Electrogenerated chemiluminescence from R(bpy)3(2+) ion-exchanged in carbon nanotube/perfluorosulfonated ionomer composite films

The electrochemistry and electrogenerated chemiluminescence (ECL) of ruthenium(II) tris(bipyridine) (Ru(bpy)(3)(2+)) ion-exchanged in carbon nanotube (CNT)/Nafion composite films were investigated with tripropylamine (TPA) as a coreactant at a glassy carbon (GC) electrode. The major goal of this work was to investigate and develop new materials and immobilization approaches for the fabrication of ECL-based sensors with improved sensitivity, reactivity, and long-term stability. Ru(bpy)(3)(2+) could be strongly incorporated into Nafion film, but the rate of charge transfer was relative slow and its stability was also problematic. The interfusion of CNT in Nafion resulted in a high peak current of Ru(bpy)(3)(2+) and high ECL intensity. The results indicated that the composite film had more open structures and a larger surface area allowing faster diffusion of Ru(bpy)(3)(2+) and that the CNT could adsorb Ru(bpy)(3)(2+) and also acted as conducting pathways to connect Ru(bpy)(3)(2+) sites to the electrode. In the present work, the sensitivity of the ECL system at the CNT/Nafion film-modified electrodes was more than 2 orders of magnitude higher than that observed at a silica/Nafion composite film-modified electrode and 3 orders of magnitude higher than that at pure Nafion films. The CNT/Nafion composite film-modified GC electrodes also exhibited long-term stability.     

Electrogenerated chemiluminescence of tris (2,2'-bipyridyl)ruthenium(II) ion-exchanged in nafion-silica composite films

The voltammetry and electrogenerated chemiluminescence (ECL) of tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)3 2+) ion-exchanged in Nafion and Nafion-silica composite materials have been investigated. The major goal of this work was to investigate and develop new materials and immobilization approaches for the fabrication of ECL-based sensors with improved reactivity and long-term stability. Nation-silica composite materials with varying contents of Nation (53-100 wt% relative to silica) were prepared via the two-step acid/base hydrolysis and condensation of tetramethoxysilane. The Nafion doped sols were spin cast on glassy carbon electrodes, dried, and then ion-exchanged with Ru(bpy)3 2+. The shapes of the cyclic voltammetric curves and the amount of Ru(bpy)3 2+ exchanged into the films strongly depends on the amount of Nafion incorporated into the hybrid sol. Nafion-silica films with a low content of Nafion ion-exchanged less Ru(bpy)3 2+ and exhibited tail-shaped voltammetry at 100 mV/s. The ECL of immobilized Ru(bpy)3 2+ in the presence of either tripropylamine or sodium oxalate in pH 5 acetate buffer was also strongly dependent on the amount of Nafion introduced into the composite with greater ECL observed for the Nafion-silica films relative to pure Nafion.     

Chemiluminescence detection using regenerable tris(2,2'-bipyridyl)ruthenium(II) immobilized in Nafion.

The development of a detection method based on the electrogenerated chemiluminescence of tris(2,2'-bipyridine)ruthenium(II), (Ru(bpy)3(2+], immobilized in a Nafion film coated on an electrode is discussed. Control of the electrode potential controls creation of the reactive reagent Ru(bpy)3(3+) which reacts with certain analytes to yield chemiluminescence emission of intensity proportional to the analyte concentration. The reaction results in Ru(bpy)3(3+) being converted to Ru(bpy)3(2+), which then is recycled to Ru(bpy)3(3+) again at the electrode. This sensor has been used in flow injection to determine oxalate, alkylamines, and NADH. Detection limits are 1 microM, 10 nM, and 1 microM, respectively, with working ranges extending over 4 decades in concentration. Sensitivity is constant over the wide pH range from 3 to 10. With oxalate, and to a small extent with amines, emission intensities increase with increasing ionic strength; this was shown to be a phenomenon related to the Nafion film and not to the chemiluminescence reaction. Emission intensities increase with temperature. The sensor remains stable for several days with suitable storage conditions. Significant amounts of Ru(bpy)3(3+) are shown to be capable of storage within the film.     

