Electrogenerated chemiluminescence

In Situ "Confocal" Electrochemiluminescence 3D Imaging: From Cell to Tissue Section

Endowing electrochemiluminescence (ECL) imaging technique with three-dimensional (3D) resolution to investigate specimens at varying axial depths poses a challenging yet significant objective. Herein, a "confocal" 3D ECL imaging method was developed using luminol as ECL probe, in which excited luminophore was formed in the vicinity of electrode surface through homogeneous chemical reactions between oppositely diffusing ECL precursors, luminol diazaquinone intermediate (L), and hydrogen peroxide (H2O2), confining the ECL emission in a thin plane (ECL focal plane) parallel to electrode surface at their intersection. The regulating ability of electrochemical method on the reaction fluxes of L and H2O2 was validated, regulating the axial location of the ECL focal plane from 0 to 63 µm, which can even extend to 400 µm by using the stable coreactant of ClO-. Leveraging the optical sectioning capability of the ECL focal plane, the "confocal" 3D ECL imaging method was applied to bioimaging, from cells to tissue sections. It revealed cellular morphology changes during cell polarity establishment and the heterogeneous distribution of complex tubule structure in kidney tissue sections. The optical sectioning capability of "confocal" 3D ECL imaging makes it a powerful tool for studying complex biological samples.

The electrochemical modulation of single molecule fluorescence

Recently it has been shown that electrochemistry, instead of using high intensity lasers, can be used to modulate the intensity of emission of fluorophores and even switch fluorophores between their ON and OFF states as required for single molecule localisation microscopy. This modulation of fluorescence does not necessarily correlate with direct oxidation and reduction of the dyes. Questions arise from this unexpected observation related to what is the electrochemistry that occurs, what are the important variables in switching fluorophores electrochemically and what range of dyes can be modulated with electrochemistry. Herein we seek to answer some of these questions. We demonstrate how to effectively modulate the fluorescence intensity of organic dye-labelled cell samples on an indium tin oxide surface using electrochemistry with redox-active mediators present in an oxygen scavenger buffer. We showed the electrochemical fluorescence modulation is sensitive to the applied potential and the excitation laser intensity, indicating the possibility of coupled photochemical and electrochemical reactions occurring. We also compared the electrochemical fluorescence modulation of representative oxazine, rhodamine, and cyanine dyes using ATTO 655, Alexa Fluor 488, and Alexa Fluor 647. Different dyes with distinctly different structural cores show fluorescence modulation to different extents. The electrochemical fluorescence modulation will be applicable in fluorescence imaging techniques as well as biosensing.

Unlocking the potential of chitosan in immunoassay sensor

Using new materials to improve detection accuracy and efficiency is important to broaden the application of immunoassay sensors. Among numerous materials for improving sensors, chitosan, as a natural polysaccharide, has excellent biocompatibility, mechanical adjustability, stimulation sensitivity and porous structure, which holds significant potential for enhancing the performance of immunoassay sensors. However, at present, there are few systematic reviews on the application of chitosan in immune sensors. In this paper, the principle of immunoassay is discussed systematically, we reviewed the recent development of chitosan enhancement strategies in various immunoassay sensors, including surface plasmon resonance immunoassay sensors, colorimetric immunoassay sensors, electrochemical immunoassay sensor, electrochemical luminescence immunoassay sensors are reviewed. Focused on the theoretical basis of improving sensor performance in immunoassay by use chitosan, as well as the various functions and applications of chitosan, and discussed how to solve the challenges of immunoassay sensors by using chitosan and the future research trend. By providing a robust foundation for the development of more efficient detection platforms, it provides insights for advancing the use of chitosan in the detection of complex biological samples. This is crucial for promoting the widespread application of immunoassay sensors with high performance in clinical diagnosis, environmental monitoring and food safety.

Dual-Coreactants Enhanced Electrochemiluminescence

The electrochemiluminescence (ECL) of ruthenium(II) tris(2,2'-bipyridyl) (Ru(bpy)3 2+) with tri-n-propylamine (TPrA) as the good coreactant can be unexpectedly enhanced by a weak coreactant, such as triethanolamine (TEOA). First, the intensity of ECL emitted by Ru(bpy)3 2+/TPrA can be remarkably amplified by 10.8-fold after adding some amount of TEOA. Moreover, the ECL layer thickness, measured by self-interference spectroscopy, is also doubled. The enhancement far exceeding the superposition of respective contribution of TPrA and TEOA was elucidated by a "chemical oxidation mechanism", in which TEOA+⋅ acts as a chemical enhancer to oxidize TPrA in solution and to accelerate significantly the ECL reaction kinetics. This mechanism was proved by single-photon counting experiment and finite element simulations. In addition, the dual-coreactants strategy works well not only in solution with freely diffusive Ru(bpy)3 2+, but also on Ru(bpy)3 2+-functionalized microbeads, suggesting that ethanolamines could act as cheap, easily available and low-background enhancers for ECL-based bioanalysis and microscopy.

ECLStat: A robust machine learning based visual imaging tool for electrochemiluminescence biosensing

Visual electrochemiluminescence (ECL) has emerged as a prominent diagnostic method for accurately quantifying various disease markers even at point of care setting with high sensitivity and accuracy. It does not employ complicated instruments such as potentiostat and expensive imaging microscopy for quantifying trace amounts of molecules. The ECL system offers significant advantages over other detection processes, such as high sensitivity, selectivity, rapid response, multiplexing, and miniaturization capabilities, making it well-suited for future commercialization. However, the current ECL system lacks standardization and accuracy in the resulting output data due to the manual measurement of ECL signal response using open-source image processing software, which often limits the efficiency of the ECL process in real-time applications. To address the shortcomings of the existing approach and advance the ECL detection process, a fully automated machine learning-assisted standalone graphical user interface (GUI) application was developed for dedicated measurement and management of ECL-emitted light signals. The working performance of the developed program is evaluated for its real-time utility by detecting hydrogen peroxide, which is an important reactive oxygen species, and glucose, which is a significant biomarker of diabetes. The obtained results show the detection limit of 0.024 mM and 0.035 mM for H2O2 and glucose, with a quantification limit of 0.074 mM and 0.10 mM, respectively. The ultimate objective of the developed application is to improve accuracy by enabling users to apply machine learning algorithms to raw image data seamlessly without deeply comprehending the underlying computational processes and establish a standard protocol for ECL signal measurements. Moreover, the developed application can be used in other optical detection approaches such as chemiluminescence, colorimetric, and fluorescence.

