Cardiac Troponin I: Ultrasensitive Detection Using Faradaic Electrochemical Impedance

Dendritic quinary PtRhMoCoFe high-entropy alloy as a robust immunosensing nanoplatform for ultrasensitive detection of biomarker

Recently, high-entropy alloys have superior physicochemical properties as compared to conventional alloys for their glamorous "cocktail effect". Nevertheless, they are scarcely applied to electrochemical immunoassays until now. Herein, uniform PtRhMoCoFe high-entropy alloyed nanodendrites (HEANDs) were synthesized by a wet-chemical co-reduction method, where glucose and oleylamine behaved as the co-reducing agents. Then, a series of characterizations were conducted to illustrate the synergistic effect among multiple metals and fascinating structural characteristics of PtRhMoCoFe HEANDs. The obtained high-entropy alloy was adopted to build a electrochemical label-free biosensor for ultrasensitive bioassay of biomarker cTnI. In the optimized analytical system, the resultant sensor exhibited a dynamic linear range of 0.0001-200 ng mL-1 and a low detection limit of 0.0095 pg mL-1 (S/N = 3). Eventually, this sensing platform was further explored in serum samples with satisfied recovery (102.0 %). This research renders some constructive insights for synthesis of high-entropy alloys and their expanded applications in bioassays and bio-devices.

Quantitative Fluorescent Lateral Flow Strip Sensor for Myocardial Infarction Using Purity-Color Upconversion Nanoparticles

Acute myocardial infarction is a serious cardiovascular disease and poses significant risks to human health. Its early diagnosis and real-time detection are of great importance. Herein, we design a low-cost device that has a high sensitivity of cTnT and cTnI detection. Dual-color upconversion nanoparticles (UCNPs) are prepared as probes, which not only have high-purity red upconversion luminescence (UCL) under 980 or 808 nm excitation but also achieve good temperature sensing. Temperature-dependent multicolor emission excitation is obtained, and the color turns from white to orange and red with increasing temperature. In particular, the maximum SR and SA values based on nonthermally coupled levels are 4.76% K-1 and 8.6% K-1, which are higher than those based on thermally coupled levels. With the UCNPs-based lateral flow strip (LFS), the specific detection of cTnI and cTnT antigens in samples is achieved with a detection limit of 0.001 ng/mL, which is 1 order of magnitude lower than that of their clinical cutoff. The UCNPs-LFS device has a low-cost laser diode and a simplified laser and permits a mobile-phone camera to collect the results, which has an important influence on the field of biomarker sensing.

Enhanced Electrochemical Biosensing of the Sp17 Cancer Biomarker in Serum Samples via Engineered Two-Dimensional MoS2 Nanosheets on the Reduced Graphene Oxide Interface

In the present investigation, we reported a label-free and highly effective immunosensor for the first time employing a nanostructured molybdenum disulfide nanosheets@reduced graphene oxide (nMoS2 NS@rGO) nanohybrid interface for the determination of sperm protein 17 (Sp17), an emerging cancer biomarker. We synthesized the nMoS2 NS@rGO nanohybrid using a one-step hydrothermal technique and then functionalized it with 3-aminopropyltriethoxysilane (APTES). Furthermore, the anti-Sp17 monoclonal antibodies were covalently attached to the APTES/nMoS2 NS@rGO/indium tin oxide (ITO) electrode utilizing 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide-N-hydroxy succinimide (EDC-NHS) coupling chemistry. Bovine serum albumin (BSA) was then used to block nonspecific binding regions on the anti-Sp17/APTES/nMoS2 NS@rGO/ITO bioelectrode. The morphological and structural features of the synthesized nanohybrid and the modified electrodes were studied using transmission electron microscopy, scanning electron microscopy with energy dispersive X-ray (EDX) composition studies, atomic force microscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. The immunoreaction between the Sp17 antigen and anti-Sp17 antibodies on the surface of the BSA/anti-Sp17/APTES/nMoS2 NS@rGO/ITO sensing bioelectrode was applied as the basis for the detection technique, which measured the electrocatalytic current and impedimetric response change. The designed BSA/anti-Sp17/APTES/nMoS2 NS@rGO/ITO bioelectrode showed improved amperometric and impedimetric biosensing performance in the response studies, including remarkable sensitivity (23.2 μA ng-1mL cm-2 and 0.48 kΩ mL ng-1 cm-2), wider linearity (0.05-8 and 1-8 ng mL-1), an excellent lower detection limit (0.13 and 0.23 ng mL-1), and a rapid response time of 20 min. The biosensor exhibited impressive storage durability lasting 7 weeks and showed remarkable precision in identifying Sp17 in serum samples from cancer patients, as confirmed using the enzyme-linked immunosorbent assay method.

