Recent advances in electrochemiluminescence-based simultaneous detection of multiple targets

Application of Nanozymes and its Progress in the Treatment of Ischemic Stroke

Nanozymes are a new kind of material which has been applied since the beginning of this century, and its birth has promoted the development of chemistry, materials science, and biology. Nanozymes can be used as a substitute for natural enzyme and has a wide range of applications; therefore, it has attracted extensive attention from all sectors of the community, and the number of studies has constantly increasing. In this paper, we introduced the outstanding achievements in the field of nanozymes in recent years from the main function, the construction of nanozyme-based biosensors, and the treatment of ischemic stroke, and we also illustrated the internal mechanism and the catalytic principle. In the end, the obstacles and challenges in the future development of nanozymes were proposed.

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.

Chiral electrochemiluminescence for simultaneous enantiomeric detection of aspartic acid and phenylalanine

The burgeoning interest in rapid, simultaneous multi-target detection has propelled advancements in chiral electrochemiluminescence (ECL) assays. This study presents the design and implementation of a potential-resolved dual-color ECL sensor, engineered for the concurrent detection of aspartic acid (Asp) and phenylalanine (Phe) enantiomers. The sensor array was meticulously constructed by amalgamating anodic chiral ECL probe Ru(phen)2(L-Cys) nanocrystals with cathodic ECL probe ZnO nanoflowers (ZnO NFs). This research explored the potential of executing multianalyte assays via a potential-resolved ECL strategy, contributing to the advancements in the field of chiral ECL assays.

Binary-amplifying electrochemiluminescence sensor for sensitive assay of catechol and luteolin based on HKUST-1 derived CuO nanoneedles as a novel luminophore

Herein, a highly novel and effective electrochemiluminescence (ECL) sensor based on metal-organic framework (MOF, HKUST-1) derived CuO nanoneedles (HKUST-1 derived CuO NNs), gold nanoparticles (AuNPs) and TiO2 was developed for ultrasensitive detection of catechol and luteolin. The HKUST-1 derived CuO NNs were employed as luminophore for the first time, which were successfully fabricated by using HKUST-1 as precursor. The results revealed that the HKUST-1 derived CuO NNs exhibit excellent ECL activity ascribed to its abundant active site and the high specific surface area, thus obviously promoting the separation and transfer of charge and further improving the current density of ECL sensor. To binary-amplify the signal of the ECL sensor, the AuNPs and TiO2 nano-materials with good biocompatibility, great electron transport efficiency and high catalytic activity were used as co-reaction accelerators in the ECL process. Dependent on the above brilliant strategy, the proposed ECL sensor achieved wide linear ranges from 3 × 10-9 - 1 × 10-4 M for catechol and 1 × 10-8 - 2 × 10-4 M for luteolin, with the detection limits of 1.5 × 10-9 M for catechol and 5.3 × 10-9 M for luteolin, respectively. Furthermore, the ECL sensor exhibited outstanding selectivity, repeatability, stability and obtained great feedback on determination of catechol and luteolin in actual samples. The method not only filled a gap in the ECL application of MOF-derived materials but also provided a novel sight for design other highly efficient luminescent materials.

Advancements in Chemical and Biosensors for Point-of-Care Detection of Acrylamide

Acrylamide (AA), an odorless and colorless organic small-molecule compound found generally in thermally processed foods, possesses potential carcinogenic, neurotoxic, reproductive, and developmental toxicity. Compared with conventional methods for AA detection, bio/chemical sensors have attracted much interest in recent years owing to their reliability, sensitivity, selectivity, convenience, and low cost. This paper provides a comprehensive review of bio/chemical sensors utilized for the detection of AA over the past decade. Specifically, the content is concluded and systematically organized from the perspective of the sensing mechanism, state of selectivity, linear range, detection limits, and robustness. Subsequently, an analysis of the strengths and limitations of diverse analytical technologies ensues, contributing to a thorough discussion about the potential developments in point-of-care (POC) for AA detection in thermally processed foods at the conclusion of this review.

Distinguishable Magnetic Reporter Coordination with Buoyancy-Magnetism Separation for Immobilization-Free Dual-Target Electrochemical Immunosensing

Simultaneous sensitive and precise determination of multibiomarkers is of great significance for improving detection efficiency, reducing diagnosis and treatment expenses, and elevating survival rates. However, the development of simple and portable biosensors for simultaneous determination of multiplexed targets in biological fluids still faces challenges. Herein, a unique and versatile immobilization-free dual-target electrochemical biosensing platform, which combines distinguishable magnetic signal reporters with buoyancy-magnetism separation, was designed and constructed for simultaneous detection of carcinoembryonic (CEA) and α-fetoprotein (AFP) in intricate biological fluids. To construct such distinguishable magnetic signal reporters with signal transduction, amplification, and output, secondary antibodies of CEA and AFP were respectively functionalized on methylene blue (MB) and 6-(ferrocenyl)hexanethiol (FeC) modified Fe3O4@Au magnetic nanocomposites. Meanwhile, a multifunctional flotation probe with dual target recognition, capture, and isolation capability was prepared by conjugating primary antibodies (Ab1-CEA, Ab1-AFP) to hollow buoyant microspheres. The target antigens of CEA and AFP can trigger a flotation-mediated sandwich-type immunoreaction and capture a certain amount of the distinguishable magnetic signal reporter, which enables the conversion of the target CEA and AFP quantities to the signal of the potential-resolved MB and FeC. Thus, the MB and FeC currents of magnetically adsorbed distinguishable magnetic reporters can be used to determine the CEA and AFP targets simultaneously and precisely. Accordingly, the proposed strategy exhibited a delightful linear response for CEA and AFP in the range of 100 fg·mL-1-100 ng·mL-1 with detection limits of 33.34 and 17.02 fg·mL-1 (S/N = 3), respectively. Meanwhile, no significant nonspecific adsorption and cross-talk were observed. The biosensing platform has shown satisfactory performance in the determination of real clinical samples. More importantly, the proposed approach can be conveniently extended to universal detection just by simply substituting biorecognition events. Thus, this work opens up a new promising perspective for dual and even multiple targets and offers promising potential applications in clinical diagnosis.