A Novel Molecularly Imprinted Electrochemiluminescence Sensor Based on Mxene Quantum Dots for Selective Detection of Oseltamivir in Biological Samples

Oseltamivir is a drug that has been widely used to prevent and treat influenza A and B. In this work, an ultrasensitive, simple, and novel electrochemiluminescence (ECL) sensor combined with molecularly imprinted polymers (MIP-ECL) based on a graphene-like two-dimensional material, Mxene quantum dots (MQDs) was constructed to selectively detect oseltamivir. A molecularly imprinted polymer membrane containing an oseltamivir template was constructed by electropolymerization and elution of modified MQDs on a glassy carbon electrode. Under optimized experimental conditions, the MIP-ECL sensor could detect oseltamivir in the range of 10-10 to 10-6 M (R2 = 0.9816), with a low limit of detection of 6.5 × 10-11 M (S/N = 3), and the recovery rates of oseltamivir in biological samples were 92.21-104.2%, with relative standard deviations of 3.70%~5.70%. The developed MIP-ECL sensor provides a new idea for detecting oseltamivir, which was successfully applied to the determination of oseltamivir in serum samples, indicating great potential for application in clinical diagnostics.

Cutting-edge 3D printing in immunosensor design for early cancer detection

Cancer is a major cause of death globally, and early detection is a key to improving outcomes. Traditional diagnostic methods have limitations such as being invasive and lacking sensitivity. Immunosensors, which detect cancer biomarkers using antibodies, offer a solution with high sensitivity and selectivity. When combined with 3D printing, these immunosensors can be customized to detect specific cancer markers, creating rapid, cost-effective, and scalable diagnostic tools. The article reviews the principles behind immunosensors, different 3D fabrication methods such as Fused Deposition Modeling (FDM) and Stereolithography (SLA), and discusses how functionalization strategies, such as surface modifications, can enhance the sensitivity of these devices. The integration of 3D printing allows for the creation of complex sensor structures, offering advantages such as customization, rapid prototyping, and multi-material printing. These advancements make immunosensors arrays highly promising for early cancer detection, tumor profiling, and personalized medicine. The article also explores challenges like scalability, material biocompatibility, and the need for clinical validation. Future perspectives suggest the potential of integrating nanomaterials, multiplexed detection, and wearable technology to further improve the performance and accessibility of these diagnostic tools.

Bioinformatics design of peptide binding to the human cardiac troponin I (cTnI) in biosensor development for myocardial infarction diagnosis

Cardiovascular disease has reached a mortality rate of 470,000 patients each year. Myocardial infarction accounts for 49.2% of these deaths, and the cTnI protein is a crucial target in diagnosing myocardial infarction. A peptide-based bioreceptor design using a computational approach is a good candidate to be developed for a rapid, effective, and selective detection method for cTnI although it is still lacking in study. Hence, to address the scientific gap, we develop a new candidate peptide for the cTnI biosensor by bioinformatics method and present new computational approaches. The sequential point mutations were made to the selected peptide to increase its stability and affinity for cTnI. Next, molecular docking was performed to select the mutated peptide, and one of the best results was subjected to the molecular dynamics simulation. Finally, the results showed that the best peptide showed the lowest affinity and good stability among other mutated peptide designs for interacting with the cTnI protein. In addition, the peptide has been tested to have a higher specificity towards cTnI than its major isomer, sTnI, through molecular docking and molecular dynamics simulation. Therefore, the peptide is considered a good potential bioreceptor for diagnosing myocardial infarction diseases.

Model-Based Interspecies Scaling for Predicting Human Pharmacokinetics of CB 4332, a Complement Factor I Protein

Interspecies scaling of the pharmacokinetics (PK) of CB 4332, a 150 kDa recombinant complement factor I protein, was performed using traditional and model-based approaches to inform first-in-human dose selection. Plasma concentration versus time data from four preclinical PK studies of single intravenous and subcutaneous (SC) CB 4332 dosing in mice, rats and nonhuman primates (NHPs) were modeled simultaneously using naive pooling including allometric scaling. The human-equivalent dose was calculated using the preclinical no observed adverse effect level (NOAEL) as part of the dose-by-factor approach. Pharmacokinetic modeling of CB 4332 revealed species-specific differences in the elimination, which was accounted for by including an additional rat-specific clearance. Signs of anti-drug antibodies (ADA) formation in all rats and some NHPs were observed. Consequently, an additional ADA-induced clearance parameter was estimated including the time of onset. The traditional dose-by-factor approach calculated a maximum recommended starting SC dose of 0.9 mg/kg once weekly, which was predicted it to result in a trough steady-state concentration lower than the determined efficacy target range for CB 4332 in humans. Model simulations predicted the efficacy target range to be reached using 5 mg/kg once weekly SC dosing.

From theory to practice: understanding the challenges in the implementation of electrogenerated chemiluminescence for analytical applications

Electrogenerated chemiluminescence (ECL) stands out as a remarkable phenomenon of light emission at electrodes initiated by electrogenerated species in solution. Characterized by its exceptional sensitivity and minimal background optical signals, ECL finds applications across diverse domains, including biosensing, imaging, and various analytical applications. This review aims to serve as a comprehensive guide to the utilization of ECL in analytical applications. Beginning with a brief exposition on the theory at the basis of ECL generation, we elucidate the diverse systems employed to initiate ECL. Furthermore, we delineate the principal systems utilized for ECL generation in analytical contexts, elucidating both advantages and challenges inherent to their use. Additionally, we provide an overview of different electrode materials and novel ECL-based protocols tailored for analytical purposes, with a specific emphasis on biosensing applications.

