Immunosensors: electrochemical sensing and other engineering approaches

Ultrasensitive immunosensor for multiplex detection of cancer biomarkers carcinoembryonic antigen (CEA) and yamaguchi sarcoma viral oncogene homolog 1 (YES1) based on eco-friendly synthesized gold nanoparticles

Cancer is one of the most extensive diseases with the highest mortality rate, accounting for almost 10 million deaths in 2020. The most common cancers are breast, lung, colon and rectum and prostate cancers. Of these, lung cancer, accounted for about 1.8 million of all cancer deaths (25%) in 2020. Detection of cancer relies on presence of biomarkers such as DNA molecules, proteins and metabolites released by cancerous cells into the circulation. Carcinoembryonic antigen (CEA) is one of the biomarkers that has been used for the detection of lung cancer. However, CEA is not specific to lung cancer since it is also manifested in gastric cancer, pancreatic cancer, colorectal cancer, and breast cancer. Recently, v-YES1 Yamaguchi sarcoma viral oncogene homolog 1 (YES1) was described as a specific biomarker for lung cancer. The detection of both CEA and YES1 would give more precise and authentic information for detecting lung cancer. This is because detection of a single tumor marker usually limits the precision in tumor diagnosis, due to the fact that several cancers have more than one marker linked with their prevalence. Whereas traditional methods have been used for the detection of CEA, electrochemical immunosensors have attracted considerable attention owing to their profound advantages, including fast response, miniaturization, high selectivity, low sample requirements and magnificent sensitivity. The fabrication of a multiplex and simultaneous immunosensor is met with challenge of preparation of distinguishable immunoprobes with different redox activities. This can be addressed by incorporation of electroactive Nano metals into the sensing platform. In this study, gold nanoparticles were used for the fabrication of an ultrasensitive sandwich electrochemical multiplex immunosensor for simultaneous detection of CEA and YES1. Under optimized conditions, the electrochemical immunosensor detection limit for YES1 and CEA was found to be 0.0022 and 0.0034 ng/mL respectively within a linear range of 0.1-50 ng/mL. The proposed immunosensor proved to be stable for up to 2 weeks and had negligible cross reactivity towards various interfering compounds in human plasma. This study reports that gold nanoparticles can be bio synthesized using shade dried Mangifera indica leaves extract. The bio-synthesized gold nanoparticles coupled with thiolated protein G can be used for fabrication of a multiplex immunosensor for detection of CEA and YES1. The proposed immunosensor can provide a new approach for early diagnosis of circulating cancer biomarkers and holds great promise for application in clinical diagnosis.

Advancement in COVID-19 detection using nanomaterial-based biosensors

Coronavirus disease 2019 (COVID-19) pandemic has exemplified how viral growth and transmission are a significant threat to global biosecurity. The early detection and treatment of viral infections is the top priority to prevent fresh waves and control the pandemic. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been identified through several conventional molecular methodologies that are time-consuming and require high-skill labor, apparatus, and biochemical reagents but have a low detection accuracy. These bottlenecks hamper conventional methods from resolving the COVID-19 emergency. However, interdisciplinary advances in nanomaterials and biotechnology, such as nanomaterials-based biosensors, have opened new avenues for rapid and ultrasensitive detection of pathogens in the field of healthcare. Many updated nanomaterials-based biosensors, namely electrochemical, field-effect transistor, plasmonic, and colorimetric biosensors, employ nucleic acid and antigen-antibody interactions for SARS-CoV-2 detection in a highly efficient, reliable, sensitive, and rapid manner. This systematic review summarizes the mechanisms and characteristics of nanomaterials-based biosensors for SARS-CoV-2 detection. Moreover, continuing challenges and emerging trends in biosensor development are also discussed.

Emerging bioanalytical sensors for rapid and close-to-real-time detection of priority abiotic and biotic stressors in aquaculture and culture-based fisheries

Abiotic stresses of various chemical contamination of physical, inorganic, organic and biotoxin origin and biotic stresses of bacterial, viral, parasitic and fungal origins are the significant constraints in achieving higher aquaculture production. Testing and rapid detection of these chemical and microbial contaminants are crucial in identifying and mitigating abiotic and biotic stresses, which has become one of the most challenging aspects in aquaculture and culture-based fisheries. The classical analytical techniques, including titrimetric methods, spectrophotometric, mass spectrometric, spectroscopic, and chromatographic techniques, are tedious and sometimes inaccessible when required. The development of novel and improved bioanalytical methods for rapid, selective and sensitive detection is a wide and dynamic field of research. Biosensors offer precise detection of biotic and abiotic stressors in aquaculture and culture-based fisheries within no time. This review article allows filling the knowledge gap for detection and monitoring of chemical and microbial contaminants of abiotic and biotic origin in aquaculture and culture-based fisheries using nano(bio-) analytical technologies, including nano(bio-)molecular and nano(bio-)sensing techniques.

