Self-Luminescent Lanthanide Metal-Organic Frameworks as Signal Probes in Electrochemiluminescence Immunoassay

Protein-inorganic hybrid flowers with a two-stage accelerated strategy for stimulated activation of CRISPR/Cas12a enhance polynucleotide kinase biosensing

Polynucleotide kinases (PNK) play a crucial role in DNA damage repair and are closely associated with specific diseases, making them promising targets for therapeutic intervention. In this study, we propose a two-stage accelerated strategy that utilizes protein-inorganic hybrid flowers (PHFs) to enhance the performance of the terminal deoxynucleotidyl transferase (TdT)-combined CRISPR/Cas12a system (TCS) for efficient detection of PNK activity. In TCS, the participation of PHFs confines the substrate probes (SPs) to a limited space, thereby significantly enhancing the local concentration of phosphorylated 3' termini of SPs and effectively promoting the enzymatic reaction kinetics as the first step in the accelerated strategy. Upon encountering the target PNK, the phosphorylated 3' termini were promptly recognized and dephosphorylated to 3'-OH termini. Subsequently, TdT catalyzed the assembly of deoxyadenosine triphosphates (dATPs) without a template, rapidly activating the CRISPR/Cas12a system by forming multiple polyadenine (poly-A) chains. PHF-fixed poly-A chains then substantially boosted the localized concentration of CRISPR/Cas12a systems and vastly enhanced their efficacy in cleaving reporter nucleic acids. Our findings indicated that the spatial confinement effect facilitated by PHFs promoted frequent molecular collisions and accelerated multiple enzymatic reactions. The developed sensing strategy allows for the detection of PNK activity within a linear range of 0.001-1 U/mL, with a detection limit of 1.82 × 10-4 U/mL. Additionally, this strategy has been successfully applied to detect PNK activity in cell extracts and to screen for PNK inhibitors. Owing to these advantages, PNK can be rapidly and accurately detected with a high sensitivity, specificity, and biostability.

Research progress on electrochemiluminescence nanomaterials and their applications in biosensors - A review

BACKGROUND

Electrochemiluminescence (ECL) is a promising analytical technique that combines electrochemistry with chemiluminescence. The performance of ECL systems depends on luminophores. Nonetheless, conventional luminophores present certain limitations. At first, their ECL efficiencies often fall short of the requirements for accurate detection. Moreover, in complex environments, traditional materials struggle to selectively identify target compounds and are prone to interference. Furthermore, these materials exhibit a deficiency in flexibility and tunability, attributed to their rigid structure and inherent characteristics. Advancing ECL technology necessitates the creation of novel materials that improve efficiency, selectivity, stability, and flexibility.

RESULTS

This review emphasizes the recent advances in ECL nanomaterials and their applications in biosensors. The discussion starts with a comprehensive examination of two main mechanisms of ECL emission: quenching ECL and co-reactant ECL. Various nanomaterials are then discussed, including semiconductor nanomaterials, metal nanoclusters, carbon nanomaterials, nanoscale aggregation-induced emission materials, organic nanomaterials, and composite nanomaterials, with emphasis on their unique ECL properties. Examples illustrate specific applications in disease diagnosis, environmental monitoring, and food safety testing. The review further examines the structural and luminescent characteristics of nanomaterials, which facilitate the advancement of novel ECL detection methodologies. Finally, we examine the existing challenges and propose possible avenues for the future advancement of innovative ECL nanomaterials.

SIGNIFICANCE

ECL nanomaterials possess unique quantum sizes and surface effects. Through the design and selection of appropriate nanomaterials, extremely sensitive, selective, and stable ECL biosensors may be developed for the detection of particular targets, applicable in disease diagnostics, food safety, and environmental monitoring.

Development of Pt/Au/PPy-COOH multisegmental nanowires modified label-free impedimetric immunosensor to determine mucin 1 (MUC1)

In this study, a label-free nanowire-based impedimetric immunosensor was developed for the purpose of determining cancer biomarkers mucin 1 (MUC1). Nanowires were selected for sensor modification due to their high catalytic properties and high enzyme loading capacity. The synthesis, characterization, and application of Pt/Au/PPy-COOH nanowires to modify SPE electrodes were conducted. The nanowire-based immunosensors developed as a result of this research demonstrated a broad linear working range for MUC1 (20-3000 fg/mL), a low LOD value (0.244 fg/mL), and a low LOQ value (0.815 fg/mL). The nanowire-based immunosensor exhibited several notable characteristics. Firstly, it demonstrated excellent reproducibility, selectivity, and long-term stability. Furthermore, it demonstrated notable regenerative capabilities. It is noteworthy that the sensor exhibited the capability to detect MUC1 in commercial human serum samples, even in the presence of interfering agents. The affordability, simplicity, and expeditious analysis of nanowire-based immunosensors render them more appealing than alternative commercial kits. Consequently, these sensors hold considerable promise for clinical applications.

Self-luminescent dual-ligand metal-organic framework based electrochemiluminescence probes for organophosphorus pesticides determination

In this study, a signal amplification strategy was developed, which tris (2, 2'-bipyridyl) ruthenium (II) (Ru(bpy)32+) was incorporated as a guest molecule into the preparation system of lanthanide-based metal-organic framework (MOF). This strategy relied on strong electrostatic interactions and coordination competition to influence the growth process of the MOF, resulting in the firm immobilization of Ru(bpy)32+ within the MOF structure. The spatial confinement effect of the MOF effectively improved the efficiency of electron transfer in the electrochemiluminescence (ECL) reaction. The constructed ECL aptasensor using this MOF exhibited excellent performance, with limits of detection (LODs) for four organophosphorus pesticides (OPs), phorate, profenofos, isocarbophos and omethoate, as low as 0.0482 ng/mL, 0.0093 ng/mL, 0.0085 ng/mL, and 0.0893 ng/mL, respectively. This work has paved the way for a clever strategy of immobilizing Ru(bpy)32+ molecules and amplifying signals, expanding the application of dual-ligand MOF, which provides valuable insights for future biosensor design.

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

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

Cutting-Edge Exploration of a Molecularly Imprinted Polymer-Coupled Electrochemiluminescence Mechanism Based on Organic Cation Side-Chain Construction for the Identification and Detection of Escherichia coli O157: H7

In this paper, an organic semiconductor bacterial biosensor was developed for selective detection of facultative anaerobic Escherichia coli O157: H7, which combines electrochemiluminescence (ECL) and bacterial imprinted polymer technologies. Fe2+ and Mn2+ were used to prepare irregular nanocluster ECL emitters (Fe-Mn NCs) via Cu2O, which served as excellent catalysts in the cathodic coreactant (K2S2O8) reaction system, to enhance the ECL signal intensity. Through electropolymerization, the cationic side chains of functional monomers could bind to proteins (such as cytochrome proteins) on the cell membrane of E. coli O157: H7 under aerobic conditions, and transfer to the interior of E. coli O157: H7 and participate in the cyclic regeneration of nicotinamide adenine dinucleotide, which greatly amplifies the detected ECL signal and accelerates the consumption of oxygen by the respiratory chain. When oxygen was consumed, lactic acid was produced by bacteria during the low-oxygen process, in which E. coli O157: H7 can cause a change in the direction of electron flow, resulting in a reduction in the production of SO4•- and a significant decrease in the ECL signal. And when oxygen was readded to the system, the ECL signal recovers or becomes even stronger, where the mechanism of action of cationic semiconductors in this system had been well elucidated. This sensor has a good linear relationship in the range of 101-108 CFU/mL, with a detection limit of 2.29 CFU/mL (S/N = 3), which offers a new detection method for foodborne pathogens, as well as a rapid and accessible identification tool for different types of microorganisms.

