Gold nanoparticles-reduced graphene oxide based electrochemical immunosensor for the cardiac biomarker myoglobin

Target-regulated Ag2S/FeOOH heterojunction activity: a direct label-free photoelectrochemical immunosensor

Myoglobin (Mb), an important cardiac marker, plays a crucial role in diagnosing, monitoring, and evaluating the condition of patients with cardiovascular diseases. Here, we propose a label-free photoelectrochemical (PEC) sensor for the detection of Mb through target regulated the photoactivity of Ag2S/FeOOH heterojunction. The Ag2S/FeOOH nanospindles were synthesized and served as a sensing platform for the fabrication of bio-recognized process for Mb. Mb-aptamer was used as the responsive group to grasp the target Mb in a real sample due to its advantages of strong affinity, high stability, and ease of preparation. Mb-aptamer immunocomplex is formed in the presence of Mb, which hinders the interfacial electron transfer and then reduce the photocurrent. The proposed PEC aptasensor exhibited excellent analytical performance including wide linear range (1.0 pg mL-1 ~ 50 ng mL-1), low limit of detection (0.28 pg mL-1), and good selectivity and stability. This work introduces an innovative approach to PEC aptasensor, offering a promising method for precise determination of human biomarkers.

Functionalized Triangular Carbon Quantum Dot Stabilized Gold Nanoparticles Decorated Boron Nitride Nanosheets Interfaced for Electrochemical Detection of Cardiac Troponin T

The fast, and highly sensitive estimation of cardiac troponin T (cTnT) is crucial for the early identification of acute myocardial infarction (AMI). The electrochemical immunoassay-based (EIB) sensors are highly promising for this purpose, as they offer precise measurements and can be directly assessed in intricate matrices, including blood. To increase sensitivity, EIB sensors use nanomaterials or amplification processes, which can be laborious to develop. With this, we develop an electrochemical immunosensor for the sensitive detection of cardiac troponin T (cTnT). The sensing platform is composed of functionalized triangular carbon quantum dots stabilized gold nanoparticles which are integrated with boron nitride nanosheets (caf-TCQDs@AuNPs on HO-BNNS). Ferrocene carboxylic acid (Fc-COOH) serves as the signal label. The composite was developed and examined using several techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), cyclic voltammetry, and chronocoulometry. The caf-TCQDs@AuNPs supported on HO-BNNS, have a large surface area and excellent electrical conductivity, and serve as an effective platform for the immobilization of anti-cTnT monoclonal antibodies via carbodiimide coupling. The Fc-COOH, functioning as a signal label through the oxidation process, was integrated with caf-TCQDs@AuNPs on the HO-BNNS platform to establish an electrochemical immunosensor for the detection of cTnT. The electrochemical immunosensor demonstrated excellent performance for the determination of cTnT under optimal conditions, exhibiting a linearity range spanning from 0.0001 to 100 ng mL-1, accompanied by a low detection limit of 0.0013 ng mL-1. Notably, the immunosensor revealed high specificity, as well as excellent levels of reproducibility and reliability for the examination of human serum samples.

Electrochemical and Plasmonic Detection of Myocardial Infarction Using Microfluidic Biochip Incorporated with Mesoporous Nanoscaffolds

This paper reports a microfluidic device for the electrochemical and plasmonic detection of cardiac myoglobin (cMb) and cardiac troponin I (cTnI) with noticeable limits of detection (LoD) as low as a few picograms per milliliter (pg/mL) ranges, achieved in a short detection time. The device features two working electrodes, each with a mesoporous Ni3V2O8 nanoscaffold grafted with reduced graphene oxide (rGO) that improves the interaction of diffusing analyte molecules with the sensing surface by providing a high surface area and reaction kinetics. Electrochemical studies reveal sensitivities as high as 9.68 μA ng/mL and a LoD of 2.0 pg/mL for cTnI, and 8.98 μA ng/mL and 4.7 pg/mL for cMb. Additionally, the surface plasmon resonance (SPR) studies demonstrate a low-level LoD of 8.8 pg/mL for cMb and 7.3 pg/mL for cTnI. The dual-modality sensor enables dynamic tracking of kinetic antigen-antibody interactions during sensing, self-verification through providing signals of two modes, and reduced false readout. This study demonstrates the complementary nature of the electrochemical and SPR modes in biosensing, with the electrochemical mode being highly sensitive and the SPR mode providing superior tracking of molecular recognition behaviors. The presented sensor represents a significant innovation in cardiovascular disease management and can be applied to monitor other clinically important biomolecules.

Mulberry-like porous-hollow AuPtAg nanorods for electrochemical immunosensing of biomarker myoglobin

Mulberry-like AuPtAg porous hollow nanorods (PHNR) were facilely synthesized for the first time via a wet chemical method, where Au nanorods (Au NR) behaved as sacrificed template. The anisotropic oriented growth and etching process are involved in this synthesis. Their structural and electronic characteristics were scrutinously examined by TEM, EDS, XPS, and electrochemical techniques. The AuPtAg PHNR provided a large specific surface area and exposed a large number of active sites, showing highly enhanced catalytic activity. On this foundation, a label-free electrochemical immunosensor was developed for myoglobin (Myo) assay based on the AuPtAg PHNR. Further, the built sensor exhibited fast and ultrasensitive responses in a linear range of 0.0001 ~ 1000 ng mL^-1 with a low limit of detection (LOD = 0.46 pg mL^-1, S/N = 3), and enabled efficient application to human serum samples with acceptable results. Consequently, the developed AuPtAg PHNR-based platform has a broad prospect in practically monitoring Myo and other biomarkers in clinics.