Electron Transfer Efficiency-Regulated Electrochemiluminescence for Rapid Crystallinity Analysis in Layered Materials

The electrochemiluminescence (ECL) signal is largely determined by the electron transfer efficiency. Therefore, in the nanomaterial-involved ECL system, the structure-related electron distribution could affect the electron transfer efficiency and further alter the ECL intensity. These features make the design of versatile ECL-based analytical techniques for probing the correlated structure possible. And it is generally accepted that the increased crystallinity of nanomaterials usually leads to a uniform electron distribution, which provides higher conductivity. Therefore, the crystallinity-improved conductivity could facilitate electron transfer, promote the electrochemical activity of support materials, and boost the efficiency of the ECL reaction. In this study, we have demonstrated that the ECL signal of the graphitic carbon nitride reporter was proportional to the crystallinity of layered double hydroxides (LDHs), which meets the supposition well. On the basis of this phenomenon, an ECL-based crystallinity analysis approach has been established using CdAl-LDHs as the model materials. The universality of this proposed technique was further validated by the rapid and accurate crystallinity determination of ZnAl-LDH samples with diverse crystallinities. This work not only contributes an alternative to the X-ray diffraction technique for the rapid screening of crystallinity in layered materials but also opens a new avenue for the design of ECL-based structure analysis techniques toward nanomaterials and even organic materials by involving electron transfer regulation correlation.

Multiplex Aptamer-Based Fluorescence Assay Using Magnetism-Encoded Nanoparticles for Simultaneous Detection of Multiple Pathogenic Bacteria

Multiplex assay has emerged as a robust and versatile method for the simultaneous detection of multiple analytes in a single test. However, challenges in terms of poor accuracy and complexity remained. In this work, we developed a multiplex aptamer-based fluorescence assay using magnetism-encoded nanoparticles for the simultaneous detection of multiple pathogenic bacteria. The encapsulation of different amounts of Fe3O4 nanoparticles in zeolitic imidazolate framework-90 (ZIF-90) leads to the formation of Fe3O4@ZIF-90 (FZ) composites with distinct magnetism strengths. By functionalizing a specific aptamer on the surface of the FZ composites, target bacteria can be specifically and precisely separated from a mixed sample in a sequential manner. This property allows for the simultaneous quantitative analysis of multiple target bacteria by using a single-color fluorescence label, thereby resulting in minimal spectral crosstalk interference and improved accuracy. The successful determination of multiple bacteria in contaminated milk samples demonstrates the applicability of this multiplex assay in complex biological matrices. Compared to conventional multiplex fluorescence assays, this approach offers distinct advantages of simplicity, efficiency, and implementation. We believe that this study can provide valuable insights into the development of the multiplex assay while introducing a new method for the simultaneous detection of multiple bacteria.

Droplet-Based Preparation of ZnO-nanostructure Array for Microfluidic Fluorescence Biodetection

Nanostructure-enhanced biodetection is widely used for early diagnosis and treatment, which plays an essential role in improving the cure rates of cancer patients. ZnO nanostructure-based fluorescence immunoassay has been demonstrated to enable effective and sensitive detection of cancer biomarkers for their excellent biocompatibility, high electrical point, and unique fluorescence enhancement properties. Further optimization of such fluorescence detection technology is still in demand to meet the requirements of highly sensitive, multiplex detection, and user-friendly devices. Droplet microfluidics is a promising platform for high-throughput analysis of biological assays, and they have been intensively used in analytical chemistry and synthesis of nanoparticles. Here, we propose a simple droplet chip, where a static droplet array was successfully obtained for in situ growth of ZnO nanostructures with varied diameters by changing the entire growth time and replenishment interval. This device provides a novel and alternative approach for patterned growth of ZnO nanostructures and understanding the growth condition of ZnO nanostructures in static droplet, which offers some guidance toward the design of multiple fluorescence amplification platforms potentially for biosensing. As a demonstration, we used the patterned grown ZnO nanostructures for multiple detection of cancer biomarkers, achieving a low limit of detection as low as 138 fg/mL in the human α-fetoprotein assay and 218 fg/mL in the carcinoembryonic antigen assay with a large dynamic range of 8 orders. These results suggest that such multifunctional microfluidic devices may be useful tools for efficient fluorescence diagnostic assays.

