Electrogenerated chemiluminescence. 72. Determination of immobilized DNA and C-reactive protein on Au(111) electrodes using tris(2,2'-bipyridyl)ruthenium(II) labels

Electrochemiluminescence Amplification in Bead-Based Assays Induced by a Freely Diffusing Iridium(III) Complex

Heterogeneous electrochemiluminescence (ECL) assays employing tri-n-propylamine as a co-reactant and a tris(2,2'-bipyridine)ruthenium(II) ([Ru(bpy)₃]²⁺) derivative as an emissive label are integral to the majority of academic and commercial applications of ECL sensing. This model system is an active research area and constitutes the basis of successfully commercialized bead-based ECL immunoassays. Herein, we propose a novel approach to the enhancement of such conventional ECL assays via the incorporation of a second metal coordination complex, [Ir(sppy)₃]^3- (where sppy = 5'-sulfo-2-phenylpyridinato-C²,N), to the experimental system. By employing ECL microscopy, we are able to map the spatial distribution of ECL emission at the surface of the bead, from [Ru(bpy)₃]²⁺ labels, and solution-phase emission, from [Ir(sppy)₃]^3-. The developed [Ir(sppy)₃]^3--mediated enhancement approach elicited a significant improvement (70.9-fold at 0.9 V and 2.9-fold at 1.2 V vs Ag/AgCl) of the ECL signal from [Ru(bpy)₃]²⁺ labels immobilized on the surface of a polystyrene bead. This dramatic enhancement in ECL signal, particularly at low oxidation potentials, has important implications for the improvement of existing heterogeneous ECL assays and ECL-based microscopy, by amplifying the signal, opening new bioanalytical detection schemes, and reducing both electrode surface passivation and deleterious side reactions.

Carbon nanodot-based electrogenerated chemiluminescence biosensor for miRNA-21 detection

A simple carbon nanodot–based electrogenerated chemiluminescence biosensor is described for sensitive and selective detection of microRNA-21 (miRNA-21), a biomarker of several pathologies including cardiovascular diseases (CVDs). The photoluminescent carbon nanodots (CNDs) were obtained using a new synthesis method, simply by treating tiger nut milk in a microwave reactor. The synthesis is environmentally friendly, simple, and efficient. The optical properties and morphological characteristics of the CNDs were exhaustively investigated, confirming that they have oxygen and nitrogen functional groups on their surfaces and exhibit excitation-dependent fluorescence emission, as well as photostability. They act as co-reactant agents in the anodic electrochemiluminescence (ECL) of [Ru(bpy)₃]²⁺, producing different signals for the probe (single-stranded DNA) and the hybridized target (double-stranded DNA). These results paved the way for the development of a sensitive ECL biosensor for the detection of miRNA-21. This was developed by immobilization of a thiolated oligonucleotide, fully complementary to the miRNA-21 sequence, on the disposable gold electrode. The target miRNA-21 was hybridized with the probe on the electrode surface, and the hybridization was detected by the enhancement of the [Ru(bpy)₃]²⁺/DNA ECL signal using CNDs. The biosensor shows a linear response to miRNA-21 concentration up to 100.0 pM with a detection limit of 0.721 fM. The method does not require complex labeling steps, and has a rapid response. It was successfully used to detect miRNA-21 directly in serum samples from heart failure patients without previous RNA extraction neither amplification process.

DNA-Based Nanoswitches: Insights into Electrochemiluminescence Signal Enhancement

Electrochemiluminescence (ECL) is a powerful transduction technique that has rapidly gained importance as a powerful analytical technique. Since ECL is a surface-confined process, a comprehensive understanding of the generation of ECL signal at a nanometric distance from the electrode could lead to several highly promising applications. In this work, we explored the mechanism underlying ECL signal generation on the nanoscale using luminophore-reporter-modified DNA-based nanoswitches (i.e., molecular beacon) with different stem stabilities. ECL is generated according to the "oxidative-reduction" strategy using tri-n-propylamine (TPrA) as a coreactant and Ru(bpy)₃²⁺ as a luminophore. Our findings suggest that by tuning the stem stability of DNA nanoswitches we can activate different ECL mechanisms (direct and remote) and, under specific conditions, a "digital-like" association curve, i.e., with an extremely steep transition after the addition of increasing concentrations of DNA target, a large signal variation, and low preliminary analytical performance (LOD 22 nM for 1GC DNA-nanoswtich and 16 nM for 5GC DNA-nanoswitch). In particular, we were able to achieve higher signal gain (i.e., 10 times) with respect to the standard "signal-off" electrochemical readout. We demonstrated the copresence of two different ECL generation mechanisms on the nanoscale that open the way for the design of customized DNA devices for highly efficient dual-signal-output ratiometric-like ECL systems.

