Myelin basic protein immunosensor for multiple sclerosis detection based upon label-free electrochemical impedance spectroscopy

Recent Advances in Biosensors for Diagnosis of Autoimmune Diseases

Over the last decade, autoimmune diseases (ADs) have undergone a significant increase because of genetic and/or environmental factors; therefore, their simple and fast diagnosis is of high importance. The conventional diagnostic techniques for ADs require tedious sample preparation, sophisticated instruments, a dedicated laboratory, and qualified personnel. For these reasons, biosensors could represent a useful alternative to these methods. Biosensors are considered to be promising tools that can be used in clinical analysis for an early diagnosis due to their high sensitivity, simplicity, low cost, possible miniaturization (POCT), and potential ability for real-time analysis. In this review, recently developed biosensors for the detection of autoimmune disease biomarkers are discussed. In the first part, we focus on the main AD biomarkers and the current methods of their detection. Then, we discuss the principles and different types of biosensors. Finally, we overview the characteristics of biosensors based on different bioreceptors reported in the literature.

Immunosensors for Autoimmune-Disease-Related Biomarkers: A Literature Review

Immunosensors are a special class of biosensors that employ specific antibodies for biorecognition of the target analyte. Immunosensors that target disease biomarkers may be exploited as tools for disease diagnosis and/or follow-up, offering several advantages over conventional analytical techniques, such as rapid and easy analysis of patients' samples at the point-of-care. Autoimmune diseases have been increasingly prevalent worldwide in recent years, while the COVID-19 pandemic has also been associated with autoimmunity. Consequently, demand for tools enabling the early and reliable diagnosis of autoimmune diseases is expected to increase in the near future. To this end, interest in immunosensors targeting autoimmune disease biomarkers, mainly, various autoantibodies and specific pro-inflammatory proteins (e.g., specific cytokines), has been rekindled. This review article presents most of the immunosensors proposed to date as potential tools for the diagnosis of various autoimmune diseases, such as type 1 diabetes, rheumatoid arthritis, and multiple sclerosis. The signal transduction and the immunoassay principles of each immunosensor have been suitably classified and are briefly presented along with certain sensor elements, e.g., special nano-sized materials used in the construction of the immunosensing surface. The main concluding remarks are presented and future perspectives of the field are also briefly discussed.

Nanoimmunosensor for the electrochemical detection of oncostatin M receptor and monoclonal autoantibodies in systemic sclerosis

Systemic sclerosis (SSc) is a chronic, autoimmune disease that primarily affects connective tissue. SSc can be classified into limited cutaneous (lSSc) and diffuse cutaneous (dSSc). Oncostatin M receptor (sOSMR) is an important inflammatory biomarker expressed in the serum of patients with autoimmune diseases. A nanoengineered immunosensor surface was developed. The biosensor was composed of a conductive layer of polypyrrole, electrodeposited gold nanoparticles, and sOSMR protein for anti-human OSMR monoclonal antibody biorecognition. The electrochemical response evaluated by cyclic voltammetry and electrochemical impedance spectroscopy indicated the detection of the target analyte present in clinical samples from lSSc and dSSc patients. The voltammetric anodic shift for lSSc specimens was 82.7% ± 0.9-93.6% ± 3.2, and dSSc specimens was 118.7 ± 2.6 to 379.6 ± 2.6, revealing a differential diagnostic character for SSc subtypes. The sensor platform was adapted for identifying sOSMR, using anti-OSMR antibodies as bioreceptors. With a linear response range estimated from 0.005 to 500 pg mL^-1 and a limit of detection of 0.42 pg mL^-1, the sensing strategy demonstrated high sensitivity in identifying the human OSMR protein in clinical samples. The proposed biosensor is a promising and innovative tool for SSc-related biomarker research.

