Electrogenerated chemiluminescence and its biorelated applications

Mesostructured Silica Xerogel-Encapsulated Gold Nanoclusters as an Electrochemiluminescence Emitter Combined with a DNA Walker Amplification Strategy for Detection of Ochratoxin A

Gold nanoclusters (AuNCs) exhibit unique optical properties and satisfactory biocompatibility, enabling them as highly promising electrochemiluminescence (ECL) emitters. However, the low ECL efficiency, resulting from the free movement of ligands, significantly hinders the development of AuNCs in the sensing field. In this work, polyelectrolytes were utilized to encapsulate AuNCs within the mesostructured silica xerogel, forming mesostructured silica xerogel-encapsulated gold nanoclusters (AuNCs@MSX). The space-confinement effect of the MSX and the uniform spatial distribution of encapsulated AuNCs reduced energy loss and the self-quenching effect. Compared with the aggregated AuNCs, the ECL efficiency of AuNCs@MSX increases by more than 2-fold. Meanwhile, the quantum yield can reach 16.98%. Furthermore, based on the ECL-resonance energy transfer (ECL-RET), an "on-off" ECL biosensor was designed. By the integration of a DNA walker cyclic amplification strategy, the exonuclease III (Exo III)-assisted biosensor enabled precise detection of ochratoxin A (OTA). As expected, the ECL biosensor exhibited an ideal linear ranging from 0.001 to 100 ng/mL, achieving a low detection limit of 0.31 pg/mL. The results confirm that encapsulating AuNCs in MSX to enhance ECL efficiency is a viable approach for preparing emitters in trace biomarker detection.

Exploring Surface State and Exciplex Dominated Aggregation Induced Electrochemiluminescence of Graphene Quantum Dots Prepared via Electrochemical Exfoliation

Graphene quantum dots (GQDs) have emerged as promising materials for electrochemiluminescence (ECL) applications due to their unique optical and electronic properties. In this study, GQDs were synthesized via electrochemical exfoliation of graphite in a constant current density mode, enabling scalable production with controlled size and surface functionalization. GQDs-4 and GQDs-20, synthesized at applied current densities of 4 mA/cm2 and 20 mA/cm2 to the graphite electrode, respectively, were investigated on roles of surface states and exciplex dominated aggregation-induced emission (AIE) in their ECL performance. GQDs-4 obtained an absolute ECL quantum efficiency of 0.0012 %±0.0002 %. GQDs-20, with a smaller particle size, achieved an absolute ECL quantum efficiency of 0.028±0.002 %, demonstrating high efficiency in converting electrons into photons. While GQDs-4 exhibited minor intensity in PL and ECL, they displayed a similar emission spectrum to GQDs-20 in the ECL process. This finding highlights the significant role of surface states and AIE in influencing the emission properties of GQDs, independent from core-state transitions. These results provide critical insights into the mechanisms governing GQD-based ECL and offer pathways for optimizing these materials for use in biosensing, optoelectronics, and imaging applications. Keywords: Electrochemiluminescence, Graphene Quantum Dots, Exciplex, Surface States, Multi-color Emission.

Signal Enhancement of Luminol-Based Electrochemiluminescence Systems and Their Applications

Electrochemiluminescence (ECL) has emerged as a powerful analytical tool owing to its low background, high sensitivity, and wide dynamic range. Luminol, a commonly used ECL emitter, is widely applied in ECL-based analysis due to its low triggering potential, cost-effectiveness, and low toxicity. Despite the significant advantages of the luminol ECL system, its relatively low luminescence efficiency limits its application in high-sensitivity detection. As a result, numerous strategies have been proposed to enhance the luminol ECL signal intensity. This review summarizes four typical ECL signal amplification strategies and analyzes their roles in improving the effectiveness of luminol-based ECL signals. Furthermore, the applications of luminol ECL in fields such as sensing, imaging analysis, and material characterization are discussed. Finally, the future research directions and potential applications of the luminol ECL system are highlighted.

Electrogenerated Chemiluminescence Coupled with Molecularly Imprinted Polymer for Sensitive and Selective Detection of N,N-Dimethyltryptamine

A simple and efficient approach that combined electrogenerated chemiluminescence (ECL) and molecularly imprinted polymers (MIPs) for selective and sensitive detection of the hallucinogenic drug N,N-dimethyltryptamine (DMT) was developed. ECL, one of the most sensitive analytical techniques for ultratrace analyte detection, offers the advantage of light-free spectroscopic analysis initiated by electrochemistry. MIPs, on the other hand, provide specific binding sites, allowing the target analyte to become selectively imprinted within the polymer matrix. In this study, an ECL coupled-MIP sensor was fabricated using para-aminobenzoic acid (p-ABA) as the monomer and DMT as the template molecule. The MIP was electropolymerized onto a glassy carbon electrode coated with a Nafion film entrapping [Ru(bpy)3]2+ species. Following elution, the imprinted sites were reoccupied by DMT, generating ECL signals in a phosphate buffered solution during anodic potential scanning. The ECL-MIP sensor demonstrated a wide dynamic range for DMT detection, from 0.5 to 300 μM, with an estimated detection limit of 0.5-1.0 μM (S/N = 3). The sensor's reproducibility, stability, and selectivity were also evaluated. Finally, density functional theory was employed to investigate the structure-property relationship of the p-ABA-DMT interaction. This work demonstrated the potential of ECL coupled with MIP technology for identifying structurally related molecules, achieving enhanced selectivity with a simple and cost-effective design.

Spatial Profiling of Multiple Enzymatic Activities at Single Tissue Sections via Fenton-Promoted Electrochemiluminescence

Profiling multiple enzymatic activities in tissue is crucial for understanding complex metabolic and signaling networks, yet remains a challenge with existing optical microscopies. Here, we developed a Fenton-promoted luminol electrochemiluminescence (ECL) imaging method to achieve the spatial mapping of multiple enzymatic activities within a single tissue section. This method quantitatively visualizes individual enzymatic activity by combining the enzymatic conversion of substrates with the chemical confinement of the locally produced hydrogen peroxide. To achieve high-resolution spatial imaging by limiting the diffusion (∼500 μm) of hydrogen peroxide, iron oxide nanoparticles were coated on the tissue surface to initiate the Fenton process, locally converting hydrogen peroxide into short-lived hydroxyl radicals with a nanometer-scale diffusion range. The Fenton-promoted ECL emission is confined at the enzymatic conversion sites, offering unprecedented spatial visualization of four tumor-associated oxidases within a single tissue section. Colocalization revealed a synergistic effect between lysyl oxidase and quiescin sulfhydryl oxidase on post-translational modifications of tumor extracellular matrix proteins, along with a previously undiscovered interaction with amiloride-sensitive amine oxidase, which could not be distinguished based on expressions or single enzymatic activity alone. This approach offers a novel activity-based protein profiling tool at the tissue level, providing new data for future enzynomic research and multimodal imaging.

Target-induced reconstruction of Ru(bpy)32+-loaded gold nanocage for one-step highly sensitive detection of Hg2

In this work, Ru(bpy)32+-loaded gold nanocage (AuNCs) (Ru-AuNCs) was prepared and found to display a distinct property of electrochemiluminescence (ECL) enhancement under mercury ions (Hg2+) interaction. Based on this, we designed a screen-printed bipolar electrode-ECL (SPBPE-ECL) sensing platform by coupling with the thymine-Hg2+-thymine (T-Hg2+-T) binding pattern for one-step highly sensitive detection of Hg2+. This ECL sensor showed a wide linear detection range (0.75 - 850 μg L-1) and low detection limit (0.1290 μg L-1) toward Hg2+, with a one-step detection procedure and disposable feature, displaying potential applicability in the point-of-care-testing (POCT) of Hg2+ in the environment. In addition, the Hg2+-mediated ECL signal enhancement mechanism of Ru-AuNCs was also investigated. It was confirmed that Hg2+ interaction etched the cage structure of Ru-AuNCs, which sped up the release of more Ru(bpy)32+ around the sensing electrode. Furthermore, Au-Hg alloy structure was formed on the surface of Ru-AuNCs, which also improved the ECL signal. This target-induced in-situ sensing material surface reconstruction strategy would provide a better design concept for the construction of ECL POCT sensor.

