Development of optical biosensor technologies for cardiac troponin recognition

Acute myocardial infarction (AMI) is the leading cause of death among cardiovascular diseases. Among the numerous attempts to develop coronary marker concepts into clinical strategies, cardiac troponin is known as a specific marker for coronary events. The cardiac troponin concentration level in blood has been shown to rise rapidly for 4–10 days after onset of AMI, making it an attractive approach for a long diagnosis window for detection. The extremely low clinical sensing range of cardiac troponin levels consequently makes the methods of detection highly sensitive. In this review, by taking into consideration optical methods applied for cardiac troponin detection, we discuss the most commonly used methods of optical immunosensing and provide an overview of the various diagnostic cardiac troponin immunosensors that have been employed for determination of cardiac troponin over the last several years.     

Immunosensors for detection of pesticide residues

Immunosensors are biosensors that use antibodies or antigens as the specific sensing element and provide concentration-dependent signals. There is great potential in the applications of immunosensing technologies for rapid detection of pesticide residues in food and environment. This paper presents an overview of various transduction systems, such as electrochemical, optical, piezoelectric, and nanomechanics methods, which have been reported in the literature in the design and fabrication of immunosensors for pesticide detection. Various immobilization protocols used for formation of a biorecognition interface are also discussed. In addition, techniques of regeneration, signal amplification, miniaturization, and antibodies are evaluated for the development and applications of these immunosensors. It can be concluded that despite some limitations of the immunosensing technologies, these immuosensors for pesticide monitoring are becoming more and more relevant in environmental and food analysis.     

Nanostructured material-based optical and electrochemical detection of amoxicillin antibiotic

The penicillin derivative amoxicillin (AMX) plays an important role in treating various types of infections caused by bacteria. However, excessive use of AMX may have negative health effects. Therefore, it is of utmost importance to detect and quantify the AMX in pharmaceutical drugs, biological fluids, and environmental samples with high sensitivity. Therefore, this review article provides valuable and up-to-date information on nanostructured material-based optical and electrochemical sensors to detect AMX in various biological and chemical samples. The role of using different nanostructured materials on the performance of important optical sensors such as colorimetric sensors, fluorescence sensors, surface-enhanced Raman scattering sensors, chemiluminescence/electroluminescence sensors, optical immunosensors, optical fibre-based sensors, and several important electrochemical sensors based on different electrode types have been discussed. Moreover, nanocomposites, polymer, and MXenes-based electrochemical sensors have also been discussed, in which such materials are being used to further enhance the sensitivity of these sensors. Furthermore, nanocomposite-based photo-electrochemical sensors and the market availability of biosensors including AMX have also been discussed briefly. Finally, the conclusion, challenges, and future perspectives of the above-mentioned sensing techniques for AMX detection are presented.     

Rapid and label-free bacteria detection by surface plasmon resonance (SPR) biosensors

Surface Plasmon Resonance (SPR) biosensor technology has been successfully used for the detection of various analytes such as proteins, drugs, DNA, and microorganisms. SPR-based immunosensors that coupled with a specific antigen-antibody reaction, have become a promising tool for the quantification of bacteria as it offers sensitive, specific, rapid, and label-free detection. In this paper, we review the important issues in the development of SPR-based immunoassays for bacteria detection, concentrating on instrumentation, surface functionalization, liquid handling, and surface regeneration. In addition, this review touches on the recent advances in SPR biosensing for sensitivity enhancement.     

Advances in ovarian cancer diagnosis: A journey from immunoassays to immunosensors

This review focuses on the technological advancements, challenges and trends in immunoassay technologies for ovarian cancer diagnosis. Emphasis is placed on the principles of the technologies, their merits and limitations and on the evolution from laboratory-based methods to point-of-care devices. While the current market is predominantly associated with clinical immunoassay kits, over the last decade a major thrust in development of immunosensors is evident due to their potential in point-of-care devices. Technological advancements in immunosensors, extending from labeled to label-free detection, with and without mediators, for enhancing proficiencies and reliability have been dealt with in detail. Aspects of the utilisation of nanomaterials and immobilization strategies for enhancing sensitivity and altering the detection range have also been addressed. Finally, we have discussed some distinct characteristics and limitations associated with the recently commericalised technologies used for quantitation of relevant ovarian cancer markers.     