Applications of Gelatin in Biosensors: Recent Trends and Progress

Gelatin is a natural protein from animal tissue with excellent biocompatibility, biodegradability, biosafety, low cost, and sol-gel property. By taking advantage of these properties, gelatin is considered to be an ideal component for the fabrication of biosensors. In recent years, biosensors with gelatin have been widely used for detecting various analytes, such as glucose, hydrogen peroxide, urea, amino acids, and pesticides, in the fields of medical diagnosis, food testing, and environmental monitoring. This perspective is an overview of the most recent trends and progress in the development of gelatin-based biosensors, which are classified by the function of gelatin as a matrix for immobilized biorecognition materials or as a biorecognition material for detecting target analytes.

An Update on the Laboratory Diagnosis of Neuromyelitis Optica Spectrum Disorders

Neuromyelitis optica spectrum disorder (NMOSD) is an autoimmune disorder of the central nervous system that is specifically associated with demyelination of spinal cord and optic nerves. The discovery of specific autoantibody markers such as aquaporin-4 IgG and myelin oligodendrocyte glycoprotein IgG has led to several methodologies being developed and validated. There have been numerous investigations of the clinical and radiological presentations used in the clinical diagnosis of NMOSD. However, although various laboratory diagnostic techniques have been standardized and validated, a gold-standard test has yet to be finalized due to uncertain sensitivities and specificities of the methodologies. For this review, the literature was surveyed to compile the standardized laboratory techniques utilized for the differential diagnosis of NMOSD. Enzyme-linked immunosorbent assays enable screening of NMOSD, but they are considered less sensitive than cell-based assays (CBAs), which were found to be highly sensitive and specific. However, CBAs are laborious and prone to batch variations in their results, since the expression levels of protein need to be maintained and monitored meticulously. Standardizing point-of-care devices and peptide-based assays would make it possible to improve the turnaround time and accessibility of the test, especially in resource-poor settings.

Recent advancements in nanoparticle-mediated approaches for restoration of multiple sclerosis

Multiple Sclerosis (MS) is an autoimmune disease with complicated immunopathology which necessitates considering multifactorial aspects for its management. Nano-sized pharmaceutical carriers named nanoparticles (NPs) can support impressive management of disease not only in early detection and prognosis level but also in a therapeutic manner. The most prominent initiator of MS is the domination of cellular immunity to humoral immunity and increment of inflammatory cytokines. The administration of several platforms of NPs for MS management holds great promise so far. The efforts for MS management through in vitro and in vivo (experimental animal models) evaluations, pave a new way to a highly efficient therapeutic means and aiding its translation to the clinic in the near future.

Blood Trace Element Status in Multiple Sclerosis: a Systematic Review and Meta-analysis

The aim of this meta-analysis was to investigate whether the blood concentrations of patients with multiple sclerosis (MS) are associated with those of the healthy control group in terms of trace elements including zinc (Zn), iron (Fe), manganese (Mn), magnesium (Mg), selenium (Se), and copper (Cu). A comprehensive search was performed in online databases including PubMed, Scopus, Embase, and Web of Science for studies, which have addressed trace elements in MS up to July 23, 2020. The chi-square test and I² statistic were utilized to evaluate inter-study heterogeneity across the included studies. Weighted mean differences (WMDs) and corresponding 95% CI were considered as a pooled effect size (ES). Twenty-seven articles (or 32 studies) with a total sample comprised of 2895 participants (MS patients (n = 1567) and controls (n = 1328)) were included. Pooled results using random-effects model indicated that the levels of Zn (WMD = - 7.83 mcg/dl, 95% CI = - 12.78 to - 2.87, Z = 3.09, P = 0.002), and Fe (WMD = - 13.66 mcg/dl, 95% CI = - 23.13 to - 4.19, Z = 2.83, P = 0.005) were significantly lower in MS patients than in controls. However, it was found that levels of Mn (WMD = 0.03 mcg/dl, 95% CI = 0.01 to 0.04, Z = 2.89, P = 0.004) were significantly higher in MS patients. Yet, no significant differences were observed in the levels of Mg, Se, and Cu between both groups. This meta-analysis revealed that the circulating levels of Zn and Fe were significantly lower in MS patients and that Mn level was significantly higher than those in the control group. However, it was found that there was no significant difference between MS patients and controls with regard to levels of Mg, Se, and Cu.

