Highly Efficient Dual-Polar Electrochemiluminescence from Au25 Nanoclusters: The Next Generation of Multibiomarker Detection in a Single Step

Electron-Accelerator-Induced Fast Electron Transfer for Enhancing Electrochemiluminescence of Gold Nanoclusters and Its Bioanalysis Application: A Novel Avenue for Developing High-Efficient Emitters

Herein, the gold nanoclusters/CaFe2O4 nanospheres (Au NCs/CaFe2O4) heterostructure as a novel electrochemiluminescence (ECL) emitter was developed. Excitingly, Au NCs/CaFe2O4 displayed highly efficient and greatly stable ECL based on the newly defined electron-accelerator p-type semiconductor CaFe2O4 NS-induced fast electron transfer; it solved one key obstacle of metal NC-based ECL emitters: sluggish through-covalent bond electron transport kinetics-caused inferior ECL performance. Specifically, on account of the energy level matching between emitter Au NCs and electron-accelerator CaFe2O4 NSs, the valence band (VB) of the electron-accelerator could provide abundant holes for rapidly transporting the electrogenerated electron from the highest occupied molecular orbital (HOMO) of Au NCs to the electrode, generating massive excited species of Au NCs for strong ECL emission. Notably, Au NCs/CaFe2O4 emerged 5.4-fold higher ECL efficiency with 3.5-fold higher electrochemical oxidation current in comparison with pure Au NCs, exhibiting great prospects in extensive lighting installations, ultrasensitive biosensing, and high-resolution ECL imagery. As applications, an ECL bioassay platform was constructed with Au NCs/CaFe2O4 as an emitter and U-like structure-fueled catalytic hairpin assembly (U-CHA) as a signal amplifier for fast and trace analysis of aflatoxin B1 (AFB1) with the detection limit (LOD) down to 2.45 fg/mL, which was 3 orders of magnitude higher than that of the previous ECL biosensors with much better stability. This study developed an entirely new avenue for enlarging the ECL performance of metal NCs, and it is a very attractive orientation for directing the reasonable design of prominent metal NC-based ECL emitters and broadening the practical application of metal NCs.

Construction of self-enhanced luminescence probes based on Ti3C2 reducibility for ultrasensitive PNK analysis

Au nano-clusters (Au NCs) were promising electrochemiluminescence (ECL) nano-materials. However, the small size of Au NCs presented a challenge in terms of their immobilization during the construction of an ECL biosensing platform. This limitation significantly hindered the wider application of Au NCs in the ECL field. In this work, we successfully used the reducibility of Ti3C2 to fabricate in situ a self-enhanced nano-probe Ti3C2-TiO2-Au NCs. The strategy of in situ generation not only improved the immobilization of Au NCs on the probe but also eliminated the requirement of adding reducing agents during preparation. In addition, in situ generated TiO2 could serve as a co-reaction accelerator, shortening the electron transfer distance between S2O82- and Au NCs, thereby improving the utilization of intermediates and enhancing the ECL response of Au NCs. The constructed ECL sensing platform could achieve sensitive detection of polynucleotide kinase (PNK). At the same time, the 5'-end phosphate group of DNA phosphorylation could chelate with a large amount of Ti on the surface of Ti3C2, thereby achieving the goal of specific detection of PNK. The sensor based on self-enhanced ECL probes had a broad dynamic range spanning for PNK detection from 10.0 to 1.0 × 107 μU mL-1, with a limit of detection of 1.6 μU mL-1. Moreover, the ECL sensor showed satisfactory detection performance in HeLa cell lysate and serum. This study not only provided insights for addressing the issue of ECL luminescence efficiency in Au NCs but also presented novel concepts for ECL self-enhancement strategies.

