Rare Self-Luminous Mixed-Valence Eu-MOF with a Self-Enhanced Characteristic as a Near-Infrared Fluorescent ECL Probe for Nondestructive Immunodetection

The rational design of europium complex based electrochemiluminescence sensor for highly efficient carbaryl detection

To address the issue that most of the reported electrochemiluminescence (ECL) sensors are usually subjected to various complicated chemical modifications, we proposed a sensitive ECL sensor by using a neutral mononuclear lanthanide metal europium complex Eu(L)3 (L = 2-pyrazol-1-yl-6-(1H-tetrazol-5-yl)-pyridine) as luminophore with simple chemical composition for the accurate detection of carbaryl pesticide residues. The three conjugated tridentate pyrazo-pyridine- tetrazol ligands could put significant effect on the physical and chemical behavior of the central Eu3+ ion, leading to the excellent luminescent performance of the Eu(L)3 complex enhanced by "antenna effect" of the auxiliary anionic organic ligands. The naphthol obtained from the hydrolysis reaction of carbaryl in an alkaline working solution could effectively and quantitatively quench the luminescence intensity of the Eu(L)3 complex, which has been theoretically confirmed by the detailed density functional theory (DFT) and time-dependent DFT (TDDFT) calculations, thus obviously strengthening the target detection capability on carbaryl. Based-on such the idea, the skillfully constructed ECL sensor showed superior carbaryl detection performance with good linearity in the range of 1 pg/mL to 1000 ng/mL, and a satisfied detection limit of 8.8 pg/mL (S/N = 3) under the optimized conditions. The current simple ECL carbaryl detection platform exhibited the conspicuous superiority to those existed commercial ones and thus, more importantly, provided a very promising practical value in the field of environmental detection (oil, soil, water, etc.) of organic phenol pollutants.

Polyfluorene-Enhanced Near-Infrared Electrochemiluminescence of Heptamethine Cyanine Dye for Coreactants-Free Bioanalysis

The near-infrared electrochemiluminescence (NIR-ECL) technique has received special attention in cell imaging and biomedical analysis due to its deep tissue penetration, low background interference, and high sensitivity. Although cyanine-based dyes are promising NIR-ECL luminophores, limited ECL efficiency and the need for exogenous coreactants have prevented their widespread application. In this work, poly[9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorene]-alt-2,7-(9,9-dioctylfluorene)] (PFN) was innovatively developed to significantly invigorate the NIR-ECL performance of heptamethine cyanine dye IR 783 by the resonance energy transfer (RET) strategy. Astonishingly, the IR@PFN nanoparticles (NPs) synthesized from IR 783 and PFN by a nanoprecipitation method emitted a strong coreactant-free NIR-ECL signal at +1.05 V, and the maximum emission wavelength was 815 nm. IR@PFN NPs were integrated in a spontaneous entropy-driven chain replacement (ESDR) reaction to achieve ECL analysis of microRNA-21 (miRNA-21), and the limit of detection was as low as 0.25 fM. IR@PFN NPs created a promising coreactant-free NIR-ECL platform for bioanalysis and imaging, providing a novel NIR-ECL detection method for miRNA-21.

Mixed-valence metal-organic frameworks: concepts, opportunities, and prospects

Owing to increasing global demand for the development of multifunctional advanced materials with various practical applications, great attention has been paid to metal-organic frameworks due to their unique properties, such as structural, chemical, and functional diversity. Several strategies have been developed to promote the applicability of these materials in practical fields. The induction of mixed-valency is a promising strategy, contributing to exceptional features in these porous materials such as enhanced charge delocalization, conductivity, magnetism, etc. The current review provides a detailed study of mixed-valence MOFs, including their fundamental properties, synthesis challenges, and characterization methods. The outstanding applicability of these materials in diverse fields such as energy storage, catalysis, sensing, gas sorption, separation, etc. is also discussed, providing a roadmap for future design strategies to exploit mixed valency in advanced materials. Interestingly, mixed-valence MOFs have demonstrated fascinating features in practical fields compared to their homo-valence MOFs, resulting from an enhanced synergy between mixed-valence states within the framework.

A sensitive electrochemiluminescence immunosensor for CEA detection based on the ECL-RET between zinc-based metal-organic frameworks and ZiF-8@PDA

In this study, we developed a new system that using zinc-based metal-organic frameworks NH2-Zn-PTC as the donor and ZiF-8@PDA as the acceptor to achieve highly sensitive detection of carcinoembryonic antigen (CEA), using the fundamentals of electrochemiluminescence resonance energy transfer (ECL-RET). Firstly, the aggregation-induced quenching effect (ACQ) was eliminated by the coordination of PTC in MOF and the ECL signal was improved. Secondly, the ECL signal was further amplified by using Au NPs and amino groups as co-reaction promoters to generate more SO4.-. In addition, the introduction of ZiF-8@PDA as an acceptor and NH2-Zn-PTC as a donor took advantage of the feature of partial overlap of the UV-vis absorption spectrum and ECL emission spectra between the two, thereby effectively initiating the ECL-RET behavior, which improved the detection sensitivity of the sensor. The prepared immunosensor showed good linearity in the concentration range of 10-4 to 80 ng/mL with a detection limit of 18.20 fg/mL. This makes it promising for clinical testing of tumor markers.

Conjugated polymer-boosted near-infrared electrochemiluminescence of organic dye for detecting acetamiprid

BACKGROUND

The near-infrared electrochemiluminescence (NIR-ECL) has excellent penetration and near zero background interference, and has shown unique advantages in clinical medicine and bioimaging. Among various types of NIR-ECL emitters, NIR organic dyes have arouse the concern of researchers due to their adjustable structure and diverse optical properties. However, the currently available NIR dyes usually have inherent self-quenching effect and poor photostability, so their ECL efficiency is low, and it is a great challenge to improve their ECL performance.

RESULT

Conjugated polymer-boosted NIR-ECL strategy was creatively developed to overcome ECL performance limitations of NIR dyes. IR 783, as one of heptamethine cyanine dyes, was performed a nanoprecipitation in the presence of poly[(9,9-dlhexyfluoren-2,7-dlyl)-co-(anthracen-9,10-dlyl)] (PFAD) to prepare IR polymer nanoparticles (IR PNPs). Due to resonance energy transfer (RET) from PFAD to IR 783 and encapsulation of IR 783 by PFAD, the resulting IR PNPs exhibited a strong and stable NIR-ECL emission with a maximum ECL wavelength of 802 nm under coreactant tripropylamine (TPrA) and H2O2 can effectively quench it. IR PNPs coupled proximity ligation assay (PLA)-induced DNA walker to achieve acetamiprid (ACE) analysis. ACE triggered PLA to form bipedal DNA walker, and further release G-rich secondary target (ST). With ST and hemin being captured on IR PNPs modified electrode, hemin/G-quadruplex was assembled to consume H2O2, thereby restoring ECL signal for ACE detection with a limit of detection of 4.74 × 10-15 M.