Technological advances in electrochemical biosensors for the detection of disease biomarkers

With an increasing focus on health in contemporary society, interest in the diagnosis, treatment, and prevention of diseases has grown rapidly. Accordingly, the demand for biosensors for the early diagnosis of disease is increasing. However, the measurement range of existing electrochemical sensors is relatively high, which is not suitable for early disease diagnosis, requiring the detection of small amounts of biocomponents. Various attempts have been made to overcome this and amplify the signal, including binding with various labeling molecules, such as DNA, enzymes, nanoparticles, and carbon materials. Efforts are also being made to increase the sensitivity of electrochemical sensors, and the combination of nanomaterials, materials, and biotechnology offers the potential to increase sensitivity in a variety of ways. Recent studies suggest that electrochemical sensors can be a powerful tool in providing comprehensive insights into the targeting and detection of disease-associated biomarkers. Significant advances in nanomaterial and biomolecule approaches for improved sensitivity have resulted in the development of electrochemical biosensors capable of detecting multiple biomarkers in real time in clinically relevant samples. In this review, we have discussed the recent studies on electrochemical sensors for detection of diseases such as diabetes, degenerative diseases, and cancer. Further, we have highlighted new technologies to improve sensitivity using various materials, including DNA, enzymes, nanoparticles, and carbon materials.

Gold Nanoparticles: Multifaceted Roles in the Management of Autoimmune Disorders

Gold nanoparticles (GNPs) have been recently applied for various diagnostic and therapeutic purposes. The unique properties of these nanoparticles (NPs), such as relative ease of synthesis in various sizes, shapes and charges, stability, high drug-loading capacity and relative availability for modification accompanied by non-cytotoxicity and biocompatibility, make them an ideal field of research in bio-nanotechnology. Moreover, their potential to alleviate various inflammatory factors, nitrite species, and reactive oxygen production and the capacity to deliver therapeutic agents has attracted attention for further studies in inflammatory and autoimmune disorders. Furthermore, the characteristics of GNPs and surface modification can modulate their toxicity, biodistribution, biocompatibility, and effects. This review discusses in vitro and in vivo effects of GNPs and their functionalized forms in managing various autoimmune disorders (Ads) such as rheumatoid arthritis, type 1 diabetes, and multiple sclerosis.

Advances in the diagnosis of autoimmune diseases based on citrullinated peptides/proteins

Introduction: Autoimmune diseases are still one of the hard obstacles associated with humanity. There are many exogenous and endogenous etiological factors behind autoimmune diseases, which may be combined or dispersed to stimulate the autoimmune responses. Protein citrullination represents one of these factors. Harnessing specific citrullinated proteins/peptides could early predict and/or diagnose some of the autoimmune diseases. Many generations of diagnostic tools based on citrullinated peptides with comparable specificity/sensitivity are available worldwide.Areas covered: In this review, we discuss the deimination reaction behind the citrullination of most known autoantigens targeted, different generations of diagnostic tools based on citrullinated probes with specificity/sensitivity of each as well as newly developed assays. Furthermore, the most advanced molecular analytical tools to detect the citrullinated residues in the biological fluid and their performance are also evaluated, providing new avenues to early detect autoimmune diseases with high accuracy.Expert opinion: With the current specificity/sensitivity tools available for autoimmune disease detection, emphasis must be placed on developing more advance and effective, early, rapid, and simple diagnostic devices for autoimmune disease monitoring (similar to a portable device for sugar test at home). The molecular analytical devices with dual and/or multiplexe functions should be more simplified and invested in clinical laboratories.

A literature review of biosensors for multiple sclerosis: Towards personalized medicine and point-of-care testing

