Emission of Tris(2,2‘-bipyridine)ruthenium(II) by Coreactant Electrogenerated Chemiluminescence: From O2-Insensitive to Highly O2-Sensitive

Etching of Ag nanoparticles triggered bidirectional regulation for electrochemiluminescence ratiometric immunoassay

A highly efficient ratiometric electrochemiluminescence (ECL) immunoassay was explored by bidirectionally regulating the ECL intensity of two luminophors. The immunoassay was conducted in a split-type mode consisting of an ECL detection procedure and a sandwich immunoreaction. The ECL detection was executed using a dual-disk glassy carbon electrode modified with two potential-resolved luminophors (g-C3N4-Ag and Ru-MOF-Ag nanocomposites), and the sandwich immunoreaction using glucose oxidase (GOx)-modified SiO2 nanospheres as labels was carried out in a 96-well plate. The Ag nanoparticles (NPs) acted as bifunctional units both for triggering the resonance energy transfer (RET) with g-C3N4 and for accelerating the electron transfer rate of the Ru-MOF-Ag ECL reaction. When the H2O2 catalyzed by GOx in the 96-well plate was transferred to the dual-disk glass carbon electrode, the doped Ag NPs in the two luminophors could be etched, thus destroying the RET between C3N4 and the accelerated reaction to Ru-MOF, resulting in an opposite trend in the ECL signal outputted from the dual disks. Using the ratio of the two signals for quantification, the constructed immunosensor for a model target, i.e. myoglobin, exhibited a low detection limit of 4.7 × 10-14 g/mL. The ingenious combination of ECL ratiometry, bifunctional Ag NPs, and a split-type strategy effectively reduces environmental and human errors, offering a more precise and sensitive analysis for complex samples.

Controllable and Low-Loss Electrochemiluminescence Waveguide Supported by a Micropipette Electrode

One-dimensional molecular crystal waveguide (MCW) can transmit self-generated electrochemiluminescence (ECL), but heavy optical loss occurs because of the small difference in the refractive index between the crystal and its surroundings. Herein, we report a micropipette electrode-supported MCW (MPE/MCW) for precisely controlling the far-field transmission of ECL in air with a low optical loss. ECL is generated from one terminal of the MCW positioned inside the MPE, which is transmitted along the MCW to the other terminal in air. In comparison with conventional waveguides on solid substrates or in solutions, the MPE/MCW is propitious to the total internal reflection of light at the MCW/air interface, thus confining the ECL efficiently in MCW and improving the waveguide performance with an extremely low-loss coefficient of 4.49 × 10-3 dB μm-1. Moreover, by regulation of the gas atmosphere, active and passive waveguides can be resolved simultaneously inside MPE and in air. This MPE/MCW offers a unique advantage of spatially controlling and separating ECL signal readout from its generation, thus holding great promise in biosensing without or with less electrical/chemical disturbance.

Tris(2,2'-bipyridyl)ruthenium (II) complex as a universal reagent for the fabrication of heterogeneous electrochemiluminescence platforms and its recent analytical applications

In recent years, electrochemiluminescence (ECL) has received enormous attention and has emerged as one of the most successful tools in the field of analytical science. Compared with homogeneous ECL, the heterogeneous (or solid-state) ECL has enhanced the rate of the electron transfer kinetics and offers rapid response time, which is highly beneficial in point-of-care and clinical applications. In ECL, the luminophore is the key element, which dictates the overall performance of the ECL-based sensors in various analytical applications. Tris(2,2'-bipyridyl)ruthenium (II) complex, Ru(bpy)32+, is a coordination compound, which is the gold-standard luminophore in ECL. It has played a key role in translating ECL from a "laboratory curiosity" to a commercial analytical instrument for diagnosis. The aim of the present review is to provide the principles of ECL and classical reaction mechanisms-particularly involving the heterogeneous Ru(bpy)32+/co-reactant ECL systems, as well as the fabrication methods and its importance over solution-phase Ru(bpy)32+ ECL. Then, we discussed the emerging technology in solid-state Ru(bpy)32+ ECL-sensing platforms and their recent potential analytical applications such as in immunoassay sensors, DNA sensors, aptasensors, bio-imaging, latent fingerprint detection, point-of-care testing, and detection of non-biomolecules. Finally, we also briefly cover the recent advances in solid-state Ru(bpy)32+ ECL coupled with the hyphenated techniques.