Recent advancements of nanomodified electrodes - Towards point-of-care detection of cardiac biomarkers

The increasing number of deaths from cardiovascular diseases has become a substantial concern in both developed and underdeveloped countries. Rapid and on-site monitoring of this disease is urgently important to control, prevent and make awareness of public health. Recently, a lot of focus has been placed on nanomaterials and modify these nanomaterials have been explored to detect cardiac biomarkers. By implementing biosensors that are modified with novel recognition elements and more stable nanomaterials, the use of electrochemistry for point-of-care devices is more realistic every day. This review focuses on the current state of nanomaterials conjugated biorecognition elements (enzyme integrated with nanomaterials, antibody conjugated nanomaterials and aptamer conjugated nanomaterials) for electrochemical cardiovascular disease detection. Specifically, a lot of attention has been given to the trends toward more stable biosensors that have increased the potential to be used as point-of-care devices for the detection of cardiac biomarkers due to their high stability and specificity. Moreover, the recent progress on biomolecule-free electrochemical nanosensors for cardiovascular disease detection has been considered. At last, the possibility and drawbacks of some of these techniques for point-of-care cardiac device development in the future have been discussed.

Nanobiosensors Design Using 2D Materials: Implementation in Infectious and Fatal Disease Diagnosis

Nanobiosensors are devices that utilize a very small probe and any form of electrical, optical, or magnetic technology to detect and analyze a biochemical or biological process. With an increasing population today, nanobiosensors have become the broadly used electroanalytical tools for the timely detection of many infectious (dengue, hepatitis, tuberculosis, leukemia, etc.) and other fatal diseases, such as prostate cancer, breast cancer, etc., at their early stage. Compared to classical or traditional analytical methods, nanobiosensors have significant benefits, including low detection limit, high selectivity and sensitivity, shorter analysis duration, easier portability, biocompatibility, and ease of miniaturization for on-site monitoring. Very similar to biosensors, nanobiosensors can also be classified in numerous ways, either depending on biological molecules, such as enzymes, antibodies, and aptamer, or by working principles, such as optical and electrochemical. Various nanobiosensors, such as cyclic voltametric, amperometric, impedimetric, etc., have been discussed for the timely monitoring of the infectious and fatal diseases at their early stage. Nanobiosensors performance and efficiency can be enhanced by using a variety of engineered nanostructures, which include nanotubes, nanoparticles, nanopores, self-adhesive monolayers, nanowires, and nanocomposites. Here, this mini review recaps the application of two-dimensional (2D) materials, especially graphitic carbon nitride (g-C₃N₄), graphene oxide, black phosphorous, and MXenes, for the construction of the nanobiosensors and their application for the diagnosis of various infectious diseases at very early stage.

Label-Free Myoglobin Biosensor Based on Pure and Copper-Doped Titanium Dioxide Nanomaterials

In this study, using pure and copper-doped titanium dioxide (Cu-TiO₂) nanostructures as the base matrix, enzyme-less label free myoglobin detection to identify acute myocardial infarction was performed and presented. The Cu-TiO₂ nanomaterials were prepared using facile sol-gel method. In order to comprehend the morphologies, compositions, structural, optical, and electrochemical characteristics, the pure and Cu-TiO₂ nanomaterials were investigated by several techniques which clearly revealed good crystallinity and high purity. To fabricate the enzyme-less label free biosensor, thick films of synthesized nanomaterials were applied to the surface of a pre-fabricated gold screen-printed electrode (Au-SPE), which serves as a working electrode to construct the myoglobin (Mb) biosensors. The interference study of the fabricated biosensor was also carried out with human serum albumin (HSA) and cytochrome c (cyt-c). Interestingly, the Cu-doped TiO₂ nanomaterial-based Mb biosensor displayed a higher sensitivity of 61.51 µAcm^-2/nM and a lower detection limit of 14 pM with a response time of less than 10 ms.

Zero-Biased Photoelectrochemical Detection of Cardiac Biomarker Myoglobin Based on CdSeS/ZnS Quantum Dots and Barium Titanate Perovskite

Cardiovascular diseases are considered one of the leading causes of premature mortality of patients worldwide. Therefore, rapid diagnosis of these diseases is crucial to ensure the patient's survival. During a heart attack or severe muscle damage, myoglobin is rapidly released in the body to constitute itself as a precise biomarker of acute myocardial infarction. Thus, we described the photoelectrochemical immunosensor development to detect myoglobin. It was based on fluorine-doped tin oxide modified with CdSeS/ZnSe quantum dots and barium titanate (BTO), designated as CdSeS/ZnSQDS/BTO. It was characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and amperometry. The anodic photocurrent at the potential of 0 V (vs. Ag/AgCl) and pH 7.4 was found linearly related to the myoglobin (Mb) concentration from 0.01 to 1000 ng mL^-1. Furthermore, the immunosensor showed an average recovery rate of 95.7-110.7% for the determination of myoglobin.