Paper-Based All-in-One Origami Nanobiosensor for Point-of-Care Detection of Cardiac Protein Markers in Whole Blood

Rapid and accurate diagnosis of cardiovascular diseases (CVDs) at the earliest stage is of paramount importance to improve the treatment outcomes and avoid irreversible damage to a patient's cardiovascular system. Microfluidic paper-based devices (μPADs) represent a promising platform for rapid CVD diagnosis at the point of care (POC). This paper presents an electrochemical μPAD (E-μPAD) with an all-in-one origami design for rapid and POC testing of cardiac protein markers in whole blood. Based on the label-free, electrochemical impedance spectroscopy (EIS) immunoassay, the E-μPAD integrates all essential components on a single chip, including three electrochemical cells, a plasma separation membrane, and a buffer absorption pad, enabling easy and streamlined operations for multiplexed detection of three cardiac protein markers [cardiac troponin I (cTnI), brain natriuretic peptide (BNP)-32, and D-Dimer] on a finger-prick whole blood sample within 46 min. Superior analytical performance is achieved through sensitive EIS measurement on carbon electrodes decorated with semiconductor zinc oxide nanowires (ZnO NWs). Using spiked human plasma samples, ultralow limits of detection (LODs) of E-μPAD are achieved at 4.6 pg/mL (190 fM) for cTnI, 1.2 pg/mL (40 fM) for BNP-32, and 146 pg/mL (730 fM) for D-Dimer. Real human blood samples spiked with purified proteins are also tested, and the device's analytical performance was proven to be comparable to commercial ELISA kits. The all-in-one E-μPAD will allow rapid and sensitive testing of cardiac protein markers through easy operations, which holds great potential for on-site screening of acute CVDs in nonlaboratory settings such as emergency rooms, doctor's offices, or patient homes.

Biocompatible epoxysilane substituted polymer-based nano biosensing platform for label-free detection of cancer biomarker SP17 in patient serum samples

Herein, we report the results of the studies relating to developing a simple, sensitive, cost-effective, and disposable electrochemical-based label-free immunosensor for real-time detection of a new cancer biomarker, sperm protein-17 (SP17), in complex serum samples. An indium tin oxide (ITO) coated glass substrate modified with self-assembled monolayers (SAMs) of 3-glycidoxypropyltrimethoxysilane (GPTMS) was functionalized via covalent immobilization of monoclonal anti-SP17 antibodies using EDC(1-(3-(dimethylamine)-propyl)-3-ethylcarbodiimide hydrochloride) - NHS (N-hydroxy succinimide) chemistry. The developed immunosensor platform (BSA/anti-SP17/GPTMS@SAMs/ITO) was characterized via scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle (CA), Fourier transform infrared (FT-IR) spectroscopic, and electrochemical techniques such as cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) techniques. The fabricated BSA/anti-SP17/GPTMS@SAMs/ITO immunoelectrode platform was used to measure changes in the magnitude of the current of the electrodes through an electrochemical CV and DPV technique. A calibration curve between current and SP17 concentrations exhibited a broad linear detection range of (100-6000 & 50-5500 pg mL^-1), with enhanced sensitivity (0.047 & 0.024 μA pg mL^-1 cm^-2), limit of detection (LOD) and limit of quantification (LOQ) of 47.57 & 142.9 pg mL^-1 and 158.58 & 476.3 pg mL^-1, by CV and DPV technique, respectively with a rapid response time of 15 min. It possessed exceptional repeatability, outstanding reproducibility, five-time reusability, and high stability. The biosensor's performance was evaluated in human serum samples, giving satisfactory findings obtained via the commercially available enzyme-linked immunosorbent assay (ELISA) technique, proving the clinical applicability for early diagnosis of cancer patients. Moreover, various in vitro studies in murine fibroblast cell line L929 have been performed to assess the cytotoxicity of GPTMS. The results demonstrated that GPTMS has excellent biocompatibility and can be used for biosensor fabrication.