Recent advances in enrichment, isolation, and bio-electrochemical activity evaluation of exoelectrogenic microorganisms

Exoelectrogenic microorganisms (EEMs) catalyzed the conversion of chemical energy to electrical energy via extracellular electron transfer (EET) mechanisms, which underlay diverse bio-electrochemical systems (BES) applications in clean energy development, environment and health monitoring, wearable/implantable devices powering, and sustainable chemicals production, thereby attracting increasing attentions from academic and industrial communities in the recent decades. However, knowledge of EEMs is still in its infancy as only ~100 EEMs of bacteria, archaea, and eukaryotes have been identified, motivating the screening and capture of new EEMs. This review presents a systematic summarization on EEM screening technologies in terms of enrichment, isolation, and bio-electrochemical activity evaluation. We first generalize the distribution characteristics of known EEMs, which provide a basis for EEM screening. Then, we summarize EET mechanisms and the principles underlying various technological approaches to the enrichment, isolation, and bio-electrochemical activity of EEMs, in which a comprehensive analysis of the applicability, accuracy, and efficiency of each technology is reviewed. Finally, we provide a future perspective on EEM screening and bio-electrochemical activity evaluation by focusing on (i) novel EET mechanisms for developing the next-generation EEM screening technologies, and (ii) integration of meta-omics approaches and bioinformatics analyses to explore nonculturable EEMs. This review promotes the development of advanced technologies to capture new EEMs.

Graphdiyne: A New Carbon Allotrope for Electrochemiluminescence

Graphdiyne (GDY), a well-known 2D carbon allotrope, demonstrates increasing fantastic performance in various fields owing to its outstanding electronic properties. Owing to its unique properties, electrochemiluminescence (ECL) technology is one powerful tool for understanding fundamental questions and for ultrasensitive sensing and imaging. Here, we firstly find that GDY without any functionalization or treatment shows a strong ECL emission with potassium persulfate (K₂ S₂ O₈ ) as coreactant, which is totally different with other carbon allotropes. Mechanistic study indicates that the ECL emission of GDY is generated by the surface state transition. Interestingly, ECL is generated at 705 nm in the near infrared region with an ECL efficiency of 424 % compared to that of Ru(bpy)₃ Cl₂ /K₂ S₂ O₈ . The study demonstrates a new character of GDY in ECL investigation and sets the stage for the development of GDY for emerging applications, including imaging and light-emitting devices.

Study of highly stable electrochemiluminescence from [Ru(bpy)3]2+/dicyclohexylamine and its application in visualizing sebaceous fingerprint

For the first time, we report a novel and highly stable visual electrochemiluminescence emission from the [Ru(bpy)₃]²⁺/dicyclohexylamine system at physiological pH conditions, with a quantum efficiency (Φ_ECL) of 95.5%. Furthermore, we have successfully demonstrated the simple and rapid smartphone-based ECL mapping of sebaceous fingerprints via a non-destructive mode.

H2O2-activated independently bidirectional regulation for a sensitive and accurate electrochemiluminescence ratiometric analysis

A novel ECL ratiometric sensor was developed based on H2O2 activated independently bidirectional regulation strategy.

Covalent organic frameworks as micro-reactors: confinement-enhanced electrochemiluminescence

Electrochemiluminescence (ECL) micro-reactors with enhanced intensity and extreme stability were first established by the assembly of tris(2,2′-bipyridyl) ruthenium(ii) (Ru(bpy)₃²⁺) onto covalent organic frameworks (COFs), in which a type of imine-linked COF (denoted as COF-LZU1) was employed as a model for ECL micro-reactors. Compared with the dominant ECL system of Ru(bpy)₃²⁺/tri-n-propylamine (TPrA) (TPrA as a co-reactant), the intensity of the COF-LZU1 micro-reactor-based electrode was significantly increased nearly 5-fold under the same experimental conditions, which is unprecedented in other Ru(bpy)₃²⁺-based ECL systems. This enhancement can be attributed to the large surface area, delimited space, and stable and hydrophobic porous structure of COF-LZU1, which not only enabled a huge amount of Ru(bpy)₃²⁺ to be loaded in/on COF-LZU1, but also enriched a large amount of TPrA from the aqueous solution into its inner hydrophobic cavity due to the lipophilicity of TPrA. More importantly, with its hydrophobic porous nanochannels, COF-LZU1 could act as micro-reactors to provide a delimited reaction micro-environment for the electrochemical oxidation of TPrA and the survival of TPrA˙, achieving significant confinement-enhanced ECL. To prove this principle, these Ru@COF-LZU1 micro-reactors were developed to prepare an ECL aptasensor for aflatoxin M1 (AFM1) detection with a wide detection range and a low detection limit. Overall, this work is the first report in which ECL micro-reactors are constructed with COFs to enhance the intensity and stability of the Ru(bpy)₃²⁺-based ECL system, and opens a new route to the design of other ECL micro-reactors for bioanalysis applications.