State of the art and recent advances in immunoanalytical systems

This article is an overview the state of the art and the recent developments in immunosensors. Homogeneous immunosensors, heterogeneous immunosensors, integrated immunosensors and biochip format immunosensors are presented, based on optical, electrochemical, magnetic or mechanical detection/transduction systems.     

Development of immunosensors using carbon nanotubes

With increasing reports on bioterrorism, avian flu, and other bio-threats, rapid and real time detection methods are highly warranted. Studies on developing highly sensitive immunosensors aiming at the early detection and clinical diagnoses of various diseases including cancer are undertaken all over the globe. Carbon nanotubes (CNTs) have been widely discussed as materials with enormous potential for a wide range of in vivo and in vitro bioapplications, ranging from drug delivery to highly sensitive biosensors, owing to their superior electronic and mechanical properties along with nanoscale dimensions. Though a lot of attention has been drawn toward carbon nanotubes for the past 15 years in academia and to a certain extent in industry, CNT-based immunosensors and other applications are still in the nascent stage, and there are many challenges to be overcome for the successful commercialization of the concepts. This article highlights on the recent developments and the possible impacts of carbon nanotube based immunosensors.     

Optical immunosensing systems--meeting the market needs

Optical immunosensors and sensing systems are biosensors which produce a quantitative measure of the amount of antibody, antigen or hapten present in a complex sample such as serum or whole blood. The market needs for such devices and their associated instrumentation are reviewed. A brief history of the development of optical immunosensors is presented and the performance of the most well-developed optical immunosensors for meeting these market needs is reviewed. One device, the fluorescent capillary fill device (FCFD) is reviewed in detail with respect to it fulfilling the market needs for an optical immunosensor. Areas for the future development of such sensing systems are also discussed.     

Electrochemical and chemiluminescent immunosensors for tumor markers

The determination of serum tumor markers plays an important role in clinical diagnoses for the patients with certain tumor-associated disease. Although many commercial kits have been applied in clinical immunoassays, conventional methods always have some disadvantages, resulting in the need of other new, efficient, and easily automated methods. Immunosensors, considered as a major development in immunochemical field, have attracted considerable attention. With the aim of rapid screening, many immunosensors that are small, semi-automated and portable are being developed. This brief review focuses on the current research of immunosensors for tumor markers based on the electrochemical and chemiluminescent detection with emphasis on recent advances, challenges, and trends. The works on series of novel immunosensors developed for the determination of tumor markers in our group in the last few years are also introduced.     

Recent trends in antibody based sensors

This review details recent advances in the fields of immunosensors and closely related immunoassays in the past decade, together with a discussion of possible future trends. Immunosensors can be classified by the way in which they transduce the signal produced upon the formation of an antibody antigen complex. Recent advancements to these methods of detection and transduction are discussed in detail, with particular focus on electrochemical, optical, piezoelectric and magnetic based sensors. The varying applications of these sensors are also discussed. Some of the most significant advances include development of immunosensors for the continuous monitoring of analytes, point of care (PoC) devices, with lower unit costs, automation, reusability and ease of use. Immunosensor technology has advanced at a prolific rate since its conception and has grown into a diverse area of ongoing research.     

Aptamers: versatile probes for flow cytometry

Aptamers are nucleic acid oligomers with distinct conformational shapes that allow them to bind targets with high affinity and specificity. Aptamers are selected from a random oligonucleotide library by their capability to bind a certain molecular target. A variety of targets ranging from small molecules like amino acids to complex targets and whole cells have been used to select aptamers. These characteristics and the ability to create specific aptamers against virtually any cell type in a process termed “systematic evolution by exponential enrichment” make them interesting tools for flow cytometry. In this contribution, we review the application of aptamers as probes for flow cytometry, especially cell-phenotyping and detection of various cancer cell lines and virus-infected cells and pathogens. We also discuss the potential of aptamers combined with nanoparticles such as quantum dots for the generation of new multivalent detector molecules with enhanced affinity and sensitivity. With regard to recent advancements in aptamer selection and the decreasing costs for oligonucleotide synthesis, aptamers may rise as potent competitors for antibodies as molecular probes in flow cytometry.     

