New Signal Amplification Strategy Using Semicarbazide as Co-reaction Accelerator for Highly Sensitive Electrochemiluminescent Aptasensor Construction

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

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

Rapid Size Determination of Quasispherical Gold Nanoparticles by Electrocatalysis Efficiency-Regulated Electrochemiluminescence

The size of gold nanoparticles (AuNPs) largely decides their properties and applications, making the rapid screening of AuNP size important. Despite the fact that AuNP-amplified electrochemiluminescence (ECL) is widely used in various ECL sensing applications, the mechanism of ECL enhancement remains elusive, especially the quantitative relationship between the enhanced ECL intensity and the size of AuNPs. In this work, taking quasispherical and citrate-stabilized AuNPs as model nanoparticles, we have reported that the ECL intensity of the S2O82--O2 system enhanced significantly with the increasing AuNP size. AuNPs acted as bielectrocatalysts for reducing the S2O82- and O2. The further study of enhancement mechanism demonstrates that AuNPs with increasing size facilitate the electron transfer and promote the generation of radicals required for the ECL emission, which produces more emitters-singlet oxygen. Meanwhile, the high surface density of citrate on small AuNPs suppresses the ECL signal by forming an electrostatic barrier. On the basis of the above phenomena, an ECL-based rapid AuNP size screening approach has been established. The accuracy of this platform is verified by the consistent results in comparison to transmission electron microscopy (TEM) measurements. This work not only provides deep insight into the correlation between the AuNP size and the ECL enhancement but also contributes an alternative to the TEM technique for the rapid AuNP size screening. Additionally, this study also extends the exploration of ECL-based structure analysis techniques toward nanomaterials through clarifying the structure-electrocatalytic activity correlation.

Ti3C2 MXene-based nanozyme as coreaction accelerator for enhancing electrochemiluminescence of glucose biosensing

Delamination of the exfoliated multilayer MXenes with electro-catalysts, not only leads to increasing surface area for high electrochemiluminescent (ECL) signal tracer loading but also provides highly sensitive achievements in a coreaction accelerator manner. To this end, herein, we used bromophenol blue (BPB)-delaminated multilayer Ti3C2 MXene as both a coreaction accelerator to promote the electrochemiluminescent (ECL) reaction rate of luminol (LUM) and the co-reactant H2O2 and a substrate for retaining high loading of glucose oxidase (GOx)-conjugated polyethylene imine (PEI) along with luminophore species into more open structure of Ti3C2 MXene for sensitive detection of glucose. In the presence of glucose, in situ generating H2O2 product through a GOx-catalyzed process could produce abundant •OH radicals via the peroxidase-like activity of the BPB@Ti3C2 in the LUM ECL reaction. Moreover, decreasing the distance between the high-content LUM into the BPB@Ti3C2 and the generated •OH, minimizes the decomposition of highly active •OH, providing a superb ECL signal. Last, the proximity of incorporated GOx into the delaminated Ti3C2 MXene near the electrode allows efficient electron transfer between the electrode and enzyme. The integration of such amplifying effects endowed high sensitivity and excellent selectivity for glucose with a low limit of detection of 0.02 μM in the wide range of 0.01 μM-40,000 μM, enabling the feasibility of the glucose analysis in human serum samples. Overall, the enhanced ECL based on the BPB@Ti3C2 opens a new horizon to develop highly sensitive MXene-based ECL toward the field of biosensors.

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

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

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.

Combination of Ternary Electrochemiluminescence System of BNQDs/AgMOG-K2S2O8 and Electrochemiluminescence Resonance Energy Transfer Strategy for Ultrasensitive Immunoassay of Amyloid-β Protein

In this work, based on boron nitride quantum dots (BNQDs) as energy donors and MnO2@MWCNTs-COOH as energy receptors, we designed an efficient electrochemiluminescence resonance energy transfer (ECL-RET) immunosensor for the detection of amyloid-β (Aβ42) protein, a biomarker of Alzheimer's disease (AD). First, the signal amplification of a ternary ECL system composed of BNQDs (as the ECL emitter), K2S2O8 (as the coreactant), and silver metal-organic gels (AgMOG, as the coreaction accelerator) was realized, and PDDA as stabilizer was added, a strong and stable initial ECL signal was obtained. AgMOG could not only support a large amount of BNQDs and Aβ42 capture antibody (Ab1) through Ag-N bond but also exhibit excellent ECL catalytic performance and enhance the luminescent intensity of BNQDs@PDDA-K2S2O8 system. In addition, due to the broad absorption spectrum of MnO2@MWCNTs-COOH and the extensive overlap with the ECL emission spectrum of BNQDs, the quenching probe Ab2-MnO2@MWCNTs-COOH could be introduced into the ternary system through a sandwich immune response. On this basis, the signal on-off ECL immunosensor was constructed to achieve the ultrasensitive detection of Aβ42 through signal transformation. Under the optimal conditions, the prepared ECL biosensor manifested a wide linear range (10 fg/mL-100 ng/mL) with a detection limit of 2.89 fg/mL and showed excellent stability, selectivity, and repeatability, which provided an effective strategy for the ultrasensitive detection of biomarkers in clinical analysis.

