Mechanism study on inorganic oxidants induced inhibition of Ru(bpy)₃²+ electrochemiluminescence and its application for sensitive determination of some inorganic oxidants

Inhibited Ru(bpy)₃²⁺ electrochemiluminescence by inorganic oxidants is investigated. Results showed that a number of inorganic oxidants can quench the ECL of Ru(bpy)₃²⁺/tri-n-propylamine (TPrA) system, and the logarithm of the decrease in ECL intensity (ΔI) was proportional to the logarithm of analyte concentrations. Based on which, a sensitive approach for detection of these inorganic oxidants was established, e.g. the log-log plots of ΔI versus the concentration of MnO₄⁻, Cr₂O₇²⁻ and Fe(CN)₆³⁻ are linear in the range of 1 × 10⁻⁷ to 3 × 10⁻⁴ M for MnO₄⁻ and Cr₂O₇²⁻, and 1 × 10⁻⁷ to 1 × 10⁻⁴ M for Fe(CN)₆³⁻, with the limit of detection (LOD) of 8.0 × 10⁻⁸ M, 2 × 10⁻⁸ M, and 1 × 10⁻⁸ M, respectively. A series of experiments such as a comparison of the inhibitory effect of different compounds on Ru(bpy)₃²⁺/TPrA ECL, ECL emission spectra, UV-Vis absorption spectra etc. were investigated in order to discover how these inorganic analytes quench the ECL of Ru(bpy)₃²⁺/TPrA system. A mechanism based on consumption of TPrA intermediate (TPrA^·) by inorganic oxidants was proposed.     

3D nanostructured Ni(OH)2 microspheres as an efficient immobilization matrix of Ru(bpy)3 for high-performance electrochemiluminescence sensor

The electrochemistry and electrochemiluminescence (ECL) of novel three-dimensional nanostructured Ru(bpy)₃²⁺/Ni(OH)₂ microspheres were investigated for the first time. The negatively charged porous Ni(OH)₂ microspheres composed of Ni(OH)₂ nanowires were specifically designed to interact with Ru(bpy)₃²⁺. The large surface area and porous structure of Ni(OH)₂ microspheres enhance loading of Ru(bpy)₃²⁺ and mass transport of the model analyte, tripropylamine (TPA). Excellent ECL performance of the presented sensor was achieved including good stability and wide linear range from 7.7 × 10⁻¹⁰ to 3.8 × 10⁻³ M with the detection limit of 2.6 × 10⁻¹⁰ M to TPA.     

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.     

Electrogenerated chemiluminescence biosensor based on Ru(bpy)3(2+) and dehydrogenase immobilized in sol-gel/chitosan/poly(sodium 4-styrene sulfonate) composite material

A new electrogenerated chemiluminescence biosensor was fabricated by immobilizing ECL reagent Ru(bpy)₃²⁺ and alcohol dehydrogenase in sol-gel/chitosan/poly(sodium 4-styrene sulfonate) (PSS) organically modified composite material. The component PSS was used to immobilize ECL reagent Ru(bpy)₃²⁺ by ion-exchange, while the addition of chitosan was to prevent the cracking of conventional sol-gel-derived glasses and provide biocompatible microenvironment for alcohol dehydrogenase. Such biosensor combined enzymatic selectivity with the sensitivity of ECL detection for quantification of enzyme substrate and it was much simpler than previous double-layer design. The detection limit was 9.3 × 10⁻⁶ M for alcohol (S/N = 3) with a linear range from 2.79 × 10⁻⁵ to 5.78 × 10⁻² M. With ECL detection, the biosensor exhibited wide linear range, high sensitivity and good stability.     

