Metal-organic frameworks-based sensitive electrochemiluminescence biosensing

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.

A self-enhanced electrochemiluminescence aptasensor Zr-porphyrin modified with polyamidoamine for sensitive detection of lincomycin

Exploring novel and sensitive analysis methods for monitoring lincomycin (Lin) residues is of great significance since overuse of it would cause a serious threat to public health. Herein, a Zr-porphyrin metal-organic frameworks (Zr-TCPP) with covalently modified polyamidoamine (PAMAM) dendrimers was synthesized as a novel intramolecular self-enhanced ECL reagent, which exhibited greatly improved ECL response due to the promotion of SO4•- generation and the shortening of the electron transfer distance. Graphene oxide modified with gold nanoparticles (Au@GO) was synthesized as the quencher for the ECL sensor construction based on the quenching strategy. The present aptasensor achieved a wide linear range of 1.0 × 10-14 - 5.0 × 10-9 g/mL and a low detection limit of 1.7 fg/mL, which was applied for the determination of Lin in different real samples with satisfactory results.

A novel electrochemiluminescent sensor based on AgMOF@N-CD composites for sensitive detection of trilobatin

In this study, a novel electrochemiluminescent (ECL) sensor for highly sensitive detection of trilobatin (Tri) was developed based on silver metal-organic frameworks (AgMOFs) and nitrogen-doped carbon quantum dots (N-CDs). N-CDs exhibited high ECL intensity but poor ECL stability, while AgMOFs had a large specific surface area, high porosity, and good adsorption properties. Compositing both of them not only improved the ECL stability of N-CDs, but also enhanced the ECL strength of materials, so AgMOF@N-CD composites were used as the luminophore of the sensor. Under the optimized conditions, the ECL sensor showed a linear range of 1.0 × 10-7 M to 1.0 × 10-3 M for the detection of Tri, and the detection limit was as low as 5.99 × 10-8 M (S/N = 3). In addition, the sensor had excellent reproducibility, stability, and anti-interference ability. It could be utilized for the detection of Tri in real samples with recoveries of 95.78-102.26%, indicating that the constructed ECL sensor for detecting Tri possessed better application prospects.

Electrochemiluminescence resonance energy transfer detection of HBsAg based on Co doped 3D porous luminol-based conjugates and quencher UiO-66-NH2@Au

An electrochemiluminescence (ECL) biosensor based on ECL resonance energy transfer (ECL-RET) was designed to sensitively detect hepatitis B virus surface antigen (HBsAg). In this ECL-RET system, luminol was employed as ECL donor, and gold nanoparticles functionalized zirconium organoskeleton (UiO-66-NH2@Au) was prepared and served as ECL acceptor. The UiO-66-NH2@Au possessed an ultraviolet-visible (UV-vis) absorption between 400 nm and 500 nm, and the absorption spectra overlapped with the ECL spectrum of luminol. Furthermore, Graphene oxide-poly(aniline-luminol)-cobalt nanoparticles conjugates (GO-PALu-Co) was prepared to optimize the ECL behavior through the catalysis of Cobalt nanoparticles and served as a stable 3D porous film to load capture probe primary antibody (Ab1). Based on the ECL-RET biosensing method, the UiO-66-NH2@Au-labeled Ab2 and target HBsAg could pair with primary antibody Ab1 to form sandwich-type structure, and the ECL signal of GO-PALu-Co was quenched. Under optimized experimental conditions, the ECL-RET analytical method represented eminent analytical performance for HBsAg detection with a wide linear relationship from 2.2 × 10-13 to 2.2 × 10-5 mg/mL, and a detection limit of 9 × 10-14 mg/mL (S/N = 3), with spiked sample recoveries ranging from 97.27 % to 102.73 %. The constructed sensor has good stability, reproducibility, and specificity. It can be used to detect HBsAg in human serum and has the potential to be used for the sensitive detection of other disease biomarkers.

Colorimetric and ECL dual-mode aptasensor for smartphone-based onsite sensitive detection of aflatoxin B1 in combination with ZnO@MWCNTs/g-C3N4 nanosheets and CuO@CuPt nanocomposites

The development of dual-mode strategies with superior sensitivity and accuracy have garnered increasing attention for researchers in Aflatoxin B1 (AFB1) analysis. Herein, a colorimetric-electrochemiluminescence (ECL) dual-mode biosensor was constructed for onsite and ultrasensitive determination of AFB1. The multi-wall carbon nanotubes (MWCNTs) were integrated with the ZnO metal organic frameworks (MOFs) to accelerate the electron transfer and boost the ECL intensity of g-C3N4 nanoemitters. Through the aptamer-based DNA sandwich assay, the CuO@CuPt nanocomposites were introduced onto the electrode and acted as the dual functional signal nanoprobes. Due to the good spectrum overlap between the CuO@CuPt nanoprobes and g-C3N4 nanosheets, ECL signal could be efficiently quenched. Additionally, the CuO@CuPt nanoprobes show superior catalytic properties towards the TMB and H2O2 colorimetric reactions, and an obvious color alteration from colorless to blue can be observed using the smartphone. Under optimized conditions, a sensitive and accurate dual-mode analysis of the AFB1 was accomplished with the colorimetric detection limit of 3.26 fg/mL and ECL detection limit of 0.971 fg/mL (S/N = 3). This study combines innovative nanomaterial properties of ZnO@MWCNTs, g-C3N4 and CuO@CuPt for ultrasensitive dual-mode detection, which offers new opportunities for the innovative engineering of the dual-mode sensors and demonstrates significant potential in food safety analysis.

