Electrochemical impedance spectroscopy analysis of A-beta (1-42) peptide using a nanostructured biochip

Combining WO3@AuNPs with Poly(amidoamine) Allows Sensitive Electrochemical Detection of DR1 Based on Dual Signal Amplification

Down-regulator of transcription 1 (DR1) is considered as a biomarker of hashimoto's thyroiditis (HT), which is a risk factor for thyroid cancer. Here, a label-free electrochemical biosensor for DR1 detection was constructed based on polyamidoamine (PAMAM) polymer and the nanocomposite (WO3@AuNPs) composed of tungsten trioxide (WO3) and gold nanoparticles (AuNPs). WO3@AuNPs was obtained by combining monolayer WO3 nanosheets, which has high conductivity, and AuNPs. The modification of WO3@AuNPs can not only increase the conductivity of the electrode but also provide more active sites for signaling units, thus greatly improve the sensitivity of the sensor. The polymer PAMAM is biocompatible and non-immunogenic, and its end functional group can bind to the target molecules, providing them with more binding sites and thus improving the sensitivity of the sensor. Under optimal conditions, the label-free biosensor showed a good linear relationship between the logarithm of DR1 concentration and the impedance in the range of 10 fg ⋅ mL-1 to 100 ng ⋅ mL-1, with a detection limit as low as 0.3 fg ⋅ mL-1. Besides, this label-free electrochemical platform exhibited satisfactory selectivity and anti-interference capability in human serum samples. Therefore, this method has considerable potential in clinical detection of DR1.

A new ITO-based Aβ42 biosensor for early detection of Alzheimer's disease

In this study, a novel label-free impedimetric immunosensor was fabricated for rapid, selective, and sensitive quantitative analysis of Aβ₄₂ protein for use in the diagnosis of Alzheimer's disease. The immunosensor was fabricated using inexpensive and disposable indium tin oxide polyethylene terephthalate (ITO-PET) electrodes. After the electrodes were modified with 3-glycidoxypropyldimethoxymethylsilane (GPDMMS), the antibody specific to the Aβ₄₂ protein (anti-Aβ₄₂) was immobilized. The affinity interaction between anti-Aβ₄₂ and Aβ₄₂ in the immobilization steps in immunosensor fabrication and in the quantitation of Aβ₄₂ were analyzed using Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV) techniques. Additionally, the morphological changes occurring on the electrode surface during each immobilization step were imaged using scanning electron microscopy (SEM). The linear detection range of the immunosensor was determined as 1-100 pg/mL with the limit of detection value of 0.37 pg/mL. Analytical properties of the biosensor, including reproducibility, repeatability, storage stability, selectivity, and regeneration were investigated. The kinetic behavior of antibody-antigen complex formation was determined for the first time using single frequency impedance (SFI) analysis on an Aβ₄₂ biosensor. The potential for use of the immunosensor in clinical studies was demonstrated by analysis of Aβ₄₂ in commercially purchased human serum.

SiC Electrochemical Sensor Validation for Alzheimer Aβ42 Antigen Detection

Alzheimer's disease (AD) is a neurodegenerative disease with only late-stage detection; thus, diagnosis is made when it is no longer possible to treat the disease, only its symptoms. Consequently, this often leads to caregivers who are the patient's relatives, which adversely impacts the workforce along with severely diminishing the quality of life for all involved. It is, therefore, highly desirable to develop a fast, effective and reliable sensor to enable early-stage detection in an attempt to reverse disease progression. This research validates the detection of amyloid-beta 42 (Aβ₄₂) using a Silicon Carbide (SiC) electrode, a fact that is unprecedented in the literature. Aβ₄₂ is considered a reliable biomarker for AD detection, as reported in previous studies. To validate the detection with a SiC-based electrochemical sensor, a gold (Au) electrode-based electrochemical sensor was used as a control. The same cleaning, functionalization and Aβ_1-28 antibody immobilization steps were used on both electrodes. Sensor validation was carried out by means of Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) aiming to detect an 0.5 µg·mL^-1 Aβ₄₂ concentration in 0.1 M buffer solution as a proof of concept. A repeatable peak directly related to the presence of Aβ₄₂ was observed, indicating that a fast SiC-based electrochemical sensor was constructed and may prove to be a useful approach for the early detection of AD.