Tris(2,2′-bipyridyl)ruthenium(II) electrogenerated chemiluminescence sensor based on carbon nantube dispersed in sol-gel-derived titania-Nafion composite films

A highly sensitive and stable tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) electrogenerated chemiluminescence (ECL) sensor was developed based on carbon nanotube (CNT) dispersed in mesoporous composite films of sol-gel titania and perfluorosulfonated ionomer (Nafion). Single-wall (SWCNT) and multi-wall carbon nanotubes (MWCNT) can be easily dispersed in the titania-Nafion composite solution. The hydrophobic CNT in the titania-Nafion composite films coated on a glassy carbon electrode certainly increased the amount of Ru(bpy)₃²⁺ immobilized in the ECL sensor by adsorption of Ru(bpy)₃²⁺ onto CNT surface, the electrocatalytic activity towards the oxidation of hydrophobic analytes, and the electronic conductivity of the composite films. Therefore, the present ECL sensor based on the CNT-titania-Nafion showed improved ECL sensitivity for tripropylamine (TPA) compared to the ECL sensors based on both titania-Nafion composite films without CNT and pure Nafion films. The present Ru(bpy)₃²⁺ ECL sensor based on the MWCNT-titania--Nafion composite gave a linear response (R² = 0.999) for TPA concentration from 50 nM to 1.0 mM with a remarkable detection limit (S/N = 3) of 10 nM while the ECL sensors based on titania-Nafion composite without MWCNT, pure Nafion films, and MWCNT-Nafion composite gave a detection limit of 0.1 μM, 1 μM, and 50 nM, respectively. The present ECL sensor showed outstanding long-term stability (no signal loss for 4 months).     

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.     

Determination of itopride hydrochloride by high-performance liquid chromatography with Ru(bpy)3 electrogenerated chemiluminescence detection

In this work, a stable electrogenerated chemiluminescence (ECL) detector was developed. The detector was prepared by packing cation-exchanged resin particles in a glass tube, followed by inserting Pt wires (working electrode) in this tube and sealing. The leakage of Ru(bpy)₃²⁺ can be compensated by adding a small amount of Ru(bpy)₃²⁺ into solution phase. Coupled with high-performance liquid chromatography separation, the detector has been used for determination of itopride hydrochloride in human serum. Under the optimal conditions, the ECL intensity has a linear relationship with the concentration of itopride hydrochloride in the range of 1.0 × 10⁻⁸ g mL⁻¹ to 1.0 × 10⁻⁶ g mL⁻¹ and the detection limit was 3 × 10⁻⁹ g mL⁻¹ (S/N = 3). The as-prepared ECL detector displayed good sensitivity and stability.     

Electrochemiluminescence immunosensor for ultrasensitive detection of biomarker using Ru(bpy)3-encapsulated silica nanosphere labels

Here, we describe a new approach for electrochemiluminescence (ECL) assay with Ru(bpy)₃²⁺-encapsulated silica nanoparticle (SiO₂@Ru) as labels. A water-in-oil (W/O) microemulsion method was employed for one-pot synthesis of SiO₂@Ru nanoparticles. The as-synthesized SiO₂@Ru nanoparticles have a narrow size distribution, which allows reproducible loading of Ru(bpy)₃²⁺ inside the silica shell and of α-fetoprotein antibody (anti-AFP), a model antibody, on the silica surface with glutaraldehyde as linkage. The silica shell effectively prevents leakage of Ru(bpy)₃²⁺ into the aqueous solution due to strong electrostatic interaction between the positively charged Ru(bpy)₃²⁺ and the negatively charged surface of silica. The porous structure of silica shell allowed the ion to move easily through the pore to exchange energy/electrons with the entrapped Ru(bpy)₃²⁺. The as-synthesized SiO₂@Ru can be used as a label for ultrasensitive detection of biomarkers through a sandwiched immunoassay process. The calibration range of AFP concentration was 0.05-30 ng mL⁻¹ with linear relation from 0.05 to 20 ng mL⁻¹ and a detection limit of 0.035 ng mL⁻¹ at 3σ. The resulting immunosensors possess high sensitivity and good analytical performance.     