Unique electrochemiluminescence behavior of Ru(bpy)3 in a gold/Nafion/Ru(bpy)3 composite

The unique electrochemiluminescence (ECL) behavior of tris(bipyridine) ruthenium(II) (Ru(bpy)₃²⁺) immobilized in a gold/Nafion/Ru(bpy)₃²⁺ composite material was investigated. In this composite, the Ru(bpy)₃²⁺ ECL was found mainly occurred at 0-0.4 V during the cathodic scan process and the ECL peak was at about 0.1 V, which was quite different to the reported Ru(bpy)₃²⁺ ECL. Similar to the generally observed Ru(bpy)₃²⁺ ECL, the present ECL also could be enhanced by tri-n-propylamine (TPA). It is also unique that in the presence of TPA, another ECL peak at about 0.38 V occurred. These two ECL peak potentials all could be used as characteristic potential for the ECL determination of TPA.     

Electrogenerated chemiluminescence sensors using Ru(bpy)3(2+) doped in silica nanoparticles

A novel electrogenerated chemiluminescence (ECL) sensor based on Ru(bpy)3(2+)-doped silica (RuDS) nanoparticles conjugated with a biopolymer chitosan membrane was developed. These uniform RuDS nanoparticles (approximately 40 nm) were prepared by a water-in-oil microemulsion method and were characterized by electrochemical and transmission electron microscopy technology. The Ru(bpy)3(2+)-doped interior maintained its high ECL efficiency, while the exterior nanosilica prevented the luminophor from leaching out into the aqueous solution due to the electrostatic interaction. This is the first attempt to branch out the application of RuDS nanoparticles into the field of ECL, and since a large amount of Ru(bpy)3(2+) was immobilized three-dimensionally on the electrode, the Ru(bpy)3(2+) ECL signal could be enhanced greatly, which finally resulted in the increased sensitivity. This sensor shows a detection limit of 2.8 nM for tripropylamine, which is 3 orders of magnitude lower than that observed at a Nafion-based ECL sensor. Furthermore, the present ECL sensor displays outstanding long-term stability.     

Fabrication of chemiluminescence sensor based on conducting polymer@SiO2/Nafion composite film

Tris(2,2'-bipyridyl)ruthenium (II) (Ru(bpy)2+) electrogerated chemiluminescence (ECL) sensor was fabricated by immobilization of Ru(bpy)2+ complex on conducting polymer@SiO2/Nafion composite film on surface of glassy carbon electrode. The conducting polymer@SiO2 nanocomposites were prepared by coating polyaniline (PANI), polypyrrole (PPy), and polythiophene (PTh) on the surface of the SiO2 sphere. The conducting polymer@SiO2 nanocomposite was characterized by scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and atomic force microscopy (AFM). The sensitivity and reproducibility of the prepared ECL sensor to tripropylamine (TPA) was evaluated. As a result, the PPy@SiO2 composite electrode exhibited high sensitivity and good reproducibility compared to that obtained with PANI@SiO2 and PTh@SiO2 composite electrodes because of the strong interaction between PPy@SiO2 and Ru(bpy)2+ complex.     

Nafion-tris(2-2'-bipyridyl)ruthenium(II) Ultrathin Langmuir-Schaefer films: redox catalysis and electrochemiluminescent properties

A simple procedure to incorporate tris(2-2'-bipyridyl)ruthenium(II), [Ru(bpy)3]2+, into Nafion Langmuir-Schaefer (LS) films is described. Nafion LS films (tens of nanometers thick) were formed on quartz glass and indium tin oxide (ITO) directly from Nafion-[Ru(bpy)3]2+ Langmuir films assembled at the water-air interface. This procedure allowed the direct incorporation of [Ru(bpy)3]2+ into Nafion films without the need for subsequent loading. UV-vis spectroscopy confirmed the successful incorporation of [Ru(bpy)3]2+ within the LS films and showed that the amount of [Ru(bpy)3]2+ immobilized in this way scaled with film thickness. Voltammetric studies on ITO-modified electrodes confirmed the successful incorporation of [Ru(bpy)3]2+ and demonstrated that [Ru(bpy)3]2+ was retained within the ultrathin films over a long time scale. These electrodes were tested for the electrocatalytic reduction of tripropylamine. Significant catalysis was observed due to the rapid turnover of [Ru(bpy)3]2+/3+ between the electrode surface and outer boundary of the film, as a direct consequence of the ultrathin film dimensions. Concomitant electrochemiluminescence (ECL) was demonstrated highlighting the potential of this material for sensing applications.     