Application of aminobenzoic acid electrodeposited screen-printed carbon electrode in the beta-amyloid electrochemical impedance spectroscopy immunoassay

Alzheimer's disease (AD) is one of the important neurodegenerative diseases, in the modern aging society, it has become an issue people need to work on. Of the pathogenic factor which leads to AD, beta-amyloid (Aβ) is the most important one. It can form the senile plaque which aggregates in the neuron and interrupts the signal transmission. This research is based on the electrochemical system and screen-printed carbon electrode (SPCE) incorporated with pretreatment, electrodeposition, electrochemical impedance spectroscopy (EIS), antibody, and blocking agent. This immunosensor is applied to detect the different concentrations of Aβ. The standard curve between electrical impedance and concentration of Aβ is calculated. The specificity of the immunosensor is tested. This survey optimizes the electrodeposition condition for 4-aminobenzoic acid (4-ABA) and the parameter for antibody and blocking agents. This study fabricates a more dense, uniform, and stable film of 4-ABA. This sensor presents a range of detection from 1 fg/ml to 100 pg/ml and a limit of detection to 3.84 fg/ml. This sensor can identify the isoform of Aβ. This research shortens the fabricating time to 3.5 h. This study fabricates a label-free and low-cost immunosensor for Aβ with a short fabricating time, high stability, wide range of detection, low limit of detection, and good specificity. The impedance of the carbon printed electrodes is very high and is always measured by its current but this study provides a fabrication technique for high-efficiency carbon printed electrodes for electrochemical impedance spectroscopy sensing.

Label-free electrochemical immunosensor for picomolar detection of the cervical cancer biomarker MCM5

An immunosensor for label-free electrochemical detection of MiniChromosome Maintenance Protein 5, MCM5, a protein overexpressed in cervical cancer, based on a gold electrode is reported. The electrode was first modified with a submonolayer (capture layer) of 11-mercaptoundecanoic acid (11-MUA) and then activated with N-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) to immobilize the capture antibody. The change in electrode surface properties (wettability) during the formation of the 11-MUA layers was determined using the static water contact angle (WCA). The binding of MCM5 antigens to the capture antibody was monitored by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) using 5 mM [Fe(CN)⁶]^3-/4- in 0.1 M LiClO₄(aq) as an electroactive probe. AC Impedance was used to measure charge transfer resistance (R_ct), which reflects impeded electron transfer when the antigen is bound to the antibody functionalized surface. After exposing the antibody-functionalized surface to MCM5 antigens, R_ct increases linearly with the logarithmic value of MCM5 antigen concentration, with a linear dynamic range of 10^-6 to 10^-11 g/mL, a correlation coefficient of 0.99, and a detection limit of 2.9 pM (10^-11 g/mL). This excellent sensitivity was achieved with simple preparation steps and minimal reagent consumption, without the need for complicated procedures such as enzymatic amplification, fluorescent labeling, or nanoparticle modification.

Potentiometric Biosensor Based on Artificial Antibodies for an Alzheimer Biomarker Detection

This paper presents a potentiometric biosensor for the detection of amyloid β-42 (Aβ-42) in point-of-care analysis. This approach is based on the molecular imprint polymer (MIP) technique, which uses covalently immobilised Aβ-42 to create specific detection cavities on the surface of single-walled carbon nanotubes (SWCNTs). The biosensor was prepared by binding Aβ-42 to the SWCNT surface and then imprinting it by adding acrylamide (monomer), N,N’-methylene-bis-acrylamide (crosslinker) and ammonium persulphate (initiator). The target peptide was removed from the polymer matrix by the proteolytic action of an enzyme (proteinase K). The presence of imprinting sites was confirmed by comparing a MIP-modified surface with a negative control (NIP) consisting of a similar material where the target molecule had been removed from the process. The ability of the sensing material to rebind Aβ-42 was demonstrated by incorporating the MIP material as an electroactive compound in a PVC/plasticiser mixture applied to a solid conductive support of graphite. All steps of the synthesis of the imprinted materials were followed by Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). The analytical performance was evaluated by potentiometric transduction, and the MIP material showed cationic slopes of 75 mV-decade−1 in buffer pH 8.0 and a detection limit of 0.72 μg/mL. Overall, potentiometric transduction confirmed that the sensor can discriminate Aβ-42 in the presence of other biomolecules in the same solution.