Recent Advances in Impedimetric Biosensors Focusing on Myocardial Infarction Diagnosis

Acute myocardial infarction is the most common cardiovascular disease and 85% of cardiovascular disease-related deaths are associated with it. The variation in the cardiac troponin concentration is considered as the most significant judge index for acute myocardial infarction diagnosis. Here, a comprehensive insights is given about the impedimetric methods as powerful electrochemical biosensing platforms for cardiac troponin evaluation. Focusing on nano materials, various impedimetric techniques including faradaic and non-faradaic techniques and different transducer modification techniques are addressed. The steps taken by each of the studied platforms to solve the existing problems are discussed and their advantages and drawbacks are highlighted. A glance at the provided table is given a mind into the features of each impedimetric sensors and their comparison are provided.

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.

Electroanalytical point-of-care detection of gold standard and emerging cardiac biomarkers for stratification and monitoring in intensive care medicine - a review

Determination of specific cardiac biomarkers (CBs) during the diagnosis and management of adverse cardiovascular events such as acute myocardial infarction (AMI) has become commonplace in emergency department (ED), cardiology and many other ward settings. Cardiac troponins (cTnT and cTnI) and natriuretic peptides (BNP and NT-pro-BNP) are the preferred biomarkers in clinical practice for the diagnostic workup of AMI, acute coronary syndrome (ACS) and other types of myocardial ischaemia and heart failure (HF), while the roles and possible clinical applications of several other potential biomarkers continue to be evaluated and are the subject of several comprehensive reviews. The requirement for rapid, repeated testing of a small number of CBs in ED and cardiology patients has led to the development of point-of-care (PoC) technology to circumvent the need for remote and lengthy testing procedures in the hospital pathology laboratories. Electroanalytical sensing platforms have the potential to meet these requirements. This review aims firstly to reflect on the potential benefits of rapid CB testing in critically ill patients, a very distinct cohort of patients with deranged baseline levels of CBs. We summarise their source and clinical relevance and are the first to report the required analytical ranges for such technology to be of value in this patient cohort. Secondly, we review the current electrochemical approaches, including its sub-variants such as photoelectrochemical and electrochemiluminescence, for the determination  of important CBs highlighting the various strategies used, namely the use of micro- and nanomaterials, to maximise the sensitivities and selectivities of such approaches. Finally, we consider the challenges that must be overcome to allow for the commercialisation of this technology and transition into intensive care medicine.

Chronocoulometric signalling of BNP using a novel quantum dot aptasensor

This study is a first-time report of the development of a quantum dot based aptasensor for brain natriuretic peptide (BNP) detection using chronocoulometry for real-time analysis.

5G-Enabled intelligent construction of a chest pain center with up-conversion lateral flow immunoassay

Acute myocardial infarction (AMI) has become a worldwide health problem because of its rapid onset and high mortality. Cardiac troponin I (cTnI) is the gold standard for diagnosis of AMI, and its rapid and accurate detection is critical for early diagnosis and management of AMI. Using a lateral flow immunoassay with upconverting nanoparticles as fluorescent probes, we developed an up-conversion fluorescence reader capable of rapidly quantifying the cTnI concentration in serum based upon the fluorescence intensity of the test and control lines on the test strip. Reliable detection of cTnI in the range 0.1-50 ng mL^-1 could be achieved in 15 min, with a lower detection limit of 0.1 ng mL^-1. The reader was also adapted for use on a 5th generation (5G) mobile network enabled intelligent chest pain center. Through Bluetooth wireless communication, the results achieved using the reader on an ambulance heading to a central hospital could be transmitted to a 5G smartphone and uploaded for real-time edge computing and cloud storage. An application in the 5G smartphone allows users to upload their medical information to establish dedicated electronic health records and doctors to monitor patients' health status and provide remote medical services. Combined with mobile internet and big data, the 5G-enabled intelligent chest pain center with up-conversion lateral flow immunoassay may predict the onset of AMI and save valuable time for patients suffering an AMI.

Generation, selection and modification of anti-cardiac troponin I antibodies with high specificity and affinity

Current diagnosis of acute myocardial infarction involves quantification of circulating cTn levels. This work endeavoured to generate and enhance recombinant antibody fragments targeting various epitopes on the N- and C-terminals of the cTnI molecule, thereby facilitating highly sensitive detection of the troponin molecule. From this approach, two anti-cTnI scFv antibodies were successfully selected using either phage display or structural reformatting of full length anti-cTnI IgG. Their antibody binding affinity was further optimised via chain shuffling and/or site directed mutagenesis, resulting in scFv with heightened sensitivity when compared to the wild-type scFv. If used in conjunction with existing anti-mid fragment cTnI antibodies, these N- and C- terminal-targeting scFvs show high potential for the enhancement of current cTnI detection assays by limiting the effects from cTnI degradation or troponin complex formation.