Green electrochemiluminescence from ortho-metalated tris(2-phenylpyridine)iridium(III)

The electrochemiluminescence (ECL) of Ir(ppy)3 (ppy = 2-phenylpyridine) is reported in acetonitrile (CH3CN), mixed CH3CN/H20 (50:50 v/v), and aqueous (0.1 M KH2PO4) solutions with tri-n-propylamine as an oxidative-reductive coreactant. ECL efficiencies (phi(ecl), photons emitted per redox event) of 0.00092 in aqueous, 0.0044 in mixed, and 0.33 in CH3CN solutions for Ir(ppy)3 were obtained using Ru(bpy)3(2+) (bpy = 2,2'-bipyridine) as a relative standard (phi(ecl) = 1). Photoluminescence (PL) efficiencies of 0.039, 0.050, and 0.069 were obtained in aqueous, mixed, and acetonitrile solutions, respectively, compared to Ru(bpy)3(2+) (phi(em) = 0.042). The ECL spectra were identical to photoluminescence spectra (lambda(max) approximately equal to 517 nm), indicating formation of the same metal-to-ligand (MLCT) excited states in both ECL and PL. The ECL is linear over several orders of magnitude in mixed and acetonitrile solution with theoretical detection limits (blank plus three times the standard deviation of the noise) of 1.23 nM in CH3CN and 0.23 microM in CH3CN/ H20 (50:50 v/v).     

Electrochemiluminescence sensor based on partial sulfonation of polystyrene with carbon nanotubes

Herein, homogenously partial sulfonation of polystyrene (PSP) was performed. An effective electrochemiluminescence (ECL) sensor based on PSP with carbon nanotube (CNTs) composite film was developed. Cyclic voltammetry and electrochemical impendence spectroscopy were applied to characterize this composite film. The PSP was used as an immobilization matrix to entrap the ECL reagent Ru(bpy)3(2+) due to the electrostatic interactions between sulfonic acid groups and Ru(bpy)3(2+) cations. The introduction of CNTs into PSP acted not only as a conducting pathway to accelerate the electron transfer but also as a proper matrix to immobilize Ru(bpy)3(2+) on the electrode by hydrophobic interaction. Furthermore, the results indicated the ECL intensity produced at this composite film was over 3-fold compared with that of the pure PSP film due to the electrocatalytic activity of the CNTs. Such a sensor was verified by the sensitive determinations of 2-(dibutylamino)ethanol and tripropylamine.     

Electrochemiluminescence of ruthenium (II) tris(bipyridine) encapsulated in sol-gel glasses

The electrogenerated chemiluminescence (ECL) of Ru(bpy)3 2+ and tripropylamine, tributylamine, triethylamine, trimethylamine, or sodium oxalate encapsulated within sol-gel-derived silica monoliths have been investigated using an immobilized ultramicroelectrode assembly. The major purpose of this study was to investigate the role of the reductant on the magnitude and stability of the ECL in this solid host matrix. For gel-entrapped Ru(bpy)3 2-/tertiary amines, the shape and intensity of the ECL-potential curves were highly dependent on scan rate. At 10 mV/s, the ECL intensity was ca. 6-fold higher relative to that observed at 500 mV/s. When the ECL acquired at low scan rates was normalized by that obtained in solution under similar conditions, a value of 0.03-0.06 was obtained. In direct contrast, the ECL of the Ru(bpy)3 2+-oxalate system showed little dependence on scan rate, and the ECL was ca. 65-75% of that measured in solution. These differences can be attributed to differences in rotational and translational mobility between the reductants (amines vs oxalate) trapped in this porous solid host For both systems, the ECL was found to be stable upon continuous oxidation or upon drying the gels in a high-humidity environment for over 10 days.     