SIGNIFICANCE

This work opens up a new and simple way to boost NIR-ECL of organic dyes, and IR PNPs create a promising NIR-ECL platform for pesticide detection.

Aggregation-Induced Electrochemiluminescence of Silica-Confined Tetraphenylethylene with Pd Nanocube-Loaded Co3O4 Nanosheets as a Coreaction Accelerator for Sensitive Bioanalysis

Aggregation-induced electrochemiluminescence (AIECL) provides a new approach for the development of novel electrochemiluminescence (ECL) strategies. Herein, a biosensor was constructed by incorporating 1,1,2,2-tetra(4-carboxylphenyl)ethylene (H4TCPE) into a mesoporous silica nanosphere (MSN) to obtain a highly organized AIECL luminophore of (MSN-H4TCPE) for signal antibody (Ab2) labeling and using Pd nanocube (NC)-loaded Co3O4 nanosheets (NSs) (PdNCs/Co3O4NSs) as a novel coreaction accelerator. The confinement of H4TCPE molecules in the MSN restricted the intramolecular rotation and thus enhanced the radiation transition of H4TCPE. In addition, the PdNCs/Co3O4NSs exhibited efficient mutual conversion of the Co2+/Co3+ redox couple with the perfect catalytic performance of PdNCs and facilitated the decomposition of the coreactant, leading to a substantial enhancement in ECL signal. Subsequently, the localization and fixation strategy with HWRGWVC (HWR) heptapeptides as a specific antibody immobilization agent was introduced, which further maintained the biological activity of the antibody on the PdNCs/Co3O4NSs and MSN-H4TCPE surface and significantly improved the incubation performance. Benefiting from the perfect sensing strategy, the obtained ECL immunosensor revealed an admirable manifestation for the precise detection of neuron-specific enolase (NSE) with a broad concentration range of 1 fg/mL to 5 ng/mL and a detection limit of 0.33 fg/mL.

Facile synthesis of sulfur quantum dots with red light emission: Implications for electrochemiluminescence analysis application

Sulfur quantum dots (SQDs) have been reported as a potential candidate due to their low toxicity and high luminescent performance. Here, SQDs with red light fluorescence (FL) emission were synthesized by a one-step hydrothermal method using Na2CO3 as an etching agent, using sublimed sulfur powder as a sulfur source, and using bovine serum albumin (BSA) as a stabilizer. The choice of etching agent (NaOH or Na2CO3) realized the tuning of SQDs' FL emission with blue and red light. The synthesized SQDs showed good FL stability and high FL efficiency, with a quantum yield of 1.03 % in an aqueous solution at 575 nm. In addition, stable and efficient electrochemiluminescence (ECL) emission was achieved by employing SQDs as ECL emitters with K2S2O8 as the co-reactant. The resorcinol (RS) can enhance the ECL intensity of the SQDs-K2S2O8 system, and the ECL intensity had a good linear relationship with the concentration of RS in a range from 2.5 nM to 25 nM with a detection limit of 0.61 nM. This work provides an emerging red-light luminescent SQDs, which would open up a way for the development of new types of luminophor in FL or ECL analysis. It also provides convenience for bio-labeling of live cells, in vivo imaging and provide new materials for photoelectric devices.

A novel dual-detection electrochemiluminescence sensor for the selective detection of Hg2⁺ and Zn2⁺: Signal suppression and activation mechanisms

In this study, we developed a novel covalent organic framework (COF) material, termed RuCOFs, specifically designed and synthesized for electrochemiluminescence (ECL) sensor applications. RuCOFs are based on the classic ECL emitter Ru(dcbpy)32+, ingeniously integrating 4,4',4''-(1,3,5-triazine-2,4,6-triyl) triphenylamine (TAPT) with [2,2'-bipyridine]-5,5'-diamine (BPYDA), forming a structure with a high specific surface area. This configuration not only significantly enhances the stability of the ECL signal but also provides ideal N,N'-bipyridine chelating sites for efficient metal ion recognition. Utilizing Ru(dcbpy)32+-functionalized COF (RuCOFs), a novel dual-function ECL sensor was developed, achieving high sensitivity and selectivity in detecting mercury (Hg2⁺) and zinc (Zn2⁺) ions. Experimental results indicate that Hg2⁺ significantly quenches the ECL signal, while Zn2⁺ markedly enhances it, with detection limits of 4.71 nM for Hg2⁺ and 6.57 nM for Zn2⁺ across a wide linear response range from 1 μM to 1 nM. This research not only demonstrates the significant advantages of COF-based ECL sensing platforms in tracking environmental metal ions but also opens new possibilities for environmental monitoring.

Photoelectrochemical signal polarity transition mediated by quercetin for the detection of neuron-specific enolase

A photoelectrochemical (PEC) biosensor with a wide linear detection range was developed for the sensitive detection of neuron-specific enolase (NSE), which was achieved by applying a photocurrent polarity transition strategy mediated by quercetin. The coupling reaction between Cr(VI) and quercetin drives the signal polarity from anodic to cathodic. When only quercetin is present in the test solution, photogenerated electrons are transferred to the electrode to generate anodic photocurrent. However, in the presence of the target, the signal probe released Cr(VI), which interacted with quercetin, and the electron transfer direction was changed to achieve signal polarity conversion. Meanwhile, protoporphyrin-sensitized Bi:SrTiO3 nanocubes were used as matrix photoactive materials to provide basic photocurrent. The doping of Bi element would adjust the bandgap of SrTiO3, and the organic-inorganic composite material exhibits good photostability and chemical stability that can maintain stable photoelectric properties over a long period of time. Such a novel signal polarity transition strategy greatly broadened the sensor detection to the range of 0.00007-170 ng mL-1 and obtained a relatively low detection limit (25 fg mL-1), which greatly improved the detection sensitivity and accuracy of the biosensor.

A magnetic plasma Fe3O4@Cu@Cu2O photoelectrochemical sensor for the detection of fumonisin B1

Fumonisin B1 (FB1) is a mycotoxin, a water-soluble metabolite produced by Fusarium cepacia, which mainly contaminates grain and its products and is acutely toxic and potentially carcinogenic to certain domestic animals. In this work, plasma nanocomposites of Fe3O4@Cu@Cu2O with magnetic and optoelectronic properties were synthesized as a sensing platform. On one hand, the surface plasmon resonance (SPR) of metallic Cu accelerates the electron transfer rate. On the other hand, plasma-induced resonance energy transfer of metals and semiconductors can improve the utilization efficiency of light energy. A split photoelectrochemical (PEC) sensor based on Fe3O4@Cu@Cu2O was proposed for the detection of FB1. The sensor has a wide linear range of 1.0-10 000 pg mL-1 and a low detection limit of 0.28 pg mL-1 (LOD, S/N = 3), which can realize the specific detection of FB1 in real samples.

