Bimodal Oxidation Electrochemiluminescence Mechanism of Coreactant-Embedded Covalent Organic Frameworks via Postsynthetic Modification

Electrochemiluminescence (ECL) efficiency is determined by charge transfer between coreactants and emitters in coreactant systems, which are usually limited by their slow intermolecular charge transfer. In this study, a covalent organic framework (COF) with aldehyde residue was synthesized, and then coreactants were covalently integrated into the skeleton through the postsynthetic modification strategy, resulting in a crystalline coreactant-embedded COF nanoemitter (C-COF). Compared to the pristine COF with an equivalent external coreactant, C-COF exhibited an extraordinary 1008-fold enhancement of ECL intensity due to the rapid intrareticular charge transfer. Significantly, with the pH increase, C-COF shows protonation-induced ECL enhancement for the first ECL peaked at +1.1 V and an opposite trend for the second ECL at +1.4 V, which were attributed to the antedating oxidation of coreactant in framework and COF self-oxidation, respectively. The resulting bimodal oxidation ECL mechanism was rationalized by spectral characterization and density functional theory calculations. The postsynthetic coreactant-embedded nanoemitters present innovative and universal avenues for advancing ECL systems.

Validation and Suitability Assessment of Multiplex Mesoscale Discovery Immunogenicity Assay for Establishing Serological Signatures Using Vaccinated, Non-Vaccinated and Breakthrough SARS-CoV-2 Infected Cases

Antibody responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are multi-targeted and variable over time. Multiplex quantitative serological assays are needed to provide accurate and robust seropositivity data for the establishment of serological signatures during vaccination and or infection. We describe here the validation and evaluation of an electro-chemiluminescence (ECL)-based Mesoscale Discovery assay (MSD) for estimation of total and functional IgG relative to SARS-CoV-2 spike, nucleocapsid and receptor binding (RBD) proteins in human serum samples to establish serological signatures of SARS-CoV-2 natural infection and breakthrough cases. The 9-PLEX assay was validated as per ICH, EMA, and US FDA guidelines using a panel of sera samples, including the NIBSC/WHO reference panel (20/268). The assay demonstrated high specificity and selectivity in inhibition assays, wherein the homologous inhibition was more than 85% and heterologous inhibition was below 10%. The assay also met predetermined acceptance criteria for precision (CV < 20%), accuracy (70-130%) and dilutional linearity. The method's applicability to serological signatures was demonstrated using sera samples (n = 45) representing vaccinated, infected and breakthrough cases. The method was able to establish distinct serological signatures and thus provide a potential tool for seroprevalence of SARS-CoV-2 during vaccination or infection.

Silver Nanoparticles In Situ Enhanced Electrochemiluminescence of the Porphyrin Organic Matrix for Highly Sensitive and Rapid Monitoring of Tetracycline Residues

Accurate monitoring of tetracycline (TC) residues in the environment is crucial for avoiding contaminant risk. Herein, a novel TC biosensor was facilely designed by integrating silver nanoparticles (Ag NPs) into the porphyrin metal-organic matrix (Ag@AgPOM) as a bifunctional electrochemiluminescence (ECL) probe. Different from the step-by-step synthesis of the co-reaction accelerator and ECL emitter, the co-reaction accelerators Ag NPs were in situ-grown on the surface of 5,10,15,20-tetrakis (4-carboxyphenyl) porphyrin (TCPP) via a simple one-pot approach. Symbiotic Ag NPs on Ag@AgPOM formed an intimate interface and increased the collision efficiency of the ECL reaction, achieving the ECL enhancement of TCPP. Under the optimized conditions, the ternary ECL biosensor showed a wide linear detection range toward TC with a low detection limit of 0.14 fmol L-1. Compared with the traditional HPLC and ELISA methods, satisfied analytical adaptability made this sensing strategy feasible to monitor TC in complex environmental samples.

Ultrastable Anion Radicals in Ligand-Dimerized Frameworks for Self-Accumulated Electrochemiluminescence

Electrochemiluminescence (ECL) is a light-emitting process that occurs via an annihilation reaction among energetic radical intermediates, whose stabilities determine the ECL efficiency. In this study, a ligand-dimerized metal-organic framework (MOF) with ultrastable anion radical is designed as an efficient nanoemitter for self-accumulated ECL. Due to the nonplanar structure of perylene diimide (PDI) derivate, two PDI ligands in the framework form a J-dimer unit with a vertical distance of ∼5.74 Å. In cathodic scanning, the ligand-dimerized MOF demonstrates three-step ECL emissions with a gradual increase in ECL intensity. Unlike the decrease in the PDI ligand, the self-accumulated ECL of the MOF was observed with 16.8-fold enhancement due to the excellent stability of radical intermediates in frameworks. Electron paramagnetic resonance demonstrated the ultrastability of free radicals in the designed frameworks, with 82.2% remaining even after one month of storage. Density functional theory calculations supported that PDI dimerization was energetically favorable upon successive electron injection. Moreover, the ECL wavelength is 610 nm, corresponding to the emission of excited dimers. The radical-stabilized reticular nanoemitters open up a new platform for decoding the fundamentals of self-accumulated ECL systems.

Off-Grid Electrogenerated Chemiluminescence with Customized p-i-n Photodiodes

Electrochemiluminescence (ECL) is the generation of light induced by an electrochemical reaction, driven by electricity. Here, an all-optical ECL (AO-ECL) system is developped, which triggers ECL by the illumination of electrically autonomous "integrated" photoelectrochemical devices immersed in the electrolyte. Because these systems are made using small and cheap devices, they can be easily prepared and readily used by any laboratories. They are based on commercially available p-i-n Si photodiodes (≈1 € unit-1), coupled with well-established ECL-active and catalytic materials, directly coated onto the component leads by simple and fast wet processes. Here, a Pt coating (known for its high activity for reduction reactions) and carbon paint (known for its optimal ECL emission properties) are deposited at cathode and anode leads, respectively. In addition to its optimized light absorption properties, using the commercial p-i-n Si photodiode eliminates the need for a complicated manufacturing process. It is shown that the device can emit AO-ECL by illumination with polychromatic (simulated sunlight) or monochromatic (near IR) light sources to produce visible photons (425 nm) that can be easily observed by the naked eye or recorded with a smartphone camera. These low-cost off-grid AO-ECL devices open broad opportunities for remote photodetection and portable bioanalytical tools.

Extending the Operational Lifetime of Electrochemiluminescence Devices by Installing a Floating Bipolar Electrode

Electrochemiluminescence (ECL) holds significant promise for the development of cost-effective light-emitting devices because of its simple structure. However, conventional ECL devices (ECLDs) have a major limitation of short operational lifetimes, rendering them impractical for real-world applications. Typically, the luminescence of these devices lasts no longer than a few minutes during operation. In the current study, a novel architecture is provided for ECLDs that addresses this luminescence lifespan issue. The device architecture features an ECL active layer between two coplanar driving electrodes and a third floating bipolar electrode. The inclusion of the floating bipolar electrode enables modulating the electrical-field distribution within the active layer when a bias is applied between the driving electrodes. This, in turn, enables the use of opaque yet electrochemically stable noble metals as the driving electrodes while allowing ECL light to escape through the transparent floating bipolar electrode. A significant extension on operational lifetime is achieved, defined as the time required for the initial luminance (>100 cd m-2) to decrease by 50%, surpassing 1 h. This starkly contrasts the short lifetime (<1 min) attained by ECLDs in a conventional sandwich-type architecture with two transparent electrodes. These results provide simple strategies for developing durable ECL-based light-emitting devices.

Chiral Ru-Based Covalent Organic Frameworks as An Electrochemiluminescence-Active Platform for the Enantioselective Sensing of Amino Acids

Although several studies related with the electrochemiluminescence (ECL) technique have been reported for chiral discrimination, it still has to face some limitations, namely, complex synthetic pathways and a relatively low recognition efficiency. Herein, this study introduces a facile strategy for the synthesis of ECL-active chiral covalent organic frameworks (COFs) employed as a chiral recognition platform. In this artificial structure, ruthenium(II) coordinated with the dipyridyl unit of the COF and enantiopure cyclohexane-1,2-diamine was harnessed as the ECL-active unit, which gave strong ECL emission in the presence of the coreactant reagent (K2S2O8). When the as-prepared COF was used as a chiral ECL-active platform, clear discrimination was observed in the response of the ECL intensity toward l- and d-enantiomers of amino acids, including tryptophan, leucine, methionine, threonine, and histidine. The biggest ratio of the ECL intensity between different configurations was up to 1.75. More importantly, a good linear relationship between the enantiomeric composition and the ECL intensity was established, which was successfully employed to determine the unknown enantiomeric compositions of the real samples. In brief, we believe that the proposed ECL-based chiral platform provides an important reference for the determination of the configuration and enantiomeric compositions.