Solid-state electrochemiluminescence sensor through the electrodeposition of Ru(bpy)3/AuNPs/chitosan composite film onto electrode

Tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) has been successfully immobilized onto electrode through the electrodeposition of Ru(bpy)₃²⁺/AuNPs/chitosan composite film. In the experiments, chitosan solution was first mixed with Au nanoparticles (AuNPs) and Ru(bpy)₃²⁺. Then, during chronopotentiometry experiments in this mixed solution, a porous 3D network structured film containing Ru(bpy)₃²⁺, AuNPs and chitosan has been electrodeposited onto cathode due to the deposition of chitosan when pH value is over its pK_a (6.3). The applied current density is crucial to the film thickness and the amount of the entrapped Ru(bpy)₃²⁺. Additionally, these doping Ru(bpy)₃²⁺ in the composite film maintained their intrinsic electrochemical and electrochemiluminescence activities. Consequently, this Ru(bpy)₃²⁺/AuNPs/chitosan modified electrode has been used in ECL to detect tripropylamine, and the detection limit was 5 × 10⁻¹⁰ M.     

Solid-state electrochemiluminescence sensor based on the Nafion/poly(sodium 4-styrene sulfonate) composite film

An effective electrochemiluminescence (ECL) sensor based on Nafion/poly(sodium 4-styrene sulfonate) (PSS) composite film-modified ITO electrode was developed. The Nafion/PSS/Ru composite film was characterized by atomic force microscopy, UV-vis absorbance spectroscopy and electrochemical experiments. The Nafion/PSS composite film could effectively immobilize tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) via ion-exchange and electrostatic interaction. The ECL behavior of Ru(bpy)₃²⁺ immobilized in Nafion/PSS composite film was investigated using tripropylamine (TPA) as an analyte. The detection limit (S/N = 3) for TPA at the Nafion/PSS/Ru composite-modified electrode was estimated to be 3.0 nM, which is 3 orders of magnitude lower than that obtained at the Nafion/Ru modified electrode. The Nafion/PSS/Ru composite film-modified indium tin oxide (ITO) electrode also exhibited good ECL stability. In addition, this kind of immobilization approach was simple, effective, and timesaving.     

Polyelectrolyte-based electrochemiluminescence enhancement for Ru(bpy)3 loaded by SiO2 nanoparticle carrier and its high sensitive immunoassay

In this paper the strong electrochemiluminescence (ECL) nanoparticles have been prepared based on the anionic polyelectrolyte sodium polyacrylate (PAA)-ECL enhancement for Ru(bpy)₃²⁺, which were loaded by the carrier of SiO₂ nanoparticle. There were two kinds of Ru(bpy)₃²⁺ for the as-prepared nanoparticles, the doped one and the exchanged one. The former was loaded inside the ECL nanoparticles by doping, in a form of ion-pair macromolecules PAA–Ru(bpy)₃²⁺. The corresponding ECL was enhanced about 2 times owing to the doping increase of Ru(bpy)₃²⁺. The latter was loaded on the PAA-doped Nafion membrane by ion exchange. The corresponding ECL was enhanced about 3 times owing to the ion-exchanging increase of Ru(bpy)₃²⁺. At the same time, ECL intensity of the doped-inside Ru(bpy)₃²⁺ was further enhanced 13 times because polyelectrolyte PAA in the doped membrane could obviously enhance electron transfer between the doped Ru(bpy)₃²⁺ and the working electrode. Furthermore, based on hydrophobic regions of the doped membrane antibody labeling could be easily realized by the as-prepared nanoparticles and then a high sensitive ECL immunoassay for HBsAg was developed. The linear range was between 1.0 and 100 pg mL⁻¹ (R² = 0.9912). The detection limit could be as low as 0.11 pg mL⁻¹ (signal-to-noise ratio = 3).     