Dual-Ligand Europium-Organic Gels as a Highly Efficient Anodic Annihilation Electrochemiluminescence Emitter for Ultrasensitive Detection of MicroRNA

In this study, a novel europium dual-ligand metal-organic gel (Eu-D-MOGs) with high-efficient anodic annihilation electrochemiluminescence (ECL) was synthesized as an ECL emitter to construct a biosensor for ultrasensitive detection of microRNA-221 (miR-221). Impressively, compared to the ECL signal of europium single-ligand metal-organic gels (Eu-S-MOGs), the ECL signal of Eu-D-MOGs was significantly improved since the two organic ligands could jointly replace the H2O and coordinate with Eu3+, which could remarkably reduce the nonradiative vibrational energy transfer caused by the coordination between H2O and Eu3+ with a high coordination demand. In addition, Eu-D-MOGs could be electrochemically oxidized to Eu-D-MOGs•+ at 1.45 V and reduced to Eu-D-MOGs•- at 0.65 V to achieve effective annihilation of ECL, which overcame the side reaction brought by the remaining emitters at negative potential. This benefited from the annihilation ECL performance of the central ion Eu3+ caused by its redox in the electrochemical process. Furthermore, the annihilation ECL signal of Eu3+ could be improved by sensitizing Eu3+ via the antenna effect. In addition, combined with the improved rolling circle amplification-assisted strand displacement amplification strategy (RCA-SDA), a sensitive biosensor was constructed for the sensitive detection of miR-221 with a low detection limit of 5.12 aM and could be successfully applied for the detection of miR-221 in the lysate of cancer cells. This strategy offered a unique approach to synthesizing metal-organic gels as ECL emitters without a coreactant for the construction of ECL biosensing platforms in biomarker detection and disease diagnosis.

Double-enhanced sandwich electrochemiluminescence aptasensor based on g-C3N4-Au-luminol nanocomposites and ZnCuS nanosheets for highly sensitive detection of mucin 1

The traditional luminol electrochemiluminescence (ECL) sensing suffers from low signal response and instability issues. Here, an Au/ZnCuS double-enhanced g-C3N4-supported luminol ECL aptasensor is constructed for the sensitive detection of human mucin 1 (MUC1). In this platform, g-C3N4 of a large specific surface area is beneficial to load more luminol illuminants. Au nanoparticles promote the decomposition of H2O2 coreactants to generate more reactive oxygen (•OH and O2•-) intermediates, while ZnCuS can immobilize the aptamer and simultaneously catalyze H2O2 decomposition, realizing the double-wing signal amplification. Under optimal conditions, this sensor shows a good detection capability within 1.0 × 10-4-1.0 × 103 ng mL-1 and a low detection limit of 5.0 × 10-5 ng mL-1, as well as ideal stability, selectivity, and reproducibility. This double-enhanced aptasensor highlights a new signal-enhancement approach for early biomarker detection.

Dendritic quinary PtRhMoCoFe high-entropy alloy as a robust immunosensing nanoplatform for ultrasensitive detection of biomarker

Recently, high-entropy alloys have superior physicochemical properties as compared to conventional alloys for their glamorous "cocktail effect". Nevertheless, they are scarcely applied to electrochemical immunoassays until now. Herein, uniform PtRhMoCoFe high-entropy alloyed nanodendrites (HEANDs) were synthesized by a wet-chemical co-reduction method, where glucose and oleylamine behaved as the co-reducing agents. Then, a series of characterizations were conducted to illustrate the synergistic effect among multiple metals and fascinating structural characteristics of PtRhMoCoFe HEANDs. The obtained high-entropy alloy was adopted to build a electrochemical label-free biosensor for ultrasensitive bioassay of biomarker cTnI. In the optimized analytical system, the resultant sensor exhibited a dynamic linear range of 0.0001-200 ng mL-1 and a low detection limit of 0.0095 pg mL-1 (S/N = 3). Eventually, this sensing platform was further explored in serum samples with satisfied recovery (102.0 %). This research renders some constructive insights for synthesis of high-entropy alloys and their expanded applications in bioassays and bio-devices.

Narrow-Band Green-Emitting Hybrid Organic-Inorganic Eu (II)-Iodides for Next-Generation Micro-LED Displays

Low-dimensional metal halide perovskites are an emerging class of light-emitting materials for LED-based displays; however, their B-site cations are confined to ns2, d5, and d10 metals. Here, the design of divalent rare earth ions at B-site is presented and a novel Eu(II)-based iodide hybrid is reported with efficient (PLQY ≈98%) narrow-band (FWHM ≈43 nm) green emission and high thermal stability (97%@150 °C). Owing to reduced lattice vibrations and shrunken average distance of Eu(II)-iodide bonds in the face-sharing 1D-structure, photoluminescence from Eu(II) 4f-5d transition appears along with elevated crystal-field splitting of 5d energy level. The Eu(II)-based iodide hybrid is further demonstrated for color-pure green phosphor-converted LEDs with a maximum brightness of ≈396 000 cd m-2 and photoelectric efficiency of 29.2%. High-resolution micrometer-scale light-emitting diode (micro-LED) displays (2540 PPI) via the solution-processed screen is also presented. This work thus showcases a compelling narrow-band green emitter for commercial micro-LED displays.

Ultrasensitive detection of zearalenone based on electrochemiluminescent immunoassay with Zr-MOF nanoplates and Au@MoS2 nanoflowers

In this work, an effective competitive-type electrochemiluminescence (ECL) immunosensor was constructed for zearalenone determination by using Zr-MOF nanoplates as the ECL luminophore and Au@MoS2 nanoflowers as the substrate material. Zr-MOF have an ultra-thin sheet-like structure that accelerates the transfer of electrons, ions and co-reactant intermediates, which exhibited strong and stable anodic luminescence. The three-dimensional Au@MoS2 nanoflowers would form a thin film modification layer on the glassy carbon electrode (GCE). And its good electrical conductivity and higher specific surface area utilization further improving the sensitivity of the ECL immunosensor. Under the optimized conditions, the proposed immunosensor exhibited satisfactory stability, sensitivity and accuracy, and its ECL signal was proportional to the logarithm of ZEN concentration (0.0001-100 ng/mL) and the limit of detection (LOD) was 0.034 pg/mL. In addition, the results of recovery experiment acquired for wheat flour and pig urine samples further proved the feasibility of the immunosensor for the detection of real samples, indicating its potential for ultrasensitive detection of ZEN.