A novel microfluidic immunoassay system based on electrochemical immunosensors: an application for the detection of NT-proBNP in whole blood

Electrochemical immunosensors have attracted great interest in the search for a selective, simple and reliable system for molecular recognition. Presently, electrochemical immunosensors have been widely studied for biomedical molecular's detection, but the regeneration of these immunosensors has restricted their wide application. To prepare a regeneration-free immunosensor, which may be more suitable for clinical determination, a repeatable immunoassay system was developed based on an electrochemical immunosensor with magnetic nanoparticles, biotin-avidin system (BAS) and Fab antibodies for the heart failure markers aminoterminal pro-brain natriuretic peptides (NT-proBNP). At the same time, a microfluidic system was combined into the proposed system, which enabled continuous determination. Using NT-proBNP as a model system, the proposed immunosensor exhibited rapid and sensitive amperometric response to NT-proBNP with good selectivity, stability, and a wide linear range (0.005-1.67 ng/mL and 1.67-4 ng/mL with a detection limit of 0.003 ng/mL under optimal conditions). Importantly, the proposed immunosensor was also suitable for the detection of other proteins and provided new opportunities for disease diagnosis.     

A comparative study of protein immobilization techniques for optical immunosensors.

This paper presents the results of a study of a number of antibody immobilization techniques for application to optical immunosensors. In particular, well-known methods such as covalent binding and physical adsorption have been extended to the Langmiur-Blodgett method in an attempt to improve the density and possibly the uniformity of orientation of monoclonal antibodies on an optical surface. The surface density of active immobilized antibodies was determined from enzyme immunoassay and their thickness and refractive index were deduced from ellipsometry. It is shown that, although high surface densities (500 ng/cm2) of antibody can be obtained, the major obstacle to the detection of low concentrations of antigens or haptens is the non-specific binding of foreign molecules to the sensing surface.     

Interplay between the cellular autophagy machinery and positive-stranded RNA viruses

Autophagy is a conserved cellular process that acts as a key regulator in maintaining cellular homeostasis. Recent studies implicate an important role for autophagy in infection and immunity by removing invading pathogens and through modulating innate and adaptive immune responses. However, several pathogens, notably some positive-stranded RNA viruses, have subverted autophagy to their own ends. In this review, we summarize the current understanding of how viruses with a positive-stranded RNA genome interact with the host autophagy machinery to control their replication and spread. We review the mechanisms underlying the induction of autophagy and discuss the pro- and anti-viral functions of autophagy and the potential mechanisms involved.     

Advances in molecular detection of Aspergillus: an update

Filamentous cosmopolitan fungi of the genus Aspergillus can be harmful in two ways, directly they can be opportunistic pathogens causing aspergillosis and indirectly due to aflatoxin production on food products which can lead to aflatoxicosis. Therefore, a number of methods have been proposed so far for detection of the fungi with lowest possible concentration at the earliest. Molecular methods such as PCR and/or in combination with certain techniques have been found to be useful for Aspergillus detection. We discuss here various technologies that have emerged in recent years and can possibly be used for the molecular detection of Aspergillus in an efficient way. These methods like RSIC, C-probe, and inversion probe with pyrosequencing or direct ss/dsDNA detection have been used for the identification of fungal or bacterial pathogens and thus formulate a ‘gold standard’ for Aspergillus detection.     

Plasmodesmata: the battleground against intruders

Plasmodesmata are intercellular channels that establish a symplastic communication pathway between neighboring cells in plants. Owing to this role, opportunistic microbial pathogens have evolved to exploit plasmodesmata as gateways to spread infection from cell to cell within the plant. However, although these pathogens have acquired the capacity to breach the plasmodesmal trafficking pathway, plants are unlikely to relinquish control over a structure essential for their survival so easily. In this review, we examine evidence that suggests plasmodesmata play an active role in plant immunity against viral, fungal and bacterial pathogens. We discuss how these pathogens differ in their lifestyles and infection modes, and present the defense strategies that plants have adopted to prevent the intercellular spread of an infection.     

