Coreactant electrochemiluminescence at nanoporous gold electrodes

From theory to practice: understanding the challenges in the implementation of electrogenerated chemiluminescence for analytical applications

Electrogenerated chemiluminescence (ECL) stands out as a remarkable phenomenon of light emission at electrodes initiated by electrogenerated species in solution. Characterized by its exceptional sensitivity and minimal background optical signals, ECL finds applications across diverse domains, including biosensing, imaging, and various analytical applications. This review aims to serve as a comprehensive guide to the utilization of ECL in analytical applications. Beginning with a brief exposition on the theory at the basis of ECL generation, we elucidate the diverse systems employed to initiate ECL. Furthermore, we delineate the principal systems utilized for ECL generation in analytical contexts, elucidating both advantages and challenges inherent to their use. Additionally, we provide an overview of different electrode materials and novel ECL-based protocols tailored for analytical purposes, with a specific emphasis on biosensing applications.

Recent Progress in Plasmonic based Electrochemiluminescence Biosensors: A Review

Electrochemiluminescence (ECL) analysis has become a powerful tool in recent biomarker detection and clinic diagnosis due to its high sensitivity and broad linear range. To improve the analytical performance of ECL biosensors, various advanced nanomaterials have been introduced to regulate the ECL signal such as graphene, gold nanomaterials, and quantum dots. Among these nanomaterials, some plasmonic nanostructures play important roles in the fabrication of ECL biosensors. The plasmon effect for the ECL signal includes ECL quenching by resonant energy transfer, ECL enhancement by surface plasmon resonance enhancement, and a change in the polarized angle of ECL emission. The influence can be regulated by the distance between ECL emitters and plasmonic materials, and the characteristics of polarization angle-dependent surface plasmon coupling. This paper outlines the recent advances of plasmonic based ECL biosensors involving various plasmonic materials including noble metals and semiconductor nanomaterials. The detection targets in these biosensors range from small molecules, proteins, nucleic acids, and cells thanks to the plasmonic effect. In addition to ECL biosensors, ECL microscopy analysis with plasmonic materials is also highlighted because of the enhanced ECL image quality by the plasmonic effect. Finally, the future opportunities and challenges are discussed if more plasmonic effects are introduced into the ECL realm.

Electrogenerated chemiluminescence of luminol at a boron-doped diamond electrode for the detection of hypochlorite

Electrogenerated chemiluminescence (ECL) of luminol at a boron-doped diamond electrode has been used for hypochlorite determination. The presence of H₂O₂ induces the generation of the ECL signals of luminol. In contrast, the presence of hypochlorite oxidizes luminol directly to decrease the ECL signals of luminol. Accordingly, a decrease of the ECL signals of luminol in the presence of H₂O₂ was used as the signal response for hypochlorite detection. A linear decrease of ECL signals with the NaClO concentration in the range from 0 to 20 μM was observed with a sensitivity of 18.56 a.u. μM^-1 cm^-2. An estimated detection limit of 0.88 μM was achieved, which is around one order lower than the detection limit obtained using the normal electrochemical method with the same electrode. The system also provides a good selectivity towards Cu²⁺ and Na⁺. A reproducibility of 3.40%RSD was noted for 15 repetitive measurements. The analytical performance was found to be favourable in comparison to those of other typical electrochemical and electrochemiluminescence methods, indicating that it is applicable for real sample detection.

Gold nanoparticle-based signal amplified electrochemiluminescence for biosensing applications

Since the content levels of biomarkers at the early stage of many diseases are generally lower than the detection threshold concentration, achieving ultrasensitive and accurate detection of these biomarkers is still one of the major goals in bio-analysis. To achieve ultrasensitive and reliable bioassay, it requires developing highly sensitive biosensors. Among all kinds of biosensors, electrogenerated chemiluminescence (ECL) based biosensors have attracted enormous attention due to their excellent properties. In order to improve the performance of ECL biosensors, gold nanoparticles (Au NPs) have been widely utilized as signal amplification tags. The introduction of Au NPs could dramatically enhance the performance of the constructed ECL biosensors via diverse ways such as electrode modification material, efficient energy acceptor in ECL resonant energy transfer (ECL-RET), reaction catalyst, surface plasmon resonance (SPR) enhancer, and as nanocarrier. Herein, we summarize recent developments and progress of ECL biosensors based on Au NPs signal amplification strategies. We will cover ECL applications of Au NPs as a signal amplification tag in the detection of proteins, metal ions, nucleic acids, small molecules, living cells, exosomes, and cell imaging. Finally, brief summary and future outlooks of this field will be presented.