Highly Electroactive Co2+-Based Metal-Organic Frameworks as an Efficient Coreaction Accelerator for Amplifying Near-Infrared Electrochemiluminescence of Gold Nanoclusters in Biomarkers Immunoassay

Metal nanoclusters (NCs) as a new kind of luminophore have acquired sufficient interest, but their widespread application is restricted on account of their relatively low electrochemiluminescence (ECL) efficiency. Then, aqueous metal NCs with high ECL efficiency were strongly anticipated, especially for the ultrasensitive analysis of biomarkers. Herein, a near-infrared (NIR) ECL biosensing strategy for the test of neuron-specific enolase (NSE) was proposed by utilizing N-acetyl-l-cysteine (NAC)- and cysteamine (Cys)-stabilized gold NCs (NAC/Cys-AuNCs) as ECL emitters with the NIR ECL emission around 860 nm and a metal-organic framework/palladium nanocubes (ZIF-67/PdNCs) hybrid as the coreaction accelerator through their admirable electrocatalytic activity. The NIR emission would reduce photochemical injury to the samples and even realize nondestructive analysis with highly strong susceptibility and suitability. Furthermore, the utilization of ZIF-67/PdNCs could improve the ECL response of NAC/Cys-AuNCs by facilitating the oxidation of the coreactant triethylamine (TEA), leading to the production of a larger quantity of reducing intermediate radical TEA•+. Consequently, NAC/Cys-AuNCs with ZIF-67/PdNCs displayed 2.7 fold enhanced ECL emission compared with the single NAC/Cys-AuNCs using TEA as the coreactant. In addition, HWRGWVC (HWR), a heptapeptide, was introduced to immobilize antibodies for the specially binding Fc fragment of the antibodies, which improved the binding efficiency and sensitivity. As a result, a "signal-on" immunosensor for NSE analysis was obtained with an extensive linear range of 0.1 to 5 ng/mL and a low limit of detection (0.033 fg/mL) (S/N = 3). This study provides a wonderful method for the development of an efficient nondestructive immunoassay.

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.

Silver Nanocluster-Tagged Electrochemiluminescence Immunoassay with a Sole and Narrow Triggering Potential Window

The commercialized electrochemiluminescence (ECL) immunoassay is carried out by holding luminophore Ru(bpy)32+ at a given potential. Designing an electrochemiluminophore with a narrow triggering potential window is strongly anticipated to decrease the electrochemical cross-talk and improve the flux of the commercialized ECL immunoassay in a potential-resolved way. Herein, L-penicillamine-capped silver nanoclusters (LPA-AgNCs) are facilely synthesized and utilized as tags to perform the ECL immunoassay with a sole and narrow triggering potential window of 0.24 V by employing hydrazine (N2H4) as a coreactant. The maximum ECL emission of the LPA-AgNCs/N2H4 system is located ca. +1.27 V. Upon immobilizing LPA-AgNCs onto the electrode surface via forming a sandwich immunocomplex, the ECL of LPA-AgNCs/N2H4 can be utilized to sensitively and selectively determine human carcinoembryonic antigen from 0.5 to 1000 pg/mL with a low limit of detection of 0.1 pg/mL (S/N = 3). This work might open a way to screen electrochemiluminophores for the multiple ECL immunoassay in a potential-resolved way.

Utilizing the Oxygen Reduction Reaction in Particle Impact Electrochemistry: A Step toward Mediator-Free Digital Electrochemical Sensors

The current blockade particle impact method opens a route toward highly parallelized single-entity electrochemical assays. An important limitation is, however, that a redox mediator must be present in the sample, which can detrimentally interfere with molecular recognition processes. Dissolved O2 that is naturally present in aqueous solutions under ambient conditions can in principle serve as a suitable mediator via the oxygen reduction reaction (ORR). Here, we demonstrate the validity of this concept by performing current blockade experiments to capture and detect individual microparticles at Pt microelectrodes using solely the ORR. The readout modality is independent of the absolute O2 concentration, allowing operation under varying conditions. We further determine how the trajectories of individual microparticles are influenced by the combination of electrophoresis and electroosmotic flows and how these can be utilized to provide continuous detection of cationic particles in water for environmental monitoring.

