SAM-Support-Based Electrochemical Sensor for Aß Biomarker Detection of Alzheimer's Disease.

Alzheimer's disease has taken the spotlight as a neurodegenerative disease which has caused crucial issues to both society and the economy. Specifically, aging populations in developed countries face an increasingly serious problem due to the increasing budget for patient care and an inadequate labor force, and therefore a solution is urgently needed. Recently, diverse techniques for the detection of Alzheimer's biomarkers have been researched and developed to support early diagnosis and treatment. Among them, electrochemical biosensors and electrode modification proved their effectiveness in the detection of the Aß biomarker at appropriately low concentrations for practice and point-of-care application. This review discusses the production and detection ability of amyloid beta, an Alzheimer's biomarker, by electrochemical biosensors with SAM support for antibody conjugation. In addition, future perspectives on SAM for the improvement of electrochemical biosensors are also proposed and discussed.

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 (KD) 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.

Using Nanomaterials for SARS-CoV-2 Sensing via Electrochemical Techniques.

Advancing low-cost and user-friendly innovations to benefit public health is an important task of scientific and engineering research. According to the World Health Organization (WHO), electrochemical sensors are being developed for low-cost SARS-CoV-2 diagnosis, particularly in resource-limited settings. Nanostructures with sizes ranging from 10 nm to a few micrometers could deliver optimum electrochemical behavior (e.g., quick response, compact size, sensitivity and selectivity, and portability), providing an excellent alternative to the existing techniques. Therefore, nanostructures, such as metal, 1D, and 2D materials, have been successfully applied in in vitro and in vivo detection of a wide range of infectious diseases, particularly SARS-CoV-2. Electrochemical detection methods reduce the cost of electrodes, provide analytical ability to detect targets with a wide variety of nanomaterials, and are an essential strategy in biomarker sensing as they can rapidly, sensitively, and selectively detect SARS-CoV-2. The current studies in this area provide fundamental knowledge of electrochemical techniques for future applications.

Sensitive Electrochemical Non-Enzymatic Detection of Glucose Based on Wireless Data Transmission.

Miniaturization and wireless continuous glucose monitoring are key factors for the successful management of diabetes. Electrochemical sensors are very versatile and can be easily miniaturized for wireless glucose monitoring. The authors report a microneedle-based enzyme-free electrochemical wireless sensor for painless and continuous glucose monitoring. The microneedles (MNs) fabricated consist of a 3 × 5 sharp and stainless-steel electrode array configuration. Each MN in the 3 × 5 array has 575 µm × 150 µm in height and width, respectively. A glucose-catalyzing layer, porous platinum black, was electrochemically deposited on the tips of the MNs by applying a fixed cathodic current of 2.5 mA cm-2 for a period of 200 s. For the non-interference glucose sensing, the platinum (Pt)-black-coated MN was carefully packaged into a biocompatible ionomer, nafion. The surface morphologies of the bare and modified MNs were studied using field-emission scanning electron microscopy (FESEM) and energy-dispersive X-ray analysis (EDX). The wireless glucose sensor displayed a broad linear range of glucose (1→30 mM), a good sensitivity and higher detection limit of 145.33 µA mM-1 cm-2 and 480 µM, respectively, with bare AuMN as a counter electrode. However, the wireless device showed an improved sensitivity and enhanced detection limit of 445.75, 165.83 µA mM-1 cm-2 and 268 µM, respectively, with the Pt-black-modified MN as a counter electrode. The sensor also exhibited a very good response time (2 s) and a limited interference effect on the detection of glucose in the presence of other electroactive oxidizing species, indicating a very fast and interference-free chronoamperometric response.

Removal of Thiol-SAM on a Gold Surface for Re-Use of an Interdigitated Chain-Shaped Electrode.

The self-assembled monolayer (SAM) is the most common organic assembly utilized for the formation of the monolayers of alkane-thiolates on gold electrode, resulting in a wide range of applications for the modified SAM on gold in various research areas. This study examined the desorption of a SAM that was developed on the gold surface of an interdigitated chain-shaped electrode (the ICE, a unique electrode design, was fabricated by our group) with the goal of determining the most efficient strategy of SAM removal for the ICE to be re-used. A simple and proficient solution-based cleaning procedure was applied for the removal of a SAM on the gold surface of the ICE by using a sodium borohydride solution within short-term treatment, resulting in efficiency for the recovery of the originally electrochemical characteristic of ICE of 90.3%. The re-use of ICE after the removal process was confirmed by the successful re-deposition of a SAM onto the electrode surface, resulting in the high efficiency percentage of 90.1% for the reusability of ICE with the SAM modification. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used as tools to investigate the changes in the electrode interface at each stage of the SAM removal and the electrode recycling. X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy were employed, being powerful spectrum techniques, for the characterization of the bonding structure and chemical state of the bare ICE and the modified ICE at each treatment step. Based on the comprehensive discussion of analytical chemistry from the obtained EIS and CV data in this study, we confirmed and proved the effectiveness of this promising method for the removal of a SAM from the ICE and the re-use of ICE in the field of material deposition, with the aims of saving money, improving experimental handling, and protecting the environment.