Two-Dimensional Protein Nanoarray as a Carrier of Sensing Elements for Gold-Based Immunosensing Systems

Homogeneous and high-density immobilization of proteins on gold-based sensing surface without the loss of protein activity is of great significance for high-performance immunosensing but remains challenging. To realize more sensitive immunosensing, an improved method for protein immobilization on the gold surface is urgently required. Here, we propose a biological and mild approach by combining a genetically encoded SpyTag-SpyCatcher interaction system with a redesigned S-layer of bacteria. This method allows proteins of interest to be covalently linked with the S-layer in a biological manner and arranged orderly in a two-dimensional nanoarray on the gold surface. The activity of African swine fever virus proteins was significantly preserved after immobilization. In addition, our S-layer-based immobilization method exhibited an eightfold increase in detection sensitivity compared with the conventional chemical cross-linking for protein immobilization during serological tests. Together, our S-layer-based immobilization method provides an innovative approach for building a quality gold-based biosensing interface and should greatly contribute to the high-sensitivity sensing for a deeper understanding of pathogen infection and host immunity.

Mathematical Analysis of Reaction-Diffusion Equations Modeling the Michaelis-Menten Kinetics in a Micro-Disk Biosensor

In this study, we have investigated the mathematical model of an immobilized enzyme system that follows the Michaelis-Menten (MM) kinetics for a micro-disk biosensor. The film reaction model under steady state conditions is transformed into a couple differential equations which are based on dimensionless concentration of hydrogen peroxide with enzyme reaction (H) and substrate (S) within the biosensor. The model is based on a reaction-diffusion equation which contains highly non-linear terms related to MM kinetics of the enzymatic reaction. Further, to calculate the effect of variations in parameters on the dimensionless concentration of substrate and hydrogen peroxide, we have strengthened the computational ability of neural network (NN) architecture by using a backpropagated Levenberg-Marquardt training (LMT) algorithm. NNs-LMT algorithm is a supervised machine learning for which the initial data set is generated by using MATLAB built in function known as "pdex4". Furthermore, the data set is validated by the processing of the NNs-LMT algorithm to find the approximate solutions for different scenarios and cases of mathematical model of micro-disk biosensors. Absolute errors, curve fitting, error histograms, regression and complexity analysis further validate the accuracy and robustness of the technique.

Application of dendrimer-based nanosensors in immunodiagnosis

Conventional immunoassays such as ELISA and FLISA have been used for clinical diagnosis for a long time. These assays are complex, time-consuming, and uneconomical. They have been overwhelmed with newer and more efficient methods such as electrochemical and electrochemiluminescent immunosensors that are cost-effective and require less time. Immunosensor is a biosensor that consists of a signal transducer and a biologically interactive system such as antigen and antibody interaction. Recent advances in nanotechnology have seen numerous efforts towards the usage of nanoparticles such as dendrimers in immunoassays. Dendrimers are highly branched structures with a high density of active peripheral groups, expanding their wide range of applications in immunoassays. A vast number of peripheral groups enrich the sensitivity of the immunosensor by governing the orientation of the antibody on the sensor surface. The current review highlights recent progress and developments in applying dendrimers for different immunoassays and their applicability in analyzing various biomarkers in clinical disease diagnosis.

Review of Detection and Quantification of Rabies Virus Antibodies

Rabies is an almost invariably fatal disease. According to the World Health Organization (WHO), rabies virus neutralizing antibody (RVNA) titers of ≥0.5 IU/mL are considered adequate for rabies protection. Therefore, detection and quantification of RABV antibodies are important. Many methods have been developed for detecting RABV antibodies. In the present study, we reviewed several methods of detecting RABV antibodies in human and animal samples and evaluated and compared their performance. Of 34 methods, 5 demonstrated unsatisfactory sensitivity or specificity. The others exhibited sensitivity and specificity of ≥75%. The correlation coefficient for five of eight methods was >0.8. The Bland-Altman mean bias of five of five methods was <±2.0. The kappa values of 25 of 28 methods were higher than 0.4, demonstrating at least moderate agreement. Analysis of the performance of these methods emphasized that any new technology should be considered carefully and objectively before being used as an appropriate and applicable alternative.