Potential-Resolved Electrochemiluminescence Multiplex Immunoassay for Florfenicol and Chloramphenicol in a Single Sample

The simultaneous detection of multiple antibiotic residues in food is of great significance for food safety. In this work, a novel dual-potential electrochemiluminescence (ECL) immunoassay was designed for the simultaneous detection of chloramphenicol and fluorfenicol residues in food. Ru@MOF was used as an anodic probe, and SnS2 QDs-PEI-Au-MoS2 was used as a cathodic probe. Notably, the coreactant for both luminophores was K2S2O8, avoiding interactions caused by different kinds of coreactants. Au nanoparticles functionalized with a nitrogen- and sulfur-doped graphene oxide-modified glassy carbon electrode to improve the electron transfer efficiency and provide a larger surface area for immobilization of antigen. The linear range for the detection of florfenicol was determined to be 0.1-1000 ng mL-1 with a detection limit of 0.03 ng mL-1, and the linear range for the detection of chloramphenicol was 0.01-1000 ng mL-1 with a detection limit of 3.2 pg mL-1 by recording the ECL responses at two different excitation potentials. The proposed immunoassay achieved a more stable recovery in the detection of actual samples and provided a new analytical method for the simultaneous detection of florfenicol and chloramphenicol residues with high sensitivity and specificity.

Signal-Enhanced Immunosensor-Based MOF-Derived ZrO2 Nanomaterials as Electrochemiluminescence Emitter for D-Dimer Detection

Metal oxide nanomaterials have garnered significant attention in the field of electrochemiluminescence (ECL) sensing due to their efficient, stable, and nontoxic properties. However, the current research on metal oxide nanomaterials has primarily focused on their cathodic luminescence properties, with limited reports on their anodic ECL properties. In this study, we utilized MOF-derived ZrO2 nanomaterials as luminophores to generate stable anodic ECL signals in the presence of the coreactant tripropylamine (TPrA). Additionally, a signal-enhancing immunosensor was developed to analyze D-dimer by incorporating the coreaction accelerator Cu-doped TiO2 (TiO2-Cu). The ZrO2 synthesized by calcining UiO-67 demonstrated nontoxicity and biocompatibility, exhibiting efficient and stable ECL emission in a TPrA solution. The inclusion of TiO2-Cu as a coreaction accelerator in the immunosensor resulted in the formation of a ternary system of ZrO2/TiO2-Cu/TPrA. The Cu doping effectively narrowed the bandgap of TiO2 and enhanced its conductivity. As a substrate, TiO2-Cu reacted with more TPrA, generating sufficient free radicals to effectively enhance the ECL signal of ZrO2. In this article, a short peptide ligand, NFC (NARKFYKGC), was designed to immobilize antibodies and maintain the activity of antigen-binding sites during the construction of the immunosensor. The developed immunosensor was used for the accurate detection of D-dimers, with a wide linear range of 0.05-600 ng/mL and a low detection limit of 21 pg/mL..

An electrochemiluminescence immunosensor based on multipath signal catalytic amplification integrated in a Cu2+-PEI-Pt/AuNC nanocomposite

Here, the nanocomposite Cu²⁺-PEI-Pt/AuNCs with multipath signal catalytic amplification for a peroxydisulfate-dissolved oxygen electrochemiluminescence (ECL) system was prepared to fabricate a sensitive ECL immunosensor. Using polyethyleneimine (PEI), a linear polymer, as the reductant and template, Pt/Au nanochains (Pt/AuNCs) were prepared. Abundant PEI would adsorb on the surface of Pt/AuNCs via Pt-N or Au-N bonds, and further coordinate with Cu²⁺ to give the final nanocomposite Cu²⁺-PEI-Pt/AuNCs which possessed multipath signal catalytic amplification for the ECL of the peroxydisulfate-dissolved oxygen system in the presence of H₂O₂. First, PEI, as an effective co-reactant, could directly enhance the ECL intensity. Second, Pt/AuNCs could not only act as a mimicking enzyme to promote the decomposition of H₂O₂ to produce more oxygen in situ, but also act as an effective co-reaction accelerator to facilitate the generation of more co-reactive intermediate groups from peroxydisulfate, resulting in an obviously enhanced ECL signal. Then, Cu²⁺ could also accelerate the decomposition of H₂O₂ to produce more oxygen in situ, leading to a further improvement of the ECL response. Using Cu²⁺-PEI-Pt/AuNCs as a loading platform, a sandwiched ECL immunosensor was fabricated. As a result, the obtained ECL immunosensor possessed an ultra-sensitive detection performance for α-1-fetoprotein, providing effective information on the diagnosis and treatment of related diseases.

Intramolecular Enhancement of a Zirconium-Based Metal-Organic Framework for Coordination-Induced Electrochemiluminescence Bleomycin Analysis

It is significantly vital to develop a convenient assay method in clinical treatment due to an atypically low abundance (∼5 μM) of bleomycin (BLM) used in clinics. Herein, an electrochemiluminescence (ECL) biosensor using a zirconium-based metal-organic frameworks (Zr-MOFs) as an intramolecular coordination-induced electrochemiluminescence (CIECL) emitter was proposed for sensitive detection of BLM. Zr-MOFs were synthesized using Zr(IV) as metal ions and 4,4',4″-nitrilotribenzoic acid (H₃NTB) as ligands for the first time. The H₃NTB ligand not only acts as coordination units bonding with Zr(IV) but functions as a coreactant to enhance ECL efficiency rooted in its tertiary nitrogen atoms. Specifically, a long guanine-rich (G-rich) single-stranded DNA (ssDNA) was released by the target-BLM-controlled DNA machine that could perform π-π stacking with another G-quadruplex, ssDNA-rhodamine B (S-RB), by shearing DNA's fixed sites 5'-GC-3' and the auxiliary role of exonuclease III (Exo III). Finally, due to the quenching effect of rhodamine B, a negative correlation trend was obtained between ECL intensity and BLM concentration in the range from 5.0 nM to 50 μM and the limit of detection was 0.50 nM. We believe that it is a promising approach to guide the preparation of CIECL-based functional materials and establishment of analytical methods.