Electrochemical Detection of Alzheimer’s Disease Biomarker, β-Secretase Enzyme (BACE1), With One-Step Synthesized Reduced Graphene Oxide

β-Secretase1 (BACE1) catalyzes the rate-limiting step in the generation of amyloid-β peptides, that is, the principal component involved in the pathology of Alzheimer’s disease (AD). Recent research studies show correlation between blood and cerebrospinal fluid (CSF) levels of BACE1 with the pathophysiology of AD. In this study, we report one-step synthesized reduced graphene oxide (rGO), activated via carbodiimide chemistry, conjugated with BACE1 antibody (Ab), and immobilized on fluorine-doped tin oxide (FTO) electrodes for rapid detection of BACE1 antigen (Ag) for AD diagnosis. The synthesis and fabrication steps were characterized using different types of spectroscopic, X-ray analytic, microscopic, and voltametric techniques. Various parameters including nanomaterial/Ab concentration, response time, pH, temperature, and rate of scan were standardized for maximum current output using the modified electrode. Final validation was performed via detection of BACE1 Ag ranging from 1 fM to 1 µM, with a detection limit of 0.64 fM in buffer samples and 1 fM in spiked serum samples, as well as negligible cross-reactivity with neurofilament Ag in buffer, spiked serum, and spiked artificial CSF. The proposed immunosensor gave a quick result in 30 s, and good repeatability and storage stability for a month, making it a promising candidate for sensitive, specific, and early diagnosis of AD. Thus, the fabricated electrochemical biosensor for BACE-1 detection improves detection performance compared to existing sensors as well as reduces detection time and cost, signifying its potential in early diagnosis of AD in clinical samples.

High-Sensitivity and Trace-Amount Specimen Electrochemical Sensors for Exploring the Levels of β-Amyloid in Human Blood and Tears

As the occurrence of Alzheimer's disease (AD) has increased, the detection and treatment of AD have become global social issues. Effective early detection and wide-range screening of AD allow patients to gain early control and delay brain degeneration. For these reasons, we choose electrochemical sensors to complete the detection task. Although bio-electrochemical technology for antibody and antigen sensing is not a new technology, considering the scarcity of tear samples for dementia and since the existing AD detection techniques are highly invasive and expensive for subjects, we have to use the traditional detection techniques for the early screening of Alzheimer's disease via trace-amount specimens. An AD-related protein in the eye is thought to be an important biomarker for early detection. To carry out detection using tear samples as a test specimens, a tear collection device was developed in this study that extracted 10 μL of tear fluid from a tear Schirmer strip. In this research, we distinguished healthy people in different age groups and detect Aβ in both tear and blood samples. We developed a biosensor, which could detect Aβ in tear specimen from 1 to 100 pg/mL. Also, this biosensor is inexpensive, disposable, and easy to use. In our result, the concentration of Aβ in tears was approximately 10 times more than that in blood. This study demonstrates the feasibility and prospects of future screening for AD-associated biomarkers by a dynamic comparison between blood and tears.