Co3O4/NiCo2O4 heterojunction as oxygen evolution reaction catalyst for efficient luminol anode electrochemiluminescence

Luminol has garnered significant attention from analysts as one of the most effective and commonly used electrochemiluminescence (ECL) reagents. However, the efficient luminescence of luminol anode is limited by the excitation of various reactive oxygen species (ROS). Typically, ROS are generated through co-reactive reagents and dissolved oxygen. Unfortunately, the former suffers from two drawbacks, namely biotoxicity and instability, while the latter cannot offer sufficient oxygen due to its limited solubility in aqueous solutions. Consequently, a low decomposition rate is usually obtained, leading to insufficient ROS. Therefore, there is an urgent need to develop efficient luminol anode systems. This study focuses on the use of zeolitic imidazolate framework-67 (ZIF-67) as a template, employing a controlled chemical etching method to create a ZIF-67/Ni-Co-layered double hydroxide (LDH). The intermediate composite is then annealed in air, resulting in the formation of a Co3O4/NiCo2O4 double-shelled nanobox (DSNB) heterostructure. Due to its structural advantages, the DSNB exhibits excellent electrocatalytic performance in the oxygen evolution reaction (OER). Furthermore, it was found that both the intermediates and products of OER can directly participate in the luminol chemiluminescence process, ultimately resulting in a 700-fold increase in the electrochemiluminescence (ECL) signal compared to an equal molar concentration of luminol solution. This work not only establishes the OER-mediated ECL system but also deepens the understanding of the relationship between ROS and luminol, providing a new pathway to study the luminol anodic ECL luminescence system.

Eu3+-Doped Anionic Zinc-Based Organic Framework Ratio Fluorescence Sensing Platform: Supersensitive Visual Identification of Prescription Drugs

Advanced techniques for both environmental and biological prescription drug monitoring are of ongoing interest. In this work, a fluorescent sensor based on an Eu3+-doped anionic zinc-based metal-organic framework (Eu3+@Zn-MOF) was constructed for rapid visual analysis of the prescription drug molecule demecycline (DEM), achieving both high sensitivity and selectivity. The ligand 2-amino-[1,1'-biphenyl]-4,4'-dicarboxylic acid (bpdc-NH2) not only provides stable cyan fluorescence (467 nm) for the framework through intramolecular charge transfer of bpdc-NH2 infinitesimal disturbanced by Zn2+ but also chelates Eu3+, resulting in red (617 nm) fluorescence. Through the synergy of photoinduced electron transfer and the antenna effect, a bidirectional response to DEM is achieved, enabling concentration quantification. The Eu3+@Zn-MOF platform exhibits a wide linear range (0.25-2.5 μM) to DEM and a detection limit (LOD) of 10.9 nM. Further, we integrated the DEM sensing platform into a paper-based system and utilized a smartphone for the visual detection of DEM in water samples and milk products, demonstrating the potential for large-scale, low-cost utilization of the technology.

Co-Reactive Ligand In Situ Engineered Gold Nanoclusters with Ultra-Bright Near-Infrared Electrochemiluminescence for Ultrasensitive and Label-Free Detection of Carboxylesterase Activity

Ultrasensitive and accurate monitoring of carboxylesterase (CE) activity is extremely crucial for the early diagnosis of hepatocellular carcinoma (HCC), which is still a considerable challenge. Herein, using a co-reactive ligand engineering strategy, ultra-bright near-infrared (λmax = 830 nm) and self-enhanced electrochemiluminescence (ECL) Au nanoclusters (NCs) were in situ prepared with 2-(diethylamino) ethanethiol (DEAET) as a co-reactive ligand. Remarkably, the co-reactive ligand not only acts as a stabilizer like traditional ligands but also plays a crucial role as a co-reactant to ensure a confinement effect to shorten the charge transfer distance and increase the local concentration, significantly improving the collision efficiency between the electrogenerated free radicals. Consequently, the DEAET Au NCs exhibited a record and stable anodal ECL without the addition of an exogenous co-reactant, dramatically superior to classical Au NCs and Ru(bpy)32+ with a certain amount of the co-reactant. As a proof of concept, a convenient and label-free CE biosensor was innovatively constructed using 1-naphthyl acetate as a selective substrate, achieving ultrasensitive detection for CE activity with a low limit of detection of 9.1 × 10-7 U/L. Therefore, this work not only paves a co-reactive ligand engineering strategy for in situ preparation of high-efficiency metal NCs but also provides an ultrasensitive and convenient platform for the early diagnosis of HCC.

Double-Amplified Electrochemiluminescence Immunoassay Sensor for Highly Sensitive Detection of CA19-9 Using a Ternary Semiconductor CdSSe

In this paper, an electrochemiluminescence (ECL) immunosensor for ultrasensitive detection of CA19-9 was constructed using ternary compound CdSSe nanoparticles as ECL emitter. The immunosensor employs Cu2S and gold-doped diindium trioxide (Au-In2O3) nanocubes as coreaction accelerators to achieve a double-amplification strategy. In general, a hexagonal maple leaf-shaped Cu2S with a large surface area was selected as the template, and the in situ growth of CdSSe on its surface was achieved using a hydrothermal method. The presence of Cu2S not only inhibited the aggregation of CdSSe nanoparticles to reduce their surface energy but also acted as an ECL cathode coreaction promoter, facilitating the generation of SO4•-. Consequently, the ECL intensity of CdSSe was significantly enhanced, and the reduction potential was significantly lower. In addition, the template method was employed to synthesize Au-In2O3 nanocubes, which offers the advantage of directly connecting materials with antibodies, resulting in a more stable construction of the immunosensor. Furthermore, In2O3 serves as a coreaction promoter, enabling the amplification strategy for ECL intensity of CdSSe, thus contributing to the enhanced sensitivity and performance of the immunosensor. The constructed immunosensor exhibited a wide linear range (100 μU mL-1 to 100 U mL-1) and a low detection limit of 80 μU mL-1, demonstrating its high potential and practical value for sensitive detection of CA19-9.

Functionalized nanomaterials-based electrochemiluminescent biosensors and their application in cancer biomarkers detection

To detect a range of trace biomarkers associated with human diseases, researchers have been focusing on developing biosensors that possess high sensitivity and specificity. Electrochemiluminescence (ECL) biosensors have emerged as a prominent research tool in recent years, owing to their potential superiority in low background signal, high sensitivity, straightforward instrumentation, and ease of operation. Functional nanomaterials (FNMs) exhibit distinct advantages in optimizing electrical conductivity, increasing reaction rate, and expanding specific surface area due to their small size effect, quantum size effect, and surface and interface effects, which can significantly improve the stability, reproducibility, and sensitivity of the biosensors. Thereby, various nanomaterials (NMs) with excellent properties have been developed to construct efficient ECL biosensors. This review provides a detailed summary and discussion of FNMs-based ECL biosensors and their applications in cancer biomarkers detection.

