinetically analyzed by quenching experiments of excited Ru(II) complexes by MV²⁺ or SPV, the photosensitized reactions of the TEOA–Ru(II) complex–MV²⁺ or -SPV systems, and the dye laser photolysis of the Ru(II) complex–MV²⁺ or -SPV systems.     

A novel tris(2,2′-bipyridine)ruthenium(II)/tripropylamine cathodic electrochemiluminescence in acetonitrile for the indirect determination of hydrogen peroxide

A novel tris(2,2′-bipyridine)ruthenium(II) (Ru(bpy)₃²⁺) cathodic electrochemiluminescence (ECL) was generated at −0.78 V at the Pt electrode in acetonitrile (ACN), which suggested that the cathodic ECL differed from conventional cathodic ECL. It was found that tripropylamine (TPrA) could enhance this cathodic ECL and the linear range (log-log plot) was 0.2 μM-0.2 mM. In addition, hydrogen peroxide (H₂O₂) could inhibit the cathodic ECL and was indirectly detected with the linear range of 27-540 μM. The RSD (n = 12) of the ECL intensity in the presence of 135 μM H₂O₂ was 0.87%. This method was also demonstrated for the fast determination of H₂O₂ in disinfectant sample and satisfactory results were obtained.     

Cantilever tip near-field surface-enhanced Raman imaging of tris(bipyridine)ruthenium(II) on silver nanoparticles-coated substrates

The near-field surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence (SEF) images of tris(bipyridine)ruthenium(II) adsorbed on a silver nanoparticles-coated substrate were obtained with a scanning near-field optical microscope (SNOM, or near-field scanning optical microscopy, NSOM) using a cantilever tip. In comparison with the most widely used fiber tip for SNOM, the cantilever tip has higher optical throughput and better thermal stability, making it more suitable for detecting the extremely low Raman signal in the near-field spectroscopic investigations. Our preliminary results show that the near-field SERS with the higher spatial resolution can provide richer fingerprint information than the far-field SERS. A comparison of the two types of images shows that there are more SERS than SEF hot spots, and the two types of hot spots do not overlap. More surprisingly, the near-field SERS spectra differ from the far-field SERS spectra obtained on the same sample in the band frequency and relative intensities of some major Raman bands, and some IR-active bands were observed with the near-field mode. These results are explained mainly by the electric field gradient effect and heterogeneous polarization character that operate only in the near-field SERS.     

Vitamin C derivatives as new coreactants for tris(2,2'-bipyridine)ruthenium(II) electrochemiluminescence

Vitamin C derivatives (VCDs) have been widely used as the alternative and stable sources of vitamin C, and accordingly exhibit many new applications, such as anti-tumor and central nervous system drug delivery. In this study, their Ru(bpy)₃²⁺ electrochemiluminescence (ECL) properties have been investigated for the first time using well-known ascorbyl phosphate and ascorbyl palmitate as representative VCDs. Ascorbyl phosphate and ascorbyl palmitate are VCDs with different substituted positions. Both of them increase Ru(bpy)₃²⁺ ECL, indicating that other VCDs may also enhance Ru(bpy)₃²⁺ ECL signal. The calibration plot for ascorbyl phosphate is linear from 3 × 10⁻⁶ to 1.0 × 10⁻³ M with a detection limit of 1.4 × 10⁻⁶ M at a signal-to-noise ratio of 3. The relative standard deviation is 3.6% for six replicate measurements of 0.01 mM ascorbyl 2-phosphate solution. The proposed method is about one order of magnitude more sensitive than electrochemical and UV–vis methods for the determination of ascorbyl phosphate, and is used successfully for the determination of ascorbyl phosphate in whitening and moisturising body wash.     

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%.     

Enhanced electrochemiluminescence sensor from tris(2,2'-bipyridyl)ruthenium(II) incorporated into MCM-41 and an ionic liquid-based carbon paste electrode

The electrochemiluminescence (ECL) of tris(2,2'-bipyridyl)ruthenium(II) [Ru(bpy)(3)(2+)] ion-exchanged in the sulfonic-functionalized MCM-41 silicas was developed with tripropylamine (TPrA) as a co-reactant in a carbon paste electrode (CPE) using a room temperature ionic liquid (IL) as a binder. The sulfonic-functionalized silicas MCM-41 were used for preparing an ECL sensor by the electrostatic interactions between Ru(bpy)(3)(2+) cations and sulfonic acid groups. We used the IL as a binder to construct the CPE (IL-CPE) to replace the traditional binder of the CPE (T-CPE)--silicone oil. The results indicated that the MCM-41-modified IL-CPE had more open structures to allow faster diffusion of Ru(bpy)(3)(2+) and that the ionic liquid also acted as a conducting bridge to connect TPrA with Ru(bpy)(3)(2+) sites immobilized in the electrode, resulting in a higher ECL intensity compared with the MCM-41-modified T-CPE. Herein, the detection limit for TPrA of the MCM-41-modified IL-CPE was 7.2 nM, which was two orders of magnitude lower than that observed at the T-CPE. When this new sensor was used in flow injection analysis (FIA), the MCM-41-modified IL-CPE ECL sensor also showed good reproducibility. Furthermore, the sensor could also be renewed easily by mechanical polishing whenever needed.     