Multiple sclerosis (MS) is a chronic neuroinflammatory disease of the central nervous system that leads to severe motor and sensory deficits in patients. Although some biomolecules in serum or cerebrospinal fluid have been suggested as biomarkers for MS diagnosis, following disease activity and monitoring treatment response, most of these potential biomarkers are not currently in clinical use and available for all patients. The reasons behind this are generally related to insufficient robustness of biomarker or technical difficulties, high prices, and requirements for technical personnel for their detection. Point-of-care testing (POCT) is an emerging field of healthcare that can be applied at the hospital as well as at home without the need for a centralized laboratory. Biosensor devices offer a convenient means for POCT. A biosensor is a compact analytical device that uses a bioreceptor, such as an antibody, enzyme, or oligonucleotide, to capture the analyte of interest. The interaction between the analyte and the bioreceptor is sensed and transduced into a suitable signal by the signal transducer. The advantages of using a biosensor for detecting the biomolecule of interest include speed, simplicity, accuracy, relatively lower cost, and lack of requirements for highly qualified personnel to perform the testing. Owing to these advantages and with the help of innovations in biosensor development technologies, there has been a great interest in developing biosensor devices for MS in recent years. Hence, the purpose of this review was to provide researchers with an up-to-date summary of the literature as well as to highlight the challenges and opportunities in this translational research field. In addition, because this is a highly interdisciplinary field of study, potentially concerning MS specialists, neurologists, biomedical researchers, and engineers, another aim of this review was to bridge the gap between these disciplines.

A preliminary study of the concentration of metallic elements in the blood of patients with multiple sclerosis as measured by ICP-MS

It is estimated that multiple sclerosis (MS) affects 35,000 Brazilians and 2.5 million individuals worldwide. Many studies have suggested a possible role of metallic elements in the etiology of MS, but their concentration in the blood of MS patients is nonetheless little investigated in Brazil. In this work, these elements were studied through Inductively Coupled Plasma Mass Spectrometry (ICP-MS), whose analysis provides a tool to quantify the concentrations of metal elements in the blood samples of individuals with neurodegenerative disorders. This study aimed to compare the concentration of metallic elements in blood samples from patients with MS and healthy individuals. Blood was collected from 30 patients with multiple sclerosis and compared with the control group. Blood samples were digested in closed vessels using a microwave and ICP-MS was used to determine the concentrations of 12 metallic elements (Ba, Be, Ca, Co, Cr, Cu, Fe, Mg, Mo, Ni, Pb and Zn). In MS patients, we observed a reduction in the concentrations of beryllium, copper, chromium, cobalt, nickel, magnesium and iron. The mean concentration of lead in blood was significantly elevated in the MS group. However, no difference was observed in the concentrations of Mo, Ba, Ca and Zn in blood samples from MS patients and the control group. According to our data, there is a possible role for the concentrations of 8 of the 12 evaluated metallic elements in multiple sclerosis. Abnormalities in transition metals levels in biological matrices have been reported in several neurological diseases.

Early Diagnosis of Multiple Sclerosis Based on Optical and Electrochemical Biosensors: Comprehensive Perspective

Background:

Multiple Sclerosis (MS) involves an immune-mediated response in which body’s immune system destructs the protective sheath (myelin). Part of the known MS biomarkers are discovered in cerebrospinal fluid like oligoclonal lgG (OCGB), and also in blood like myelin Oligodendrocyte Glycoprotein (MOG). The conventional MS diagnostic methods often fail to detect the disease in early stages such as Clinically Isolated Syndrome (CIS), which considered as a concerning issue since CIS highlighted as a prognostic factor of MS development in most cases.

Methods:

MS diagnostic techniques include Magnetic Resonance Imaging (MRI) of the brain and spinal cord, lumbar puncture (or spinal tap) that evaluate cerebrospinal fluid, evoked potential testing revealing abnormalities in the brain and spinal cord. These conventional diagnostic methods have some negative points such as extensive processing time as well as restriction in the quantity of samples that can be analyzed concurrently. Scientists have focused on developing the detection methods especially early detection which belongs to ultra-sensitive, non-invasive and needed for the Point of Care (POC) diagnosis because the situation was complicated by false positive or negative results.

Results:

As a result, biosensors are utilized and investigated since they could be ultra-sensitive to specific compounds, cost effective devices, body-friendly and easy to implement. In addition, it has been proved that the biosensors on physiological fluids (blood, serum, urine, saliva, milk etc.) have quick response in a non-invasive rout. In general form, a biosensor system for diagnosis and early detection process usually involves; biomarker (target molecule), bio receptor (recognition element) and compatible bio transducer.