Glucose oxidation induced pH stimuli response controlled release electrochemiluminescence biosensor for ultrasensitive detection of CYFRA 21-1

Herein, a self on electrochemiluminescence (ECL) biosensor was constructed by pH stimuli response controlled release strategy, in which SiO2-PEI as the carrier, BSA/luminol-Ab2 as the encapsulated substance, gold nanoparticles (Au NPs) as the blocking cap, glucose as the inducer. In addition, CeO2-Au was used as catalyst, which generated more O2•- to increase the ECL signal. Under the action of voltage, the glucose was oxidized to gluconic acid, which induced the pH to decrease accordingly. Therefore, Au NPs were stimulated to fall from the surface of SiO2-PEI, releasing the BSA/luminol-Ab2 to realize self on mode. With such design, the constructed self on ECL biosensor owned an ultrasensitive detection capacity of CYFRA 21-1, showing an excellent linear relationship in the range of 0.001-100000 ng/L and 0.4 fg/mL low limit of detection (LOD). It provided an innovative idea for the biosensor construction to clinical detection of lung cancer.

Synergetic-effect-enhanced electrochemiluminescence of zein-protected Au-Ag bimetallic nanoclusters for CA15-3 detection

In this work, a sandwich-type electrochemiluminescence (ECL) system was constructed for the detection of CA15-3. Gold-silver bimetallic nanoclusters (Au-Ag BNCs) with zein as a protective ligand were synthesized, and the excellent ECL performance of this material was demonstrated for the first time. Zein carrying a variety of groups that ligated with Au-Ag BNCs, forming a protective shell of zein, effectively prevented clusters from aggregating or growing into larger nanoparticles. The synergistic effect of the bimetal promotes the ECL emission, making this nanoscale material an ideal ECL probe. GO-PANI, which effectively promoting the production of sulfate radicals of the co-reactant and significantly increasing the ECL strength, was a good sensing platform for antibody immobilization. Consequently, we constructed an ECL sensor with GO-PANI as the sensing platform and Au-Ag BNCs@zein as the ECL probe, with a detection range of 0.001-100 U mL-1 and a detection limit of 0.0003 U mL-1, provided a strong support for the sensor for future CA15-3 detection applications.

Copper nanoclusters electrochemiluminescence with tunable near-infrared emission wavelength for ultrasensitive detection of matrix metalloproteinase-2

Herein, the methionine (Met)/N-acetyl-L-cysteine (NAC) templated copper nanoclusters (Met/NAC-Cu NCs) with tunable near-infrared region (NIR) electrochemiluminescence (ECL) emission wavelength was firstly synthesized as emitter for the ultrasensitive detection of matrix metalloproteinase-2 (MMP-2). Significantly, the NAC played the role of template and reductant of cupric to acquire Cu NCs, and the surface defect regulator Met was used to connect NAC through -S-S- bond, which could heighten the surface defect of Cu NCs to continuously regulate the maximum ECL emission by successively controlling the molar ratio of Met and NAC, leading to the ECL emission wavelength of Cu NCs ranged from 680 nm to 750 nm. In addition, a rapid target triggered catalyst hairpin assembly (CHA) recycling amplification strategy was constructed through orderly and equidistantly arranging hairpin to increase its local concentration, resulting in greatly accelerated signal amplification efficiency and reaction rate. As a proof of concept, based on Met/NAC-Cu NCs as NIR ECL emitter and effective signal amplification tactic, a super-sensitive ECL biosensor was fabricated to detect target MMP-2 with the detection limit (LOD) as low as 1.65 fg/mL and successfully utilized for detecting of MMP-2 that from Hela and MCF-7 cancer cells. This research provided a wonderful avenue for regulating the optical performance of metal nanoclusters-based ECL emitters, and the developed neoteric NIR ECL emitter with the merits of less photochemical damage and deeper tissue penetration exhibited great potential in ultrasensitive biosensing and high-definition ECL imaging.

Electrochemiluminescence Sensor with Controlled-Release Triggering Electrostatic Attraction Elimination Mechanism for Trenbolone Trace Detection

A controlled-release strategy can meet the needs of sensitive environmental monitoring for pollutants through a self-on/off mode. In this work, an electrochemiluminescence (ECL) biosensor with controlled-release triggering electrostatic attraction elimination and biomolecular stimulated response strategies was constructed to detect environmental steroid hormones sensitively. The blocked pores on the aminated mesoporous silica nanocontainers were opened by specific binding between the trenbolone (TB) antigen and the antibody. The released l-cysteine counteracted the negative charge on the MnO2 NF surface through the redox reaction between -SH and MnO2, making the electrostatic interaction between the MnO2 NFs and the Ru(dcbpy)32+ disappear. Ru(dcbpy)32+ released an ECL signal on the electrode, thus completing the controlled-release triggering electrostatic attraction elimination strategy. In addition, with the TB antibody as the target and the competition strategy between the TB antigen and the standard substance, the constructed controlled-release ECL biosensor was used to detect the TB standard substance. Moreover, MnO2 NFs as the substrate of the ECL biosensor increased the active specific surface area of the electrode, effectively catalyzing the production of OH• and O2•-, thus endowing the ECL biosensor with coreactant-catalytic enhancement characteristic and further improving its ECL performance. This sensitive signal response brought about a low limit of detection of 2.53 fg/mL for the constructed ECL biosensor, which contributed a feasible idea for efficient trace analysis of pollutants in the environment.

Electrochemiluminescence nanoemitters for immunoassay of protein biomarkers

The family of electrochemiluminescent luminophores has witnessed quick development since the electrochemiluminescence (ECL) phenomenon of silicon nanoparticles was first reported in 2002. Moreover, these developed ECL nanoemitters have extensively been applied in sensitive detection of protein biomarker by combining with immunological recognition. This review firstly summarized the origin and development of various ECL nanoemitters including inorganic and organic nanomaterials, with an emphasis on metal-organic frameworks (MOFs)-based ECL nanoemitters. Several effective strategies to amplify the ECL response of nanoemitters and improve the sensitivity of immunosensing were discussed. The application of ECL nanoemitters in immunoassay of protein biomarkers for diagnosis of cancers and other diseases, especially lung cancer and heart diseases, was comprehensively presented. The recent development of ECL imaging with the nanoemitters as ECL tags for detection of multiplex protein biomarkers on single cell membrane also attracted attention. Finally, the future opportunities and challenges in the ECL biosensing field were highlighted.