A Comparison of Commercially Available Screen-Printed Electrodes for Electrogenerated Chemiluminescence Applications

We examined a series of commercially available screen-printed electrodes (SPEs) for their suitability for electrochemical and electrogenerated chemiluminescence (ECL) detection systems. Using cyclic voltammetry with both a homogeneous solution-based and a heterogeneous bead-based ECL assay format, the most intense ECL signals were observed from unmodified carbon-based SPEs. Three commercially available varieties were tested, with Zensor outperforming DropSens and Kanichi in terms of sensitivity. The incorporation of nanomaterials in the electrode did not significantly enhance the ECL intensity under the conditions used in this evaluation (such as gold nanoparticles 19%, carbon nanotubes 45%, carbon nanofibers 21%, graphene 48%, and ordered mesoporous carbon 21% compared to the ECL intensity of unmodified Zensor carbon electrode). Platinum and gold SPEs exhibited poor relative ECL intensities (16% and 10%) when compared to carbonaceous materials, due to their high rates of surface oxide formation and inefficient oxidation of tri-n-propylamine (TPrA). However, the ECL signal at platinum electrodes can be increased ∼3-fold with the addition of a surfactant, which enhanced TPrA oxidation due to increasing the hydrophobicity of the electrode surface. Our results also demonstrate that each SPE should only be used once, as we observed a significant change in ECL intensity over repeated CV scans and SPEs cannot be mechanically polished to refresh the electrode surface.

A novel label-free solid-state electrochemiluminescence sensor based on the resonance energy transfer from Ru(bpy)32+ to GO for DNA hybridization detection

Based on electrochemiluminescence resonance energy transfer (ERET) from Ru(bpy)₃²⁺ to graphene oxide (GO), a novel label-free solid-state ECL sensor for sensitive detection of DNA was proposed. First, Ru(bpy)₃²⁺/AuNPs was successfully prepared by using a simple and green method and characterized by transmission electron microscopy (TEM), Energy Dispersive X-ray (EDX), and UV-vis spectroscopy. Then, the Ru(bpy)₃²⁺/AuNPs colloid was assembled on the gold electrode surface for solid-state ECL film which also later could be used to immobilize thiol-derivatized, single-stranded DNA (HS-ssDNA) via Au-S interactions. The stepwise modification procedure was characterized by cyclic voltammetry(CV), electrochemical impedance spectroscopy (EIS), probe approach curves (PAC) and ECL, respectively. The resulting modified electrode was tested as ECL biosensor for DNA detection. Upon addition of GO, the strong noncovalent interaction between HS-ssDNA and GO led to ECL quenching because of ERET. When in the presence of target ssDNA (t-ssDNA), the distance between the HS-ssDNA and GO increased, which significantly hindered the ERET and, thus, resulted in the restoration of ECL. The ECL intensity of the biosensor increased linearly with t-ssDNA concentration in the range of 50-1000pM, and the detection limit is 20pM. To the best of our knowledge, this is the first application of solid-state ERET from Ru(bpy)₃²⁺ to GO and opens new opportunities for sensitive detection of biorecognition events.

Spatially resolved electrochemiluminescence through a chemical lens

Electrochemiluminescence (ECL) microscopy is an emerging technique with a wide range of imaging applications and unique properties in terms of high spatial resolution, surface confinement and favourable signal-to-noise ratio. Despite its successful analytical applications, tuning the depth of field (i.e., thickness of the ECL-emitting layer) is a crucial issue. Indeed, the control of the thickness of this ECL region, which can be considered as an "evanescent" reaction layer, limits the development of cell microscopy as well as bioassays. Here we report an original strategy based on chemical lens effects to tune the ECL-emitting layer in the model [Ru(bpy)3]2+/tri-n-propylamine (TPrA) system. It consists of microbeads decorated with [Ru(bpy)3]2+ labels, classically used in bioassays, and TPrA as the sacrificial coreactant. In particular we exploit the buffer capacity of the solution to modify the rate of the reactions involved in the ECL generation. For the first time, a precise control of the ECL light distribution is demonstrated by mapping the luminescence reactivity at the level of single micrometric bead. The resulting ECL image is the luminescent signature of the concentration profiles of diffusing TPrA radicals, which define the ECL layer. Therefore, our findings provide insights into the ECL mechanism and open new avenues for ECL microscopy and bioassays. Indeed, the reported approach based on a chemical lens controls the spatial extension of the "evanescent" ECL-emitting layer and is conceptually similar to evanescent wave microscopy. Thus, it should allow the exploration and imaging of different heights in substrates or in cells.