Endogenous Free-Electron-Involved Coreactant-Free Electrochemiluminescence from Nanoclusters and Its Immunoassay Application

All of the commercialized electrochemiluminescence (ECL) immunoassays are automatically conducted at +1.40 V (vs Ag/AgCl) in the coreactant route. To alleviate the exogenous effect of coreactants and simplify the operation procedures, herein, a sulfur-vacancy-involved and free electron strategy is proposed to exploit Au nanoclusters (NCs) as anodic electrochemiluminophores and perform a coreactant-free immunoassay. The deficient coordination between the sulfhydryl of Met and the Au core might induce the departure of partial S atoms and enable Met-capped AuNCs (Met-AuNCs) with a sulfur-vacancy-involved electron-rich nature. The electron-rich nature tends to endow Met-AuNCs with unpaired endogenous free electrons, which can directly combine exogenous holes for light emitting. Coreactant-free ECL at around +0.86 V is consequently and conveniently achieved by merely oxidizing Met-AuNCs at the anode. The coreactant-free ECL is qualified to determine human carcinoembryonic antigen from 10 to 5000 pg/mL with a limit of detection of 5 pg/mL. Electron paramagnetic resonance provides clear evidence that endogenous free electrons within Met-AuNCs play an important role in the generation of coreactant-free ECL. This sulfur-vacancy-involved and free electron strategy is promising for designing nanoelectrochemiluminophores with improved immunoassay performance.

Tetrahedral DNA nanostructures, graphene and carbon nanodots-based electrochemiluminescent biosensor for BRCA1 gene mutation detection

In this study, we present a novel electrochemiluminescent DNA biosensor designed for detecting breast cancer type 1 (BRCA1) gene mutations. The biosensor integrates graphene nanosheets (Graph-NS), tetrahedral DNA nanostructures (TDNs), and carbon nanodots (CNDs) to enhance sensitivity and specificity. Graph-NS are employed to structure the transducer and serve as a platform for DNA immobilization. TDNs are engineered with a BRCA1 gene-specific capture probe located at the apex (TDN-BRCA1), facilitating efficient biorecognition. Additionally, the basal vertices of TDNs are functionalized with amino groups, enabling their attachment to the CSPE/Graph-NS surface via amino-graphene interaction. This platform effectively identifies single-base mutations in the BRCA1 gene utilizing synthesized CNDs as a coreactant and [Ru(bpy)3]2+ as the luminophore through the coreactant pathway. The developed biosensor demonstrates exceptional sensitivity and can detect a single mutation in the BRCA1 gene. Furthermore, it has been successfully validated in real samples obtained from breast cancer patients, showcasing a remarkable detection limit of 1.41 aM.

Impacts of electrogenerated chemiluminescence mechanism on the emission spectra and intensities

In this mini-review, recent progress in electrogenerated chemiluminescence (ECL) reported by our group is mainly introduced. First, the general principles of ECL and standard molecules for ECL are described, and then the ECL properties of thermally activated delayed fluorescence (TADF) molecules, pyrrolopyrrole aza-BODIPYs (PPABs), pyrene (Py) and its derivative, Eu(III) and Tb(III) complexes are introduced. The ECL efficiency of TADF molecules is increased by spin up-conversion from the T1 to S1 state, and that of PPABs is incremented kinetically due to the slower rate for the T1 state formation than the S1 state formation. The excimer formation mechanism of Py and its derivative in ECL is discussed. It is shown that very sharp ECL spectra can be obtained from Eu(III) and Tb(III) complexes. Furthermore, intense ECL for binary mixed systems using Ir(ppy)3 and electron donor or acceptor molecules is described. These results provide insight into how the ECL mechanism affects emission intensity, efficiency, and spectrum.

The electrochemical modulation of single molecule fluorescence

Recently it has been shown that electrochemistry, instead of using high intensity lasers, can be used to modulate the intensity of emission of fluorophores and even switch fluorophores between their ON and OFF states as required for single molecule localisation microscopy. This modulation of fluorescence does not necessarily correlate with direct oxidation and reduction of the dyes. Questions arise from this unexpected observation related to what is the electrochemistry that occurs, what are the important variables in switching fluorophores electrochemically and what range of dyes can be modulated with electrochemistry. Herein we seek to answer some of these questions. We demonstrate how to effectively modulate the fluorescence intensity of organic dye-labelled cell samples on an indium tin oxide surface using electrochemistry with redox-active mediators present in an oxygen scavenger buffer. We showed the electrochemical fluorescence modulation is sensitive to the applied potential and the excitation laser intensity, indicating the possibility of coupled photochemical and electrochemical reactions occurring. We also compared the electrochemical fluorescence modulation of representative oxazine, rhodamine, and cyanine dyes using ATTO 655, Alexa Fluor 488, and Alexa Fluor 647. Different dyes with distinctly different structural cores show fluorescence modulation to different extents. The electrochemical fluorescence modulation will be applicable in fluorescence imaging techniques as well as biosensing.

Surface Charge Redistribution-Induced Electrochemiluminescence Enhancement of Gold Nanoclusters: The Novel Generation of Efficient Illuminants

Herein, we developed the agmatine/6-aza-2-thiothymine templated gold nanoclusters (Agm/ATT-Au NCs) as a novel electrochemiluminescence (ECL) illuminant, which exhibited high ECL in the annihilation path via the newly defined surface charge redistribution-induced ECL enhancement (SCRIE). Impressively, the electrochemical redox reaction of Agm/ATT-Au NCs was enhanced owing to the boosted electron transfer kinetics of the illuminant by the positively charged Agm-triggered surface charge redistribution of ATT-Au NCs, resulting in an ∼110-fold higher ECL signal of Agm/ATT-Au NCs than ATT-Au NCs. This work digs deep into the electrogenerated process of the annihilation mechanism to direct the rational design of an efficient illuminant. Moreover, the Agm/ATT-Au NCs as a powerful illuminant was successfully applied in a highly sensitive bioassay platform for detecting glial fibrillary acidic protein (GFAP) with the detection limit down to 27.5 ag/mL, an intense organic light-emitting diode (OLED), and high-definition ECL imaging.

Infrared Electrochemiluminescence from A Water-Soluble Anion-π+ Emitter for Sensitive Perfluorooctanoic Acid Sensing

Electrochemiluminescence (ECL) analysis stands out among various analytical methods due to its exceptional sensitivity and accuracy. However, the poor solubility of most ECL probes limits their effectiveness in aqueous environments. To address this challenge, we developed a water-soluble anion-π+ ECL luminophore, DPBC-OTS. With its remarkable water solubility and electron transfer characteristics, the study detailed revealed that DPBC-OTS exhibited excellent ECL performance in the infrared region. Additionally, leveraging ion electrostatic interactions, the DPBC-OTS-based ECL system achieved ultrasensitive detection of the organic fluorine pollutant PFOA, with a detection limit as low as 28.9 nM. This study not only enhances ECL performance in aqueous media through the introduction of the anion-π+ compound but also highlights the significant potential of ECL in the trace detection of organic fluorine pollutants.