Near-IR Photoinduced Electrochemiluminescence Imaging with Structured Silicon Photoanodes

Infrared (IR) imaging devices that convert IR irradiation (invisible to the human eye) to a visible signal are based on solid-state components. Here, we introduce an alternative concept based on light-addressable electrochemistry (i.e., electrochemistry spatially confined under the action of a light stimulus) that involves the use of a liquid electrolyte. In this method, the projection of a near-IR image (λexc = 850 or 840 nm) onto a photoactive Si-based photoanode, immersed into a liquid phase, triggers locally the photoinduced electrochemiluminescence (PECL) of the efficient [Ru(bpy)3]2+-TPrA system. This leads to the local conversion of near-IR light to visible (λPECL = 632 nm) light. We demonstrate that compared to planar Si photoanodes, the use of a micropillar Si array leads to a large enhancement of local light generation and considerably improves the resolution of the PECL image by preventing photogenerated minority carriers from diffusing laterally. These results are important for the design of original light conversion devices and can lead to important applications in photothermal imaging and analytical chemistry.

A perovskite-based electrochemiluminescence aptasensor for tetracycline screening

Tetracyclines are currently the most commonly used class of antibiotics, and their residue issue significantly impacts public health safety. In this study, a surface modification of perovskite with cetyltrimethylammonium bromide led to the generation of stable electrochemiluminescence (ECL) emitters in aqueous systems and improved the biocompatibility of perovskite. A perovskite quantum dot-based ECL sensing strategy was developed. Utilizing the corresponding aptamer of the antibiotics, strain displacement reactions were triggered, disrupting the ECL quenching system composed of perovskite and Ag nanoclusters (Ag NCs) on the electrode surface, generating a signal to achieve quantitative detection of several common tetracycline antibiotics. The perovskite quantum dot provided a strong and stable initial signal, while the efficient catalytic activity of the silver cluster enhanced the recognition sensitivity. Tetracycline, chlortetracycline, and oxytetracycline were used as examples to demonstrate the differentiation and quantitative detection through this method. In addition, the aptasensor exhibited analytical performance with the linear range (0.1-10 μM OTC) and good recovery rates of 94.7% to 101.6% in real samples. This approach has the potential to become a sensitive and practical approach for assessing antibiotic residues.

NiCo-LDH Hollow Nanocage Oxygen Evolution Reaction Promotes Luminol Electrochemiluminescence

Conventional luminol co-reactant electrochemiluminescence (ECL) systems suffer from low stability and accuracy due to factors such as the ease of decomposition of hydrogen peroxide and inefficient generation of reactive oxygen species (ROS) from dissolved oxygen. Inspired by the luminol ECL mechanism mediated by oxygen evolution reaction (OER), the nickel-cobalt layered double hydroxide (NiCo-LDH) hollow nanocages with hollow structure and defect state are used as co-reaction promoters to enhance the ECL emission from the luminol-H2 O system. Thanks to the hollow structure and defect state, NiCo-LDH hollow nanocages show excellent OER catalytic activity, which can stabilize and efficiently produce ROS and enhance the ECL emission. Additionally, mechanistic exploration suggests that the ROS involved in the co-reaction of the luminol-H2 O system are derived from the OER reaction process, and there is a positive correlation between ECL intensity and the OER catalytic activity of the co-reaction promoter. The selection of catalysts with excellent OER catalytic activity is a key factor in improving ECL emission. Finally, a dual-mode immunosensor is constructed for the detection and analysis of alpha-fetoprotein (AFP) based on the promoting effect of NiCo-LDH hollow nanocages on the luminol-H2 O ECL system.

Exogenous Co-Reactant-Free Electrochemiluminescent Biosensor for Ratiometric Measurement of α-Glucosidase Based on a ZIF-67-Regulated Hydrogen-Bonded Organic Framework

The development of highly sensitive and selective analytical approaches for monitoring enzymatic activity is critical for disease diagnosis and biomedical research. Herein, we develop an exogenous co-reactant-free electrochemiluminescence (ECL) biosensor for the ratiometric measurement of α-glucosidase (α-Glu) based on a zeolitic imidazolate framework (ZIF-67)-regulated pyrene-based hydrogen-bonded organic framework (HOF-101). Target α-Glu can hydrolyze maltose to α-d-glucose, which can subsequently react with GOx to produce gluconic acid. The resultant gluconic acid can dissolve ZIF-67, leading to the recovery of the HOF-101 cathodic ECL signal and the decrease of the luminol anodic ECL signal. The long-range ordered structure of HOF-101 can speed up charge transfer, resulting in a stable and strong cathodic ECL signal. Moreover, ZIF-67 can not only efficiently quench the ECL signal of HOF-101 due to ECL resonance energy transfer between HOF-101 and ZIF-67 as well as the steric hindrance effect of ZIF-67 but also enhance the anodic ECL emission of luminol in dissolved O2 system because of its ordered and porous crystalline structure and the atomically dispersed Co2+. Notably, HOF-101 possesses a higher ECL efficiency (32.22%) compared with the Ru(bpy)32+ standard. Importantly, this ratiometric ECL biosensor shows high sensitivity (a detection limit of 0.19 U L-1) and a broad linear range (0.2-50 U L-1). This biosensor can efficiently eliminate systematic errors and enhance detection reliability without the involvement of exogenous co-reactants, and it displays good assay performance in human serum samples, holding great promise in biomedical research studies.

Cyanuric Acid-Functionalized Perovskite Nanocrystals toward Low Interface Impedance, High Environmental Stability, and Superior Electrochemiluminescence

Perovskite nanocrystals (PNs) have received much attention as luminescence materials in the field of electrochemiluminescence (ECL). However, as one key factor for determining the optoelectronic properties of the surface state of PNs, the surface passivation layer of PNs has enormous difficulty in simultaneously meeting the requirements of high ECL efficiency, conductivity, and stability. Herein, an effective surface modification strategy with cyanuric acid (CA) is used to solve such issue. As confirmed, the CA molecules are chemically anchored onto the surface of PNs via the Lewis interaction between π electrons of the triazine ring and the empty orbit of Pb2+. Benefiting from the above interaction, the electrochemical impedance of PNs is decreased greatly without the loss of light-emitting efficiency. Moreover, the stability of PNs under O2 exposure is improved by almost sixfold. These improvements are confirmed to be beneficial for enhancing the ECL behaviors of PNs under electrochemical operation. Upon cathode ECL driving conditions in aqueous media, the ECL intensity and efficiency of PNs are increased to 200 and 170%, respectively. This work provides a new modification strategy to holistically improve the ECL performance of PNs, which is instructive to exploring robust perovskite nanomaterials for electrochemical applications.

Ultrasensitive Electrochemiluminescence Sensor Utilizing Aggregation-Induced Emission Active Probe for Accurate Arsenite Quantification in Rice Grains

Arsenic (As) constitutes a substantial threat to global ecosystems and public health. An accurate quantification of inorganic arsenite (As(III)) in rice grains is crucial for ensuring food safety and human well-being. Herein, we constructed an electrochemiluminescence (ECL) biosensor utilizing aggregation-induced emission (AIE) active Pdots for the sensitive detection of As(III) in rice. We synthesized tetraphenylethylene-based AIE-active Pdots, exhibiting stable and highly efficient ECL emission in their aggregated states. Owing to the overlap of spectra, we employed an electrochemiluminescence resonance energy transfer (ECL-RET) system, with the Pdots as the donor and black hole quencher (BHQ) as the acceptor. Upon the introduction of As(III), the conformational changes of As(III)-specific aptamer could trigger the detachment of BHQ-labeled DNA aptamer from the electrode surface, leading to the recovery of the ECL signal. The target-induced "signal-on" bioassay enabled the sensitive and specific detection of As(III) with a linear range of 10 pM to 500 nM, with an ultralow limit of detection (LOD) of 5.8 pM/0.4 ppt. These values significantly surpass those of existing sensors designed for As(III) quantification in rice. Furthermore, by employing amylase hydrolysis for efficient extraction, we successfully applied our sensor to measure As(III) in actual rice samples sourced from diverse regions of China. The results obtained using our sensor were in close agreement with those derived from the reference method of HPLC-ICP-MS. This study not only presents a sensitive and reliable method for detecting arsenite but also underscores its potential applications in enhancing food safety, agriculture practices, and environmental monitoring.

