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.     

Biosensors

Biosensors are analytical devices that respond selectively to analytes in an appropriate sample and convert their concentration into an electrical signal via a combination of a biological recognition system and an electrochemical, optical or other transducer. Such devices will find application in medicine, agriculture, environmental monitoring and the bioprocessing industries. The last few years have seen great advances in the design of sensor architectures, the marriage of biological systems with monolithic silicon and optical technologies, the development of effective electron-transfer systems and the configuration of direct immunosensors. Recent progress in these areas has already led to the introduction of new-generation biosensors into the competitive diagnostics market place.     

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.     

Immunosensors: Antibody-based biosensors

The challenges in developing practical immunosensors lie in converting (without added reagents) the binding event into an electrical or optical signal, and in creating fully reversible systems capable of monitoring both increases and decreases in analyte concentration. Numerous approaches are under investigation, some of which should lead to commercial products within a couple of years; their strengths and limitations are reviewed.     

Optical Immunosensors for the Efficient Detection of Target Biomolecules

Recently, immunosensors have attracted attention because they are widely applied for the detection of various pathogens. Among the commonly used immunosensors, the optical immunosensor features prominently as an effective tool for the quantification of the amount of antibodies, antigens, or haptens in complex samples with high sensitivity and specificity. However, very few studies provide comprehensive overviews of optical immunosensors. In this review, we present various methods and applications of optical immunosensors in pathogen detection. We introduced a concise definition of optical immunosensors and the principle of using them for detection. We subsequently discuss the main categories of optical immunosensors and their application to the detection of pathogens, as well as their advantages and limitations. Recent publications from 2006 to 2015 on variously designed optical immunosensors have also been updated. We conclude the review with a brief summary and discuss future directions of optical immunosensors.     

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.     

DNA生物传感器进展

近几年来,酶传感器、免疫传感器及微生物传感器等发展较为成熟,而DNA生物传感器的研究相对较少.文章从核酸杂交的原理出发介绍了DNA生物传感器的工作原理,举例说明了电化学、光学和声学等几种典型的DNA生物传感器,指出了其固有的优缺点,肯定了DNA传感器发展前景.     

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.     

Novel immunosensors

The development of practical immunosensors is an important topic for biosensor research. Recently the authors have demonstrated novel immuno-sensors called, respectively, the reactor-type enzyme immunosensor, the potentiometric sensing system for pathogenic microbes, the piezo-immunosensor, the pulse immunoassay, the bio-image sensor and the photofluctuation immunosensor. These six types of immunosensors based on novel principles are described.     

Current developments in optical biochemical sensors

By combining modern fibre optics and opto-electronic instrumentation with chemical and biochemical reagent systems, it has become possible to fabricate optical biosensors. The current state of the art in this development is reviewed in this paper. Many developments describe selective and sensitive methods for sensing bioanalytes and it is likely that such a development will continue to be a very active area of analytical research. However, these biosensing devices can be regarded as successful only if their practicality and reliability can be demonstrated.     

An assay for human chorionic gonadotrophin using the capillary fill immunosensor

Recently there has been much research effort directed towards the development of immunosensors. Optical technologies are currently proving very attractive for the construction of such sensors. The fluorescence capillary fill device (FCFD) has been designed to fulfil these needs. The development of an assay for human chorionic gonadotrophin (hCG) in the FCFD for a variety of body fluids (whole blood, serum, urine and saliva) demonstrates the versatility and assay performance of the device.     

Towards development of chemosensors and biosensors with metal-oxide-based nanowires or nanotubes

The emerging nanotechnology has opened new exciting opportunities to explore analytical applications of the freshly prepared nanostructured materials. Among them, metal-oxide-based nanowires or nanotubes attracted great attention due to their one-dimensional (1D) morphology, extraordinary physical and chemical properties, which offer great promise in the development of chemical sensing or biosensing, facilitating the great improvement of the selectivity and sensitivity of the current methods. In this review, the recent advances in the development of sensors including gas sensors, humidity sensors, and immunosensors using semiconducting metal-oxide-based nanowires or nanotubes are highlighted. Titanate (H(2)Ti(3)O(7)) nanotubes are of multilayered structures with a nanometer-scale inner-core cavity exposed to the outer surface and display different oxidation states with possible redox-activity, which make them attractive for sensing. Therefore, the use of titanate nanotubes for the development of electrochemical sensors is overviewed. Finally, the prospects and challenge in the further exploration of nanoscaled sensors are discussed.     

Tapered plastic optical fiber-based biosensor--tests and application

Cells detection is crucial in microbiological analysis of clinical, food, water or environmental samples. However, currently employed methods are time consuming. Plastic optical fiber (POF) biosensors consist in a viable alternative for rapid and inexpensive scheme for detection. In order to study the sensitivity of tapers for microbiological detection, geometric parameters are studied, such as the taper waist diameter since the formation of taper regions are the key sensing element in this particular type of sensors. In this study, a series of POF taper sensors were prepared using a specially developed tapering machine, and the dispersion of geometric dimensions is evaluated, aiming to achieve the best tapering characteristics which will provide a better sensitivity on the sensor response. The fiber tapers that presented the finest results were those constructed in U-shaped (bended) configurations, with taper waist diameters ranging from 0.40 mm up to 0.50 mm. These fiber tapers were used as the main section of the monitoring device, and when chemically treated as immunosensors for the detection of bacteria, yeast and erythrocytes.     