Electrochemical strategies for the detection of cTnI

Acute myocardial infarction (AMI) is the main cause of death from cardiovascular diseases. Thus, early diagnosis of AMI is essential for the treatment of irreversible damage from myocardial infarction. Traditional electrocardiograms (ECG) cannot meet the specific detection of AMI. Cardiac troponin I (cTnI) is the main biomarker for the diagnosis of myocardial infarction, and the detection of cTnI content has become particularly important. In this review, we introduced and compared the advantages and disadvantages of various cTnI detection methods. We focused on the analysis and comparison of the main indicators and limitations of various cTnI biosensors, including the detection range, detection limit, specificity, repeatability, and stability. In particular, we pay more attention to the application and development of electrochemical biosensors in the diagnosis of cardiovascular diseases based on different biological components. The application of electrochemical microfluidic chips for cTnI was also briefly introduced in this review. Finally, this review also briefly discusses the unresolved challenges of electrochemical detection and the expectations for improvement in the detection of cTnI biosensing in the future.

The role of antibody-based troponin detection in cardiovascular disease: A critical assessment

Cardiovascular disease has remained the world's biggest killer for 30 years. To aid in the diagnosis and prognosis of patients suffering cardiovascular-related disease accurate detection methods are essential. For over 20 years, the cardiac-specific troponins, I (cTnI) and T (cTnT), have acted as sensitive and specific biomarkers to assist in the diagnosis of various types of heart diseases. Various cardiovascular complications were commonly detected in patients with COVID-19, where cTn elevation is detectable, which suggested potential great prognostic value of cTn in COVID-19-infected patients. Detection of these biomarkers circulating in the bloodstream is generally facilitated by immunoassays employing cTnI- and/or cTnT-specific antibodies. While several anti-troponin assays are commercially available, there are still obstacles to overcome to achieve optimal troponin detection. Such obstacles include the proteolytic degradation of N and C terminals on cTnI, epitope occlusion of troponin binding-sites by the cTnI/cTnT complex, cross reactivity of antibodies with skeletal troponins or assay interference caused by human anti-species antibodies. Therefore, further research into multi-antibody based platforms, multi-epitope targeting and rigorous validation of immunoassays is required to ensure accurate measurements. Moreover, with combination and modification of various latest technical (e.g. microfluidics), antibody-based troponin detection systems can be more specific, sensitive and rapid which could be incorporated into portable biosensor systems to be used at point-of care.

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.

Fluorescence Based on Surface Plasmon Coupled Emission for Ultrahigh Sensitivity Immunoassay of Cardiac Troponin I

This work demonstrates the quantitative assay of cardiac Troponin I (cTnI), one of the key biomarkers for acute cardiovascular diseases (the leading cause of death worldwide) using the fluorescence-based sandwich immune reaction. Surface plasmon coupled emission (SPCE) produced by non-radiative coupling of dye molecules with surface plasmons being excitable via the reverse Kretschmann format is exploited for fluorescence-based sandwich immunoassay for quantitative detection of cTnI. The SPCE fluorescence chip utilizes the gold (2 nm)-silver (50 nm) bimetallic thin film, with which molecules of the dye Alexa 488 (conjugated with detection antibodies) make a near field coupling with the plasmonic film for SPCE. The experimental results find that the SPCE greatly improves the sensitivity via enhancing the fluorescence signal (up to 50-fold) while suppressing the photo-bleaching, permitting markedly enhanced signal-to-noise ratio. The limit of detection of 21.2 ag mL-1 (atto-gram mL-1) is obtained, the lowest ever reported to date amid those achieved by optical technologies such as luminescence and label-free optical sensing techniques. The features discovered such as ultrahigh sensitivity may prompt the presented technologies to be applied for early diagnosis of cTnI in blood, particularly for emergency medical centers overloaded with patients with acute myocardial infarction who would suffer from time-delayed diagnosis due to insufficient assay device sensitivity.

Hierarchical structure of molybdenum disulfide-reduced graphene oxide nanocomposite for the development of a highly efficient serotonin biosensing platform

Molybdenum disulfide-reduced graphene oxide nanocomposite based immunosensor for the serotonin detection.