AgInZnS quantum dots as anodic emitters with strong and stable electrochemiluminescence for biosensing application

Quantum dots (QDs) have become promising electrochemiluminescence (ECL) emitters with high quantum yield and size-tunable luminescence. However, most QDs generate strong ECL emission at the cathode, developing anodic ECL-emitting QDs with excellent performance is challenging. In this work, low-toxic quaternary AgInZnS QDs synthesized by a one-step aqueous phase method were used as novel anodic ECL emitters. AgInZnS QDs exhibited strong and stable ECL emission and a low excitation potential, which could avoid the side reaction of oxygen evolution. Furthermore, AgInZnS QDs displayed high ECL efficiency (Φ_ECL) of 5.84, taking the Φ_ECL of Ru(bpy)₃²⁺/tripropylamine (TPrA) ECL system as 1. Compared to AgInS₂ QDs without Zn doping and traditional anode luminescent CdTe QDs, the ECL intensity of AgInZnS QDs was 1.62 times and 3.64 times higher than that of AgInS₂ QDs and CdTe QDs, respectively. As a proof-of-concept, we further designed an "on-off-on" ECL biosensor for detecting microRNA-141 based on a dual isothermal enzyme-free strand displacement reaction (SDR), which not only to achieve the cyclic amplification of the target and ECL signal, but also to construct a switch of the biosensor. The ECL biosensor had a wide linear range from 100 aM to 10 nM with a low detection limit of 33.3 aM. Together, the constructed ECL sensing platform is a promising tool for rapid and accurate diagnosis of clinical diseases.

Luminophore-Surface-Engineering-Enabled Low-Triggering-Potential and Coreactant-Free Electrochemiluminescence for Protein Determination

Coreactant-free electrochemiluminescence (ECL) is promising for removing the exogenous effects of coreactant and simplify the operation procedures and setups of commercialized ECL bioassays. Herein, an electrosterically involved strategy for achieving a low-triggering-potential (+0.21 V vs Ag/AgCl) and coreactant-free ECL from dual-stabilizer-capped CdTe nanocrystals (NCs) is proposed with mercaptopropionic acid (MPA) and hexametaphosphate (HMP) as the capping agents of luminophores. Upon employing the CdTe NCs as the ECL tag for the immunoassay, all the tags in the bioconjugates of the CdTe NCs and the secondary antibody (Ab₂|CdTe) as well as in the final achieved sandwich-type immunocomplexes can exhibit efficient coreactant-free ECL with an electrosterically involved triggering potential nature. The bioconjugates of Ab₂|CdTe with Ab₂ no more than 30 kDa, such as the thyroid stimulating hormone (30 kDa) and the recombinant pro-gastrin releasing peptide (ProGRP, 14 kDa), merely exhibit coreactant-free ECL around +0.24 V, while bioconjugates of Ab₂|CdTe with an Ab₂ beyond 30 kDa only give off coreactant-free ECL around +0.82 V. Due to the further enhanced electrosteric effect in sandwich-type immunocomplexes, only the ECL immunosensor with ProGRP as the target can give off coreactant-free ECL around +0.24 V. The electrosterically involved and coreactant-free ECL of CdTe NCs is consequently utilized to sensitively and selectively determine the molecular protein ProGRP, which demonstrates a wide linearity range from 0.1 to 2000 pg/mL and a low limit of detection at 0.05 pg/mL (S/N = 3). This low-triggering-potential and coreactant-free combined ECL platform indicates that engineering the surface of CdTe NCs with a protein can improve the performance of ECL tags in a protein-weight-involved electrosterical way.

Zn2+-Induced Gold Cluster Aggregation Enhanced Electrochemiluminescence for Ultrasensitive Detection of MicroRNA-21

Herein, Zn²⁺-induced gold cluster aggregation (Zn²⁺-GCA) as a high-efficiency electrochemiluminescence (ECL) emitter is first employed to construct an ECL biosensor to ultrasensitively detect microRNA-21 (miRNA-21). Impressively, Zn²⁺ not only can induce the aggregation of monodispersed gold clusters (Au NCs) to limit the ligand vibration of Au NCs for improving ECL emission but also can be utilized as a coreaction accelerator to catalyze the dissociation of coreactant S₂O₈^2- into sulfate radicals (SO₄^•-) to improve the interaction efficiency between Zn²⁺-GCA and S₂O₈^2-, resulting in further intense ECL emission. Compared to Au NCs stabilized by bovine serum albumin with ECL efficiency of 0.40%, Zn²⁺-GCA possessed high ECL efficiency of 10.54%, regarding the [Ru(bpy)₃]²⁺/S₂O₈^2- system as a standard. Furthermore, output DNA modified with poly adenine (polyA) obtained from enzyme-free target recycling amplification can be efficiently immobilized on the surface of gold nanoparticles (Au NPs) to reduce the defect of special design, cumbersome operation, and low stability. Thus, an ultrasensitive ECL biosensor based on the Zn²⁺-GCA/S₂O₈^2- ECL system and enzyme-free target recycling amplification achieved ultrasensitive detection of miRNA-21 with the detection limit of 44.7 aM. This strategy presents a new idea to design highly efficient ECL emitters, which is expected to be used in the field of bioanalysis for clinical diagnosis.

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.