Ultrasensitive Electrochemiluminescence Biosensor with Silver Nanoclusters as a Novel Signal Probe and α-Fe2O3-Pt as an Efficient Co-reaction Accelerator for Procalcitonin Immunoassay

Herein, a high-efficiency biosensor based on ternary electrochemiluminescence (ECL) system was constructed for procalcitonin (PCT) detection. Specifically, silver nanoclusters (Ag NCs) with stable luminescence properties were prepared with small-molecule lipoic acid (LA) as the ligand, and its ECL emission in persulfate (S₂O₈^2-) was first reported. Meanwhile, the prepared Ag NCs possessed ligand-to-metal charge-transfer characteristics, thus transferring energy from LA to Ag⁺ for luminescence. Based on the small particle size, good biocompatibility, and molecular binding ability, Ag NCs-LA was used as an ideal luminescent probe. In addition, α-Fe₂O₃-Pt was introduced to facilitate the activation of S₂O₈^2-, thereby generating more sulfate radicals to react with the free radicals of Ag NCs to enhance ECL emission. The synergistic effect of the variable valence state of transition metals and high catalytic activity of noble metals endows α-Fe₂O₃-Pt with excellent catalytic ability for S₂O₈^2-. Importantly, the sensing mechanism was systematically demonstrated by UV-vis, fluorescence, and ECL analysis, as well as density functional theory calculations. At last, NKFRGKYKC was designed for specific immobilization of antibodies, thus releasing the antigen binding sites to improve the antigen recognition efficiency. Based on this, the developed biosensor showed high sensitivity for PCT detection, with a wide linear range (10 fg/mL-100 ng/mL) and a low detection limit (3.56 fg/mL), which could be extended to clinical detection of multiple biomarkers.

Advances in electrochemiluminescence for single-cell analysis

Recent years have witnessed the emergence of innovative analytical methods with high sensitivity and spatiotemporal resolution that allowed qualitative and quantitative analysis to be carried out at single-cell and subcellular levels. Electrochemiluminescence (ECL) is a unique chemiluminescence of high-energy electron transfer triggered by electrical excitation. The ingenious combination of electrochemistry and chemiluminescence results in the distinct advantages of high sensitivity, a wide dynamic range and good reproducibility. Specifically, single-cell ECL (SCECL) analysis with excellent spatiotemporal resolution has emerged as a promising toolbox in bioanalysis for revealing individual cells' heterogeneity and stochastic processes. This review focuses on advances in SCECL analysis and bioimaging. The history and recent advances in ECL probes and strategies for system design are briefly reviewed. Subsequently, the latest advances in representative SCECL analysis techniques for bioassays, bioimaging and therapeutics are also highlighted. Then, the current challenges and future perspectives are discussed.

Zinc-Based Metal-Organic Framework with MLCT Properties as an Efficient Electrochemiluminescence Probe for Trace Detection of Trenbolone

In this work, we utilized polycyclic aromatic hydrocarbon (PAH) derivatives as ligands to develop a zinc-based metal-organic framework (Zn-MOF) as an effective detection probe to construct an electrochemiluminescence (ECL) sensor for trenbolone detection. As traditional ECL emitters, PAHs and their derivatives have limited luminescence efficiency because of the aggregation-induced quenching (ACQ) effect. Therefore, Zn-PTC was designed by the coordination of 3,4,9,10-perylenetetracarboxylic (PTC) in the MOF to eliminate the ACQ effect. Meanwhile, Zn-PTC formed based on an aromatic ligand possessed the metal-to-ligand charge-transfer (MLCT) effect, which could transfer the energy of Zn²⁺ to the aromatic ligand for strong luminescence. The ECL efficiency of Zn-PTC was calculated to be approximately 2.2 times that of the ligand (K₄PTC). Second, the Ag@Fe core-shell bimetallic nanocrystal was prepared for efficient activation of persulfate (S₂O₈^2-), thereby generating more sulfate radicals (SO₄^•-) to further promote ECL emission. According to ECL characterizations, UV-vis and fluorescence spectra, and density functional theory calculations, the luminescence and signal amplification mechanisms were investigated. In addition, NKFRGKYKC (NKF) was introduced as an affinity ligand to directionally immobilize the target antibodies, thus releasing specific sites in their Fab fragment to enhance binding activity. Based on the above strategies, the constructed biosensor exhibited high sensitivity, realizing trace detection of TBE with a wide detection range (10 fg/mL-100 ng/mL) and a low detection limit (3.28 fg/mL). This study provided an important reference for sensitive monitoring of steroid pollutants in the environment.

A Portable Microfluidic-Based Electrochemiluminescence Sensor for Trace Detection of Trenbolone in Natural Water

In this study, a portable electrochemiluminescence sensor chip was designed for trenbolone (TBE) trace detection in environmental water. First, a stable ECL signal was obtained with low-toxicity 3,4,9,10-perylenetetracarboxylic acid (PTCA) as a luminophore and persulfate (S₂O₈^2-) as a coreactant. Second, hollow-structured Cu₂MoS₄ was introduced as a coreaction accelerator to catalyze S₂O₈^2- reduction. The reversible conversion of the mixed-valence transition metal ions in Cu₂MoS₄ (Cu⁺/Cu²⁺ and Mo⁴⁺/Mo⁶⁺) greatly promoted the generation of the sulfate radical (SO₄^•-). Meanwhile, the special porous structure of Cu₂MoS₄ possessed a large specific surface area, thus enhancing its catalytic performance. Based on these enhancement mechanisms, a strong ECL signal was acquired, which improved the detection sensitivity of the constructed sensor. Importantly, a microfluidic chip was introduced for sensing detection, thereby improving the practicality of the sensor. The developed sensor chip was miniature and portable, exhibiting high sensitivity for TBE detection with a wide linear range (10 fg/mL-100 ng/mL) and lower detection limit (3.32 fg/mL). This was of great significance for timely and rapid analysis of steroid pollutants in natural water.