Design and development of opto-electrochemical biosensing devices for diagnosing chronic kidney disease

Chronic kidney disease (CKD) is emerging as one of the major causes of the increase in mortality rate and is expected to become 5th major cause by 2050. Many studies have shown that it is majorly related to various risk factors, and thus becoming one of the major health issues around the globe. Early detection of renal disease lowers the overall burden of disease by preventing individuals from developing kidney impairment. Therefore, diagnosis and prevention of CKD are becoming the major challenges, and in this situation, biosensors have emerged as one of the best possible solutions. Biosensors are becoming one of the preferred choices for various diseases diagnosis as they provide simpler, cost-effective and precise methods for onsite detection. In this review, we have tried to discuss the globally developed biosensors for the detection of CKD, focusing on their design, pattern, and applicability in real samples. Two major classifications of biosensors based on transduction systems, that is, optical and electrochemical, for kidney disease have been discussed in detail. Also, the major focus is given to clinical biomarkers such as albumin, creatinine, and others related to kidney dysfunction. Furthermore, the globally developed sensors for the detection of CKD are discussed in tabulated form comparing their analytical performance, response time, specificity as well as performance in biological fluids.     

Recognition of bacterial pathogens and mucosal immunity

Rapid detection and elimination of pathogens invasive to intestinal tissue is essential to avoid prolonged gut inflammation, or systemic sepsis. The discovery of transmembrane or intracytoplasmic pattern recognition receptors that detect the presence of conserved microbial macromolecular structures has significantly advanced the understanding of how metazoans respond to and eliminate bacteria that have entered the intestinal mucosa. In this review, we highlight recent advances in the field of host recognition of bacterial pathogens and subsequent mucosal innate immune response. Additionally, some bacteria are pathogenic because they have evolved sophisticated mechanisms to evade the host mucosal innate immune response. We discuss advances in identifying the mechanisms by which pathogens evade detection by dampening the immune response.     

Exosomes and other microvesicles in infection biology: organelles with unanticipated phenotypes

The release of exosomes and other microvesicles by diverse prokaryotic and eukaryotic cells and organisms was first appreciated early in the 20th century. The functional properties of these organelles, however, have only recently been the focus of rigorous investigation. In this review, we discuss the release of microvesicles of varying complexity by diverse microbial pathogens. This includes vesicle secretion by Gram-negative bacteria, eukaryotic parasites of the kinetoplast lineage and opportunistic fungal pathogens of both the ascomycetes and basidiomycetes lineages. We also discuss vesicle release from mammalian cells brought about as a result of infection with bacteria, viruses and prions. In addition, we review the evidence showing that in their specific microenvironments, release of these organelles from diverse pathogens contributes to pathogenesis. Germane to this and based upon recent findings with Leishmania, we propose a model whereby exosome release by an intracellular pathogen serves as a general mechanism for effector molecule delivery from eukaryotic pathogen to host cell cytosol. These new findings linking exosomes and other microvesicles to infection biology have important implications for understanding the immune response to infection and for the design of research strategies aimed at the development of novel therapeutics and vaccines.     

Nanoparticle labels in immunosensing using optical detection methods

Efforts to improve the performance of immunoassays and immunosensors by incorporating different kinds of nanostructures have gained considerable momentum over the last decade. Apart from liposomes, which will not be discussed here, most groups focus on artificial, particulate marker systems, both organic and inorganic. The underlying detection procedures may be based either on electro-magnetical or optical techniques. This review will be confined to the latter only, comprising nanoparticle applications generating signals as diverse as static and time-resolved luminescence, one- and two-photon absorption, Raman and Rayleigh scattering as well as surface plasmon resonance and others. In general, all endeavors cited are geared to achieve one or more of the following goals: lowering of detection limits (if possible, down to single-molecule level), parallel integration of multiple signals (multiplexing), signal amplification by several orders of magnitude and prevention of photobleaching effects with concomitant maintenance of antigen binding specificity and sensitivity. Inorganic nanoparticle labels based on noble metals, semiconductor quantum dots and nanoshells appear to be the most versatile systems for these bioanalytical applications of nanophotonics.