Electrochemiluminescent detection based on solid-phase extraction at tris(2,2'-bipyridyl)ruthenium(II)-modified ceramic carbon electrode

A sensitive electrochemiluminescent detection scheme by solid-phase extraction at Ru(bpy)3(2+)-modified ceramic carbon electrodes (CCEs) was developed. The as-prepared Ru(bpy)3(2+)-modified CCEs show much better long-term stability than other Nafion-based Ru(bpy)3(2+)-modified electrodes and enjoy the inherent advantages of CCEs. The log-log calibration plot for dioxopromethazine is linear from 1.0 x 10(-9) to 1.0 x 10(-4) mol L(-1) using the new detection scheme. The detection limit is 6.6 x 10(-10) mol L(-1) at a signal-to-noise ratio of 3. The new scheme improves the sensitivity by approximately 3 orders of magnitude, which is the most sensitive Ru(bpy)3(2+) ECL method. The scheme allows the detection of dioxopromethazine in a urine sample within 3 min. Since Ru(bpy)3(2+) ECL is a powerful technique for determination of numerous amine-containing substances, the new detection scheme holds great promise in measurement of free concentrations, investigation of protein-drug interactions and DNA-drug interactions, pharmaceutical analysis, and so on.     

The effects of nonionic surfactants on the tris(2,2'-bipyridyl)ruthenium(II)--tripropylamine electrochemiluminescence system

The electrochemistry and electrogenerated chemiluminescence (ECL) of Ru(bpy)3(2+) (bpy = 2,2'-bipyridyl) were studied in the presence of the nonionic surfactants Triton X-100, Thesit, and Nonidet P40. The anodic oxidation of Ru(bpy)3(2+) produces ECL in the presence of tri-n-propylamine in both aqueous and surfactant solutions. Increases in both ECL efficiency (> or =8-fold) and duration of the ECL signal were observed in surfactant media. A shift to lower energies of the Ru(bpy)3(2+) ECL emission by approximately 8 nm was also observed. The one-electron oxidation of Ru(bpy)3(2+) to Ru(bpy)3(3t) occurs at + 1.03 V vs Ag/AgCl in aqueous buffered (0.2 M potassium phosphate) solution as found by square wave voltammetry. This potential did not shift in surfactant systems, indicating that the redshifts in ECL emission are due to stabilization of ligand pi* orbitals in the metal-to-ligand charge-transfer excited state. These results are consistent with hydrophobic interactions between Ru(bpy)3(2+) and the nonionic surfactants.     

Surfactant chain length effects on the light emission of tris(2,2'-bipyridyl)ruthenium(II)/ tripropylamine electrogenerated chemiluminescence

The effects of nonionic surfactant chain length on the properties of tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)3(2+) where bpy = 2,2'-bipyridine) electrochemiluminescence (ECL) have been investigated. The electrochemistry, photophysics, and ECL of Ru(bpy)3(2+) in the presence of a series of nonionic surfactants are reported (Triton X-100, 114, 165, 405, 305, and 705-70). These surfactants differ in the number of poly(ethylene oxide) units incorporated into the surfactant molecule. The anodic oxidation of Ru(bpy)3(2+) produces ECL in the presence of tri-n-propylamine (TPrA) in aqueous surfactant solution. Increases in ECL efficiency (> or = 5-fold) and TPrA oxidation current (> or = 2-fold) have been observed in surfactant media. Slight decreases in ECL intensity are observed as the chain length of the nonionic surfactant increases. The data supports adsorption of surfactant on the electrode surface, thus facilitating TPrA and Ru(bpy)3(2+) oxidation and leading to higher ECL efficiencies.     