Application of Nanotechnology in Analysis and Removal of Heavy Metals in Food and Water Resources

Toxic heavy metal contamination in food and water from environmental pollution is a significant public health issue. Heavy metals do not biodegrade easily yet can be enriched hundreds of times by biological magnification, where toxic substances move up the food chain and eventually enter the human body. Nanotechnology as an emerging field has provided significant improvement in heavy metal analysis and removal from complex matrices. Various techniques have been adapted based on nanomaterials for heavy metal analysis, such as electrochemical, colorimetric, fluorescent, and biosensing technology. Multiple categories of nanomaterials have been utilized for heavy metal removal, such as metal oxide nanoparticles, magnetic nanoparticles, graphene and derivatives, and carbon nanotubes. Nanotechnology-based heavy metal analysis and removal from food and water resources has the advantages of wide linear range, low detection and quantification limits, high sensitivity, and good selectivity. There is a need for easy and safe field application of nanomaterial-based approaches.

Rapid electrochemical detection of Escherichia coli using nickel oxidation reaction on a rotating disk electrode

A standalone electrochemical method for detecting the bacterium Escherichia coli in water was developed using a nickel electrode and no biorecognition element. Electric current responses from different E. coli concentrations were recorded based on their interaction with a locally formed electrocatalyst. A rotating disk electrode was used to minimize the mass transport limitations at the interface. Results from experiments with the rotating disk electrode also paved the way for hypothesizing the detection mechanism. The operating conditions were established for sensing the electric current responses in the presence of E. coli. The least-squares linear regression model was fit to the data obtained from currents of some known E. coli concentrations. This probe had a detection limit in the order of 104 CFU/ml. The response time to detect the presence/absence of E. coli was less than half a second, while the total assay time, including quantification of its concentration, was 10 min. The electric current response from a solution mixed with E. coli and S. aureus showed current similar to E. coli only solution indicating the specificity of the sensor to respond to signals from E. coli. This electrochemical microbial sensor's uniqueness lies in its ability to rapidly detect E. coli by forming the catalyst locally on demand without the attachment of biorecognition elements.

Advances in nanomaterial-based electrochemical biosensors for the detection of microbial toxins, pathogenic bacteria in food matrices

There is a growing demand to protect food products against the hazard of microbes and their toxins. To satisfy such goals, it is important to develop highly sensitive, reliable, sophisticated, rapid, and cost-effective sensing techniques such as electrochemical sensors/biosensors. Although diverse forms of nanomaterials (NMs)-based electrochemical sensing methods have been introduced in markets, the reliability of commercial products is yet insufficient to meet the practical goal. In this review, we focused on: 1) sources of pathogenic microbes and their toxins; 2) possible routes of their entrainment in food, and 3) current development of NM-based biosensors to realize real-time detection of the target analytes. At last, future prospects and challenges in this research field are discussed.

A reusable colorimetric assay based on mixed valence state Ce-MOF@Pt nanoparticles for highly sensitive detection of visfatin

In this work, a colorimetric assay for visfatin detection is described. The mixed valence state Ce-MOF (MVCM) modified by platinum nanoparticles (Pt NPs) is used as a novel catalyst. MVCM exhibits excellent intrinsic peroxidase-like catalytic activity due to the spontaneous recycling of the Ce(III)/Ce(IV) system. Pt NPs serve not only as a carrier of the -NH₂-modified single strand DNA (S1) but also as a synergistic catalyst of MVCM. The capture probe (S2) attached to the streptavidin-modified magnetic beads (Mag-SA) could combine with the aptamer to form the Mag-SA/S2/aptamer complex. When in the presence of the target visfatin, aptamer specifically combines with the visfatin, which induces the release of Mag-SA/S2 from the Mag-SA/S2/aptamer complex. At this time, the MVCM@Pt/S1 complex connects with the released Mag-SA/S2, which quickly catalyzes the 3,3,3',3'-tetramethylbenzidine (TMB), leading to a color change. Under optimal conditions, the absorbance increases linearly when the concentration ranges from 1 ng mL^-1 to 100 ng mL^-1, and the detection limit is as low as 0.11 ng mL^-1. Furthermore, Mag-SA/S2 can be reused at least five times by using the uracil-DNA glycosylase (UDG) and an external magnetic field. The proposed method shows satisfying reproducibility, stability, specificity, and sensitivity, and it was successfully applied to detect visfatin in spiked human serum samples. Thus, it has great potential for clinical research, detection, and catalytic applications.