Aggregation-Induced Enhanced Electrochemiluminescence from Tris(bipyridine)ruthenium(II) Derivative Nanosheets for the Ultrasensitive Detection of Human Telomerase RNA

The traditional tris(bipyridine)ruthenium(II) complex suffers from the notorious aggregation-caused quenching effect, which greatly compromises its electrochemiluminescence (ECL) efficiency, thus hindering further applications in biosensing and clinical diagnosis. Here, the ultrathin tetraphenylethylene-active tris(bipyridine)ruthenium(II) derivative nanosheets (abbreviated as Ru-TPE NSs) are synthesized through a protein-assisted self-assembly strategy for ultrasensitive ECL detection of human telomerase RNA (hTR) for the first time. The synthesized Ru-TPE NSs exhibit the aggregation-induced enhanced ECL behavior and excellent water-dispersion. Surprisingly, up to a 106.5-fold increase in the ECL efficiency of Ru-TPE NSs is demonstrated compared with the dispersed molecules in an organic solution. The restriction of intramolecular motions is confirmed to be responsible for the significant ECL enhancement. Therefore, this proposed ECL biosensor shows high sensitivity and excellent selectivity for hTR based on Ru-TPE NSs as efficient ECL beacons and the catalytic hairpin assembly as signal amplification, whose detection limit is as low as 8.0 fm, which is far superior to the previously reported works. Here, a promising analytical method is provided for early clinical diagnosis and a new type of efficient ECL emitters with great application prospects is represented.

Electrochemiluminescence Enhancement and Passivation Mitigation in Carbon Nitride Semiconductors via an Integrated Ternary Heterostructure Strategy

In recent years, carbon nitride (CN) has attracted substantial attention in the field of electrochemiluminescence (ECL) applications, owing to its outstanding optical and electronic properties. However, the passivation of CN during the ECL process has contributed to reduced stability and poor repeatability. While some studies have tried to boost ECL performance by altering CN through doping and vacancies, effectively suppressing CN passivation at high potentials continues to be challenge. In this study, the built-in electric field and the Schottky barrier effect is used to expedite the transfer of electrons from CN to the molybdenum disulfide (MoS2 ) conduction band. This transfer deterred excessive electron injection into the CN band, thus mitigating its electrochemical degradation. Moreover, by introducing nickel nanoparticles (Ni NPs) as catalytic active sites, it is facilitated that the decomposition of potassium persulfate (K2 S2 O8 ), thereby enhancing both the stability and intensity of ECL emission. In the end, the application of ternary heterostructure as sensing platform for the cancer biomarker carcinoembryonic antigen (CEA) demonstrated high sensitivity. This research introduces a novel approach to overcome CN passivation, paving the way for more promising applications of CN in energy, environmental, and biosensing fields.

Circular DNAzyme-Switched CRISPR/Cas12a Assay for Electrochemiluminescent Response of Demethylase Activity

DNA nanostructure provides powerful tools for DNA demethylase activity detection, but its stability has been significantly challenged. By virtue of circular DNA with resistance to exonuclease degradation, herein, the circular DNAzyme duplex with artificial methylated modification was constructed to identify the target and output the DNA activators to drive the CRISPR/Cas12a, constructing an "on-off-on" electrochemiluminescence (ECL) biosensor for monitoring the activity of the O6-methylguanine-DNA methyltransferase (MGMT). Specifically, the circular DNAzyme duplex consisted of the chimeric RNA-DNA substrate ring with double activator sequences and two single-stranded DNAzymes, whose catalytic domains were premodified with the methyl groups. When the MGMT was present, the methylated DNAzymes were repaired and restored the catalytic activity to cleave the chimeric RNA-DNA substrates, followed by the output of DNA activators to initiate the CRISPR/Cas12a. Subsequently, the ECL signals of silver nanoparticle-modified SnO2 nanospheres (Ag@SnO2) were recovered by releasing the ferrocene-labeled quenching probes (Fc-DNA) from the electrode surface because of the trans-cleavage activity of CRISPR/Cas12a, thus achieving the specific and sensitive ECL detection of MGMT from 2.5 × 10-4 to 2.5 × 102 ng/mL with a low limit (9.69 × 10-5 ng/mL). This strategy affords novel ideas and insights into research on how to project stable nucleic acid probes to detect DNA demethylases beyond traditional methods.

Development of a Potential-Modulated Electrochemiluminescence Measurement System for Selective and Sensitive Determination of the Controlled Drug Codeine

Codeine is a common analgesic drug that is a pro-drug of morphine. It also has a high risk of abuse as a recreational drug because of its extensive distribution as an OTC drug. Therefore, sensitive and selective screening methods for codeine are crucial in forensic analytical chemistry. To date, a commercial analytical kit has not been developed for dedicated codeine determination, and there is a need for an analytical method to quantify codeine in the field. In the present work, potential modulation was combined with electrochemiluminescence (ECL) for sensitive determination of codeine. The potential modulated technique involved applying a signal to electrodes by superimposing an AC potential on the DC potential. When tris(2,2'-bipyridine)ruthenium(II) ([Ru(bpy)3]2+) was used as an ECL emitter, ECL activity was confirmed for codeine. A detailed investigation of the electrochemical reaction mechanism suggested a characteristic ECL reaction mechanism involving electrochemical oxidation of the opioid framework. Besides the usual ECL reaction derived from the amine framework, selective detection of codeine was possible under the measurement conditions, with clear luminescence observed in an acidic solution. The sensitivity of codeine detection by potential modulated-ECL was one order of magnitude higher than that obtained with the conventional potential sweep method. The proposed method was applied to codeine determination in actual prescription medications and OTC drug samples. Codeine was selectively determined from other compounds in medications and showed good linearity with a low detection limit (150 ng mL-1).

Signal-to-noise ratio to assess magnitude, kinetics and impact on pharmacokinetics of the immune response to an adalimumab biosimilar

Background: The antidrug antibody (ADA) signal-to-noise (S/N) ratio was explored as a novel immunogenicity measure to evaluate the immune response of healthy subjects to a single dose of GP2017, an adalimumab biosimilar. Methodology/results: Bioanalytical methods used for the analysis of ADA S/N ratios and ADA titers were validated for sensitivity, precision and drug interference. ADA S/N ratios strongly correlated with ADA titers. Correlations between ADA area under the curve and ADAmax and pharmacokinetics (PK) were stronger for ADA S/N ratio than for ADA titers. Conclusion: ADA S/N ratio allowed for a more sensitive evaluation of the magnitude and kinetics of the immune response, was better correlated with adalimumab PK and was superior to ADA titers in assessing the impact of the immune response on PK.

Recent Advances in Electrochemiluminescence Biosensors for MicroRNA Detection

Electrochemiluminescence (ECL) as an analytical technology with a perfect combination of electrochemistry and spectroscopy has received considerable attention in bioanalysis due to its high sensitivity and broad dynamic range. Given the selectivity of bio-recognition elements and the high sensitivity of the ECL analysis technique, ECL biosensors are powerful platforms for the sensitive detection of biomarkers, achieving the accurate prognosis and diagnosis of diseases. MicroRNAs (miRNAs) are crucial biomarkers involved in a variety of physiological and pathological processes, whose aberrant expression is often related to serious diseases, especially cancers. ECL biosensors can fulfill the highly sensitive and selective requirements for accurate miRNA detection, prompting this review. The ECL mechanisms are initially introduced and subsequently categorize the ECL biosensors for miRNA detection in terms of the quenching agents. Furthermore, the work highlights the signal amplification strategies for enhancing ECL signal to improve the sensitivity of miRNA detection and finally concludes by looking at the challenges and opportunities in ECL biosensors for miRNA detection.

Engineered Electrochemiluminescence Biosensors for Monitoring Heavy Metal Ions: Current Status and Prospects

Metal ion contamination has serious impacts on environmental and biological health, so it is crucial to effectively monitor the levels of these metal ions. With the continuous progression of optoelectronic nanotechnology and biometrics, the emerging electrochemiluminescence (ECL) biosensing technology has not only proven its simplicity, but also showcased its utility and remarkable sensitivity in engineered monitoring of residual heavy metal contaminants. This comprehensive review begins by introducing the composition, advantages, and detection principles of ECL biosensors, and delving into the engineered aspects. Furthermore, it explores two signal amplification methods: biometric element-based strategies (e.g., HCR, RCA, EDC, and CRISPR/Cas) and nanomaterial (NM)-based amplification, including quantum dots, metal nanoclusters, carbon-based nanomaterials, and porous nanomaterials. Ultimately, this review envisions future research trends and engineered technological enhancements of ECL biosensors to meet the surging demand for metal ion monitoring.