An "on-off" electrochemical immunosensor for the detection of the glycan antigen CA125 by amplification signals using electropositive COFs

Cancer Antigen 125 (CA125), is a high molecular weight mucinous glycoprotein found on the surface of ovarian cancer cells. Generally, 90 % of women may appear a high concentration of CA125 when they got the cancer; thus, CA125 can act as a marker for ovarian cancer diagnosis and therapeutic evaluation. COFs have been widely used for disease detection due to their structural stability, high loading capacity and biocompatibility. However, the limited variety of electroactive COFs used as signal probes, fewer enriched signaling molecules, weaker electrical signals generated, and higher oxidation or reduction potentials of electroactive substances, a series of side reactions are easily triggered causing serious interference. To solve the above problems, [Fe(CN)6]3/4- as a signal probe and COFs for signal amplification were selected to creating a highly sensitive electrochemical immunosensor for glycan antigen CA125. Firstly, two-dimensional (2D) EP-TD-COF with ultra-high specific surface area was modified on bare GCE, which could covalently bound numerous Ab1 molecules due to the epoxy-rich functional groups. Then, the electropositive AuNPs@2DCOFBTT-DGMH was prepared by the in situ growth of AuNPs, proved an effective platform for loading Ab2 molecules via Au-S bonds. Based on the positively charged AuNPs@COFBTT-DGMH/Ab2 and negatively charged [Fe(CN)6]3/4- of electrostatic interactions, which could significantly enchaned signal for quantitative and sensitive detection of CA125. The constructed immunosensor exhibits excellent stability performance and high sensitivity, enabling ultrasensitive detection of trace glycan antigens. This study provided a new idea for the use of non-electroactive substances for the construction of electrochemical immunosensors and provided an effective signal amplification strategy.

Ultrasensitive photoelectrochemical detection of cancer markers based on heterojunctions constructed from Bi2O3 star-like flower nanoclusters and CdS hollow nanorods

CYFRA21-1 is a tumor marker for lung cancer, and its rapid and accurate detection can provide evidence for the early diagnosis of lung cancer. In this work, Bi-Fe turnbull blue analogues (Bi-Fe-TBA) were synthesized by the self-templating method. Bi2O3-SFNs was prepared by simple oxidation in air using Bi-Fe-TBA as a template. Bi2O3 Star-like Flower Nanoclusters (Bi2O3-SFNs) and CdS Hollow Nanorods (CdS-HNRs) were used to form a unique type II heterojunction for the first time. The arrangement of energy levels between CdS-HNRs and Bi2O3-SFNs, along with their hollow structure and star shape, effectively suppressed the recombination of photogenerated electrons and holes while shortening carrier transport distance. An ultra-sensitive PEC biosensor was developed to detect the lung cancer marker CYFRA21-1, leveraging the superior photoelectric conversion capabilities of Bi2O3-SFNs/CdS-HNRs. The sensor demonstrates outstanding stability, specificity, reproducibility as well as a wide linear range (10-4 - 10 ng mL-1) and low detection limit (4.23 × 10-5 ng mL-1). This study is valuable for the preparation of other functional materials using TBA as a template.

Interactions of metal-based nanozymes with aptamers, from the design of nanozyme to its application in aptasensor: Advances and perspectives

Nanozymes, characterized by enzyme-like activity, have been extensively used in quantitative analysis and rapid detection due to their small size, batch fabrication, and ease of modification. Researchers have combined aptamers, an emerging molecular probe, with nanozymes for biosensing to address the limited reaction specificity of nanozymes. Nanozyme aptasensors are currently experiencing significant growth, offering a promising solution to the lack of rapid detection methods across various fields. Unlike traditional nanozyme research, the development of nanozyme aptasensors is challenging as it requires the design of highly active nanozymes as well as the establishment of efficient and agile interactions between aptamers and nanozymes. Therefore, this review summarizes the active species and catalytic mechanisms of various nanozymes along with classical design options, discussing the future development of nanozyme aptasensors. It is anticipated that this review will inspire researchers in this domain, leading to the design of more enzymatically active nanozymes and advanced nanozyme aptasensors.

Label-free electrochemiluminescence aptasensor for rapid and accurate detection of cardiac troponin I

Acute myocardial infarction (AMI) is the most common cause of death in individuals with cardiovascular disease. Cardiac troponin I (cTnI) is acknowledged as the most prominent biomarker for AMI. However, the key problem of practical applications is how to effectively improve the detection speed and sensitivity. In this study, we designed a novel electrochemiluminescence (ECL) aptasensor for the rapid and quantitative determination of cTnI. This sensor employs self-luminous europium-based metal-organic framework@CdS quantum dots (Eu-MOF@CdS QDs) as a signal probe. The Eu-MOF@CdS QDs can produce a robust cathodic ECL signal via a synergistic effect. Furthermore, a ferrocene-labeled aptamer was used as a quenching probe for quenching the ECL emission of the Eu-MOF@CdS QDs. In the presence of cTnI, the ECL intensity increased with increasing cTnI concentration after ferrocene-labeled aptamer specifically recognized cTnI and was detached from the electrode interface. Under optimal conditions, the aptasensor demonstrated precise analytical capabilities for cTnI ranging from 1.0 pg/mL to 1.0 ng/mL with a notably low detection limit of 0.08 pg/mL within 60 min. The results show that the developed ECL sensing device demonstrates the potential applications and perspectives for the detection of cTnI in serum samples as well as in the field of biomedical analyses.

Flower-like tailored carbon nitride oligomer as an excellent aggregation-induced electrochemiluminescence emitter for sensitive immunoassay of neuron-specific enolase via dual quenching by bimetallic phenolic networks

The adjustment of the electrochemiluminescence (ECL) of polymeric carbon nitride (C3N4) is essential for its application in sensitive immunoassays. However, such modification through aggregation-induced emission (AIE) has not yet been reported. Herein, aggregation-induced ECL in C3N4 oligomer (CNO) was induced through the introduction of a rotatable imine moiety, with the resulting material exhibiting excellent performance in the targeted immunodetection of neuron-specific enolase. Phenyl-modified CNO was synthesized through one-step pyrolysis at a reduced temperature. The rotatable benzene ring and triazine group formed a dynamic structure, which exhibited strong aggregation in water-doped solvents. compared to unmodified graphitic C3N4, CNO demonstrated higher intrinsic ECL efficiency and more readily accessible ECL signals. AIE inducing polymerization was conducted via nanoprecipitation, and the resulting CNO micro-flowers were employed as a sensing platform. A CNO-based sensor was prepared by combining CNO micro-flowers with copper-based bimetallic phenolic network nanoparticles as a quencher. Sensitive signal quenching was achieved owing to the electron transfer of Cu2+ and antioxidation properties of polyphenolic structures. The prepared sandwich-type immunosensor for neuron-specific enolase showed a limit of detection of 0.12 pg/mL in the detection range of 0.001-100 ng/mL. This study presents an effective strategy for the ECL signal amplification of C3N4, which is conducive to fundamental research in ECL and the application of the proposed sensor in the early diagnosis of diseases.