Visualization of the enzymatic activity in living systems using activated NMR contrast agents

New approaches to the development and some applications of novel paramagnetic "sensing" contrast agents designed for specific visualization of the enzymatic activity in living systems are reviewed. The activation of the above sensing agents includes either the cleavage or the synthesis of reactive precursor compounds that recombine with macromolecules with the formation of immobilized or rotationally inhibited paramagnetic cations. This effect results in strong changes of water proton relaxivity. The need in such agents is justified by efforts to utilize magnetic resonance imaging (MRI) for the visualization of fine structures in the living tissue as well as for increasing the molecular specificity of MRI. The review also contains information regarding recent efforts of increasing the sensitivity of MRI to the presence of paramagnetic cations in living systems.     

Immunosensors

The current trends and future aspects of the research and development of immunosensors are overviewed. A non-labelled immunosensor, whose selectivity depends on immunochemical affinity of an antigen for its corresponding antibody, has been developed as the basis for the potentiometric determination of an antigen, with an antibody-bound membrane or electrode. Non-labelled immunosensors for syphilis antibody, blood typing, human chorionic gonadotropin (HCG), and human serum albumin have been investigated. In contrast with non-labelled immunosensors, labelled immunosensors may be characterized by marked enhancement of sensitivity. Of these labelled immunosensors, enzyme immunosensors that use the chemical amplification of a labelling enzyme for sensitivity are promising. Enzyme immunosensors with an oxygen electrode have been developed to determine AFP, HCG, IgG and toxin. Bioaffinity sensors with a preformed metastable ligand-receptor complex, which are similar to the enzyme immunosensor have been found effective for the determination of thyroxine (T4), biotin, and insulin.     

Development of an immunosensor based on pressure transduction

Traditional strategies for signal transduction in immunosensors are based on piezoelectric, thermometric, electrochemical, magnetic and optical methods. The use of pressure as a signal transduction method in immunosensors has not been reported previously. An immunosensor incorporating the detection of a change in pressure as the signal-transducing mechanism was investigated. A commercially available ultra-low pressure sensor was used in conjunction with a sealed chamber to assess the feasibility of this strategy. A key feature of the current approach is the use of a thin membrane (or film) in which to perform an immunoassay and subsequently to detect production of gas. The thinness contributes to efficient gas evolution and minimizes the effect of liquid acting as a "sink" for gas molecules. This feature also simplifies measurement of evolved gas, which traditionally was based on the use of bulk solutions, shaking and pH changes to "release" dissolved gas (especially carbon dioxide). Gas generation in the current approach is achieved by the coupling of catalase to haptens or antibodies for use in competitive or sandwich immunoassays, respectively. Hydrogen peroxide is used as the substrate. Performance characteristics of the sensor apparatus were assessed in several ways. Injection of various volumes of air from a gas-tight syringe produced an essentially linear relationship from 0.2 to 2.0 microl of injected volume, with a slope of approximately 5 V/microl. Depending on the duration of the sampling period, specific signals in excess of 2 V have been obtained for 0.01 units of catalase (approximately 0.4 ng of protein). Development and use of this sensing apparatus will be described for both competitive and sandwich immunoassays.     

OPTICAL MONITORING AND FORECASTING SYSTEMS FOR HARMFUL ALGAL BLOOMS: POSSIBILITY OR PIPE DREAM?

Monitoring programs for harmful algal blooms (HABs) are currently reactive and provide little or no means for advance warning. Given this, the development of algal forecasting systems would be of great use because they could guide traditional monitoring programs and provide a proactive means for responding to HABs. Forecasting systems will require near real-time observational capabilities and hydrodynamic/biological models designed to run in the forecast mode. These observational networks must detect and forecast over ecologically relevant spatial/ temporal scales. One solution is to incorporate a multiplatform optical approach utilizing remote sensing and in situ moored technologies. Recent advances in instrumentation and data-assimilative modeling may provide the components necessary for building an algal forecasting system. This review will outline the utility and hurdles of optical approaches in HAB detection and monitoring. In all the approaches, the desired HAB information must be isolated and extracted from the measured bulk optical signals. Examples of strengths and weaknesses of the current approaches to deconvolve the bulk optical properties are illustrated. After the phytoplankton signal has been isolated, species-recognition algorithms will be required, and we demonstrate one approach developed for Gymnodinium breve Davis. Pattern-recognition algorithms will be species-specific, reflecting the acclimation state of the HAB species of interest.Field data will provide inputs to optically based ecosystem models, which are fused to the observational networks through data-assimilation methods. Potential model structure and data-assimilation methods are reviewed.     

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.     

Covalent bound sensing layers on surface acoustic wave (SAW) biosensors

This paper reports on the development of immunosensors based on commercially available surface acoustic wave (SAW) devices working at 380 MHz. Approaches for coating the sensor surface with a sensing layer of receptive biomolecules are presented and discussed. It was found that the sensitivity strongly relates to the immobilization method. Additionally, the sensitivity can be influenced by the density of accessible biomolecules on the active sensing area. Usually, by most of the standard immobilization procedures, two-dimensional layers of receptive biomolecules are obtained. We present a three-dimensional layer, which provides a higher absolute amount of recognition molecules. A dextran layer is photoimmobilized to the sensor surface and the recognition molecules are covalently embedded into the dextran matrix. The feasibility of specific immunosensing is investigated using SAW sensors connected to a fluid handling system.     

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.