Green syntheses of graphene and its applications in internet of things (IoT)-a status review

Internet of Things (IoT) is a trending technological field that converts any physical object into a communicable smarter one by converging the physical world with the digital world. This innovative technology connects the device to the internet and provides a platform to collect real-time data, cloud storage, and analyze the collected data to trigger smart actions from a remote location via remote notifications, etc. Because of its wide-ranging applications, this technology can be integrated into almost all the industries. Another trending field with tremendous opportunities is Nanotechnology, which provides many benefits in several areas of life, and helps to improve many technological and industrial sectors. So, integration of IoT and Nanotechnology can bring about the very important field of Internet of Nanothings (IoNT), which can re-shape the communication industry. For that, data (collected from trillions of nanosensors, connected to billions of devices) would be the 'ultimate truth', which could be generated from highly efficient nanosensors, fabricated from various novel nanomaterials, one of which is graphene, the so-called 'wonder material' of the 21st century. Therefore, graphene-assisted IoT/IoNT platforms may revolutionize the communication technologies around the globe. In this article, a status review of the smart applications of graphene in the IoT sector is presented. Firstly, various green synthesis of graphene for sustainable development is elucidated, followed by its applications in various nanosensors, detectors, actuators, memory, and nano-communication devices. Also, the future market prospects are discussed to converge various emerging concepts like machine learning, fog/edge computing, artificial intelligence, big data, and blockchain, with the graphene-assisted IoT field to bring about the concept of 'all-round connectivity in every sphere possible'.

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.

Graphene Quantum Dots-Based Electrochemical Biosensing Platform for Early Detection of Acute Myocardial Infarction

Heart failure resulting from acute myocardial infarction (AMI) is an important global health problem. Treatments of heart failure and AMI have improved significantly over the past two decades; however, the available diagnostic tests only give limited insights into these heterogeneous conditions at a reversible stage and are not precise enough to evaluate the status of the tissue at high risk. Innovative diagnostic tools for more accurate, more reliable, and early diagnosis of AMI are urgently needed. A promising solution is the timely identification of prognostic biomarkers, which is crucial for patients with AMI, as myocardial dysfunction and infarction lead to more severe and irreversible changes in the cardiovascular system over time. The currently available biomarkers for AMI detection include cardiac troponin I (cTnI), cardiac troponin T (cTnT), myoglobin, lactate dehydrogenase, C-reactive protein, and creatine kinase and myoglobin. Most recently, electrochemical biosensing technologies coupled with graphene quantum dots (GQDs) have emerged as a promising platform for the identification of troponin and myoglobin. The results suggest that GQDs-integrated electrochemical biosensors can provide useful prognostic information about AMI at an early, reversible, and potentially curable stage. GQDs offer several advantages over other nanomaterials that are used for the electrochemical detection of AMI such as strong interactions between cTnI and GQDs, low biomarker consumption, and reusability of the electrode; graphene-modified electrodes demonstrate excellent electrochemical responses due to the conductive nature of graphene and other features of GQDs (e.g., high specific surface area, π-π interactions with the analyte, facile electron-transfer mechanisms, size-dependent optical features, interplay between bandgap and photoluminescence, electrochemical luminescence emission capability, biocompatibility, and ease of functionalization). Other advantages include the presence of functional groups such as hydroxyl, carboxyl, carbonyl, and epoxide groups, which enhance the solubility and dispersibility of GQDs in a wide variety of solvents and biological media. In this perspective article, we consider the emerging knowledge regarding the early detection of AMI using GQDs-based electrochemical sensors and address the potential role of this sensing technology which might lead to more efficient care of patients with AMI.

A membraneless self-powered photoelectrochemical biosensor based on Bi2S3/BiPO4 heterojunction photoanode coupling with redox cycling signal amplification strategy

The photoelectrochemical (PEC) self-powered system has attracted great attention in disease detection. The determination of a simple and efficient approach for disease-related biomarkers is highly interesting and appealing. Herein, an ingenious visible light-induced membraneless self-powered PEC biosensing platform was constructed, integrating a signal amplification strategy for ultrasensitive split-type PEC bioanalysis. The system was comprised of a Bi₂S₃/BiPO₄ heterojunction photoanode and a platinum (Pt) cathode in a one compartment chamber. An alkaline phosphatase (ALP)-loaded sandwich immunoassay was used to generate the signal reporter ascorbic acid (AA) in a 96-well plate, and myoglobin (Myo) was used as a model protein. In the presence of AA, ferrocene (Fc), and Tris (2-carboxyethyl) phosphine (TCEP), the chemical-chemical redox cycling scheme was operated upon the initial oxidation of Fc by the holes in the Bi₂S₃/BiPO₄ photoelectrode, and Fc was regenerated from Fc⁺ by AA. Subsequently, AA was regenerated by TCEP after its oxidation, and cycling was triggered. As a result, the proposed self-powered PEC sensing exhibited excellent performance with a wide linear range from 5.0 × 10^-13 to 1.0 × 10^-7 g/mL, and a low detection limit of 2.0 × 10^-13 g/mL for Myo. This work provided a new design of a redox cycling strategy in the self-powered PEC biosensor, and showed an effective approach for the clinical diagnosis.

Application of Functionalized Graphene Oxide Based Biosensors for Health Monitoring: Simple Graphene Derivatives to 3D Printed Platforms

Biosensors hold great potential for revolutionizing personalized medicine and environmental monitoring. Their construction is the key factor which depends on either manufacturing techniques or robust sensing materials to improve efficacy of the device. Functional graphene is an attractive choice for transducing material due to its various advantages in interfacing with biorecognition elements. Graphene and its derivatives such as graphene oxide (GO) are thus being used extensively for biosensors for monitoring of diseases. In addition, graphene can be patterned to a variety of structures and is incorporated into biosensor devices such as microfluidic devices and electrochemical and plasmonic sensors. Among biosensing materials, GO is gaining much attention due to its easy synthesis process and patternable features, high functionality, and high electron transfer properties with a large surface area leading to sensitive point-of-use applications. Considering demand and recent challenges, this perspective review is an attempt to describe state-of-the-art biosensors based on functional graphene. Special emphasis is given to elucidating the mechanism of sensing while discussing different applications. Further, we describe the future prospects of functional GO-based biosensors for health care and environmental monitoring with a focus on additive manufacturing such as 3D printing.