Electrochemiluminescence immunosensor using a lanthanum-based metal-organic framework as signal probe and Cu2MoS4 as a co-reaction promoter for the sensitive detection of anti-Müllerian hormone

In this study, we used meso-tetra (4-carboxyphenyl) porphyrin (TCPP) as an organic ligand to modify a lanthanide-based metal-organic framework as an electrochemiluminescence (ECL) platform to sensitively detect anti-Müllerian hormone (AMH). La-MOF amplified the ECL signal by suppressing the aggregation-caused quenching created by TCPP self-aggregation. Utilizing the reversible cycling of the mixed-valence transition metal ion (Cu+/Cu2+ and Mo4+/Mo6+) and the electrical conductivity of Cu2MoS4 and silver nanoparticle (AgNP), Cu2MoS4-AgNP as a dual co-reaction promoter constantly generated sulfate radical anions (SO4•-) and thus amplified the ECL signal. Based on this strategy, we built a sandwich-type ECL immunosensor for the sensitive detection of AMH with a linear range of 1 × 10-4 to 50 ng/mL and a limit of detection of 24 fg/mL. This study provides a novel approach for the sensitive and selective detection of AMH, demonstrating its high potential and practical value for the sensitive detection of AMH.

Boron Ligands Boosting the Electrochemiluminescence Performance of Europium Metal-Organic Frameworks by Facilitating the Electronic Bridging

For optimal energy transfer in self-luminous lanthanide metal-organic frameworks (Ln-MOFs), the energy of the lowest triplet excited state must align with ideal energy levels. Failure to meet this condition can lead to reverse energy transfer, reducing luminous efficiency. In this study, we developed a mixed-ligand MOF, Eu-TCPP-BOP, which exists as an ECL self-enhancing luminophore. We used SPECM to study the role of boron ligands as a bridge for electron transport in improving the ECL performance of Eu-TCPP. The ligands H4TCPP and 5-BOP act as electron donor and shuttle, facilitating electron transport during the synthesis of Eu-TCPP-BOP and promoting energy transfer to the excited state of the acceptor Ln3+, thus enhancing overall energy transfer in Ln-MOF. The results indicate that the introduction of boron ligands enhances the ECL intensity of Eu-TCPP by a factor of 1.4 under voltage excitation. As an ECL sensing platform, it demonstrates high sensitivity and selectivity for the detection of catechol, with a concentration range of 1∼70 μM and a detection limit of 0.35 μM.

Porphyrin-Based Metal-Organic Frameworks for PD-L1 Detection via "Coordination Disaggregation-Induced Enhancement" Strategy

Porphyrins, known for their exceptional photoelectrochemical properties and high luminescence, are promising candidates for electrochemiluminescence (ECL) applications. However, their tendency to aggregate in aqueous solutions due to π-π stacking leads to luminescence quenching and reduced efficiency. To address this, we developed a "coordination disaggregation-induced enhancement" strategy, utilizing metal-organic frameworks (MOFs) as stable platforms for immobilizing porphyrin. These porphyrin-based MOFs not only increase the loading of luminescent groups and suppress the aggregation-caused quenching (ACQ) effect but also enhance electron transfer via uniform dispersion of pyrrole N in the porphyrin ligand, thereby improving ECL intensity. Additionally, they exhibit favorable biocompatibility and low toxicity, making them suitable for biomedical applications. By combining porphyrin-based MOFs as donors with PDA@MnO2 composites as quenchers, we constructed a quenching-type ECL immunosensor for detecting programmed death ligand 1 (PD-L1). This sensor achieves a detection range of 10 fg/mL to 100 ng/mL, with a limit of detection as low as 2.48 fg/mL, which demonstrates great potential for highly sensitive biomarker detection and promising applications in early cancer diagnosis and other medical diagnostics.

Unmasking the UV Photobleaching of β-Diketonate [Eu(BTFA)4]- Complexes as an Energy-Driven Photoreduction Process

We elucidate the nature of the gradual attenuation of luminescence under sustained ultraviolet (UV) radiation exposure in europium [Eu(BTFA)4]- complexes, revealing that it originates from a nonlinear energy-driven process, wherein Eu(III) is irreversibly reduced to Eu(II). This photoreduction was confirmed via the electrochemical techniques cyclic voltammetry and chronoamperometry, which, coupled with luminescence experiments, provided direct evidence of the Eu3+/Eu2+ reduction and the disappearance of Eu(III) after UV exposure. Indeed, extended UV exposure induces a gradual decrease in Eu(III) luminescence, paired with an increased intensity of Eu(II) luminescence, upon direct excitation of the metal ion. To provide an adequate description of this process, we advanced a photochemical law in the energy domain (rather than the time domain) and introduced the concept of photobleaching energy to facilitate comparisons of photostability among various complexes in different solvents. The nonlinearities detected in the energy domain suggest an underlying multiphoton process. As a consequence, we uncovered a trade-off between photostability and luminescence: enhancing one implies diminishing the other. Specifically, the proximity between the complex and cation in nonpolar solvents induces asymmetry in the complex, enhancing luminescence but reducing photostability. Conversely, distancing the cation leaves the complex within a more symmetrical solvent enclosure, decreasing luminescence and increasing photostability. Our findings also indicate that exposing Eu(III) complexes to UV light can function as a method for the photochemical synthesis of Eu(II) complexes, a process further substantiated by our electrochemical experiments.

A mixed-organic ligands Ru(bpy)32+@Zn mMOFs-NH2 nanoreactors integrated co-reaction accelerator and morphologic regulator for the electrochemiluminescence detection of ATP

The functionalized architecture within the nanoreactor could dramatically change the electron transport and reaction efficiency of ECL during electrochemical processes. Here, we've devised a novel mixed-ligand strategy that combines co-reaction accelerator and morphologic regulator onto the same metal node. This innovative approach effectively addressed the critical issue that some co-reactants cannot be covalently linked due to their special states, while enhancing the stability and electroactivity of MOFs nanoreactors. Ru(bpy)32+ was in-situ encapsulated within Zn mMOFs-NH2 nanocages in which the 2-aminoterephthalic acid (NH2-BDC) ligand functioned as an effective co-reaction accelerator. While S2O82- underwent electron exchange on the surface of GCE to form SO4•-, Zn mMOFs-NH2 was electrochemically oxidized to Zn mMOFs-NH•, which could significantly catalyze S2O82- to form SO4•-. This greatly increased the local concentration of SO4•- in the vicinity of Ru(bpy)32+, thus achieving self-enhancing ECL. At the same time, 1,4-benzenedicarboxylic acid (BDC) ligands were used as morphologic regulator, yielding ultra-thin MOFs nanosheets that significantly boosted the loading capacity for Ru(bpy)32+ and enhanced electrical conductivity. The luminous efficiency of Ru(bpy)32+ is further enhanced by this synergy. A highly sensitive ECL biosensor was crafted for the detection of ATP. Optimal conditions allowed a robust linear correlation between the ECL intensity and the logarithm of ATP concentration, enabling a sensitive detection limit down to 1.18 nM. Our findings underscore the exceptional self-enhanced ECL properties of the devised Ru(bpy)32+@Zn mMOFs-NH2 nanoreactors, presenting a novel and promising platform for biomolecular analysis.

