Simultaneous detection of six biohazardous agents using a planar waveguide array biosensor

A surface plasmon resonance nanostructure containing graphene and BaTiO3 layers for sensitive defection of organic compounds

Organic compound-based sensors are used in a variety of significant fields, including medical research, azeotropic calibration, vegetable oil extraction, the shoe industry and geothermal power plants. Here, a high-performance, two-dimensional material-based organic compound sensor has been proposed using a surface plasmon resonance (SPR) nanostructure consisting of a BK7 glass prism, Ag, BaTiO₃, Ag, graphene and sensing layer. The reflectivity curves of the SPR device have been investigated when the sensing media are Pentane, n-Hexane, n-Heptane and n-Octane. The thickness of the BaTiO₃ layer and the number of graphene sheets have been optimized to maximize the sensitivity. The highest sensitivity attained is 220.83 deg/RIU for n-Octane with 45 nm silver/10 nm BaTiO₃/8 nm silver and four layers of graphene. We believe that the SPR-based sensors are simple and can replace the spectrometry, chromatography and electrochemical based sensors. The proposed design is extremely effective for diverse applications in biological, industrial and chemical detection because of its simple structure and great performance.

Waveguide-based chemo- and biosensors: complex emulsions for the detection of caffeine and proteins

We report on a new modular sensing approach in which complex emulsions serve as efficient transducers in optical evanescent field-based sensing devices. Specifically, we leverage the tunable refractive index upon chemically triggered changes in droplet morphology or orientation. Variations in the optical coupling result in readily detectable changes in the light transmitted from a waveguide.

Detecting Biothreat Agents: From Current Diagnostics to Developing Sensor Technologies

Although a fundamental understanding of the pathogenicity of most biothreat agents has been elucidated and available treatments have increased substantially over the past decades, they still represent a significant public health threat in this age of (bio)terrorism, indiscriminate warfare, pollution, climate change, unchecked population growth, and globalization. The key step to almost all prevention, protection, prophylaxis, post-exposure treatment, and mitigation of any bioagent is early detection. Here, we review available methods for detecting bioagents including pathogenic bacteria and viruses along with their toxins. An introduction placing this subject in the historical context of previous naturally occurring outbreaks and efforts to weaponize selected agents is first provided along with definitions and relevant considerations. An overview of the detection technologies that find use in this endeavor along with how they provide data or transduce signal within a sensing configuration follows. Current "gold" standards for biothreat detection/diagnostics along with a listing of relevant FDA approved in vitro diagnostic devices is then discussed to provide an overview of the current state of the art. Given the 2014 outbreak of Ebola virus in Western Africa and the recent 2016 spread of Zika virus in the Americas, discussion of what constitutes a public health emergency and how new in vitro diagnostic devices are authorized for emergency use in the U.S. are also included. The majority of the Review is then subdivided around the sensing of bacterial, viral, and toxin biothreats with each including an overview of the major agents in that class, a detailed cross-section of different sensing methods in development based on assay format or analytical technique, and some discussion of related microfluidic lab-on-a-chip/point-of-care devices. Finally, an outlook is given on how this field will develop from the perspective of the biosensing technology itself and the new emerging threats they may face.

A portable optical waveguide resonance light-scattering scanner for microarray detection

In the present work, a portable and low-cost planar waveguide based resonance light scattering (RLS) scanner (termed as: PW-RLS scanner) has been developed for microarray detection. The PW-RLS scanner employs a 2 × 4 white light emitting diode array (WLEDA) as the excitation light source, a folded optical path with a complementary metal oxide semiconductor (CMOS) as the signal/image acquisition device and stepper motors with gear drives as the mechanical drive system. The biological binding/recognizing events on the microarray can be detected with an evanescent waveguide-directed illumination and light-scattering label (e.g., nanoparticles) while the microarray slide acts as an evanescent waveguide substrate. The performance of the as-developed PW-RLS scanner has been evaluated by analyzing type 2 diabetes mellitus (T2DM) risk genes. Highly selective and sensitive (less than 1% allele frequency at the attomole-level) T2DM risk gene detection is achieved using single-stranded DNA functionalized gold nanoparticles (ssDNA-GNPs) as detection probes. Additionally, the successful simultaneous analysis of 15 T2DM patient genotypes suggests that the device has great potential for the realization of a personalized diagnostic test for a given disease or patient follow-up.