Clinically oriented Alzheimer's biosensors: expanding the horizons towards point-of-care diagnostics and beyond

The development of minimally invasive and easy-to-use sensor devices is of current interest for ultrasensitive detection and signal recognition of Alzheimer's disease (AD) biomarkers. Over the years, tremendous effort has been made on diagnostic platforms specifically targeting neurological markers for AD in order to replace the conventional, laborious, and invasive sampling-based approaches. However, the sophistication of analytical outcomes, marker inaccessibility, and material validity strongly limit the current strategies towards effectively predicting AD. Recently, with the promising progress in biosensor technology, the realization of a clinically applicable sensing platform has become a potential option to enable early diagnosis of AD and other neurodegenerative diseases. In this review, various types of biosensors, which include electrochemical, fluorescent, plasmonic, photoelectrochemical, and field-effect transistor (FET)-based sensor configurations, with better clinical applicability and analytical performance towards AD are highlighted. Moreover, the feasibility of these sensors to achieve point-of-care (POC) diagnosis is also discussed. Furthermore, by grafting nanoscale materials into biosensor architecture, the remarkable enhancement in durability, functionality, and analytical outcome of sensor devices is presented. Finally, future perspectives on further translational and commercialization pathways of clinically driven biosensor devices for AD are discussed and summarized.

Nanoconstructs as a versatile tool for detection and diagnosis of Alzheimer biomarkers

The current review focuses towards the advancements made in the past decade in the field of nanotechnology for the early Alzheimer's disease (AD) diagnosis. This review includes the application of nanomaterials and nanosensors for the early detection of the main AD biomarkers (amyloid beta, phosphorylated tau, apolipoprotein E4 allele or APOE4, microRNAs, cholesterol, hydrogen peroxide etc) in biological fluids, to detect the biomarkers at a very low concentration ranging in pico, femto and even atto molar concentrations. The field of drug development has always aimed and is constantly working on developing disease modifying drugs, but these drugs will only succeed when given in the early disease stages. Thus, developing efficient diagnostic tools is of vital importance. Various nanomaterials such as liposomes; dendrimers; polymeric nanoparticles; coordination polymers; inorganic nanoparticles such as silica, manganese oxide, zinc oxide, iron oxide, super paramagnetic iron oxides; quantum dots, silver nanoparticles, gold nanoparticles, and carbon based nanostructures (carbon nanotubes, graphene oxide, nanofibres, nanodiamonds, carbon dots); Up-conversion nanoparticles; 2D nanomaterials; and radioactive nanoprobes have been used in constructing and improving efficiency of nano-sensors for AD biosensing at an early stage of diagnosis.

Graphene FET Sensors for Alzheimer's Disease Protein Biomarker Clusterin Detection

We report on the fabrication and characterisation of graphene field-effect transistor (GFET) biosensors for the detection of Clusterin, a prominent protein biomarker of Alzheimer’s disease (AD). The GFET sensors were fabricated on Si/SiO₂ substrate using photolithographic patterning and metal lift-off techniques with evaporated chromium and sputtered gold contacts. Raman Spectroscopy was performed on the devices to determine the quality of the graphene. The GFETs were annealed to improve their performance before the channels were functionalized by immobilising the graphene surface with linker molecules and anti-Clusterin antibodies. Concentration of linker molecules was also independently verified by absorption spectroscopy using the highly collimated micro-beam light of Diamond B23 beamline. The detection was achieved through the binding reaction between the antibody and varying concentrations of Clusterin antigen from 1 to 100 pg/mL, as well as specificity tests using human chorionic gonadotropin (hCG), a glycoprotein risk biomarker of certain cancers. The GFETs were characterized using direct current (DC) 4-probe electrical resistance (4-PER) measurements, which demonstrated a limit of detection of the biosensors to be ∼ 300 fg/mL (4 fM). Comparison with back-gated Dirac voltage shifts with varying concentration of Clusterin show 4-PER measurements to be more accurate, at present, and point to a requirement for further optimisation of the fabrication processes for our next generation of GFET sensors. Thus, we have successfully fabricated a promising set of GFET biosensors for the detection of Clusterin protein biomarker. The developed GFET biosensors are entirely generic and also have the potential to be applied to a variety of other disease detection applications such as Parkinson’s, cancer, and cardiovascular.