Ultrasensitive capacitance sensor to detect amyloid-beta 1-40 in human serum using supramolecular recognition of ß-CD/RGO/ITO micro-disk electrode.

In this paper, we developed a new ultrasensitive capacitance sensor for detection of amyloid beta 1-40 (aß40) protein (one of Alzheimer's disease core biomarkers) in human serum based on the high supramolecular recognition of the ß-cyclodextrin/reduced graphene oxide (ß-CD/RGO) nanohybrid toward the anti-aß40 antibody molecule. The sensor was established by immobilizing specific anti-aß40 antibody onto the ß-CD/RGO nanohybrid functionalized on indium tin oxide micro-disk electrode (anti-aß40/ß-CD/RGO/ITO). Detection of aß40 in the human serum (HS) using the sensor anti-aß40/ß-CD/RGO/ITO is carried out by capacitance measurement without a redox probe to prevent protein denaturation, serving as a convenient strategy for point-of-care diagnosis. In comparison with other studies, the sensor shows a very low limit of detection of 0.69 fg mL-1 in HS, demonstrating its ability for the ultrasensitive detection of aß40. Using this sensor, the dissociation constant KD of the binding interaction between anti-aß40 and aß40 in HS is found to be 2.9 × 10-7 nM, indicating the high binding affinity of antibody-antigen and the suitability of the anti-aß40/ß-CD/RGO/ITO sensor for aß40 protein detection. The good selectivity of the anti-aß40/ß-CD/RGO/ITO sensor in the presence of differential analytes was also performed in this paper.

Nanomaterial-based Optical and Electrochemical Biosensors for Amyloid beta and Tau: Potential for early diagnosis of Alzheimer's Disease.

INTRODUCTION: Alzheimer's disease (AD), a heterogeneous pathological process representing the most common causes of dementia worldwide, has required early and accurate diagnostic tools. Neuropathological hallmarks of AD involve the aberrant accumulation of Amyloid beta (Aß) into Amyloid plaques and hyperphosphorylated Tau into neurofibrillary tangles, occurring long before the onset of brain dysfunction.Areas covered:Considering the significance of Aß and Tau in AD pathogenesis, these proteins have been adopted as core biomarkers of AD, and their quantification has provided precise diagnostic information to develop next-generation AD therapeutic approaches. However, conventional diagnostic methods may not suffice to achieve clinical criteria that are acceptable for proper diagnosis and treatment. The advantages of nanomaterial-based biosensors including facile miniaturization, mass fabrication, ultra-sensitivity, make them useful to be promising tools to measure Aß and Tau simultaneously for accurate validation of low-abundance yet potentially informative biomarkers of AD.. EXPERT OPINION: The study has identified the potential application of advanced biosensors as standardized clinical diagnostic tools for AD, evolving the way for new and efficient AD control with minimum economic and social burden. After clinical trial, nanobiosensors for measuring Aß and Tau simultaneously possess innovative diagnosis of AD to provide significant contributions to primary Alzheimer's care intervention.

Deciphering the Disaggregation Mechanism of Amyloid Beta Aggregate by 4-(2-Hydroxyethyl)-1-Piperazinepropanesulfonic Acid Using Electrochemical Impedance Spectroscopy.