Gold-Nanohybrid Biosensors for Analyzing Blood Circulating Clinical Biomacromolecules: Current Trend toward Future Remote Digital Monitoring

Mortality level is worsening the situation worldwide thru blood diseases and greatly jeopardizes the human health with poor diagnostics. Due to the lack of successful generation of early diagnosis, the survival rate is currently lower. To overcome the present hurdle, new diagnostic methods have been choreographed for blood disease biomarkers analyses with the conjunction of ultra-small ideal gold nanohybrids. Gold-hybrids hold varieties of unique features, such as high biocompatibility, increased surface-to-volume ratio, less-toxicity, ease in electron transfer and have a greater localized surface plasmon resonance. Gold-nanocomposites can be physically hybrid on the sensor surface and functionalize with the biomolecules using appropriate chemical conjugations. Revolutionizing biosensor platform can be prominently linked for the nanocomposite applications in the current research on medical diagnosis. This review encloses the new developments in diagnosing blood biomarkers by utilizing the gold-nanohybrids. Further, the current state-of-the-art and the future envision with digital monitoring for facile telediagnosis were narrated.

Multinuclear PtII Complexes: Why Three is Better Than Two to Enhance Photophysical Properties

The self-assembly of platinum complexes is a well-documented process that leads to interesting changes of the photophysical and electrochemical behavior as well as to a change in reactivity of the complexes. However, it is still not clear how many metal units must interact in order to achieve the desired properties of a large assembly. This work aimed to clarify the role of the number of interacting PtII units leading to an enhancement of the spectroscopic properties and how to address inter- versus intramolecular processes. Therefore, a series of neutral multinuclear PtII complexes were synthesized and characterized, and their photophysical properties at different concentration were studied. Going from the monomer to dimers, the growth of a new emission band and the enhancement of the emission properties were observed. Upon increasing the platinum units up to three, the monomeric blue emission could not be detected anymore and a concentration independent bright-yellow/orange emission, due to the establishment of intramolecular metallophilic interactions, was observed.

Magnetic Particles: Their Applications from Sample Preparations to Biosensing Platforms

The growing interest in magnetic materials as a universal tool has been shown by an increasing number of scientific publications regarding magnetic materials and its various applications. Substantial progress has been recently made on the synthesis of magnetic iron oxide particles in terms of size, chemical composition, and surface chemistry. In addition, surface layers of polymers, silica, biomolecules, etc., on magnetic particles, can be modified to obtain affinity to target molecules. The developed magnetic iron oxide particles have been significantly utilized for diagnostic applications, such as sample preparations and biosensing platforms, leading to the selectivity and sensitivity against target molecules and the ease of use in the sensing systems. For the process of sample preparations, the magnetic particles do assist in target isolation from biological environments, having non-specific molecules and undesired molecules. Moreover, the magnetic particles can be easily applied for various methods of biosensing devices, such as optical, electrochemical, and magnetic phenomena-based methods, and also any methods combined with microfluidic systems. Here we review the utilization of magnetic materials in the isolation/preconcentration of various molecules and cells, and their use in various techniques for diagnostic biosensors that may greatly contribute to future innovation in point-of-care and high-throughput automation systems.

Reagentless Redox Capacitive Assaying of C-Reactive Protein at a Polyaniline Interface

Methods that enable the sensitive and label-free detection of protein biomarkers are well-positioned to make potentially significant contributions to diagnostics and derived personalized healthcare. In support of this goal, a myriad of (electrochemical) methodologies have been developed; recently, electrochemical capacitance spectroscopy emerged as an impedance-derived approach which, in employing surface-confined redox-transducers, circumvents problems associated with the use of solution-phase redox-probes. Herein, we expand this scope by utilizing phytic acid-doped polyaniline as a novel redox-charging polymer support enabling the reagentless assaying of C-reactive protein in serum with good sensitivity. The construction of the sensory interface via electropolymerization allows facile tuning of the surface coverage and redox (capacitive) properties of the polymers, which, in turn, modulate both assay selectivity, fouling, and sensitivity. Significantly, this methodology is readily extendable to a wide range of electrode materials and analytes.