Biosensors for detecting viral and bacterial infections using host biomarkers: a review

A schematic diagram showing multiple modes of biosensing platforms for the diagnosis of bacterial or viral infections.

Electrogenerated chemiluminescence aptasensor for lysozyme based on copolymer nanospheres encapsulated black phosphorus quantum dots

Black phosphorus quantum dots (BPQDs) can react with Ru(bpy)₃²⁺ to generate strong anodic electrogenerated chemiluminescence (ECL). However, the instability and the lack of functional groups on BPQDs limit its further application in the fabrication of ECL biosensor. In the present work, uniform BPQDs-styrene-acrylamide (St-AAm) nanospheres (BSAN) are synthesized by encapsulating BPQDs into St-AAm copolymer nanospheres. Sufficient amount of BPQDs can be embedded into nanospheres, and react with Ru(bpy)₃²⁺ to generate strong anodic ECL which is comparable to that of pure BPQDs. Amino group of polymer endows BPQDs the ability to connect with DNA, and can be used to fabricate ECL aptasensor for the sensitive detection of lysozyme. The proposed aptasensor shows high sensitivity, good selectivity and stability for the detection of lysozyme in the range of 0.1-100 pg mL^-1 with a detection limit of 0.029 pg mL^-1 (3σ). The proposed method reveals the promising ECL sensing application of BP nanomaterials in the detection of various proteins.

A Novel Gold Nanoprobe for a Simple Electrochemiluminescence Determination of a Prostate-specific Antigen Based on a Peptide Cleavage Reaction

A novel gold nanoprobe for a sensitive and simple determination of a prostate-specific antigen (PSA) was designed on the basis of homogeneous detection and a peptide cleavage reaction. The gold nanoprobe (AuNPs-peptide-Ru1) consisted of a specific peptide tagged with a ruthenium(II) complex (Ru1) and gold nanoparticles (AuNPs) conjugated with the peptide via the strong Au-S bond between the AuNPs surface and the thiol group of the peptide. The electrochemiluminescence (ECL) enzymatic-cleavage-reaction-based bioanalytic system based on homogeneous detection has overcome shortcomings from a complicated fabrication process of traditional electrodes. In the presence of the target PSA, it specifically cleaved the peptide of the AuNPs-peptide-Ru1, and the ECL signal substance (Ru1) part dissociated from AuNPs-peptide-Ru1. This resulted in an increase in the ECL intensity. The ECL biosensor could detect PSA concentrations in the range from 1.0 × 10^-12 to 1.0 × 10^-9 g/mL, the detection limit was 4.0 × 10^-13 g/mL. The assay with the advantages of a simple method for PSA was selective and fast. It is superior to the immunoassay, and is a promising strategy to develop biosensors based on enzymatic cleavage including electrochemistry and optics.

Enhancing Luminol Electrochemiluminescence by Combined Use of Cobalt-Based Metal Organic Frameworks and Silver Nanoparticles and Its Application in Ultrasensitive Detection of Cardiac Troponin I

Electrochemiluminescence (ECL) has emerged as one of the most important methods for in vitro diagnosis and detection, but it is still limited in sensitivity for ultrasensitive biodetections. Fast and ultrasensitive detection of biomolecules is critical, especially for the clinical detection of cardiac troponin I (cTnI) for cardiac infarction diagnosis. In this study, an effective tactic was developed to enhance ECL efficiency of the luminol system, by combined use of Co²⁺-based metal organic frameworks (MOF), zeolitic imidazolate frameworks (ZIF-67), and luminol-capped Ag nanoparticles (luminol-AgNPs). The integration leads to a pronounced ∼115-fold enhancement in luminol ECL. On the basis of this fascinating sensing platform, a robust label-free ECL immunosensor was constructed for ultrasensitive detection of cTnI, the main marker of myocardial infarction, with good stability and a detection limit as low as 0.58 fg mL^-1 (S/N = 3).