Ratiometric electrochemical immunosensor for simultaneous detection of C-myc and Bcl-2 based on multi-role alloy composites

A ratiometric electrochemical immunosensor is proposed for simultaneous detection of cellular-myelocytomatosis oncoprotein (C-myc) and B-cell lymphoma 2 (Bcl-2) via the potential-resolved strategy. It relied on multi-role co-loaded alloy composites (CLACs) and poly(3,4-ethylenedioxythiophene) (PEDOT)-graphene oxide (GO)-multiwalled carbon nanotubes (MWCNTs) (PGM) modified electrodes. CLACs with good catalytic and enzyme-like properties were synthesized in one step by loading tetramethylbenzidine (TMB) or methylene blue (MB) into Pt-Pd alloy and used as label materials. After immunological reactions, CLACs showed distinguishable dual differential pulse voltammetry signals at  - 0.26 V and 0.38 V, corresponding to C-myc and Bcl-2, and the PGM had an electrochemical signal at 1.2 V, which could be used as a reference signal to construct a ratiometric sensor. CLACs had a satisfactory synergistic effect with the PGM, and eventually achieved quadruple signal amplification. Thus, benefiting from multiple magnification and ratiometric self-calibration functions, sensitive detections of C-myc and Bcl-2 were achieved, with detection limits as low as 0.5 and 2.5 pg mL-1, respectively. Additionally, when the designed method was applied to blood samples from lymphoma patients, results consistent with the ELISA kit were obtained. This will open avenues for constructing multiple protein detection sensors.

Nanobiosensing Based on Electro-Optically Modulated Technology

At the nanoscale, metals exhibit special electrochemical and optical properties, which play an important role in nanobiosensing. In particular, surface plasmon resonance (SPR) based on precious metal nanoparticles, as a kind of tag-free biosensor technology, has brought high sensitivity, high reliability, and convenient operation to sensor detection. By applying an electrochemical excitation signal to the nanoplasma device, modulating its surface electron density, and realizing electrochemical coupling SPR, it can effectively complete the joint transmission of electrical and optical signals, increase the resonance shift of the spectrum, and further improve the sensitivity of the designed biosensor. In addition, smartphones are playing an increasingly important role in portable mobile sensor detection systems. These systems typically connect sensing devices to smartphones to perceive different types of information, from optical signals to electrochemical signals, providing ideas for the portability and low-cost design of these sensing systems. Among them, electrochemiluminescence (ECL), as a special electrochemically coupled optical technology, has good application prospects in mobile sensing detection due to its strong anti-interference ability, which is not affected by background light. In this review, the SPR is introduced using nanoparticles, and its response process is analyzed theoretically. Then, the mechanism and sensing application of electrochemistry coupled with SPR and ECL are emphatically introduced. Finally, it extends to the relevant research on electrochemically coupled optical sensing on mobile detection platforms.

Dual-potential encoded electrochemiluminescence for multiplexed gene assay with one luminophore as tag

Multiplexed gene assay for simultaneously detecting the multi-targets of nucleic acids is strongly anticipated for the accurate diseases diagnosis and prediction, and all commercial available gene assays for IVD are a kind of single-target assay. Herein, a dual-potential encoded and coreactant-free electrochemiluminescence (ECL) strategy is proposed for the multiplexed gene assay, which can be conveniently carried out by directly oxidizing the same luminescent tag of dual-stabilizers-capped CdTe nanocrystals (NCs). The CdTe NCs linked with sulfhydryl-RNA via Cd-S bond merely exhibits one ECL process around 0.32 V with a narrow triggering-potential-window of 0.35 V, while CdTe NCs linked with amino-RNA via amide linkage solely gives off one ECL process around 0.82 V with a narrow triggering-potential-window of 0.30 V. Multiplexing ECL of both sulfhydryl-RNA-functionalized CdTe NCs and amino-RNA-functionalized CdTe NCs can be utilized to simultaneously detect the open reading frame 1ab (ORF1ab) and the nucleoprotein (N) genes without crosstalk, in which ECL of sulfhydryl-RNA-functionalized CdTe NCs can dynamically determine ORF1ab from 200 aM to 10 fM with a limit of detection (LOD) of 100 aM, while ECL of amino-RNA-functionalized CdTe NCs can linearly detect N gene from 5 fM to 1 pM with a LOD of 2 fM. Post-engineering CdTe NCs with RNA in a labeling-bond engineering way would provide a potential-selective and encoded ECL strategy for multiplexed gene assay with one luminophore.

An electrochemiluminescence immunosensor with double co-reaction accelerators based on Ag3PO4@EuPO4-AgNP for detecting squamous cell carcinoma antigen

This study aimed to design a sandwich electrochemiluminescence (ECL) immunosensor with double co-reaction accelerators for sensitively detecting squamous cell carcinoma antigen (SCCA). First, silver orthophosphate (Ag3PO4) nanoparticles were modified on the surface of EuPO4 nanowires to improve their poor dispersibility/solubility. At the same time, EuPO4 was used as a co-reaction accelerator to catalyze S2O82- to produce more intermediates (SO4•-), significantly enhancing the ECL signal of Ag3PO4. Ag nanoparticles (AgNP) modified on Ag3PO4@EuPO4 composite nanomaterials were used not only as linkers of luminescence groups and biomarkers but also as a co-reaction accelerator to effectively enhance ECL signal. The designed ECL immunosensor displayed several advantages, including good stability and reproducibility. Under the optimal conditions, its linear range in detecting SCCA was 0.0001-50 ng·mL-1, the detection limit was 25 fg·mL-1 (S/N = 3), the recovery was 96.6-100.4%, and the relative standard deviation was less than 4.8%. It was successfully applied to detect SCCA in human serum.