Non-enzymatic electrochemiluminescence biosensor for ultrasensitive detection of ochratoxin A based on efficient DNA walker

Ochratoxin A (OTA) with high toxicity represents a serious threat to the agriculture and food chain, consequently to human health. Herein, a simple electrochemiluminescence (ECL) biosensor was constructed for ultrasensitive detection of OTA based on mercaptopropionic acid templated Au nanoclusters (Au NCs) as intensive signal probe and a non-enzymatic 2D DNA walking machine as the effective amplification strategy. Specifically, the target related bipedal DNA walker efficiently moved along 2D DNA tracks through toehold-mediated DNA strand displacement, which triggered abundant signal probes for combining to the DNA tracks. Moreover, the Au NCs could exhibit strong ECL emission due to fast electron transfer from massive Au-S electronic pathways under the electrochemical excitation. Thus, the biosensor possessed significant ECL response for achieving ultrasensitive detection toward OTA with low detection limit of 3.19 fg/mL. Impressively, the sensing platform was also applied to detect OTA from edible oils, exhibiting great application potential in food analysis.

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.

Recent progress in assembly strategies of nanomaterials-based ultrasensitive electrochemiluminescence biosensors for food safety and disease diagnosis

The Electrochemiluminescence (ECL)-based biosensors have received considerable attention in food contaminants and disease diagnosis, due to their fascinating advantages such as low cost, fast analysis speed, wide linear range, high sensitivity, and excellent anti-interference ability. Meanwhile, with the vigorous development and improvement of nanotechnology, biosensor assembly strategies tend to diversify and be multifunctional. This review focuses on the representative ECL biosensors in food safety and disease diagnosis reported by our research group and other research groups based on nanomaterials assembly strategies in recent years. According to the different roles of nanomaterials played in the constitution of ECL biosensors, nanomaterials would be divided into the following two categories to be summarized: (1) Nanomaterials for signal amplification. (2) Nanomaterials as ECL emitters. Finally, this review prospects the perspectives on the future development direction of ECL biosensor in food safety and disease diagnosis.

2D Zn-Porphyrin-Based Co(II)-MOF with 2-Methylimidazole Sitting Axially on the Paddle-Wheel Units: An Efficient Electrochemiluminescence Bioassay for SARS-CoV-2

High electrocatalytic activity with tunable luminescence is crucial for the development of electrochemiluminescence (ECL) luminophores. In this study, a porphyrin-based heterobimetallic 2D metal organic framework (MOF), [(ZnTCPP)Co2(MeIm)] (1), is successfully self-assembled from the zinc(II) tetrakis(4-carboxyphenyl)porphine (ZnTCPP) linker and cobalt(II) ions in the presence of 2-methylimidazole (MeIm) by a facile one-pot reaction in methanol at room temperature. On the basis of the experimental results and the theoretical calculations, the MOF 1 contains paddle-wheel [Co2(-CO2)4] secondary building units (SBUs) axially coordinated by a MeIm ligand, which is very beneficial to the electron transfer between the Co(II) ions and oxygen. Combining the photosensitizers ZnTCPP and the electroactive [Co2(-CO2)4] SBUs, the 2D MOF 1 possesses an excellent ECL performance, and can be used as a novel ECL probe for rapid nonamplified detection of the RdRp gene of SARS-CoV-2 with an extremely low limit of detection (≈30 aM).

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

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

Recent progress of metal nanoclusters in electrochemiluminescence

Metal nanoclusters (MeNCs), composed of a few to hundreds of metal atoms and appropriate surface ligands, have attracted extensive interest in the electrochemiluminescence (ECL) realm owing to their molecule-like optical, electronic, and physicochemical attributes and are strongly anticipated for discrete energy levels, fascinating electrocatalytic activity, and good biocompatibility. Over the past decade, huge efforts have been devoted to the synthesis, properties, and application research of ECL-related MeNCs, and this field is still a subject of heightened concern. Therefore, this perspective aims to provide a comprehensive overview of the recent advances of MeNCs in the ECL domain, mainly covering the emerged ECL available MeNCs, unique chemical and optical properties, and the general ECL mechanisms. Synthesis strategies for desirable ECL performance are further highlighted, and the resulting ECL sensing applications utilizing MeNCs as luminophores, quenchers, and substrates are discussed systematically. Finally, we anticipate the future prospects and challenges in the development of this area.