Highly Efficient PTCA/Co3O4/CuO/S2O82- Ternary Electrochemiluminescence System Combined with a Portable Chip for Bioanalysis

Herein, we reported an efficient electrochemiluminescence (ECL) biosensor chip for sensitive detection of neuron-specific enolase (NSE). First, 3,4,9,10-perylenetetracarboxylic acid with good luminescence characteristics was used as a luminophore to obtain a stable ECL signal. Subsequently, hollow porous Co₃O₄/CuO concave polyhedron nanocages (CPNCs) were designed as co-reaction promoters to amplify the luminescence signals for highly sensitive trace detection of NSE. In brief, the rapid cyclic conversion of Co³⁺/Co²⁺ and Cu²⁺/Cu⁺ redox pairs could continuously catalyze the reduction of persulfate (S₂O₈^2-), thus providing a large number of essential active intermediates (SO₄^•-) for ECL emission. Meanwhile, the unique structure of Co₃O₄/CuO CPNCs possessed a large specific surface area, which greatly improved its catalytic efficiency. Third, NKFRGKYKC was developed as an affinity ligand for specific antibody fixation, which improved incubation efficiency and protected bioactivity of antibodies. Finally, we independently designed a microchip and applied it for ECL detection to improve the practical application ability of the sensor. The developed biosensor exhibited good sensitivity with a wide linear range (10 fg/mL to 100 ng/mL) and a low detection limit (3.42 fg/mL), which played an active role in the clinical application of sensing analysis.

High-bioactivity microfluidic immunosensing platform for electrochemiluminescence determination of CYFRA 21-1 with the introduction of Fe3O4@Cu@Cu2O

Relying on the electrochemiluminescence (ECL) and microfluidic technology, an immunosensor chip with high bioactivity was designed for sensitive determination of cytokeratin 19 fragment 21-1 (CYFRA 21-1). The mesoporous nanomaterial Fe₃O₄@Cu@Cu₂O as the co-reaction accelerator was used to catalyze the S₂O₈^2- to produce more SO₄^•- to achieve the amplification of the ECL signal. In fact, the generating of SO₄^•- could not only be done with the aid of the reversible cycles of Fe²⁺ and Fe³⁺ and Cu⁺ and Cu²⁺, but could be achieved also through the catalase-like function of Fe₃O₄. What is more, it has also been proved that Fe₃O₄@Cu@Cu₂O exhibited better catalytic performance than single Fe₃O₄, Cu₂O, and Cu@Cu₂O, which supported its application in this system. In addition, a portable microfluidic immunosensor chip for CYFRA 21-1-sensitive determination was assembled, which showed high selectivity, sensitivity, and strong universality in clinical cancer screening and diagnosis. It should be noted that HWRGWVC (HWR) was introduced as the antibody fixator to improve the incubation and binding efficiency of the antibody, which increased the ECL intensity and improved the sensitivity of the immunosensor. This strategy provided a new idea for cancer identification and diagnosis in clinical medicine.

Efficient ABEI-Dissolved O2-Ce(III, IV)-MOF Ternary Electrochemiluminescent System Combined with Self-Assembled Microfluidic Chips for Bioanalysis

A signal-amplified electrochemiluminescent (ECL) sensor chip was developed for sensitive analysis of procalcitonin (PCT). Herein, we first prepared a self-enhanced luminophore, which enhanced ECL responses through intramolecular reactions. Second, Au-Pd bimetallic nanocrystals and mixed-valence Ce-based metal-organic frameworks (MOFs) were introduced as co-reaction promoters to facilitate the reduction of dissolved O₂. Based on the synergistic catalysis of Au and Pd, the spontaneous cyclic reaction of Ce(III)/Ce(IV), and the high electrochemical active surface area of Ce(III, IV) MOF, a large number of superoxide anion radicals (O₂^•-) and hydroxyl radicals (OH^•) were produced. Therefore, the luminescence efficiency of N-(aminobutyl)-N-(ethylisoluminol)-dissolved O₂ (ABEI-O₂) systems were greatly improved, providing a new prospect for the application of dissolved O₂ in ECL analysis. In addition, the affinity peptide ligands were used for the directional connection of antibodies to provide protection for the bioactivity of the proposed sensor. Finally, the microfluidic technology was applied to ECL analysis to integrate the three-electrode detection system into the self-assembled microfluidic chip, which realized the automation and portability of the detection process. The developed sensor showed high sensitivity for PCT detection with a detection limit of 3.46 fg/mL, which possessed positive significance for the clinical diagnosis of sepsis.

Hollow Double-Shell CuCo2O4@Cu2O Heterostructures as a Highly Efficient Coreaction Accelerator for Amplifying NIR Electrochemiluminescence of Gold Nanoclusters in Immunoassay

The evolution of electrochemiluminescence (ECL) emission amplified by coreaction accelerator in near-infrared (NIR) area has been overwhelmingly anticipated for ultrasensitive detection of disease biomarkers. Herein, the hollow double-shell CuCo₂O₄@Cu₂O (HDS-CuCo₂O₄@Cu₂O) heterostructures were conveniently prepared and utilized as an attractive coreaction accelerator to improve the NIR ECL performance of gold nanoclusters (AuNCs) for the first time. Benefiting from perfect-matched lattice spacing, unique Cu₂O nanoparticles (NPs) were formed in situ on the layered-hollow CuCo₂O₄ nanospheres (NSs) to obtain HDS-CuCo₂O₄@Cu₂O heterostructures. The formed heterojunctions supplied shorter charge transfer distance and better interfacial charge transfer efficiency as well as more effective separation performance. Consequently, HDS-CuCo₂O₄@Cu₂O heterostructures as an admirable electroactive substrate could significantly promote the formation of sufficient coreactant intermediate radicals to react with AuNCs cationic radicals, realizing about 3-folds stronger NIR ECL response than that of individual AuNCs. In addition, the AuNCs templated by l-methionine (l-Met) exhibited NIR ECL emission around 830 nm, which could decrease the photochemical damage to even realize a nondestructive detection with improved susceptibility and circumambient adaptability. Subsequently, a well site-oriented fixation strategy utilizing HWRGWVC heptapeptide as the specific antibody immobilizer was introduced to further preserve the bioactivity of antibody on the HDS-CuCo₂O₄@Cu₂O and AuNCs surface along with enhancing the incubation performance markedly. In view of the progressive sensing mechanism, a NIR immunosensor was obtained for the ultrasensitive analysis of CYFRA21-1, which achieved a broad linear ranging from 2 fg/mL to 50 ng/mL and a low limit of detection (LOD) of 0.67 fg/mL (S/N = 3).

Pyrenecarboxaldehyde encapsulated porous TiO2 nanoreactors for monitoring cellular GSH levels

Recently, ternary electrochemiluminescence (ECL) system has become a hot research topic due to its great potential for improving ECL efficiency by promoting the generation of intermediates. However, it is still a great challenge to increase the utilization rate of intermediates in a ternary ECL system. Herein, we propose a strategy to increase the utilization rate of intermediates by designing pyrenecarboxaldehyde (Pyc) encapsulated porous titania (pTiO₂) nanospheres (Pyc@pTiO₂) as ECL nanoreactors for an integrated ternary (luminophore/coreactant/co-reaction accelerator, Pyc/S₂O₈^2-/TiO₂) ECL system construction. Specifically, pTiO₂ acted as an ECL co-reaction accelerator, in which Pyc could obtain electrons from the conduction band of TiO₂ to produce more SO₄˙^-, increasing its emissions. Simultaneously, pTiO₂ could provide confined reaction spaces to effectively shorten the diffusion distance, extend the lifetime of free radicals, increase the utilization rate of intermediates and improve the efficiency of the ternary ECL system. As a proof of concept, the Pyc@pTiO₂ nanoreactors-based sensing platform was successfully constructed to sensitively monitor cellular GSH levels. Overall, this work for the first time proposed an avenue to increase the utilization rate of intermediates in a ternary ECL system, which opened a new route for ECL biosensing in cell analysis applications.