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

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

Strong aggregation-induced electrochemiluminescence of pyrene-coordination metal-organic frameworks coupled with zero-valent iron as novel accelerator for ultrasensitive immunoassay

Polycyclic aromatic hydrocarbons (PAHs) are excellent alternative luminophores for electrochemiluminescence (ECL) immunoassays. However, they are inevitably limited by the aggregation-caused quenching effect. In this study, aimed at eliminating the aggregation quenching of PAHs, luminescent metal-organic frameworks (MOFs) with 1,3,6,8-tetra(4-carboxybenzene)pyrene (H4TBAPy) as the ligand were exploited as a novel nano-emitter for the construction of ECL immunoassays. The luminophore exhibits efficient aggregation-induced emission enhancement, good acid-base resistance property and unusual ECL reactivity. In addition, the simultaneous use of potassium persulfate and hydrogen peroxide as dual co-reactants resulted in a synergistic enhancement of the cathodic ECL efficiency. The use of magnetic iron-nickel alloys as the multifunctional sensing platform can further enhance the ECL activity, and its enriched zero-valent iron as a co-reactant accelerator effectively drives ECL analytical performance. Profiting from the excellent characteristics, signal-on ECL immunoassays have been constructed. With carcinoembryonic antigen as the model analysis target, a detection limit of 0.63 pg/mL was obtained within the linear range of 1 pg/mL to 50 ng/mL, accompanied by excellent analytical performance. This report opens a new window for the rational design of efficient ECL illuminators, and the proposed ECL immunoassays may find promising applications in the detection of disease markers.

Pyrenetetrasulfonate-grafted 2D ultrathin metal-organic layer as new electrochemiluminescence emitters for ultrasensitive microRNA-21 assay

The exploration of novel electrochemiluminescence (ECL) luminophores with excellent ECL properties is a current research hotspot in the ECL field. Herein, a novel high-efficiency Ru-complex-free ECL emitter PyTS-Zr-BTB-MOL has been prepared by using porous ultrathin Zr-BTB metal-organic layer (MOL) as carrier to coordinatively graft the cheap and easily available polycyclic aromatic hydrocarbon (PAH) derivative luminophore PyTS whose ECL performance has never been investigated. Gratifyingly, the ECL intensity and efficiency of PyTS-Zr-BTB-MOL were markedly enhanced compared to both PyTS monomers and PyTS aggregates. The main reason was that the distance between pyrene rings was greatly expanded after the PyTS grafting on the Zr6 clusters of Zr-BTB-MOL, which overcame the aggregation-caused quenching (ACQ) effect of PyTS and thus enhanced the ECL emission. Meanwhile, the porous nanosheet structure of PyTS-Zr-BTB-MOL could distinctly increase the exposure of PyTS luminophores and shorten the diffusion paths of coreactants and electrons/ions, which effectively promoted the electrochemical excitation of more PyTS luminophores and thus achieved a further ECL enhancement. In light of the remarkable ECL property of PyTS-Zr-BTB-MOL, it was employed as an ECL indicator to build a novel high-sensitivity ECL biosensor for microRNA-21 determination, possessing a satisfactory response range (100 aM to 100 pM) and an ultralow detection limit (10.4 aM). Overall, this work demonstrated that using MOLs to coordinatively graft the PAH derivative luminophores to eliminate the ACQ effect and increase the utilization rate of the luminophores is a promising and efficient strategy to develop high-performance Ru-complex-free ECL materials for assembling ultrasensitive ECL biosensing platforms.

Metal-organic framework (MOF)-based biosensors for miRNA detection

MicroRNAs (miRNAs) play several crucial roles in the physiological and pathological processes of the human body. They are considered as important biomarkers for the diagnosis of various disorders. Thus, rapid, sensitive, selective, and affordable detection of miRNAs is of great importance. However, the small size, low abundance, and highly similar sequences of miRNAs impose major challenges to their accurate detection in biological samples. In recent years, metal-organic frameworks (MOFs) have been applied as promising sensing materials for the fabrication of different biosensors due to their distinctive characteristics, such as high porosity and surface area, tunable pores, outstanding adsorption affinities, and ease of functionalization. In this review, the applications of MOFs and MOF-derived materials in the fabrication of fluorescence, electrochemical, chemiluminescence, electrochemiluminescent, and photoelectrochemical biosensors for the detection of miRNAs and their detection principle and analytical performance are discussed. This paper attempts to provide readers with a comprehensive knowledge of the fabrication and sensing mechanisms of miRNA detection platforms.

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) modified metal-organic frameworks boosting carbon dots electrochemiluminescence emission for sensitive miRNA detection

Highly efficient luminescent materials play an important role in electrochemiluminescence (ECL) biosensing systems. Herein, the poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) modified carbon dots (CDs)/zeolitic imidazolate framework-8 (ZIF-8) compositing metal-organic frameworks (MOFs) materials with excellent luminescence performance were prepared as the ECL emitters for biosensing application. In this novel ternary composites, CDs were used as emitters, ZIF-8 was used as a carrier, and the luminescent performance was finally improved by introducing PEDOT:PSS to improve the conductivity of the nanomaterials. As a result, CDs/PEDOT:PSS/ZIF-8 exhibited an approximately 8 times ECL intensity compared to CDs alone. By further modifying with AuNPs, the enhancement factor reached ≈10 in reference to the individual CDs. After combining with a DNAzyme-based two-cycle target amplification principle, an ECL biosensor was constructed to achieve high-sensitivity detection of miRNA-21 with a detection limit of 50 aM. The biosensor also demonstrated desirable selectivity, excellent stability, and quantitative ability for human serum target detection. Overall, these findings not only provide a promising pathway for high luminous efficiency ECL emitters synthesis, but also provide a platform for ultrasensitive miRNA sensing.