Integrated Experimental and Theoretical Studies on an Electrochemical Immunosensor

Electrochemical immunosensors (EIs) integrate biorecognition molecules (e.g., antibodies) with redox enzymes (e.g., horseradish peroxidase) to combine the advantages of immunoassays (high sensitivity and selectivity) with those of electrochemical biosensors (quantitative electrical signal). However, the complex network of mass-transfer, catalysis, and electrochemical reaction steps that produce the electrical signal makes the design and optimization of EI systems challenging. This paper presents an integrated experimental and modeling framework to address this challenge. The framework includes (1) a mechanistic mathematical model that describes the rate of key mass-transfer and reaction steps; (2) a statistical-design-of-experiments study to optimize operating conditions and validate the mechanistic model; and (3) a novel dimensional analysis to assess the degree to which individual mass-transfer and reaction steps limit the EI's signal amplitude and sensitivity. The validated mechanistic model was able to predict the effect of four independent variables (working electrode overpotential, pH, and concentrations of catechol and hydrogen peroxide) on the EI's signal magnitude. The model was then used to calculate dimensionless groups, including Damkohler numbers, novel current-control coefficients, and sensitivity-control coefficients that indicated the extent to which the individual mass-transfer or reaction steps limited the EI's signal amplitude and sensitivity.

Antibodies Versus Aptamers: A Comparative View

Antibodies are large proteins generated in vivo to bind specifically to a wide spectrum of targets ranging from biological to environmental molecules. They play a vital role in research, diagnostics, sensing, and therapeutic applications. Over the past few decades, advancements have been made to improve the performance of antibodies, specifically in the area of immunosensors. However, there has been an urgent need for alternative high-quality recognition probes that can be produced synthetically in bulk quantity to ensure better reproducibility and lower cost, as well as avoiding the need of using animals in the production process. Aptamers are synthetic nucleic acid single-stranded (ss) DNAs or RNAs that can bind with high affinity and specificity to their targets. They can be generated via in vitro section protocol, known as systematic evolution of ligands by exponential enrichment (SELEX). The advantages of aptamers promoted their successful incorporation in several signal transduction schemes, some of which reached the commercial market for point-of-care and in-field applications. This chapter describes the two types of affinity reagents: antibodies and aptamers, and their methods of production, advantages, and limitations. The focus will be directed at their incorporation in analytical transduction methods and how aptamer molecular size as well as unique conformational change upon target binding has triggered the evolution of new sensing methods.

The Role of Electrochemical Immunosensors in Clinical Analysis

An immunosensor is a kind of affinity biosensor based on interactions between an antigen and specific antigen immobilized on a transducer surface. Immunosensors possess high selectivity and sensitivity due to the specific binding between antibody and corresponding antigen, making them a suitable platform for several applications especially in the medical and bioanalysis fields. Electrochemical immunosensors rely on the measurements of an electrical signal recorded by an electrochemical transducer and can be classed as amperometric, potentiometric, conductometric, or impedimetric depending on the signal type. Among the immunosensors, electrochemical immunosensors have been more perfected due to their simplicity and, especially their ability to be portable, and for in situ or automated detection. This review addresses the potential of immunosensors destined for application in clinical analysis, especially cancer biomarker diagnosis. The emphasis is on the approaches used to fabricate electrochemical immunosensors. A general overview of recent applications of the developed electrochemical immunosensors in the clinical approach is described.

Amperometric myeloperoxidase immunoassay based on the use of CuPdPt nanowire networks

This research describes a nanowire network-based method for detecting the activity of myeloperoxidase (MPO), a biomarker of acute coronary syndromes (ACS). Trimetallic CuPdPt nanowire networks (CuPdPt NWNWs) were prepared by a one-step chemical reduction method. The metallic precursors quickly form nanowire network structures without the need for additional capping agents or surfactants. This process creates a product with a clean surface. The NWNWs were dropped onto a glassy carbon electrode (GCE) to obtain a sensor with good catalytic activity towards the reduction of hydrogen peroxide (H₂O₂), which was used as an electrochemical probe working at -0.4 V (vs. SCE). It also provided a large surface for further modification. Next, an antibody against MPO was immobilized on the modified GCE via the stable conjunction between Cu, Pt, Pd and amino groups. Upon binding of MPO to the antibody on the GCE, the current response to H₂O₂ was reduced by 35 μA·cm^-2. The immunosensor had a linear response within the 100 fg·mL^-1 to 50 ng·mL^-1 MPO concentration range and a 33 fg·mL^-1 detection limit (at an S/N ratio of 3). The recovery of spiked serum samples ranged from 99.8 to 103.6%. This result suggests that the method can be applied to the quantitation of MPO in human serum samples. Graphical abstract A trimetallic CuPdPt nanowire networks was placed on a glassy cabon electrode (GCE) to design an immunosensor for myeloperoxidase (MPO), a biomarker for the acute coronary syndrome (ACS). Antibody against MPO was immobilized on the network via conjugation between Cu, Pt, Pd and amino groups. Amperometric i-t measurements were conducted to quantify the amount of MPO that binds to the antibody on the surface of the modified GCE.