Research progress on the synthesis, performance regulation, and applications of Prussian blue nanozymes

Nanocatalytic medicine offers a novel solution to address the issues of low efficacy, potential side effects, and the development of drug resistance associated with traditional therapies. Therefore, developing highly efficient and durable nanozymes is of great significance for treating diseases related to oxidative stress. In recent years, prussian blue nanoparticles (PBNPs) have been demonstrated to possess multiple enzyme-like catalytic activities and are thus referred to as prussian blue nanozymes (PBNZs). Their excellent biocompatibility and biodegradability make PBNZs promising candidates as biomedical materials. Due to their remarkable catalytic activities, PBNZs have shown great potential in various biomedical applications, such as heavy metal detoxification, antioxidative damage, and anticancer therapies. This paper systematically summarizes the Synthetic strategies of PBNZs, analyzes the regulatory factors of their catalytic performance, and highlights the corresponding modulation methods. Furthermore, the biomedical applications of PBNZs are also reviewed. This study aims to provide researchers with insights and inspirations for the design and preparation of high-performance PBNZs.

Deciphering a volcano-shaped relationship between radical stability and reticular electrochemiluminescence

Electrochemiluminescence (ECL) is a light-emitting process in which the stability of electrochemically generated radicals has a crucial impact on the efficiency and durability of excited state generation. Therefore, deciphering a relationship between radical stability and ECL performance is highly appealing. In this work, three sp2 carbon-conjugated covalent organic framework (COF) reticular nanoemitters compositing of same pyrene luminophores but different acrylonitrile linkers are designed with progressive electron affinities, named as CN-COF-1, 2, and 3. By precisely modulating the electron affinity of CN-COFs, a volcano relationship between ECL and radical stability is discovered with 78 folds enhancement in ECL intensity. Density functional theoretical calculations indicate that CN-COF-2 exhibits moderate radical stabilization capacity as well as efficient electron transport between the pyrene cores, facilitating ECL generation. Significantly, the appropriate radical stability of CN-COF-2 not only achieves the self-enhanced cathodic ECL but also promotes durability of the ECL intensity. The rational regulation of radical stability paves the way for developing efficient reticular nanoemitters and decoding the ECL fundamentals.

A mini-review on the research progress and application of nanomaterials in electrochemiluminescent sensors in the detection of water environmental pollutants

With the increasingly serious problem of environmental pollution, the development of new and efficient detection technology has become an urgent need. Electrochemiluminescence (ECL) sensors have attracted wide attention in environmental pollution detection due to their advantages of low cost, fast analysis speed, high sensitivity, and good selectivity. At the same time, with the rapid development of nanotechnology, nanomaterials are widely used to construct ECL sensors. Based on the different roles of nanomaterials in the construction of ECL sensors, they can be summarized as (1) nanomaterials for signal amplification; (2) ECL nanoemitters; (3) Nanomaterials as receptors for ECL resonance energy transfer. In this paper, the construction and luminescence mechanism of ECL sensors are discussed from the above three aspects. Finally, the challenges and prospects of nanomaterials ECL sensors in the field of environmental pollution detection in the future are discussed.

A sensitive electrochemical biosensor based on Pd@PdPtCo mesoporous nanopolyhedras as signal amplifiers for assay of cardiac troponin I

Cardiac troponin I (cTnI) has been widely used in clinical diagnosis of acute myocardial infarction (AMI). Herein, a sensitive electrochemical biosensor for cTnI analysis was designed, in which the simple synthesized Pd@PdPtCo mesoporous nanopolyhedras (MNPs) were utilized as signal amplifiers. The mesoporous polyhedral structure of Pd@PdPtCo MNPs endows them with more specific surface area and more active sites, as well as the synergistic effect between multiple metal elements, all of which increase the electrocatalytic performance of Pd@PdPtCo MNPs in efficiently oxidizing hydroquinone (HQ) to benzoquinone (BQ). Experimental results showed that Pd@PdPtCo MNPs had better performance in oxidation of HQ to BQ compared with their corresponding monometallic and bimetallic nanomaterials. With the aid of the interaction between antigens and antibodies, the peak current of HQ to BQ showed an upward trend with increasing concentration of cTnI, thus the quantitative detection of cTnI could be achieved. Under optimal conditions, the biosensor prepared in this work has a wider linear range (1.0 × 10-4-200 ng mL-1) and a lower detection limit (0.031 pg mL-1) than other sensors reported in literatures, coupled by good stability and high sensitivity. More importantly, it also performed well in complex serum environment, proving that the electrochemical sensor has a practical application potential in this field.

Low-potential bionic electrochemiluminescence sensing platform based on SnS2/CuNWs synergistic promotion for highly selective detection of glycocholic acid

BACKGROUND

Glycholic acid (GCA) can dynamically reflect the process of liver injury, and can be used for early diagnosis and curative effect evaluation of early hepatitis and cirrhosis. The highly sensitive detection of liver injury markers is conducive to a more accurate and effective auxiliary diagnosis of liver diseases. In addition, the low trigger potential helps to avoid more chemical interference and improve the detection sensitivity. It is of great significance to develop a high sensitive and low potential ECL sensor for GCA detection.

RESULTS

In this work, a low trigger potential molecularly imprinted electrochemiluminescence sensor (MIECLS) combining SnS2 and CuNWs was proposed for highly selective and sensitive detection of GCA, a marker of liver injury. The stabilization and enhancement of ECL signal can be attributed to the synergistic promotion strategy of SnS2 and CuNWs. CuNWs not only has good ECL performance, but also serves as a substrate material for loading SnS2 to enhance the film forming performance. In addition, the Sn4+ active site can be regenerated by redox reaction, significantly improving the efficiency of the co-reactant and the stability of the sensor. By studying the ECL luminescence mechanism and specific recognition quenching mechanism of MIECLS in detail, a selective detection method for GCA was established. Under optimal conditions, in the range of 5 × 10-10 to 5 × 10-6 mol L-1, the quenching value of ECL intensity is proportional to LgCGCA, and the limit of detection is 1.30 × 10-10 mol L-1.

SIGNIFICANCE AND NOVELTY

In addition, satisfactory recovery rate was obtained in human serum samples, showing good practical application, providing a new way for clinical detection of GCA. At the same time, it not only broadens the development of CuNWs in the ECL field, but also provides a new way to reduce the triggering potential.

Ultrasensitive detection of holoTC for analysis of Vitamin B12 levels using Ag2MoO4 deposited PEDOT sensing platform

Vitamin B12 is an essential micronutrient required for the proper functioning of the human body. Vitamin B12 deficiency is primarily causative of various neurolological disorders alongwith recurrence of oral ulcers and burning sensations which are early signs of condition such as pernicious anemia. Other complications associated with Vitamin B12 deficiency include risk of heart failure due to anemia, risk of developing autoimmune disorders and gastric cancer. Therefore, to obstruct these communal health issues, early detection of Vit B12 is highly needed. However, screening of vitamin B12 insufficiency is hindered by the low sensitivity of the conventional vitamin B12 test. Holotranscobalamin (holoTC) is an early indicator of the negative vitamin B12 balance as it is the first protein to decline in the serum. We report a novel impedimetric immunosensor based on flower-like poly (3,4-ethylenedioxythiophene) (PEDOT) nanostructural film impregnated with silver molybdate nanoparticles (Ag2MoO₄ NPs) deposited on fluorine-doped tin oxide electrode. The prepared electrodes were characterized by Field emission scanning electron microscopy (FE-SEM) with energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and electrochemical studies. The activated anti-holoTC antibody was immobilized and optimized to capture the target in a response time of 15 min. The electrochemical performance of the sensor was carried out by using the electrochemical impedance spectroscopy technique (EIS) and a good linear relationship between ΔRct and holoTC was obtained in the range from 0.1 pg mL-1 to 100 ng mL-1 with a detection limit of 0.093 pg mL-1. The proposed sensor was successfully applied in human serum samples for holoTC detection. The experimental results showed that the immunosensor is highly selective towards holoTC and presented an acceptable stability of 20 days with reproducibility RSD ≤4%. To the best of our knowledge, this is the first developed electrochemical immunosensor for holoTC detection.