Multi-walled carbon nanotubes and Ru(bpy)3/nano-Au nano-sphere as efficient matrixes for a novel solid-state electrochemiluminescence sensor

An effective method for immobilization of Ru(bpy)₃²⁺ on glassy carbon electrode surface (GCE) is developed for the preparation of a novel electrochemiluminescence sensor. First of all, the positively charged Ru(bpy)₃²⁺ is modified on the surface of negatively charged gold nanoparticles (nano-Au) via the electrostatic interactions to obtain the Ru(bpy)₃²⁺/nano-Au nano-sphere (abbreviate as Ru-AuNPs). Subsequently, the large amount of Ru-AuNPs are immobilized on the multi-wall carbon nanotubes (MWCNTs)-Nafion homogeneous composite coated GCE by dual interaction: firstly, the Nafion, a kind of typical cation-exchange membrane, can absorb the Ru-AuNPs as the enrichment of cation Ru(bpy)₃²⁺ on the Ru-AuNPs surface; secondly, the employment of carboxylic MWCNTs in the Nafion film can also chemosorb the Ru(bpy)₃²⁺ cation on the Ru-AuNPs surface to increase the carrier content. At the same time, the experiment confirms that the enhancement of the ECL intensity on the sensor is attributed to following reasons. One hand, the employment of MWCNTs in the Nafion film enlarged the electro-active surface areas to benefit the contact between the signal probe on the composite film and coreactant used as reinforcing agent. On the other hand, the nano-materials of MWCNTs and nano-Au also improve the conductivity of the assembled film to increase the quantity of excited state of Ru(bpy)₃²⁺ in the unit time under the electrochemical condition and finally cause better properties in luminescence. In the experiment, the influence of the coreactant tripropylamine (TPA) on proposed ECL sensor is investigated. The logarithm of ECL intensity is proportional to the logarithm of TPA concentration on the range of 4 × 10⁻¹⁰ M to 2.8 × 10⁻⁶ M and 2.8 × 10⁻⁶ M to 0.71 × 10⁻³ M. After optimizing these conditions, the ECL sensor with TPA as coreactant is employed to detect a kind of alkaloid medicine, Matrine, for evaluating the practical application in the medicine analysis. The present sensor with TPA as coreactant shows the good response to the medicine concentration of the Matrine from 2.0 × 10⁻⁶ M to 6.0 × 10⁻³ M, which is used to detect the Matrine concentration in the Matrine injection.     

Detection of thrombin using electrogenerated chemiluminescence based on Ru(bpy)3(2+)-doped silica nanoparticle aptasensor via target protein-induced strand displacement

A sensitive and selective aptasensor using tri(2,2′-bipyridyl)ruthenium(II)-doped silica nanoparticles (Ru(bpy)₃²⁺-doped SNPs) as DNA tags for detection of thrombin is developed based on the target protein-induced strand displacement of the DNA probe. For the proposed aptasensor, the aptamer was assembled on the surface of the Au electrode through Au-S binding. The hybridization event between the DNA probe labeled by the Ru(bpy)₃²⁺-doped SNPs and the aptamer was evaluated by electrogenerated chemiluminescence (ECL) measurements. Then, the DNA probe was displaced by thrombin and the binding event between the thrombin and the aptamer was monitored by ECL measurements again. The difference of ECL intensity (ΔI_ECL) of the two events could be used to quantify the thrombin. Other proteins, such as bovine serum albumin and bovine hemoglobin, had almost negligible ΔI_ECL. Under the optimal conditions, the ΔI_ECL was linearly related to the concentration of the thrombin in the range of 10 fM to 10 pM and the detection limit was down to 1.0 fM since SNPs containing a large number of Ru(bpy)₃²⁺ molecules were labeled on the DNA probe.     

Fabrication of a new electrochemiluminescent sensor for fentanyl citrate based on glassy carbon microspheres and ionic liquid composite paste electrode