Carbon nanomaterials for cardiovascular theranostics: Promises and challenges

Cardiovascular diseases (CVDs) are the leading cause of death worldwide. Heart attack and stroke cause irreversible tissue damage. The currently available treatment options are limited to "damage-control" rather than tissue repair. The recent advances in nanomaterials have offered novel approaches to restore tissue function after injury. In particular, carbon nanomaterials (CNMs) have shown significant promise to bridge the gap in clinical translation of biomaterial based therapies. This family of carbon allotropes (including graphenes, carbon nanotubes and fullerenes) have unique physiochemical properties, including exceptional mechanical strength, electrical conductivity, chemical behaviour, thermal stability and optical properties. These intrinsic properties make CNMs ideal materials for use in cardiovascular theranostics. This review is focused on recent efforts in the diagnosis and treatment of heart diseases using graphenes and carbon nanotubes. The first section introduces currently available derivatives of graphenes and carbon nanotubes and discusses some of the key characteristics of these materials. The second section covers their application in drug delivery, biosensors, tissue engineering and immunomodulation with a focus on cardiovascular applications. The final section discusses current shortcomings and limitations of CNMs in cardiovascular applications and reviews ongoing efforts to address these concerns and to bring CNMs from bench to bedside.

Simultaneous electrochemical determination of two hepatitis B antigens using graphene-SnO2 hybridized with sea urchin-like bimetallic nanoparticles

The hepatitis B virus (HBV) can cause chronic hepatitis and hepatocellular carcinoma. Hepatitis B surface antigen (HBs-Ag) and Hepatitis B e-antigen (HBe-Ag) are key markers for the diagnosis of HBV. In this study, electrodeposited gold was used as a sensing platform. Three-dimensional (3D) SnO₂-loaded graphene sheets functionalized by Thionine (Thi) and ferrocene (Fc) and hybridized by sea urchin-like bimetallic nanoparticles (GS-SnO₂-BMNPs) were used as redox probes for labeling antibodies to fabricate sandwich-type immunosensors for the simultaneous determination of HBs-Ag and HBe-Ag. The bimetallic nanoparticles, gold hybrid platinum nanoparticles (Au@Pt) and L-cysteine-connected gold-silver nanoparticles (Ag-cys-Au), have large electroactive surface areas. They were prepared by an efficient and economical method. Additionally, the sea urchin morphology accelerates spatial utilization, thus increasing the number of combination sites. Therefore, the immune probe can load a mass of signal source molecules (Thi and Fc). Furthermore, GS-SnO₂-BMNPs (GS-SnO₂-Au@Pt and GS-SnO₂-Ag-cys-Au) with excellent electrical conductivity and bimetallic synergy can enhance the square wave voltammetry (SWV) signal. SWV was used to record the electrochemical signal by scanning the potential from - 0.6 to 0.6 V (vs. SCE). The signal peaks resulted from the reduction reaction of Thi and Fc, and two signal peaks were completely separate. The peak position and current intensity reflect the identity and level of the corresponding antigens. Therefore, the simultaneous detection of two viral biomarkers was achieved by the proposed immunosensor. The fabricated immunosensor showed a linear concentration range for HBs-Ag (0.01-100 ng·mL^-1) and HBe-Ag (0.01-100 ng·mL^-1), with detection limits for HBs-Ag and HBe-Ag of  4.67 pg·mL^-1 and 4.68 pg·mL^-1, respectively.  The RSD of HBs-Ag ranged between 2.0 and 4.4%and the recovery was in the range 98.7 to 99.4%. For  HBe-Ag the RSD  was between 2.6 and 3.3% andrecoveries  in the range 99.2 to 100.5% were obtained.

Nanostructure-Based Electrochemical Immunosensors as Diagnostic Tools

Electrochemical immunosensors are affinity-based biosensors characterized by several useful features such as specificity, miniaturizability, low cost and simplicity, making them very interesting for many applications in several scientific fields. One of the significant issues in the design of electrochemical immunosensors is to increase the system’s sensitivity. Different strategies have been developed, one of the most common is the use of nanostructured materials as electrode materials, nanocarriers, electroactive or electrocatalytic nanotracers because of their abilities in signal amplification and biocompatibility. In this review, we will consider some of the most used nanostructures employed in the development of electrochemical immunosensors (e.g., metallic nanoparticles, graphene, carbon nanotubes) and many other still uncommon nanomaterials. Furthermore, their diagnostic applications in the last decade will be discussed, referring to two relevant issues of present-day: the detection of tumor markers and viruses.

Label-Free Bimetallic In Situ-Grown 3D Nickel-Foam-Supported NH2-MIL-88B(Fe2Co)-MOF-based Impedimetric Immunosensor for the Detection of Cardiac Troponin I

In this study, a simple and competent metal-organic framework (MOF)-based nickel foam (NF)-supported three-dimensional (3D) immunosensor (Ab-NH₂-MIL-88B(Fe₂Co)-MOF/NF) was constructed and utilized for the specific recognition of the biomarker cardiac troponin (I) (cTnI). In the present work, biosensor fabrication was progressed through the modification of the NF substrate with the MOF material (NH₂-MIL-88B(Fe₂Co)-MOF) to enable an amine-functionalized electrode. This amine-functionalized NF electrodes (NH₂-MIL-88B(Fe₂Co)-MOF/NF) were then biointerfaced with anti-cTnI antibodies, which ended up as Ab-NH₂-MIL-88B(Fe₂Co)-MOF/NF electrodes. Analytical executions of the constructed bioelectrode were investigated for the quantitative analysis of cTnI in both buffered and serum solutions. Then, the electrochemical studies were carried out using the electrochemical impedance spectroscopy (EIS) method by monitoring changes concerning the charge transfer resistance (R_ct) characteristics. The limit of detection (LOD) of the Ab-NH₂-MIL-88B(Fe₂Co)-MOF/NF immunosensor was achieved to be 13 fg/mL with great specificity. This kind of immunosensor imparts a new platform for the construction and application of MOF-hybrid 3D electrode materials with enhanced electrochemical behavior in cTnI sensing for the first time.