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

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

Magnetism-Functionalized Lanthanide MOF-on-MOF with Plasmonic Differential Signal Amplification for Ultrasensitive Fluorescence Immunoassays

The successful application of fluorescence immunoassays for clinical diagnosis requires stable photoluminescent materials and highly efficient signal amplification strategies. In this work, the magnetism-functionalized lanthanide MOF-on-MOF (Fe3O4@SiO2@MOF-on-MOF) was synthesized through intermolecular (van der Waals) interaction-assisted growth and further homogeneous epitaxial growth, which significantly improved the fluorescence performances and uncovered the underlying mechanism. The quantum chemical theory calculation and experimental studies revealed that the introduced magnetic Fe3O4@SiO2 not only endowed magnetic separation capability but also promoted fluorescence performances, which increased the energy transfer of the intersystem crossing process and suppressed the luminescence of ligands and aggregation-induced quenching. Furthermore, the plasmonic Ag/Au nanocages were developed as highly efficient fluorescence quenchers to improve the sensitivity of the fluorescence immunoassay. On the basis of the proposed differential signal amplification (DSA) strategy, the immunoassay displayed superior detection ability, with a limit of detection of 0.13 pg·mL-1 for severe acute respiratory syndrome coronavirus 2 nucleocapsid protein. The designed magnetic lanthanide MOF-on-MOF and proposed DSA strategy give new insights into ultrasensitive fluorescence immunoassays.

Protein-driven interaction enhanced electrochemiluminescence biosensor of hydrogen-bonded biohybrid organic frameworks for sensitive immunoassay of disease markers

The oriented design of reticular materials as emitters can significantly enhance the sensitivity of electrochemiluminescence (ECL) sensing analysis for disease markers. However, due to the structural fragility of hydrogen bonds, relational research on hydrogen-bonded organic frameworks (HOFs) has not been thoroughly conducted. Additionally, the modulation of luminescence behavior through HOFs has been rarely reported. In view of this, hydrogen-bonded biohybrid organic frameworks (HBOFs) were synthesized and recruited for ECL immunoassay applications. HBOFs was easily prepared using 6,6',6″,6‴-(pyrene-1,3,6,8-tetrayl)tetrakis(2-naphthoic acid) as linkers via bovine serum albumin (BSA) activated hydrogen-bonded cross-linking. The material exhibited good fluorescence emission characteristics. And the highly ordered topological structure and molecular motion limitation mediated by BSA overcome aggregation-caused quenching and generate strong aggregation induced emission, expressing hydrogen-bond interaction enhanced ECL (HIE-ECL) activity with the participation of tri-n-propylamine. Furthermore, a sandwich immunosensor was constructed employing cobalt-based metal-phenolic network (CMPN) coated ferrocene nanoparticles (FNPs) as quenchers (CMPN@FNPs). Signal closure can be achieved by annihilating the excited state through electron transfer from both CMPN and FNPs. Using a universal disease marker, carcinoembryonic antigen, as the analysis model, the signal-off sensor obtained a detection limit of 0.47 pg/mL within the detection range of 1 pg/mL - 50 ng/mL. The synthesis and application of highly stable HBOFs triggered by proteins provide a reference for the development of new reticular ECL signal labels, and electron transfer model provides flexible solutions for more sensitive sensing analysis.

Regulating the work function and surface hydrophobicity of an indium tin oxide electrode for enhanced electrochemiluminescence analysis

The electrochemical properties of the indium tin oxide (ITO) electrode were improved significantly by surface modification with ethephon and an ultrathin polydimethylsiloxane (PDMS) layer to regulate the work function and surface hydrophobicity of ITO. Based on this strategy, the electrochemiluminescence (ECL) intensity of tris(2,2'-bipyridyl)ruthenium (Ru(bpy)32+) and tri-n-propylamine (TPrA) in solution and on a microbead surface can be enhanced by 110 and 2 times, respectively. When using the modified electrode to detect nicotinamide adenine dinucleotide (NADH), the linear range (5-1000 μM) was increased dramatically in comparison with a bare ITO electrode, with a limit of detection of 1.65 μM. The modified electrode with improved electrochemical properties holds great potential for applications in ECL bioassays and imaging analysis.

Ultrasensitive Electrochemiluminescence Biosensor with ZIF-67@MXene as an Efficient Co-Reaction Accelerator and Plasmonic Nanozyme as a Smart Signal Amplification Probe

Exploring novel electrochemiluminescence (ECL) co-reaction accelerators to construct ultrasensitive sensing systems is a prominent focus for developing advanced ECL sensors. However, challenges still remain in finding highly efficient accelerators and understanding their promoting mechanisms. In this paper, ZIF-67@MXene nanosheet composites, with highly conductive in-plane structure and confined-stable pore/channel, are designed to act as high-efficient co-reaction accelerators and achieve a significant enhancement in the luminol-H2O2 based ECL system. Mechanism investigation suggests that hydroxyl radicals (·OH) and singlet oxygen (1O2) can be selectively and preferentially generated on ZIF-67@MXene due to the stable and efficient absorption of ·OH and 1O2, leading to a remarkable enhancement in the ECL efficiency of luminol (830%). Finally, by designing a plasmonic NH2-MIL-88@Pd nanozyme, an "on-off" switch immunosensor is constructed for the detection of prostate-specific antigen (PSA). Based on the multiple signal amplification effect, the linear detection range for PSA is expanded by three orders of magnitude. The detection limit is also improved from 1.44 × 10-11 to 9.1 × 10-13 g mL-1. This work proposes an effective method for the preparation of highly efficient co-reaction accelerators and provides a new strategy for the sensitive detection of cancer markers.

Electroluminescence aptasensor based on tetrahedral DNA nanostructure with exonuclease-assisted target cycling for detection of acetamiprid

In this study, an electroluminescent (ECL) aptasensor that could efficiently and sensitively detect acetamiprid (ACE) in vegetables was constructed based on an exonuclease-assisted target cycling amplification strategy. Bimetallic RuZn-based metal-organic framework (RuZn-MOF), nucleic acid exonuclease VII (Exo VII) and tetrahedral DNA nanostructure (TDN) were used as constituent materials. First, RuZn-MOF was a substrate material with good luminescence performance and was synthesized by a hydrothermal method. Second, TDN was autonomously assembled by an adapted single-step annealing way. In this experiment, an aptamer labeled with ferrocene (Fc) at one end was firstly bound to the tip of TDN. In the presence of the target pesticide of ACE, the stronger affinity of ACE for the aptamer made the aptamer and ACE bind preferentially. At the same time, Exo VII was activated to cleave the single-stranded aptamer, resulting in ACE release and Fc detachment. As a result, Fc moved away from the electrode surface, allowing the ECL signal intensity to be restored. The limit of detection (LOD) (33.33 fg/mL) of this method was lower than those of many reported aptasensors. This strategy provides an uncomplicated and responsive technique for the detection of ACE and offers further development possibilities for detection and analysis of other biomolecules.