Fabrication of a ratiometric electrochemiluminescence biosensor using single self-enhanced nanoluminophores for the detection of spermine

A ratiometric electrochemiluminescence strategy using a single luminophore for accurate and sensitive biomolecule detection could be immensely valuable in bioanalysis. Herein, an ultrasensitive ratiometric electrochemiluminescence sensing system was fabricated using a self-enhanced luminophore with dual-signal emission for the detection of spermine. A nanocomposite was synthesized by the covalent attachment of N, N-diisopropylethylenediamine onto glutathione-protected Au-Ag bimetallic nanoclusters (DPEA-GSH@Au/Ag BNCs). The nanocomposite exhibited efficient intra-cluster charge transfer to produce strong anodic self-enhanced electrochemiluminescence emission at 0.8 V without external co-reactants. Interestingly, the DPEA@GSH@Au-Ag BNCs exhibited cathodic electrochemiluminescence emission upon the addition of the co-reactant potassium persulfate at -1.6 V, exhibiting stable and efficient dual-signal electrochemiluminescence emission features at a continuous potential window of -1.75 to 1.2 V. Thus, they were used to fabricate a single-luminophore electrochemiluminescence sensor with dual emission. The cathodic emission of the biosensor gradually increased with increasing concentrations of spermine, whereas the anodic electrochemiluminescence intensity remained almost constant, enabling the ratiometric detection of spermine. The fabricated biosensor, with an internal standard, significantly improved the accuracy and reliability of spermine detection in a wide concentration range of 0.85 pM-100 μM, with a low limit of detection of 0.12 pM (S/N = 3) under optimum conditions. This single-luminophore electrochemiluminescence sensing system could be used for the detection of spermine and could guide the construction of ratiometric electrochemiluminescence sensors in the future.

Recent Progress in Aptamer-Functionalized Metal-Organic Frameworks-Based Optical and Electrochemical Sensors for Detection of Mycotoxins

Mycotoxin contamination in foodstuffs and agricultural products has posed a serious hazard to human health and raised international concern. The progress of cost-effective, facile, rapid and reliable analytical tools for mycotoxin determination is in urgent need. In this regard, the potential utility of metal-organic frameworks (MOFs) as a class of crystalline porous materials has sparked immense attention due to their large specific surface area, adjustable pore size, nanoscale framework structure and good chemical stability. The amalgamation of MOFs with high-affinity aptamers has resulted in the progress of advanced aptasensing methods for clinical and food/water safety diagnosis. Aptamers have many advantages over classical approaches as exceptional molecular recognition constituents for versatile bioassays tools. The excellent sensitivity and selectivity of the MOF-aptamer biocomposite nominate them as efficient lab-on-chip tools for portable, label-free, cost-effective and real-time screening of mycotoxins. Current breakthroughs in the concept, progress and biosensing applications of aptamer functionalized MOFs-derived electrochemical and optical sensors for mycotoxins have been discussed in this study. We first highlighted an overview part, which provides some insights into the functionalization mechanisms of MOFs with aptamers, offering a foundation to create MOFs-based aptasensors. Then, we discuss various strategies to design high-performance MOFs-based aptamer scaffolds, which serve as either signal nanoprobe carriers or signal nanoprobes and their applications. We perceived that applications of optical aptamers are in their infancy in comparison with electrochemical MOFs-derived aptasensors. Finally, current challenges and prospective trends of MOFs-aptamer sensors are discussed.

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.

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.

Coreactant-free and Near-Infrared Electrochemiluminescence Immunoassay with n-Type Au Nanocrystals as Luminophores

The electrochemiluminescence (ECL) bioassay is prominently carried out with the involvement of the coreactant. To remove the detrimental effects of the coreactant on the ECL of luminophores, herein, a promising ECL immunoassay strategy with biocompatible nanoparticles as the luminophore is proposed, which involves directly and electrochemically oxidizing the luminophore methionine-capped Au (Met@Au) nanocrystals (NCs) without the participation of any coreactant. Met@Au NCs are a kind of n-type nanoparticles, and they can be electrochemically injected with valence band (VB) holes around +0.80 and +1.10 V (vs Ag/AgCl). The electrochemically injected exogenous VB hole can recombine with the endogenous conduction band electron of Met@Au NCs and eventually bring out two coreactant-free and near-infrared ECL processes around 0.80 V (ECL-1) and 1.10 V (ECL-2). The intensity of coreactant-free ECL is primarily determined by the electrochemical oxidation-induced hole-injection process. ECL-2 is considerably stronger than ECL-1 and can be exploited for determining the carcinoembryonic antigen (CEA) in a sandwich immunoassay procedure with a linear range from 0.1 to 50 pg/mL as well as a limit of detection of 0.03 pg/mL (S/N = 3).

The combination of highly efficient resonance energy transfer in one nanocomposite and ferrocene-quenching for ultrasensitive electrochemiluminescence bioanalysis

Sensitive and accurate detection of prostate-specific antigen (PSA) is of great significance since it is regarded as a biomarker for prostate diseases. Herein, a facile strategy for the design of highly efficient electrochemiluminescence (ECL) sensor was proposed for PSA assay. Carboxylated graphitic carbon nitride (g-C₃N₄) nanosheet (CCN) and tris (2, 2'-Bipyridyl) ruthenium (II) (Ru(bpy)₃²⁺) encapsulated in silica nanospheres (RuSi NPs) were employed as the donor and acceptor, respectively. CCN and RuSi NPs were covalently bound within one nanocomposite (CCN@RuSi) through the amide bond, which greatly shortened the electron-transfer path. Thus, the resonance energy transfer (RET) efficiency was remarkably increased, providing a high initial ECL intensity for the ECL assay. After the successive introducing of aptamer, PSA, and ferroceneboronic acid (FcBA) on the surface of CCN@RuSi modified electrode, the ECL signal remarkably decreased, which was caused by the steric hindrance of PSA and electron transfer quenching between Fc⁺ and excited-state Ru(bpy)₃²⁺*. Therefore, a highly efficient ECL platform was constructed, which achieved the ultrasensitive detection of PSA with a linear range and a limit of detection of 100 fg/mL - 50 ng/mL and 1.2 fg/mL, respectively. Furthermore, the dual-affinity of the aptamer and FcBA to PSA endowed the sensor with a high selectivity for the determination of PSA in human serum samples. The present work provides an important reference for the integration of RET and quenching strategy in the ECL study with rapid, ultrasensitive, and highly selective detection performances.