Assessing Surface Coverage of Aminophenyl Bonding Sites on Diazotised Glassy Carbon Electrodes for Optimised Electrochemical Biosensor Performance

Electrochemical biosensors using carbon-based electrodes are being widely developed for the detection of a range of different diseases. Since their sensitivity depends on the surface coverage of bioreceptor moieties, it necessarily depends on the surface coverage of amine precursors. Electrochemical techniques, using ferrocene carboxylic acid as a rapid and cheap assay, were used to assess the surface coverage of amino-phenyl groups attached to the carbon electrode. While the number of electrons transferred in the first step of diazotisation indicated a surface coverage of 8.02 ± 0.2 × l0⁻¹⁰ (mol/cm²), and those transferred in the second step, a reduction of nitrophenyl to amino-phenyl, indicated an amine surface coverage of 4–5 × l0⁻¹⁰ (mol/cm²), the number of electrons transferred during attachment of the amine coupling assay compound, ferrocene carboxylic acid, indicated a much lower available amine coverage of only 2.2 × l0⁻¹¹ (mol/cm²). Furthermore, the available amine coverage was critically dependent upon the number of cyclic voltammetry cycles used in the reduction, and thus the procedures used in this step influenced the sensitivity of any subsequent sensor. Amine coupling of a carboxyl terminated anti-beta amyloid antibody specific to Aβ(1-42) peptide, a potential marker for Alzheimer’s disease, followed the same pattern of coverage as that observed with ferrocene carboxylic acid, and at optimum amine coverage, the sensitivity of the differential pulse voltammetry sensor was in the range 0–200 ng/mL with the slope of 5.07 µA/ng·mL⁻¹ and R² = 0.98.

A visual bio-barcode immunoassay for sensitive detection of triazophos based on biochip silver staining signal amplification

Herein, a novel visual method for detecting triazophos based on competitive bio-barcode immunoassay was described. The competitive immunoassay was established by gold nanoparticles (AuNPs), magnetic microparticle (MMPs) and triazophos, combined with biochip hybridization system to detect the residual of triazophos in water and apple. Because AuNPs carried many bio-barcodes, which hybridized with labeled DNA on the biochip, catalyzed signal amplification using silver staining was detected by grayscale values as well as the naked eye. Notably, the grayscale values decreases with increasing the concentrations of triazophos, and the color change weakened gradually. The detection range was in between 0.05 and 10 ng/mL and the minimum detection limit was set at 0.04 ng/mL. Percent recovery calculated from spiked water and apple samples ranged between 55.4 and 107.8% with relative standard deviations (RSDs) of 12.4-24.9%. It has therefore been shown that this protocol provides a new insight for rapid detection of small molecule pesticides in various matrices.

Electrochemical Biosensors Based on Nanomaterials for Early Detection of Alzheimer's Disease

Alzheimer's disease (AD) is an untreatable neurodegenerative disease that initially manifests as difficulty to remember recent events and gradually progresses to cognitive impairment. The incidence of AD is growing yearly as life expectancy increases, thus early detection is essential to ensure a better quality of life for diagnosed patients. To reach that purpose, electrochemical biosensing has emerged as a cost-effective alternative to traditional diagnostic techniques, due to its high sensitivity and selectivity. Of special relevance is the incorporation of nanomaterials in biosensors, as they contribute to enhance electron transfer while promoting the immobilization of biological recognition elements. Moreover, nanomaterials have also been employed as labels, due to their unique electroactive and electrocatalytic properties. The aim of this review is to add value in the advances achieved in the detection of AD biomarkers, the strategies followed for the incorporation of nanomaterials and its effect in biosensors performance.