Conclusion:

Studies underlined that early treatment of patients with high possibility of MS can be advantageous by postponing further abnormalities on MRI and subsequent attacks.

:

This Review highlights variable disease diagnosis approaches such as Surface Plasmon Resonance (SPR), electrochemical biosensors, Microarrays and microbeads based Microarrays, which are considered as promising methods for detection and early detection of MS.

Nanoimmunosensor based on atomic force spectroscopy to detect anti-myelin basic protein related to early-stage multiple sclerosis

Multiple Sclerosis (MS) is a chronic inflammatory disorder in the central nervous system for which biomarkers for diagnosis still remain unknown. One potential biomarker is the myelin basic protein. Here, a nanoimmunosensor based on atomic force spectroscopy (AFS) successfully detected autoantibodies against the MBP_85-99 peptide from myelin basic protein. The nanoimmunosensor consisted of an atomic force microscope tip functionalization with MBP_85-99 peptide, which was made to interact with a mica surface coated either with a layer of anti-MBP_85-99 (positive control) or samples of cerebrospinal fluid (CSF) from five multiple sclerosis (MS) patients at different stages of the disease and five non-MS subjects. The adhesion forces obtained from AFS pointed to a high concentration of anti-MBP_85-99 for the two patients at early stages of relapsing-remitting multiple sclerosis (RRMS), which were indistinguishable from the positive control. In contrast, considerably lower adhesion forces were measured for all the other eight subjects, including three MS patients with longer history of the disease and under treatment, without episodes of acute MS activity. We have also shown that the average adhesion force between MBP_85-99 and anti-MBP_85-99 is compatible with the value estimated using steered molecular dynamics. Though further tests will be required with a larger cohort of patients, the present results indicate that the nanoimmunosensor may be a simple tool to detect early-stage MS patients and be useful to understand the molecular mechanisms behind MS.

Bioluminescent aptamer-based sandwich-type assay of anti-myelin basic protein autoantibodies associated with multiple sclerosis

Bioluminescent solid-phase sandwich-type microassay was developed to detect multiple sclerosis (MS)-associated autoantibodies in human sera. The assay is based on two different 2'-F-Py RNA aptamers against the target autoantibodies as biospecific elements, and Ca²⁺-regulated photoprotein obelin as a reporter. The paper describes elaboration of the assay and its application to 91 serum samples from patients with clinically definite MS and 86 ones from individuals healthy in terms of MS. Based on the receiver-operator curve (ROC) analysis, the chosen threshold value as clinical decision limit offers sensitivity of 63.7% and specificity of 94.2%. The area under the ROC curve (AUC) value of 0.87 shows a good difference between the groups under investigation. The likelihood ratio of 10.97 proves the diagnostic value of the assay and its potential as one of the laboratory MS-tests.

Electrochemical Biosensors as Potential Diagnostic Devices for Autoimmune Diseases

An important class of biosensors is immunosensors, affinity biosensors that are based on the specific interaction between antibodies and antigens. They are classified in four classes based on the type of employed transducer: electrochemical, optical, microgravimetric, and thermometric and depending on the type of recognition elements, antibodies, aptamers, microRNAs and recently peptides are integrating parts. Those analytical devices are able to detect peptides, antibodies and proteins in various sample matrices, without many steps of sample pretreatment. Their high sensitivity, low cost and the easy integration in point of care devices assuring portability are attracting features that justify the increasing interest in their development. The use of nanomaterials, simultaneous multianalyte detection and integration on platforms to form point-of-care devices are promising tools that can be used in clinical analysis for early diagnosis and therapy monitoring in several pathologies. Taking into account the growing incidence of autoimmune disease and the importance of early diagnosis, electrochemical biosensors could represent a viable alternative to currently used diagnosis methods. Some relevant examples of electrochemical assays for autoimmune disease diagnosis developed in the last several years based on antigens, antibodies and peptides as receptors were gathered and will be discussed further.