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.     

Six-fold oxygen-coordinated triplet (S = 1) palladium(II) moieties templated by tris(bipyridine)ruthenium(II) ions

Tris(bipyridine)ruthenium(II) is used as a templating agent to insert palladium(II) into three-dimensional oxalate-based networks. The templated-assembly of [Ru(bpy)(3)][Pd(2)(ox)(3)] (Pd(2)) and [Ru(bpy)(3)][PdMn(ox)(3)] (PdMn) is described. The latter compound is structurally characterized by powder X-ray diffraction and X-ray absorption spectroscopy. These techniques reveal an unusual 6-fold oxygen environment around the Pd(II) atoms with two short (2.02 Angstrom) and four long (2.17 Angstrom) Pd-O distances. As stated by magnetometry, this environment is associated with a triplet ground state (S = 1) of the palladium(II) ion: when the temperature is decreased, the chiMT product shows a monotonous decrease from 5.54 cm(3) K mol(-1) at 300 K, a value which is slightly lower than the one expected for independent paramagnetic Pd(II) (S = 1, g = 2) and Mn(II) (S = 5/2, g = 2) ions. This thermal variation is due to antiferromagnetic exchange interactions between the two spin bearers. Nevertheless, no long-range magnetic order is detected down to 2 K. These results are confirmed by an analysis of the [MII(C(2)O(4))(3)](4-) (M = Ni, Pd, Pt) complex and of a [Pd(II){mu-(C(2)O(4))Mn(II)(OH(2))(4)}(3)](2+) tetranuclear model using density functional theory.     

A novel ruthenium(II) tris(bipyridine)-zinc porphyrin-rhenium carbonyl triad: synthesis and optical properties

A novel ruthenium(II) tris(bipyridine)-zinc porphyrin-rhenium carbonyl triads and its free base porphyrin derivative were synthesized and characterized by ¹H, ¹³C NMR, UV-vis, mass-spectrometry and elemental analysis. The redox potentials of the two compounds were measured and compared to their corresponding reference complexes. The fluorescence and transient absorption spectra of the two complexes revealed the features of two different pathways for possible photoinduced intramolecular electron transfer or energy transfer in the triads.     

Electrochemiluminescence from tris(2,2′-bipyridyl)ruthenium(II)-graphene-Nafion modified electrode

An electrochemiluminescence (ECL) sensor based on Ru(bpy)₃²⁺-graphene-Nafion composite film was developed. The graphene sheet was produced by chemical conversion of graphite, and was characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), and Raman spectroscopy. The introduction of conductive graphene into Nafion not only greatly facilitates the electron transfer of Ru(bpy)₃²⁺, but also dramatically improves the long-term stability of the sensor by inhibiting the migration of Ru(bpy)₃²⁺ into the electrochemically inactive hydrophobic region of Nafion. The ECL sensor gives a good linear range over 1 × 10⁻⁷ to 1 × 10⁻⁴ M with a detection limit of 50 nM towards the determination of tripropylamine (TPA), comparable to that obtained by Nafion-CNT. The ECL sensor keeps over 80% and 85% activity towards 0.1 mM TPA after being stored in air and in 0.1 M pH 7.5 phosphate buffer solution (PBS) for a month, respectively. The long-term stability of the modified electrode is better than electrodes modified with Nafion, Nafion-silica, Nafion-titania, or sol-gel films containing Ru(bpy)₃²⁺. Furthermore, the ECL sensor was successfully applied to the selective and sensitive determination of oxalate in urine samples.     

Detection of clindamycin by capillary electrophoresis with an end-column electrochemiluminescence of tris(2,2'-bypyridine)ruthenium(II)

Coupled capillary electrophoresis (CE) with end-column electrogenerated chemiluminescence (ECL) was adopted for the quantitative detection of clindamycin. Clindamycin enhanced ECL intensity of tris(2,2'-bypyridine)ruthenium(II) (Ru(bpy)(3)(2+)) as a coreactant. Under the optimized conditions, the ECL intensity was linear with the concentration of clindamycin over the range from 5.0 x 10(-7) to 1.0 x 10(-4)M with a detection limit of 1.4 x 10(-7)M. The proposed CE-ECL was successfully applied for the detection of clindamycin in pharmaceutical and clinic samples. The interaction of clindamycin with hemoglobin was also investigated. The binding constant of clindamycin with hemoglobin was estimated to be 3.6 x 10(3)M(-1).     

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.