Enrichment-Free Rapid Detection of Phthalates in Chinese Liquor with Electrochemical Impedance Spectroscopy

A non-invasive real-time detection technique for phthalates in Chinese liquor is proposed in this paper. This method is based on the measurement of Faradaic impedance in the presence of a redox probe, [Fe(CN)₆]^3−/4−, upon the absorption of phthalates to the graphene electrode surface. This absorption activity is according to the π–π stacking interactions between phthalates and the graphene working electrode which allows direct sampling and analyte preconcentration. The absorption of phthalates retards the interfacial electron-transfer kinetics and increases the charge-transfer resistance (R_ct). Numerical values of R_ct were extracted from a simulation of electrochemical impedance spectroscopy (EIS) spectra with the corresponding equivalent circuit. Cathodic polarization was employed prior to EIS measurements to effectively eliminate the metal ion interference. The results yielded a detection limit of 0.024 ng/L for diethyl phthalate (DEP) with a linear range from 2.22 ng to 1.11 µg. These results indicate a possibility of developing a household sensor for phthalate determination in Chinese liquor.

Label-Free Impedimetric Immunosensors Modulated by Protein A/Bovine Serum Albumin Layer for Ultrasensitive Detection of Salbutamol

The sensing properties of immunosensors are determined not only by the amount of immobilized antibodies but also by the number of effective antigen-binding sites of the immobilized antibody. Protein A (PA) exhibits a high degree of affinity with the Fc part of IgG antibody to feasibly produce oriented antibody immobilization. This work proposes a simple method to control the PA surface density on gold nanostructure (AuNS)-deposited screen-printed carbon electrodes (SPCEs) by mixing concentration-varied PA and bovine serum albumin (BSA), and to explore the effect of PA density on the affinity attachment of anti-salbutamol (SAL) antibodies by electrochemical impedance spectroscopy. A concentration of 100 μg/mL PA and 100 μg/mL BSA can obtain a saturated coverage on the 3-mercaptoproponic acid (MPA)/AuNS/SPCEs and exhibit a 50% PA density to adsorb the amount of anti-SAL, more than other concentration-varied PA/BSA-modified electrodes. Compared with the randomly immobilized anti-SAL/MPA/AuNS/SPCEs and the anti-SAL/PA(100 μg/mL):BSA(0 μg/mL)/MPA/AuNS/SPCE, the anti-SAL/PA(100 μg/mL): BSA(100 μg/mL)/MPA/AuNS/SPCE-based immunosensors have better sensing properties for SAL detection, with an extremely low detection limit of 0.2 fg/mL and high reproducibility (<2.5% relative standard deviation). The mixture of PA(100 μg/mL):BSA(100 μg/mL) for the modification of AuNS/SPCEs has great promise for forming an optimal protein layer for the oriented adsorption of IgG antibodies to construct ultrasensitive SAL immunosensors.

Biosensors on the road to early diagnostic and surveillance of Alzheimer's disease

Alzheimer's disease is a debilitating and largely untreatable condition with subtle onset and slow progression over an extensive period of time, which culminate in increasing levels of disability. As Alzheimer's disease prevalence is expected to grow exponentially in the upcoming decades, there is an urgency to develop analytical technologies for the sensitive, reliable and cost-effective detection of Alzheimer's disease biomarkers. Biosensors are powerful analytical devices that translate events of biological recognition on physical or chemical transducers into electrical, thermal or optical signals. The high sensitivity and selectivity of biosensors associated with easy, rapid and low-cost determination of analytes have made this discipline one of the most intensively studied in the past decades. This review centers on recent advances, challenges and trends of Alzheimer's disease biosensing particularly in the effort to combine the unique properties of nanomaterials with biorecognition elements. In the last decade, impressive progresses have been made towards the development of biosensors, mainly electrochemical and optical, for detection of Alzheimer's disease biomarkers in the pico- and femto-molar range. Nonetheless, advances in multiplexed detection, robustness, stability and specificity are still necessary to ensure an accurate and differentiated diagnosis of this disease.