Label-Free Potentiometric Ion Flux Immunosensor for Determination of Recombinant Human Myelin Basic Protein: Application to Downstream Purification from Transgenic Milk

Recombinant human myelin basic protein (rhMBP) produced in the milk of transgenic cows was found exclusively associated with milk caseins. This hindered its direct determination without extensive sample pretreatment. Here, a label-free potentiometric immunosensor was developed and validated for the determination of rhMBP. An ion flux was generated under zero-current based on surface blocking of the polymeric membrane ion-selective electrode by anti-hMBP antibody and tetrabutylammonium bromide as a marker ion. The immunosensor was successfully employed in the quantitative determination of hMBP in the range of 0.10-20.00 μg/mL with a limit of detection of 50.00 ng/mL. The applicability of the passive ion flux immunosensor for determination of target analyte in complex matrices was investigated. Downstream purification of rhMBP from the milk of transgenic cows was achieved using cation exchange chromatography, immobilized metal affinity chromatography, and immunoaffinity chromatography. The specificity of the immunosensor along with matrix effect of milk proteins were demonstrated. Results obtained using the rhMBP immunosensor were further cross-validated using an orthogonal testing protocol assembled of RP-HPLC and SE-HPLC. It should be noted that the proposed ion flux immunosensor provided a feasible and specific tool for monitoring rhMBP concentration/purity, immunogenic activity, and stability. Such approach provides an attractive economic alternative to sophisticated biosensors required for in-process quality control of biopharmaceutical products.

An impedimetric bioaffinity sensing chip integrated with the long-range DC-biased AC electrokinetic centripetal vortex produced in a high conductivity solution

Immunoreaction of specific antibodies to antigens is widely used in numerous immunoanalysis applications. However, diffusion-dominated transport in stationary solutions limits the rate and binding density of immunoreaction. This research describes the construction of chip-type concentric multi-double ring electrodes and single central disk electrode. A +1 V-biased 6 V_pp voltage was applied to the multi-double ring electrodes to induce a long-range DC-biased AC electrokinetic flow (ACEKF). The immunoreaction was quantified by electrochemical impedance spectrum (EIS). Fluorescence-labeled secondary antibody (FLSA) and protein A were exemplified as an immunoreacting model to demonstrate the effect of ACEKF on immunoreaction efficiency. The results showed that FLSA binding can reach a plateau in 8 min with the DC-biased ACEKF vortex, and the increment of electron transfer resistance is 2.26 times larger than that obtained in the unstirred solution. The sensitivity of the calibration curves obtained by EIS detection with the aid of DC-biased ACEKF vortex is 1.51 times larger than that obtained in an unstirred solution. The label-free EIS-based sensing chip integrated with the long-range DC-biased ACEKF vortex promises to facilitate immunoreaction efficiency, which is beneficial for the development of a miniature and fast-detection in vitro diagnostic device.

Emerging Biosensing Technologies for Neuroinflammatory and Neurodegenerative Disease Diagnostics

Neuroinflammation plays a critical role in the onset and progression of many neurological disorders, including Multiple Sclerosis, Alzheimer's and Parkinson's diseases. In these clinical conditions the underlying neuroinflammatory processes are significantly heterogeneous. Nevertheless, a common link is the chronic activation of innate immune responses and imbalanced secretion of pro and anti-inflammatory mediators. In light of this, the discovery of robust biomarkers is crucial for screening, early diagnosis, and monitoring of neurological diseases. However, the difficulty to investigate biochemical processes directly in the central nervous system (CNS) is challenging. In recent years, biomarkers of CNS inflammatory responses have been identified in different body fluids, such as blood, cerebrospinal fluid, and tears. In addition, progress in micro and nanotechnology has enabled the development of biosensing platforms capable of detecting in real-time, multiple biomarkers in clinically relevant samples. Biosensing technologies are approaching maturity where they will become deployed in community settings, at which point screening programs and personalized medicine will become a reality. In this multidisciplinary review, our goal is to highlight both clinical and recent technological advances toward the development of multiplex-based solutions for effective neuroinflammatory and neurodegenerative disease diagnostics and monitoring.