Single-Atom Iron Enables Strong Low-Triggering-Potential Luminol Cathodic Electrochemiluminescence

The conventional cathodic electrochemiluminescence (ECL) always requires a more negative potential to trigger strong emission, which inevitably damages the bioactivity of targets and decreases the sensitivity and specificity. In this work, iron single-atom catalysts (Fe-N-C SACs) were employed as an efficient co-reaction accelerator for the first time to achieve the impressively cathodic emission of a luminol-H₂O₂ ECL system at an ultralow potential. Benefiting from the distinct electronic structure, Fe-N-C SACs exhibit remarkable properties for the activation of H₂O₂ to produce massive reactive oxygen species (ROS) under a negative scanning potential from 0 to -0.2 V. The ROS can oxidize the luminol anions into luminol anion radicals, avoiding the tedious electrochemical oxidation process of luminol. Then, the in situ-formed luminol anion radicals will directly react with ROS for the strong ECL emission. As a proof of concept, sensitive detection of the carcinoembryonic antigen was realized by glucose oxidase-mediated ECL immunoassay, shedding light on the superiority of SACs to construct efficient cathodic ECL systems with low triggering potential.

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.

Regulation of the Structure of Zirconium-Based Porphyrinic Metal-Organic Framework as Highly Electrochemiluminescence Sensing Platform for Thrombin

An electrochemiluminescence (ECL) sensor provides a sensitive and convenient method for early diagnosis of diseases; however, it is still a challenge to develop simple and sensitive sensing platforms based on efficient ECL signals and luminophore groups. Porphyrin-based metal-organic frameworks (MOFs) show great potential in ECL sensing; however, the mechanism and structure-activity relationship, as well as application, are rarely reported. Herein, hydrothermal reactions obtained porphyrin Zr-MOFs (PCN-222) with different specific surface areas, pore sizes, structures, and surface charge states by tuning the reaction time were developed, which served both as the ECL luminophore, coreaction promoter for S₂O₈^2-, and a connection in the ECL immunoassay. By progressively controlling the condition of the hydrothermal reaction, PCN-222 with large surface area-abundant micropores can be obtained, which has good conductivity and positively charged surfaces, obtaining excellent ECL performance. The ECL performance and the enhancement mechanism were investigated in detail. Using PCN-222-6h with the best ECL intensity as the immobilization matrix for the aptamer, a highly sensitive and selective assay for thrombin was developed. The decrease of the ECL signal was logarithmically linear with the concentration of thrombin in the range from 50 fg mL^-1 to 100 pg mL^-1 with a low detection limit of 2.48 fg/mL. This proposed strategy provides a brand new approach for tuning of the structures of MOFs as effective ECL signal probes, thus providing wider possibilities for effective ECL immunoassays in the detection of other biomarkers in diagnosis of diseases.

Epigenetic Quantification of 5-Hydroxymethylcytosine Signatures via Regulatable DNAzyme Motor Triggered by Strand Displacement Amplification

DNA methylation predominantly occurs within the CpG dinucleotide, which is the main epigenetic form of gene expression regulation in mammals. Genomic DNA with CpG sites has different sequence lengths and complex secondary structures, resulting in the complexity and diversity of the samples. Therefore, highly efficient quantification of DNA methylation in complex samples remains challenging. Herein, the regulatable DNAzyme motor triggered by strand displacement amplification (SDA) was designed to quantify 5-hydroxymethylcytosine (5hmC) signatures as a model. Briefly, the 5hmC sites as primary target were specifically labeled with DNA primers and converted into a large number of single-stranded DNA (secondary target) via the SDA reaction which could activate the DNAzyme motor. With the increase of secondary target, the DNAzyme motor gradually recovered its activity and could continuously cleave the track strands labeled quenching probes, causing electrochemiluminescence signal recovery and detection limit down to 0.49 fM for 5hmC. This strategy provides a new route to quantify natural base modifications in DNA and would hold promising potential for the early diagnosis of cancer and other diseases related to 5hmC.

A robust molecularly imprinted electrochemiluminescence sensor based on a Ni–Co nanoarray for the sensitive detection of spiramycin

A simple and robust molecularly imprinted electrochemiluminescence sensor for the detection of spiramycin is fabricated based on Ni–Co LDH nanoarrays and is directly used as a sensor platform.

Recent advances in metal/covalent organic framework-based electrochemical aptasensors for biosensing applications

The booming development of novel porous materials, metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) has been attracting a lot of attention due to their designabilities, diversities, and extensive applications. MOFs and COFs provide a new potential opportunity and platform to fabricate electrochemical aptasensors for biosensing applications. Compared to other traditional materials, MOF/COF-based electrochemical biosensors can appreciably amplify the electrochemical response signals to improve the sensing performance. Herein, we provide a comprehensive overview of MOF/COF-based electrochemical aptasensors for monitoring different ultra-trace analytes (e.g. antibiotics, pesticides, and cancer markers). This review systematically discusses the classification of electrochemical aptasensors based on various functional materials, including pure MOFs, MOF/conductive composites, metal nanoparticle/MOF composites, pure COFs, COFs/conductive composites, and other hybrid materials. Furthermore, some typical MOF/COF-based electrochemical aptasensors in the recognition of specific targets are described in detail to improve and guide further research for biosensing applications.