Recent Trends in Electrochemical Sensors for Vital Biomedical Markers Using Hybrid Nanostructured Materials

This work provides a succinct insight into the recent developments in electrochemical quantification of vital biomedical markers using hybrid metallic composite nanostructures. After a brief introduction to the biomarkers, five types of crucial biomarkers, which require timely and periodical monitoring, are shortlisted, namely, cancer, cardiac, inflammatory, diabetic and renal biomarkers. This review emphasizes the usage and advantages of hybrid nanostructured materials as the recognition matrices toward the detection of vital biomarkers. Different transduction methods (fluorescence, electrophoresis, chemiluminescence, electrochemiluminescence, surface plasmon resonance, surface-enhanced Raman spectroscopy) reported for the biomarkers are discussed comprehensively to present an overview of the current research works. Recent advancements in the electrochemical (amperometric, voltammetric, and impedimetric) sensor systems constructed with metal nanoparticle-derived hybrid composite nanostructures toward the selective detection of chosen vital biomarkers are specifically analyzed. It describes the challenges involved and the strategies reported for the development of selective, sensitive, and disposable electrochemical biosensors with the details of fabrication, functionalization, and applications of hybrid metallic composite nanostructures.

Label-Free, Highly Sensitive Electrochemical Aptasensors Using Polymer-Modified Reduced Graphene Oxide for Cardiac Biomarker Detection

Acute myocardial infarction (AMI), also recognized as a "heart attack," is one leading cause of death globally, and cardiac myoglobin (cMb), an important cardiac biomarker, is used for the early assessment of AMI. This paper presents an ultrasensitive, label-free electrochemical aptamer-based sensor (aptasensor) for cMb detection using polyethylenimine (PEI)-functionalized reduced graphene oxide (PEI-rGO) thin films. PEI, a cationic polymer, was used as a reducing agent for graphene oxide (GO), providing highly positive charges on the rGO surface and allowing direct immobilization of negatively charged single-strand DNA aptamers against cMb via electrostatic interaction without any linker or coupling chemistry. The presence of cMb was detected on Mb aptamer-modified electrodes using differential pulse voltammetry via measuring the current change due to the direct electron transfer between the electrodes and cMb proteins (Fe3+/Fe2+). The limits of detection were 0.97 pg mL-1 (phosphate-buffered saline) and 2.1 pg mL-1 (10-fold-diluted human serum), with a linear behavior with logarithmic cMb concentration. The specificity and reproducibility of the aptasensors were also examined. This electrochemical aptasensor using polymer-modified rGO shows potential for the early assessment of cMb in point-of-care testing applications.

Dual-modality microfluidic biosensor based on nanoengineered mesoporous graphene hydrogels

A dual-modality microfluidic biosensor is fabricated using a mesoporous nanostructured cysteine-graphene hydrogel for the quantification of human cardiac myoglobin (cMb). In this device, the nanoengineered mesoporous l-cysteine-graphene (Cys-RGO) hydrogel performs the role of a dual-modality sensing electrode for the measurements conducted using differential pulse voltammetry and surface plasmon resonance (SPR) techniques. High surface reactivity, mesoporous structure and fast electron transfer combined with good reaction kinetics of the graphene hydrogel in this device indicate excellent performance for the detection of human cardiac myoglobin in serum samples. In electrochemical modality, this microfluidic chip exhibits a high sensitivity of 196.66 μA ng^-1 mL cm^-2 for a linear range of concentrations (0.004-1000 ng mL^-1) with a low limit of detection (LOD) of 4 pg mL^-1 while the SPR technique shows a LOD of 10 pg mL^-1 for cMb monitoring in the range 0.01-1000 ng mL^-1. The intra-assay coefficient of variation was less than 8% for standard samples and 9% for real serum samples, respectively. This Cys-RGO hydrogel-based microfluidic SPR chip allows real-time dynamic tracking of cMb molecules with a high association constant of 4.93 ± 0.2 × 10⁵ M^-1 s^-1 and a dissociation constant of 1.37 ± 0.08 × 10^-4 s^-1, self-verification, reduced false readout, and improved detection reliability.

A potentiometric resolved photoelectrochemical system based on CdS nanowires and SnNb2O6 nanosheets: a case application for dual biomarker analysis

A potentiometric-resolved PEC immunosensor was developed for dual-target detection.