Determination of Dansyl Amino Acids and Oxalate by HPLC with Electrogenerated Chemiluminescence Detection Using Tris(2,2'-bipyridyl)ruthenium(II) in the Mobile Phase

A new electrogenerated chemiluminescence detection method is investigated for use in detection in reversed-phase and reversed-phase ion-pair HPLC with Ru(bpy)(3)(2+) in the mobile phase. In this method, different concentrations of Ru(bpy)(3)(2+) are dissolved in the mobile phase and the HPLC column flushed with the mobile phase for 1 h until the column is saturated with Ru(bpy)(3)(2+). The separated analytes along with Ru(bpy)(3)(2+) pass through an optical-electrochemical flow cell which has a dual platinum electrode held at a potential of 1250 mV vs a Ag/AgCl reference electrode. On the surface of the electrode, Ru(bpy)(3)(2+) is oxidized to Ru(bpy)(3)(3+) which reacts with the analytes to emit light. The retention times, retention orders, detection limits, and linearity in working curves are compared to those obtained with the conventional postcolumn Ru(bpy)(3)(2+) addition method. The retention times for dansyl amino acids with Ru(bpy)(3)(2+) in the mobile phase are longer than those obtained with the postcolumn addition approach. This may be caused by π-to-π interactions between the aromatic groups of the dansyl derivatives and the bipyridyl groups of Ru(bpy)(3)(2+) in the Ru(bpy)(3)(2+)-saturated reversed-phase column. Similarly, oxalate is separated from urine and blood plasma samples by reversed-phase ion-pair HPLC. Plasma samples are obtained using ultrafiltration to remove proteins from whole blood. Retention times for oxalate with the two detection techniques are identical, and detection limits for these techniques are compared.     

Miniaturized tris(2,2'-bipyridyl)ruthenium(II) electrochemiluminescence detection cell for capillary electrophoresis and flow injection analysis

The design and performance of a miniaturized chip-type tris(2,2'-bipyridyl)ruthenium(II) [Ru(bpy)3(2+)] electrochemiluminescence (ECL) detection cell suitable for both capillary electrophoresis (CE) and flow injection (FI) analysis are described. The cell was fabricated from two pieces of glass (20 x 15 x 1.7 mm), and the 0.5-mm-diameter platinum disk was used as working electrode held at +1.15 V (vs silver wire quasi-reference), the stainless steel guide tubing as counter electrode, and the silver wire as quasi-reference electrode. The performance traits of the cell in both CE and FI modes were evaluated using tripropylamine, proline, and oxalate and compared favorably to those reported for CE and FI detection cells. The advantages of versatility, sensitivity, and accuracy make the device attractive for the routine analysis of amine-containing species or oxalate by CE and FI with Ru(bpy)3(2+) ECL detection.     

A multichannel microfluidic sensor that detects anodic redox reactions indirectly using anodic electrogenerated chemiluminescence

Here, we describe a new approach for detecting redoxactive targets by electrochemical oxidation and reporting their presence by electrogenerated chemiluminescence (ECL) based on electrochemical oxidation of Ru(bpy)3(2+) (bpy = 2,2'-bipyridine) and tripropylamine (TPA). This new strategy, which complements our previous reports of using ECL to signal the presence of targets undergoing electrochemical reduction, takes advantage of many of the attractive attributes of microfluidic-based electrochemical cells. These attributes include close proximity of multiple flow channels and electrodes, ability to move reagents through channels under laminar flow conditions, and the capacity to precisely place device components relative to one another using photolithography. Specifically, the microfluidic electrochemical sensor described here consists of three channels. The analyte and ECL reporting cocktail flow through separate channels, but they share a common anode. The cathode resides in a channel containing a sacrificial reductant. In this configuration, the target analyte competes with Ru(bpy)3(2+) and TPA to provide electrons for the reductant. Accordingly, in this competitive assay approach, the presence of the analyte is signaled as a lowering of the ECL intensity. In this report, the device performance characteristics are reported, and the detection of both ferrocyanide and dopamine is demonstrated at micromolar concentrations.     