Optics Determines the Electrochemiluminescence Signal of Bead-Based Immunoassays

Electrochemiluminescence (ECL) is an optical readout technique that is successfully applied for the detection of biomarkers in body fluids using microbead-based immunoassays. This technology is of utmost importance for in vitro diagnostics and thus a very active research area but is mainly focused on the quest for new dyes and coreactants, whereas the investigation of the ECL optics is extremely scarce. Herein, we report the 3D imaging of the ECL signals recorded at single microbeads decorated with the ECL labels in the sandwich immunoassay format. We show that the optical effects due to the light propagation through the bead determine mainly the spatial distribution of the recorded ECL signals. Indeed, the optical simulations based on the discrete dipole approximation compute rigorously the electromagnetic scattering of the ECL emission by the microbead and allow for reconstructing the spatial map of ECL emission. Thus, it provides a global description of the ECL chemical reactivity and the associated optics. The outcomes of this 3D imaging approach complemented by the optical modeling provide insight into the ECL optics and the unique ECL chemical mechanism operating on bead-based immunoassays. Therefore, it opens new directions for mechanistic investigations, ultrasensitive ECL bioassays, and imaging.

Electrochemiluminescence Sensor Based on CeO2 Nanocrystalline for Hg2+ Detection in Environmental Samples

The excessive concentration of heavy-metal mercury ions (Hg2+) in the environment seriously affects the ecological environment and even threatens human health. Therefore, it is necessary to develop rapid and low-cost determination methods to achieve trace detection of Hg2+. In this paper, an Electrochemiluminescence (ECL) sensing platform using a functionalized rare-earth material (cerium oxide, CeO2) as the luminescent unit and an aptamer as a capture unit was designed and constructed. Using the specific asymmetric matching between Hg2+ and thymine (T) base pairs in the deoxyribonucleic acid (DNA) single strand, the "T-Hg-T" structure was formed to change the ECL signal, leading to a direct and sensitive response to Hg2+. The results show a good linear relationship between the concentration and the response signal within the range of 10 pM-100 µM for Hg2+, with a detection limit as low as 0.35 pM. In addition, the ECL probe exhibits a stable ECL performance and excellent specificity for identifying target Hg2+. It was then successfully used for spiked recovery tests of actual samples in the environment. The analytical method solves the problem of poor Hg2+ recognition specificity, provides a new idea for the efficient and low-cost detection of heavy-metal pollutant Hg2+ in the environment, and broadens the prospects for the development and application of rare-earth materials.

Synergistic Multieffect Catalytic Amplified Cathodic Electrochemiluminescence Biosensor via Target Binding-Induced Aptamer Conformational Changes for the Ultrasensitive Detection of Synthetic Cathinone

Signal amplification is a powerful approach to increasing the detection sensitivity of electrochemiluminescence (ECL). Here, we developed synergistic multieffect catalytic strategies based on CuCo2O4 nanorod combination of Ag NPs as coreaction accelerators to fabricate an efficient covalent organic framework (PTCA-COF)-based ternary ECL biosensor. Concretely, the high redox reversibility of Co3+/Co2+ and Cu2+/Cu+ would constantly promote the decomposition of S2O82- for ECL emission. Meanwhile, the introduction of Ag NPs with excellent electrocatalytic activity further realized multiple amplification of the ECL signal. Furthermore, the good hydrogen evolution reaction (HER) ability of Ag@CuCo2O4 nanorods could accelerate the proton transmission rate of the system to amplify ECL behavior. In the presence of the target synthetic cathinone 4-chloroethcathinone (4-CEC) as the quenching ECL signal-response probe, the Ferrocene (Fc)-labeled aptamer folded into the conformationally limited stem-loop structure, bringing Fc near the ECL luminophore and resulting in quenched ECL emission. The quenching effect was connected with target-induced aptamer conformational changes and consequently reflected the target concentration. Under optimum conditions, the proposed biosensor realized a highly sensitive assay for 4-CEC with a large dynamic range from 1.0 × 10-12 to 1.0 × 10-6 g/L and a detection limit as low as 2.5 × 10-13 g/L. This study integrated multiple amplification strategies for efficient ECL enhancement, which provided a novel approach to constructing highly bioactive and sensitive sensors.

Development of a P-tau217 Electrochemiluminescent Immunosensor Reinforced with Au-Cu Nanoparticles for Alzheimer's Disease Precaution

To simply and rapidly detect the highly phosphorylated tau protein at threonine 217 (p-tau217) as a precautionary measure against Alzheimer's disease and distinguish it from other neurodegenerative diseases, a novel immunosensor was prepared using luminol as the electrochemiluminescent (ECL) sensing probe reinforced by Au-Cu nanoparticles (Au-Cu NPs). The Au-Cu alloy NPs were prepared via a co-reduction reaction, exhibiting excellent conductivity and catalytic activity. These properties remarkably enhanced the ECL of luminol, providing a suitable background for the sensing response. After the Au-Cu NPs were decorated on the surface of indium tin oxide glass using 3-amino-propyl trimethoxysilane, the antibody of p-tau217 was immobilized via dominant Au-N bonding to enable the biological specificity of the immunosensor. When p-tau217 specifically interacted with an antibody to form an immune complex on the sensing interface, the ECL signal of the sensor was considerably inhibited by the resulting giant biomolecular complex. This complex prevented luminol diffusion to the electrode surface and electron transfer. The resulting immunosensor showed remarkable sensitivity to p-tau217, with a wide linear detection range from 5 to 600 pg/mL. A detection limit of 0.56 pg/mL was achieved, with recoveries in human serum ranging from 92.3 to 109%. This ECL immunosensor demonstrated high sensitivity and specificity toward p-tau217, along with good reproducibility and stability, providing a new approach for clinical research on Alzheimer's disease.

Electrochemiluminescence Sensor Based on CTS-MoS2 and AB@CTS with Functionalized Luminol for Detection of Malathion Pesticide Residues

The accumulation of pesticide residues poses a significant threat to the health of people and the surrounding ecological systems. However, traditional methods are not only costly but require expertise in analysis. An electrochemiluminescence (ECL) aptasensor was developed using chitosan and molybdenum disulfide (CTS-MoS2), along with acetylene black (AB@CTS) for the rapid detection of malathion residues. Due to the weak interaction force, simple composite may lead to uneven dispersion; MoS2 and AB were dissolved in CTS solution, respectively, and utilized the biocompatibility of CTS to interact with each other on the electrode. The MoS2 nanosheets provided a large specific surface area, enhancing the utilization rate of catalytic materials, while AB exhibited excellent conductivity. Additionally, the dendritic polylysine (PLL) contained numerous amino groups to load abundant luminol to catalyze hydrogen peroxide (H2O2) and generate reactive oxygen species (ROS). The proposed ECL aptasensor obtained a low detection limit of 2.75 × 10-3 ng/mL (S/N = 3) with a good detection range from 1.0 × 10-2 ng/mL to 1.0 × 103 ng/mL, demonstrating excellent specificity, repeatability, and stability. Moreover, the ECL aptasensor was successfully applied for detecting malathion pesticide residues in authentic samples with recovery rates ranging from 94.21% to 99.63% (RSD < 2.52%). This work offers valuable insights for advancing ECL sensor technology in future applications.