One Step Visual Homogeneous Immunoassay of a Rheumatoid Arthritis Biomarker in Serum via Target-Regulated Steric Hindrance and Competitive Recognition

Homogeneous analysis techniques offer several advantages as alternatives to heterogeneous immunoassays, such as simplicity and rapidity. In this study, a visual homogeneous immunoassay without a labeling process was developed based on target-induced steric hindrance to regulate competitive recognition mechanism. Specifically, as the analyte concentration varies, the change of microenvironment based on steric hindrance could affect the recognition of Cu2+ by signal probes. Herein, taking anticyclic citrullinated peptide antibody (anti-CCP) as an example, the method was verified. Cu2+ can bind to histidine (His), as well as signal probes. Cyclic citrullinated peptide containing His was served as the capture antigen, and the fluorescence of both CdTe quantum dots and calcein can be quenched by Cu2+. Then, this quenching effect can be regulated by the change of steric hindrance, so that anti-CCP analysis can be realized. The limit of detection of anti-CCP was as low as 0.002 and 0.01 U/mL in fluorescence mode and red, green, and blue (RGB) mode, respectively. Furthermore, clinical practicality was validated through 46 clinical samples, including rheumatoid arthritis patients (n = 28) and healthy donors (n = 18), with the assay demonstrating a sensitivity and specificity of 96.4% and 88.9%, respectively. Indeed, the results were consistent with those of clinical electrochemiluminescence immunoassays and digital radiography images. Overall, this method shows great potential for clinical application and offers a universal template for a label-free homogeneous immunoassay.

Highly Efficient Aggregation-induced Electrochemiluminescence Performance of Covalent Organic Frameworks with Electron-rich Conjugated Structures

Since aggregation-induced electrochemiluminescence (AIECL) luminophore overcomes the restriction of aggregation-caused quenching in solid luminescent materials, AIECL luminophore has become a promising material in the field of electrochemiluminescence (ECL) engineering. However, the lack of ECL emitters with high AIECL performance limits its wide application. Herein, imine-linked covalent organic frameworks (COFs) with C4 symmetrical tetraphenyl ethylene and C2 symmetrical five-membered heteroaromatic monomers are designed as ECL emitter in aqueous media. Significantly, the ECL intensity of COFs with terthienyl units (TTA-TAPE) is 206 times that of COFs with furan units in the presence of tri-n-propylamine (TPrA), which is the result of enhancing ECL signals by increasing the thiophene units and π-π conjugation of COFs. Furthermore, the ECL mechanism of these COFs is vested in the bandgap model. Thus, the study provides a strategy for designing highly efficient ECL-active COFs emitters with excellent AIECL efficiency.

Remote On-Paper Electrochemiluminescence-Based High-Safety and Multilevel Information Encryption

The escalating needs in information protection underscore the urgency of developing advanced encryption strategies. Herein we report a novel chemical approach that enables information encryption by on-paper electrochemiluminescence (ECL). Dendritic porous silica nanospheres modified with polyetherimide and bovine serum albumin were prepared as the chemical ink to write the secret message on a paper. Attaching the paper to an electrode, immersing it in a solution containing tris(2,2'-bipyridyl)ruthenium (Ru(bpy)3 2+) and then applying a suitable voltage, a remote "catalytic route" electrochemical reaction produces ECL that functions as the key to decrypt and visualize the message by imaging. In addition, proteins can be also used as the biological ink to write the secret message, which is then decrypted by a combined use of immunochemistry and ECL imaging as two keys. We believe the ECL-based strategy holds great promise in high-safety and multilevel information encryption, as it is protected not only by encoding, like conventional invisible inks, but also by the unique ECL decoding approach.

Proline-Selective Electrochemiluminescence Detecting a Single Amino Acid Variation Between A1 and A2 β-Casein Containing Milks

The proline amino acid and prolyl residues of peptides/proteins confer unique biological and biochemical properties that motivates the development of proline-selective analysis. The study focuses on one specific class of problem, the detection of single amino acid variants involving proline, and reports a Pro-selective electrochemiluminescence (ECL) method. To develop this method, the A1-/A2- variants of milk's β-casein protein are investigated because it is a well-established example and abundant samples are readily available. Specifically, β-casein has 209 amino acids with 34 (or 35) proline residues: the A1-variant has a Pro-to-His substitution at position 67 (relative to the A2 variant). The study shows that proline's strong luminescence allows the generic discrimination of: Pro from other amino acids; an A2-oligopeptide from an A1-oligopeptide; the A2-β-casein variant from the A1-variant; and commercially-available A2 milks from A1-containing regular milks. The evidence indicates that luminescence depends on proline content and accessibility, as well as signal quenching. Compared to conventional immunoassays, the ECL method is simple, rapid, and inexpensive. Further, the ECL-method is Pro-selective (vs molecularly-selective like typical immunoassays) which should make it broadly useful for studying the role of proline in biology and especially useful for tracking the digestion of proline-rich proteins in the diet.

High -Sensitive Detection of Malachite Green Based on Surface-Enhanced Electrochemiluminescence

This article introduces a novel unlabeled surface-enhanced electrochemiluminescence (SEECL) sensor for malachite green (MG) detection. The SEECL sensor was prepared by modifying the Ru(bpy)32+ doped gold-SiO2 core-shell nanocomposites (Au@SiO2-Ru(bpy)32+) on the gold electrode. Ru(bpy)32+ of nanocomposites can not only emit electrochemiluminescence (ECL) with electrochemical reaction, but also induce the local surface plasmon resonance (LSPR) of gold core. That is beneficial to enhance the ECL signa of sensor. However, in the existence of MG, the luminescence of sensor would be quenched by the fluorescence resonance energy transfer (FRET) between MG and Ru(bpy)32+. In this paper, both fluorescence and ECL of the Au@SiO2-Ru(bpy)32+ were investigated for MG detection. And the results show that the SEECL sensor has high sensitive to MG. Under the optimal experimental conditions, the minimum detection concentration could be achieved about 1.0 nM of MG, which fully meets the China national standard detection requirements of veterinary drug residue in seafood.

Enhanced Protein Immobilization Capacity through Grafting of Poly(sodium methacrylate) onto Magnetic Bead Surface

This study aims to improve the signal-to-noise ratio (SNR) of chemiluminescence immunoassay (CLIA) by increasing the amount of protein immobilized on the surface of the magnetic bead (MB). Proteins are macromolecules with three-dimensional structures, and merely increasing the density of functional groups on the two-dimensional surface of the MB cannot significantly enhance protein immobilization. Therefore, we grafted spatially extended functional polymer to not only increase the density of functional groups on the MB surface but also expand their distribution in three-dimensional space, ultimately increasing protein immobilization. We synthesized poly(sodium methacrylate) (P-COONa) using atom transfer radical polymerization (ATRP) and examined its grafting density and behavior on the MB surface via nuclear magnetic resonance (NMR). Dynamic light scattering (DLS) results showed that grafting P-COONa increased the hydrodynamic radius of MBs, indicating its spatial extension. Next, we investigated the effect of P-COONa grafting on the immobilization of bovine serum albumin (BSA). Experimental results demonstrated that P-COONa grafting increased BSA immobilization from 19.9 to 42.92 mg/g. Finally, we evaluated the impact of P-COONa grafting on the SNR by detecting the D-dimer biomarker using CLIA. The results indicated that P-COONa grafting increased the low-value-to-background and high-value-to-background ratios by 4.21× and 17.17×, respectively. This study demonstrates that grafting spatially extended P-COONa increases protein immobilization on the MB surface, significantly improving the SNR of CLIA.

Ru-OH-Zr Site over Metal-Organic Frameworks Boosts Coreactant Activation for Efficient Electrochemiluminescence

Metal-organic frameworks (MOFs) are promising electrochemiluminescent (ECL) nanoemitters. Great endeavors have been made to optimize the inherent luminescent properties, yet most MOFs suffer from poor coreactant activation ability, resulting in limited ECL. Therefore, it is urgent to integrate and design efficient catalytic centers within MOFs. Herein, we decorate atomically dispersed Ru onto the Zr-nodes of NU-1000, constructing Ru-OH-Zr centers to synergistically activate coreactants. The proposed NU-Ru enables 7.8 times enhancement in ECL efficiency. Theoretical investigations reveal that Ru atoms with strong electronegativity not only accelerate the charge transfer but also provide superior Lewis acid sites for promoting peroxysulfate binding and activation. Assisted by Bro̷nsted acid groups, the Ru-OH-Zr centers efficiently split the O-O bonds to enrich radicals through a proton-coupled electron transfer process. Furthermore, a direct mode sensor was established for sensitive organophosphorus pesticide analysis based on the interaction between the P═O bond and Lewis acid sites.