Due to the high performance of glassy carbon in the aspects of mechanical strength, electrical conductivity and high corrosion resistance, etc., glassy carbon has been widely used in the electrochemistry. A new form of glassy carbon, glassy carbon microsphere, was utilized to couple with ionic liquid in preparing a new electrochemiluminescent platform for Ru(bpy)₃Cl₂. Room temperature ionic liquid has been proposed to be very interesting and efficient pasting binder to replace the non conductive organic binders for the fabrication of composite paste electrode. Attributed to the special characteristics of glassy carbon microspheres and room temperature ionic liquid [N-octylpyridium tetrafluoroborate (OPFP)], this new electrochemiluminescent sensor exhibited excellent electrochemiluminescent performance in Ru(bpy)₃²⁺ solution. We first found that fentanyl citrate could increase the ECL of Ru(bpy)₃²⁺, hence an ECL approach was developed for the determination of fentanyl citrate based on this glassy carbon microspheres based electrochemiluminescent platform with high sensitivity. Under the optimized conditions, the enhanced electrochemiluminescent intensity versus fentanyl citrate concentration was linear in the range of 1.0 × 10⁻⁸ to 1.0 × 10⁻⁴ mol L⁻¹ with a detection limit of 8.5 × 10⁻⁹ mol L⁻¹, and the relative standard deviation for 1.0 × 10⁻⁶ mol L⁻¹ fentanyl citrate was 1.90% (n = 10). This protocol has extended the application scopes of glassy carbon material and promoted the application of glassy carbon microspheres in electroanalysis.     

Sensitive determination of verticine and verticinone in Bulbus Fritillariae by ionic liquid assisted capillary electrophoresis-electrochemiluminescence system

CE/Ru(bpy)₃²⁺ electrochemiluminescence (ECL) system with the assistance of ionic liquids (ILs) was successfully established for sensitive determination of verticine and verticinone in Bulbus Fritillariae for the first time. Migration behavior of alkaloid largely relies on the hydrogen bonding interactions between alkyl imidazolium cations in ILs and the alkaloids. Running buffer containing 40 mmol/L 1-butyl-3-methylimidazolium tetrafluoroborate (BMImBF₄) IL-8 mmol/L phosphate resulted in significant changes in separation selectivity for alkaloids with similar structures. The highest sensitivity of the detection was obtained by maintaining the detection potential at 1.2 V. Under the optimized conditions, relative standard derivations of the ECL intensity and the migration time were 3.27 and 2.84% for verticine and 4.42 and 1.69% for verticinone, respectively. The standard curves were linear between 1 × 10⁻⁸ and 1 × 10⁻⁶ mol/L for verticine and between 5 × 10⁻⁸ and 1 × 10⁻⁶ mol/L for verticinone, respectively. Detection limits of 1.25 × 10⁻¹⁰ mol/L for verticine and 1 × 10⁻¹⁰ mol/L for verticinone were obtained (S/N = 3). Developed method was successfully applied to determine the amounts of alkaloids in Bulbus Fritillariae.     

Development of an ultrasensitive electrochemiluminescence inhibition method for the determination of tetracyclines

An electrochemiluminescence (ECL) inhibition method is developed for quantitative determination of four tetracyclines (TCs) in honey samples, including tetracycline (TC), oxytetracycline (OTC), chlortetracycline (CTC) and doxycycline (DC). It was found that the four TCs strongly inhibited the ECL signal of the Ru(bpy)₃²⁺/DBAE system. Based on the ECL signal changes, a simple and ultrasensitive detection method for TCs was thus established. The optimum experimental conditions including the scan mode and scan rate of the applied potential, the type of the buffer solution and its pH, and the concentration of Ru(bpy)₃²⁺ and DBAE for the ECL inhibition method, were investigated in detail. Under the optimized conditions, the quenched ECL intensity versus the logarithm of the concentration of TCs is in good linear relationship over a concentration range from 4.0 × 10⁻¹¹ to 4.0 × 10⁻⁹ g mL⁻¹. The detection limits were found to be 2.0 × 10⁻¹² g mL⁻¹. The results obtained by the proposed ECL system, in terms of sensitivity, were much better than those of previously reported methods. In addition, the method was applied successfully to determine the total residuals of the four TCs in honey samples. The relative standard deviations were found in a range of 4.9–14.3%, and the recoveries were obtained from 87.5% to 115.0%. A possible mechanism for the quenching effects of Ru(bpy)₃²⁺/DBAE system was also proposed.     