Recent advances in biosensors for diagnosis and detection of sepsis: A comprehensive review

Sepsis is one of the leading causes of mortality among critically ill patients globally. According to WHO report 2018, it is estimated to affect beyond 30 million people worldwide every year. It causes loss of human lives, which arise from infection and inflammation and long term stay in intensive care unit (ICU) in hospitals. Despite the availability of satisfactory prognostic markers contributing to the diagnosis of sepsis, millions of people die even after admission to the hospitals. Correct and early diagnosis of sepsis leads to rapid administration of appropriate antibiotics can thus potentially avert the attainment to critical stages of sepsis, thereby saving human lives. Conventional diagnostic practices are costly, time consuming and they lack adequate sensitivity and selectivity, provoking an urgent need for developing alternate sepsis diagnosis systems. Nevertheless, biosensors have the much-treasured scope for reasonable sepsis diagnosis. Advancement in nano-biotechnology has provided new paradigm for biosensor platforms with upgraded features. Here, we provide an overview of the recent advances in biosensors with a brief introduction to sepsis, followed by the conventional methods of diagnosis and bio-sensing. To conclude, a proactive role and an outlook on technologically advanced biosensor platforms are discoursed with possible biomedical applications.

Electrogenerated chemiluminescence of Ru(bpy)32+at a black phosphorus quantum dot modified electrode and its sensing application

Strong anodic electrogenerated chemiluminescence (ECL) of Ru(bpy)₃²⁺can be obtained under neutral conditions at a black phosphorus quantum dot (BPQD) modified electrode due to the catalytic effect of BPQDs. Dopamine exhibits an apparent inhibiting effect on the ECL signal, and as a result, can be sensitively detected.

Immobilised Electrocatalysts: Nafion Particles Doped with Ruthenium(II) Tris(2,2'-bipyridyl)

Nafion particles doped with ruthenium(II) tris(2,2'-bipyridyl) are synthesized by using a re-precipitation method. Characterization including SEM sizing and quantification of Ru(bpy)₃²⁺ in the Nafion particles using UV/Vis spectroscopy was conducted. The synthesized Ru-Nafion particles were investigated electrochemically at both ensemble and single particle levels. Voltammetry of the drop-cast Ru-Nafion particles evidences the successful incorporation of Ru(bpy)₃²⁺ into the Nafion particle but only a small fraction of the incorporated Ru(bpy)₃²⁺ was detected due at least in part to the formation of the likely agglomerated and irregular "mat" associated with the dropcast technique. In contrast, nano-impact experiments provided a quantitative determination of the amount of Ru(bpy)₃²⁺ in single Ru-Nafion particles. Finally, oxidation of solution-phase oxalate mediated by Ru(bpy)₃²⁺ within individual Nafion particles was observed, showing the electrocatalytic properties of the Ru-Nafion particles.

Coated and uncoated cellophane as materials for microplates and open-channel microfluidics devices

This communication describes the use of uncoated cellophane (regenerated cellulose films) for the fabrication of microplates, and the use of coated cellophane for the fabrication of open-channel microfluidic devices. The microplates based on uncoated cellophane are particularly interesting for applications that require high transparency in the ultraviolet (UV) regime, and offer a low-cost alternative to expensive quartz-well plates. Uncoated cellophane is also resistant to damage by various solvents. The microfluidic devices, based on coated cellophane, can have features with dimensions as small as 500 μm, and complex, non-planar geometries. Electrodes can be printed on the surface of the coated cellophane, and embedded in microfluidic devices, to develop resistive heaters and electroanalytical devices for flow injection analysis, and continuous flow electrochemiluminescence (ECL) applications. These open-channel devices are appropriate for applications where optical transparency (especially in the visible regime), resistance to damage by water, biocompatibility and biodegradability are important. Cellophane microfluidic systems complement existing cellulose-based paper microfluidic systems, and provide an alternative to other materials used in microfluidics, such as synthetic polymers or glass. Cellulose films are plausible materials for uses in integrated microfluidic systems for diagnostics, analyses, cell-culture, and MEMS.