Construction and Potential Applications of Biosensors for Proteins in Clinical Laboratory Diagnosis

Biosensors for proteins have shown attractive advantages compared to traditional techniques in clinical laboratory diagnosis. In virtue of modern fabrication modes and detection techniques, various immunosensing platforms have been reported on basis of the specific recognition between antigen-antibody pairs. In addition to profit from the development of nanotechnology and molecular biology, diverse fabrication and signal amplification strategies have been designed for detection of protein antigens, which has led to great achievements in fast quantitative and simultaneous testing with extremely high sensitivity and specificity. Besides antigens, determination of antibodies also possesses great significance for clinical laboratory diagnosis. In this review, we will categorize recent immunosensors for proteins by different detection techniques. The basic conception of detection techniques, sensing mechanisms, and the relevant signal amplification strategies are introduced. Since antibodies and antigens have an equal position to each other in immunosensing, all biosensing strategies for antigens can be extended to antibodies under appropriate optimizations. Biosensors for antibodies are summarized, focusing on potential applications in clinical laboratory diagnosis, such as a series of biomarkers for infectious diseases and autoimmune diseases, and an evaluation of vaccine immunity. The excellent performances of these biosensors provide a prospective space for future antibody-detection-based disease serodiagnosis.

Electrochemical Detection of Plasma Immunoglobulin as a Biomarker for Alzheimer's Disease

The clinical diagnosis and treatment of Alzheimer’s disease (AD) represent a challenge to clinicians due to the variability of clinical symptomatology as well as the unavailability of reliable diagnostic tests. In this study, the development of a novel electrochemical assay and its potential to detect peripheral blood biomarkers to diagnose AD using plasma immunoglobulins is investigated. The immunosensor employs a gold electrode as the immobilizing substrate, albumin depleted plasma immunoglobulin as the biomarker, and polyclonal rabbit Anti-human immunoglobulin (against IgA, IgG, IgM) as the receptor for plasma conjugation. The assay showed good response, sensitivity and reproducibility in differentiating plasma immunoglobulin from AD and control subjects down to 10⁻⁹ dilutions of plasma immunoglobulin representing plasma content concentrations in the pg mL⁻¹ range. The newly developed assay is highly sensitive, less time consuming, easy to handle, can be easily modified to detect other dementia-related biomarkers in blood samples, and can be easily integrated into portable devices.

Label-Free and Regenerative Electrochemical Microfluidic Biosensors for Continual Monitoring of Cell Secretomes

Development of an efficient sensing platform capable of continual monitoring of biomarkers is needed to assess the functionality of the in vitro organoids and to evaluate their biological responses toward pharmaceutical compounds or chemical species over extended periods of time. Here, a novel label-free microfluidic electrochemical (EC) biosensor with a unique built-in on-chip regeneration capability for continual measurement of cell-secreted soluble biomarkers from an organoid culture in a fully automated manner without attenuating the sensor sensitivity is reported. The microfluidic EC biosensors are integrated with a human liver-on-a-chip platform for continual monitoring of the metabolic activity of the organoids by measuring the levels of secreted biomarkers for up to 7 d, where the metabolic activity of the organoids is altered by a systemically applied drug. The variations in the biomarker levels are successfully measured by the microfluidic regenerative EC biosensors and agree well with cellular viability and enzyme-linked immunosorbent assay analyses, validating the accuracy of the unique sensing platform. It is believed that this versatile and robust microfluidic EC biosensor that is capable of automated and continual detection of soluble biomarkers will find widespread use for long-term monitoring of human organoids during drug toxicity studies or efficacy assessments of in vitro platforms.

Immunosensors for Biomarker Detection in Autoimmune Diseases

Autoimmune diseases occur when the immune system generates proinflammatory molecules and autoantibodies that mistakenly attack their own body. Traditional diagnosis of autoimmune disease is primarily based on physician assessment combined with core laboratory tests. However, these tests are not sensitive enough to detect early molecular events, and quite often, it is too late to control these autoimmune diseases and reverse tissue damage when conventional tests show positivity for disease. It is fortunate that during the past decade, research in nanotechnology has provided enormous opportunities for the development of ultrasensitive biosensors in detecting early biomarkers with high sensitivity. Biosensors consist of a biorecognition element and a transducer which are able to facilitate an accurate detection of proinflammatory molecules, autoantibodies and other disease-causing molecules. Apparently, novel biosensors could be superior to traditional metrics in assessing the drug efficacy in clinical trials, especially when specific biomarkers are indicative of the pathogenesis of disease. Furthermore, the portability of a biosensor enables the development of point-of-care devices. In this review, various types of biomolecule sensing systems, including electrochemical, optical and mechanical sensors, and their applications and future potentials in autoimmune disease treatment were discussed.

