Electrochemical Impedance Analysis of Biofunctionalized Conducting Polymer-Modified Graphene-CNTs Nanocomposite for Protein Detection

A carbon quantum layer modified BiVO4 photoelectrochemical aptamer biosensor for ultra-sensitive cTnI biomarker detection based on the interface nephelauxetic effect and heterojunction assistance

The sensitivity and specificity of a semiconductor photoelectrochemical (PEC) aptamer biosensor are determined by the separation and transport of the photoinduced carriers as well as aptamer probe immobilization. In this study, an in situ thermal transformation organic polymer strategy was employed to produce an ∼2.5 nm carbon quantum layer on the surface of the BiVO4(BVO) photoanode. Experimental tests and theoretical calculations have revealed that this carbon quantum layer-coated BVO(C@BVO) heterostructure could generate surface charge depletion regions through an interface nephelauxetic effect. These charge depletion regions facilitated the efficient immobilization of DNA aptamer probes of the acute myocardial infarction biomarker cardiac troponin I (cTnI), while showing almost no immobilization capability on a pure-phase C quantum layer or BVO crystals. Simultaneously, the formation of the C@BVO heterostructure also enhanced the directional transport of photo-generated holes from BVO to the C quantum layer. Due to the above reasons, the C@BVO PEC aptamer biosensor achieved a linear detection range for cTnI from 10-14 g L-1 to 10-10 g L-1, with a record detection limit (LOD) of ∼0.33 × 10-14 g L-1 (N > 3). Meanwhile, the biosensor also demonstrated well the detection reproducibility and specificity for cTnI detection. Therefore, the strategy of using a carbon quantum layer-coated PEC electrode shows good potential to develop PEC biosensors with high sensitivity, specificity, and robustness.

Electrochemical impedance-based biosensor for label-free determination of plasma P-tau181 levels for clinically accurate diagnosis of mild cognitive impairment and Alzheimer's disease

Plasma phosphorylated-tau threonine 181 (p-tau181) is a promising biomarker for predicting Alzheimer's disease (AD) and mild cognitive impairment (MCI), which is the symptomatic pre-dementia stage of AD. To date, there are limitations in the current diagnosis and classification of the two stages of MCI and AD in clinical practice remain a dilemma. In this study, we aimed to discriminate and diagnose patients with MCI, AD, and healthy participants based on the accurate, label-free, and ultrasensitive detection of p-tau181 levels in human clinical plasma samples using our developed electrochemical impedance-based biosensor, which allows to detect p-tau181 at a very low concentration of 0.92 fg mL^-1. Human plasma samples were collected from 20 patients with AD, 20 patients with MCI, and 20 individuals with healthy control. The change in charge-transfer resistance of the developed impedance-based biosensor caused by capturing p-tau181 in plasma samples was recorded to evaluate the determination of plasma p-tau181 levels in human clinical samples for discrimination and diagnosis of AD, MCI, and healthy control individuals, respectively. Receiver operating characteristic (ROC) curve, a standard analysis to judge the clinically diagnostic capability of our biosensor platform based on the estimated levels of plasma p-tau181, resulted a sensitivity of 95%, a specificity of 85%, the area under the ROC curve (AUC) value of 0.94 of the accuracy for discriminating AD patients from healthy controls; a sensitivity of 70%, a specificity of 70%, the AUC of 0.75 to discriminate MCI patients from healthy controls. Statistical analysis (one-way analysis of variance (ANOVA)) was used to compare the estimated plasma p-tau181 levels in clinical samples, indicated significantly higher for AD patients with healthy controls (***p ≤ 0.001), AD with MCI patients (***p ≤ 0.001), and MCI patients with healthy controls (*p ≤ 0.05), respectively. In addition, we compared our sensor to the global cognitive function scales and discovered that it performed noticeably improvement in diagnosing the stages of AD. These results demonstrated the good application of our developed electrochemical impedance-based biosensor in the identification of clinical disease stages. Moreover, in this study, a small dissociation constant (K_D) of 0.533 pM was first determined to evaluate the high binding affinity between the p-tau181 biomarker and its antibody, providing a reference parameter for future studies of the p-tau181 biomarker and AD.

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.

A portable analog front-end system for label-free sensing of proteins using nanowell array impedance sensors

Proteins are useful biomarkers for a wide range of applications such as cancer detection, discovery of vaccines, and determining exposure to viruses and pathogens. Here, we present a low-noise front-end analog circuit interface towards development of a portable readout system for the label-free sensing of proteins using Nanowell array impedance sensing with a form factor of approximately 35cm². The electronic interface consists of a low-noise lock-in amplifier enabling reliable detection of changes in impedance as low as 0.1% and thus detection of proteins down to the picoMolar level. The sensitivity of our system is comparable to that of a commercial bench-top impedance spectroscope when using the same sensors. The aim of this work is to demonstrate the potential of using impedance sensing as a portable, low-cost, and reliable method of detecting proteins, thus inching us closer to a Point-of-Care (POC) personalized health monitoring system. We have demonstrated the utility of our system to detect antibodies at various concentrations and protein (45 pM IL-6) in PBS, however, our system has the capability to be used for assaying various biomarkers including proteins, cytokines, virus molecules and antibodies in a portable setting.