Democratization of Nanoscale Imaging and Sensing Tools Using Photonics

Providing means for researchers and citizen scientists in the developing world to perform advanced measurements with nanoscale precision can help to accelerate the rate of discovery and invention as well as improve higher education and the training of the next generation of scientists and engineers worldwide. Here, we review some of the recent progress toward making optical nanoscale measurement tools more cost-effective, field-portable, and accessible to a significantly larger group of researchers and educators. We divide our review into two main sections: label-based nanoscale imaging and sensing tools, which primarily involve fluorescent approaches, and label-free nanoscale measurement tools, which include light scattering sensors, interferometric methods, photonic crystal sensors, and plasmonic sensors. For each of these areas, we have primarily focused on approaches that have either demonstrated operation outside of a traditional laboratory setting, including for example integration with mobile phones, or exhibited the potential for such operation in the near future.

Evaluation of optical detection platforms for multiplexed detection of proteins and the need for point-of-care biosensors for clinical use

This review investigates optical sensor platforms for protein multiplexing, the ability to analyze multiple analytes simultaneously. Multiplexing is becoming increasingly important for clinical needs because disease and therapeutic response often involve the interplay between a variety of complex biological networks encompassing multiple, rather than single, proteins. Multiplexing is generally achieved through one of two routes, either through spatial separation on a surface (different wells or spots) or with the use of unique identifiers/labels (such as spectral separation-different colored dyes, or unique beads-size or color). The strengths and weaknesses of conventional platforms such as immunoassays and new platforms involving protein arrays and lab-on-a-chip technology, including commercially-available devices, are discussed. Three major public health concerns are identified whereby detecting medically-relevant markers using Point-of-Care (POC) multiplex assays could potentially allow for a more efficient diagnosis and treatment of diseases.

Methods for Detection of Aflatoxins in Agricultural Food Crops

Aflatoxins are toxic carcinogenic secondary metabolites produced predominantly by two fungal species: Aspergillus flavus and Aspergillus parasiticus. These fungal species are contaminants of foodstuff as well as feeds and are responsible for aflatoxin contamination of these agro products. The toxicity and potency of aflatoxins make them the primary health hazard as well as responsible for losses associated with contaminations of processed foods and feeds. Determination of aflatoxins concentration in food stuff and feeds is thus very important. However, due to their low concentration in foods and feedstuff, analytical methods for detection and quantification of aflatoxins have to be specific, sensitive, and simple to carry out. Several methods including thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), mass spectroscopy, enzyme-linked immune-sorbent assay (ELISA), and electrochemical immunosensor, among others, have been described for detecting and quantifying aflatoxins in foods. Each of these methods has advantages and limitations in aflatoxins analysis. This review critically examines each of the methods used for detection of aflatoxins in foodstuff, highlighting the advantages and limitations of each method. Finally, a way forward for overcoming such obstacles is suggested.

Porous silicon integrated Mach-Zehnder interferometer waveguide for biological and chemical sensing

Optical waveguides comprised of nanoporous materials are uniquely suited for on-chip sensing applications, because they allow for a target chemical or analyte to directly infiltrate the optical material that comprises the core of the waveguide. We describe here the fabrication and characterization of nanoporous waveguides, and demonstrate their usefulness in measuring small changes in refractive index when exposed to a test analyte. We use a process of electrochemical etching and laser oxidation to produce channel waveguides and integrated on-chip Mach-Zehnder structures, and we compare the responsivity and interferometric stability of the integrated sensor to that of a fiber-based interferometer. We quantify the detection capability by selectively applying isopropanol to a 200 μm length waveguide segment in one arm of the interferometer, which produces a phase shift of 9.7 π. The integrated interferometer is shown to provide a more stable response in comparison to a comparable fiber-based implementation.