Aggregation of amyloid-ß (aß) peptides into toxic oligomers, fibrils, and plaques is central in the molecular pathogenesis of Alzheimer's disease (AD) and is the primary focus of AD diagnostics. Disaggregation or elimination of toxic aß aggregates in patients is important for delaying the progression of neurodegenerative disorders in AD. Recently, 4-(2-hydroxyethyl)-1-piperazinepropanesulfonic acid (EPPS) was introduced as a chemical agent that binds with toxic aß aggregates and transforms them into monomers to reduce the negative effects of aß aggregates in the brain. However, the mechanism of aß disaggregation by EPPS has not yet been completely clarified. In this study, an electrochemical impedimetric immunosensor for aß diagnostics was developed by immobilizing a specific anti-amyloid-ß (aß) antibody onto a self-assembled monolayer functionalized with a new interdigitated chain-shaped electrode (anti-aß/SAM/ICE). To investigate the ability of EPPS in recognizing AD by extricating aß aggregation, commercially available aß aggregates (aßagg) were used. Electrochemical impedance spectroscopy was used to probe the changes in charge transfer resistance (Rct) of the immunosensor after the specific binding of biosensor with aßagg. The subsequent incubation of the aßagg complex with a specific concentration of EPPS at different time intervals divulged AD progression. The decline in the Rct of the immunosensor started at 10 min of EPPS incubation and continued to decrease gradually from 20 min, indicating that the accumulation of aßagg on the surface of the anti-aß/SAM/ICE sensor has been extricated. Here, the kinetic disaggregation rate k value of aßagg was found to be 0.038. This innovative study using electrochemical measurement to investigate the mechanism of aßagg disaggregation by EPPS could provide a new perspective in monitoring the disaggregation periods of aßagg from oligomeric to monomeric form, and then support for the prediction and handling AD symptoms at different stages after treatment by a drug, EPPS.

Sensitive Electrochemical Detection of Phosphorylated-Tau Threonine 231 in Human Serum Using Interdigitated Wave-Shaped Electrode.

The development of an electrochemical biosensor for the detection of phosphorylated-tau threonine 231 (p-tau231), a biomarker of Alzheimer's disease (AD), has yet to be achieved. Therefore, in this study, we developed a simple, small size, cheap, and sensitive electrochemical biosensor based on an interdigitated wave-shaped electrode via an activated self-assembled monolayer to preserve a specific anti-p-tau231 antibody (IWE/SAM/EDC-NHS/anti-p-tau231). Detection of p-tau231 in human serum (HS) using the biosensor was undertaken using electrochemical impedance spectroscopy (EIS). The change in charge-transfer resistance (Rct) in the EIS analysis of the biosensor indicated the detection of p-tau231 in HS within a wide linear range of detection (10-4-101 ng mL-1), and a low limit of detection (140 pg mL-1). This lower limit is less than the detection level of p-tau231 in cerebrospinal fluid (CSF) (700 pg mL-1) of AD patients and the level of CSF p-tau231 of patients with mild cognitive impairment (501 pg mL-1), demonstrating the possibility of using the biosensor in detection of p-tau231 at early stage AD. A high binding affinity and low dissociation constant (Kd) between anti-p-tau231 and p-tau231 in HS was demonstrated by using a biosensor and Kd was 7.6 pM, demonstrating the high specific detection of p-tau231 by the biosensor. The good selectivity of the biosensor for the detection of p-tau231 with differential analytes was also examined in this study.

A Probeless Capacitive Biosensor for Direct Detection of Amyloid Beta 1-42 in Human Serum Based on an Interdigitated Chain-Shaped Electrode.

Amyloid beta (aß) 1-42, a peptide that is 1-42 amino acids long, is a major component of senile plaques in the brains of patients with Alzheimer's disease. Aß detection has become an essential antecedence to predict the declining mental abilities of patients. In this paper, a probeless capacitive biosensor for the non-Faradaic detection of aß 1-42 peptide was developed by immobilizing a specific anti-aß antibody onto a self-assembled monolayer functionalized interdigitated chain-shaped electrode (anti-aß/SAM/ICE). The novelty and difference of this article from previous studies is the direct detection of aß peptide with no redox probe ((Fe(CN)6)3-/4-), which can avoid the denaturation of the protein caused by the metallization (binding of aß to metal ion Fe which is presented in the redox couple). The direct detection of aß with no redox probe is performed by non-Faradaic capacitive measurement, which is greatly different from the Faradaic measurement of the charge transfer resistance of the redox probe. The detection of various aß 1-42 peptide concentrations in human serum (HS) was performed by measuring the relative change in electrode interfacial capacitance due to the specific antibody-aß binding. Capacitance change in the anti-aß/SAM/ICE biosensor showed a linear detection range between 10 pg mL-1 and 104 pg mL-1, and a detection limit of 7.5 pg mL-1 in HS, which was much lower than the limit of detection for CSF aß 1-42 (~500 pg mL-1) and other biosensors. The small dissociation constant Kd of the antibody-antigen interaction was also found to be 0.016 nM in HS, indicating the high binding affinity of the anti-aß/SAM/ICE biosensor in the recognizing of aß 1-42. Thus, the developed sensor can be used for label-free and direct measurement of aß 1-42 peptide and for point-of-care diagnosis of Alzheimer's disease without redox probe.