A Non-Enzymatic Sensor Based on Trimetallic Nanoalloy with Poly (Diallyldimethylammonium Chloride)-Capped Reduced Graphene Oxide for Dynamic Monitoring Hydrogen Peroxide Production by Cancerous Cells

Catching cancer at an early stage is necessary to make it easier to treat and to save people's lives rather than just extending them. Reactive oxygen species (ROS) have sparked a huge interest owing to their vital role in various biological processes, especially in tumorigenesis, thus leading to the potential of ROS as prognostic biomarkers for cancer. Herein, a non-enzymatic biosensor for the dynamic monitoring of intracellular hydrogen peroxide (H2O2), the most important ROS, via an effective electrode composed of poly (diallyldimethylammonium chloride) (PDDA)-capped reduced graphene oxide (RGO) nanosheets with high loading trimetallic AuPtAg nanoalloy, is proposed. The designed biosensor was able to measure H2O2 released from different cancerous cells promptly and precisely owing to the impressive conductivity of RGO and PDDA and the excellent synergistic effect of the ternary alloy in boosting the electrocatalytic activity. Built upon the peroxidase-like activity of the nanoalloy, the developed sensor exhibited distinguished electrochemical performance, resulting in a low detection limit of 1.2 nM and a wide linear range from 0.05 μM to 5.5 mM. Our approach offers a significant contribution toward the further elucidation of the role of ROS in carcinogenesis and the effective screening of cancer at an early stage.

Fluorometric determination of cardiac myoglobin based on energy transfer from a pyrene-labeled aptamer to graphene oxide

The authors describe a fluorometric assay for cardiac myoglobin (Mb), a marker for myocardial infarction. An Mb-binding aptamer was labeled with pyrene and adsorbed on the surface of graphene oxide (GO) via noncovalent and reversible binding forces. This causes the fluorescence of pyrene (best measured at excitation/emission wavelengths of 275/376 nm) to be quenched. However, fluorescence is restored on addition of pyrene due to the strong affinity between Mb and aptamer which causes its separation from GO. Fluorescence increases linearly in the 5.6-450 pM Mb concentration range, and the lower detection limit is 3.9 pM (S/N = 3). The assay was applied to the determination of cardiac Mb in spiked serum, and satisfactory results were obtained. Graphical abstract Schematic presentation of the detection of Mb (cardiac myoglobin) by using a fluorometric method based on pyrene-modified anti-Mb aptamer and GO (graphene oxide) through fluorescence quenching and subsequent recovery.

Pushing the limits of electrochemistry toward challenging applications in clinical diagnosis, prognosis, and therapeutic action

Constant progress in the identification of biomarkers at different molecular levels in samples of different natures, and the need to conduct routine analyses, even in limited-resource settings involving simple and short protocols, are examples of the growing current clinical demands not satisfied by conventional available techniques. In this context, the unique features offered by electrochemical biosensors, including affordability, real-time and reagentless monitoring, simple handling and portability, and versatility, make them especially interesting for adaptation to the increasingly challenging requirements of current clinical and point-of-care (POC) diagnostics. This has allowed the continuous development of strategies with improved performance in the clinical field that were unthinkable just a few years ago. After a brief introduction to the types and characteristics of clinically relevant biomarkers/samples, requirements for their analysis, and currently available methodologies, this review article provides a critical discussion of the most important developments and relevant applications involving electrochemical biosensors reported in the last five years in response to the demands of current diagnostic, prognostic, and therapeutic actions related to high prevalence and high mortality diseases and disorders. Special attention is paid to the rational design of surface chemistry and the use/modification of state-of-the-art nanomaterials to construct electrochemical bioscaffolds with antifouling properties that can be applied to the single or multiplex determination of biomarkers of accepted or emerging clinical relevance in particularly complex clinical samples, such as undiluted liquid biopsies, whole cells, and paraffin-embedded tissues, which have scarcely been explored using conventional techniques or electrochemical biosensing. Key points guiding future development, challenges to be addressed to further push the limits of electrochemical biosensors towards new challenging applications, and their introduction to the market are also discussed.

Cardiovascular therapies utilizing targeted delivery of nanomedicines and aptamers

Cardiovascular ailments are the foremost trigger of death in the world today, including myocardial infarction and ischemic heart diseases. To date, extraordinary measures have been prescribed, from the perspectives of both conventional medical therapies and surgeries, to enforce cardiac cell regeneration post cardiac traumas, albeit with limited long-term success. The prospects of successful heart transplants are also grim, considering exorbitant costs and unavailability of suitable donors in most cases. From the perspective of cardiac revascularization, use of nanoparticles and nanoparticle mediated targeted drug delivery have garnered substantial attention, attributing to both active and passive heart targeting, with enhanced target specificity and sensitivity. This review focuses on this aspect, while outlining the progress in targeted delivery of nanomedicines in the prognosis and subsequent therapy of cardiovascular disorders, and recapitulating the benefits and intrinsic challenges associated with the incorporation of nanoparticles. This article categorically provides an overview of nanoparticle-mediated targeted delivery systems and their implications in handling cardiovascular diseases, including their intrinsic benefits and encountered procedural trials and challenges. Additionally, the solicitations of aptamers in targeted drug delivery with identical objectives, are presented. This includes a detailed appraisal on various aptamer-navigated nanoparticle targeted delivery platforms in the diagnosis and treatment of cardiovascular maladies. Despite a few impending challenges, subject to additional investigations, both nanoparticles as well as aptamers show a high degree of promise, and pose as the next generation of drug delivery vehicles, in targeted cardiovascular therapy.