Cyclodextrin-Based Supramolecular Multilayer Assemblies for the Design of Biological Optical Sensors Using Tilted Fiber Bragg Gratings

In this work, we demonstrate the possibility to use optical fiber incorporating photowritten tilted fiber Bragg gratings (TFBG) as optical detection system for the real time monitoring of interfacial adsorption events and biological recognition. For this purpose, immobilization of cyclodextrin polymers onto the surface of optical fiber was envisioned through the layer-by-layer self-assembly method with the aim of developing sensing layers with well-defined host properties. To develop a biological sensor, amphiphilic dextran, acting as intermediate layer between the polyelectrolyte multilayer assembly and the biological probe, was immobilized though inclusion complex formation. The dextran layer exhibit a dual functionality: (i) it prevents non-specific proteins adsorption and (ii) it allows covalent immobilization of anti-bovine serum albumine through activation of the hydroxyl groups with 1,1’-carbonyl diimidazole. To verify the feasibility of our strategy, fluorescence microscopy was applied to evidence the effective inclusion of fluorescent macromolecular – flurorescein labelled dextran bearing adamantane as side-grafts – species within the cyclodextrin cavities present onto the optical fiber interface and at the last layer to prove the grafting of anti bovin serum albumin onto the amphiphilic dextran by a capture of fluorescein bovin serum albumin by the antibody layer. In a further step, it was demonstrated that the elaboration of the multilayer assembly can be monitored in real time using the TFBG sensor.

Use of a novel micro-fluidic device to create arrays for multiplex analysis of large and small molecular weight compounds by surface plasmon resonance

There is an increasing demand to develop biosensor monitoring devices capable of biomarker profiling for predicting animal adulteration and detecting multiple chemical contaminants or toxins in food produce. Surface plasmon resonance (SPR) biosensors are label free detection systems that monitor the binding of specific biomolecular recognition elements with binding partners. Essential to this technology are the production of biochips where a selected binding partner, antibody, biomarker protein or low molecular weight contaminant, is immobilised. A micro-fluidic immobilisation device allowing the covalent attachment of up to 16 binding partners in a linear array on a single surface has been developed for compatibility with a prototype multiplex SPR analyser. The immobilisation unit and multiplex SPR analyser were respectively evaluated in their ability to be fit-for-purpose for binding partner attachment and detection of high and low molecular weight molecules. The multiplexing capability of the dual technology was assessed using phycotoxin concentration analysis as a model system. The parent compounds of four toxin groups were immobilised within a single chip format and calibration curves were achieved. The chip design and SPR technology allowed the compartmentalisation of the binding interactions for each toxin group offering the added benefit of being able to distinguish between toxin families and perform concentration analysis. This model is particularly contemporary with the current drive to replace biological methods for phycotoxin screening.

Detection of pathogens in foods: the current state-of-the-art and future directions

Over the last fifty years, microbiologists have developed reliable culture-based techniques to detect food borne pathogens. Although these are considered to be the "gold-standard," they remain cumbersome and time consuming. Despite the advent of rapid detection methods such as ELISA and PCR, it is clear that reduction and/or elimination of cultural enrichment will be essential in the quest for truly real-time detection methods. As such, there is an important role for bacterial concentration and purification from the sample matrix as a step preceding detection, so-called pre-analytical sample processing. This article reviews recent advancements in food borne pathogen detection and discusses future methods with a focus on pre-analytical sample processing, culture independent methods, and biosensors.

Feasibility study for the rapid screening of target molecules using translational diffusion coefficients: diffusion-ordered NMR spectroscopy of biological toxins

A panel of 15 biological toxins ranging between approximately 60-28,000 g/mol was used to evaluate the feasibility of screening aqueous samples for toxin analytes based on their translational diffusion coefficients, D(t). Toxin D(t) values were measured by pulsed-field gradient (1)H NMR spectroscopy using a bipolar pulse pair, longitudinal eddy current delay pulse sequence incorporating water suppression to achieve the maximum dynamic range for toxin signals. To collect data for an effective screening protocol, reference D(t) values were determined from five independent measurements at both 25 and 37 degrees C for all toxins in the panel. In the protocol, D(t) values are measured at both temperatures for a suspected toxin target in a sample, and for assignment as a potential toxin analyte, the measurements are required to fall within +/-0.25 x 10(-6) cm(2)/s of both reference D(t) values for at least one toxin in the panel. Only solution viscosity was found to influence sample D(t) measurements appreciably; however, the measurements are easily corrected for viscosity effects by calculating the D(t) value of the suspected toxin at infinite dilution. In conclusion, the protocol provides a rapid and effective means for screening aqueous samples for all toxins in the panel, narrowing toxin identification to < or = 2 possibilities in virtually all cases.