Recent advancements in the specific determination of carcinoembryonic antigens using MOF-based immunosensors

Carcinoembryonic antigens (CEAs) are prominent cancer biomarkers that enable the early detection of numerous cancers. For effective CEA screening, rapid, portable, efficient, and sensitive diagnosis approaches should be devised. Metal-organic frameworks (MOFs) are porous crystalline materials that have received major attention for application in high-efficiency signal probes owing to their advantages such as large specific surface area, superior chemical stability and tunability, high porosity, easy surface functional modification, and adjustable size and morphology. Immunoassay strategies using antigen-antibody specific interaction are one of the imperative means for rapid and accurate measurement of target molecules in biochemical fields. The emerging MOFs and their nanocomposites are synthesized with excellent features, providing promising potential for immunoassays. This article outlines the recent breakthroughs in the synthesis approaches of MOFs and overall functionalization mechanisms of MOFs with antigen/antibody and their uses in the CEA immunoassays, which operate according to electrochemical, electrochemiluminescent and colorimetric techniques. The prospects and limitations of the preparation and immunoassay applications of MOF-derived hybrid nanocomposites are also discussed at the end.

Size-matching compositing nanoprobe of AIE-type gold nanocluster supramolecular nanogels wrapped by hypergravity-tailored MnO2 nanosheets for cellular glutathione detection

Compositing has been the main approach for material creation via wisely combining material components with different properties. MnO2 nanosheets (MNSs) with thin 2 D morphology are usually applied to composite molecules or nanomaterials for biosensing and bioimaging applications. However, such composition is actually structurally unmatched, albeit performance matching. Here, a series of benefits merely on the basis of structural match have been unearthed via tailoring MNSs with four sizes by synthesis under controllable hypergravity field. The classical fluorophore-quencher couple was utilized as the subject model, where the soft supramolecular nanogels based on aggregation-induced emission (AIE)-active gold nanoclusters were wrapped by MNSs of strong absorption. By comparative study of one-on-one wrapping and one-to-many encapsulation with geometrical selection of different MNSs, we found that the one-on-one wrapping model protected weakly-bonded nanogels from combination-induced distortion and strengthened nanogel networks via endowing exoskeleton. Besides, wrapping pattern and size-match significantly enhanced the quenching efficiency of MNSs towards the emissive nanogels. More importantly, the well-wrapped nanocomposites had considerable enhanced biological compatibility with much lower cytotoxicity and higher transfection capacity than the untailored MNSs composite and could serve as cellular glutathione detection.

Recent progress of metal-organic framework-based nanozymes with oxidoreductase-like activity

Nanozymes, a class of synthetic nanomaterials possessing enzymatic catalytic properties, exhibit distinct advantages such as exceptional stability and cost-effectiveness. Among them, metal-organic framework (MOF)-based nanozymes have garnered significant attention due to their large specific surface area, tunable pore size and uniform structure. MOFs are porous crystalline materials bridged by inorganic metal ions/clusters and organic ligands, which hold immense potential in the fields of catalysis, sensors and drug carriers. The combination of MOFs with diverse nanomaterials gives rise to various types of MOF-based nanozyme, encompassing original MOFs, MOF-based nanozymes with chemical modifications, MOF-based composites and MOF derivatives. It is worth mentioning that the metal ions and organic ligands in MOFs are perfectly suited for designing oxidoreductase-like nanozymes. In this review, we intend to provide an overview of recent trends and progress in MOF-based nanozymes with oxidoreductase-like activity. Furthermore, the current obstacles and prospective outlook of MOF-based nanozymes are proposed and briefly discussed. This comprehensive analysis aims to facilitate progress in the development of novel MOF-based nanozymes with oxidoreductase-like activity while serving as a valuable reference for scientists engaged in related disciplines.

A review of nanomaterials for biosensing applications

A biosensor is a device that reacts with the analyte to be analyzed, detects its concentration, and generates readable information, which plays an important role in medical diagnosis, detection of physiological indicators, and disease prevention. Nanomaterials have received increasing attention in the fabrication and improvement of biosensors due to their unique physicochemical and optical properties. In this paper, the properties of nanomaterials such as the size effect, optical and electrical properties, and their advantages in the field of biosensing are briefly summarized, and the application of nanomaterials can effectively improve the sensitivity and reduce the detection limit of biosensors. The advantages of commonly used nanomaterials such as gold nanoparticles (AuNPs), carbon nanotubes (CNTs), quantum dots (QDs), graphene, and magnetic nanobeads for biosensor applications are also reviewed. Besides, the two main types of biosensors using nanomaterials involved in their construction and their working principles are described, and the toxicity and biocompatibility of nanomaterials and the future direction of nanomaterial biosensors are discussed.