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).

Tetrahedral DNA Nanostructure with Multiple Target-Recognition Domains for Ultrasensitive Electrochemical Detection of Mucin 1

In this work, a tetrahedral DNA nanostructure (TDN) designed with multiple biomolecular recognition domains (m-TDN) was assembled to construct an ultrasensitive electrochemical biosensor for the quantitative detection of tumor-associated mucin 1 (MUC-1) protein. This new nanostructure not only effectively increased the capture efficiency of target proteins compared to the traditional TDN with a single recognition domain but also enhanced the sensitivity of the constructed electrochemical biosensors. Once the target MUC-1 was captured by the protein aptamers, the ferrocene-marked DNA strands as electrochemical signal probes at the vertices of m-TDN would be released away from the electrode surface, causing significant reduction of the electrochemical signal, thereby enhancing significantly the detection sensitivity. As a result, this well-designed biosensor achieved ultrasensitive detection of the biomolecule at a linear range from 1 fg mL^-1 to 1 ng mL^-1, with the limit of detection down to 0.31 fg mL^-1. This strategy provides a new approach to enhance the detection sensitivity for the diagnosis of diseases.

An Iron(III)-Based Metal-Organic Gel-Catalyzed Dual Electrochemiluminescence System for Cytosensing and In Situ Evaluation of the VEGF165 Subtype

The recent surge of interest in metal-organic gels (MOGs) has emerged for their soft porous structure, large surface area, and abundant active metal sites, making them a promising candidate for building catalyst matrices. In this work, facilely synthesized Fe(III)-organic gel was directly used as a robust electrode matrix. Detailed studies illustrated that their Fe(III) centers can speed up the electro-oxidation/reduction of the H₂O₂ coreactant to produce reactive oxygen species for enhancing a potential-resolved dual electrochemiluminescence (ECL) emission. Among them, the anodic signal of luminol varied with the cell concentration based on the impedance ECL mechanism, while the cathodic signal of CdS quantum dots traced the VEGF₁₆₅ subtype at cell surface by specific aptamer recognition. Based on this, a ratiometric strategy was proposed for accurate cytosensing by eliminating environmental interference. Moreover, by cooperating these two signals, a novel strategy was developed for direct evaluation of the VEGF₁₆₅ subtype, further realizing rapid drug screening and subtype assessment on different cell lines. This work not only opens up the promising application of MOGs as an effective catalyst matrix but also develops reliable cell assays and protein subtype identification for clinical diagnosis and research.

Universal point-of-care detection of proteins based on proximity hybridization-mediated isothermal exponential amplification

A lateral flow biosensor has been fabricated for protein detection based on a protein-to-DNA signal transducer, isothermal exponential amplification and catalytic hairpin assembly with high sensitivity and specificity.

Au nanoclusters modulated macrophages polarization and synoviocytes apoptosis for enhanced rheumatoid arthritis treatment

The persistent progression of synovial inflammation and cartilage destruction was contributed to the cross-talk of pro-inflammatory macrophages and activated fibroblast-like synoviocytes (FLS) in synovial microenvironment. In this work, a structurally...

Absolute Electrochemiluminescence Efficiency Quantification Strategy Exemplified with Ru(bpy)32+ in the Annihilation Pathway

This work presents a thorough guide to procedures for absolute electrochemiluminescence (ECL) quantum efficiency (Φ_ECL) measurements, which if employed effectively should raise the research impact of ECL studies for any luminophore. Absolute measurements are not currently employed in ECL research. Instead, ECL efficiencies have been determined relative to Ru(bpy)₃²⁺ under similar conditions, regardless of whether the conditions are favorable for Ru(bpy)₃²⁺ emissions or not. In fact, the most cited Ru(bpy)₃²⁺ Φ_ECL is from the pioneering work by the Bard research group in 1973 by means of a rotating ring-disk electrode revolving at 52 rotations per second measured with a silicon photodiode. Our presented technique uses a common disk electrode, spectrometer, and photomultiplier tube to measure the Φ_ECL. The more common light detection hardware and electrodes combined with an in-depth calculation walkthrough will provide ECL researchers the necessary tools to implement Φ_ECL measurement procedures in their own laboratories. Following a facile instrument setup and calculation, a systematic study of Ru(bpy)₃²⁺ Φ_ECL finds comparable results to those performed by Bard and co-workers.