Smartphone-based 3D-printed electrochemiluminescence enzyme biosensor for reagentless glucose quantification in real matrices

Three-dimensional (3D) printed electrochemical devices are increasingly used in point-of-need and point-of-care testing. They show several advantages such as simple fabrication, low cost, fast response, and excellent selectivity and sensitivity in small sample volumes. However, there are only a few examples of analytical devices combining 3D-printed electrodes with electrochemiluminescence (ECL) detection, an electrochemical detection principle widely employed in clinical chemistry analysis. Herein, a portable, 3D-printed miniaturized ECL biosensor for glucose detection has been developed, based on the luminol/H₂O₂ ECL system and employing a two-electrode configuration with carbon black-doped polylactic acid (PLA) electrodes. The ECL emission is obtained by means of a 1.5V AA alkaline battery and detected using a smartphone camera, thus providing easy portability of the analytical platform. The ECL system was successfully applied for sensing H₂O₂ and, upon coupling the luminol/H₂O₂ system with the enzyme glucose oxidase, for glucose detection. The incorporation of luminol and glucose oxidase in an agarose hydrogel matrix allowed to produce ECL devices preloaded with the reagents required for the assay, so that the analysis only required sample addition. The ECL biosensor showed an excellent ability to detect glucose up to 5 mmol L^-1, with a limit of detection of 60 μmol L^-1. The biosensor was also used to analyse real samples (i.e., glucose saline solutions and artificial serum samples) with satisfactory results, thus suggesting its suitability for point-of-care analysis. Coupling with other oxidases could further extend the applicability of this analytical platform.

Particle Size-Controlled Oxygen Reduction and Evolution Reaction Nanocatalysts Regulate Ru(bpy)32+'s Dual-potential Electrochemiluminescence for Sandwich Immunoassay

Multiple signal strategies remarkably improve the accuracy and efficiency of electrochemiluminescence (ECL) immunoassays, but the lack of potential-resolved luminophore pairs and chemical cross talk hinders their development. In this study, we synthesized a series of gold nanoparticles (AuNPs)/reduced graphene oxide (Au/rGO) composites as adjustable oxygen reduction reaction and oxygen evolution reaction catalysts to promote and modulate tris(2,2'-bipyridine) ruthenium(II) (Ru(bpy)₃²⁺)'s multisignal luminescence. With the increase in the diameter of AuNPs (3 to 30 nm), their ability to promote Ru(bpy)₃²⁺'s anodic ECL was first impaired and then strengthened, and cathodic ECL was first enhanced and then weakened. Au/rGOs with medium-small and medium-large AuNP diameters remarkably increased Ru(bpy)₃²⁺'s cathodic and anodic luminescence, respectively. Notably, the stimulation effects of Au/rGOs were superior to those of most existing Ru(bpy)₃²⁺ co-reactants. Moreover, we proposed a novel ratiometric immunosensor construction strategy using Ru(bpy)₃²⁺'s luminescence promoter rather than luminophores as tags of antibodies to achieve signal resolution. This method avoids signal cross talk between luminophores and their respective co-reactants, which achieved a good linear range of 10^-7 to 10^-1 ng/ml and a limit of detection of 0.33 fg/ml for detecting carcinoembryonic antigen. This study addresses the previous scarcity of the macromolecular co-reactants of Ru(bpy)₃²⁺, broadening its application in biomaterial detection. Furthermore, the systematic clarification of the detailed mechanisms for converting the potential-resolved luminescence of Ru(bpy)₃²⁺ could facilitate an in-depth understanding of the ECL process and should inspire new designs of Ru(bpy)₃²⁺ luminescence enhancers or applications of Au/rGOs to other luminophores. This work removes some impediments to the development of multisignal ECL biodetection systems and provides vitality into their widespread applications.

Facial Preparation of Cyclometalated Iridium (III) Nanowires as Highly Efficient Electrochemiluminescence Luminophores for Biosensing

In this study, highly efficient ECL luminophores composed of iridium complex-based nanowires (Ir-NCDs) were synthesized via covalently linking bis(2-phenylpyridine)-(4-carboxypropyl-2,2'-bipyridyl) iridium(III) hexafluorophosphate with nitrogen-doped carbon quantum dots (NCDs). The ECL intensity of the nanowires showed a five-fold increase in ECL intensity compared with the iridium complex monomer under the same experimental conditions. A label-free ECL biosensing platform based on Ir-NCDs was established for Salmonella enteritidis (SE) detection. The ECL signal was quenched linearly in the range of 10²-10⁸ CFU/mL for SE with a detection limit of 10² CFU/mL. Moreover, the relative standard deviations (RSD) of the stability within and between batches were 0.98% and 3.9%, respectively. In addition, the proposed sensor showed high sensitivity, selectivity and stability towards SE in sheep feces samples with satisfactory results. In summary, the excellent ECL efficiency of Ir-NCDs demonstrates the prospects for Ir(III) complexes in bioanalytical applications.