Cysteine Modification of Glutathione-Stabilized Au Nanoclusters to Red-Shift and Enhance the Electrochemiluminescence for Sensitive Bioanalysis

Screening new electrochemiluminescence (ECL) emitters for the design of sensitive detection strategies with even long emission wavelength is intensively anticipated in ECL evolution. Herein, a promising modification strategy for improving the ECL performance of Au nanoclusters (AuNCs) as a water-soluble luminophore was proposed. Upon the introduction of l-cysteine (l-Cys) onto the surface of glutathione (GSH)-stabilized AuNCs (GSH-AuNCs), the dual-thiol bond between l-Cys and GSH was formed to limit the intramolecular motion and nonradiative relaxation of the excited state from the capping agents, which resulted in the enhancement of monochromatic ECL emission of GSH-AuNCs with a red-shifted wavelength. By utilizing triethylamine as a coreactant, the ECL of l-Cys/GSH-AuNCs was about 1.5-fold stronger than that of GSH-AuNCs, and the emission wavelength red-shifted from 660 to 780 nm at a relatively low potential, which could decrease the interference in bioassay and the photochemical damage in nondestructive detection. As a proof of application, a sandwich-type immunosensing method for CYFRA 21-1 was proposed with l-Cys/GSH-AuNCs as the signal tag, which displayed a wide linear ranging from 0.2 fg/mL to 2 ng/mL and a limit of detection down to 0.067 fg/mL at 3S/N. This work provides a wonderful strategy for promoting the performance of ECL emitters.

Plasmon-Enhanced Electrochemiluminescence of PTP-Decorated Eu MOF-Based Pt-Tipped Au Bimetallic Nanorods for the Lincomycin Assay

Plasmonic bimetal nanostructures can be employed to amplify electrochemiluminescence (ECL) signals. In this work, a high-performance ECL platform was constructed using a europium metal-organic framework (MOF) as a luminophore and Au-Pt bimetallic nanorods (NRs) as a plasma source. Due to the SPR effect of Au-Pt NRs, the aptasensor exhibits 2.6-fold ECL intensity compared to that of pure polyaniline (PANI)-decorated perylene tetracarboxylic dianhydride (PTCA)/Eu MOF. Moreover, decoration with PTP greatly enhances the conductivity and stability of Eu MOF, resulting in sizeable plasmon-enhanced electrochemical luminescence. The as-designed plasmon-enhanced ECL aptasensor displayed highly sensitive detection for lincomycin (Lin). The as-proposed aptasensor could quantify Lin from 0.1 mg/mL to 0.1 ng/mL with a limit of detection (LOD) of 0.026 ng/mL.

Copper-Doped Terbium Luminescent Metal Organic Framework as an Emitter and a Co-reaction Promoter for Amplified Electrochemiluminescence Immunoassay

This work designed a signal amplification strategy for construction of a highly sensitive electrochemiluminescence (ECL) biosensor by doping Cu²⁺ in a terbium luminescent metal organic framework (Cu:Tb-MOF) to act as a co-reaction promoter, which enhanced the generation of SO₄^•- radical during the cathodic process in the presence of K₂S₂O₈ as a co-reactant. The porous and hollow morphology and the size of Cu:Tb-MOF could be efficiently tuned via changing the molar ratio of Cu²⁺ and Tb³⁺ and the reaction time, which were related to the specific surface area, pore diameter, and the ECL intensity of the MOF structure. To further improve the sensitivity of the ECL biosensor, H₂O₂ was introduced into the ECL system to act as another co-reaction promoter, leading to a new ECL mechanism involving dual co-reaction promoters. In view of the low electron transfer resistance of Cu:Tb-MOF, a label-free ECL immunosensor was conveniently constructed by co-immobilizing Cu:Tb-MOF and the capture antibody on the electrode surface. Using pro-gastrin-releasing peptide (ProGRP, a biomarker of small-cell lung cancer) as the model target, the proposed immunosensor exhibited excellent performance with a detection range of 1.0 pg·mL^-1 to 50 ng·mL^-1 and a limit of detection down to 0.68 pg·mL^-1 (3σ). This work demonstrated a strategy to use the MOF structures as both an emitter and a co-reaction promoter for amplified ECL emission and proposed an innovative route to extend the application of lanthanide MOFs.

Peptide-Based Electrochemiluminescence Biosensors Using Silver Nanoclusters as Signal Probes and Pd-Cu2O Hybrid Nanoconcaves as Coreactant Promoters for Immunoassays

Metal nanoclusters (NCs) possess high light stability and biocompatibility because of their unique quantum size effect, which has gradually become a new type of electrochemiluminescence (ECL) nanomaterial for immunoassays. However, the luminescence efficiency of metal NCs is too low to meet the needs of trace analysis, which limits its application. Herein, Ag NCs served as signal probes and Pd-Cu₂O hybrid nanoconcaves served as coreaction promoters, developing a highly efficient peptide-based biosensor for neuron-specific enolase (NSE) detection. Utilizing the reversible cycle of Cu⁺/Cu²⁺ and the reduction characteristics of Pd NPs, Pd-Cu₂O greatly accelerates the reduction of S₂O₈^2-. Meanwhile, Pd-Cu₂O has good hydrogen evolution activity, which promotes the generation of oxygen by improving the redox efficiency of the overall reaction, thus increasing the yield of active intermediates (OH^•) to promote the reduction of S₂O₈^2-. Specially, this is an effective attempt to use the hydrogen evolution reaction (HER) to accelerate the ECL emission of the S₂O₈^2- system. In addition, a short peptide ligand (NARKFYKGC, NFC) was developed to implement the targeted immobilization of antibodies, which can specifically bind to the Fc fragment of antibodies, thereby avoiding the occupation of the antigen binding site (Fab fragment). The introduction of NFC not only improves the binding efficiency of antibodies but also protects its bioactivity, thus significantly improving the sensitivity of the biosensor. Based on these strategies, the proposed biosensor provides a new perspective for the applications of metal NCs in ECL systems.