Recent advances in designing nanomaterial based biointerfaces for electrochemical biosensing cardiovascular biomarkers

Early diagnosis of cardiovascular disease (CVD) is critically important for successful treatment and recovery of patients. At present, detection of CVD at early stages of its progression becomes a major issue for world health. The nanoscale electrochemical biosensors exhibit diverse outstanding properties, rendering them extremely suitable for the determination of CVD biomarkers at very low concentrations in biological fluids. The unique advantages offered by electrochemical biosensors in terms of sensitivity and stability imparted by nanostructuring the electrode surface together with high affinity and selectivity of bioreceptors have led to the development of new electrochemical biosensing strategies that have introduced as interesting alternatives to conventional methodologies for clinical diagnostics of CVD. This review provides an updated overview of selected examples during the period 2005-2018 involving electrochemical biosensing approaches and signal amplification strategies based on nanomaterials, which have been applied for determination of CVD biomarkers. The studied CVD biomarkers include AXL receptor tyrosine kinase, apolipoproteins, cholesterol, C-reactive protein (CRP), D-dimer, fibrinogen (Fib), glucose, insulin, interleukins, lipoproteins, myoglobin, N-terminal pro-B-type natriuretic peptide (BNP), tumor necrosis factor alpha (TNF-α) and troponins (Tns) on electrochemical transduction format. Identification of new specific CVD biomarkers, multiplex bioassay for the simultaneous determination of biomarkers, emergence of microfluidic biosensors, real-time analysis of biomarkers and point of care validation with high sensitivity and selectivity are the major challenges for future research.

Recent progress on the sensitive detection of cardiovascular disease markers by electrochemical-based biosensors

Cardiovascular disease is the most reason for deaths in all over the world. Hence, biomarkers of cardiovascular diseases are very crucial for diagnosis and management process. Biomarker detection demand is opened the important way in biosensor development field. Rapid, cheap, portable, precise, selective and sensitive biomarker sensing devices are needed at this point to detect and predict disease. A cardiac biomarker can be orderable as C-reactive protein, troponin I or T, myoglobin, tumor necrosis factor alpha, interleukin-6, interleukin-1, lipoprotein-associated phospholipase, low-density lipoprotein and myeloperoxidase. They are used for prediction of cardiovascular diseases. There are many methods for early diagnosis of cardiovascular diseases, but these have long time process and expensive devices. In recent studies, different biosensors have been developed to remove the problems in this field. Electrochemical devices and developed biosensors have many superiorities than others such as low cost, mobile, reliable, repeatable, need a little amount of solution. In this review, recent studies were presented as details for cardiovascular disease biomarkers detection using electrochemical methods.

Photogenerated Hole-Induced Chemical Redox Cycling on Bi2S3/Bi2Sn2O7 Heterojunction: Toward General Amplified Split-Type Photoelectrochemical Immunoassay

This work reports the elegant bridging of enzymatic generation of electron donor with photogenerated hole-induced chemical redox cycling amplification (RCA) for innovative photoelectrochemical (PEC) immunoassay, by the aid of a heterojunction photoelectrode with split-type strategy. Specifically, the system was exemplified by the alkaline phosphatase (ALP) catalytic generation of ascorbic acid (AA), the redox cycling of AA by tris (2-carboxyethyl) phosphine (TCEP) as reductant, and the use of a novel Bi₂S₃/Bi₂Sn₂O₇ heterojunction and myoglobin (Myo) as the photoelectrode and the target, respectively. After the immunoreaction and ALP-induced production of AA, the subsequent oxidation of AA by the photogenerated holes of the Bi₂S₃/Bi₂Sn₂O₇ heterojunction could be cycled via the regeneration of AA by TCEP from the oxidized product of dehydroascorbic acid, leading to easy signal amplification for the sensitive immunoassay of Myo in real samples. It is believed that this work provided a basis for further design and development of general RCA-based PEC immunoassays.

Nanostructured aptamer-based sensing platform for highly sensitive recognition of myoglobin

A composite was prepared from PtSn nanoparticles and carbon nanotubes (PtSnNP/CNTs) and applied to the electrochemical determination of myoglobin (Mb). An Mb-aptamer was immobilized on a glassy carbon electrode (GCE), and hexcyanoferrate was used as an electrochemical probe. The PtSnNP/CNTs were synthesized by a microwave-aided ethylene glycol reduction method. Detection is based on electron transfer inhibition that is caused by the folding and conformational change of the Mb-aptamer in the presence of Mb. The amperometric signal for hexacyanoferrate, best measured at 0.2 V vs. Ag/AgCl depends on the concentration of Mb that interacts with the aptamer on the GCE. This approach is selective and sensitive for Mb due to (a) the highly specific recognition ability of the aptamer for Mb, (b) the powerful electronic properties of carbon nanotubes, (c) the arranged decoration of CNTs with PtSnNPs, and (d), the superior electron transfer to hexacyanoferrate. The assay is highly selective, with linear relationships from 0.01-1 nM and 10 nM-200 nM, and a limit of detection as low as 2.2 ± 0.1 pM. The modified GCE was applied to the quantitation of Mb in spiked human serum samples. Graphical abstract Schematic illustration of the method for Mb detection.

Enhanced Plasmonic Biosensors of Hybrid Gold Nanoparticle-Graphene Oxide-Based Label-Free Immunoassay

In this study, we propose a modified gold nanoparticle-graphene oxide sheet (AuNP-GO) nanocomposite to detect two different interactions between proteins and hybrid nanocomposites for use in biomedical applications. GO sheets have high bioaffinity, which facilitates the attachment of biomolecules to carboxyl groups and has led to its use in the development of sensing mechanisms. When GO sheets are decorated with AuNPs, they introduce localized surface plasmon resonance (LSPR) in the resonance energy transfer of spectral changes. Our results suggest a promising future for AuNP-GO-based label-free immunoassays to detect disease biomarkers and rapidly diagnose infectious diseases. The results showed the detection of antiBSA in 10 ng/ml of hCG non-specific interfering protein with dynamic responses ranging from 1.45 nM to 145 fM, and a LOD of 145 fM. Considering the wide range of potential applications of GO sheets as a host material for a variety of nanoparticles, the approach developed here may be beneficial for the future integration of nanoparticles with GO nanosheets for blood sensing. The excellent anti-interference characteristics allow for the use of the biosensor in clinical analysis and point-of-care testing (POCT) diagnostics of rapid immunoassay products, and it may also be a potential tool for the measurement of biomarkers in human serum.