Electrochemiluminescence from Os(phen)2(dppene)2+ (phen = 1,10-phenanthroline and dppene = bis(diphenylphosphino)ethene)

The electrochemiluminescence (ECL) of Os(phen)2(dppene)2+ (phen = 1,10-phenanthroline and dppene = bis(diphenylphosphino)ethene) is reported in mixed CH3CN/H2O (50:50 v/v) and aqueous (0.1 M KH2PO4) solutions with tri-n-propylamine (TPrA) as an oxidative-reductive coreactant. ECL efficiencies (phi(ecl) = photons emitted/redox event) of 2.0 in aqueous, and 0.95 in mixed for Os(phen)2(dppene)2+ were obtained using Ru(bpy)3(2+) (bpy = 2,2'-bipyridine) as a relative standard (phi(ecl) = 1). Photoluminescence (PL) efficiencies of 0.094 and 0.053 were obtained in aqueous and mixed solutions, respectively, as compared to Ru(bpy)3(2+) (phi(em) = 0.042). The ECL spectra were identical to photoluminescence spectra (lambda(max) approximately 584 nm), indicating formation of the same metal-to-ligand (MLCT) excited states in both ECL and PL. The ECL is linear over several orders of magnitude in aqueous and mixed solution, with theoretical detection limits (blank plus three times the standard deviation of the noise) of 16.9 nM in H2O and 0.29 nM in CH3CN/H2O (50:50 v/v).     

Electrochemiluminescent detection of metal cations using a ruthenium(II) bipyridyl complex containing a crown ether moiety

The effects of metal ions on the electrochemiluminescence (ECL) properties of (bpy)2Ru(AZA-bpy) (bpy = 2,2'-bipyridine; AZA-bpy = 4-(N-aza-18-crown-6-methyl-2,2'-bipyridine) have been investigated. The electrochemistry, photophysics and ECL of Ru(bpy)3(2+) in the presence of Pb2+, Hg2+, Cu2+, and K+ are reported. The anodic oxidation of Ru(bpy)3(2+) produces ECL in the presence of tri-n-propylamine (TPrA) in 50:50 (v/v) CH3CN:H2O solution. Increases in ECL efficiency (photons generated per redox event) up to 20-fold that depend on both the concentration and nature of the metal ion have been observed, making this an interesting system for electrochemiluminescence metal ion sensing.     

Method for effective immobilization of Ru(bpy)(3)2+ on an electrode surface for solid-state electrochemiluminescene detection

A novel method for effective immobilization of Ru(bpy)3(2+) on an electrode surface is developed. The whole process involves two steps: the electrostatic interactions between citrate-capped gold nanoparticles (AuNPs) and Ru(bpy)3Cl2 in aqueous medium were used to fabricate Ru(bpy)(3)2+-AuNP aggregates (Ru-AuNPs) first, and then the Au-S interactions between as-formed Ru-AuNPs and sulfhydryl groups were used to effectively immobilize the Ru-AuNPs on a sulfhydryl-derivated indium tin oxide (ITO) electrode surface. As-prepared ITO electrode shows excellent stability, and the ECL active species Ru(bpy)3(2+) contained therein exhibit excellent ECL behaviors.     

Electrochemiluminescent metallopolymer coatings: combined light and current detection in flow injection analysis

The application of thin films of the metallopolymer [Ru(bpy)2PVP10]2+ for the electrochemiluminescent (ECL) detection of oxalate in a flow injection analysis system is reported, where bpy is 2,2'-bipyridyl and PVP is poly(4-vinylpyridine). Immobilization of the ECL reagent means that it can be regenerated in situ, eliminating the need to constantly deliver it to the reaction zone. Electrochemically generated Ru3+ reacts with the analyte to form the excited-state [Ru2+]*, which luminesces at 610 nm. The reaction is optimal at low pH, where the layer is swollen and homogeneous charge transport through the layer is more facile. Unlike traditional approaches, we simultaneously monitor both the amperometric and luminescent response of the modified electrode. The precision of both signals is similar at approximately 2% (n = 10). However, the ECL response has a larger dynamic range extending from the low-micromolar to high-millimolar range and a lower limit of detection, approximately 0.2 microM or 4 pmol of oxalate injected. The ECL approach displays excellent selectivity for oxalate over a wide range of potential interferences including oxygen, amines, iron sulfate, ammonium nitrate, urea, and glucose. Ascorbic acid represents the most significant ECL interference. However, the signal observed for a 1 mM solution of ascorbic acid is still only 2.6% of the response observed for the injection of a similar concentration of oxalate.