AuPt/NF prepared with the lattice induction of substrate was applied to construct the electrochemical immunosensor for PCT detection

For the electrodeposition, the conductivity and lattice structure of substrate is important to the morphology and lattice of the deposited material. In this study, gold-platinum (AuPt) nanopartical was deposited on nickel foam (NF) based on the lattice induced orientation of the Ni substrate, and the obtained AuPt/NF was applied to construct electrochemical impedimetric immunosensor for procalcitonin (PCT) detection. As a new immunosensor matrix, NF with higher electrical conductance, flexibility and specific surface area, which can improve the plasticity, sensitivity and universality of the immunoelectrode. Due to the lattice matching between Au and Ni, ultrathin AuPt nanolayer with good biocompatibility and large surface area can be modified on the NF surface, which can bind more biomolecules and amplifies the change of impedance signal. Based on the synergistic effect between AuPt and NF, PCT detection based on this electrochemical impedimetric immunosensor with a wide linear range (0.2 pg mL-1 to 20 ng mL-1) and low detection limit (0.11 pg mL-1). In addition, this impedimetric immunosensor exhibits high recovery in the PCT detection of serum samples. This work provides a new thought and method for the construction of electrochemical immunosensor.

A novel and facile oxygen-activated time-temperature indicator with wide temperature monitoring range and good stability based on the laccase-like nanozyme

BACKGROUND

Time-Temperature Indicator (TTI) is an indicator device for real-time monitoring of the thermal history of the product. Due to the enzymatic reactions are affected by both time and temperature, enzymatic TTIs have been extensively studied and developed in recent years. However, enzymatic TTIs contain biologically active molecules (enzymes), which require high storage and use conditions. Most of them are designed to mix the system species together and irreversible reaction is undertaken. Nanozymes are the synthetic nanomaterials with similar biocatalytic functions as natural enzymes, which have extensive applications in analytical chemistry, biosensing, and environmental protection due to their facile synthesis, low cost, high stability and durability.

RESULTS

This work proposed to replace the natural laccase to laccase-like nanozyme, designed a novel and facile O2-activated time-temperature indicator for the first time. Nanozyme had excellent thermal and storage stability, which could maintain fabulous catalytic activity in the wide temperature range of 10-80 °C and after a long-term storage. Based on the O2 was required to participate in the oxidation of laccase-catalyzed substrates, a squeeze-type O2-activated TTI was designed by controlling O2 in the TTI system. The TTI was activated through extruding the O2-coated airbag ruptured and producing an irreversible color reaction. Combined with a smartphone to extract the chromaticity for portable visual real-time monitoring. Five sets of TTIs were prepared based on the concentration of nanozyme, and the activation energies (Ea) ranging from 28.45 to 72.85 kJ mol-1, which were able to be fitted to products with Ea ranging from 3.45 to 97.8 kJ mol-1 and the monitoring-time of less than 7 days.

SIGNIFICANCE

Compared to the traditional enzymatic TTI, the TTIs designed based on nanozyme has the advantages of controlled activation, wider temperature monitor range and good stability. Providing a new approach to the development of real-time monitoring of smart devices.

Imaging dendrite growth in solid-state sodium batteries using fluorescence tomography technology

Dendrite growth in solid-state sodium batteries (SSBs) is one of the most concerned issues that critically affect the battery efficiency and cycling performance. Here, by designing a fluorescent Eu3+-doped Na3Zr2Si2PO12 solid electrolyte (SE) to facilitate three-dimensional (3D) optical imaging on a confocal laser scanning microscopy, a fluorescence tomography (FT) method is developed for observing the sodium dendrite growth during charge/discharge cycles of the SSBs in a 3D view. It is quantitatively revealed that small-size sodium islands appear after several cycles, and with the cycles increasing, large-size dendrites in tens of micrometers gradually form until a critical sodium dendrite volume arrives where a short circuit or severe performance deterioration occurs. Furthermore, by regulating the Eu3+ doping ratio, a record-high sodium plating/stripping cycling stability for more than 1 year (487.5 days) is achieved at 25°C. This work demonstrates an FT method observing sodium dendrite growth in SSBs and will promote the functional design of high-performance SEs.

Highly efficient electrochemiluminescent properties of porphyrin-based metal-organic framework Zn-TCPP and its immunoassay application to the detection of ochratoxin A

BACKGROUND

Ochratoxin A (OTA) is a group of mycotoxins that are widely distributed in food and feed and are closely associated with human health, so it is particularly important to detect OTA in cereal-based foods. Porphyrins and their derivatives have been widely investigated for their excellent electrochemical luminescence properties. Tetrakis 4-carboxyphenyl) porphyrin (TCPP) has limited applications because of its tendency to aggregate in water.

RESULTS

To enhance the luminescence efficiency of TCPP, the porphyrin can be immobilized as an organic ligand in a metal-organic framework. This allows the preparation of a novel zinc-porphyrin-based MOF (Zn-TCPP nanorods), which in turn provides highly efficient and stable cathodic ECL signals. Herein, an ultra-sensitive electrochemiluminescence immunoassay was proposed using Zn-TCPP nanorods as high-efficiency luminophores and Bi2S3@Au nanoflowers as electrode substrate materials for the detection of ochratoxin A in foodstuffs. Zn-TCPP has a strong and stable signal, and has been used as an immunosensor probe material. The Bi2S3@Au nanoflowers was used to decorate the glass carbon electrode and support for antibody immobilization due to its good electrical conductivity and large specific surface area. Under the optimized conditions, the constructed immunosensor could realize the sensitive detection of ochratoxin A in the detection range of 0.0004 ng mL-1 to 500 ng mL-1 with the detection limit as low as 0.13 pg mL-1. In addition, the sensing platform has been used for the detection of OTA in wheat flour and feed.

SIGNIFICANCE

Hence, it is worth believing that this strategy can pave a bright research direction for the detection of ochratoxin A or other small molecule mycotoxins content in foods, as well as contributing to the further study of MOF in the field of ECL.

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

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

Wireless single-electrode electrochemiluminescence device based on wireless reverse charging or on-the-go USB transmission for multiplex analysis

A wireless electrochemiluminescence (ECL) device employing the wireless reverse charging function or on-the-go (OTG) USB transmission function of smartphones is designed. It was coupled with a multi-channel single-electrode electrochemical system based on the resistance-induced potential difference for multiple ECL analyses using a smartphone as the detector.

Molecular Planar Rigidity Promoted Aggregation-Induced Delayed Electrochemiluminescence of Organic Dots for Nucleic Acid Assay

Developing organic aggregation-induced delayed electrochemiluminescence (AIDECL) active emitters is attractive due to their full utilization of excited species. However, current molecular designs primarily focus on the electron-deficient core benzophenone, resulting in relatively low ECL efficiency due to its flexible skeleton. Herein, we design a rigid electron acceptor, i.e., xanthenone, by inserting an oxygen bridge into the benzophenone moiety, and an AIDECL-active organic dot (OD) composed of a xanthenone-dimethylacridine compound is constructed. High ECL efficiency is achieved for the resultant ODs, with a 3-fold enhancement compared to control ODs. Oxygen bridge-induced planar moiety rigidifies the molecular configuration, further inhibiting intramolecular motions and thus suppressing nonradiative decay, supported by the single-crystal data together with theoretical calculations. Significantly, an ECL biosensor is constructed employing these ODs as emitters for the sensitive analysis of miR-21 associated with pancreatic cancer, which demonstrates a low detection limit of 2.8 fM. Our investigation provides a promising way to design efficient ECL emitters and deepens the understanding of structure-property relationships.