Nanomaterials towards Biosensing of Alzheimer's Disease Biomarkers

Alzheimer's disease (AD) is an incurable and highly debilitating condition characterized by the progressive degeneration and/or death of nerve cells, which leads to manifestation of disabilities in cognitive functioning. In recent years, the development of biosensors for determination of AD's main biomarkers has made remarkable progress, particularly based on the tremendous advances in nanoscience and nanotechnology. The unique and outstanding properties of nanomaterials (such as graphene, carbon nanotubes, gold, silver and magnetic nanoparticles, polymers and quantum dots) have been contributing to enhance the electrochemical and optical behavior of transducers while offering a suitable matrix for the immobilization of biological recognition elements. Therefore, optical and electrochemical immuno- and DNA-biosensors with higher sensitivity, selectivity and longer stability have been reported. Nevertheless, strategies based on the detection of multiple analytes still need to be improved, as they will play a crucial role in minimizing misdiagnosis. This review aims to provide insights into the conjugation of nanomaterials with different transducers highlighting their crucial role in the construction of biosensors for detection of AD main biomarkers.

AuCu xO-Embedded Mesoporous CeO2 Nanocomposites as a Signal Probe for Electrochemical Sensitive Detection of Amyloid-Beta Protein

A sandwich-type electrochemical immunosensor for detecting amyloid-beta protein was fabricated based on Au NP-functionalized reduced graphene oxide (Au@rGO) as an effective sensing platform and AuCu _xO-embedded mesoporous CeO₂ (AuCu _xO@m-CeO₂) nanocomposites as the catalytic matrix. The AuCu _xO@m-CeO₂ composites were obtained by adjusting the amount of m-CeO₂ in the reaction to expose enormous active sites. Also, AuCu _xO@m-CeO₂ was applied as a matrix to immobilize antibodies by forming bridged bonds between m-CeO₂ and carboxyl functional groups of antibodies without additional agents. Furthermore, AuCu _xO with prominent catalytic activities dramatically improved the performance of the fabricated immunosensor. Also, the morphology, structure, and electronic state of the surface were characterized by SEM, XRD, TEM, and XPS. In addition, the immunosensor demonstrated a wide linear range of 100 fg mL^-1 to 10 ng mL^-1. This study may provide a way for sensitively detecting various biomarkers.

Biosensors for Alzheimer's disease biomarker detection: A review

Alzheimer's disease (AD) is a chronic disease amongst people aged 65 and older. Increasing evidence has illustrated that early diagnosis holds the key to effective treatment of AD. A variety of detection techniques have been developed. Biosensors are excellent analytical tools which have applications in detecting the biomarkers of AD. This review includes appropriate bioreceptors to achieve highly sensitive and selective quantification of AD biomarkers by using transducers. AD biomarkers such as tau protein, amyloid β peptides and apolipoprotein E4, are firstly summarized. The most commonly used bioreceptors, including aptamers and antibodies, are also reviewed. We introduce aptamers specific to AD biomarkers, list the sequences of aptamers designed to capture AD biomarkers and compare the properties of aptamers with those of antibodies with regard to their efficiency as bio-recognition elements. We discuss the recent progress of aptamer systems' applications in AD biomarkers in biosensing. The review also discusses novel strategies used for signal amplification in sensing AD biomarkers.

Nano-biosensors to detect beta-amyloid for Alzheimer's disease management

Beta-amyloid (β-A) peptides are potential biomarkers to monitor Alzheimer's diseases (AD) for diagnostic purposes. Increased β-A level is neurotoxic and induces oxidative stress in brain resulting in neurodegeneration and causes dementia. As of now, no sensitive and inexpensive method is available for β-A detection under physiological and pathological conditions. Although, available methods such as neuroimaging, enzyme-linked immunosorbent assay (ELISA), and polymerase chain reaction (PCR) detect β-A, but they are not yet extended at point-of-care (POC) due to sophisticated equipments, need of high expertize, complicated operations, and challenge of low detection limit. Recently, β-A antibody based electrochemical immuno-sensing approach has been explored to detect β-A at pM levels within 30-40 min compared to 6-8h of ELISA test. The introduction of nano-enabling electrochemical sensing technology could enable rapid detection of β-A at POC and may facilitate fast personalized health care delivery. This review explores recent advancements in nano-enabling electrochemical β-A sensing technologies towards POC application to AD management. These analytical tools can serve as an analytical tool for AD management program to obtain bio-informatics needed to optimize therapeutics for neurodegenerative diseases diagnosis management.