A novel solid-state electrochemiluminescence detector for capillary electrophoresis based on tris(2,2'-bipyridyl)ruthenium(II) immobilized in Nafion/PTC-NH2 composite film

A new electrochemiluminescence (ECL) detector for capillary electrophoresis (CE) based on tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) immobilized in Nafion/PTC-NH₂ (an ammonolysis product of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA)) composite film was presented for the first time. The Nafion/PTC-NH₂ composite film could effectively immobilize tris(2,2′-bipyridyl)ruthenium(II) via ion-exchange and electrostatic interaction. Cyclic voltammetric and ECL behavior of Nafion/PTC-NH₂/Ru composite film was investigated compared to Nafion/Ru composite. The Nafion/PTC-NH₂/Ru composite film exhibited good ECL stability and simple operability. Then the CE with solid-state ECL detector system was successfully used to detect sophora - a quinolizidine type - alkaloids as sophoridine (SR) and matrine (MT). The CE-ECL parameters that affected separation and detection were optimized. Under the optimized conditions, the linear range was from 2.5 × 10⁻⁸ to 2 × 10⁻⁶ mol/L for SR, 1.0 × 10⁻⁸ to 1.0 × 10⁻⁶ mol/L for MT. The detection limit (S/N = 3) was estimated to be 5 × 10⁻⁹ and 10⁻⁹ mol/L for SR and MT, respectively. It was shown that the CE coupling with solid-state ECL detector system exhibited satisfying sensitivity of analysis.     

Paper-based solid-state electrochemiluminescence sensor using poly(sodium 4-styrenesulfonate) functionalized graphene/nafion composite film

Herein, highly efficient solid-state ECL sensor was introduced for the first time onto the screen printed electrodes of the paper-based chips (PCs) based on the composite film of poly(sodium 4-styrenesulfonate) functionalized graphene (PSSG) and Nafion. Attributed to the cooperative characteristics of both PSS and graphene, PSSG ensured both effective Ru(bpy)₃²⁺ immobilization and fast electron transfer of Ru(bpy)₃²⁺ in the composite film. The ECL behaviors at the developed sensor were investigated using tripropylamine as a representative analyte and low detection limit (S N⁻¹ = 3) of 5.0 nM was obtained. It also exhibited more excellent reproducibility (relative standard deviations of 0.63% for continuous 45 cycles) and long-term stability (∼80% of its initial ECL intensity could be retained over 3 months). More importantly, assisted by the developed ECL sensor, discrimination of 1.0 nM single-nucleotide mismatch in human urine matrix could be realized on the PCs for the first attempt. Thus, the developed sensor was confirmed with the advantages of highly sensitivity, long-term stability, simplicity, low cost, disposability, high efficiency and potential applicability.     

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.     

The role of direct oxalate oxidation in electrogenerated chemiluminescence of poly(4-vinylpyridine)-bound Ru(bpy)2Cl/oxalate system on indium tin oxide electrodes

The electrochemical and electrogenerated chemiluminescence (ECL) properties of indium tin oxide (ITO) electrodes modified with poly(4-vinylpyridine) (PVP)-bound Ru(bpy)₂Cl⁺ (where bpy = 2,2′-bipyridine) have been studied. In a sodium oxalate solution, two irreversible oxidation waves as well as two ECL emission waves were observed during the potential scan in the range 0.4-1.4 V (versus Ag/AgCl/saturated KCl reference). The first ECL wave appeared at ca. 0.8 V, which was caused by the excited-state Ru^2+* generated through a bimolecular redox reaction between electrogenerated Ru³⁺ and the strong reducing agent, C⁻O₂. The latter was formed via a Ru³⁺-mediated oxidation of oxalate. Direct oxidation of oxalate was not involved in the first ECL process. The second ECL wave started at ca. 1.1 V, which was also from the excited-state Ru^2+* generated via the redox reaction between Ru³⁺ and C⁻O₂. However, both direct and Ru³⁺-mediated oxidation of oxalate contributed to the formation of C⁻O₂. The important role of the direct oxidation of oxalate in the ECL mechanism of PVP-bound Ru(bpy)₂Cl⁺/oxalate system was demonstrated. The relative contribution of direct oxidation of oxalate to the observed ECL depended upon the surface concentration of PVP-bound Ru²⁺, the concentration of oxalate and the electrode potential applied.