Signal differentiation models for multiple microRNA detection: a critical review

MicroRNAs (miRNAs) are a class of small, single-stranded non-coding RNAs which have critical functions in various biological processes. Increasing evidence suggested that abnormal miRNA expression was closely related to many human diseases, and they are projected to be very promising biomarkers for non-invasive diagnosis. Multiplex detection of aberrant miRNAs has great advantages including improved detection efficiency and enhanced diagnostic precision. Traditional miRNA detection methods do not meet the requirements of high sensitivity or multiplexing. Some new techniques have opened novel paths to solve analytical challenges of multiple miRNA detection. Herein, we give a critical overview of the current multiplex strategies for the simultaneous detection of miRNAs from the perspective of two different signal differentiation models, including label differentiation and space differentiation. Meanwhile, recent advances of signal amplification strategies integrated into multiplex miRNA methods are also discussed. We hope this review provides the reader with future perspectives on multiplex miRNA strategies in biochemical research and clinical diagnostics.

A cloth-based single-working-electrode electrochemiluminescence sensor for simultaneous detection of diabetes complication markers

As one of the most common noninfectious diseases, diabetes and diabetic complications (DDC) have attracted great attention in the field of life and health. However, simultaneous detection of DDC markers usually requires labor- and time-consuming steps. Here, a novel cloth-based single-working-electrode electrochemiluminescence (SWE-ECL) sensor was designed for the simultaneous detection of multiple DDC markers. For this sensor, three independent ECL cells are distributed on the SWE, which is a simplification of the configuration of traditional sensors for simultaneous detection. In this way, the modification processes and ECL reactions occur at the back of the SWE, eliminating the adverse effects caused by human intervention on the electrode. Under optimized conditions, glucose, uric acid and lactate were determined, with corresponding linear dynamic ranges of 80-4000 μM, 45-1200 μM and 60-2000 μM, and detection limits of 54.79 μM, 23.95 μM and 25.82 μM, respectively. In addition, the cloth-based SWE-ECL sensor exhibited good specificity and satisfactory reproducibility, and its actual application potential was verified by measuring complex human serum samples. Overall, this work developed a simple, sensitive, low-cost and rapid method for the simultaneous quantitative determination of multiple markers related to DDC and demonstrated a new route for multiple-marker detection.

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.

Fluorescence immunosensor based on functional nanomaterials and its application in tumor biomarker detection

An immunosensor is defined as an analytical device that detects the binding of an antigen to its specific antibody by coupling an immunochemical reaction to the surface of a device called a transducer. Fluorescence immunosensing is one of the most promising immunoassays at present, and has the advantages of simple operation, fast response and high stability. A traditional fluorescence immunosensor often uses an enzyme-labelled antibody as a recognition unit and an organic dye as a fluorescence probe, so it is easily affected by environmental factors with low sensitivity. Nanomaterials have unique photostability, catalytic properties and biocompatibility, which open up a new path for the construction of stable and sensitive fluorescence immunosensors. This paper briefly introduces different kinds of immunosensors and the role of nanomaterials in the construction of immunosensors. The significance of fluorescent immunosensors constructed from functional nanomaterials to detect tumor biomarkers was analyzed, and the strategies to further improve the performance of fluorescent immunosensors and their future development trend were summarized.

Electrochemiluminescence in paired signal electrode (ECLipse) enables modular and scalable biosensing

Electrochemiluminescence (ECL) has an inherently low background and enables precise chemical reactions through electrical control. Here, we report an advanced ECL system, termed ECLipse (ECL in paired signal electrode). We physically separated ECL generation from target detection: These two processes were carried out in isolated chambers and coupled through an electrode. The strategy allowed us to minimize cross-chemical reactions, design electrodes for high ECL signals, and integrate multiple sensors in a chip. As a proof of concept, we implemented an eight-plex ECLipse and applied it to detect host factors in human plasma. ECLipse achieved higher signal-to-noise ratio than conventional ECL assays and was >7000-fold more sensitive than enzyme-linked immunosorbent assay. In a pilot clinical study, we could detect septic conditions by measuring host factors [i.e., interleukin-3 (IL-3), IL-6, and procalcitonin (PCT)]. ECLipse assay further revealed distinct IL-3 and IL-6 patterns in patients with severe acute respiratory syndrome coronavirus 2 infection.

Simple, rapid, and visual electrochemiluminescence sensor for on-site catechol analysis

Environmental pollution caused by aromatic compounds such as catechol (Cat) has become a major issue for human health. However, there is no simple, rapid, and low-cost method for on-site monitoring of Cat. Here, based on ECL quenching mechanism, we develop a simple, rapid and visual mesoporous silica (MSNs)-electrochemiluminescence (ECL) sensor for on-site monitoring of Cat. The mechanism of ECL quenching is due to the interaction between Cat and Ru(bpy)₃^2+* and the interactions between the oxidation products of Cat and DBAE. MSNs films with ordered perpendicular mesopore channels exhibit an amplification effect of ECL intensity due to the negatively charged pore channel. There is a good linear relationship between ECL intensity and Cat concentration in the range of 10 ∼ 1000 μM with the limit of detection (LOD) of 9.518 μM (R² = 0.99). The on-site sensor is promising to offer new opportunities for pharmaceuticals analysis, on-site monitoring, and exposure risk assessment.