Photoluminescent and Electrochemiluminescent Detection of Fe3+ Using Cyclometalated Iridium Complexes via Fe3+-Catalyzed Hydrolysis

Ferric ion (Fe3+) is a biologically abundant and important metal ion. We developed several cyclometalated iridium complex-based molecular sensors (1, ppy-1, 1-phen, 1 a, and 1_OMe) for the detection of Fe3+ using an acetal moiety as the reaction site. The acetal moiety in iridium complexes undergoes Fe3+-catalyzed hydrolysis and subsequent formation of a formyl group, resulting in turn-off photoluminescent and electrochemiluminescent responses. Sensor 1 showed excellent selectivity toward Fe3+ over other biologically important metal ions. Furthermore, we compared the performance of the sensors based on the structural differences of the iridium complexes, and revealed a relationship between the structure and chemical properties through electrochemical experiments and computational calculations.

Laser-Treated Screen-Printed Carbon Electrodes for Electrochemiluminescence imaging

Electrochemiluminescence (ECL) is nowadays a powerful technique widely used in biosensing and imaging, offering high sensitivity and specificity for detecting and mapping biomolecules. Screen-printed electrodes (SPEs) offer a versatile and cost-effective platform for ECL applications due to their ease of fabrication, disposability, and suitability for large-scale production. This research introduces a novel method for improving the ECL characteristics of screen-printed carbon electrodes (SPCEs) through the application of CO2 laser treatment following fabrication. Using advanced ECL microscopy, we analyze three distinct carbon paste-based electrodes and show that low-energy laser exposure (ranging from 7 to 12 mJ·cm-2) enhances the electrochemical performance of the electrodes. This enhancement results from the selective removal of surface binders and contaminants achieved by the laser treatment. We employed ECL microscopy to characterize the ECL emission using a bead-based system incorporating magnetic microbeads, like those used in commercial platforms. This approach enabled high-resolution spatial mapping of the electrode surface, offering valuable insights into its electrochemical performance. Through quantitative assessment using a photomultiplier tube (PMT), it was observed that GST electrodes could detect biomarkers with high sensitivity, achieving an approximate detection limit (LOD) of 11 antibodies per μm2. These findings emphasize the potential of laser-modified GST electrodes in enabling highly sensitive electrochemiluminescent immunoassays and various biosensing applications.

Enhanced Electrochemiluminescence Detection of Dopamine Using Antifouling PEDOT-Modified SPEs for Complex Biological Samples

Detecting medically important biomarkers in complex biological samples without prior treatment or extraction poses a major challenge in biomedical analysis. Electrochemical methods, specifically electrochemiluminescence (ECL), show potential due to their high sensitivity, minimal background noise, and straightforward operation. This study investigates the ECL performance of screen-printed electrodes (SPEs) modified with the conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT) and its derivatives for dopamine (DA) detection. PEDOT modification significantly enhances ECL intensity, improves sensitivity, and expands the linear range for DA detection. Functionalizing PEDOT with ethylene glycol (EG) further enhances stability, specificity, and resistance to interferences for DA detection. These modified SPEs demonstrate the linear range of 1-200 μM and a detection limit as low as 0.887 nM (S/N = 3), surpassing many previous studies using SPEs. Moreover, the PEDOT-EG4-OMe-modified SPEs can reliably detect DA in solutions with high protein concentrations or artificial cerebrospinal fluid. These results suggest that the PEDOT derivative-modified SPE can serve as reusable and sensitive DA sensors in complex biological environments, highlighting the potential of the ECL system for a range of challenging applications.

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.

Coordination-Based Site-Specific Labeling Strategy for Electrogenerated Chemiluminescence Biosensing of Matrix Metalloproteinase 2

Matrix metalloproteinase 2 (MMP-2) is an important biomarker for some diseases. Herein, one first-case coordination-based site-specific labeling strategy is proposed for electrogenerated chemiluminescence (ECL) biosensing of MMP-2 by employing an iridium(III) solvent complex as a signal reagent and a histidine (His)-containing peptide as a molecular recognition substrate. One ECL probe was prepared via coordination labeling of the His-containing peptide with one iridium(III) solvent complex ([(3-(2-pyridyl)benzoic acid)2Ir(DMSO)Cl], Ir1-DMSO). High ECL efficiency and good cleavage ability by MMP-2 were obtained for the ECL probe. By combining the high sensitivity of the ECL method, the good specificity of the peptide, and the simpleness of the magnetic bead-based assay, one "cleavage-magnetic enrichment type" ECL biosensing method was developed to detect MMP-2. MMP-2 can be sensitively detected in the linear range of 1.0-10 ng/mL with a limit of quantification of 1.0 ng/mL and a limit of detection of 0.3 ng/mL. Moreover, the ECL biosensing method was successfully applied for the determination of MMP-2 in serum samples with recoveries from 98.0% ± 8.0% to 108.0% ± 6.0%. Further, high affinity (Kd = 0.11 nM) was obtained for the Ir1-DMSO-labeled His-containing peptide and MMP-2. This work may pave the way for the labeling of His-containing biomolecules with an iridium(III) solvent complex and provides a promising method in point-of-care testing of MMP-2.

Recent Advances in Electrochemiluminescence Visual Biosensing and Bioimaging

Electrochemiluminescence (ECL) is one of the most powerful techniques that meet the needs of analysis and detection in a variety of scenarios, because of its highly analytical sensitivity and excellent spatiotemporal controllability. ECL combined with microscopy (ECLM) offers a promising approach for quantifying and mapping a wide range of analytes. To date, ECLM has been widely used to image biological entities and processes, such as cells, subcellular structures, proteins and membrane transport properties. In this review, we first introduced the mechanisms of several classic ECL systems, then highlighted the progress of visual biosensing and bioimaging by ECLM in the last decade. Finally, the characteristics of ECLM were summarized, as well as some of the current challenges. The future research interests and potential directions for the application of ECLM were also outlooked.

Emerging trends and recent advances in MXene/MXene-based nanocomposites toward electrochemiluminescence sensing and biosensing

Electrochemiluminescence (ECL) sensing systems have surged in popularity in recent years, making significant strides in sensing and biosensing applications. The realization of high-throughput ECL sensors hinges on the implementation of novel signal amplification strategies, propelling the field toward a new era of ultrasensitive analysis. A key strategy for developing advanced ECL sensors and biosensors involves utilizing novel structures with remarkable properties. The past few years have witnessed the emergence of MXenes as a captivating class of 2D materials, with their unique properties leading to exploitation in diverse applications. This review provides a comprehensive summary of the latest advancements in MXene-modified materials specifically engineered for ECL sensing and biosensing applications. We thoroughly analyze the structure, surface functionalization, and intrinsic properties of MXenes that render them exceptionally suitable candidates for the development of highly sensitive ECL sensors and biosensors. Furthermore, this study explores the broad spectrum of applications of MXenes in ECL sensing, detailing their multifaceted roles in enhancing the performance and sensitivity of ECL (bio)sensors. By providing a comprehensive overview, this review is expected to promote progress in related areas.