High-Efficient Electrochemiluminescence of Au Nanoclusters Induced by the Electrosensitizer Cu2O: The Mechanism Insights from the Electrogenerated Process

Herein, a novel Au nanoclusters/Cu₂O (Au NCs/Cu₂O) heterostructure exhibited exceptionally strong electrochemiluminescence (ECL) emission, in which the p-type semiconductor Cu₂O was defined as the electrosensitizer to provide the electrogenerated holes for rapidly transferring the electrogenerated hot electrons of Au NCs. Thus, the fast charge transfer of Au NCs/Cu₂O was achieved by the electrosensitizer compared to the sluggish one via intramolecular covalent bond charge transfer of traditional Au NCs, resulting in a greatly higher ECL efficiency (63.8%) than that of pure Au NCs (2.7%) versus the standard [Ru(bpy)₃]²⁺. It solved one main challenge of electrochemiluminophore-based metal NCs: high efficiency with energic charge-transport kinetics. As a proof of concept, Au NCs/Cu₂O was successfully employed in an ultrasensitive ECL biosensing platform for determining the biological antioxidant glutathione with a limit of detection (LOD) as low as 6.3 pM. The heterostructure as an ECL emitter is a very promising start for guiding the rational design of efficient electrochemiluminophores in intense light-emitting devices and high-definition ECL imaging.

Functionalized europium-porphyrin coordination polymer: Rational design of high performance electrochemiluminescence emitter for mucin 1 sensing

The excellent characteristics of porphyrins have inspired widespread interest in electrochemiluminescence (ECL). However, the limited ECL intensity and poor stability of porphyrins in aqueous solution are still severely restricted further biological application. Here, we subtly synthesized a functionalized europium and 5,10,15,20-tetrakis (4-carboxyphenyl) porphyrin (TCPP) coordination polymer (Eu-PCP) by a one-step solvothermal method. In sharp contrast to the pristine TCPP, Eu-PCP showed a higher and more stable ECL red-light emission (673 nm) at low potential (-1.1 V, vs Ag/AgCl), which was 7.7-fold higher ECL intensity and 4.6-fold efficiency. In view of the crucial role of mucin 1 (MUC1) in tumor overexpression, it was selected as the target molecule. Combined with exonuclease III (Exo III)-assisted recycling amplification strategy, a ternary ECL biosensor was constructed for the MUC1 detection based on Eu-PCP as a satisfied ECL emitter, gold nanoparticles capped CeO₂ (CeO₂@Au) as the coreactant accelerator and peroxydisulfate as coreactant. Meanwhile, gold nanoparticles capped MnO₂ (MnO₂@Au) was used as the quenching probe to achieve a highly sensitive detection of MUC1. The proposed biosensor exhibited a wide linear range from 1 fg mL^-1 to 10 ng mL^-1 with a low limit of detection (0.32 fg mL^-1). By changing the corresponding target recognition DNA, this strategy could be expanded to detect other biomarkers.

Diagnosis of cancer at early stages based on the multiplex detection of tumor markers using metal nanoclusters

Traditional cancer diagnosis strategies are not considered by most people until the last resort, which delays many cancer treatments leading to advanced stages. Tumor marker sensors show great potential for detecting cancer because of its cost-effective and harmless checking procedures. Normally, one tumor marker is detected each time by using one type of sensor, but the accuracy to declare cancer is not always satisfied. Metal nanoclusters are ultra-small nanomaterials with low toxicity, distinct optical properties, catalytic activities, and cost-effective performance. Some metal nanoclusters have been designed to detect more than one tumor marker in a single step. The consideration of combined parameters using such facile sensing strategies has the potential to simplify the test procedure, and increase the diagnostic accuracy of early cancer. Therefore, various sensing strategies for the multiplex detection of tumor markers using metal nanoclusters are summarized.