The electrochemiluminescence (ECL) micro-reactors with enhanced intensity and extreme stability were firstly established, unravelling the mechanism of ECL micro-reactors using COF-LZU1 assembled Ru(bpy)₃²⁺ as a case study.

Bioimaging using bipolar electrochemical microscopy with improved spatial resolution

In this study, we developed bipolar electrochemical microscopy (BEM) using a closed bipolar electrode (cBPE) array with an electrochemiluminescence (ECL) detecting system.

Oxygen-Resistant Electrochemiluminescence System with Polyhedral Oligomeric Silsesquioxane

We report the oxygen-resistant electrochemiluminescence (ECL) system from the polyhedral oligomeric silsesquioxane (POSS)-modified tris(2,2'-bipyridyl)ruthenium(II) complex (Ru-POSS). In electrochemical measurements, including cyclic voltammetry (CV), it is shown that electric current and ECL intensity increase in the mixture system containing Ru-POSS and tripropylamine (TPrA) on the indium tin oxide (ITO) working electrode. The lower onset potential (E_onset) in CV is observed with Ru-POSS compared to tris(2,2'-bipyridyl)ruthenium(II) complex (Ru(bpy)₃²⁺). From the series of mechanistic studies, it was shown that adsorption of Ru-POSS onto the ITO electrode enhances TPrA oxidation and subsequently the efficiency of ECL with lower voltage. Moreover, oxygen quenching of ECL was suppressed, and it is proposed that the enhancement to the production of the TPrA radical could contribute to improving oxygen resistance. Finally, the ECL-based detection for water pollutant is demonstrated without the degassing treatment. The commodity system with Ru(bpy)₃²⁺ is not applicable in the absence of degassing with the sample solutions due to critical signal suppression, meanwhile the present system based on Ru-POSS was feasible for estimating the amount of the target even under aerobic conditions by fitting the ECL intensity to the standard curve. One of critical disadvantages of ECL can be solved by the hybrid formation with POSS.

Signal enhancement and low oxidation potentials for miniaturized ECL biosensors via N-butyldiethanolamine

We present studies on ruthenium-based electrochemiluminescence (ECL) focusing on conditions supporting signal enhancement and low oxidation potentials. Low oxidation potentials (LOPs) are especially attractive for miniaturized ECL biosensors, as microfabricated electrodes tend to detach from their support when used with high currents and operated at high potentials. Furthermore, high potentials or current densities can lead to damage of typical biosensor surface coatings and biological probes. The possibility of generating LOP ECL signals at a potential below 900 mV was therefore studied for Ru(bpy)₃²⁺ with two typical coreactants, i.e. 2-(dibutylamino)ethanol (DBAE) and tripropylamine (TPA), as well as with the tertiary amine N-butyldiethanolamine (NBEA). Furthermore, the effect of buffer components and pH values on ECL signal generation was investigated. We could show a significant LOP ECL signal for NBEA. We found that Tris buffer, with its ability to form complexes with transition metal ions, has a positive influence on this ECL signal in terms of signal strength and LOP capabilities. Specifically, at basic pH values significant increases in ECL signals were observed at 900 mV and at 1.2 V. In fact, the ECL signal at 1.2 V was three times higher than the signal observed in phosphate buffer at a pH of 7, and it was thirty times higher than the ECL signal for TPA under these conditions. The LOP signal for NBEA in Tris buffer at pH 8.5 was similar to the signal obtained for TPA in phosphate buffer at pH 8.5 but three times higher than for TPA at pH 7.0. Interestingly, the coreactant DBAE was neither significantly influenced by the buffer system or pH nor did it present a valuable LOP ECL signal. Finally, it was found that high peak currents in cyclic voltammograms are not the indicators for high ECL signals, which should be obvious because the ECL mechanism requires more complex electron transfers. Overall, the standard TPA ECL at 1.2 V in phosphate buffer at pH 7.0 can successfully be replaced by NBEA ECL at 900 mV in Tris at pH 8.5 providing significantly higher signals accompanied by more gentle electrochemical conditions.

Detection of ferrocenemethanol and molecular oxygen based on electrogenerated chemiluminescence quenching at a bipolar electrode

Small molecules, such as ferrocenemethanol (FcMeOH) and O2, that are capable of quenching the Ru(bpy)3(2+) excited state via energy or electron transfer can be quantitatively detected in a bipolar electrochemical cell based on the attenuation of steady-state electrogenerated chemiluminescence (ECL). FcMeOH quenches ECL generated by the Ru(bpy)3(2+) oxalate coreactant system, exhibiting a linear dependence on [FcMeOH] with a Stern-Volmer slope of 921 M(-1), corresponding to a quenching rate constant of 2 × 10(9) M(-1) s(-1). We used the bipolar ECL quenching platform to measure dissolved O2 and validated the results using a standard Clark electrode. The detection limit for local [O2] measured using ECL quenching was found to be 300 ppb. This work opens up the possibility of utilizing ECL quenching at bipolar electrodes for a wide range of applications.