Reactive surface coatings based on polysilsesquioxanes: controlled functionalization for specific protein immobilization

The key designing in reliable biosensors is the preparation of thin films in which biomolecular functions may be immobilized and addressed in a controlled and reproducible manner. This requires the controlled preparation of specific binding sites on planar surfaces. Poly(methylsilsesquioxane)-poly(pentafluorophenyl acrylates) (PMSSQ-PFPA) are promising materials to produce stable and adherent thin reactive coatings on various substrates. Those reactive surface coatings could be applied onto various materials, for example, gold, polycarbonate (PC), poly(tetrafluoroethylene) (PTFE), and glass. By dipping those substrates in a solution of a desired amine, specific binding sites for protein adsorption could be immobilized on the surface. The versatile strategy allowed the attachment of various linkers, for example, biotin, l-thyroxine, and folic acid. The adsorption processes of streptavidin, pre-albumin, and folate-binding protein were monitored using surface plasmon resonance (SPR), Fourier transform infrared (FTIR) spectroscopy, fluorescence spectroscopy, and atomic force microscopy (AFM). The presented protein immobilization strategy, consisting of four steps (a) spin-coating of PMSSQ-PFPA hybrid polymer from tetrahydrofuran (THF) solution, (b) annealing at 130 degrees C for 2 h to induce thermal cross-linking of the PMSSQ part, (c) surface analogues reaction with different amino-functionalized specific binding sites for proteins, and (d) controlled assembly of proteins on the surface, may find various applications in future biosensor design.

A multifunctional thin film Au electrode surface formed by consecutive electrochemical reduction of aryl diazonium salts

A multifunctional thin film surface capable of immobilizing two diverse molecules on a single gold electrode was prepared by consecutive electrodeposition of nitrophenyl and phenylboronic acid pinacol ester (PBA-PE) diazonium salts. Activation of the stacked film toward binding platinum nanoparticles (PtNPs) and yeast cells occurred via chemical deprotection of the pinacol ester followed by electroreduction of nitro to amino groups. FTIR spectral analysis was used to study and verify film composition at each stage of preparation. The affect of electrodeposition protocol over the thickness of the nitrophenyl and PBA-PE layers was explored and had a profound impact on the film properties. Thicker nitrophenyl films led to diminished PBA-PE diazonium reduction currents during assembly and decreased phenylboronic acid (PBA) layer thickness while allowing for higher PtNP loading and catalytic currents from PtNP-mediated peroxide reduction. Multilayer PBA films could be formed over the nitrophenyl film; however, only submonlayer PBA films permitted access to the underlying layer. The sequence of functional group activation toward binding was also shown to be significant, as perchlorate used to remove pinacol ester also converted aminophenyl groups accessible to the solution to nitrophenyl groups, preventing electrostatic PtNP binding. Finally, SEM images show PtNPs immobilized in close proximity (nanometers) to captured yeast cells on the PBA-aminophenyl-Au film. Such multibinding functionality films that maintain conductivity for subsequent electrochemical measurements hold promise for the development of electrochemical and/or optical platforms for fundamental cell studies, genomic and proteomic analysis, and biosensing.

Fluoroimmunoassays using the NRL array biosensor

Array-based biosensor technology offers the user the ability to detect and quantify multiple targets in multiple samples simultaneously (Analytical Sciences 23:5-10, 2007). The NRL Array Biosensor has been developed with the aim of creating a system for sensitive, rapid, on-site screening for multiple targets of interest. This system is fluorescence-based, using evanescent illumination of a waveguide, and has demonstrated the use of both sandwich and competitive immunoassays for the detection of both high and low molecular weight targets, respectively. The current portable, automated system has demonstrated detection of a wide variety of analytes ranging from simple chemical compounds to entire bacterial cells, with applications in food safety, disease diagnosis, homeland security and environmental monitoring.