Ultrasensitive dual-quenching electrochemiluminescence immunosensor for prostate specific antigen detection based on graphitic carbon nitride quantum dots as an emitter

Early monitoring of prostate-specific antigen (PSA) is crucial in diagnosis and proactive treatment of prostate disease. Herein, a dual-quenching ternary ECL immunosensor was designed for PSA detection based on graphitic carbon nitride quantum dots (g-CNQDs, as an emitter), potassium persulfate (K2S2O8, as a coreactant), and silver nanoparticles doped multilayer Ti3C2 MXene hybrids (Ag@TCM, as a coreaction accelerator). First, Ag@TCM was immobilized on the surface of a glassy carbon electrode, then g-CNQDs was further adsorbed on Ag@TCM to acquire a higher initial ECL signal at a potential window from - 1.3 to 0.0 V (vs. Ag/AgCl). Ag@TCM not only acted as the coreaction accelerator, but also as a matrix to load enormous g-CNQDs and prostate-specific capture antibody via Ag-N bond. Meanwhile, prostate-specific detection antibody was marked by gold nanoparticles modified manganese dioxide as a dual-quenching probe (Ab2- Au@MnO2). When Ab2-Au@MnO2 was introduced into the ternary ECL system via sandwiched immuno-reaction, the high-sensitive detection of PSA was achieved by the dual-quenching effect, caused by the resonant energy transfer from g-CNQDs (energy donor) to Au@MnO2 (energy acceptor). As a result, this ECL immunosensor showed a good dynamic concentration range from 10 fg·mL-1 to 100 ng·mL-1 with a detection limit of 6.9 fg·mL-1 for PSA detection. The dual-quenching ECL strategy presented high stability and good specificity to open up a new pathway for ultrasensitive immunoassay.

A Novel Electrochemical Aptasensor for the Ultrasensitive Detection of Adenosine Triphosphate Based on DNA-Templated Copolymers

Adenosine triphosphate (ATP) is a small but significant biological molecule that plays an important role in regulating cellular metabolism processes. Accurate and sensitive analytical techniques for detecting ATP are urgently needed. Herein, a new electrochemical aptasensor was designed in light of DNA-templated copolymers that parallel to the electrode for sensitive gauging of ATP. The ATP aptamer decorated by the electronic medium ferrocene can be regarded as a ″bridge″ connecting two DNA-templated copolymers. When ATP exists, because of the extraordinary binding selectivity of DNA-templated copolymers for target ATP, the rapid electron transfer of ferrocene was beneficial to the sensitive detection of target ATP. Specifically, our parallel DNA copolymers are more stable than upright DNA copolymers and have a faster signal transmission because of the close distance to the electrode; meanwhile, the nonspecific pollution is less. Consequently, the developed novel aptasensor exhibited a wide range of linear response toward ATP that was from 0.1 to 10 000 pM and high selectivity with a detection limit down to 11.5 fM. The electrochemical aptasensor has a broad application prospect in the detection of small biological molecules.

Peptide-Based Biosensor with a Luminescent Copper-Based Metal-Organic Framework as an Electrochemiluminescence Emitter for Trypsin Assay

A copper-based metal-organic framework (JUC-1000) has emerged as a promising electrochemiluminescence (ECL) emitter in the domains of bioanalysis and immunoassay. Herein, a highly efficient signal "on-off" peptide-based biosensor was constructed for trypsin (TPN) assay. JUC-1000 synthesized using an organic ligand of H₄BDPO was functionalized as the ECL emitter, whose cathodic ECL behavior in aqueous media was first investigated using potassium persulfate (K₂S₂O₈) as the coreactant. To further amplify the ECL signal, highly catalytic Ag@CeO₂ nanoparticles were fabricated as both a substrate and an coreaction accelerator, which can efficiently catalyze the reduction of S₂O₈^2- to generate more sulfate anion radicals (SO₄^•-) for ECL enhancement, thereby generating strong and stable ECL signals in a "signal on" state. The functionalized JUC-1000 emitter was connected to the Ag@CeO₂ sensing layer though a heptapeptide (HWRGWVC, HGC), and TPN as the target can specifically cleave the carboxyl side of arginine residues in HGC, leading to the release of emitters in a "signal off" state. Based on the efficient signal-switching, the biosensor exhibited linear ECL responses to the added TPN concentration, realizing sensitive detection of TPN in 10 fg/mL to 100 ng/mL with a limit of detection of 3.46 fg/mL. This work proposed an attractive orientation for the fundamental research of applying transition metal-organic frameworks as ECL emitters in bioanalysis and immunoassay.

Aptamer-functionalized metal-organic frameworks (MOFs) for biosensing

As a class of crystalline porous materials, metal-organic frameworks (MOFs) have attracted increasing attention. Due to the nanoscale framework structure, adjustable pore size, large specific surface area, and good chemical stability, MOFs have been applied widely in many fields such as biosensors, biomedicine, electrocatalysis, energy storage and conversions. Especially when they are combined with aptamer functionalization, MOFs can be utilized to construct high-performance biosensors for numerous applications ranging from medical diagnostics and food safety inspection, to environmental surveillance. Herein, this article reviews recent innovations of aptamer-functionalized MOFs-based biosensors and their bio-applications. We first briefly introduce different functionalization methods of MOFs with aptamers, which provide a foundation for the construction of MOFs-based aptasensors. Then, we comprehensively summarize different types of MOFs-based aptasensors and their applications, in which MOFs serve as either signal probes or signal probe carriers for optical, electrochemical, and photoelectrochemical detection, with an emphasis on the former. Given recent substantial research interests in stimuli-responsive materials and the microfluidic lab-on-a-chip technology, we also present the stimuli-responsive aptamer-functionalized MOFs for sensing, followed by a brief overview on the integration of MOFs on microfluidic devices. Current limitations and prospective trends of MOFs-based biosensors are discussed at the end.