Electrogenerated chemiluminescence of the tris(2,2′-bipyridine)ruthenium(ii)/aliphatic amine system: a universal effect of perchlorate salts

Simply adding perchlorate salts leads to enhanced Ru(bpy)₃²⁺ECL emission of different pathways by 1.5–6.6 times with a variety of aliphatic amines as coreactants in a wide pH range from pH 5 to 12.

Anodic Electrogenerated Chemiluminescence of Ru(bpy)3(2+) with CdSe Quantum Dots as Coreactant and Its Application in Quantitative Detection of DNA

In the present paper, we report that CdSe quantum dots (QDs) can act as the coreactant of Ru(bpy)₃²⁺ electrogenerated chemiluminescence (ECL) in neutral condition. Strong anodic ECL signal was observed at ~1.10 V at CdSe QDs modified glassy carbon electrode (CdSe/GCE), which might be mainly attributed to the apparent electrocatalytic effect of QDs on the oxidation of Ru(bpy)₃²⁺. Ru(bpy)₃²⁺ can be intercalated into the loop of hairpin DNA through the electrostatic interaction to fabricate a probe. When the probe was bound to the CdSe QDs modified on the GCE, the intense ECL signal was obtained. The more Ru(bpy)₃²⁺ can be intercalated when DNA loop has larger diameter and the stronger ECL signal can be observed. The loop of hairpin DNA can be opened in the presence of target DNA to release the immobilized Ru(bpy)₃²⁺, which can result in the decrease of ECL signal. The decreased ECL signal varied linearly with the concentration of target DNA, which showed the ECL biosensor can be used in the sensitive detection of DNA. The proposed ECL biosensor showed an excellent performance with high specificity, wide linear range and low detection limit.

Self-enhanced electrogenerated chemiluminescence of ruthenium(ii) complexes conjugated with Schiff bases

Self-enhanced electrochemiluminescence based on ruthenium complexes conjugated with Schiff bases is studied and used for co-reactant free metal anion recognition.

Ruthenium polypyridine complexes combined with oligonucleotides for bioanalysis: a review

Ruthenium complexes are among the most interesting coordination complexes and they have attracted great attention over the past decades due to their appealing biological, catalytic, electronic and optical properties. Ruthenium complexes have found a unique niche in bioanalysis, as demonstrated by the substantial progress made in the field. In this review, the applications of ruthenium complexes coordinated with polypyridine ligands (and analogues) in bioanalysis are discussed. Three main detection methods based on electrochemistry, electrochemiluminescence, and photoluminscence are covered. The important targets, including DNA and other biologically important targets, are detected by specific biorecognition with the corresponding oligonucleotides as the biorecognition elements (i.e., DNA is probed by its complementary strand and other targets are detected by functional nucleic acids, respectively). Selected examples are provided and thoroughly discussed to highlight the substantial progress made so far. Finally, a brief summary with perspectives is included.

NIR electrochemiluminescence from Au25− nanoclusters facilitated by highly oxidizing and reducing co-reactant radicals

By means of spooling spectroscopy, we demonstrate our discovery on near-infrared electrochemiluminescence of Au₂₅⁻ nanoclusters at 950 and 900 nm, which can be attributed to the Au₂₅⁻*, Au₂₅⁰* and Au₂₅⁺* excited species being controllable chemically and electrochemically.

Current trends in the development of the electrochemiluminescent immunosensors

This review presents a general picture of the current trends and developments (2008-2013) related to electrochemiluminescence-based immunosensors. It briefly covers the milestones of qualitative changes in the field of electrochemiluminescent immunosensors; the peculiarities of the electrochemiluminescent immunoassay formats; the basic mechanisms of ECL detection, main features of early and ongoing approaches in electrochemiluminescent immunoassay commercial instruments, and the recent developments in fabrication of solid-state electrochemiluminescent immunosensors. Moreover, systematized data on biomarkers, immunoassay formats, and novel types of electrochemiluminescent label and immobilization support, such as semiconductor nanocrystals, porous noble metals, graphene, TiO2 nanotube arrays, metal-organic composites, multiwall carbon nanotubes, liposomes, photolummonescent carbone nanocrystals are presented as a table. Considerable efforts have also been devoted towards the following two key points: multiplexing analysis (multi-label, and the multianalyte strategies) and integration in microfluidic lab-on-paper devices with capabilities for point-to-care diagnostics. An immuno-like electrochemiluminescent sensor (based on synthetic receptors-molecularly imprinted polymers), as a new alternative to traditional electrochemiluminescent immunoassay is highlighted. Future perspectives and possible challenges in this rapidly developing area are also discussed.