Analysis of biomolecules using surface plasmons

Surface plasmon resonance (SPR) biosensors are optical sensors that use special electromagnetic waves (surface plasmon-polaritons) to probe interactions between an analyte in solution and a biomolecular recognition element immobilized on the SPR sensor surface. Major application areas include the detection of biological analytes and analysis of biomolecular interactions, where SPR biosensors provide benefits of label-free real-time analytical technology. The information obtained is both qualitative and quantitative and it is possible to obtain the kinetic parameters of the interaction. This new technology has been used to study a diverse set of interaction partners of biological interest, such as protein-protein, protein-lipids, protein-nucleic acids, or protein and low molecular weight molecules such as drugs, substrates, and cofactors. In addition to basic biomedical research, the SPR biosensor has recently been used in food analysis, proteomics, immunogenicity, and drug discovery. This chapter reviews the major developments in SPR technology. The main application areas are outlined and examples of applications of SPR sensor technology are presented. Future prospects of SPR sensor technology are discussed.

Automated analytical microarrays: a critical review

Microarrays provide a powerful analytical tool for the simultaneous detection of multiple analytes in a single experiment. The specific affinity reaction of nucleic acids (hybridization) and antibodies towards antigens is the most common bioanalytical method for generating multiplexed quantitative results. Nucleic acid-based analysis is restricted to the detection of cells and viruses. Antibodies are more universal biomolecular receptors that selectively bind small molecules such as pesticides, small toxins, and pharmaceuticals and to biopolymers (e.g. toxins, allergens) and complex biological structures like bacterial cells and viruses. By producing an appropriate antibody, the corresponding antigenic analyte can be detected on a multiplexed immunoanalytical microarray. Food and water analysis along with clinical diagnostics constitute potential application fields for multiplexed analysis. Diverse fluorescence, chemiluminescence, electrochemical, and label-free microarray readout systems have been developed in the last decade. Some of them are constructed as flow-through microarrays by combination with a fluidic system. Microarrays have the potential to become widely accepted as a system for analytical applications, provided that robust and validated results on fully automated platforms are successfully generated. This review gives an overview of the current research on microarrays with the focus on automated systems and quantitative multiplexed applications.

Label-free and dynamic detection of biomolecular interactions for high-throughput microarray applications

Direct monitoring of primary molecular-binding interactions without the need for secondary reactants would markedly simplify and expand applications of high-throughput label-free detection methods. A simple interferometric technique is presented that monitors the optical phase difference resulting from accumulated biomolecular mass. As an example, 50 spots for each of four proteins consisting of BSA, human serum albumin, rabbit IgG, and protein G were dynamically monitored as they captured corresponding antibodies. Dynamic measurements were made at 26 pg/mm(2) SD per spot and with a detectable concentration of 19 ng/ml. The presented method is particularly relevant for protein microarray analysis because it is label-free, simple, sensitive, and easily scales to high-throughput.

Recent biosensing developments in environmental security

Environmental security is one of the fundamental requirements of our well being. However, it still remains a major global challenge. Therefore, in addition to reducing and/or eliminating the amounts of toxic discharges into the environment, there is need to develop techniques that can detect and monitor these environmental pollutants in a sensitive and selective manner to enable effective remediation. Because of their integrated nature, biosensors are ideal for environmental monitoring and detection as they can be portable and provide selective and sensitive rapid responses in real time. In this review we discuss the main concepts behind the development of biosensors that have most relevant applications in the field of environmental monitoring and detection. We also review and document recent trends and challenges in biosensor research and development particularly in the detection of species of environmental significance such as organophosphate nerve agents, heavy metals, organic contaminants, pathogenic microorganisms and their toxins. Special focus will be given to the trends that have the most promising applications in environmental security. We conclude by highlighting the directions towards which future biosensors research in environmental security sector might proceed.

Multiplexed spectroscopic detections

This review describes various platforms used for multiplexed spectroscopic analysis. We highlight the use of different types of spectroscopy for multiplexed detections, including Raman spectroscopy, surface-enhanced Raman spectroscopy, surface plasmon resonance, and fluorescence. This review also explores the use of cross-reactive sensors in combination with pattern-recognition algorithms to monitor multiple analytes in aqueous and vapor matrices. It also discusses applications of these techniques, paying special attention to their use in the detection of biologically relevant analytes.