Advances in electrochemiluminescence co-reaction accelerator and its analytical applications

Electrochemiluminescence (ECL) can be produced through two main routes: annihilation route and coreactant route. The vast majority of applications of ECL are based on coreactant ECL which can be generated in aqueous media at relatively low potentials compared with organic solvents. However, the development of more efficient ECL systems remains a compelling goal. Co-reaction accelerator (CRA) can significantly enhance the ECL signal through promoting more production of the coreactant intermediate. Compared with other ECL enhancement strategies, the CRA protocol is distinctive owing to its diverse, simple, and highly effective features. Various species such as inorganic compound, organic compound, and nanomaterials (NMs) have been developed as CRA and NM CRA has gained particular attention owing to their unique properties of excellent catalytic behavior and large surface area. By integration with the inherent advantages of ECL, bioanalysis based on CRA-enhanced ECL showed excellent performance such as ultrahigh sensitivity, wide dynamic range, low cost, simple instrumentation, and measurements in complex media. It has been extensively applied in various fields including clinical diagnosis, environmental monitoring, and food safety. Therefore, it is of great interest to present a systematic and critical review on the advances in ECL CRA. Herein, the recent progress on CRA and its applications in ECL bioanalysis are summarized by illustrating some representative work and a discussion of the future development trends of CRA ECL is offered.

Highly Stable Covalent Organic Framework Nanosheets as a New Generation of Electrochemiluminescence Emitters for Ultrasensitive MicroRNA Detection

A pyrene-based sp² carbon-conjugated covalent organic framework (COF) nanosheet (Py-sp²c-CON) with strong and stable electrochemiluminescence (ECL) emission was constructed by C═C polycondensation of tetrakis(4-formylphenyl)pyrene (TFPPy) and 2,2'-(1,4-phenylene)diacetonitrile, which was employed as a highly efficient ECL emitter to fabricate an ECL biosensor for the first time. The Py-sp²c-CON exhibited higher ECL intensity and efficiency than those of TFPPy, bulk Py-sp²c-COF, and imine-linked pyrene COF, not only because the pyrene luminophores and aggregation-induced emissive luminogens (cyano-substituted phenylenevinylene) were topologically linked into Py-sp²c-CON, which greatly increased the immobilization amount of luminophores and decreased the aggregation-caused quenching effect and nonradiative transition but also because the porous ultrathin structure of Py-sp²c-CON effectively shortened transport distances of an electron, ion, and co-reactant (S₂O₈^2-), which made more ECL luminophores be activated and thus efficiently increased the utilization ratio of luminophores. More interestingly, when Bu₄NPF₆ was introduced into the Py-sp²c-CON/S₂O₈^2- system as a co-reaction accelerator, the ECL signal of Py-sp²c-CON was further amplified. As expected, the average ECL intensity of the Py-sp²c-CON/S₂O₈^2-/Bu₄NPF₆ system was about 2.03, 5.76, 24.31, and 190.33-fold higher than those of Py-sp²c-CON/S₂O₈^2-, Py-sp²c-COF/S₂O₈^2-, TFPPy/S₂O₈²,^- and imine-linked pyrene COF/S₂O₈^2- systems. Considering these advantages, the Py-sp²c-CON/S₂O₈^2-/Bu₄NPF₆ system was employed to prepare an ECL biosensor for microRNA-21 detection, which exhibited a broad linear response (100 aM to 1 nM) and a low detection limit (46 aM). Overall, this work demonstrated that sp² carbon CONs can be directly used as a high-performance ECL emitter, thus expanding the application scope of COFs and opening a new horizon to develop new types of ECL emitters.

Electrochemiluminescence biosensor for microRNA determination based on AgNCs@MoS2 composite with (AuNPs-Semicarbazide)@Cu-MOF as coreaction accelerator

A novel electrochemiluminescence (ECL) biosensor was fabricated for miRNA-162a detection by using silver nanoclusters/molybdenum disulfide (AgNCs@MoS₂) as an ECL material, peroxodisulfate (S₂O₈^2-) as a co-reactant, and semicarbazide (Sem) as a co-reaction accelerator. Firstly, hairpin probe H_a modified on AgNCs@MoS₂/GCE was unfolded based on its hybridization with target microRNA. Then, the unfolded H_a can further be hybridized with another hairpin DNA of H_b on (AuNPs-semicarbazide)@Cu-MOF, resulting in the release of target microRNA, which further causes a cyclic hybridization. This creates more (AuNPs-semicarbazide)@Cu-MOF on the electrode surface, achieving cyclic hybridization signal amplification. Strikingly, due to the presence of Sem, accelerating the reduction of S₂O₈^2- and resulting in the generation of more oxidant intermediates of SO₄^2-, the amount of excited states of Agincreases to further amplify the ECL signal. The biosensor exhibited high sensitivity with a low LOD of 1.067 fM, indicating that the introduction of co-reaction accelerators can provide an effective method for signal amplification. The applicability of this method was assessed by investigating the effect of Pb(II) ion on miRNA-162a expression level in maize seedling leaves. A novel electrochemiluminescence biosensor was fabricated for miRNA-162a detection by using silver nanoclusters/molybdenum disulfide as an ECL material, peroxodisulfate as a co-reactant, and semicarbazide as a co-reaction accelerator.