Electrogenerated chemiluminescence from luminol-labelled microbeads triggered by in situ generation of hydrogen peroxide

We developed a sensing strategy that mimics the bead-based electrogenerated chemiluminescence immunoassay. However, instead of the most common metal complexes, such as Ru or Ir, the luminophore is luminol. The electrogenerated chemiluminescence of luminol was promoted by in situ electrochemical generation of hydrogen peroxide at a boron-doped diamond electrode. The electrochemical production of hydrogen peroxide was achieved in a carbonate solution by an oxidation reaction, while at the same time, microbeads labelled with luminol were deposited on the electrode surface. For the first time, we proved that was possible to obtain light emission from luminol without its direct oxidation at the electrode. This new emission mechanism is obtained at higher potentials than the usual luminol electrogenerated chemiluminescence at 0.3-0.5 V, in conjunction with hydrogen peroxide production on boron-doped diamond at around 2-2.5 V (vs Ag/AgCl).

Biocompatible WSe2@BSA Dots with Merged Catalyst and Coreactant for Efficient Electrochemiluminescence

Electrochemiluminescence (ECL) is a powerful tool for clinical diagnosis due to its exceptional sensitivity. However, the standard tripropylamine (TPrA) coreactant for Ru(bpy)3Cl2, the most widely studied and used ECL system, is highly toxic. Despite extensive research on alternative coreactants, they often fall short in poor efficiency. From a reaction kinetics perspective, accelerating electrooxidation rate of Ru(bpy)3Cl2 is an essential way to compensate the efficiency limitation of coreactants, but is rarely reported. Here, a hybrid electrocatalyst@coreactant dots for the ECL of Ru(bpy)3Cl2 is reported. The as-prepared WSe2@bovine serum albumin (WSe2@BSA) dots is biocompatible, and demonstrate dual functions, i.e., the BSA shell works as a coreactant, meanwhile, the WSe2 core effectively catalyzes Ru(bpy)3Cl2 oxidation. As a result, WSe2@BSA dots exhibit an exceptionally high efficiency comparable to TPrA for the ECL of Ru(bpy)3Cl2. In addition, the procedure for synthesizing WSe2@BSA dots is facile (room temperature, atmospheric conditions), rapid (5 min), and scalable (for millions of bioassays). A biosensor utilizing WSe2@BSA dots shows promise for highly sensitive detecting glypican-3 in clinical liver cancer serum samples, especially for alpha-fetoprotein-negative patients. This work opens a new avenue for developing a highly efficient ECL system for biosensing and clinical diagnosis.

Low-potential anodic electrochemiluminescence of terbium metal-organic frameworks for selective microRNA-155 detection

High excitation potential is recognized as a harmful factor for the biological activity of biomacromolecules, such as proteins and nucleic acids, in electrochemiluminescence (ECL) biosensing. Developing low-potential ECL luminophores is vital for improving ECL accuracy in actual sample sensing. In this work, based on porous metal-organic framework (MOF) structure with multiple active sites and energy transfer between the excited ligands and Ln nodes, we designed a series of Ln-MOFs and observed ECL emission at low potential, providing a novel method to realize low-potential ECL. The MOF nanoemitters were prepared using 1,3,5-tri (4-carboxyphenyl)benzene ligand and several lanthanide ions as nodes through mild hydrothermal reaction. Interestingly, strong ECL emission at +0.75 V of peak potential was observed in the ECL-potential curve of Tb-based MOF using 2,2',2″-nitrilotriethanol as coreactant, which was beneficial for reducing background interference in biosensing, and this ECL emission was attributed to the energy transfer between Tb and excited ligand. This low-potential ECL was then applied to construct an ECL biosensor with newly developed Cas12a-based method for selective detection of microRNA-155 without the help of strand displacement or reverse transcription. For this ECL system, the limit of detection was 0.78 nM, and the overall detection time was 2.5 h. The Ln-MOF nanoemitter provides a robust ECL platform to selectively detect various targets by integrating new bio-related techniques.

Unary Au Nanocrystal with Prestored Electrons and Intrinsic Low Hole-Injected Potential for Low-Triggering Potential Electrochemiluminescence

Screening a novel electrochemiluminescence (ECL) system and lowering the ECL triggering potential are essential to ECL evolution. Herein, the near-infrared (NIR) ECL system with low-triggering potential ECL was constructed with weakly reductive tert-butylamine borane as coreactant and mercaptosuccinic acid/citrate (MSA/Cit)-capped Au (MSA/Cit@AuNCs) as luminophores. Toxic-element-free and dual-ligand MSA/Cit@AuNCs were prepared via ligand exchange and utilized as a model for developing unary metal NCs-based luminophores with more enhanced ECL performance than monoligand Au nanocrystals (AuNCs), which exhibited a two hole-injected process at around 0.48 and 0.80 V, respectively. Beneficial to the intrinsic low hole-injected potential of AuNCs, MSA/Cit@AuNCs exhibited similar low-triggering ECL potential at around 0.57 V with the participation of series coreactants or not, originating from the recombination of an internal prestored electron within the conduction band (CB) and electroinjected holes at around 0.25 V. Furthermore, the enhanced low-triggering potential around 0.57 V and NIR ECL around 835 nm of MSA/Cit@AuNCs was eventually obtained with the reductive tert-butylamine borane or N2H4·H2O containing a -C-N single-bond structure merely as coreactant. The low-triggering potential ECL of MSA/Cit@AuNCs/tert-butylamine borane system at 0.57 V can be harnessed to selectively determine a carcinoembryonic antigen (CEA) with one linear range spanning from 2 to 20000 fg/mL and a limit of detection of 0.33 fg/mL (S/N = 3). This study will contribute to a more comprehensive understanding of the ECL mechanism in terms of both regulating NCs and selecting coreactants.

Donor-Acceptor MOF Enabling Efficient Electrochemiluminescence Based on TSCT-TADF

Electrochemiluminescence (ECL) is an extensively studied luminescence technique recognized for its efficacy in investigating surface energy states. Effective utilization of ECL to explore and probe the charge transfer mechanisms facilitated by novel luminescent materials is crucial. In this study, we demonstrate thermally activated delayed fluorescence (TADF) based on spatial charge transfer through the precisely controlled synthesis of luminescent materials, which is achieved by incorporating phenyl-carbazole derivatives as donor guests within acceptor-hosted metal-organic frameworks (D-A MOFs). These hybrid structures exhibit superior ECL intensities compared with their monomeric counterparts. Mechanistic investigation by DFT calculation reveals that the physically separated yet spatially closed D-A configuration induces efficient intermolecular through-spatial charge transfer (TSCT), leading to efficient ECL through tuning of the dihedral angle of the guest molecules to enhance π-π interactions. This study introduces a strategy for precise modulation of spatial charge transfer at the molecular level in the programmable synthesis of ECL luminophores.

Metal-Organic Frameworks (MOFs): Classification, Synthesis, Modification, and Biomedical Applications

Metal-organic frameworks (MOFs) are a new variety of solid crystalline porous functional materials. As an extension of inorganic porous materials, it has made important progress in preparation and application. MOFs are widely used in various fields such as gas adsorption storage, drug delivery, sensing, and biological imaging due to their high specific surface area, porosity, adjustable pore size, abundant active sites, and functional modification by introducing groups. In this paper, the types of MOFs are classified, and the synthesis methods and functional modification mechanisms of MOFs materials are summarized. Finally, the application prospects and challenges of metal-organic framework materials in the biomedical field are discussed, hoping to promote their application in multidisciplinary fields.

Ultralow Potential Cathodic Electrochemiluminescence Aptasensor for Detection of Kanamycin Using Copper Nanoribbons as Coreaction Accelerator

An ultralow cathodic potential electrochemiluminescence (ECL) aptasensor was designed, employing DNA nanoribbon template self-assembly copper nanoclusters (DNR-CuNCs) as a novel coreaction accelerator within the luminol-H2O2 system for the sensitive detection of kanamycin (KANA). Mechanistic investigations revealed that the DNR-CuNCs preferred to generate highly active hydroxyl radicals by facilitating the reduction of the coreactant H2O2 under neutral pH conditions, consequently enhancing cathodic luminescence. By the strong π-π stacking effect of KANA aptamer and graphene as a signal modulation switch, DNR-CuNCs were displaced from the electrode surface due to the affinity of KANA and its aptamer, resulting in the inhibition of the luminol-H2O2 system and a decrease in the ECL signal. Under optimal experiments, the aptasensor demonstrated exceptional sensitivity in detecting KANA within the concentration range from 1 × 10-2 to 5 × 105 pg/mL, with the detection limit as low as 0.18 fg/mL. This innovative strategy provided a novel approach to designing effective ECL emitters for monitoring food safety.