Molecularly imprinted polymers via reversible addition-fragmentation chain-transfer synthesis in sensing and environmental applications

Molecularly imprinted polymers (MIP) have shown their potential as artificial and selective receptors for environmental monitoring. These materials can be tailor-made to achieve a specific binding event with a template through a chosen mechanism. They are capable of emulating the recognition capacity of biological receptors with superior stability and versatility of integration in sensing platforms. Commonly, these polymers are produced by traditional free radical bulk polymerization (FRP) which may not be the most suitable for enhancing the intended properties due to the poor imprinting performance. To improve the imprinting technique and the polymer capabilities, controlled/living radical polymerization (CRP) has been used to overcome the main drawbacks of FRP. Combining CRP techniques such as RAFT (reversible addition-fragmentation chain transfer) with MIP has achieved higher selectivity, sensitivity, and sorption capacity of these polymers when implemented as the transductor element in sensors. The present work focuses on RAFT-MIP design and synthesis strategies to enhance the binding affinities and their implementation in environmental contaminant sensing applications.

Sensitive impedimetric detection of troponin I with metal-organic framework composite electrode

Metal-organic frameworks (MOFs) are promising materials for biosensing applications due to their large surface to volume ratio, easy assembly as thin films, and better biocompatibility than other nanomaterials. Their application in electrochemical biosensing devices can be realized by integrating them with other conducting materials, like polyaniline (PANI). In the present research, a composite of a copper-MOF (i.e., Cu3(BTC)2) with PANI has been explored to develop an impedimetric sensor for cardiac marker troponin I (cTnI). The solvothermally synthesized Cu3(BTC)2/PANI composite has been coated as a thin layer on the screen-printed carbon electrodes (SPE). This electroconductive thin film was conjugated with anti-cTnI antibodies. The above formed immunosensor has allowed the impedimetric detection of cTnI antigen over a clinically important concentration range of 1-400 ng mL-1. The whole process of antigen analysis could be completed within 5 min. The detection method was specific to cTnI even in the co-presence of other possibly interfering proteins.

α-MoO3 nanostructure on carbon cloth substrate for dopamine detection

Orthorhombic molybdenum oxide (α-MoO₃) nanostructures were deposited on the surface of carbon cloth (CC) as a flexible and high conductive scaffold by reactive RF magnetron sputtering technique. Structure and morphology of the as prepared molybdenum coated carbon cloth (MoO₃CC) were thoroughly characterized with field emission scanning electron microscopy, x-ray diffraction, energy dispersive x-ray and Raman spectroscopy. Benefiting from high surface area and superior conductivity of CC as well as electrocatalytic activity of α-MoO₃ nanostructures, an electrochemical sensor was fabricated. The electrochemical behavior of this new sensor toward determination of dopamine was studied in detail by cyclic voltammetry, amperometry (AM) and square wave voltammetry (SWV). Results reported here reveal that using SWV not only enhances the sensitivity of sensors to dopamine by more than 14 times compared to AM, but also offers higher linear dynamic range (1-700 μM compared to 5-550 μM). Limit of detection, for signal to noise ratio 3, was calculated to be 0.48 μM. Applicability of the proposed sensor for measurement of dopamine in real samples, like urine and pharmaceutical formulation, was also evaluated that concluded to satisfactory results.

Point-of-Care Compatibility of Ultra-Sensitive Detection Techniques for the Cardiac Biomarker Troponin I-Challenges and Potential Value

Cardiac biomarkers are frequently measured to provide guidance on the well-being of a patient in relation to cardiac health with many assays having been developed and widely utilised in clinical assessment. Effectively treating and managing cardiovascular disease (CVD) relies on swiftly responding to signs of cardiac symptoms, thus providing a basis for enhanced patient management and an overall better health outcome. Ultra-sensitive cardiac biomarker detection techniques play a pivotal role in improving the diagnostic capacity of an assay and thus enabling a better-informed decision. However, currently, the typical approach taken within healthcare depends on centralised laboratories performing analysis of cardiac biomarkers, thus restricting the roll-out of rapid diagnostics. Point-of-care testing (POCT) involves conducting the diagnostic test in the presence of the patient, with a short turnaround time, requiring small sample volumes without compromising the sensitivity of the assay. This technology is ideal for combatting CVD, thus the formulation of ultra-sensitive assays and the design of biosensors will be critically evaluated, focusing on the feasibility of these techniques for point-of-care (POC) integration. Moreover, there are several key factors, which in combination, contribute to the development of ultra-sensitive techniques, namely the incorporation of nanomaterials for sensitivity enhancement and manipulation of labelling methods. This review will explore the latest developments in cardiac biomarker detection, primarily focusing on the detection of cardiac troponin I (cTnI). Highly sensitive detection of cTnI is of paramount importance regarding the rapid rule-in/rule-out of acute myocardial infarction (AMI). Thus the challenges encountered during cTnI measurements are outlined in detail to assist in demonstrating the drawbacks of current commercial assays and the obstructions to standardisation. Furthermore, the added benefits of introducing multi-biomarker panels are reviewed, several key biomarkers are evaluated and the analytical benefits provided by multimarkers-based methods are highlighted.

Recent Progress in the Development of Conducting Polymer-Based Nanocomposites for Electrochemical Biosensors Applications: A Mini-Review

Among various immobilizing materials, conductive polymer-based nanocomposites have been widely applied to fabricate the biosensors, because of their outstanding properties such as excellent electrocatalytic activity, high conductivity, and strong adsorptive ability compared to conventional conductive polymers. Electrochemical biosensors have played a significant role in delivering the diagnostic information and therapy monitoring in a rapid, simple, and low cost portable device. This paper reviews the recent developments in conductive polymer-based nanocomposites and their applications in electrochemical biosensors. The article starts with a general and concise comparison between the properties of conducting polymers and conducting polymer nanocomposites. Next, the current applications of conductive polymer-based nanocomposites of some important conducting polymers such as PANI, PPy, and PEDOT in enzymatic and nonenzymatic electrochemical biosensors are overviewed. This review article covers an 8-year period beginning in 2010.