Using Temporally and Spatially Resolved Measurements to Improve the Sensitivity of Fluorescence-Based Immunoassays

Detecting low concentrations of biomarkers is essential in clinical laboratories. To improve analytical sensitivity, especially in identifying fluorescently labeled molecules, typical optical detection systems, consisting of a photodetector or camera, utilize time-resolved measurements. Taking a different approach, magnetic modulation biosensing (MMB) is a novel technology that combines fluorescently labeled probes and magnetic particles to create a sandwich assay with the target molecules. By concentrating the target molecules and then using time-resolved measurements, MMB provides the rapid and highly sensitive detection of various biomarkers. Here, we propose a novel signal-processing algorithm that enhances the detection and estimation of target molecules at low concentrations. By incorporating both temporally and spatially resolved measurements using human interleukin-8 as a target molecule, we show that the new algorithm provides a 2-4-fold improvement in the limit of detection and an ~25% gain in quantitative resolution.

Timescale correlation of shallow trap states increases electrochemiluminescence efficiency in carbon nitrides

Highly efficient interconversion of different types of energy plays a crucial role in both science and technology. Among them, electrochemiluminescence, an emission of light excited by electrochemical reactions, has drawn attention as a powerful tool for bioassays. Nonetheless, the large differences in timescale among diverse charge-transfer pathways from picoseconds to seconds significantly limit the electrochemiluminescence efficiency and hamper their broad applications. Here, we report a timescale coordination strategy to improve the electrochemiluminescence efficiency of carbon nitrides by engineering shallow electron trap states via Au-N bond functionalization. Quantitative electrochemiluminescence kinetics measurements and theoretic calculations jointly disclose that Au-N bonds endow shallow electron trap states, which coordinate the timescale of the fast electron transfer in the bulk emitter and the slow redox reaction of co-reagent at diffusion layers. The shallow electron trap states ultimately accelerate the rate and kinetics of emissive electron-hole recombination, setting a new cathodic electrochemiluminescence efficiency record of carbon nitrides, and empowering a visual electrochemiluminescence sensor for nitrite ion, a typical environmental contaminant, with superior detection range and limit.

Portable microfluidic plasmonic chip for fast real-time cardiac troponin I biomarker thermoplasmonic detection

Acute myocardial infarction is one of the most serious cardiovascular pathologies, impacting patients' long-term outcomes and health systems worldwide. Significant effort is directed toward the development of biosensing technologies, which are able to efficiently and accurately detect an early rise of cardiac troponin levels, the gold standard in detecting myocardial injury. In this context, this work aims to develop a microfluidic plasmonic chip for the fast and accurate real-time detection of the cardiac troponin I biomarker (cTnI) via three complementary detection techniques using portable equipment. Furthermore, the study focuses on providing a better understanding of the thermoplasmonic biosensing mechanism taking advantage of the intrinsic photothermal properties of gold nanoparticles. Specifically, a plasmonic nanoplatform based on immobilized gold nanobipyramids was fabricated, exhibiting optical and thermoplasmonic properties that promote, based on a sandwich-like immunoassay, the "proof-of-concept" multimodal detection of cTnI via localized surface plasmon resonance, surface enhanced Raman spectroscopy and thermoplasmonic effects under simulated conditions. Furthermore, after the integration of the plasmonic nanoplatform in a microfluidic channel, the determination of cTnI in 16 real plasma samples was successfully realized via thermoplasmonic detection. The results are compared with a conventional high-sensitivity enzyme-linked immunosorbent clinical assay (ELISA), showing high sensitivity (75%) and specificity (100%) as well as fast response features (5 minutes). Thus, the proposed portable and miniaturized microfluidic plasmonic chip is successfully validated for clinical applications and transferred to clinical settings for the early diagnosis of cardiac diseases, leading towards the progress of personalized medicine.

Unraveling Mechanisms of Highly Efficient Yet Stable Electrochemiluminescence from Quantum Dots

With CdSe/CdS/ZnS core/shell/shell quantum dots (QDs) as the model system, time- and potential-resolved spectroelectrochemical measurements are successfully applied for studying the general mechanisms and kinetics of electrochemiluminescence (ECL) generation. The rate constant of electron injection from the cathode into a QD to form a negatively charged QD (QD-) increases monotonically from -0.88 V to -1.2 V (vs Ag/AgCl). Mainly due to the deep LUMO of the QDs, the resulting QD- as the key intermediate for ECL generation is structurally stable and possesses very slow spontaneous deionization channels. The latter (the main non-ECL channels) are usually 3-4 orders of magnitude slower than the rate constant of the successive hole injection from an active co-reactant into a QD-. The kinetic studies quantify the internal ECL quantum yield of ideal QD ECL emitters to be nearly identical to that of photoluminescence, which is near unity for the current system. Identification of the key intermediate, discovery of the related elementary steps, and determination of all rate constants not only establish a general framework for understanding ECL generation but also offer basic design rules for ECL emitters.