The Fabrication of a Probe-Integrated Electrochemiluminescence Aptasensor Based on Double-Layered Nanochannel Array with Opposite Charges for the Sensitive Determination of C-Reactive Protein

The effective and sensitive detection of the important biomarker, C-reactive protein (CRP), is of great significance in clinical diagnosis. The development of a convenient and highly sensitive electrochemiluminescence (ECL) aptasensor with an immobilized emitter probe is highly desirable. In this work, a probe-integrated ECL aptamer sensor was constructed based on a bipolar silica nanochannel film (bp-SNF) modified electrode for the highly sensitive ECL detection of CRP. The bp-SNF, modified on an ITO electrode, consisted of a dual-layered SNF film, including the negatively charged inner SNF (n-SNF) and the outer SNF with a positive charge and amino groups (p-SNF). The ECL emitter, tris(bipyridine) ruthenium (II) (Ru(bpy)32+), was stably immobilized in a nanochannel of bp-SNF using the dual electrostatic interactions with n-SNF attracting and p-SNF repelling. The amino groups on the outer surface of bp-SNF were aldehyde derivatized, allowing for the covalent immobilization of recognitive aptamers (5'-NH2-CGAAGGGGATTCGAGGGGTGATTGCGTGCTCCATTTGGTG-3'), leading to the recognition interface. When CRP bound to the aptamer on the recognition interface, the formed complex increased the interface resistance and reduced the diffusion of the co-reactant tripropylamine (TPA) into the nanochannels, leading to a decrease in the ECL signal. Based on this mechanism, the constructed aptamer sensor could achieve a sensitive ECL detection of CRP ranging from 0.01 to 1000 ng/mL, with a detection limit (DL) of 8.5 pg/mL. The method for constructing this probe-integrated ECL aptamer sensor is simple, and it offers a high probe stability, good selectivity, and high sensitivity.

Quartz Crystal Microbalance Platform for SARS-CoV-2 Immuno-Diagnostics

Rapid and accurate serological analysis of SARS-CoV-2 antibodies is important for assessing immune protection from vaccination or infection of individuals and for projecting virus spread within a population. The quartz crystal microbalance (QCM) is a label-free flow-based sensor platform that offers an opportunity to detect the binding of a fluid-phase ligand to an immobilized target molecule in real time. A QCM-based assay was developed for the detection of SARS-CoV-2 antibody binding and evaluated for assay reproducibility. The assay was cross-compared to the Roche electrochemiluminescence assay (ECLIA) Elecsys® Anti-SARS-CoV-2 serology test kit and YHLO's chemiluminescence immunoassay (CLIA). The day-to-day reproducibility of the assay had a correlation of r2 = 0.99, p < 0.001. The assay linearity was r2 = 0.96, p < 0.001, for dilution in both serum and buffer. In the cross-comparison analysis of 119 human serum samples, 59 were positive in the Roche, 52 in the YHLO, and 48 in the QCM immunoassay. Despite differences in the detection method and antigen used for antibody capture, there was good coherence between the assays, 80-100% for positive and 96-100% for negative test results. In summation, the QCM-based SARS-CoV-2 IgG immunoassay showed high reproducibility and linearity, along with good coherence with the ELISA-based assays. Still, factors including antibody titer and antigen-binding affinity may differentially affect the various assays' responses.

LuMA-Functionalized Thermosensitive Hydrogel: A Versatile and Robust Dopamine-Triggered Platform for Diverse Biomolecules Sensing

It is of great significance for the analysis of multiple biomarkers because a single biomarker is difficult to accurately achieve early diagnosis, disease course monitoring, and prognosis evaluation. Herein, a luminescence thermosensitive hydrogel was synthesized by radical polymerization using a methacrylic acid derivative monomer of luminol (LuMA) as luminescent, N-isopropylacrylamide (NIPAM) as thermosensitive monomer, and acrydite-oligonucleotides [dopamine (DA) aptamer, DNA C1, and DNA C2] as recognition elements. The combined DA based on the affinity interaction between the DA and the aptamer on the hydrogel polymer chain was electrochemically oxidized to dopamine quinone during the electrochemiluminescence (ECL) scanning, which effectively quenched the ECL signal of LuMA due to the resonance energy transfer (RET). In addition, the thermosensitive hydrogel showed swelling-collapse characteristics when the temperature was below and above the volume phase transition temperature. Undergoing the collapse process initiated by the temperature, the RET efficiency was further enhanced due to the shortened distance between the energy donor and acceptor, showing a 1.4 times signal amplification and achieving sensitive detection of DA with a limit of detection (LOD) of 1.7 × 10-10 M. For a proof of concept application, coupled with the target-induced release of DA from the DNA-magnetic beads bioconjugations based on duplex-specific nuclease (DSN)-assisted target recycling amplification strategy and DNAzyme cleavage reaction, this ECL-RET approach was successfully used to evaluate multiple targets including miRNA-141 and MUC1 with the LOD of 2.5 aM and 1.6 fg/mL, respectively. The excellent performances of the versatile and robust ECL-RET hydrogel in multiple target sensing showed potential applications in clinical diagnosis and disease therapeutic assay.

Beyond External Light: On-Spot Light Generation or Light Delivery for Highly Penetrated Photodynamic Therapy

External light sources, such as lasers, light emitting diodes (LEDs) and lamps, are widely applied in photodynamic therapy (PDT); however, their use is severely limited by the nature of shallow tissue penetration depth. The recent exploration of light delivery or local generation on tumor sites has attracted much attention, owing to the fact that these systems are significantly endowed with high tissue penetration. In this review, we briefly introduced the principle of "on-spot light generation or delivery systems" in PDT. These systems are divided into different categories: (1) implantable luminescence, (2) mechanoluminescence, (3) electrochemiluminescence, (4) Cerenkov luminescence, (5) chemiluminescence, and (6) bioluminescence. Finally, their applications, advantages, and disadvantages in PDT will be appropriately summarized and further discussed in detail. We believe that this review will provide general guidance for the further design of light generation or delivery systems and clinical studies for PDT-mediated cancer treatments with unparalleled merits.

Highly Efficient Electrochemiluminescence from Imidazole-Based Thermally Activated Delayed Fluorescence Emitters

A family of novel thermally activated delayed fluorescence (TADF) emitters has been synthesized by a straightforward and metal-free synthesis, and structurally characterized. In this work we kept the acceptor moiety, 4-(1H-imidazol-1-yl)benzonitrile, fixed and systemically tested different donors to correlate their photophysical and electrochemical properties with their performance in electrochemiluminescence using both benzoyl peroxide as co-reactant and co-reactant free (annihilation) conditions. Some compounds exceeded the efficiency of the standard [Ru(bpy)3 ]Cl2 by up to 28 times with benzoyl peroxide and 38 times in annihilation. Interestingly, we found that the efficiency is mainly dictated by the electrochemical reversibility of the redox processes rather than by the photophysical properties in terms of photoluminescence quantum yields or excited-state lifetime. In addition, the annihilation electrochemiluminescence efficiency strongly depends on the pulse sequence. The imidazole moiety can be conveniently alkylated, thus allowing the insertion of functional groups, such a carboxylic acid, and enabling practical applications.

Emerging Insights into the Use of Advanced Nanomaterials for the Electrochemiluminescence Biosensor of Pesticide Residues in Plant-Derived Foodstuff

Pesticides have an important role in rising the overall productivity and yield of agricultural foods by eliminating and controlling insects, pests, fungi, and various plant-related illnesses. However, the overuse of pesticides has caused pesticide pollution of water bodies and food products, along with disruption of environmental and ecological systems. In this regard, developing low-cost, simple, and rapid-detecting approaches for the accurate, rapid, efficient, and on-site screening of pesticide residues is an ongoing challenge. Electrochemiluminescence (ECL) possesses the benefits of great sensitivity, the capability to resolve several analytes using different emission wavelengths or redox potentials, and excellent control over the light radiation in time and space, making it a powerful strategy for sensing various pesticides. Cost-effective and simple ECL systems allow sensitive, selective, and accurate quantification of pesticides in agricultural fields. Particularly, the development and progress of nanomaterials, aptamer/antibody recognition, electric/photo-sensing, and their integration with electrochemiluminescence sensing technology has presented the hopeful potential in reporting the residual amounts of pesticides. Current trends in the application of nanoparticles are debated, with an emphasis on sensor substrates using aptamer, antibodies, enzymes, and molecularly imprinted polymers (MIPs). Different strategies are enclosed in labeled and label-free sensing along with luminescence determination approaches (signal-off, signal-on, and signal-switch modes). Finally, the recent challenges and upcoming prospects in this ground are also put forward.