Development of automated amperometric detection of antibodies against Bacillus anthracis protective antigen

Picogram levels of antibodies against the protective antigen (PA) of Bacillus anthracis were detected in an automated electrochemical sandwich-type enzyme-linked immunosorbant assay. The antibodies were captured and detected using an 8 x 3 array of 50-microm-diameter cavities. The reagent and sample volumes were as low as 200 nL in a less than 25-min assay from capture to signal generation. The electrochemical detection of the antibodies was demonstrated at 0.05-10 microg/mL containing only 10-5,000 pg antibodies. The limit of detection is 10 fg for a 200-nL sample. Detection of anti-PA immunoglobulin G performed in spiked normal human serum and fresh whole human blood did not show a significant difference from detection in a buffer. The initial automation of the assay involved the use of a digital syringe pump for the delivery of reagents to the capture surface.

Advantages and limitations of on-line solid phase extraction coupled to liquid chromatography–mass spectrometry technologies versus biosensors for monitoring of emerging contaminants in water

On-line solid phase extraction (SPE) coupled to liquid chromatography-mass spectrometry (LC-MS) and biosensors are advanced technologies that have found increasing application in the analysis of environmental contaminants although their application to the determination of emerging contaminants (previously unknown or unrecognized pollutants) has been still limited. This review covers the most recent advances occurred in the areas of on-line SPE-LC-MS and biosensors, discusses and compares the main strengths and limitations of the two approaches, and examines their most relevant applications to the analysis of emerging contaminants in environmental waters. So far, the on-line configuration most frequently used has been SPE coupled to liquid chromatography-(tandem) mass spectrometry. Sorbents used for on-line SPE have included both traditional (alkyl-bonded silicas and polymers) and novel (restricted access materials (RAMs), molecularly imprinted synthetic polymers (MIPs), and immobilized receptors or antibodies (immunosorbents) materials. The biosensor technologies most frequently applied have been based on the use of antibodies and, to a lesser extent, enzymes, bacteria, receptors and DNA as recognition elements, and the use of optical and electrochemical transducing elements. Emerging contaminants investigated by means of these two techniques have included pharmaceuticals, endocrine disrupting compounds such as estrogens, alkylphenols and bisphenol A, pesticides transformation products, disinfection by-products, and bacterial toxins and mycotoxins, among others. Both techniques offer advantageous, and frequently comparable, features such as high sensitivity and selectivity, minimum sample manipulation, and automation. Biosensors are, in addition, relatively cheap and fast, which make them ideally suited for routine testing and screening of samples; however, in most cases, they can not compete yet with on-line SPE procedures in terms of accuracy, reproducibility, reliability (confirmation) of results, and capacity for multi-analyte determination.

Array biosensor based on enzyme kinetics monitoring by fluorescence spectroscopy: Application for neurotoxins detection

The aim of the present work is to develop an evanescence wave array biosensor exploiting the "kinetic" approach of enzymatic reaction and further detection of the reaction products via pH sensitive fluorophore reporter. To demonstrate the feasibility of this approach, we have developed a biosensor array with the potential for direct detection of organophosphates using as a biorecognition element, an enzyme organophosphorus hydrolase (OPH), conjugated with a pH-sensitive fluorophore, carboxynaphthofluorescein (CNF). The presence of reference spots allows the discrimination of the enzymatic and non-enzymatic based pH changes; bovine serum albumin (BSA) was used as a non-enzymatic scaffold protein for CNF attachment at the reference spots. An array biosensor unit developed at the Naval Research Laboratories (NRL) was adopted as the detection platform and appropriately modified for enzyme-based measurements. A planar multi-mode waveguide was covered with an optically transparent TiO(2) layer to increase the surface area available for immobilization. The biosensor enabled the detection of 2.5 microM paraoxon, and 10 microM DFP and parathion, respectively. Very short response time of 30s can be achieved with a total analysis time of less than 2 min. When operated at room temperature and stored at 4 degrees C, the waveguide retained reasonable activity for greater than 45 days.