Innovative, Flexible, and Miniaturized Microfluidic Paper-Based Plasmonic Chip for Efficient Near-Infrared Metal Enhanced Fluorescence Biosensing and Imaging

The implementation of metal enhanced fluorescence (MEF) as an efficient detection tool, especially in the near-infrared region of the electromagnetic spectrum, is a rather new direction for diagnostic analytical technologies. In this context, we propose a novel microfluidic plasmonic design based on paper for efficient MEF detection of the "proof-of-concept" biotin-streptavidin recognition interaction. Our design made use of the benefits of gold nanobipyramids (AuBPs), considering the strong enhanced electromagnetic field present at their sharp tips, and filter paper to operate as a natural microfluidic channel due to excellent wicking abilities. The calligraphed plasmonic paper, obtained using a commercial pen filled with AuBPs, was integrated in a robust sandwich optically transparent polydimethylsiloxane chip, exhibiting portability and flexibility while preserving the chip's properties. To place the Alexa 680 fluorophore at an optimal distance from the nanobipyramid substrate, the human IgG-anti-IgG-conjugated biotin sandwich reaction was employed. Thus, upon the capture of Alexa 680-conjugated streptavidin by the biotinylated system, a 1.3-fold average enhancement of the fluorophore's emission was determined by bulk fluorescence measurements. However, the local enhancement factor was considerably higher with values spanning from 5 to 6.3, as proven by mapping the fluorescence emission under both re-scan microscopy and fluorescence lifetime imaging, endorsing the proposed chip's feasibility for bulk MEF biosensing as well as high-resolution MEF bioimaging. Finally, the versatility of our chip was demonstrated by adapting the biosensing protocol for cardiac troponin I biomarker detection, validated using 10 plasma samples collected from pediatric patients and corroborated with a conventional ELISA assay.

Electrochemiluminescence sensing of HeLa cells labeled with biotinylated ruthenium complex using bipolar electrode based on microwell modified optical fiber

Biotinylated ruthenium complexes exhibit improved photoluminescent (PL) properties when they bind with streptavidin, making them useful labels or probes in bio-related analysis. However, their ECL properties are still unknown to date. Herein, we reported the use of [Ru(bpy)2(biot-bpy)]2+ complexes as a new ECL luminophore, which was functionalized with biotin moiety and exhibited higher ECL efficiency after binding to streptavidin. Moreover, [Ru(bpy)2(biot-bpy)]2+ complexes could be attached to HeLa cells through the biotin-streptavidin binding. A microwell bipolar electrode (MBE) prepared at one end of an optical fiber bundle was applied to produce ECL of the labeled HeLa cells, which was remotely detected at the other end. The [Ru(bpy)2(biot-bpy)]2+-streptavidin binding effect together with the high surface/volume ratio of MBE promoted the ECL generation on HeLa cells, which was applied to sensitively detect HeLa cells with a linear range from 1.56 × 102 to 6.74 × 106 cells/mL and a detection limit of 83 cells/mL. Moreover, ECL images were successfully acquired to resolve the emission on each HeLa cell. Such cytosensor based on [Ru(bpy)2(biot-bpy)]2+ and MBE may extend the applications of ECL for cell detections.

Tris(2,2'-bipyridyl)ruthenium (II) complex as a universal reagent for the fabrication of heterogeneous electrochemiluminescence platforms and its recent analytical applications

In recent years, electrochemiluminescence (ECL) has received enormous attention and has emerged as one of the most successful tools in the field of analytical science. Compared with homogeneous ECL, the heterogeneous (or solid-state) ECL has enhanced the rate of the electron transfer kinetics and offers rapid response time, which is highly beneficial in point-of-care and clinical applications. In ECL, the luminophore is the key element, which dictates the overall performance of the ECL-based sensors in various analytical applications. Tris(2,2'-bipyridyl)ruthenium (II) complex, Ru(bpy)32+, is a coordination compound, which is the gold-standard luminophore in ECL. It has played a key role in translating ECL from a "laboratory curiosity" to a commercial analytical instrument for diagnosis. The aim of the present review is to provide the principles of ECL and classical reaction mechanisms-particularly involving the heterogeneous Ru(bpy)32+/co-reactant ECL systems, as well as the fabrication methods and its importance over solution-phase Ru(bpy)32+ ECL. Then, we discussed the emerging technology in solid-state Ru(bpy)32+ ECL-sensing platforms and their recent potential analytical applications such as in immunoassay sensors, DNA sensors, aptasensors, bio-imaging, latent fingerprint detection, point-of-care testing, and detection of non-biomolecules. Finally, we also briefly cover the recent advances in solid-state Ru(bpy)32+ ECL coupled with the hyphenated techniques.

Microfluidics on lensless, semiconductor optical image sensors: challenges and opportunities for democratization of biosensing at the micro-and nano-scale

Optical image sensors are 2D arrays of pixels that integrate semiconductor photodiodes and field effect transistors for efficient photon conversion and processing of generated electrons. With technological advancements and subsequent democratization of these sensors, opportunities for integration with microfluidics devices are currently explored. 2D pixel arrays of such optical image sensors can reach dimensions larger than one centimeter with a sub-micrometer pixel size, for high spatial resolution lensless imaging with large field of view, a feat that cannot be achieved with lens-based optical microscopy. Moreover, with advancements in fabrication processes, the field of microfluidics has evolved to develop microfluidic devices with an overall size below one centimeter and individual components of sub-micrometer size, such that they can now be implemented onto optical image sensors. The convergence of these fields is discussed in this article, where we review fundamental principles, opportunities, challenges, and outlook for integration, with focus on contact-mode imaging configuration. Most recent developments and applications of microfluidic lensless contact-based imaging to the field of biosensors, in particular those related to the potential for point of need applications, are also discussed.

Development of an electrochemiluminescent oligonucleotide-based assay for the quantification of prostate cancer associated miR-141-3p in human serum

MicroRNAs (miRNAs) are small oligonucleotides (18-25 bases), biologically relevant for epigenetic regulation of key processes, particularly in association with cancer. Research effort has therefore been directed towards the monitoring and detection of miRNAs to progress (early) cancer diagnoses. Traditional detection strategies for miRNAs are expensive, with a lengthy time-to-result. In this study we develop an oligonucleotide-based assay using electrochemistry for the specific, selective and sensitive detection of a circulating miRNA (miR-141) associated with prostate cancer. In the assay, the excitation and readout of the signal are independent: an electrochemical stimulation followed by an optical readout. A 'sandwich' approach is incorporated, consisting of a biotinylated capture probe immobilised on streptavidin-functionalised surfaces and a detection probe labelled with digoxigenin. We show that the assay allows the detection of miR-141 in human serum, even in the presence of other miRNAs, with a LOD of 0.25 pM. The developed electrochemiluminescent assay has, therefore, the potential for efficient universal oligonucleotide target detection via the redesign of capture and detection probes.