Immunosensor with Enhanced Electrochemiluminescence Signal Using Platinum Nanoparticles Confined within Nanochannels for Highly Sensitive Detection of Carcinoembryonic Antigen

Rapid, highly sensitive, and accurate detection of tumor biomarkers in serum is of great significance in cancer screening, early diagnosis, and postoperative monitoring. In this study, an electrochemiluminescence (ECL) immunosensing platform was constructed by enhancing the ECL signal through in situ growth of platinum nanoparticles (PtNPs) in a nanochannel array, which can achieve highly sensitive detection of the tumor marker carcinoembryonic antigen (CEA). An inexpensive and readily available indium tin oxide (ITO) glass electrode was used as the supporting electrode, and a layer of amino-functionalized vertically ordered mesoporous silica film (NH2-VMSF) was grown on its surface using an electrochemically assisted self-assembly method (EASA). The amino groups within the nanochannels served as anchoring sites for the one-step electrodeposition of PtNPs, taking advantage of the confinement effect of the ultrasmall nanochannels. After the amino groups on the outer surface of NH2-VMSF were derivatized with aldehyde groups, specific recognition antibodies were covalently immobilized followed by blocking nonspecific binding sites to create an immunorecognition interface. The PtNPs, acting as nanocatalysts, catalyzed the generation of reactive oxygen species (ROS) with hydrogen peroxide (H2O2), significantly enhancing the ECL signal of the luminol. The ECL signal exhibited high stability during continuous electrochemical scanning. When the CEA specifically bound to the immunorecognition interface, the resulting immune complexes restricted the diffusion of the ECL emitters and co-reactants towards the electrode, leading to a reduction in the ECL signal. Based on this immune recognition-induced signal-gating effect, the immunosensor enabled ECL detection of CEA with a linear range of 0.1 pg mL-1 to 1000 ng mL-1 with a low limit of detection (LOD, 0.03 pg mL-1). The constructed immunosensor demonstrated excellent selectivity and can achieve CEA detection in serum.

Materials for Electrochemiluminescence: TADF, Hydrogen-Bonding, and Aggregation- and Crystallization-Induced Emission Luminophores

Electrochemiluminescence (ECL) is a rapidly growing discipline with many analytical applications from immunoassays to single-molecule detection. At the forefront of ECL research is materials chemistry, which looks at engineering new materials and compounds exhibiting enhanced ECL efficiencies compared to conventional fluorescent materials. In this review, we summarize recent molecular design strategies that lead to high efficiency ECL. In particular, we feature recent advances in the use of thermally activated delayed fluorescence (TADF) emitters to produce enhanced electrochemiluminescence. We also document how hydrogen bonding, aggregation, and crystallization can each be recruited in the design of materials showing enhanced electrochemiluminescence.

An Exciplex-Based Light-Emission Pathway for Solution-State Electrochemiluminescent Devices

Electrochemiluminescence (ECL) allows the design of unique light-emitting devices that use organic semiconductors in a liquid or gel state, which allows for simpler and more sustainable device fabrication and facilitates unconventional device form-factors. Compared to solid-state organic LEDs, ECL devices (ECLDs) have attracted less attention due to their currently much lower performance. ECLD operation is typically based on an annihilation pathway that involves electron transfer between reduced and oxidized luminophore species; the intermediate radical ions produced during annihilation dramatically reduce device stability. Here, the effects of radical ions are mitigated by an exciplex formation pathway and a remarkable improvement in luminance, luminous efficacy, and operational lifetime is demonstrated. Electron donor and acceptor molecules are dissolved at high concentrations and recombined as an exciplex upon their oxidization/reduction. The exciplex then transfers its energy to a nearby dye, allowing the dye to emit light without undergoing oxidation/reduction. Furthermore, the application of a mesoporous TiO2 electrode increases the contact area and hence the number of molecules participating in ECL , thereby obtaining devices with a very high luminance of 3790 cd m-2 and a 30-fold improved operational lifetime. This study paves the way for the development of ECLDs into highly versatile light sources.

Dual Signal-Enhanced Electrochemiluminescence Strategy Based on Functionalized Biochar for Detecting Aflatoxin B1

Metal-organic frameworks (MOFs) are often used as carriers in the preparation of electrochemiluminescent (ECL) materials, and ECL materials stabilized in the aqueous phase can be prepared by encapsulating chromophores inside MOFs by an in situ growth method. In this study, nanocomposites MIL-88B(Fe)-NH2@Ru(py)32+ with excellent ECL response were prepared by encapsulating Tris(2,2'-bipyridine)ruthenium dichloride (Ru(py)32+) inside MIL-88B(Fe)-NH2 using the one-step hydrothermal method. MIL-88B(Fe)-NH2 possesses abundant amino groups, which can accelerate the catalytic activation process of K2S2O8, and its abundant pores are also conducive to the enhancement of the transmission rate of co-reactant agents, ions, and electrons, which effectively improves the ECL efficiency. In order to obtain more excellent ECL signals, we prepared aminated biochar (NH2-biochar) using Pu-erh tea dregs as precursor and loaded gold nanoparticles (Au NPs) on its surface as substrate material for modified electrodes. Both NH2-biochar and Au NPs can also be used as a co-reactant promoter to catalyze the activation process of co-reactant K2S2O8. Therefore, a sandwich-type ECL immunosensor was prepared based on a dual signal-enhanced strategy for the highly sensitive and selective detection of aflatoxin B1 (AFB1). Under the optimal experimental conditions, the sensitive detection of AFB1 was achieved in the range of 1 pg·mL-1~100 ng·mL-1 with a detection limit of 209 fg·mL-1. The proposed dual signal-enhanced ECL immunosensor can provide a simple, convenient, and efficient method for the sensitive detection of AFB1 in food and agricultural products.

Nanobiosensing Based on Electro-Optically Modulated Technology

At the nanoscale, metals exhibit special electrochemical and optical properties, which play an important role in nanobiosensing. In particular, surface plasmon resonance (SPR) based on precious metal nanoparticles, as a kind of tag-free biosensor technology, has brought high sensitivity, high reliability, and convenient operation to sensor detection. By applying an electrochemical excitation signal to the nanoplasma device, modulating its surface electron density, and realizing electrochemical coupling SPR, it can effectively complete the joint transmission of electrical and optical signals, increase the resonance shift of the spectrum, and further improve the sensitivity of the designed biosensor. In addition, smartphones are playing an increasingly important role in portable mobile sensor detection systems. These systems typically connect sensing devices to smartphones to perceive different types of information, from optical signals to electrochemical signals, providing ideas for the portability and low-cost design of these sensing systems. Among them, electrochemiluminescence (ECL), as a special electrochemically coupled optical technology, has good application prospects in mobile sensing detection due to its strong anti-interference ability, which is not affected by background light. In this review, the SPR is introduced using nanoparticles, and its response process is analyzed theoretically. Then, the mechanism and sensing application of electrochemistry coupled with SPR and ECL are emphatically introduced. Finally, it extends to the relevant research on electrochemically coupled optical sensing on mobile detection platforms.

Screening-Capture-Integrated Electrochemiluminescent Aptasensor Based on Mesoporous Silica Nanochannels for the Ultrasensitive Detection of Deoxynivalenol in Wheat

To prevent the contamination of cereals by mycotoxins, establishing a sensitive and rapid method for the detection of mycotoxins is essential. In this study, a screening-capture-integrated electrochemiluminescence (ECL) aptasensor based on mesoporous silica films (MSFs) was successfully prepared for the ultrasensitive and highly selective detection of deoxynivalenol (DON) in wheat. The narrow nanochannels of MSFs can realize size screening, thereby eliminating the influence of macromolecular substances and providing a pure environment for the signal probe (tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)32+)) to reach the indium tin oxide (ITO) conductive substrate, which significantly improves the anti-interference ability of the screening-capture-integrated ECL sensor. The aptamer (Apt) attached to the surface of the MSFs can specifically capture DON, and the resulting DON-Apt complex has a gated effect on the MSFs, triggering the inhibition of Ru(bpy)32+ in the electrolyte from reaching the ITO surface. Therefore, the ECL intensity of the sensor decreased with increasing DON concentration to achieve a quantitative detection of DON. Under optimized conditions, the linear range of the screening-capture-integrated ECL aptasensor was 0.001-200 μg/kg, and the detection limit was as low as 5.27 × 10-5 μg/kg (S/N = 3). In conclusion, this study developed a screening-capture-integrated ECL aptasensor that combines size screening and specific capture for the detection of DON in wheat, providing a new approach for the early detection of wheat mildew.