Nanomaterials for Electrochemical Immunosensing

Electrochemical immunosensors resulting from a combination of the traditional immunoassay approach with modern biosensors and electrochemical analysis constitute a current research hotspot. They exhibit both the high selectivity characteristics of immunoassays and the high sensitivity of electrochemical analysis, along with other merits such as small volume, convenience, low cost, simple preparation, and real-time on-line detection, and have been widely used in the fields of environmental monitoring, medical clinical trials and food analysis. Notably, the rapid development of nanotechnology and the wide application of nanomaterials have provided new opportunities for the development of high-performance electrochemical immunosensors. Various nanomaterials with different properties can effectively solve issues such as the immobilization of biological recognition molecules, enrichment and concentration of trace analytes, and signal detection and amplification to further enhance the stability and sensitivity of the electrochemical immunoassay procedure. This review introduces the working principles and development of electrochemical immunosensors based on different signals, along with new achievements and progress related to electrochemical immunosensors in various fields. The importance of various types of nanomaterials for improving the performance of electrochemical immunosensor is also reviewed to provide a theoretical basis and guidance for the further development and application of nanomaterials in electrochemical immunosensors.

A novel classification of prostate specific antigen (PSA) biosensors based on transducing elements

During the last few decades, there has been a tremendous rise in the number of research studies dedicated towards the development of diagnostic tools based on bio-sensing technology for the early detection of various diseases like cardiovascular diseases (CVD), many types of cancer, diabetes mellitus (DM) and many infectious diseases. Many breakthroughs have been developed in the areas of improving specificity, selectivity and repeatability of the biosensor devices. Innovations in the interdisciplinary areas like biotechnology, genetics, organic electronics and nanotechnology also had a great positive impact on the growth of bio-sensing technology. As a product of these improvements, fast and consistent sensing policies have been productively created for precise and ultrasensitive biomarker-based disease diagnostics. Prostate-specific antigen (PSA) is widely considered as an important biomarker used for diagnosing prostate cancer. There have been many publications based on various biosensors used for PSA detection, but a limited review was available for the classification of these biosensors used for the detection of PSA. This review highlights the various biosensors used for PSA detection and proposes a novel classification for PSA biosensors based on the transducer type used. We also highlight the advantages, disadvantages and limitations of each technique used for PSA biosensing which will make this article a complete reference tool for the future researches in PSA biosensing.

Advances in nanomaterials and their applications in point of care (POC) devices for the diagnosis of infectious diseases

Nanotechnology has gained much attention over the last decades, as it offers unique opportunities for the advancement of the next generation of sensing tools. Point-of-care (POC) devices for the selective detection of biomolecules using engineered nanoparticles have become a main research thrust in the diagnostic field. This review presents an overview on how the POC-associated nanotechnology, currently applied for the identification of nucleic acids, proteins and antibodies, might be further exploited for the detection of infectious pathogens: although still premature, future integrations of nanoparticles with biological markers that target specific microorganisms will enable timely therapeutic intervention against life-threatening infectious diseases.

Aptamer-Based Technologies in Foodborne Pathogen Detection

Aptamers are single stranded DNA or RNA ligands, which can be selected by a method called systematic evolution of ligands by exponential enrichment (SELEX); and they can specifically recognize and bind to their targets. These unique characteristics of aptamers offer great potentials in applications such as pathogen detection and biomolecular screening. Pathogen detection is the critical means in detecting and identifying the problems related to public health and food safety; and only the rapid, sensitive and efficient detection technologies can enable the users to make the accurate assessments on the risks of infections (humans and animals) or contaminations (foods and other commodities) caused by various pathogens. This article reviews the development in the field of the aptamer-based approaches for pathogen detection, including whole-cell SELEX and Genomic SELEX. Nowadays, a variety of aptamer-based biosensors have been developed for pathogen detection. Thus, in this review, we also cover the development in aptamer-based biosensors including optical biosensors for multiple pathogen detection by multiple-labeling or label-free models such as fluorescence detection and surface plasmon resonance, electrochemical biosensors and lateral chromatography test strips, and their applications in pathogen detection and biomolecular screening. While notable progress has been made in the field in the last decade, challenges or drawbacks in their applications such as pathogen detection and biomolecular screening remain to be overcome.