Effect of the Imidazole π-Extension on TADF Emitters in Electrochemiluminescence

Already known molecules which exhibit good electrochemiluminescence (ECL) efficiencies and high photoluminescence quantum yields (PLQY) have been structurally modified in order to increase their performance. The followed strategy is to stiffen the structures to limit the rotational and vibrational freedom degrees and favour radiative decay processes once excited. Molecules under investigation consist of donor-acceptor systems in which the acceptor fraction is a benzonitrile with an imidazole in para position, while the donor fraction consists of four diphenylamine (NPh2) or 3,6-di(tert-butyl)-9H-carbazole (t-BuCz) groups in the remaining positions on the central benzene ring. Therefore, in order to stiffen these systems and restrict the intramolecular rotations (RIR), the imidazole in the para position has been replaced with more extended π-systems, i. e., benzimidazole and phenanthro[9,10-d]imidazole. The restriction of the intramolecular rotation can be clearly observed by 1H NMR analysis. We expected to observe an increase in ECL efficiency and PLQY with the rigidity. Surprisingly, we observed a generally opposite trend: molecules with the smallest imidazole fraction showed the best performance in ECL and higher PLQY. Notably, NPh2 derivatives with benzimidazole and phenanthro[9,10-d]imidazole showed an hypsochromic shift of the emission spectra with concomitant increase of the PLQY as the solvent polarity increases.

Au Nanorings/TiO2 NPs@MXene-Based Metasurfaces with a Magnetic Mirror-Modulated ECL Strategy for Extracellular Vesicle Detection

A metasurface as an artificial electromagnetic structure can concentrate optical energy into nanometric volumes to strongly enhance the light-matter interaction, which has been becoming a powerful platform for optical sensing, nonlinear effects, and quantum optics. Herein, we developed a novel hybrid plasmonic-dielectric metasurface consisting of Au nanorings (Au NRs) and TiO2 nanoparticles derived from MXene (TiO2 NPs@MXene). The hybrid metasurface simultaneously benefited from the high near-field enhancement effect of plasmonic materials and the low loss of dielectric materials. Furthermore, the optical modulation efficiency of the hybrid metasurface can be regulated by a magnetic mirror configuration. The magnetic mirror acted like a mirror, confining the electrons to a limited region and increasing the density of the surface plasmon. Moreover, the electrochemiluminescence (ECL) of the Cu2BDC metal-organic framework (Cu2BDC-MOF) served as a light source for the Au NRs/TiO2 NPs@MXene metasurface. Due to the exceptional light manipulation capability of the hybrid metasurface and the coordination of the magnetic mirror, the isotropic ECL signal can be dynamically amplified and converted into polarized emission. Finally, a metasurface-regulated ECL (MECL)-based biosensor with a dual-positive membrane protein recognition strategy was developed for the accurate identification of gastric cancer-derived extracellular vesicles. The novel MECL research opened up a new route in the realization of dynamically tunable metasurfaces for optical sensing and novel nanophotonic devices.

Recent Advances in Luminophores for Enhanced Electrochemiluminescence Analysis

Electrochemiluminescence (ECL) detection is widely applied in many fields, including chemical measurement, biological analysis, and clinic tests, due to its high sensitivity. Currently, the fast development of many new electrochemical luminophores is continuously improving the ECL-based detection ability. Besides the enhancement of luminescence emission for a high detection sensitivity, minimizing the effect of co-reactants on ECL detection and achieving multiple analysis in one sample are also the main directions in this field. This review focuses on a summary of recently prepared new luminophores to achieve the three aims mentioned above. Especially, the review is composed by three parts, focusing on the luminophores or materials with high ECL efficiency, self-enhancing properties, and multi-color ECL luminophores. The fabrication of biosensors using these molecules is also reviewed to exhibit the advances in biological applications.

Recent Advances in On-Line Mass Spectrometry Toolbox for Mechanistic Studies of Organic Electrochemical Reactions

Electrochemical reactions are very complex and involve a variety of physicochemical processes. Accurate and systematic monitoring of intermediate process changes during the reaction is essential for understanding the mechanism of electrochemical reactions and is the basis for rational design of new electrochemical reactions. On-line electrochemical analysis based on mass spectrometry (MS) has become an important tool for studying electrochemical reactions. This technique is based on different ionization and sampling means and realizes on-line analysis of electrochemical reactions by establishing electrochemistry-MS (EC-MS) coupling devices. In particular, it provides key evidence for elucidating the reaction mechanism by capturing and identifying the reactive reaction intermediates. This review will categorize various EC-MS devices and the organic electrochemical reaction systems they study, highlighting the latest research progress in recent years. It will also analyze the properties of various devices and look forward to the future development of EC-MS.

Spotting d-band centers of single-atom catalysts by oxygen intermediate-boosted electrochemiluminescence

Catalytic activities of single-atom catalysts are strongly dependent on their d-band centers. However, it is a long-standing challenge to provide a cost-effective and accurate evaluation for the positions of d-band centers of these catalysts due to the fact that the widely applicable photoelectron spectroscopy methodologies require complicated sampling and spectral unfolding processes. In this contribution, we have proposed oxygen intermediate-boosted electrochemiluminescence (ECL) for rapid spotting of the d-band centers of single-atom catalysts, involving single atomic Au, Ag, Cu and Fe. It was disclosed that the d-band centers of single-atom catalysts closer to the Fermi level could facilitate the interaction between catalysts and oxygen intermediates, leading to higher luminol ECL intensities as a result of the promoted adsorption and reduction ability towards oxygen intermediates. Moreover, this correlation was also adapted for other metal catalysts such as Au and Ag nanoparticles. This correspondence could be utilized for an accurate identification of d-band centers of single-atom catalysts. It is anticipated that the proposed strategy could be beneficial for a deep understanding of microstructure studies of single-atom catalysts to achieve advanced catalytic performances.

A simple and cost-effective strategy for electrochemiluminescence spectral determination

BACKGROUND

Electrochemiluminescence (ECL), as a unique and powerful analytical technique, has been widely used in various fields. The determination of ECL spectra plays a crucial role in understanding ECL reaction mechanisms and conducting spectra-resolved ECL analysis. ECL intensity is typically detected using a photomultiplier tube, which offers high sensitivity for detecting extremely weak light signals but does not allow for spectral identification. Due to the time-dependent variation of ECL intensity caused by the applied potential and electrochemical reaction processes, it is challenging to perform ECL spectral detection using conventional wavelength-scanning spectrometers.

RESULTS

In this study, we present a straightforward and cost-effective ECL spectral detection strategy by incorporating an automatically controlled tunable optical filter device between a commonly used PMT detector and a specially designed ECL reaction cell. The effectiveness of this approach was confirmed through initial validation, where the spectrum of a green LED spotlight was measured and compared with a commercial spectrometer. In a dynamic system with stable ECL signals, the ECL spectrum of the typical Ru(bpy)32+/TPA system was rapidly acquired by adjusting the bandpass filters. To account for time-varying ECL signals in practical measurements, time-based correction algorithms were implemented to rectify variations in ECL intensity. By integrating time-based correction algorithms and an automatically controlled tunable optical filter device into a commonly utilized PMT detector, the rapid and sensitive ECL spectra determination was achieved. Experimental results demonstrated the reliability of the proposed strategy.