N-doped carbon quantum dots for the selective detection of OCl- ions, bioimaging, and the production of Fe3O4 nanoparticles utilized in the synthesis of substituted imidazole

Nitrogen-doped quantum dots (NCQD) were synthesized by solvothermal means using o-phenylenediamine and l-tartaric acid. The resultant NCQD produced a high quantum yield (40.3%) and a vivid green fluorescence. They were about 6 nm in size. The NCQD is useful in HeLa cell bioimaging investigations and is used for the fluorescence detection of OCl- ions. The quantum dots' Limit of Detection (LoD) was discovered to be 40 nM. Additionally, cytotoxicity testing was conducted, and we found out that HeLa cells safely endured up to 6.5 mg ml-1 of NCQD. Furthermore, NCQDs were employed to synthesize Fe3O4 nanoparticles, with the quantum dots acting as a reducing and stabilizing agent. The nanoparticles exhibited remarkable catalytic activity towards organic processes due to their size of 11 nm and surface area of 67.360 m2 g-1. Excellent yields of tri-substituted imidazole derivatives were produced using Fe3O4 nanoparticles as nanocatalysts in a solvent-free method.

A simple and cost-effective strategy for electrochemiluminescence spectral determination

BACKGROUND

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

RESULTS

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

SIGNIFICANCE

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

A new strategy for the preparation of polylactic acid composites with UV resistance, light conversion, and antibacterial properties

A novel rare earth complex, Eu(IAA)2(phen)2 (EuIP), was synthesized by solution-based synthesis method. Then, EuIP and polylactic acid (PLA) were melt-blended at 190 °C to obtain a multifunctional PLA/EuIP composite. The incorporation of EuIP provided PLA/EuIP composites with good light conversion ability. Under UV irradiation, PLA/EuIP composites converted the absorbed UV light into red light. Moreover, the PLA/1.0EuIP composite exhibited excellent light transmittance of 88 % in the visible region and showed strong red emission under UV light. After UV irradiation for 96 h, the molecular weights and mechanical properties of neat PLA decreased dramatically. Interestingly, the molecular weights and mechanical properties of PLA/EuIP composites did not deteriorate after 96 h of UV irradiation. The reason was that EuIP could absorb UV light and utilize the absorbed energy to emit red fluorescence. Furthermore, PLA/EuIP composites showed good antibacterial activities against E. coli and S. aureus. In addition, in vitro cell experiments showed that PLA/EuIP composites was suitable for the growth of murine breast cancer (4 T1) cells. Besides, enzymatic degradation testing also proved that PLA/EuIP composites had good biodegradability. This work provides an ingenious design strategy for the preparation of PLA/EuIP composites possessing light conversion ability, UV resistance, and antibacterial properties.

Antenna effect enhanced ECL immunoassay using microfloral europium porphyrin coordination polymers based on Eu3+ and TCPP for the detection of chloramphenicol in foods

The "antenna effect" is one of the most important energy transfer modes in lanthanide light-emitting polymers. In this study, novel luminescent nanostructured coordination polymers (Eu-PCP) were synthesized in one step using Eu3+ as the central metal ion and 5,10,15,20-tetrakis (4-carboxyphenyl) porphyrin (TCPP) as the organic ligand. The unique "antenna effect" observed between Eu3+ and TCPP leads to a substantial improvement in the electrochemiluminescence (ECL) emission efficiency. Eu-PCP exhibits good cathodic ECL characteristics. Additionally, Au@SnS2 nanosheets exhibit favorable electrical conductivity, biocompatibility, and a significant specific surface area. This makes them a suitable choice as substrate materials for the modification of electrode surfaces and capturing antigens. Being well known, the development of sensitive and rapid methods to detect chloramphenicol is essential for food safety. Based on this, we report a novel competitive electrochemiluminescence immunoassay to achieve ultra-sensitive and highly specific detection of chloramphenicol. The linear range was 0.0002-500 ng mL-1 and the detection limit was 0.09 pg mL-1. Apart from that, the experimental results proved that it provided a new analytical tool for the detection of antibiotic residues in food safety.

Electrochemical detection of myoglobin using an ultrasensitive label-free sensor derived from cubic-ZIF67@Au-rGOF-NH2 composite of MOF and GOF

Markers of myocardial injury, such as myoglobin (Mb), are substances swiftly released into the peripheral bloodstream upon myocardial cell injury or altered cardiac activity. During the onset of acute myocardial infarction, patients experience a significant surge in serum Mb levels. Given this, precise detection of Mb is essential, necessitating the development of innovative assays to optimize detection capabilities. This study introduces the synthesis of a three-dimensional hierarchical nanocomposite, Cubic-ZIF67@Au-rGOF-NH2, utilizing aminated reduced graphene oxide and zeolite imidazolium ester framework-67 (ZIF67) as foundational structures. Notably, this novel material, applied in a label-free electrochemical immunosensor, presents a groundbreaking approach for detecting myocardial injury markers. Experimental outcomes revealed ZIF67 and AuNPs exhibit enhanced affinity and growth on the 3D-rGOF-NH2 matrix, thus amplifying electrical conductivity while preserving the inherent electrochemical attributes of ZIF67. As a result, the Cubic-ZIF67@Au-rGOF-NH2 label-free electrochemical immunosensor exhibited a broad detection range and high sensitivity for Mb. The derived standard curve was ΔIp = 16.67552lgC+275.245 (R = 0.993) with a detection threshold of 3.47 fg/ml. Moreover, recoveries of standards spiked into samples ranged between 96.3% and 108.7%. Importantly, the devised immunosensor retained notable selectivity against non-target proteins, proving its potential clinical utility based on exemplary sample analysis performance.

Comparative study of optical fiber immunosensors based on traditional antibody or nanobody for detecting HER2

In this study, we present a novel biomarker detection platform employing a modified S-tapered fiber coated with gold nanoparticle/graphene oxide (GNP/GO) for quantifying human epidermal growth factor receptor-2 (HER2) concentrations, using antibodies as sensing elements. The fabrication of this device involves implementing an in-situ layer-by-layer technique coupled with a chemical adsorption step to achieve the self-assembly of GNP, GO, and antibodies on the STF surface. The detection mechanism relies on monitoring the refractive index changes induced by the adsorption of HER2 onto the immobilized antibodies. For comparative analysis, both monoclonal antibody (mAb) and the novel nanobody (Nb) were employed in constructing the STF immunosensor, referred to as the mAb immunosensor and Nb immunosensor, respectively. Spectral analysis results highlight that the Nb immunosensor exhibits twice the sensitivity of the mAb immunosensor. This enhanced sensitivity is attributed to the small size, high antigen affinity, strong specificity, and structural stability of Nb. The Nb immunosensor demonstrated an impressive detection limit of 0.001 nM for HER2, surpassing the detection limit of the mAb immunosensor. These findings underscore the potential of the proposed Nb immunosensor as a promising and sensitive tool for HER2 detection, contributing to the diagnosis and prognosis of breast cancer. Furthermore, the simplicity of production and excellent optical performance position the Nb immunosensor as a prospective real-time biosensor with minimal cytotoxicity.