Use of Piezoelectric Immunosensors for Detection of Interferon-Gamma Interaction with Specific Antibodies in the Presence of Released-Active Forms of Antibodies to Interferon-Gamma

In preliminary ELISA studies where released-active forms (RAF) of antibodies (Abs) to interferon-gamma (IFNg) were added to the antigen-antibody system, a statistically significant difference in absorbance signals obtained in their presence in comparison to placebo was observed. A piezoelectric immunosensor assay was developed to support these data and investigate the effects of RAF Abs to IFNg on the specific interaction between Abs to IFNg and IFNg. The experimental conditions were designed and optimal electrode coating, detection circumstances and suitable chaotropic agents for electrode regeneration were selected. The developed technique was found to provide high repeatability, intermediate precision and specificity. The difference between the analytical signals of RAF Ab samples and those of the placebo was up to 50.8%, whereas the difference between non-specific controls and the placebo was within 5%–6%. Thus, the piezoelectric immunosensor as well as ELISA has the potential to be used for detecting the effects of RAF Abs to IFNg on the antigen-antibody interaction, which might be the result of RAF’s ability to modify the affinity of IFNg to specific/related Abs.

Enlightening surface plasmon resonance effect of metal nanoparticles for practical spectroscopic application

Pictorial depiction of applications of metal nanoparticles in different fields enlightening surface plasmon resonance effect.

Electrochemical immunosensors and their recent nanomaterial-based signal amplification strategies: a review

In recent years, tremendous advances have been made in biosensors based on nanoscale electrochemical immunosensors for use in the fields of agriculture, food safety, biomedicine, quality control, and environmental and industrial monitoring.

A review on amperometric-type immunosensors based on screen-printed electrodes

In this brief review, we summarize the recent research activities involved in the development of amperometric-type immunosensors based on screen-printed electrodes (SPEs). We focus on the underlying principle involved in these types of sensors, their fabrication and electrode surface modification. We also discuss the various factors involved in the designing of such immunosensors and how they affect their performances. Finally we provide an insight into the drawbacks associated with these SPEs.

Oxovanadium–salen and –salan complexes as effective labels for electrochemical immunosensing: a case study for estradiol detection

The principle of an electrochemical estradiol immunosensor.

Magnetic nanoparticle-based immunosensor for electrochemical detection of hepatitis B surface antigen

An electrochemical immunosensor was developed for the detection of hepatitis B surface antigen (HBsAg). The biotinylated hepatitis B surface antibody was immobilized on streptavidin magnetic nanoparticles and used for targeting the HBsAg. By the addition of horseradish peroxidase conjugated with secondary antibody (HRP-HBsAb), a sandwich-type immunoassay format was formed. Aminophenol as substrate for conjugated HRP was enzymatically changed into 3-aminophenoxazone (3-APZ). This electroactive enzymatic production (3-APZ) was transferred into an electrochemical cell and monitored by cyclic voltammetry. Under optimal conditions, the cathodic current response of 3-APZ, which was proportional to the HBsAg concentration, was measured by a glassy carbon electrode. The immunosensor response was linear toward HBsAg in the concentration range from 0.001 to 0.015 ng/ml with a detection limit of 0.9 pg/ml at a signal/noise ratio of 3.

Development of biosensors for the detection of biological warfare agents: its issues and challenges

This review discusses current development in biosensors for the detection of biological warfare agents (BWAs). BWAs include bacteria, virus and toxins that are added deliberately into air water and food to spread terrorism and cause disease or death. The rapid and unambiguous detection and identification of BWAs with early warning signals for detecting possible biological attack is a major challenge for government agencies particularly military and health. The detection devices--biosensors--can be classified (according to their physicochemical transducers) into four types: electrochemical, nucleic acid, optical and piezoelectric. Advantages and limitations of biosensors are discussed in this review followed by an assessment of the current state of development of different types of biosensors. The research and development in biosensors for biological warfare agent detection is of great interest for the public as well as for governments.