Simultaneous Detection and Decontamination of Dichromate Ions: The Fluorescence Response and Photocatalysis of Thiadiazole-Modified Zr-Metal-Organic Frameworks

The simultaneous analysis and removal of highly toxic hexavalent chromium (Cr (VI)) in contaminated water via an easy method remain a serious task. Based on the guidance of bibliometric analysis, a thiadiazole ligand-modified zirconium metal-organic framework (Zr-MOF) heralds a new and simple approach to Cr (VI) treatment. The concentration can be determined by fluorescence quenching with a low detection limit of 1.4 μM and a high quenching constant of 6.88 × 103 M-1. For the sensing mechanism, the fluorescence intensity of the Zr-MOF decreased rapidly due to the competition of Cr (VI) with the Zr-MOF for absorption excitation energy and the induction of Zr-MOF aggregation. The analysis system also displayed satisfactory stability and applicability. Apart from sensing application, Zr-MOF can convert Cr (VI) to Cr (III), and the reduction rate constant was 0.004 min-1 under irradiation. Therefore, the bifunctional Zr-MOF provided a potential application method for controlling the pollution caused by Cr (VI) in wastewater.

Luminescent Metal-Organic Frameworks for Electrochemiluminescent Detection of Water Pollutants

The modern lifestyle has increased our utilization of pollutants such as heavy metals, aromatic compounds, and contaminants that are of rising concern, involving pharmaceutical and personal products and other materials that may have an important environmental impact. In particular, the ultimate results of the intense use of highly stable materials, such as heavy metals and chemical restudies, are that they turn into waste materials, which, when discharged, accumulate in environmental water bodies. In this context, the present review presents the application of metal-organic frameworks (MOFs) in electrochemiluminescent (ECL) sensing for water pollutant detection. MOF composites applied as innovative luminophore or luminophore carriers, materials for electrode modification, and the enhancement of co-reaction in ECL sensors have enabled the sensitive monitoring of some of the most common contaminants of emerging concern such as heavy metals, volatile organic compounds, pharmaceuticals, industrial chemicals, and cyanotoxins. Moreover, we provide future trends and prospects associated with ECL MOF composites for environmental sensing.

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.

Electrochemiluminescence resonance energy transfer immunoassay based on a porphyrin metal-organic framework and AuNPs/NSG for the sensitive detection of zearalenone

In this study, a novel electrochemiluminescence resonance energy transfer (ECL-RET) immunoassay was developed for the first time for the detection of zearalenone (ZEN). A porphyrin metal-organic framework (PCN-222), an emerging porphyrin-based ECL luminophore, was prepared by a simple hydrothermal method using tetrakis(4-carboxyphenyl) porphyrin, which has excellent ECL emission as well as good ECL efficiency. Because the ECL emission spectrum of PCN-222 is highly matched to the absorption spectrum of gold nanoparticle-modified graphene oxide (AuNPs/NSG) nanocomposites, they were used as donor-acceptor counterparts in this work for the ECL-RET strategy. Under optimal conditions, the ECL immunosensor showed a sensitive response to ZEN in a wide detection range, with a linearity of 0.0005-1000 ng mL-1 and a detection limit of 0.15 pg mL-1. In addition, the sensor showed good potential for application in the detection of wheat and corn samples, providing a new approach for the detection of mycotoxin-like contaminants such as ZEN in food grains.

Regulating highly photoelectrochemical activity of Zr-based mixed-linker metal-organic frameworks toward sensitive electrogenerated chemiluminescence sensing of α-glucosidase

The conductivity and emission efficiency of metal-organic frameworks (MOFs) remain challenging factors that limit their electrogenerated chemiluminescence (ECL) sensing applications. Herein, we report a facile approach to address these challenges by integrating an electroactive linker (H2-TCPP) with an ECL active electrogenerated chemiluminescence linker (H4-TBAPy) to construct a highly photoelectrochemical active mixed-linker MOFs (ML-MOFs). ECL results revealed a remarkable 15.4-fold enhancement for the top-performing ML-MOFs (M6-MOFs), surpassing the single linker MOFs. In addition, M6-MOFs also exhibit a remarkable 73-fold enhancement in ECL efficiency compared to commercial Ru (bpy)32+. This improvement should be attributed to the synergistic effects resulting from the combination of two linkers. Furthermore, M6-MOFs are found to be served as a model ECLphore for sensitive and selective detection of α-glucosidase for the first time with good potential practicability in human serum samples. This work represents a promising direction to guide for designing good conductivity and high ECL efficiency MOFs in terms of linker functionalization and thus bandgap modulation for advancing their ECL sensing applications.

MOF-Based Biosensors for the Detection of Carcinoembryonic Antigen: A Concise Review

Cancer has been considered one of the most serious diseases in recent decades. Early diagnosis of cancer is a crucial step for expedited treatment. Ideally, detection of cancer biomarkers, which are usually elevated because of cancer, is the most straightforward approach to detecting cancer. Among these biomarkers, the carcinoembryonic antigen (CEA) is considered one of the most important tumor markers for colorectal cancer. The CEA has also been recognized as a biomarker for other types of cancers, including breast, gastric, ovarian, pancreatic, and lung cancers. Typically, conventional CEA testing depends on immunoassay approaches, which are known to be complex, highly expensive, and time consuming. Accordingly, various types of biosensors have been designed for the detection of cancer biomarkers. The main prerequisites of these biosensors are high sensitivity, fast response, and low cost. Many nanostructures have been involved in the design of biosensors, such as nanoparticles of certain metals and metal oxides that are further functionalized to contribute to the sensing of the biomarkers. Alternatively, metal organic frameworks (MOFs), which are extended crystalline structures comprising metal clusters surrounded by organic linkers, have been shown to be highly promising for the development of biosensors. The 3D structure of MOFs results in a combination of high surface area and high interconnected porosity, which are believed to facilitate their function in the design of a biosensor. This review briefly classifies and describes MOF-based biosensor trials that have been published recently for the aim of detecting CEA.