A simple, rapid and visual mesoporous silica (MSNs)-electrochemiluminescence (ECL) sensor was developed for on-site monitoring of Cat.

Gold nanoparticle-based signal amplified electrochemiluminescence for biosensing applications

Since the content levels of biomarkers at the early stage of many diseases are generally lower than the detection threshold concentration, achieving ultrasensitive and accurate detection of these biomarkers is still one of the major goals in bio-analysis. To achieve ultrasensitive and reliable bioassay, it requires developing highly sensitive biosensors. Among all kinds of biosensors, electrogenerated chemiluminescence (ECL) based biosensors have attracted enormous attention due to their excellent properties. In order to improve the performance of ECL biosensors, gold nanoparticles (Au NPs) have been widely utilized as signal amplification tags. The introduction of Au NPs could dramatically enhance the performance of the constructed ECL biosensors via diverse ways such as electrode modification material, efficient energy acceptor in ECL resonant energy transfer (ECL-RET), reaction catalyst, surface plasmon resonance (SPR) enhancer, and as nanocarrier. Herein, we summarize recent developments and progress of ECL biosensors based on Au NPs signal amplification strategies. We will cover ECL applications of Au NPs as a signal amplification tag in the detection of proteins, metal ions, nucleic acids, small molecules, living cells, exosomes, and cell imaging. Finally, brief summary and future outlooks of this field will be presented.

Quantum dots for electrochemiluminescence bioanalysis - A review

Electrochemiluminescence (ECL) bioanalysis has become increasingly important in various fields from bioanalysis to clinical diagnosis due to its outstanding merits, including low background signal, high sensitivity, and simple instrumentation. Quantum dots (QDs) are a significant theme in ECL bioanalysis since their excellent optical, electrochemical properties, and ease of functionalization endow them with versatile roles and new mechanisms of signal transduction in ECL. Herein, this review details recent advances of QDs-based ECL bioanalysis by using QDs as ECL emitters, coreactants, or ECL resonance energy transfer donors/acceptors, mainly focused on their optical and electrochemical properties and ECL reaction mechanism. In the end, we will discuss the current limitations and future developments in QDs ECL bioanalysis to address the requirement about selectivity, sensitivity, toxicity, and emerging applications.

Electrochemiluminescence sensors and forensic investigations: a viable technique for drug detection?

Novel psychoactive substances (NPS) are today considered one of the major ticking public health time bombs in regard to drug abuse. The inability to identify these substances with current screening methods, sees their distribution remain uninterrupted and contributes to the high death rates amongst users. To tackle this problem, it is vital that new robust screening methods are developed, addressing the limitation of those currently in place, namely colour subjectivity and lack of compatibility with the complex matrices these substances may be found within. To this avail, electrochemical methods have been assessed. These low cost and extremely portable sensors have been successfully applied for the direct detection of a broad range of compounds of interest in a range of matrices including, herbal material, commercial drinks and biological fluids (serum, saliva, sweat and urine). With their high versatility, gifted through a significant degree of flexibility in regard to electrode material a range of sensors have to date been reported. In this review the various electrochemical sensors developed to date for NPS detection will be compared and contrasted, with a special focus upon those utilising electrochemiluminescence (ECL) technology.

Towards a Point-of-Care (POC) Diagnostic Platform for the Multiplex Electrochemiluminescent (ECL) Sensing of Mild Traumatic Brain Injury (mTBI) Biomarkers

Globally, 70 million people are annually affected by TBI. A significant proportion of all TBI cases are actually mild TBI (concussion, 70-85%), which is considerably more difficult to diagnose due to the absence of apparent symptoms. Current clinical practice of diagnosing mTBI largely resides on the patients' history, clinical aspects, and CT and MRI neuroimaging observations. The latter methods are costly, time-consuming, and not amenable for decentralized or accident site measurements. As an alternative (and/or complementary), mTBI diagnostics can be performed by detection of mTBI biomarkers from patients' blood. Herein, we proposed two strategies for the detection of three mTBI-relevant biomarkers (GFAP, h-FABP, and S100β), in standard solutions and in human serum samples by using an electrochemiluminescence (ECL) immunoassay on (i) a commercial ECL platform in 96-well plate format, and (ii) a "POC-friendly" platform with disposable screen-printed carbon electrodes (SPCE) and a portable ECL reader. We further demonstrated a proof-of-concept for integrating three individually developed mTBI assays ("singleplex") into a three-plex ("multiplex") assay on a single SPCE using a spatially resolved ECL approach. The presented methodology demonstrates feasibility and a first step towards the development of a rapid POC multiplex diagnostic system for the detection of a mTBI biomarker panel on a single SPCE.