A novel construction strategy of photoelectrochemical immunosensor for detecting neuron-specific enolase: Sensing mode integrating photoanode and photocathode

In the realm of photoelectrochemical (PEC) analysis, it is customary to employ a lone photoanode or photocathode system for analyte detection. Nonetheless, such a single detection scheme inherently carries some deficiencies. While photoanode-based PEC immunoassay methods do exhibit conspicuous photocurrent responses and heightened sensitivity, they do suffer from inadequate resistance to interference when detecting in real sample detection. Photocathode-based analysis methods are capable of effectively surmounting the limitations of photoanode-based analysis methods, but their stability is poor. Based on the above reasons, this paper reports a novel immunosensing system combining ITO/WO₃/Bi₂S₃ photoanode and ITO/CuInS₂ photocathode. The system that incorporates both photoanode and photocathode exhibits a steady and discernible photocurrent, possesses robust resistance to external interference, and has effectively accomplished the quantification of NSE in the linear range from 5 pg/mL to 30 ng/mL. Remarkably, the detection limit has been determined to be 1.59 pg/mL. Besides the notable advantages of satisfactory stability, exceptional specificity, and outstanding reproducibility, the sensing system also introduces an innovative approach to fabricate PEC immunosensors.

Electrochemiluminescence (ECL) biosensor based on tris(2,2'-bipyridyl)ruthenium(II) with glucose and lactate dehydrogenases encapsulated within alginate hydrogels

Two dehydrogenase enzymes (glucose, GDH, and lactate, LDH, dehydrogenases) encapsulated within alginate hydrogels were deposited on glassy carbon electrodes. The as-prepared enzyme modified alginate hydrogels were utilized as electrochemiluminescence (ECL)-based biosensors for the indirect detection of glucose and lactic acid upon reaction between NADH and tris(2,2'-bipyridyl) ruthenium (II) [Ru(bpy)₃]²⁺. The ECL response was obtained from the redox reaction between the substrate, the cofactor NAD⁺ and the encapsulated enzyme. The production of NADH resulting from the enzymatic reaction led to the ECL emission upon reaction with [Ru(bpy)₃]²⁺. The biosensors showed good stability and repeatability, with linear range between 0.56 and 4.2 µM and limit of detection of 0.84 µM for glucose, and linear range between 5 and 30 µM with a limit of detection of 2.52 µM for lactic acid. These ECL-based biosensors showed good sensitivity when tested in the presence of common interfering species. These biosensors were utilized in artificial sweat and were characterized by good reproducibility and repeatability. The results herein presented suggest that the dehydrogenases encapsulated within alginate hydrogels have potential for the development of biocompatible sensors for detection of glucose and lactic acid in physiological fluids.

Enzymes Encapsulated within Alginate Hydrogels: Bioelectrocatalysis and Electrochemiluminescence Applications

A simple procedure to incorporate enzymes (horseradish peroxidase, HRP, and lactate oxidase, LOx) within alginate hydrogels is reported with electrochemiluminescence (ECL) used to detect the enzymatic reactions with the corresponding substrates. First, HRP and LOx were successfully immobilized into CaCO3 microspheres, followed by the electrostatic layer-by-layer deposition of a nanoshell onto the microspheres, and finally by their dispersion into alginate solution. The as-prepared dispersion was drop cast onto the glassy carbon electrodes and cross-linked by the external and internal gelation methods using Ca2+ cations. The enzymes encapsulated within the alginate hydrogels were characterized using cyclic voltammetry and kinetic studies performed using ECL. The results showed that the enzymatic activity was significantly maintained as a result of the immobilization, with values of the apparent Michaelis-Menten constants estimated as 7.71 ± 0.62 and 8.41 ± 0.43 μM, for HRP and LOx, respectively. The proposed biosensors showed good stability and repeatability with an estimated limit of detection of 5.38 ± 0.05 and 0.50 ± 0.03 μM for hydrogen peroxide and lactic acid, respectively. The as-prepared enzymes encapsulated within the alginate hydrogels showed good stability up to 28 days from their preparation. The sensitivity and selectivity of the enzymes encapsulated within the alginate hydrogels were tested in real matrices (HRP, hydrogen peroxide, in contact lens solution; LOx, lactic acid in artificial sweat) showing the sensitivity of the ECL detection methods for the detection of hydrogen peroxide and lactic acid in real samples.

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.

Two-Dimensional Graphitic Carbon Nitride (g-C3N4) Nanosheets and Their Derivatives for Diagnosis and Detection Applications

The early diagnosis of certain fatal diseases is vital for preventing severe consequences and contributes to a more effective treatment. Despite numerous conventional methods to realize this goal, employing nanobiosensors is a novel approach that provides a fast and precise detection. Recently, nanomaterials have been widely applied as biosensors with distinctive features. Graphite phase carbon nitride (g-C3N4) is a two-dimensional (2D) carbon-based nanostructure that has received attention in biosensing. Biocompatibility, biodegradability, semiconductivity, high photoluminescence yield, low-cost synthesis, easy production process, antimicrobial activity, and high stability are prominent properties that have rendered g-C3N4 a promising candidate to be used in electrochemical, optical, and other kinds of biosensors. This review presents the g-C3N4 unique features, synthesis methods, and g-C3N4-based nanomaterials. In addition, recent relevant studies on using g-C3N4 in biosensors in regard to improving treatment pathways are reviewed.