A sandwich-type photoelectrochemical biosensor based on anthocyanin-sensitized ZnO/P5FIn heterojunction for the sensitive detection of CYFRA21-1

. A sandwich-type photoelectrochemical (PEC) immunosensor based on a ZnO/poly(5-formylindole) (P5FIn)/anthocyanin heterostructure was developed to achieve sensitive background-free detection of the tumor marker CYFRA21-1. ZnO with good photovoltaic properties is combined with narrow bandgap P5FIn to form a p-n type heterojunction. This structure reduces the electron-hole pair recombination, thereby enhancing the photocurrent response of the composite. Anthocyanidins are environmentally friendly natural compounds with excellent antioxidant, redox properties, and remarkable electrochemical activity. After sensitization by anthocyanins, the absorption and utilization of visible light in the composites are enhanced, further improving the PEC luminescence efficiency of the materials. Additionally, boron nitride quantum dots (BN QDs) are combined with Ab2 via polydopamine (PDA) as a secondary antibody marker, enhancing its sensitivity. The biosensor exhibited a linear detection range of 0.001-100 ng mL-1 with a limit of detection (LOD) of 0.00033 ng mL-1. Furthermore, this biosensor demonstrates excellent selectivity, reproducibility, and stability, as well as successful results in analyzing actual human serum samples. This approach provides a feasible method for tumor marker detection.

Weakly ionized gold nanoparticles amplify immunoassays for ultrasensitive point-of-care sensors

Gold nanoparticle-based lateral flow immunoassays (AuNP LFIAs) are widely used point-of-care (POC) sensors for in vitro diagnostics. However, the sensitivity limitation of conventional AuNP LFIAs impedes the detection of trace biomarkers. Several studies have explored the size and shape factors of AuNPs and derivative nanohybrids, showing limited improvements or enhanced sensitivity at the cost of convenience and affordability. Here, we investigated surface chemistry on the sensitivity of AuNP LFIAs. By modifying surface ligands, a surface chemistry strategy involving weakly ionized AuNPs enables ultrasensitive naked-eye LFIAs (~100-fold enhanced sensitivity). We demonstrated how this surface chemistry-amplified immunoassay approach modulates nanointerfacial bindings to promote antibody adsorption and higher activity of adsorbed antibodies. This surface chemistry design eliminates complex nanosynthesis, auxiliary devices, or additional reagents while efficiently improving sensitivity with advantages: simplified fabrication process, excellent reproducibility and reliability, and ultrasensitivity toward various biomarkers. The surface chemistry using weakly ionized AuNPs represents a versatile approach for sensitizing POC sensors.

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.

CRISPR/Cas12a integrated electrochemiluminescence biosensor for pufferfish authenticity detection based on NiCo2O4 NCs@Au as a coreaction accelerator

Meat adulteration has brought economic losses, health risks, and religious concerns, making it a pressing global issue. Herein, combining the high amplification efficiency of polymerase chain reaction (PCR) and the accurate recognition of CRISPR/Cas12, a sensitive and reliable electrochemiluminescence (ECL) biosensor was developed for the detection of pufferfish authenticity using NiCo2O4 NCs@Au-ABEI as nanoemitters. In the presence of target DNA, the trans-cleavage activity of CRISPR/Cas12a is activated upon specific recognition by crRNA, and then it cleaves dopamine-modified single stranded DNA (ssDNA-DA), triggering the ECL signal from the "off" to "on" state. However, without target DNA, the trans-cleavage activity of CRISPR/Cas12a is silenced. By rationally designing corresponding primers and crRNA, the biosensor was applied to specific identification of four species of pufferfish. Furthermore, as low as 0.1 % (w/w) adulterate pufferfish in mixture samples could be detected. Overall, this work provides a simple, low-cost and sensitive approach to trace pufferfish adulteration.

Portable, intelligent MIECL sensing platform for ciprofloxacin detection using a fast convolutional neural networks-assisted Tb@Lu2O3 nanoemitter

Environmental pollution caused by ciprofloxacin is a major problem of global public health. A machine learning-assisted portable smartphone-based visualized molecularly imprinted electrochemiluminescence (MIECL) sensor was developed for the highly selective and sensitive detection of ciprofloxacin (CFX) in food. To boost the efficiency of electrochemiluminescence (ECL), oxygen vacancies (OVs) enrichment was introduced into the flower-like Tb@Lu2O3 nanoemitter. With the specific recognition reaction between MIP as capture probes and CFX as detection target, the ECL signal significantly decreased. According to, CFX analysis was determined by traditional ECL analyzer detector in the concentration range from 5 × 10-4 to 5 × 102 μmol L-1 with the detection limit (LOD) of 0.095 nmol L-1 (S/N = 3). Analysis of luminescence images using fast electrochemiluminescence judgment network (FEJ-Net) models, achieving portable and intelligent quick analysis of CFX. The proposed MIECL sensor was used for CFX analysis in real meat samples and satisfactory results, as well as efficient selectivity and good stability.

Tetrahedral DNA-linked aptamer-antibody-based sandwich-type electrochemical sensor with Ag@Au core-shell nanoparticles as a signal amplifier for highly sensitive detection of α-fetoprotein

The conventional electrochemical detection strategy for alpha-fetoprotein (AFP) is limited by the antigen-antibody (Ag-Ab) reactions and suffers from low sensitivity and poor reproducibility due to the inconsistency of Ab-modified electrodes. Herein, we designed and explored a sandwich-type electrochemical sensor for highly sensitive detection of AFP based on aptamer (Apt)-AFP-Ab interaction mode with silver@gold (Ag@Au) core-shell nanoparticles (NPs) as a signal amplifier. AuNPs were electrodeposited onto MXene (Ti3C2TX)-modified glassy carbon electrode (GCE) to get AuNPs/MXene/GCE and further used as the signal amplification substrate. The tetrahedral DNA-linked AFP aptamers were immobilized onto AuNPs/MXene/GCE surface via Au-S bonds and used as the sensing and recognition platform for AFP capturing. Ag@AuNPs with core-shell structures were synthesized, characterized, and bound with Ab as detection elements by catalyzing H2O2 reduction. In the presence of AFP, a stable Apt-AFP-Ab sandwich structure was formed owing to the high affinities of aptamer and Ab toward the target AFP. The catalytic current produced by H2O2 reduction increased linearly with the logarithm of AFP concentration from 5 × 10-4 ng/mL to 1 × 105 ng/mL, accompanied by a low detection limit (1.6 × 10-4 ng/mL). Moreover, the novel sandwich-type electrochemical sensor shows high sensitivity, outstanding selectivity, and promising performance in the analysis of actual samples, displaying a broad application prospect in bioanalysis.

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

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

An Encyclopedic Compendium on Chemosensing Supramolecular Metal-Organic Gels

Chemosensing, an interdisciplinary scientific domain, plays a pivotal role ranging from environmental monitoring to healthcare diagnostics and (inter)national security. Metal-organic gels (MOGs) are recognized for their stability, selectivity, and responsiveness, making them valuable for chemosensing applications. Researchers have explored the development of MOGs based on different metal ions and ligands, allowing for tailored properties and sensitivities, and have even demonstrated their applications as portable sensors such as paper-based test strips for practical use. Herein, several studies related to MOGs development and their applications in the chemosensing field via UV-visible or luminance along with electrochemical approach are presented. These papers explored MOGs as versatile materials with their use in sensing bio or environmental analytes. This review provides a foundational understanding of key concepts, methodologies, and recent advancements in this field, fostering the scientific community.