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

Amplified electrochemiluminescence of Ru(dcbpy)32+ via coreactant active sites on nitrogen-doped graphene quantum dots

Searching for new alternative to tripropylamine (TPrA) with low toxicity and high chemical stability for the tris(4,4'-dicarboxylic acid-2,2'-bipyridyl)ruthenium (II) (Ru(dcbpy)32+) based coreactant electrochemiluminescence (ECL) system is essential for widespread analytical applications. Here, nitrogen-doped graphene quantum dots (NGQDs) have been discovered to significantly amplify the ECL emission and increase the ECL efficiency of Ru(dcbpy)32+ for the first time. However, the mechanism by which NGQDs act as coreactants is not well comprehended. Therefore, various optical and electrochemical technologies were employed to investigate the ECL mechanism. It is proposed that the amino and carboxyl groups on the surface of NGQDs play crucial roles as the coreactant active sites, catalyzing the oxidation of Ru(dcbpy)32+. Based on this foundation, an "on-off-on" ECL aptasensor for the quantification of acetamiprid was developed, exhibiting a broad linear range and a detection limit of 0.056 pM. Satisfactory recoveries, ranging from 98.0 % to 101.6 %, were achieved in pakchoi samples. Consequently, NGQDs could serve as coreactants for Ru(dcbpy)32+, offering new opportunities for constructing a variety of sensors with extensive analytical applications in the ECL field.

Advances on Electrochemiluminescent Biosensors for TB Biomarkers

Tuberculosis (TB) is a highly contagious bacterial infection that remains a leading cause of death and persistent threat to global health. The spread of TB is exacerbated by the major limitations of conventional diagnostic approaches, such as complex technicalities, high cost, and low sensitivity. To address these challenges, recent research has focused on using electrochemiluminescence (ECL) as an alternative detection strategy coupled to biosensors. ECL biosensors leverage electrochemically generated chemiluminescence, converting electrical energy to light, as a novel transduction mechanism for TB biosensors. This unique approach offers several advantages, namely, wide linear dynamic ranges, improved device sensitivities, and prompt response times for sensitive early detection. This Review offers a comprehensive overview of advancements in ECL biosensor configurations, including detection and amplification strategies, substrates, and the development of luminophores and coreactants tailored for TB biomarker detection. The focus is on ECL biosensor designs, including biorecognition elements like immunosensors, DNA sensors, and aptasensors, along with various immobilization strategies tailored to target specific TB biomarkers. A comprehensive discussion spans biomarker detection trends over the past decade, clinical relevance, sensitivity thresholds, and detection limits. Furthermore, widely recognized TB biomarkers commonly detected in commercial diagnostic tests are discussed alongside novel markers that, while not exclusive to TB, have demonstrated clinical importance. This Review aims to highlight the potential of ECL-based biosensors as an effective means to advance an early, reliable, and accessible TB detection approach.

Recent advances and future prospects in oxidative-reduction low-triggering-potential electrochemiluminescence strategies based on nanoparticle luminophores

The oxidative-reduction electrochemiluminescence (ECL) potential of a luminophore is one of the most significant parameters during light generation processes when considering the growing demand for anti-interference analysis techniques, electrode compatibility and the reduction of damage to biological molecules due to excessive excitation potential. Nanoparticle luminophores, including quantum dots (QDs) and metal nanoclusters (NCs), possess tremendous potential for forming various ECL sensors due to their adjustable surface states. However, few reviews focused on nanoparticle luminophore-based ECL systems for low-triggering-potential (LTP) oxidative-reduction ECL to avoid the possible interference and oxidative damage of biological molecules. This review summarizes the recent advances in the LTP oxidative-reduction ECL potential strategy with nanoparticle luminophores as ECL emitters, including matching efficient coreactants and nanoparticle luminophores, doping nanoparticle luminophores, constructing donor-acceptor systems, choosing suitable working electrodes, combining multiplex nanoparticle luminophores, and employing surface-engineering strategies. In the context of the different LTP ECL systems, potential-lowering strategies and bio-related applications are discussed in detail. Additionally, the future trends and challenges of low ECL-triggering-potential strategies are discussed.