The array biosensor: portable, automated systems

With recent advances in surface chemistry, microfluidics, and data analysis, there are ever increasing reports of array-based methods for detecting and quantifying multiple targets. However, only a few systems have been described that require minimal preparation of complex samples and possess a means of quantitatively assessing matrix effects. The NRL Array Biosensor has been developed with the goal of rapid and sensitive detection of multiple targets from multiple samples analyzed simultaneously. A key characteristic of this system is its two-dimensional configuration, which allows controls and standards to be analyzed in parallel with unknowns. Although the majority of our work has focused on instrument automation and immunoassay development, we have recently initiated efforts to utilize alternative recognition molecules, such as peptides and sugars, for detection of a wider variety of targets. The array biosensor has demonstrated utility for a variety of applications, including food safety, disease diagnosis, monitoring immune response, and homeland security, and is presently being transitioned to the commercial sector for manufacturing.

Multi-analyte SPR immunoassays for environmental biosensing of pesticides

Multi-analyte detection of environmentally relevant pesticides is performed by using a two-channelled surface plasmon resonance (SPR) biosensor. The special design of the SPR instrument allows the determination of several analytes (DDT, chlorpyrifos and carbaryl) via different immobilization formats. First, simultaneous pesticide monitoring is possible by flowing chlorpyrifos, carbaryl or DDT samples separately over each channel of the SPR system, wherein their corresponding recognition element was previously immobilized. The second approach is based on the multiple and combined immobilization of several analyte recognition elements on the sensing surface of one individual flow cell. In this format, the analysis time for all three pesticides varied from 40 to 60 min depending on the number of regeneration cycles. In most cases, similar detection limits were attained for the target analyte irrespective of the assay format, with sensitivity values at the nanogram per litre level (18-50 ng L(-1)). The assay reproducibility was proved through the repeated use of the same sensor surface for over more than 200 assay cycles, whereas the absence of biosensor response to non-related analytes showed the specificity and reliability of the analysis. The SPR instrument, including optics, electronics and microfluidics, is already commercialised by the company SENSIA, SL.

Biosensors as useful tools for environmental analysis and monitoring

Recent advances in the development and application of biosensors for environmental analysis and monitoring are reviewed in this article. Several examples of biosensors developed for relevant environmental pollutants and parameters are briefly overviewed. Special attention is paid to the application of biosensors to real environmental samples, taking into consideration aspects such as sample pretreatment, matrix effects and validation of biosensor measurements. Current trends in biosensor development are also considered and commented on in this work. In this context, nanotechnology, miniaturisation, multi-sensor array development and, especially, biotechnology arise as fast-growing areas that will have a marked influence on the development of new biosensing strategies in the near future.

Recent advances in biosensor techniques for environmental monitoring

Biosensors for environmental applications continue to show advances and improvements in areas such as sensitivity, selectivity and simplicity. In addition to detecting and measuring specific compounds or compound classes such as pesticides, hazardous industrial chemicals, toxic metals, and pathogenic bacteria, biosensors and bioanalytical assays have been designed to measure biological effects such as cytotoxicity, genotoxicity, biological oxygen demand, pathogenic bacteria, and endocrine disruption effects. This article is intended to discuss recent advances in the area of biosensors for environmental applications.

Sequential analysis of multiple analytes using a surface plasmon resonance (SPR) biosensor

A sequential analysis method for the analysis of two analytes was developed using a surface plasmon resonance (SPR) biosensor. A sample with both analytes was introduced into the single sensing region and then each analyte was analyzed sequentially. Two detection models were devised for the samples with the following composition: (1) one target analyte resulting in a sensor response without any label and the other analyte with only additional label, (2) both target analytes requiring additional labels for detection. A standard curve for each model was prepared and applied for sequential analysis of anti-bovine serum albumin (anti-BSA) antibodies and horseradish peroxidase (HRP). The errors of the sequential analysis of Models 1 and 2 were found to be less than 6%, and this method was therefore acceptable for application. No cross-reaction arising from non-specific binding among the participating antigens and antibodies was shown to occur in Models 1 and 2. For optimization of the analyte binding capacity of immunoaffinity (IA), the concentration ratio of the molecular recognition element at the immobilization step was adjusted. Subsequently, from the measurement of the maximum sensor response (R(max)), optimization of the analyte binding capacity could be made. Using Model 2, the feasibility of sequential analysis was demonstrated by detecting levels of human chorionic gonadotropin (hCG) and human albumin (hA) in healthy human urine, since both proteins are known to be related to abortion and preterm delivery during early pregnancy.