Passion fruit-inspired dendritic mesoporous silica nanospheres-enriched quantum dots coupled with magnetism-controllable aptasensor enable sensitive detection of ochratoxin A in food products

Ochratoxin A (OTA) is a powerful mycotoxin present in a variety of food products, and its detection is important for human health. Here, a fluorescent aptasensor is reported for sensitive OTA determination. Specifically, the surface of bio-inspired passion fruit-like dendritic mesoporous silica nanospheres-enriched quantum dots (MSNQs-apt) was first modified with the OTA aptamer as the recognition unit and fluorescence emitter, while the aptamer-complementary DNA (MNPs-cDNA) was linked with the magnetic nanoparticles (MNPs) as the separation element. In the range of 2.56 pg/mL to 8 ng/mL, the proposed aptasensor exhibited satisfactory linearity and a detection limit of 1.402 pg/mL. The developed aptasensor achieved recoveries of 90.98-103.20% and 94.33-107.57 % in red wine and wheat flour samples, respectively. By simply replacing the aptamer, this aptasensor can be easily extended to detection of other analytes, suggesting its potential as a universal detection platform for mycotoxins in food products.

Green-derived carbon dots: A potent tool for biosensing in food safety

The impact of food contaminants on ecosystems and human health has attracted widespread global attention, and there is an urgent need to develop reliable food safety detection methods. Recently, carbon dots (CDs) have been considered as a powerful material to construct sensors for chemical analysis. Based on the concept of resource conversion and sustainable development, the use of natural, harmless, and renewable materials for the preparation of CDs without the involvement of chemical hazards is a current hot topic. This paper reviews the research progress of green-derived CDs and their application in food safety biosensing. The fabrications of green-derived CDs using various biomasses are described in detail, and the application of CDs especially the sensing mechanisms of photoluminescence, colorimetric, electrochemiluminescence and other sensors are provided. Finally, existing shortcomings and current challenges as well as prospects for food safety monitoring are discussed. We believe that this work provides strong insight into the application of CDs in the sensing of various contaminants.

Ruthenium(II) complex-grafted conductive metal-organic frameworks with conductivity- and confinement-enhanced electrochemiluminescence for ultrasensitive biosensing application

Improving the electrochemiluminescence (ECL) performance of luminophores is an ongoing research hotspot in the ECL realm. Herein, a high-performance metal-organic framework (MOF)-based ECL material (Ru@Ni₃(HITP)₂, HITP = 2,3,6,7,10,11-hexaiminotriphenylene) with conductivity- and confinement-enhanced ECL was successfully constructed by using conductive MOF Ni₃(HITP)₂ as the carrier to graft Ru(bpydc)₃^4- (H₂bpydc = 2,2'-bipyridine-4,4'-dicarboxylic acid) into the channels of Ni₃(HITP)₂. Compared to Ru@Cu₃(HITP)₂ and Ru@Co₃(HITP)₂ with relatively low conductivity, the ECL intensity of Ru@Ni₃(HITP)₂ was prominently increased about 6.76 times and 18.8 times, respectively, which demonstrated that the increase in conductivity induced the ECL enhancement of the MOF-based ECL materials. What's more, the hydrophobic and porous Ni₃(HITP)₂ can not only effectively enrich the lipophilic tripropylamine (TPrA) coreactants in its channels to enhance the electrochemical oxidation efficiency of TPrA, but also provide a conductive reaction micro-environment to boost the ECL reaction between Ru(bpydc)₃^3- intermediates and TPrA^• in confined spaces, thus realizing a remarkable confinement-enhanced ECL. Considering the excellent ECL performance of Ru@Ni₃(HITP)₂, an ultrasensitive ECL biosensor was prepared based on the Ru@Ni₃(HITP)₂ ECL indicator combining an exonuclease I-aided target cycling amplification strategy for thrombin determination. The constructed ECL biosensor showcased a wide linear range from 1 fM to 1 nM with a low detection limit of 0.62 fM. Overall, the conductivity- and confinement-enhanced ECL based on Ru@Ni₃(HITP)₂ provided effective and feasible strategies to enhance ECL performance, which paved a promising avenue for exploring high-efficient MOF-based ECL materials and thus broadened the application scope of conductive MOFs.

Metal-Organic Frameworks as Sensors for Human Amyloid Diseases

Metal-organic frameworks (MOFs) are versatile compounds with emergent applications in the fabrication of biosensors for amyloid diseases. They hold great potential in biospecimen protection and unprecedented probing capabilities for optical and redox receptors. In this Review, we summarize the main methodologies employed in the fabrication of MOF-based sensors for amyloid diseases and collect all available data in the literature related to their performance (detection range, limit of detection, recovery, time of analysis, among other parameters). Nowadays, MOF sensors have evolved to a point where they can, in some cases, outperform technologies employed in the detection of several amyloid biomarkers (amyloid β peptide, α-synuclein, insulin, procalcitonin, and prolactin) present in biological fluids, such as cerebrospinal fluid and blood. A special emphasis has been given by researchers on Alzheimer's disease monitoring to the detriment of other amyloidosis that are underexploited despite their societal relevance (e.g., Parkinson's disease). There are still important obstacles to overcome in order to selectively detect the various peptide isoforms and soluble amyloid species associated with Alzheimer's disease. Furthermore, MOF contrast agents for imaging peptide soluble oligomers in living humans are also scarce (if not nonexistent), and action in this direction is unquestionably required to clarify the contentious link between the amyloidogenic species and the disease, guiding research toward the most promising therapeutic strategies.