Emerging biosensing and transducing techniques for potential applications in point-of-care diagnostics

With the deepening of our understanding in life science, molecular biology, nanotechnology, optics, electrochemistry and other areas, an increasing number of biosensor design strategies have emerged in recent years, capable of providing potential practical applications for point-of-care (POC) diagnosis in various human diseases. Compared to conventional biosensors, the latest POC biosensor research aims at improving sensor precision, cost-effectiveness and time-consumption, as well as the development of versatile detection strategies to achieve multiplexed analyte detection in a single device and enable rapid diagnosis and high-throughput screening. In this review, various intriguing strategies in the recognition and transduction of POC (from 2018 to 2021) are described in light of recent advances in CRISPR technology, electrochemical biosensing, and optical- or spectra-based biosensing. From the perspective of promoting emerging bioanalytical tools into practical POC detecting and diagnostic applications, we have summarized key advances made in this field in recent years and presented our own perspectives on future POC development and challenges.

Electrochemiluminescent emission potential tunable Cu-Zn-In-S/ZnS nanocrystals for multiplex microRNAs potential-resolved detection

The development of a multi-target simultaneous detection electrochemiluminescence (ECL) strategy remains a great research interest, however, the limited choice of ECL luminophores is the main limitation holding the field back. In this study, a band gap tunable Cu-Zn-In-S/ZnS nanocrystals (CZIS/ZnS NCs) was synthesized and applied to a potential-resolved ECL detection strategy. By changing the Cu ratio in the precursor, the CZIS/ZnS NCs ECL emission spectrum and emission potential were tuned from 480 to 750 nm and -2.10 to -1.11 V, respectively. In addition, an ECL biosensor was fabricated with CZIS/ZnS NCs as signal reporters to detect three types of microRNAs, which could sensitively and selectively determine microRNA-21, microRNA-141, and microRNA-155 in a single cathodic ECL process. The results showed that the ECL intensity was directly linear to the logarithm of the concentration of microRNA-21, microRNA-141, and microRNA-155 from 0.00001 to 10 nM with detection limits of 2.2, 2.6, and 2.7 fM, respectively. This study demonstrates that the emission potential tunable CZIS/ZnS NCs can be employed as a promising alternative to the toxic II-V and II-V NCs to simultaneously detect multiple disease markers, and can guide the further rational design of both ECL luminophores and multi-analyte ECL sensors.

Electrochemical Signal Substance for Multiplexed Immunosensing Interface Construction: A Mini Review

Appropriate labeling method of signal substance is necessary for the construction of multiplexed electrochemical immunosensing interface to enhance the specificity for the diagnosis of cancer. So far, various electrochemical substances, including organic molecules, metal ions, metal nanoparticles, Prussian blue, and other methods for an electrochemical signal generation have been successfully applied in multiplexed biosensor designing. However, few works have been reported on the summary of electrochemical signal substance applied in constructing multiplexed immunosensing interface. Herein, according to the classification of labeled electrochemical signal substance, this review has summarized the recent state-of-art development for the designing of electrochemical immunosensing interface for simultaneous detection of multiple tumor markers. After that, the conclusion and prospects for future applications of electrochemical signal substances in multiplexed immunosensors are also discussed. The current review can provide a comprehensive summary of signal substance selection for workers researched in electrochemical sensors, and further, make contributions for the designing of multiplexed electrochemical immunosensing interface with well signal.

Electrogenerated chemiluminescence of a Ru(bpy)32+/arginine system: a specific and sensitive detection of acetaminophen

Ru(bpy)₃Cl₂/TPrA is a prominent and widely used ECL system in analytical science. However, the co-reactant TPrA restricts the variety of applications because of its toxicity, volatility, and high cost. Here, we use arginine (Arg) as an alternative co-reactant for Ru(bpy)₃²⁺ by taking advantage of its low cost, non-toxicity, and biocompatibility. The mechanism of the Ru(bpy)₃²⁺/Arg system is that the deprotonated Arg can react with Ru(bpy)₃²⁺ to release emission. The similarity between the Ru(bpy)₃²⁺/Arg, Ru(bpy)₃²⁺/TPrA, and Ru(bpy)₃²⁺/DBAE systems demonstrates that Arg can be used as an alternative co-reactant for Ru(bpy)₃²⁺ ECL. As a proof of concept, we achieve an excellent performance for acetaminophen (Ace) detection based on the specificity of Arg and Ace, with excellent linearity, low detection limits, and good recoveries. This work is promising to expand the scope of the Ru(bpy)₃²⁺/Arg system and move forward their applications in bioassays.

We use arginine as an alternative co-reactant for Ru(bpy)₃²⁺ by taking advantage of its low cost, non-toxicity, and biocompatibility. It is promising to expand the scope of the Ru(bpy)₃²⁺/Arg system and move forward their applications in bioassays.