Carboxyl groups on carbon nanodots as co-reactant sites for anodic electrochemiluminescence of tris(2,2-bipyridine)ruthenium(II)

Carbon nanodots (C-dots) with good biocompatibility have been extensively utilized as co-reactants for electrochemiluminescence (ECL) of the tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)32+) system. However, the ECL intensity of this system is still relatively low and the mechanism of C-dots as co-reactants remains unclear, which greatly limits its further application in bio-analysis. In this work, we revealed that the carboxyl groups on C-dots are co-reactant sites for Ru(bpy)32+ ECL by systematically investigating the contribution of carboxyl, hydroxyl and carbonyl groups on the surface of C-dots to the ECL intensity. Further treatment with hydrogen peroxide to increase the carboxyl-group content on C-dots resulted in a 10-fold increase in ECL intensity over the original Ru(bpy)32+/C-dots system. This work provides new insights for the rational design of ECL systems with C-dots as co-reactants and offers new chances for further applications of C-dots in the field of ECL.

Signal-amplified electrochemiluminescence aptasensor for mucin 1 determination using CdS QDs/g-C3N4 and Au NPs@TEOA

A novel electrochemiluminescence (ECL) aptasensor, using graphite carbonitride (g-C₃N₄) capped CdS quantum dots (CdS QDs@g-C₃N₄) and Au nanoparticles decorated triethanolamine (AuNPs@TEOA) as dual coreactants, was proposed for the determination of mucin 1 (MUC1). Higher ECL efficiency was acquired due to the double enhancement contribution of CdS QDs and TEOA to Ru (bpy)₃²⁺ ECL. Additionally, AuNPs@TEOA also acted as nanocarrier for MUC1 aptamer immobilization. After the aptasensor was incubated in target MUC1, the decreased ECL emission was obtained because of the poor conductivity of MUC1. The ECL aptasensor displayed a good linear correlation for MUC1 in the range 0.1 pg mL^-1 -1000 ng mL^-1, and the detection limit was 33 fg mL^-1. MUC1 spiked into human serum samples was quantified to assess the practicability of the ECL aptasensor.

Electrochemiluminescence Systems for the Detection of Biomarkers: Strategical and Technological Advances

Electrochemiluminescence (ECL)-based sensing systems rely on light emissions from luminophores, which are generated by high-energy electron transfer reactions between electrogenerated species on an electrode. ECL systems have been widely used in the detection and monitoring of diverse, disease-related biomarkers due to their high selectivity and fast response times, as well as their spatial and temporal control of luminance, high controllability, and a wide detection range. This review focuses on the recent strategic and technological advances in ECL-based biomarker detection systems. We introduce several sensing systems for medical applications that are classified according to the reactions that drive ECL signal emissions. We also provide recent examples of sensing strategies and technologies based on factors that enhance sensitivity and multiplexing abilities as well as simplify sensing procedures. This review also discusses the potential strategies and technologies for the development of ECL systems with an enhanced detection ability.

Two in One: A Dinuclear Ru(II) Complex for Deep-Red Light-Emitting Electrochemical Cells and as an Electrochemiluminescence Probe for Organophosphorus Pesticides

The emissive properties of two Ru(II) complexes, [Ru(dmbipy)₂L₁][PF₆]₂ (1) and [Ru₂(dmbipy)₄L₂][PF₆]₄ (2), (where L₁ and L₂ are π-extended phenanthroline-based ligands and dmbipy = 4,4'-dimethyl-2,2'-bipyridine) have been explored for dual applications, namely, deep-red light-emitting electrochemical cells (LECs) and electrochemiluminescence (ECL) sensors for the detection of organophosphorus pesticides (OPs) that include chlorpyrifos (CPS). A simple single-layer deep-red LEC device comprising 2 is reported that outperforms both its mononuclear derivative 1 and all previously reported dinuclear LECs, with a maximum brightness of 524 cd/m², an external quantum efficiency of 0.62%, and a turn-on voltage of 3.2 V. Optoelectronic studies reveal that the ECL response of 2 is improved when compared to its mononuclear counterpart 1 and benchmark [Ru(bipy)₃]²⁺ (3). Modified glassy carbon electrodes coated with 2 are highly sensitive deep-red ECL sensors that facilitate the detection of CPS directly from river water and fruit samples without any complex pretreatment steps, operating over a broad logarithmic concentration range, with a low detection limit.