Atomically Fe-anchored MOF-on-MOF nanozyme with differential signal amplification for ultrasensitive cathodic electrochemiluminescence immunoassay

The successful application of electrochemiluminescence (ECL) in immunoassays for clinical diagnosis requires stable electrodes and high-efficient ECL signal amplification strategies. Herein, the authors discovered a new class of atomically dispersed peroxidase-like nanozymes with multiple active sites (CoNi-MOF@PCN-224/Fe), which significantly improved the catalytic performance and uncovered the underlying mechanism. Experimental studies and theoretical calculation results revealed that the nanozyme introduced a Fenton-like reaction into the catalytic system and the crucial synergistic effects of definite active moieties endow CoNi-MOF@PCN-224/Fe strong electron-withdrawing effect and low thermodynamic activation energy toward H2O2. Benefiting from the high peroxidase-like activity of the hybrid system, the resultant ECL electrode exhibited superior catalytic activity in the luminol-H2O2 system and resulted in an ≈17-fold increase in the ECL intensity. In addition, plasmonic Ag/Au core-satellite nanocubes (Ag/AuNCs) were designed as high-efficient co-reactant quenchers to improve the performance of the ECL immunoassay. On the basis of the differential signal amplification strategy (DSAS) proposed, the immunoassay displayed superior detection ability, with a low limit of detection (LOD) of 0.13 pg mL-1 for prostate-specific antigen (PSA). The designed atomically anchored MOF-on-MOF nanozyme and DSAS strategy provides more possibilities for the ultrasensitive detection of disease markers in clinical diagnosis.

Quantitation of neurofilament light chain protein in serum and cerebrospinal fluid from patients with multiple sclerosis using the MSD R-PLEX NfL assay

OBJECTIVES

Neurofilament light (NfL) chain is a marker of neuroaxonal damage in various neurological diseases. Here we quantitated NfL levels in the cerebrospinal fluid (CSF) and serum from patients with multiple sclerosis (MS) and controls, using the R-PLEX NfL assay, which employs advanced Meso Scale Discovery® (MSD) electrochemiluminescence (ECL)-based detection technology.

METHODS

NfL was quantitated in samples from 116 individuals from two sites (Ottawa Hospital Research Institute and Mayo Clinic), consisting of patients with MS (n=71) and age- and sex-matched inflammatory neurological controls (n=13) and non-inflammatory controls (n=32). Correlation of NfL levels between CSF and serum was assessed in paired samples in a subset of MS patients and controls (n=61). Additionally, we assessed the correlation between NfL levels obtained with MSD's R-PLEX® and Quanterix's single molecule array (Simoa®) assays in CSF and serum (n=32).

RESULTS

Using the R-PLEX, NfL was quantitated in 99% of the samples tested, and showed a broad range in the CSF (82-500,000 ng/L) and serum (8.84-2,014 ng/L). Nf-L levels in both biofluids correlated strongly (r=0.81, p<0.0001). Lastly, Nf-L measured by MSD's R-PLEX and Quanterix's Simoa assays were highly correlated for both biofluids (CSF: r=0.94, p<0.0001; serum: r=0.95, p<0.0001).

CONCLUSIONS

We show that MSD's R-PLEX NfL assay can reliably quantitate levels of NfL in the CSF and serum from patients with MS and controls, where levels correlate strongly with Simoa.

Washing-Free Electrochemiluminescence Biosensor for the Simultaneous Determination of N6 Methyladenosines Incorporating a Tri-Double Resolution Strategy

We propose a novel washing-free electrochemiluminescence (ECL) biosensor for the simultaneous detection of two types of N6 methyladenosines-RNAs (m6A-RNAs), which are potential cancer biomarkers, on the basis of binding-induced DNA strand displacement (BINSD). The biosensor integrated a tri-double resolution strategy that combined spatial and potential resolution, hybridization and antibody recognition, and ECL luminescence and quenching. The biosensor was fabricated by separately immobilizing two ECL reagents (gold nanoparticles/g-C3N4 nanosheets and ruthenium bipyridine derivative/gold nanoparticles/Nafion) and the capture DNA probe on the two sections of glassy carbon electrode. As a proof of concept, m6A-Let-7a-5p and m6A-miR-17-5p were chosen as model analytes, while m6A antibody-DNA3/ferrocene-DNA4/ferrocene-DNA5 was designed as an m6A-binding probe and DNA6/DNA7 was designed as a hybridization probe with DNA3 to release the quenching probes ferrocene-DNA4/ferrocene-DNA5. The recognition process led to the quenching of the ECL signals from both probes via BINSD. The proposed biosensor has the advantage of being washing-free. The ECL methods using the fabricated ECL biosensor with the designed probes exhibited a low detection limit of 0.03 pM for two m6A-RNAs and high selectivity. This work reveals that this strategy is promising for developing an ECL method for the simultaneous detection of two m6A-RNAs. The proposed strategy could be expanded to develop the analytical methods for the simultaneous detection of other RNA modifications by changing the antibody and hybridization probe sequences.

Novel Electrochemiluminescent Immunosensor Using Dual Amplified Signals from a CoFe Prussian Blue Analogue and Au Nanoparticle for the Detection of Lp-PLA2

Coronary heart disease (CHD) poses an important threat to human health, and its pathogenesis is the formation of atheromatous plaques in coronary ventricles. Compared to other biomarkers, lipoprotein-associated phospholipase A2 (Lp-PLA2), which is involved in multiple processes of atherosclerosis, is a noticeable inflammatory biomarker related to CHD. Herein, using a multifunctional nanocomposite containing a CoFe Prussian blue analogue (PBA) and Au nanoparticles (AuNPs) (AuNPs@CoFe PBA) as a sensing substrate, an electrochemiluminescent (ECL) immunosensor was developed for the highly sensitive detection of Lp-PLA2. Benefiting from the synergistic effect of the PBA and AuNPs, the nanocomposite exhibits excellent peroxidase-like activity and can catalyze the luminol-ECL reaction, amplifying the ECL signal by ∼29-fold. Meanwhile, the enlarged specific surface area of the nanocomposite and the presence of abundant AuNPs allow the immobilization of more antibody proteins, thereby improving the sensing response of the immunosensor. When the target Lp-PLA2 is captured by the antibody on the sensor surface, the sensor emits a reduced ECL signal because of the increased mass and electron transfer resistance due to the formation of the immune complex. Under optimized conditions, the constructed ECL immunosensor exhibits a broad linear range from 1 to 2200 ng/mL and a low detection limit of 0.21 ng/mL. Additionally, the ECL immunosensor exhibits high specificity, stability, and reproducibility. This work provides a new approach to diagnose CHD and broadened the application of the PBA in the field of ECL sensors.

Current Trends in Nanomaterials-Based Electrochemiluminescence Aptasensors for the Determination of Antibiotic Residues in Foodstuffs: A Comprehensive Review

Veterinary pharmaceuticals have been recently recognized as newly emerging environmental contaminants. Indeed, because of their uncontrolled or overused disposal, we are now facing undesirable amounts of these constituents in foodstuff and its related human health concerns. In this context, developing a well-organized environmental and foodstuff screening toward antibiotic levels is of paramount importance to ensure the safety of food products as well as human health. In this case, with the development and progress of electric/photo detecting, nanomaterials, and nucleic acid aptamer technology, their incorporation-driven evolving electrochemiluminescence aptasensing strategy has presented the hopeful potentials in identifying the residual amounts of different antibiotics toward sensitivity, economy, and practicality. In this context, we reviewed the up-to-date development of ECL aptasensors with aptamers as recognition elements and nanomaterials as the active elements for quantitative sensing the residual antibiotics in foodstuff and agriculture-related matrices, dissected the unavoidable challenges, and debated the upcoming prospects.

Electrochemiluminescence of Semiconductor Quantum Dots and Its Biosensing Applications: A Comprehensive Review

Electrochemiluminescence (ECL) is the chemiluminescence triggered by electrochemical reactions. Due to the unique excitation mode and inherent low background, ECL has been a powerful analytical technique to be widely used in biosensing and imaging. As an emerging ECL luminophore, semiconductor quantum dots (QDs) have apparent advantages over traditional molecular luminophores in terms of luminescence efficiency and signal modulation ability. Therefore, the development of an efficient ECL system with QDs as luminophores is of great significance to improve the sensitivity and detection flux of ECL biosensors. In this review, we give a comprehensive summary of recent advances in ECL using semiconductor QDs as luminophores. The luminescence process and ECL mechanism of semiconductor QDs with various coreactants are discussed first. Specifically, the influence of surface defects on ECL performance of semiconductor QDs is emphasized and several typical ECL enhancement strategies are summarized. Then, the applications of semiconductor QDs in ECL biosensing are overviewed, including immunoassay, nucleic acid analysis and the detection of small molecules. Finally, the challenges and prospects of semiconductor QDs as ECL luminophores in biosensing are featured.