Facile synthesis of nitrogen-doped graphene quantum dots as nanocarbon emitters for sensitive detection of catechol

Development of nanomaterial-based electrochemiluminescence (ECL) emitters is highly desirable for the fabrication and wide applications of ECL sensors. Herein, nitrogen-doped graphene quantum dots (NGQDs) were easily synthesized as nanocarbon emitters with anodic ECL for sensitive ECL determination of catechol (CC). Facile synthesis of NGQDs was easily achieved using molecular fusion of a carbon precursor in a one-step hydrothermal process. The synthesis has advantages of simple and convenient operation and high yield. The as-prepared NGQDs have uniform size, good crystallinity, single-layered graphene structure, and excitation-independent fluorescence. In the presence of hydrogen peroxide (H₂O₂), NGQDs exhibit high anodic ECL owing to the presence of functional hydrazide groups. As CC could significantly reduce the ECL intensity of NGQDs, sensitive determination of CC was realized with a linear range from 100 nM to 10 μM and 10 μM to 60 μM with a low limit of detection (LOD, 42 nM). The determination of CC in environmental water was also achieved with high reliability.

Nitrogen-doped graphene quantum dots are easily synthesized and can be used as nanocarbon emitters for sensitive electrochemiluminescence detection of catechol.

Multiplexed Profiling of Extracellular Vesicles for Biomarker Development

Extracellular vesicles (EVs) are cell-derived membranous particles that play a crucial role in molecular trafficking, intercellular transport and the egress of unwanted proteins. They have been implicated in many diseases including cancer and neurodegeneration. EVs are detected in all bodily fluids, and their protein and nucleic acid content offers a means of assessing the status of the cells from which they originated. As such, they provide opportunities in biomarker discovery for diagnosis, prognosis or the stratification of diseases as well as an objective monitoring of therapies. The simultaneous assaying of multiple EV-derived markers will be required for an impactful practical application, and multiplexing platforms have evolved with the potential to achieve this. Herein, we provide a comprehensive overview of the currently available multiplexing platforms for EV analysis, with a primary focus on miniaturized and integrated devices that offer potential step changes in analytical power, throughput and consistency.

A High-Throughput Platform for the Rapid Quantification of Phosphorylated Histone H2AX in Cell Lysates Based on Microplate Electrochemiluminescence Immunosensor Array

Sensitive detection of phosphorylated histone H2AX (γH2AX) in cells as a biomarker of DNA double-strand breaks has great significance in the field of molecular toxicology and life science research. However, current γH2AX detection methods require labor- and time-consuming steps. Here, for the first time, we designed a simple electrochemiluminescence (ECL) immunoassay integrated with a microplate-based sensor array to realize sensitive and high-throughput detection of γH2AX in cell lysates. Under the optimized conditions, this ECL immunosensor array could linearly respond to γH2AX concentrations in the range from 2 × 10² to 1 × 10⁵ pg/mL. In addition, our approach possessed excellent specificity and satisfactory reproducibility, and its practicality was verified in real cell lysates. The whole process including instrumental and manual operation was completed in no more than 3 h. This study provides a convenient and rapid alternative method for the sensitive quantification of γH2AX, which shows promising application in high-throughput screening of genotoxic chemicals and drug candidates.

Aggregation-induced delayed fluorescence luminogens: the innovation of purely organic emitters for aqueous electrochemiluminescence

Due to overcoming the limitation of aggregation caused quenching (ACQ) of solid-state emitters, aggregation-induced emission (AIE) organic luminogens have become a promising candidate in aqueous electrochemiluminescence (ECL). However, restricted by the physical nature of fluorescence, current organic AIE luminogen-based ECL (AIECL) faces the bottleneck of low ECL efficiency. Here, we propose to construct de novo aqueous ECL based on aggregation-induced delayed fluorescence (AIDF) luminogens, called AIDF-ECL. Compared with the previous organic AIE luminogens, purely organic AIDF luminogens integrate the superiorities of both AIE and the utilization of dark triplets via thermal-activated spin up-conversion properties, thereby possessing the capability of close-to-unity exciton utilization for ECL. The results show that the ECL characteristics using AIDF luminogens are directly related to their AIDF properties. Compared with an AIECL control sample based on a tetraphenylethylene AIE moiety, the ECL efficiency of our AIDF-ECL model system is improved by 5.4 times, confirming the excellent effectiveness of this innovative strategy.

Dual-potential electrochemiluminescence from black phosphorus and graphitic carbon nitrides for label-free enzymatic biosensing

Simultaneous anodic and cathodic electrochemiluminescence (ECL) emissions of black phosphorus nanosheets (BPNSs) and graphitic carbon nitrides (g-C₃N₄) were reported based on the co-existence of different co-reactants. Anodic ECL was obtained at the BPNSs modified electrode with tripropylamine (TPrA) as a co-reactant, while g-C₃N₄ was selected as another emitter to obtain cathodic ECL emission with K₂S₂O₈ as co-reactant. Employing the superiority of two separate ECL systems, a facile ECL method was developed for cholesterol detection based on cholesterol oxidase (ChOx) immobilized g-C₃N_4/BPNSs modified glassy carbon electrode (g-C₃N_4/BPNSs/GCE). False positive signals can be significantly reduced based on the separation of anode and cathode ECL signals from BPNSs and g-C₃N₄, respectively. The proposed biosensor provided a quantitative readout proportional to cholesterol concentrations in the range from 0.5 μM to 0.5 mM with a detection limit of 0.14 μM (cathodic system, 3σ, n = 6) and 0.32 μM (anodic system, 3σ, n = 6). The proposed biosensor demonstrated excellent analytical performance with remarkable sensitivity, manifesting its potential application in enzymatic biosensing field.