SIGNIFICANCE

This strategy is based on the widely used high-sensitivity PMT detection component, enabling the rapid and sensitive measurement of ECL spectra without altering the ECL detection hardware. It is simple, fast, efficient, and cost-effective, with the potential to be widely used for rapid ECL spectral detection and spectra-resolved ECL analysis.

COVID-19 diagnosis on the basis of nanobiosensors' prompt interactivity: A holistic review

The fast spread and severe consequences of novel coronavirus disease 2019 (COVID-19) have once again underscored the critical necessity of early detection of viral infections. Several serology-based techniques, including as point-of-care assays and high-throughput enzyme immunoassays that support the diagnosis of COVID-19 are utilized in the detection and identification of coronaviruses. A rapid, precise, simple, affordable, and adaptable diagnostic tool is required for controlling COVID-19 as well as for outbreak management, since the calculation and monitoring of viral loads are crucial for predicting the infection stage and recovery time. Nowadays, the most popular method for diagnosing COVID-19 is reverse transcription polymerase chain reaction (RT-PCR) testing, and chest computed tomography (CT) scans are also used to determine the disease's phases. This is all because of the fact that RT-PCR method caries with itself a number of downsides comprising of being immovable, expensive, and laborious. RT-PCR has not well proven to be capable of detection on the very early infection stages. Nanomaterial-based diagnostics, together with traditional clinical procedures, have a lot of promise against COVID-19. It is worthy of attention that nanotechnology has the mainstay capacity for purposes of developing even more modern stratagems fighting COVID-19 by means of focusing on state-of-the-art diagnostics. What we have centered on in this review, is bringing out even more efficient detection techniques whereby nanobiosensors are employed so that we might obstruct any further development and spreading of SARS-CoV-2.

Dual-signal ratiometric electrochemiluminescence biosensor based on Au NPs-induced low-potential emission of PFO Pdots and LSPR-ECL mechanism for ultra-sensitive detection of microRNA-141

In this study, we have for the first time constructed a ratiometric ECL biosensor for the ultrasensitive detection of microRNAs (miRNAs) using gold nanoparticles (Au NPs) to trigger both the low-potential emission from conjugated polymer poly(9,9-dioctylfluorene-2,7-diyl) dots (PFO Pdots) and the LSPR-ECL effect with sulfur-doped boron nitride quantum dots (S-BN QDs). PFO Pdots were first applied to the Au NPs-modified electrode, followed by covalent binding to capture the hairpin H1. Immediately thereafter, a small amount of miRNA-141 was able to generate a large amount of output DNA (OP) by traversing the target cycle. OP, H3-S-BN QDs, and H4-glucose oxidase (H4-GOD) were then added sequentially to the Au NPs-modified electrode surface, and the hybridization chain reaction (HCR) was initiated. This resulted in the introduction of a large amount of GOD into the system, which catalyzed the in situ formation of the co-reactant hydrogen peroxide (H2O2) from the substrate glucose. Due to the electron transfer effect, the production of H2O2 led to the ECL quenching of PFO Pdots. Meanwhile, H2O2 served as a co-reactant of S-BN QDs, resulting in strong ECL emission of S-BN QDs at the cathode. Furthermore, the cathodic ECL intensity of S-BN QDs was further enhanced by an LSPR-ECL mechanism between Au NPs and S-BN QDs. By measuring the ratio of ECL intensities at two excitation potentials, this approach could provide sensitive and reliable detection of miRNA-141 in the range of 0.1 fM ∼10 nM, with a detection limit of 0.1 fM.

Electroprecipitating the Sulfate Radical Anion Amplifies Electrochemiluminescence in Space and Time

We have discovered a strategy to synthesize reactive radical salts, effectively bottling up radicals in space and time for future use. We apply this new principle to electrochemiluminescence (ECL) through the simultaneous electro-reduction of peroxydisulfate, S2O82-, and tris(bipyridine)ruthenium(II), [Ru(bpy)3]2+ in a water/acetonitrile mixture. The electrode generates a concentration profile exceeding the solubility of the cation and anion pair, promoting precipitation. After the application of a potential, leads are disconnected, and the crystals electrolessly chemiluminesce during dissolution and can be transported to other solutions for later chemiluminescence uses. Our method extends ECL hundreds of micrometers from the electrode surface and increases the ECL lifetime by orders of magnitude. Control experiments, including electron spin resonance, validate the crystallization of SO4•-, allowing detailed mechanistic insight. We demonstrate platform generalizability by precipitating a radical salt made of calcium and SO4•-, and we demonstrate the salt's ability to drive chemiluminescence. Our results emphasize the elegant chemical tenet that extremely reactive radicals can be bottled up as solids to be used as future reagents if precipitation occurs more quickly than the radical lifetime.

Emerging electrochemical biosensors for lung cancer-associated protein biomarker and miRNA detection

Lung cancer remains a major driver of global morbidity and mortality, and diagnosing lung tumors early in their development is vital to maximizing treatment efficacy and patient survival. Several biomarkers, including CYFRA 21-1, NSE, ProGRP, CEA, and miRNA, have been identified as reliable indicators for early lung cancer detection and monitoring treatment progress. However, the minute changes in the levels of these biomarkers during the early stages of disease necessitate advanced detection platforms. In this space, electrochemical biosensors have currently emerged as robust tools for early lung cancer screening and diagnosis owing to their low costs, rapid responses, and superior sensitivity and selectivity. This review provides an up-to-date overview of the application of electrochemiluminescence, photoelectrochemical, and other electrochemical analytical strategies for detecting lung cancer-associated protein biomarkers, and miRNA. This review compares these techniques to provide a concise overview of the principles underlying these electrochemical analytical methods, the preparation of their components, and the performance of the resulting biosensors. Lastly, a discussion of the challenges and opportunities associated with electrochemical biosensors detection of lung cancer-associated biomarkers are provided.

Optical Image Sensors for Smart Analytical Chemiluminescence Biosensors

Optical biosensors have emerged as a powerful tool in analytical biochemistry, offering high sensitivity and specificity in the detection of various biomolecules. This article explores the advancements in the integration of optical biosensors with microfluidic technologies, creating lab-on-a-chip (LOC) platforms that enable rapid, efficient, and miniaturized analysis at the point of need. These LOC platforms leverage optical phenomena such as chemiluminescence and electrochemiluminescence to achieve real-time detection and quantification of analytes, making them ideal for applications in medical diagnostics, environmental monitoring, and food safety. Various optical detectors used for detecting chemiluminescence are reviewed, including single-point detectors such as photomultiplier tubes (PMT) and avalanche photodiodes (APD), and pixelated detectors such as charge-coupled devices (CCD) and complementary metal-oxide-semiconductor (CMOS) sensors. A significant advancement discussed in this review is the integration of optical biosensors with pixelated image sensors, particularly CMOS image sensors. These sensors provide numerous advantages over traditional single-point detectors, including high-resolution imaging, spatially resolved measurements, and the ability to simultaneously detect multiple analytes. Their compact size, low power consumption, and cost-effectiveness further enhance their suitability for portable and point-of-care diagnostic devices. In the future, the integration of machine learning algorithms with these technologies promises to enhance data analysis and interpretation, driving the development of more sophisticated, efficient, and accessible diagnostic tools for diverse applications.