Electrogenerated chemiluminescence biosensor incorporating ruthenium complex-labelled Concanavalin A as a probe for the detection of Escherichia coli

A novel electrogenerated chemiluminescence (ECL) biosensor for highly sensitive detection of Escherichia coli (E. coli) was first developed by employing Concanavalin A (Con A) as a biological recognition element and bis(2,2'-bipyridine)-4'-methyl-4-carboxybipyridine ruthenium (II) (Ru1) complex as the detector. The ECL biosensor was fabricated by adsorbing carboxyl-functionalised single-wall carbon nanotubes (SWNTs) onto a paraffin-impregnated graphite electrode and further covalently coupling the Ru1-Con A probe onto the surface of the SWNT-modified electrode. Upon the binding of E. coli O157:H7 (as a model target), the biosensor showed a decreased ECL intensity in the presence of tri-n-propylamine (TPrA), which was in logarithmically direct proportion to the concentration of E. coli over a range from 5.0 × 10(2) to 5.0 × 10(5)cells/mL. The detection limit of this sensor was 127 cells/mL. Additionally, the ECL biosensor also showed satisfactory selectivity in discriminating gram-negative E. coli from gram-positive bacteria. The strategy developed in this study may be a promising approach and could be extended to the design of ECL biosensors for highly sensitive and rapid detection of other desired bacteria.

Reversible oxygen gas sensor based on electrochemiluminescence

A novel and robust oxygen gas sensor based on electrochemiluminescence of Ru(bpy)3(3+/+) ion annihilation in an ionic liquid is presented. Real-time detection of environmental oxygen concentration together with selective, sensitive and reversible performance is demonstrated.

Electrogenerated chemiluminescence

In electrogenerated chemiluminescence, also known as electrochemiluminescence (ECL), electrochemically generated intermediates undergo a highly exergonic reaction to produce an electronically excited state that then emits light. These electron-transfer reactions are sufficiently exergonic to allow the excited states of luminophores, including polycyclic aromatic hydrocarbons and metal complexes, to be created without photoexcitation. For example, oxidation of [Ru(bpy)(3)](2+) in the presence of tripropylamine results in light emission that is analogous to the emission produced by photoexcitation. This review highlights some of the most exciting recent developments in this field, including novel ECL-generating transition metal complexes, especially ruthenium and osmium polypyridine systems; ECL-generating monolayers and thin films; the use of nanomaterials; and analytical, especially clinical, applications.

[Ru(bpy)3]2+-doped silica nanoparticles within layer-by-layer biomolecular coatings and their application as a biocompatible electrochemiluminescent tag material

[Ru(bpy)3]2+-doped silica (RuSi) nanoparticles were synthesized by using a water/oil microemulsion method. Stable electrochemiluminescence (ECL) was obtained when the RuSi nanoparticles were immobilized on a glassy carbon electrode by using tripropylamine (TPA) as a coreactant. Furthermore, the ECL of the RuSi nanoparticles with layer-by-layer biomolecular coatings was investigated. Squential self-assembly of the polyelectrolytes and biomolecules on the RuSi nanoparticles gave nanocomposite suspensions, the ECL of which decreased on increasing the number of bilayers. Moreover, factors that affected the assembly and ECL signals were investigated. The decrease in ECL could be assigned to steric hindrance and limited diffusion of the coreactant molecules in the silica matrix after they were attached to the biomolecules. Since surface modification of the RuSi nanoparticles can improve their biocompatibility and prevent leaking of the [Ru(bpy)3]2+ ions, the RuSi nanoparticles can be readily used as efficient and stable ECL tag materials in immunoassay and DNA detection.

Multifunctional ruthenium(II) polypyridine complex-based core-shell magnetic silica nanocomposites: magnetism, luminescence, and electrochemiluminescence

Multifunctional nanoparticles (NPs) that consist of silica-coated magnetic cores and luminescent ruthenium(II) polypyridine complexes have been prepared. These multifunctional nanocomposites were shown to exhibit superparamagnetic behavior, high emission intensity, and electrochemiluminescence. An intense low-oxidation-potential electrochemiluminescence signal was observed by attachment of these functional NPs onto a fluorosurfactant-modified gold (Au(m)) electrode via application of an external magnetic field.