Highly Efficient Dual-Color Luminophores for Sensitive and Selective Detection of Diclazepam Based on MOF/COF Bi-Mesoporous Composites

Currently, studies on electrochemiluminescence (ECL) mainly focused on the single emission of luminophores while those on multi-color ECL were rarely reported. Here, a bi-mesoporous composite of the metal-organic framework (MOF)/covalent-organic framework (COF) with strong and stable dual-color ECL was prepared to construct a novel ECL sensor for sensitive detecting targets. A PTCA-COF with excellent ECL performance was loaded with a great amount of another ECL emitter Cu₃(HHTP)₂. Remarkably, the integrated composite had both ECL properties of PTCA-COF at 520 nm and Cu₃(HHTP)₂ at 600 nm wavelengths. Furthermore, Cu₃(HHTP)₂ with good electron transfer ability can greatly enhance the electrical conductivity and promote electrochemical activation. Thus, the simultaneous enhanced two-color ECL intensity and the catalytic properties of the conductive MOF exerted a dual enhancement effect on the ECL signal of the composite. Significantly, diclazepam can not only be adsorbed well on the multi-stage porous structure MOF/COF composite by π-π interactions but also selectively quench the ECL signal of the PTCA-COF, realizing the sensitive detection. The ECL sensor showed a wide detection range from 1.0 × 10^-13 to 1.0 × 10^-8 g/L, and the limit of detection (LOD) was as low as 2.6 × 10^-14 g/L (S/N = 3). The proposed ECL sensor preparation method was simple and sensitive, providing a new perspective for the potential application of multi-color ECL in the sensing field.

Dual-Site Activation Coupling with Schottky Junction Boosts Electrochemiluminescence of Carbon Nitride

Robust electrochemiluminescence (ECL) of carbon nitride (CN) requires efficient electron-hole recombination and suppression of electrode passivation. In this work, Au nanoparticles and single atoms (AuSA+NP) loaded on CN serve as dual active sites that significantly accelerate charge transfer and activate peroxydisulfate. Meanwhile, the well-established Schottky junctions between Au NPs and CN act as electron sinks, effectively trapping over-injected electrons to prevent electrode passivation. As a result, the porous CN modified with AuSA+NP exhibits enhanced and stable ECL emission, with a minimal relative standard deviation of 0.24%. Furthermore, the designed ECL biosensor based on AuSA+NP-CN shows remarkable performance in detecting organophosphorus pesticides. This innovative strategy has the potential to offer new insights into strong and stable ECL emission for practical applications.

Study of an Ultrasensitive Label-Free Electrochemiluminescent Immunosensor Fabricated with a Composite Electrode for Detecting the Glutamate Decarboxylase Antibody

Antibody testing for the glutamic acid decarboxylase 65 antibody (GADA) is widely used as a golden standard for autoimmune diabetes diagnosis, while current methods for antibody testing are not sensitive enough for clinical usage. Here, a label-free electrochemiluminescent (ECL) immunosensor for detecting GADA in autoimmune diabetes is fabricated and investigated. In the designed immunosensor, a composite film including the multiwalled carbon nanotubes (MWCNTs), zinc oxide (ZnO), and Au nanoparticles (AuNPs) was prepared through nanofabrication processes to improve the performance of sensor. The MWCNTs, which can provide a larger specific surface area, ZnO as a good photocatalytic material, and AuNPs that can enhance the ECL signal of luminol and immobilize the GAD65 antigen were applied to prefunctionalize indium tin oxide (ITO) glass based on a nanofabrication process. The GADA concentration was detected using the ECL immunosensor after incubating with GAD65 antigen-coated prefunctionalized ITO glass. After a direct immunoreaction, it is found that the degree of decreased ECL intensity has a good linear regression toward the logarithm of the GADA concentration in the range of 0.01 to 50 ng mL^-1 with a detection limit down to 10 pg mL^-1. Human serum samples positive or negative for GADA all nicely fell in the expected area. The fabricated immunosensor with excellent sensitivity, specificity, and stability has potential capability for clinical usage in GADA detection.

Metal-Organic Frameworks (MOFs)-Based Sensors for the Detection of Heavy Metals: A Review

Metal-organic-frameworks (MOFs) have emerged as promising candidates in different scientific disciplines owing to their intriguing characteristics. Their unique structural properties, including large surface area to volume ratio with multi-functionalities and ultra-high porosity, tunability, uniformity, and easy derivation and fabrication, render them effective materials for sensing applications. The detection of heavy metals in different environmental matrices using various MOF-based sensors is in practice. They include luminescent, electrochemical, electrochemiluminescent, colorimetric, and surface-enhanced Raman scattering, are of great interest. This review elaborates on selected synthetic methods for the fabrication of MOF-based sensors, modification routes for tailoring and enhancing the desired properties, basic characterization techniques, and their limitations in the detection of heavy metals. Also, it emphasizes the use of various types of MOF-based sensors alternatively for the detection of different heavy metals such as Fe(III), Cr(III), Hg(II), Cd(II), and Pb(II) in addition to a normal metal Al(III). A collection of recent references is provided for researchers interested in such applications. Results from the literature have been summarized in tables which give an easy comparison and will help to develop efficient materials.

Newly Developed Electrochemiluminescence Based on Bipolar Electrochemistry for Multiplex Biosensing Applications: A Consolidated Review

Recently, there has been an upsurge in the extent to which electrochemiluminescence (ECL) working in synergy with bipolar electrochemistry (BPE) is being applied in simple biosensing devices, especially in a clinical setup. The key objective of this particular write-up is to present a consolidated review of ECL-BPE, providing a three-dimensional perspective incorporating its strengths, weaknesses, limitations, and potential applications as a biosensing technique. The review encapsulates critical insights into the latest and novel developments in the field of ECL-BPE, including innovative electrode designs and newly developed, novel luminophores and co-reactants employed in ECL-BPE systems, along with challenges, such as optimization of the interelectrode distance, electrode miniaturization and electrode surface modification for enhancing sensitivity and selectivity. Moreover, this consolidated review will provide an overview of the latest, novel applications and advances made in this field with a bias toward multiplex biosensing based on the past five years of research. The studies reviewed herein, indicate that the technology is rapidly advancing at an outstanding purse and has an immense potential to revolutionize the general field of biosensing. This perspective aims to stimulate innovative ideas and inspire researchers alike to incorporate some elements of ECL-BPE into their studies, thereby steering this field into previously unexplored domains that may lead to unexpected, interesting discoveries. For instance, the application of ECL-BPE in other challenging and complex sample matrices such as hair for bioanalytical purposes is currently an unexplored area. Of great significance, a substantial fraction of the content in this review article is based on content from research articles published between the years 2018 and 2023.

Recent Advances in Electrochemiluminescence Biosensors for Mycotoxin Assay

Rapid and efficient detection of mycotoxins is of great significance in the field of food safety. In this review, several traditional and commercial detection methods are introduced, such as high-performance liquid chromatography (HPLC), liquid chromatography/mass spectrometry (LC/MS), enzyme-linked immunosorbent assay (ELISA), test strips, etc. Electrochemiluminescence (ECL) biosensors have the advantages of high sensitivity and specificity. The use of ECL biosensors for mycotoxins detection has attracted great attention. According to the recognition mechanisms, ECL biosensors are mainly divided into antibody-based, aptamer-based, and molecular imprinting techniques. In this review, we focus on the recent effects towards the designation of diverse ECL biosensors in mycotoxins assay, mainly including their amplification strategies and working mechanism.

Bioinspired Single-Atom Sites Enable Efficient Oxygen Activation for Switching Anodic/Cathodic Electrochemiluminescence

Exploring advanced co-reaction accelerators with superior oxygen reduction activity that generate rich reactive oxygen species (ROS) has attracted great attention in boosting luminol-O2 electrochemiluminescence (ECL). However, tuning accelerators for efficient and selective catalytic O2 activation to switch anodic/cathodic ECL is very challenging. Herein, we report that enzyme-inspired Fe-based single-atom catalysts with axial N/C coordination structures (FeN5, FeN4(C) SACs) can generate specific ROS for cathodic/anodic ECL conversion. Mechanistic studies reveal that FeN5 sites prefer to produce highly active hydroxyl radicals and afford direct cathodic luminescence by promoting the cleavage of O-O bonds through N-induced electron redistribution. In contrast, FeN4(C) sites tend to produce superoxide radicals, resulting in inefficient anodic ECL. Benefiting from the enhanced cathodic ECL, FeN5 SAC-based immunosensor was constructed for the sensitive detection of cancer biomarkers.