Electrogenerated chemiluminescence of Ru(bpy)32+ at MoS2 nanosheets modified electrode and its application in the sensitive detection of dopamine

Electrogenerated chemiluminescence (ECL) of Ru(bpy)₃²⁺ was studied at a MoS₂ nanosheets modified glassy carbon electrode (MoS₂NS/GCE) in neutral condition. Electrochemical results revealed that MoS₂ nanosheets could significantly catalyze the electrochemical oxidation of Ru(bpy)₃²⁺, as a result, strong anodic ECL was obtained. Several impact factors, such as the modified amount of MoS₂ nanosheets suspension, the pH value, and the concentration of Ru(bpy)₃²⁺, were investigated to obtain the optimal experimental condition. Dopamine exhibited apparent inhibiting effect on ECL intensity of Ru(bpy)₃²⁺-MoS₂ nanosheets through energy transfer process, and could be sensitively detected in the range of 1.0 × 10^-9 to 1.0 × 10^-4 mol L^-1. The linear equation between the decrease of ECL intensity and the logthium of dopamine concentration was determined as ΔI = 9965.02 + 1077.03lgC (C in mol L^-1), with the detection of 8.5 × 10^-10 mol L^-1 (3σ). The modified electrode exhibited satisfactory sensitivity, selectivity, and stability, which can be used to detect dopamine in real samples.

An electrogenerated chemiluminescence aptasensor for lysozyme based on the interaction between Ru(bpy)3 2+ and cucurbit[8]uril

Strong anodic Ru(bpy)₃ ²⁺ electrogenerated chemiluminescence (ECL) was obtained at a cucurbil[8]uril (CB[8]) modified electrode in neutral conditions without the need of an additional coreactant. An ECL aptasensor was fabricated based on the strong ECL emission as well as the host-guest interaction between DNA and CB[8]. Firstly, amino group-terminated complementary DNA (DNA-NH₂ ) was firmly immobilized on CB[8]/glass carbon electrode, which could further increase ECL intensity. Then, a ferrocene group-terminated lysozyme aptamer (Fc-DNA) was hybridized with complementary DNA. The inhibiting effect of ferrocene on Ru(bpy)₃ ²⁺ ECL resulted in the apparent decrease in ECL signal. When the modified electrode was incubated in lysozyme, specific binding between lysozyme and its aptamer could release the ferrocene group from the electrode surface, and the ECL emission was recovered. As a result, an 'on-off-on' mode ECL aptasensor for lysozyme was fabricated. In the range 0.14-140 pg ml^-1 , the increased ECL intensities exhibited excellent linearity with the logarithm of lysozyme concentrations, and the detection limit was calculated as 0.093 pg ml^-1 (3σ). The proposed ECL aptasensor exhibited satisfactory analytical performance, revealing the potential application of CB[n]s in an ECL sensing field.

Signal-Off Electrogenerated Chemiluminescence Biosensing Platform Based on the Quenching Effect between Ferrocene and Ru(bpy)32+-Functionalized Metal-Organic Frameworks for the Detection of Methylated RNA