Dual-potential electrochemiluminescence of single luminophore for detection of biomarker based on black phosphorus quantum dots as co-reactant

Simultaneous cathodic and anodic electrochemiluminescence (ECL) emissions of needle-like nanostructures of Ru(bpy)₃²⁺ (RuNDs) as the only luminophore are reported based on different co-reactants. Cathodic ECL was attained from RuNDs/K₂S₂O₈ system, while anodic ECL was achieved from RuNDs/black phosphorus quantum dots (BPQDs) system. Ferrocene attached to the hairpin DNA could quench the cathodic and anodic ECL simultaneously. Subsequently, the ECL signals recovered in the presence of tumor marker mucin 1 (MUC1), which made it possible to quantitatively detect MUC1. The variation of ECL signal was related linearly to the concentrations of MUC1 in the range 20 pg mL^-1 to 10 ng mL^-1, and the detection limits were calculated to 2.5 pg mL^-1 (anodic system, 3σ) and 6.2 pg mL^-1 (cathodic system, 3σ), respectively. The recoveries were 97.0%, 105%, and 95.2% obtained from three human serum samples, and the relative standard deviation (RSD) is 5.3%. As a proof of concept, this work realized simultaneous ECL emission of  a single luminophore, which initiates a new thought in biomarker ECL detection beyond the traditional ones. Simultaneous cathodic and anodic ECL emissions of RuNDs were reported based on different co-reactants. Ferrocene could quench the ECL emission in the cathode and the anode simultaneously. Thus, an aptasensor was constructed based on the variation of ECL intensity. As a proof of concept, this work realized simultaneous ECL emission of a single luminophore, which initiates a new thought in biomarker ECL detection beyond the traditional ones by avoiding the false positive signals.

Recent advances in templated synthesis of metal nanoclusters and their applications in biosensing, bioimaging and theranostics

As a kind of promising nanomaterials, metal nanoclusters (MNCs) generally composed of several to hundreds of metal atoms have received increasing interest owing to their unique properties, such as ultrasmall size (<2 nm), fascinating physical and chemical properties, and so on. Recently, template-assisted synthesis of MNCs (e.g., Au, Ag, Cu, Pt and Cd) has attracted extensive attention in biological fields. Up to now, various templates (e.g., dendrimers, polymers, DNAs, proteins and peptides) with different configurations and spaces have been applied to prepare MNCs with the advantages of facile preparation, controllable size, good water-solubility and biocompatibility. Herein, we focus on the recent advances in the template-assisted synthesis of MNCs, including the templates used to synthesize MNCs, and their applications in biosensing, bioimaging, and disease theranostics. Finally, the challenges and future perspectives of template-assisted synthesized MNCs are highlighted. We believe that this review could not only arouse more interest in MNCs but also promote their further development and applications by presenting the recent advances in this area to researchers from various fields, such as chemistry, material science, physiology, biomedicine, and so on.

Progress in electrochemiluminescence of nanoclusters: how to improve the quantum yield of nanoclusters

Classification of nanoclusters and methods to improve their quantum yield and applications.

Cas12a-based electrochemiluminescence biosensor for target amplification-free DNA detection

CRISPR/Cas system have drawn increasing attention in accurate and sensitive nucleic acids detection. Herein, we reported a novel Cas12a-based electrochemiluminescence biosensor for target amplification-free human papilloma virus subtype (HPV-16) DNA detection. During this detection process, Cas12a employed its two-part recognition mechanism to improve the specificity and trans-cleavage capability to achieve signal amplification, while L-Methionine stabilized gold nanoclusters (Met-AuNCs) were served as high-efficiency ECL emitters to achieve ECL signal transition. Given the unique combination of Cas12a with ECL technique, the detection limit was determined as 0.48 pM and the whole detection could be completed within 70 min. We also validated the practical application of the proposed biosensor by using undiluted human blood samples, which gives impetus to the design of new generations of CRISPR/Cas detection system beyond the traditional ones with ultimate applications in sensing analysis and diagnostic technologies.