A facile label-free electrochemiluminescence biosensor for target protein specific recognition based on the controlled-release delivery system

This paper described a novel label-free electrochemiluminescence assay for target protein based on a controlled delivery system. Iron oxide magnetic mesoporous silica nanocontainers were prepared by using a general procedure. The prepared magnetic mesoporous silica nanocontainers were applied to load the guest molecules [Ru(bpy)3](2+). Aptamers were used as gatekeepers on the pore outlets of the nanocontainers. In the presence of target proteins, the specific aptamer-protein interactions were employed as triggers for uncapping the pores and releasing the guest molecules from the nanocontainers. The amount of the guest molecule [Ru(bpy)3](2+) released from the magnetic mesoporous silica nanocontainers was monitored by the electrochemiluminescence assay. The results show that the releasing amount of [Ru(bpy)3](2+) is proportional to the thrombin concentration in the range of 0.6 pM-0.8 nM with a detection limit of 0.5 pM (S/N=3). The present work demonstrates that the fabricated nanocontainer using aptamer as the cap is a highly sensitive and selective key-in lock gating system for the label-free ECL biosensor.

Sensitive point-of-care monitoring of HIV related DNA sequences with a personal glucometer

The hybridizations between the HIV target DNA and the capture probes as well as the signal probes conjugated to the multi-invertase/nanoparticle composites lead to the conversion of sucrose to glucose, which is monitored by the personal glucometer and provides quantitative digital readings for point-of-care diagnosis of HIV DNA fragments.

Electrochemiluminescence biosensor based on conducting poly(5-formylindole) for sensitive detection of Ramos cells

A signal-on electrochemiluminescence (ECL) biosensor devoted to the detection of Ramos cells was fabricated based on a novel conducting polymer, poly(5-formylindole) (P5FIn), which was synthesized electrochemically by direct anodic oxidation of 5-formylindole (5FIn). This ECL platform was presented by covalently coupling the 18-mer amino-substituted oligonucleotide (ODN) probes with aldehyde groups that are strongly reactive toward a variety of nucleophiles on the surface of solid substrates. The specific identification and high-affinity between aptamers and target cells, gold nanoparticles (AuNPs) enhanced ECL nanoprobes, along with P5FIn induced ECL quenching contributed greatly to the sensitivity and selectivity. The ECL signals were logarithmically linear with the concentration of Ramos cells in a wide determination range from 500 to 1.0 × 10(5) cells mL(-1), and the corresponding detection limit was 300 cells mL(-1).

Synthesis, characterization and electrochemiluminescent properties of cyclometalated platinum(II) complexes with substituted 2-phenylpyridine ligands

Two neutral cyclometalated platinum(II) complexes, Pt(DPP)(acac) and Pt(BPP)(acac) (DPP = 2,4-diphenylpyridine, BPP = 2-(4-tert-butylphenyl)-4-phenylpyridine, acac = acetylacetone), have been synthesized and characterized by (1)H NMR spectroscopy, mass spectrometry, elemental analyses and by X-ray crystallography for Pt(DPP)(acac). Electrogenerated chemiluminescence (ECL) of the two complexes in the absence or presence of coreactant tri-n-propylamine (TPrA) in different solvents (CH(3)CN, CH(2)Cl(2), DMF, CH(3)CN/H(2)O (V, 50 : 50)) has been studied. The ECL spectra are identical to their own PL spectra, indicating that ECL processes lead to the same metal-to-ligand charge-transfer ((3)MLCT) excited state that is generated by light excitation. The ECL potentials of Pt(DPP)(acac) and Pt(BPP)(acac)/TPrA in CH(3)CN and CH(3)CN/H(2)O solution were at ~0.75 V vs. SCE, and significantly negatively shifted by about 0.6 V compared to that of the Ru(bpy)(3)(2+)/TPrA system. The ECL quantum efficiencies of the complexes are comparable to that of the Ru(bpy)(3)(2+)/TPrA system. The significant increase of the ECL signal in the coreactant system is due to the formation of the strongly reducing intermediate TPrA˙. It is noteworthy that the ECL efficiencies of the synthesized compounds are much higher than that of the tridentate polypyridyl ligands.