An electrochemiluminescence aptasensor based on highly luminescent silver-based MOF and biotin-streptavidin system for mercury ion detection

In this study, for the first time, a silver-based metal-organic framework (Ag-MOF) was synthesized and used as the electrochemiluminescence (ECL) emitter for building an ECL sensor. After modification with chitosan (CS) and gold nanoparticles (Au NPs), the ECL stability of Ag-MOF was improved. To detect mercury ions, a biosensor was constructed using the mercury ion aptamer and steric effect of streptavidin. First, the capture strand (cDNA) with terminal-modified sulfhydryl group was attached to the electrode surface by the Au-S bond. Then, the mercury-ion aptamer (Apt-Hg) modified with biotin was anchored to the electrode by complementary pairing with cDNA. Streptavidin (SA) could be fixed on the electrode by linking with biotin, thereby reducing the ECL signal. However, in the presence of mercury ions, the aptamer was removed and streptavidin could not be immobilized on the electrode. Hence, the ECL signal of the sensor increased with the concentration of mercury ions, which was linear in the range from 1 μM to 300 fM. The detection limit could reach 66 fM (S/N = 3). The sensor provided a new method for the detection of mercury ions.

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.

High-Performance Electrochemiluminescence of a Coordination-Driven J-Aggregate K-PTC MOF Regulated by Metal-Phenolic Nanoparticles for Biomarker Analysis

The elimination of aggregation-caused quenching of polycyclic aromatic hydrocarbons by metal-ligand coordination is of immense scientific interest in solid-state electrochemiluminescence (ECL) sensing. Herein potassium ion (K⁺)-mediated J-aggregate K-PTC MOF (PTCA, perylene-3,4,9,10-tetracarboxylic) was synthesized and employed to formulate an ECL immunosensor for biomarker detection. The coordination-driven aggregates are arranged in an end-to-end side mode, which overcomes the aggregation-caused quenching related to PTCA concentration. Compared with PTCA, K-PTC MOF shows a more stable ECL emission with an unprecedented red shift to 718 nm and is equipped with ECL activity for analytical applications at a voltage of -1.1 V. Considering the requirements of accurate detection, metal-phenolic bioactive nanoparticles (MPNPs) were synthesized for the construction of a sandwich sensing platform to realize the steady-state regulation of ECL. As proof of applicability, a constructive experiment was carried out with neuron-specific enolase (NSE), a marker of small cell lung cancer (SCLC), as a targeted analyte. With optimal requirements, the configuration can provide a detection range of 10 pg/mL to 50 ng/mL and a detection limit of 7.4 pg/mL, accompanied by sufficient practical analytical performance. Collectively, this paradigm provides a deeper understanding of the ECL characteristics of coordination-driven J-aggregation and provides more possibilities for the development of ECL patterns based on luminescent metal-organic frameworks.

Sandwich-Type Electrochemiluminescence Immunosensor Based on CDs@dSiO2 Nanoparticles as Nanoprobe and Co-Reactant

In general, co-reactants are essential in highly efficient electrochemiluminescence (ECL) systems. Traditional co-reactants are usually toxic, so it is necessary to develop new environmentally friendly co-reactants. In this work, carbon dots (CDs) were assembled with dendritic silica nanospheres (CDs@dSiO₂ NPs) to form a co-reactant of Ru(bpy)₃²⁺. Subsequently, a sandwich immunosensor for detecting human chorionic gonadotropin (HCG) was constructed based on CDs@dSiO₂ NPs as co-reactants, the nanoprobe loaded with the secondary antibody, and Ru(bpy)₃²⁺ as a luminophore. In addition, compared to directly as a signal probe, the luminophore Ru (bpy)₃²⁺ as a part of the electrolyte solution is simpler in this work. The immunosensor has an extremely low limit of detection of 0.00019 mIU/mL. This work describes the synthesis of low-toxic, efficient, and environmentally friendly CDs, which have become ideal co-reactants of Ru(bpy)₃²⁺, and proposes an ECL immunosensor with excellent stability and selectivity, which has great potential in clinical applications.

Metal-organic frameworks: A promising option for the diagnosis and treatment of Alzheimer's disease

Beta-amyloid (Aβ) peptide is one of the main characteristic biomarkers of Alzheimer's disease (AD). Previous clinical investigations have proposed that unusual concentrations of this biomarker in cerebrospinal fluid, blood, and brain tissue are closely associated with the AD progression. Therefore, the critical point of early diagnosis, prevention, and treatment of AD is to monitor the levels of Aβ. In view of the potential of metal-organic frameworks (MOFs) for diagnosing and treating the AD, much attention has been focused in recent years. This review discusses the latest advances in the applications of MOFs for the early diagnosis of AD via fluorescence and electrochemiluminescence (ECL) detection of AD biomarkers, fluorescence detection of the main metal ions in the brain (Zn²⁺, Cu²⁺, Mn²⁺, Fe³⁺, and Al³⁺) in addition to magnetic resonance imaging (MRI) of the Aβ plaques. The current challenges and future strategies for translating the in vitro applications of MOFs into in vivo diagnosis of the AD are discussed.