Trace Analysis of Emerging Virus: An Ultrasensitive ECL-Scan Imaging System for Viral Infectious Disease

Emerging infectious diseases have brought a huge impact on human society in recent years. The outbreak of Zika virus (ZIKV) in the Americas resulted in a large number of babies born with microcephaly. More seriously, the Coronavirus Disease 2019 (COVID-19) was globally spread and caused immeasurable damages. Thus, the monitoring of highly pathogenic viruses is important to prevent and control emerging infectious diseases. Herein, a dendritic polymer probe-amplified ECL-scan imaging system was constructed to realize trace analysis of viral emerging infectious diseases. A dendritic polymer probe was employed as the efficient signal emitter component that could generate an amplified ECL signal on the integrated chip, and the signal was detected by a single-photon level charge coupled device-based ECL-scan imaging system. With this strategy, the ZIKV in a complex system of blood, urine, and saliva was detected. The results indicated that a high sensitivity of 50 copies and superior specificity were achieved. Furthermore, this strategy realized highly sensitive detection (10 copies) of the S and N protein gene sequence of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-Cov2) and spiked pseudovirus samples. Thus, the dendritic polymer probe-amplified ECL-scan imaging system suitably met the strict clinical requirements for trace analysis of an emerging virus, and thus has the potential to serve as a paradigm for monitoring emerging infectious diseases.

Boosting the electrochemiluminescence of luminol-O2 system by high-intensity focused ultrasound

Electrochemiluminescence (ECL) of luminol is a well-established methodology in analytical chemistry and bioimaging. Developing novel strategies to enhance the ECL signal of this model emitter is a challenging but rewarding task. In this work, we introduced the high-intensity focused ultrasound (HIFU), as a pretreatment means and a non-invasive way to trigger and boost the ECL signal with a 40-fold significant enhancement in the luminol-O₂ system without the addition of exogenous co-reactants. The superoxide anion (O₂^-•) generated in situ by HIFU was the key initiator for boosting the ECL emission as demonstrated in this study for the first time. This promising co-reactant-free strategy could find potential applications for ultrasensitive ECL detection in the analysis of complex biological entities.

Cardiac Troponin Biosensor Designs: Current Developments and Remaining Challenges

Acute myocardial infarction (AMI) is considered as one of the main causes of death, threating human lives for decades. Currently, its diagnosis relies on electrocardiography (ECG), which has been proven to be insufficient. In this context, the efficient detection of cardiac biomarkers was proposed to overcome the limitations of ECG. In particular, the measurement of troponins, specifically cardiac troponin I (cTnI) and cardiac troponin T (cTnT), has proven to be superior in terms of sensitivity and specificity in the diagnosis of myocardial damage. As one of the most life-threatening conditions, specific and sensitive investigation methods that are fast, universally available, and cost-efficient to allow for early initiation of evidence-based, living-saving treatment are desired. In this review, we aim to present and discuss the major breakthroughs made in the development of cTnI and cTnT specific biosensor designs and analytical tools, highlighting the achieved progress as well as the remaining challenges to reach the technological goal of simple, specific, cheap, and portable testing chips for the rapid and efficient on-site detection of cardiac cTnI/cTnT biomarkers in order to diagnose and treat cardiovascular diseases at an incipient stage.

Toward Next-Generation Mobile Diagnostics: Near-Field Communication-Powered Electrochemiluminescent Detection

Mobile phones have been used in combination with point of care (PoC) devices for over a decade now. However, their use seems restricted to the detection of sensing events using the video and camera functions. In contrast, the complementary ability to use mobile phones to power such PoC devices has been largely unexplored. This work demonstrates the proof-of-principle that a smartphone can be used to both power and analyze an electrochemiluminescence (ECL) detection system. A printed device is presented featuring an electrochemical cell connected in series to a rectenna that is able to use the Near Field Communication (NFC, 13.56 MHz) signal to provide the energy needed to generate ECL from Ru(bpy)₃²⁺/tri-n-propylamine. The emitted light, the intensity of which is directly proportional to the concentration of the ruthenium complex, can then be captured by the mobile phone camera and analyzed. This work presents the fabrication and the electrical and electrochemical characterization of the device. Effective voltages ranging from 0.90 to 4.50 V have been recorded, depending on the coupling between emitter and receiver, which translate into working electrode potentials ranging from 0.76 up to 1.79 V vs Ag. Detection and quantification limits of 0.64 and 1.52 μM, respectively, have been achieved for Ru(bpy)₃²⁺, and linear ranges up to 0.1 mM (red channel) and no less than 1.0 mM (green channel) have been found.

Electrochemiluminescence with semiconductor (nano)materials

Electrochemiluminescence (ECL) is the light production triggered by reactions at the electrode surface. Its intrinsic features based on a dual electrochemical/photophysical nature have made it an attractive and powerful method across diverse fields in applied and fundamental research. Herein, we review the combination of ECL with semiconductor (SC) materials presenting various typical dimensions and structures, which has opened new uses of ECL and offered exciting opportunities for (bio)sensing and imaging. In particular, we highlight this particularly rich domain at the interface between photoelectrochemistry, SC material chemistry and analytical chemistry. After an introduction to the ECL and SC fundamentals, we gather the recent advances with representative examples of new strategies to generate ECL in original configurations. Indeed, bulk SC can be used as electrode materials with unusual ECL properties or light-addressable systems. At the nanoscale, the SC nanocrystals or quantum dots (QDs) constitute excellent bright ECL nano-emitters with tuneable emission wavelengths and remarkable stability. Finally, the challenges and future prospects are discussed for the design of new detection strategies in (bio)analytical chemistry, light-addressable systems, imaging or infrared devices.

Integrated electrochemical lateral flow immunoassays (eLFIAs): recent advances

Schematic of integrated electrochemical lateral flow immunoassays.