Dual-Enhancement Electrochemiluminescence Device for Ultratrace Uranium Visualized Monitoring in Fish, Hair, and Nail Samples

Uranium is a nuclear fuel but also a hazardous contaminant due to its radioactivity and chemical toxicity. To prevent and mitigate its potential threat, the accurate monitoring of ultratrace uranium (orders of magnitude of pg g-1) in practical environmental samples has become an important scientific problem. To meet this challenge, we developed an efficient electrochemiluminescence (ECL) UO22+ detection device by a novel dual-enhancement mechanism. In detail, poly[(9,9-dioctylfuor-enyl-2,7-diyl)-alt-co-(1,4-benzo-{2,1,3}-thiadiazole)] polymer dots (Pdots) are modified by the UO22+ DNA aptamer, and rhodamine B (RhB) is combined with dsDNA to quench the ECL signal via a resonance energy transfer (RET) process. UO22+ can cut off the DNA aptamer to release RhB, which generates an ECL enhancement process, and then, UO22+ continuously combines with the DNA chain, inducing another ECL enhancement by the RET process from UO22+ to Pdots. This device achieves an ultralow detection limit (12 pg L-1) and a wide linear range (113 pg L-1-11.3 mg L-1), which can successfully give accurate determination results to the ultratrace uranium in biosamples (<1 pg g-1) to monitor the uranium simulation of fish. This work presents an efficient strategy for ultratrace uranium determination in the environment, highlighting its significance in public health and environmental fields.

Graphitic carbon nitride nanosheet supported silica nanochannel film for enhanced electrochemiluminescence sensing of 2,4,6-trichlorophenol and prochloraz

The development of simple, rapid, and sensitive methods for detecting pesticide in environmental and food samples holds significant importance. Electrochemiluminescence (ECL) sensing platforms with high resistance to interference and contamination, and reduced consumption of ECL emitters, are highly desirable for such applications. In this work, we present an ECL sensing platform based on a graphitic carbon nitride nanosheets (CNNS) supported vertically ordered mesoporous silica film (VMSF) modified glassy carbon electrode (GCE) for the highly sensitive detection of the environmental pollutant 2,4,6-trichlorophenol (TCP) and the broad-spectrum insecticide prochloraz. Two-dimensional (2D) CNNS were synthesized by exfoliating bulk graphitic carbon nitride (g-C3N4) using concentrated sulfuric acid, serving as a novel conductive and adhesive layer for the growth of a stable VMSF on GCE via an electrochemical assistance self-assembly (EASA) method to prepare VMSF/CNNS/GCE. The electrostatic enrichment capability of VMSF nanochannels for the positively charged ECL emitter tris(2,2'-bipyridyl)ruthenium(ii) (Ru(bpy)3 2+) realized stable and significantly enhanced ECL signals at a low concentration of Ru(bpy)3 2+ (10 μM). Based on the quenching effect of TCP on the ECL signal of Ru(bpy)3 2+, highly sensitive ECL detection of TCP was achieved by the VMSF/CNNS/GCE with a linear range from 10 nM to 0.7 mM and a low detection limit (DL) of 2.2 nM. As the metabolic end product of prochloraz is TCP, indirect ECL detection of prochloraz was also accomplished by measuring the produced TCP. Combined with anti-fouling and anti-interference abilities, as well as signal amplification of VMSF, the developed VMSF/CNNS/GCE sensor enabled the sensitive ECL detection of TCP in pond water and prochloraz in orange peel extract.

Multicolor Electrochemiluminescence of Binary Microcrystals of Iridium and Ruthenium Complexes

We here report the multicolor electrochemiluminescence (ECL) of binary microcrystals prepared from a blue-emissive iridium complex 1 and an orange-emissive ruthenium complex 2. These materials display a plate-like morphology with high crystallinity, as demonstrated by microscopic and powder X-ray diffraction analyses. Under light excitation, these microcrystals exhibit gradient emission color changes as a result of the efficient energy transfer between two complexes. When modified on glass carbon electrodes, these microcrystals exhibit tunable ECLs with varied emission colors including sky-blue, white, orange, and red, depending on the doping ratio of complex 2 and the applied potential. Furthermore, organic amines with different molecular sizes are used as the co-reactant to examine their influences on the ECL efficiency of the porous microcrystals of 1. The analysis on the luminance and RGB values of ECL suggests the existence of energy transfer in the generation of multicolor ECLs in these binary crystals.

Sensitive detection of uric acid based on low-triggering-potential cathodic luminol electrochemiluminescence achieved by ReS2 nanosheets

The majority of previously reported cathodic electrochemiluminescence (ECL) systems often required very negative potential to be carried out, which has greatly limited their applications in the sensing field. Screening high-performance cathodic ECL systems with low triggering potential is a promising way to broaden their applications. In this work, rhenium disulfide nanosheets (ReS2 NS) have been revealed as an efficient co-promoter to realize low-triggering-potential cathodic luminol ECL. One strong cathodic ECL signal appeared at a potential of -0.3 V and one anodic ECL peak was obtained at -0.15 V under the reverse potential scan, which were caused by electrogenerated reactive oxygen species (ROS) from hydrogen peroxide. The generation of strong luminol ECL at low potential was the result of the electrocatalytic effect of ReS2 NS on the reduction of H2O2. The scavenging effect of uric acid (UA) on the ROS could significantly inhibit the cathodic ECL. As a result, an ECL sensor was proposed, which showed outstanding performance for the detection of UA in the range of 10 nM to 0.1 mM with a low detection limit of 1.53 nM. Moreover, the ECL sensor was successfully applied in the sensitive detection of UA in real samples. This work provides a new avenue to establish a low-potential cathodic ECL system, which will sufficiently expand the potential application of cathodic ECL in the sensing field.

MoS2/MXene Van der Waals heterojunction-based electrochemiluminescence sensor for triple negative breast cancer detection

The van der Waals heterojunction is able to combine the advantages of different materials and has potential to be used in biosensing researches. In this study, we developed a novel van der Waals heterojunction by combining MXene and MoS2 nanosheets for the electrochemiluminescence (ECL) sensing applications. This van der Waals heterojunction material not only possessed the superior conductivity of MXene, but also regulated the electron transport. Additionally, the incorporation of MoS2 nanosheets into the MXene interlayers significantly enhances the material stability. Meanwhile, nitrogen-rich quantum dots (N dots) were synthesized as ECL tags with an impressive nitrogen content of up to 75 %. By integrating the ECL response of N dots within the van der Waals heterojunction, we established a highly efficient sensing system for miRNA-373, which overexpressed in triple negative breast cancer tissues. The van der Waals heterojunction-based biosensor can enhance the ECL signal of N dots effectively to detect miRNA-373 from 1 fM to 1 μM. Consequently, the developed sensing system holds promise for the early detection of metastasis of the triple-negative breast cancer, paving the way for the effective clinical interventions.

Iridium(III) solvent complex-based electrogenerated chemiluminescence method for the detection of 3-methylhistidine in urine

3-Methylhistidine (3-MeHis) is increasingly used as an indicator of muscle protein breakdown. The development of a sensitive, simple, and non-invasive method for 3-MeHis assay is important in clinical practice. Herein, a sensitive, simple, and non-invasive electrogenerated chemiluminescence (ECL) method was proposed for the quantitation of 3-MeHis in urine by using an iridium(III) solvent complex ([Ir(dfppy)2(DMSO)Cl], dfppy = 2-(2,4-difluorophenyl)pyridine, Ir-DMSO) as a signal reagent. The photoluminescence (PL) and ECL responses of Ir-DMSO to 3-MeHis were studied. The ECL intensity of Ir-DMSO was enhanced in the presence of 3-MeHis because of the coordination recognition between Ir-DMSO and the imidazole group of 3-MeHis. Based on the enhancement of ECL intensity, 3-MeHis can be sensitively detected in the range of 5 to 25 μM. The detection limit was 0.4 μM. This is the first report of an ECL method for the quantitation of 3-MeHis. Further, to investigate the feasibility of the Ir-DMSO-based ECL method in practical applications, the developed ECL method was applied for 3-MeHis assay in urine samples of 28 healthy volunteers and 2 patients. The urine samples from patients hospitalized with obesity and kidney disease and healthy individuals were distinguished by the ECL responses of Ir-DMSO. The proposed ECL method based on the coordination recognition between iridium(III) solvent complex and the imidazole group of 3-MeHis allows inexpensive, fast, non-invasive, and sensitive detection of 3-MeHis in urine, which is promising for assessing large volumes of patients for routine analysis in clinical practices.