Nanomaterial-Based Fluorescent Biosensor for Food Safety Analysis

Food safety issues have become a major threat to public health and have garnered considerable attention. Rapid and effective detection methods are crucial for ensuring food safety. Recently, nanostructured fluorescent materials have shown considerable potential for monitoring the quality and safety of food because of their fascinating optical characteristics at the nanoscale. In this review, we first introduce biomaterials and nanomaterials for food safety analysis. Subsequently, we perform a comprehensive analysis of food safety using fluorescent biosensors based on nanomaterials, including mycotoxins, heavy metals, antibiotics, pesticide residues, foodborne pathogens, and illegal additives. Finally, we provide new insights and discuss future approaches for the development of food safety detection, with the aim of improving fluorescence detection methods for the practical application of nanomaterials to ensure food safety and protect human health.

Nanomaterials-Based Electrochemiluminescence Biosensors for Food Analysis: Recent Developments and Future Directions

Developing robust and sensitive food safety detection methods is important for human health. Electrochemiluminescence (ECL) is a powerful analytical technique for complete separation of input source (electricity) and output signal (light), thereby significantly reducing background ECL signal. ECL biosensors have attracted considerable attention owing to their high sensitivity and wide dynamic range in food safety detection. In this review, we introduce the principles of ECL biosensors and common ECL luminophores, as well as the latest applications of ECL biosensors in food analysis. Further, novel nanomaterial assembly strategies have been progressively incorporated into the design of ECL biosensors, and by demonstrating some representative works, we summarize the development status of ECL biosensors in detection of mycotoxins, heavy metal ions, antibiotics, pesticide residues, foodborne pathogens, and other illegal additives. Finally, the current challenges faced by ECL biosensors are outlined and the future directions for advancing ECL research are presented.

Recent Advances in CRISPR/Cas-Based Biosensors for Protein Detection

CRISPR is an acquired immune system found in prokaryotes that can accurately recognize and cleave foreign nucleic acids, and has been widely explored for gene editing and biosensing. In the past, CRISPR/Cas-based biosensors were mainly applied to detect nucleic acids in the field of biosensing, and their applications for the detection of other types of analytes were usually overlooked such as small molecules and disease-related proteins. The recent work shows that CRISPR/Cas biosensors not only provide a new tool for protein analysis, but also improve the sensitivity and specificity of protein detections. However, it lacks the latest review to summarize CRISPR/Cas-based biosensors for protein detection and elucidate their mechanisms of action, hindering the development of superior biosensors for proteins. In this review, we summarized CRISPR/Cas-based biosensors for protein detection based on their mechanism of action in three aspects: antibody-assisted CRISPR/Cas-based protein detection, aptamer-assisted CRISPR/Cas-based protein detection, and miscellaneous CRISPR/Cas-based methods for protein detection, respectively. Moreover, the prospects and challenges for CRISPR/Cas-based biosensors for protein detection are also 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.

Enhancing Electrochemiluminescence Efficiency through Introducing Atomically Dispersed Ruthenium in Nickel-Based Metal-Organic Frameworks

The successful application of electrochemiluminescence (ECL) in various fields required continuous exploration of novel ECL signal emitters. In this work, we have proposed a pristine ECL luminophor named NiRu MOFs, which owned extremely high and stable ECL transmission efficiency and was synthesized via a straightforward two-step hydrothermal pathway. The foundation framework of pure Ni-MOFs with the initial structure was layered-pillared constructed by the coordinated octahedrally divalent between nickel and terephthalic acid (BDC). The terephthalates were coordinated and pillared directly to the nickel hydroxide layers and the three-dimensional framework was formed, which had a weak ECL response strength. Then, the ruthenium pyridine complex was recombined with pure Ni-MOFs to produce NiRu MOFs and part of the introduced ruthenium was atomically dispersed in the layered-pillared structure through an ion-exchange method, which led to the ECL luminous efficiency being significantly boosted more than pure Ni-MOFs. In order to verify the superiority of this newly synthesized illuminant, an ECL immunoassay model has been designed, and the results demonstrated that it had extremely strong and steady signal output in practical application. This study realized an efficient platform in ECL immunoassay application with the limit of detection of 0.32 pg mL^-1 for neuron-specific enolase (NSE). Therefore, the approach which combined the pristine pure Ni-MOFs and the star-illuminant ruthenium pyridine complex would provide a convenient and meaningful solution for exploring the next-generation ECL emitters.

Nanomaterials and metal-organic frameworks for biosensing applications of mutations of the emerging viruses

The world today lives in a state of terrible fear due to the mutation of the emerging COVID-19. With the continuation of this pandemic, there is an urgent need for fast, accurate testing devices to detect the emerging SARS-CoV-2 pandemic in terms of biosensors and point-of-care testing. Besides, the urgent development in personal defense tools, anti-viral surfaces and wearables, and smartphones open the door for simplifying the self-diagnosis process everywhere. This review introduces a quick COVID-19 overview: definition, transmission, pathophysiology, the identification and diagnosis, mutation and transformation, and the global situation. It also focuses on an overview of the rapidly advanced technologies based on nanomaterials and MOFs for biosensing, diagnosing, and viral control of the SARS-CoV-2 pandemic. Finally, highlight the latest technologies, applications, existing achievements, and preventive diagnostic strategies to control this epidemic and combat the emerging coronavirus. This humble effort aims to provide a helpful survey that can be used to develop a creative solution and to lay down the future vision of diagnosis against COVID-19.