Plasmon-Enhanced Nitrogen Vacancy-Rich Carbon Nitride Electrochemiluminescence Aptasensor for Highly Sensitive Detection of miRNA

The development of biosensors for biologically important substances with ultralow content such as microRNA is of great significance. Herein, a novel surface plasmon-enhanced electrogenerated chemiluminescence-based aptasensor was developed for ultrasensitive sensing of microRNA by using nitrogen vacancy-rich carbon nitride nanosheets as effective luminophores and gold nanoparticles as plasmonic sources. The introduction of nitrogen vacancies improved the electrochemiluminescence behavior due to improved conductance and electrogenerated chemiluminescence activity. The introduction of plasmonic gold nanoparticles increased the electrochemiluminescence signal intensity by more than eightfold. The developed surface plasmon-enhanced electrogenerated chemiluminescence aptasensor exhibited good selectivity, ultrasensitivity, excellent stability, and reproducibility for the determination of microRNA-133a, with a dynamic linear range of 1 aM to 100 pM and a limit of detection about 0.87 aM. Moreover, the surface plasmon-enhanced electrogenerated chemiluminescence sensor obtained a good recovery when detecting the content of microRNA in actual serum.

Innate Immunity Modulating Impurities and the Immunotoxicity of Nanobiotechnology-Based Drug Products

Innate immunity can be triggered by the presence of microbial antigens and other contaminants inadvertently introduced during the manufacture and purification of bionanopharmaceutical products. Activation of these innate immune responses, including cytokine secretion, complement, and immune cell activation, can result in unexpected and undesirable host immune responses. These innate modulators can also potentially stimulate the activation of adaptive immune responses, including the formation of anti-drug antibodies which can impact drug effectiveness. To prevent induction of these adverse responses, it is important to detect and quantify levels of these innate immunity modulating impurities (IIMIs) that may be present in drug products. However, while it is universally agreed that removal of IIMIs from drug products is crucial for patient safety and to prevent long-term immunogenicity, there is no single assay capable of directly detecting all potential IIMIs or indirectly quantifying downstream biomarkers. Additionally, there is a lack of agreement as to which of the many analytical assays currently employed should be standardized for general IIMI screening. Herein, we review the available literature to highlight cellular and molecular mechanisms underlying IIMI-mediated inflammation and its relevance to the safety and efficacy of pharmaceutical products. We further discuss methodologies used for direct and indirect IIMI identification and quantification.

On-Chip Optical Anodic Stripping with Closed Bipolar Cells and Cathodic Electrochemiluminescence Reporting

The aim of this work was to develop a simple, accessible, and point-of-use sensor to measure heavy metal ions in water in low-resource areas that cannot accommodate expensive or technical solutions. This report describes a new bipolar electrochemical sensor platform that reimagines conventional anodic stripping voltammetry in a wireless bipolar format with an optical electrochemiluminescent readout that can be quantified with any simple optical sensor like that found on most modern cell phone cameras. We call this technique as optical anodic stripping. Using a new nonlithographic fabrication process, devices could be produced rapidly and simply at <$1/sensor. The sensing scheme was developed, characterized, and optimized using electrochemical and optical methods. Quantitation of Pb²⁺ in both lab and natural water samples was rapid (2-3 min), accurate, precise, and highly linear in the 25-1000 ppb range and was shown to be sufficiently selective in the presence of other common heavy metal ions such as Cu²⁺, Cd²⁺, and Zn²⁺.

Recent Progress in Electrochemical Immunosensors

Biosensors used for medical diagnosis work by analyzing physiological fluids. Antibodies have been frequently used as molecular recognition molecules for the specific binding of target analytes from complex biological solutions. Electrochemistry has been introduced for the measurement of quantitative signals from transducer-bound analytes for many reasons, including good sensitivity. Recently, numerous electrochemical immunosensors have been developed and various strategies have been proposed to detect biomarkers. In this paper, the recent progress in electrochemical immunosensors is reviewed. In particular, we focused on the immobilization methods using antibodies for voltammetric, amperometric, impedimetric, and electrochemiluminescent immunosensors.

FMRP Levels in Human Peripheral Blood Leukocytes Correlates with Intellectual Disability

Fragile X syndrome (FXS) is the most common form of inherited intellectual disability. FXS is an X-linked, neurodevelopmental disorder caused by a CGG trinucleotide repeat expansion in the 5′ untranslated region (UTR) of the Fragile X Mental Retardation gene, FMR1. Greater than 200 CGG repeats results in epigenetic silencing of the gene leading to the deficiency or absence of Fragile X mental retardation protein (FMRP). The loss of FMRP is considered the root cause of FXS. The relationship between neurological function and FMRP expression in peripheral blood mononuclear cells (PBMCs) has not been well established. Assays to detect and measure FMR1 and FMRP have been described; however, none are sufficiently sensitive, precise, or quantitative to properly characterize the relationships between cognitive ability and CGG repeat number, FMR1 mRNA expression, or FMRP expression measured in PBMCs. To address these limitations, two novel immunoassays were developed and optimized, an electro-chemiluminescence immunoassay and a multiparameter flow cytometry assay. Both assays were performed on PMBCs isolated from 27 study participants with FMR1 CGG repeats ranging from normal to full mutation. After correcting for methylation, a significant positive correlation between CGG repeat number and FMR1 mRNA expression levels and a significant negative correlation between FMRP levels and CGG repeat expansion was observed. Importantly, a high positive correlation was observed between intellectual quotient (IQ) and FMRP expression measured in PBMCs.