N⁶-methyladenine (m⁶A), one of the most common chemical modifications of eukaryotic RNA, participates in many important biological processes. An effective strategy for the quantitative determination of m⁶A is of great significance. Herein, we used methylated microRNA-21 (miRNA21) as the model target to propose a simple and sensitive electrogenerated chemiluminescence (ECL) biosensing platform to detect a specific m⁶A RNA sequence. This strategy is based on the fact that the anti-m⁶A-antibody can specifically recognize and bind to the m⁶A site in the RNA sequence, resulting in a quenching effect between Ru(bpy)₃²⁺-functionalized metal-organic frameworks and ferrocene. Luminescent metal-organic frameworks (Ru@MOFs) not only act as ECL indicators but also serve as nanoreactors for the relative ECL reactions owing to their porous or multichannel structure, which overcomes the fact that Ru(bpy)₃²⁺ is easily released when used for aqueous-phase detection, thus enhancing the ECL efficiency. Moreover, the ECL method has fewer modification steps and uses only one antibody to recognize the target RNA sequence, which simplifies the operation process and reduces the detection time, presenting a wide linear range (0.001-10 nM) for m⁶A RNA determination with a low detection limit (0.0003 nM). Additionally, this developed strategy was validated for m⁶A RNA detection in human serum. Thus, the ECL biosensing method provides a new method for m⁶A RNA determination that is simple, highly specific, and sensitive.

Triple-helix molecular switch-based versatile "off-on" electrochemiluminescence and fluorescence biosensing platform for ultrasensitive detection of lipopolysaccharide by multiple-amplification strategy

Herein, a novel biosensing platform for versatile electrochemiluminescence (ECL) "off" and fluorescence (FL) "on" detection of lipopolysaccharide (LPS) with multiple-amplification strategy is proposed. The specific recognition of target to aptamer on the magnetic beads (MB) firstly released abundant DNA sequences of three kinds. The sequences hybridized with multifunctional molecular beacon (MMB) and initiated numerous bidirectional polymerization and shearing reactions, generating a large number of DNA fragments (a1) by multiple cycling amplification. Then a1 was introduced to the triple-helix sensing system, opening the triple-helix structure. In ECL system, the G-rich chains S2 were exposed to form G-quadruplex-hemin complex in the presence of hemin, which could efficiently quench ECL for "off" detection of LPS. In FL system, the fluorophore FAM and quencher BHQ on S1 chain were separated with opening of triple-helix structure, achieving fluorescence "on" signal for LPS assay. So the versatile platform can achieve greatly amplified ECL and FL signal changes for sensitive assay of LPS, showing wide linear ranges (0.1 fg/mL-0.1 ng/mL by ECL and 10 fg/mL^-1-1 μg/mL by FL) and low detection limits (0.012 fg/mL by ECL and 1.269 fg/mL by FL). Therefore, the present ECL "Off" and FL "On" dual-signal detection patterns for LPS displayed many advantages over other reported methods, which provided an outlook for future applications in clinical diagnosis.

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.

Application of hairpin DNA-based biosensors with various signal amplification strategies in clinical diagnosis

Biosensors have been commonly used in biomedical diagnostic tools in recent years, because of a wide range of application, such as point-of-care monitoring of treatment and disease progression, drug discovery, commonly use food control, environmental monitoring and biomedical research. Additionally, development of DNA biosensors has been increased enormously over the past few years as confirmed by the large number of scientific publications in this field. A wide range of techniques can be used for the development of DNA biosensors, such as DNA nano-machines and various signal amplification strategies. This article selectively reviews the recent advances in DNA base biosensors with various signal amplification strategies for detection of cancer DNA and microRNA, infectious microorganisms, and toxic metal ions.

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.

Self-electrochemiluminescence of CdTe nanocrystals capped with 2-diethylaminoethanethiol

The self-electrochemiluminescence of CdTe nanocrystals capped with 2-diethylaminoethanethiol was achieved via protective reagent exchange.

A review of electrogenerated chemiluminescent biosensors for assays in biological matrices

Electrogenerated chemiluminescence (ECL) is the production of light via electron transfer reactions between electrochemically produced reagents. ECL-based biosensors use specific biological interactions to recognize an analyte and produce a luminescent signal. Biosensors fabricated with novel biorecognition species have increased the number of analytes detected. Some of these analytes include peptides, cells, enzymes and nucleic acids. ECL biosensors are selective, simple, sensitive and have low detection limits. Traditional methods use ruthenium complexes or luminol to generate ECL. Nanomaterials can be incorporated into ECL biosensors to improve efficiency, but also represent a new class of ECL emitters. This article reviews the application of ruthenium complex, luminol and nanomaterial-based ECL biosensors to making measurements in biological matrices over the past 4 years.