An "on-off" electrochemiluminescence immunosensor for PIVKA-II detection based on the dual quenching of CeO2-Au-g-C3N4 hybrids by Ag nanocubes-VB2

Herein, we report a novel dual-quenching electrochemiluminescence (ECL) immunosensor for detecting protein induced by vitamin K absence or antagonist-II (PIVKA-II) based on ECL resonance energy transfer (ECL-RET). In this protocol, self-accelerated ECL hybrids of CeO₂ and Au nanoparticles functionalized g-C₃N₄ nanosheets (CeO₂-Au-g-C₃N₄) were prepared, which exhibited high ECL emission in the presence of S₂O₈^2- as a coreactant for "signal on" state. Concretely, CeO₂ with a reproducible redox couple of Ce³⁺ and Ce⁴⁺ could act as an efficient co-reaction accelerator to generate more oxidizing intermediate (SO₄^•-) to significantly self-promote the ECL emission of g-C₃N₄ NSs/S₂O₈^2- ECL system. Besides, Au nanoparticles not only accelerated electron transfer in the ECL process, but also provided massive active sites for biomolecules immobilization. The dual quenching labels of Ag nanocubes modified with vitamin B₂ (AgNCs-VB₂) were firstly proposed towards g-C₃N₄ NSs/S₂O₈^2- ECL system by ECL-RET, resulting in the remarkable ECL decrease for "signal off" state. Based on the sandwich immunoreaction, the "on-off" PIVKA-II ECL immunosensor gratifyingly possessed excellent detection sensitivity with the linear range of 0.4 pg mL^-1-10 ng mL^-1 and the low detection limit of 28.46 fg mL^-1 (S/N = 3). This presented strategy might provide a potential alternative tool for PIVKA-II detection in medical research and early clinical diagnostics of hepatocellular carcinoma.

Paper-Based Bipolar Electrode Electrochemiluminescence Platform for Detection of Multiple miRNAs

This paper introduces a novel potential-resolved paper-based biosensor for simultaneous detection of multiple microRNAs (miRNAs) (taking miRNA-155 and miRNA-126 as examples) based on the bipolar electrode (BPE) electrochemiluminescence (ECL) strategy. The proposed multiple-channel paper-based sensing microfluidic platform was prepared by wax-printing technology, screen-printing method, and in situ Au nanoparticles (AuNPs) growth to form hydrophilic areas, hydrophobic boundaries, waterproof electronic bridge, driving electrode regions, and parallel bipolar electrode regions. CdTe quantum dots (QDs)-H2 and Au@g-C₃N₄ nanosheets (NSs)-DNA1 were used as dual electrochemiluminescence signal probes, and carboxylated Fe₃O₄ magnetic nanoparticles existed as carriers. CdTe QDs-H2/S₂O₈^2- and Au@g-C₃N₄ NSs-DNA1/S₂O₈^2- could exhibit two strong and stable ECL emissions at a drive voltage of 9 and 12 V, respectively, which can be used as effective potential-resolved signal tags. In addition, the proposed three-dimensional (3D) DNA nanomachine model and the target miRNA cycle strategy were used to achieve double amplification of electrochemiluminescence intensity. More importantly, the combination of the bipolar electrode system and the potential-resolved multitarget electrochemiluminescence method can greatly reduce the spatial interference between substances. The prepared ECL biosensor showed a favorable linear response for the detection of miRNA-155 and miRNA-126 with relatively low detection limits of 5.7 and 4.2 fM, respectively. With excellent sensitivity, the strategy may provide an efficient method for clinical application, especially in detection of trace multiple targets.

Postsynthesis Ligand Exchange Induced Porphyrin Hybrid Crystalloid Reconstruction for Self-Enhanced Electrochemiluminescence

In traditional coreactant electrochemiluminescence (ECL), the efficiency of the coreactant catalyzed into an active intermediate is one of the dominant factors restricting the luminous intensity. In this work, Co-2-MI-ZnTCPP is designed as a composite material integrating coreaction accelerator (Co-N) and luminophore. Through the catalytic effect of Co-N structures on hydrogen peroxide, the in situ generation and accumulation of active intermediates are achieved, which will react with porphyrin anion radical, thereby bringing out self-enhanced ECL. By adjusting the scanning potential range, the ECL mechanism is thoroughly studied and the contribution of each potential window to the luminescence is obtained. This work provides inspiration for the design of integrated ECL emitters with a coreaction accelerator and luminophore, providing a new way for the construction of a self-enhanced ECL emitter.

A synergistic promotion strategy remarkably accelerated electrochemiluminescence of SnO2 QDs for MicroRNA detection using 3D DNA walker amplification

Developing low-cost and efficient methods to enhance the electrochemiluminescence (ECL) intensity of luminophores is highly desirable and challenging. Herein, we develop a synergistic promotion strategy based on three types of co-reaction accelerators to achieve an efficient SnO2 quantum dots (SnO2 QDs)-based ternary ECL system. Specifically, the MnO2 nanoflowers (MnO2 NFs), Ag nanoparticles (Ag NPs) and hemin/G-quadruplex were rationally selected as co-reaction accelerators. Owing to the synergistic effect, the deft integration of three types of co-reaction accelerators enabled better structural stability, more exposed catalytic active sites, and faster charge transfer, thus more effectively facilitating the reduction of co-reactant (S2O82-) compared with that of the single co-reaction accelerator. To demonstrate the practical utility of this principle, an "on-off-super on" ECL biosensor was constructed in combination with a 3D DNA walker, which showed a superior linear range (10 aM-100 pM) and a low detection limit (2.9 aM) for the highly-sensitive miRNA-21 detection. In general, this work firstly reported that three types of co-reaction accelerators were deftly integrated to remarkably amplify the ECL emission of SnO2 QDs, and provided brand-new perspectives for research on the ingenious design of the structure and component of highly efficient co-reaction accelerators.