Trifluoromethyl substitution enhances photoinduced activity against breast cancer cells but reduces ligand exchange in Ru(ii) complex

A series of five ruthenium complexes containing triphenyl phosphine groups known to enhance both cellular penetration and photoinduced ligand exchange, cis-[Ru(bpy)2(P(p-R-Ph)3)(CH3CN)]2+, where bpy = 2,2'-bipyridine and P(p-R-Ph)3 represent para-substituted triphenylphosphine ligands with R = -OCH3 (1), -CH3 (2) -H (3), -F (4), and -CF3 (5), were synthesized and characterized. The photolysis of 1-5 in water with visible light (λ irr ≥ 395 nm) results in the substitution of the coordinated acetonitrile with a solvent molecule, generating the corresponding aqua complex as the single photoproduct. A 3-fold variation in quantum yield was measured with 400 nm irradiation, Φ 400, where 1 is the most efficient with a Φ 400 = 0.076(2), and 5 the least photoactive complex, with Φ 400 = 0.026(2). This trend is unexpected based on the red-shifted metal-to-ligand charge transfer (MLCT) absorption of 1 as compared to that of 5, but can be correlated to the substituent Hammett para parameters and pK a values of the ancillary phosphine ligands. Complexes 1-5 are not toxic towards the triple negative breast cancer cell line MDA-MB-231 in the dark, but 3 and 5 are >4.2 and >19-fold more cytotoxic upon irradiation with blue light, respectively. A number of experiments point to apoptosis, and not to necrosis or necroptosis, as the mechanism of cell death by 5 upon irradiation. These findings provide a foundation for understanding the role of phosphine ligands on photoinduced ligand substitution and show the enhancement afforded by -CF3 groups on photochemotherapy, which will aid the future design of photocages for photochemotherapeutic drug delivery.

Electrochemiluminescence of Tris(2,2'-bipyridine)ruthenium(II)/Tri-n-propylamine with an Electric Contactless Power Transfer System

An electrochemiluminescence (ECL) analytical device was developed using an electric contactless power transfer system. A mutually induced electromotive voltage was generated by wrapping an enameled wire around a commercial contactless charger. There was no electrical contact between the power supply and the electrochemical cell. For the tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)₃²⁺)/tri-n-propylamine system, a weak ECL signal was observed. When an inexpensive rectifier diode was introduced between the coil and the working electrode, the ECL intensity detection sensitivity increased by more than 100 times. The relationship between the waveform of the applied voltage and the ECL response was clarified, and the optimum conditions were determined. The intensity of the induced electromotive voltage was easily controlled by changing the number of turns in the coil. The proposed method is a safe, simple, and inexpensive technique without electrical contact.

Electrochemical Affinity Assays/Sensors: Brief History and Current Status

The advent of electrochemical affinity assays and sensors evolved from pioneering efforts in the 1970s to broaden the field of analytes accessible to the selective and sensitive performance of electrochemical detection. The foundation of electrochemical affinity assays/sensors is the specific capture of an analyte by an affinity element and the subsequent transduction of this event into a measurable signal. This review briefly covers the early development of affinity assays and then focuses on advances in the past decade. During this time, progress on electroactive labels, including the use of nanoparticles, quantum dots, organic and organometallic redox compounds, and enzymes with amplification schemes, has led to significant improvements in sensitivity. The emergence of nanomaterials along with microfabrication and microfluidics technology enabled research pathways that couple the ease of use of electrochemical detection for the development of devices that are more user friendly, disposable, and employable, such as lab-on-a-chip, paper, and wearable sensors.

Multiplexed Prostate Cancer Companion Diagnostic Devices

Prostate cancer (PCa) remains one of the most prominent forms of cancer for men. Since the early 1990s, Prostate-Specific Antigen (PSA) has been a commonly recognized PCa-associated protein biomarker. However, PSA testing has been shown to lack in specificity and sensitivity when needed to diagnose, monitor and/or treat PCa patients successfully. One enhancement could include the simultaneous detection of multiple PCa-associated protein biomarkers alongside PSA, also known as multiplexing. If conventional methods such as the enzyme-linked immunosorbent assay (ELISA) are used, multiplexed detection of such protein biomarkers can result in an increase in the required sample volume, in the complexity of the analytical procedures, and in adding to the cost. Using companion diagnostic devices such as biosensors, which can be portable and cost-effective with multiplexing capacities, may address these limitations. This review explores recent research for multiplexed PCa protein biomarker detection using optical and electrochemical biosensor platforms. Some of the novel and potential serum-based PCa protein biomarkers will be discussed in this review. In addition, this review discusses the importance of converting research protocols into multiplex point-of-care testing (xPOCT) devices to be used in near-patient settings, providing a more personalized approach to PCa patients’ diagnostic, surveillance and treatment management.

Lighting up the Electrochemiluminescence of Carbon Dots through Pre- and Post-Synthetic Design

Carbon dots (CDs), defined by their size of less than 10 nm, are a class of photoluminescent (PL) and electrochemiluminescent (ECL) nanomaterials that include a variety of carbon-based nanoparticles. However, the control of their properties, especially ECL, remains elusive and afflicted by a series of problems. Here, the authors report CDs that display ECL in water via coreactant ECL, which is the dominant mechanism in biosensing applications. They take advantage of a multicomponent bottom-up approach for preparing and studying the luminescence properties of CDs doped with a dye acting as PL and ECL probe. The dependence of luminescence properties on the surface chemistry is further reported, by investigating the PL and ECL response of CDs with surfaces rich in primary, methylated, or propylated amino groups. While precursors that contribute to the core characterize the PL emission, the surface states influence the efficiency of the excitation-dependent PL emission. The ECL emission is influenced by surface states from the organic shell, but states of the core strongly interact with the surface, influencing the ECL efficiency. These findings offer a framework of pre- and post-synthetic design strategies to improve ECL emission properties, opening new opportunities for exploring biosensing applications of CDs.

Biosensors Designed for Clinical Applications

Emerging and validated biomarkers promise to revolutionize clinical practice, shifting the emphasis away from the management of chronic disease towards prevention, early diagnosis and early intervention. The challenge of detecting these low abundance protein and nucleic acid biomarkers within the clinical context demands the development of highly sensitive, even single molecule, assays that are also capable of selectively measuring a small number of defined analytes in complex samples such as whole blood, interstitial fluid, saliva or urine. Success relies on significant innovations in nanomaterials, bioreceptor engineering, transduction strategies and microfluidics. Primarily using examples from our work, this article discusses some recent advance in the selective and sensitive detection of disease biomarkers, highlights key innovations in sensor materials and identifies issues and challenges that need to be carefully considered especially for researchers entering the field.