Gold nanoparticle-decorated reduced-graphene oxide targeting anti hepatitis B virus core antigen

Hepatitis B virus core antigen (HBcAg) is the major structural protein of hepatitis B virus (HBV). The presence of anti-HBcAg antibody in a blood serum indicates that a person has been exposed to HBV. This study demonstrated that the immobilization of HBcAg onto the gold nanoparticles-decorated reduced graphene oxide (rGO-en-AuNPs) nanocomposite could be used as an antigen-functionalized surface to sense the presence of anti-HBcAg. The modified rGO-en-AuNPs/HBcAg was then allowed to undergo impedimetric detection of anti-HBcAg with anti-estradiol antibody and bovine serum albumin as the interferences. Upon successful detection of anti-HBcAg in spiked buffer samples, impedimetric detection of the antibody was then further carried out in spiked human serum samples. The electrochemical response showed a linear relationship between electron transfer resistance and the concentration of anti-HBcAg ranging from 3.91ngmL^-1 to 125.00ngmL^-1 with lowest limit of detection (LOD) of 3.80ngmL^-1 at 3σm^-1. This established method exhibits potential as a fast and convenient way to detect anti-HBcAg.

Electrochemical prostate specific antigen aptasensor based on hemin functionalized graphene-conjugated palladium nanocomposites

An electrochemical aptasensor is described for the detection of prostate specific antigen (PSA). The aptasensor is based on the use of hemin-functionalized graphene-conjugated palladium nanoparticles (H-Gr/PdNPs) deposited on a glassy carbon electrode. The nanocomposites integrate the high electrical conductivity of graphene with the easily functionalized surface chemistry of PdNPs and their excellent catalytic property. The hemin placed on graphene acts as both a protective agent and an in-situ redox probe. The PdNPs provide numerous binding sites for the immobilization of DNA-biotin via coordinative binding between Pd and amino groups. A sensitive and specific PSA assay was attained by immobilizing the PSA aptamer via biotin-streptavidin interaction. The resulting aptasensor has a linear response that covers the PSA concentration range from 0.025 to 205 ng·mL^-1, with a 8 pg·mL^-1 lower detection limit (at -0.362 V, scan rate: 0.1 mV·s^-1, S/N = 3). The method was applied to the quantitation of PSA in spiked serum samples, giving recoveries ranging from 95.0 to 100.3%. Graphical abstract A signal amplified and approving electrochemical aptasensor was constructed for the determination of prostate specific antigen (PSA) based on the use of hemin-functionalized graphene conjugated to palladium nanoparticles (H-Gr/PdNPs). The sensor has a wide linear range, a relatively low detection limit, satisfying stability and high specificity.

Tetrahedral DNA probe coupling with hybridization chain reaction for competitive thrombin aptasensor

A novel competitive aptasensor for thrombin detection is developed by using a tetrahedral DNA (T-DNA) probe and hybridization chain reaction (HCR) signal amplification. Sulfur and nitrogen co-doped reduced graphene oxide (SN-rGO) is firstly prepared by a simple reflux method and used for supporting substrate of biosensor. Then, T-DNA probe is modified on the electrode by Au-S bond and a competition is happened between target thrombin and the complementary DNA (cDNA) of aptamer. The aptamer binding to thrombin forms an aptamer-target conjugate and make the cDNA remained, and subsequently hybridizes with the vertical domain of T-DNA. Finally, the cDNAs trigger HCR, which results in a great current response by the catalysis of horseradish peroxidase to the hydrogen peroxide + hydroquinone system. For thrombin detection, the proposed biosensor shows a wide linearity range of 10^-13-10^-8M and a low detection limit of 11.6fM (S/N = 3), which is hopeful to apply in biotechnology and clinical diagnosis.

Liquid exfoliation of 2D MoS2 nanosheets and their utilization as a label-free electrochemical immunoassay for subclinical ketosis

We report the step-by-step fabrication of a 2D MoS₂ nanostructure-based disposable electrochemical immunosensor to detect β-hydroxybutyrate (βHBA), a novel subclinical ketosis biomarker. The MoS₂ nanosheets were exfoliated in the liquid phase by ultrasonication, and then followed by deposition on gold colloid modified screen-printed electrodes (Au-SPE). The MoS₂-modified electrodes were thoroughly characterized by physical, electrochemical as well as spectroscopic techniques, and the obtained results indicate the successful and irreversible electrodeposition of MoS₂ nanosheets. These MoS₂-modified disposable electrodes were subsequently bioconjugated with anti-βHBA antibodies and then employed for the label-free immunosensing of the βHBA biomarker to detect subclinical ketosis. A simple electrochemical Differential Pulse Voltammetry (DPV) technique based immunodetection was realized for the sensing of varying concentrations of βHBA antigen. The bioassay demonstrated remarkable sensitivity and specificity having a dynamic linear response range of 0.7 mM to 10 mM for βHBA in standard antigen solutions, spiked serum, blood, milk and clinical samples, with linear results being obtained with R² ∼ 0.9923. The sensor electrodes were also studied with other relative interferents to investigate cross reactivity and non-specificity. These electrodes showed a linear, specific, reproducible and stable response towards the βHBA antigen over a wide range of concentrations.