Single frequency analysis for clinical immunosensor design

A novel bioelectrochemical approach: Tau protein determination for the diagnosis of neurodiseases via time-dependant phase angle shift.

Electrochemical impedance immunosensor for sub-picogram level detection of bovine interferon gamma based on cylinder-shaped TiO₂ nanorods

Bovine interferon gamma (BoIFN-γ) released by T cells plays very important roles in early diagnosis of Mycobacterium tuberculosis (MTB) infections and control of bovine tuberculosis. In this work, a label-free electrochemical impedance immunosensor is for the first time developed for highly sensitive determination of BoIFN-γ. Cylinder-shaped TiO2 nanorods are synthesized by a facile hydrothermal method, and show high surface area and good hydrophicility. The immunosensor is fabricated by the immobilization of BoIFN-γ monoclonal antibody on the TiO2 nanorods modified glassy carbon electrode. The prepared TiO2 and immunosensor are characterized using transmission electron microscopy, scanning electron microscopy, X-ray diffraction, contact angle measurement, cyclic voltammetry, and electrochemical impedance spectra. The BoIFN-γ concentration is measured through the relative increase of impedance values in corresponding specific binding of BoIFN-γ antigen and BoIFN-γ antibody. The relative increased impedance values are proportional to the logarithmic value of BoIFN-γ concentrations in a wide range of 0.0001 to 0.1 ng/mL with a low detection limit of 0.1 pg/mL. The developed BoIFN-γ immunosensor shows a 249-fold decrease in detection limit in comparison with current enzyme-linked immunosorbent assay. This study provides a new, simple, and highly sensitive approach for very potential application in early diagnosis of MTB infections and control of bovine tuberculosis.

Microstructural and electrochemical impedance characterization of bio-functionalized ultrafine ZnS nanocrystals-reduced graphene oxide hybrid for immunosensor applications

We report a mercaptopropionic acid capped ZnS nanocrystals decorated reduced graphene oxide (RGO) hybrid film on a silane modified indium-tin-oxide glass plate, as a bioelectrode for the quantitative detection of human cardiac myoglobin (Ag-cMb). The ZnS nanocrystals were anchored over electrochemically reduced GO sheets through a cross linker, 1-pyrenemethylamine hydrochloride, by carbodiimide reaction and have been characterized by scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. The transmission electron microscopic characterization of the ZnS-RGO hybrid shows the uniform distribution of ultra-fine nanoparticles of ZnS in nano-sheets of GO throughout the material. The protein antibody, Ab-cMb, was covalently linked to ZnS-RGO nanocomposite hybrid for the fabrication of the bioelectrode. A detailed electrochemical immunosensing study has been carried out on the bioelectrode towards the detection of target Ag-cMb. The optimal fitted equivalent circuit model that matches the impedance response has been studied to delineate the biocompatibility, sensitivity and selectivity of the bioelectrode. The bioelectrode exhibited a linear electrochemical impedance response to Ag-cMb in a range of 10 ng to 1 μg mL(-1) in PBS (pH 7.4) with a sensitivity of 177.56 Ω cm(2) per decade. The combined synergistic effects of the high surface-to-volume ratio of ZnS(MPA) nanocrystals and conducting RGO has provided a dominant charge transfer characteristic (R(et)) at the lower frequency region of <10 Hz showing a good biocompatibility and enhanced impedance sensitivity towards target Ag-cMb. The impedance response sensitivity of the ZnS-RGO hybrid bioelectrode towards Ag-cMb has been found to be about 2.5 fold higher than that of a bare RGO modified bioelectrode.