A double reaction system induced electrochemiluminescence enhancement based on SnS2 QDs@MIL-101 for ultrasensitive detection of CA242

At present, the development of electrochemiluminescence (ECL) immunosensor with excellent performance is still the research focus of immunoassay and detection. Herein, SnS₂ quantum dots (SnS₂ QDs) and metal-organic framework (MIL-101 (Cr)) are effectively combined to achieve synergistic signal amplification based on K₂S₂O₈ co-reactant, thereby constructing SnS₂ QDs/SO₄^•- and SO₄^•-/O₂ ECL double reaction luminous systems. SnS₂ QDs and singlet oxygen (¹(O₂)₂*) produced from the system as light-emitting devices jointly enhance the ECL response and significantly improve the sensitivity of the ECL immunosensor. Dissolved oxygen and SnS₂ QDs respectively generate HOO^• and SnS₂ QDs^•- under negative potential, and react with transient SO₄^•- to emit strong light respectively, so as to jointly enhance the ECL response. MIL-101 catalyzes the oxygen cathode reduction reaction to promote the conversion of dissolved oxygen into HOO^•, which greatly improves the ECL response of ¹(O₂)₂*. CuS with spherical nanoflower-like form as a co-reaction promoter of K₂S₂O₈ generate more SO₄^•- active substances, which further enhance the ECL response of the immunosensor. The constructed ECL immunosensor has the advantages of low detection limit, high sensitivity and better stability. Under the optimal conditions, the detection range is 0.1 mU/mL∼100 U/mL, and the detection limit is 0.015 mU/mL. The results show that the constructed ECL immunosensor can detect human CA242 samples and have a broad application prospect in biological analysis and early diagnosis of diseases.

Disposable biosensor based on novel ternary Ru-PEI@PCN-333(Al) self-enhanced electrochemiluminescence system for on-site determination of caspase-3 activity

The number of death due to cancer-related diseases each year is at the alarming level and is constantly growing. Tools that can effectively and conveniently detect cancer cell apoptosis can play a significant role in cancer research, cancer therapy, and other related industries. Herein, we fabricated, for the first time, an ultrasensitive, disposable, self-enhanced off-on electrochemiluminescence (ECL) biosensor based on ternary Ru-PEI@PCN-333(Al) system to determine caspase-3 activity, the biomarker of apoptosis. The biosensor had a low detection limit of 0.017 pg/mL and was able to enhance the ECL emission and stability. A solid-state (SS) ECL strategy was adopted to overcome the relatively weak ECL emission due to the long distance between electrochemiluminophore and electrode surface. The analysis requires only one incubation step, which can significantly reduce the operational complexity and time. The biosensor had higher sensitivity, and the off-on ECL mode was achieved using caspase-3 as a switch. The on-site and rapid detection capability of the biosensor was achieved by the introduction of disposable screen-printed electrodes (SPEs). This study lays a foundation for the development of more advanced, ingenious, portable and reliable ECL devices for biosensing not only caspase-3, but also other bioanalytes.

Fabricated Metal-Organic Frameworks (MOFs) as luminescent and electrochemical biosensors for cancer biomarkers detection

In the health domain, a major challenge is the detection of diseases using rapid and cost-effective techniques. Most of the existing cancer detection methods show poor sensitivity and selectivity and are time consuming with high cost. To overcome this challenge, we analyzed porous fabricated metal-organic frameworks (MOFs) that have better structures and porosities for enhanced biomarker sensing. Here, we summarize the use of fabricated MOF luminescence and electrochemical sensors in devices for cancer biomarker detection. Various strategies of fabrication and the role of fabricated materials in sensing cancer biomarkers have been studied and described. The structural properties, sensing mechanisms, roles of noncovalent interactions, limits of detection, modeling, advantages, and limitations of MOF sensors have been well-discussed. The study presents an innovative technique to detect the cancer biomarkers by the use of luminescence and electrochemical MOF sensors. In addition, the potential association studies have been opening the way for personalized patient treatments and the development of new cancer-detecting devices.

Preparation of a disposable electrochemiluminescence sensor chip based on an MXene-loaded ruthenium luminescent agent and its application in the detection of carcinoembryonic antigens

We developed a novel type of disposable ECL sensor chip for CEA detection in serum samples of healthy humans and cancer patients. The disposable ECL sensor chip has many advantages including convenience, rapid detection, low cost, and easy mass production.

Enhancing K2S2O8 electrochemiluminescence based on silver nanoparticles and zinc metal–organic framework composite (AgNPs@ZnMOF) for the determination of l-cysteine

A silver nanoparticle-doped Zn(ii) metal–organic framework composite (AgNPs@ZnMOF) was investigated as an electrochemiluminescence (ECL) signal enhancer for potassium persulfate. First, ZnMOF was prepared by a one-step hydrothermal method, and then AgNPs@ZnMOF composite was obtained by depositing AgNPs on the surface and interior of ZnMOF. After the AgNPs@ZnMOF composite was modified on the glass carbon electrode (GCE), the cathode luminescence of potassium persulfate on bare GCE was enhanced by 8 times. A dual amplification mechanism provided by Zn(ii) and Ag nanoparticles in the AgNPs@ZnMOF composite has been validated by ECL spectra, fluorescence spectra, and electrochemical methods. The interaction between the sulfhydryl groups in l-cysteine (l-Cys) and AgNPs significantly affects the catalytic luminescence of the AgNPs@ZnMOF composite. Thus, a sensitive ECL method for the determination of l-Cys was developed based on the inhibition effect of l-Cys on the ECL signal within the linear range from 5.0 nM to 1.0 μM and the limit of detection was found to be 2 nM (S/N = 3). The established method has been successfully applied to the determination of l-Cys in human urine.

A silver nanoparticle-doped Zn(ii) metal–organic framework composite (AgNPs@ZnMOF) was investigated as an electrochemiluminescence (ECL) signal enhancer for potassium persulfate.