Sensitivity Enhancement of Point-of-Care for Cardiac Markers Detection using Micro-Impedimetric Immunosensor Arrays

This paper describes the development and characterisation of a novel, electrical impedance spectroscopy-based (EIS) immunosensor array for point-of-care applications. EIS is a highly sensitive, label-free, real time technique suitable for single use, point-of-care cardiac marker detection devices. However, the underlying source of the observed change in EIS immunoassay response has not been well characterised or understood. A full understanding of the relationship between target binding and impedance response would significantly advance biosensor design and most probably increase detection limit sensitivity. The development of micro-/nano- structured electrodes for multi-frequency EIS procedure propose substantial benefits over classical macro-structured systems.Countless manipulations of electrode features and inter-electrode spacing will enhance the electrode surface area, increase the charge-transfer resistance and reduce the double-layer capacitance. These in turn give rise to improved signal-to-noise ratios, therefore affording greater sensitivity, lower detection limits and faster detection times.The sensor sensitivity range was within that required for human myoglobin determination, following acute myocardial infarction (heart attack). Real-time MyAb-MyAg interaction monitoring, permitted the determination of the binding events in less than one minute.

A surface-enhanced electrochemiluminescence sensor based on Au-SiO2 core–shell nanocomposites doped with Ru(bpy)32+ for the ultrasensitive detection of prostate-specific antigen in human serum

This study reports a surface-enhanced electrochemiluminescence (SEECL) sensor for the ultrasensitive detection of prostate-specific antigen (PSA) in human serum.

A conceptual framework for the development of iridium(iii) complex-based electrogenerated chemiluminescence labels

Translation of the highly promising electrogenerated chemiluminescence (ECL) properties of Ir(iii) complexes (with tri-n-propylamine (TPrA) as a co-reactant) into a new generation of ECL labels for ligand binding assays necessitates the introduction of functionality suitable for bioconjugation. Modification of the ligands, however, can affect not only the photophysical and electrochemical properties of the complex, but also the reaction pathways available to generate light. Through a combined theoretical and experimental study, we reveal the limitations of conventional approaches to the design of electrochemiluminophores and introduce a new class of ECL label, [Ir(C^N)2(pt-TOxT-Sq)]+ (where C^N is a range of possible cyclometalating ligands, and pt-TOxT-Sq is a pyridyltriazole ligand with trioxatridecane chain and squarate amide ethyl ester), which outperformed commercial Ir(iii) complex labels in two commonly used assay formats. Predicted limits on the redox potentials and emission wavelengths of Ir(iii) complexes capable of generating ECL via the dominant pathway applicable in microbead supported ECL assays were experimentally verified by measuring the ECL intensities of the parent luminophores at different applied potentials, and comparing the ECL responses for the corresponding labels under assay conditions. This study provides a framework to tailor ECL labels for specific assay conditions and a fundamental understanding of the ECL pathways that will underpin exploration of new luminophores and co-reactants.

Thionin functionalized signal amplification label derived dual-mode electrochemical immunoassay for sensitive detection of cardiac troponin I

A sensitive sandwich-type electrochemical immunosensor was established by employing Au@Pt core-shell multi-branched nanoparticles, and thionin functionalized nitrogen/sulfur co-doped graphene oxide (N/S-cGO/L-lys/Au@Pt MBs/Thi) as a double signal label to detect cardiac troponin I (cTnI). In this work, Au nanorods functionalized polydopamine (Au NR@PDA) with high adsorption capacity and superior electroconductivity can provide an efficient substrate for immobilizing primary antibodies (Ab₁). In the proposed N/S-cGO/L-lys/Au@Pt MBs/Thi, an electrochemically active molecule, Thi was covalently bonded in the N/S-cGO/L-lys/Au@Pt MBs. It presented a strong differential pulse voltammetry (DPV) current signal without electron transfer mediators, and showed a high electrocatalytic activity toward H₂O₂ reduction by using amperometric i-t (i-t). Impressively, with the synergistic effect of N/S-cGO/L-lys/Au@Pt MBs/Thi and Au NR@PDA, the developed dual-mode electrochemical immunosensor for cTnI detection showed a wide linear concentration range (50 fg/mL to 250 ng/mL, 750 fg/mL to 100 ng/mL) and a low detection limit (16.7 fg/mL, 250 fg/mL) via i-t and DPV, respectively. Furthermore, this immunosensor exhibited acceptable reproducibility, high sensitivity and good stability under optimal conditions. More importantly, the satisfactory results were obtained in detection of cTnI-spiked human serum samples, and the presented method may be a promising application in clinical bioanalysis.