A flexible and bright surface-enhanced electrochemiluminescence film constructed from efficient aggregation-induced emission luminogens for biomolecular sensing

A bright surface-enhanced electrochemiluminescence film (SEEF) was fabricated from an organic luminogen with aggregation-induced emission (AIEgen) features on flexible substrates. Flexible carbonous substrates including carbon fiber cloth (GCFC) and carbon fiber paper (GCFP) were decorated with gold nanoparticles (AuNPs) through electrochemical deposition methods, followed by facilely casting AIEgen solutions. The resulting SEEF had a low driving potential of +0.84 V, and its electrochemiluminescence (ECL) was readily observed by the naked eye. The systematic investigation showed that the bright ECL was associated with the promoted electrochemical oxidation and radiative decay of excited AIEgens enhanced by AuNP deposition. Intriguingly, the ECL intensity of the film was linearly enhanced by increasing AIEgen loadings, which allowed tuning of ECL brightness on demand. Moreover, the SEEF was flexible and immune to folding. The ECL intensity rarely changed even when consecutively folding the film 20 times due to the strong interaction between the AIEgen and substrate. The SEEF was further used to sense biomolecules in aqueous media. The ECL of the film was linearly quenched in the presence of dopamine (DA) in the range of 10^-15-10^-6 M with a record-low limit of detection of 3.16 × 10^-16 M. Furthermore, a simple method based on grayscale analysis of ECL images (GAEI) was used for visual sensing of DA. This work provides a kind of novel bright ECL film, useful for the ultrasensitive monitoring of biomolecules in aqueous media.

Boron-Doped Diamond Electrode Outperforms the State-of-the-Art Electrochemiluminescence from Microbeads Immunoassay

Electrochemiluminescence (ECL) is a powerful transduction technique where light emission from a molecular species is triggered by an electrochemical reaction. Application to biosensors has led to a wide range of electroanalytical methods with particular impact on clinical analysis for diagnostic and therapeutic monitoring. Therefore, the quest for increasing the sensitivity while maintaining reproducible and easy procedures has brought investigations and innovations in (i) electrode materials, (ii) luminophores, and (iii) reagents. Particularly, the ECL signal is strongly affected by the electrode material and its surface modification during the ECL experiments. Here, we exploit boron-doped diamond (BDD) as an electrode material in microbead-based ECL immunoassay to be compared with the approach used in commercial instrumentation. We conducted a careful characterization of ECL signals from a tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)₃²⁺)/tri-n-propylamine (TPrA) system, both homogeneous (i.e., free diffusing Ru(bpy)₃²⁺) and heterogeneous (i.e., Ru(bpy)₃²⁺ bound on microbeads). We investigated the methods to promote TPrA oxidation, which led to the enhancement of ECL intensity, and the results revealed that the BDD surface properties greatly affect the ECL emission, so it does the addition of neutral, cationic, or anionic surfactants. Our results from homogeneous and heterogeneous microbead-based ECL show opposite outcomes, which have practical consequences in ECL optimization. In conclusion, by using Ru(bpy)₃²⁺-labeled immunoglobulins bound on microbeads, the ECL resulted in an increase of 70% and a double signal-to-noise ratio compared to platinum electrodes, which are actually used in commercial instrumentation for clinical analysis. This research infers that microbead-based ECL immunoassays with a higher sensitivity can be realized by BDD.

A mass-amplifying electrochemiluminescence film (MAEF) for the visual detection of dopamine in aqueous media

A bright and metal-free mass-amplifying electrochemiluminescence film (MAEF) performing in aqueous media was reported for the first time. Systematic studies demonstrated that the film substrates have a remarkable influence on the electrochemiluminescence (ECL) performance. Gold substrates promote ECL reactions and the subsequent radiative decay process simultaneously, affording an unconventional 507-fold ECL enhancement. Such a gold-enhanced MAEF is opposite to ECL systems previously reported, in which the use of gold electrodes normally results in decreased ECL intensity due to passivation of the gold surface by oxide formation. More importantly, the ECL intensity of the MAEF is linearly amplified through facilely regulating luminogen loading. Morphological analysis reveals that the film consists of grass-like nanowires with a diameter of 57 nm, which facilitate electrical communication between the luminogen, electrode, and supporting electrolyte, giving rise to the mass-amplifying ECL. The bright ECL of the solid film in aqueous media can be readily observed by the naked eye, entirely different from visible ECL systems reported in which ruthenium complexes dissolved/dispersed in solution are used as the luminogens. The film is further utilized to detect dopamine (DA), an important biomolecule related to nervous diseases, in aqueous media, with a low detection limit of 3.3 × 10-16 M. Furthermore, a facile method based on grayscale analysis of ECL images (GAEI) of the film was developed for visual and ultrasensitive DA detection in aqueous media.

Electrogenerated Chemiluminescence by in Situ Production of Coreactant Hydrogen Peroxide in Carbonate Aqueous Solution at a Boron-Doped Diamond Electrode

An electrogenerated chemiluminescence (ECL) system by in situ coreactant production, where Ru(bpy)₃²⁺ emission is generated at a boron-doped diamond (BDD) electrode, is presented. The system takes advantage of the unique properties of BDD to promote oxidation of carbonate (CO₃^2-) into peroxydicarbonate (C₂O₆^2-), which further reacts with water to form hydrogen peroxide (H₂O₂), which acts as a coreactant for Ru(bpy)₃²⁺ ECL. Investigation of the mechanism reveals that ECL emission is triggered by the reduction of H₂O₂ to hydroxyl radicals (OH^•), which later react with the reduced Ru(bpy)₃⁺ molecules to form excited states, followed by light emission. The ECL signal was found to increase with the concentration of CO₃^2-; therefore, with the concentration of electrogenerated H₂O₂, although at the same time, higher concentrations of H₂O₂ can quench the ECL emission, resulting in a decrease in intensity. The carbonate concentration, pH, and oxidation parameters, such as potential and time, were optimized to find the best emission conditions.