Recent Advances in Electrochemiluminescence and Chemiluminescence of Metal Nanoclusters

Metal nanoclusters (NCs), including Au, Ag, Cu, Pt, Ni and alloy NCs, have become more and more popular sensor probes with good solubility, biocompatibility, size-dependent luminescence and catalysis. The development of electrochemiluminescent (ECL) and chemiluminescent (CL) analytical methods based on various metal NCs have become research hotspots. To improve ECL and CL performances, many strategies are proposed, from metal core to ligand, from intermolecular electron transfer to intramolecular electron transfer. Combined with a variety of amplification technology, i.e., nanostructure-based enhancement and biological signal amplification, highly sensitive ECL and CL analytical methods are developed. We have summarized the research progresses since 2016. Also, we discuss the current challenges and perspectives on the development of this area.

Fluorescent Noble Metal Nanoclusters Loaded Protein Hydrogel Exhibiting Anti-Biofouling and Self-Healing Properties for Electrochemiluminescence Biosensing Applications

Electrochemiluminescence (ECL) showed great potential in various analytical applications, especially in the sensing of biotargets, taking advantage of its high sensitivity, selectivity, ease of spatial and temporal control, and simplified optical setup. However, during the sensing of complex biological samples, ECL sensors often suffered severe interferences from unavoidable nonspecific-binding of biomacromolecules and physical damages of ECL sensing interfaces. Herein, a hydrogel based ECL biosensing system exhibiting excellent anti-biofouling and self-healing properties is developed. A protein hydrogel composed of bovine serum albumin (BSA) directed fluorescent Au/Ag alloy nanoclusters (Au/Ag NCs) is applied in building ECL sensing systems. The hydrogel matrix facilitates the immobilization of fluorescent Au/Ag NCs as excellent ECL probes, and the porous hydrophilic structure allows the free diffusion of small molecular biotargets while rejecting macromolecular interferences. Moreover, the hydrogel exhibits excellent self-healing property, with the ECL intensity recovered rapidly in 10 min after cutting. The hydrogel ECL system is successfully applied in sensing glutathione (GSH) in serum, confirming the applicability of the hydrogel based anti-biofouling ECL sensing system in sensing complex biological samples. This research may inspire the development of novel anti-biofouling and self-healing ECL biosensors for biosensing applications.

Highly efficient electrochemiluminescence of ruthenium complex-functionalized CdS quantum dots and their analytical application

The electrochemiluminescence (ECL) method has attracted increasing attention in analytical fields. However, ECL luminophores with high ECL efficiency both at positive and negative potentials still remain rare. Herein, we synthesized ruthenium complex-functionalized CdS quantum dots (QDs) with high ECL efficiency both at positive and negative potentials in aqueous solution. CdS QDs were chosen as the ECL donor while bis(2,2'-bipyridine)-(5-aminophenanthroline)ruthenium bis(hexafluorophosphate) (Ru-NH2) was employed as the ECL acceptor. Ru-NH2 was covalently coupled to the surface of CdS QDs via diazonium salt chemistry to form CdS-Ru nanoparticles. ECL resonance energy transfer (ECL-RET) occurred inside the CdS-Ru nanoparticles and strong ECL emissions were obtained from CdS-Ru nanoparticles at both positive potential in the presence of tri-n-propylamine and at negative potential in the presence of peroxydisulfate. Further, the combination of the excellent recognition ability of the aptamer and the good ECL behavior of CdS-Ru nanoparticles, as a proof-of-concept, showed that two sensitive ECL methods for the detection of thrombin were readily achieved under different ECL measurement conditions with a low detection limit of 0.6 pM and 0.7 pM. This work demonstrates that CdS-Ru nanoparticles with intramolecular ECL-RET are good ECL luminophores in the sensitive detection of targets, which is promising in multiple assays with spectrum-resolved and potential-resolved possibility for biological applications.