Biosensor detection of botulinum toxoid A and staphylococcal enterotoxin B in food

Immunoassays were developed for the simultaneous detection of staphylococcal enterotoxin B and botulinum toxoid A in buffer, with limits of detection of 0.1 ng/ml and 20 ng/ml, respectively. The toxins were also spiked and measured in a variety of food samples, including canned tomatoes, sweet corn, green beans, mushrooms, and tuna.

Multi-analyte surface plasmon resonance biosensing

Surface plasmon resonance (SPR) biosensors are affinity sensing devices exploiting a special mode of electromagnetic field-surface plasmon-polariton-to detect the binding of analyte molecules from a liquid sample to biomolecular recognition elements immobilized on the surface of the sensor. In this paper, we review advances of SPR biosensor technology towards detection systems for the simultaneous detection of multiple analytes (multi-analyte detection). In addition, we report application of a recently developed multichannel SPR sensor based on spectroscopy of surface plasmons and wavelength division multiplexing of sensing channels to multi-analyte detection.

A “do-it-yourself” array biosensor

We have developed an array biosensor for the simultaneous detection of multiple targets in multiple samples within 15-30 min. The biosensor is based on a planar waveguide, a modified microscope slide, with a pattern of small (mm2) sensing regions. The waveguide is illuminated by launching the emission of a 635 nm diode laser into the proximal end of the slide via a line generator. The evanescent field excites fluorophores bound in the sensing region and the emitted fluorescence is measured using a Peltier-cooled CCD camera. Assays can be performed on the waveguide in multichannel flow chambers and then interrogated using the detection system described here. This biosensor can detect many different targets, including proteins, toxins, cells, virus, and explosives with detection limits rivaling those of the ELISA detection system.

Detection of bacterial toxins with monosaccharide arrays

A large number of bacterial toxins, viruses and bacteria target carbohydrate derivatives on the cell surface to attach and gain entry into the cell. We report here the use of a monosaccharide-based array to detect protein toxins. The array-based technique provides the capability to perform simultaneous multianalyte analyses. Arrays of N-acetyl galactosamine (GalNAc) and N-acetylneuraminic acid (Neu5Ac) derivatives were immobilized on the surface of a planar waveguide and were used as receptors for protein toxins. These arrays were probed with fluorescently labeled bacterial cells and protein toxins. While Salmonella typhimurium, Listeria monocytogenes, Escherichia coli and staphylococcal enterotoxin B (SEB) did not bind to either of the monosaccharides, both cholera toxin and tetanus toxin bound to GalNAc and Neu5Ac. The results show that the binding of the toxins to the carbohydrates is density dependent and semi-selective. Both toxins were detectable at 100 ng/ml.

Evanescent wave fluorescence biosensors

Since discovery and first use in the mid-1970s, evanescent wave fluorescence biosensors have developed into a diverse range of instruments, each designed to meet a particular detection need. In this review, we provide a brief synopsis of what evanescent wave fluorescence biosensors are, how they work, and how they are used. In addition, we have summarized the important patents that have impacted the evolution from laboratory curiosities to fully automated commercial products. Finally, we address the critical issues that evanescent wave fluorescence biosensors will face in the coming years.

Simultaneous determination of renal clinical analytes in serum using hydrolase- and oxidase-encapsulated optical array biosensors

An optical array biosensor encapsulated with hydrolase and oxidoreductase using sol-gel immobilization technique has been fabricated for simultaneous analysis and screening of multiple samples to determine the presence of multianalytes which are clinically important in relation to renal failure. Urease and creatinine deiminase were used to detect urea and creatinine, while glucose oxidase and uricase were coimmobilized with horseradish peroxidase to quantify glucose and uric acid. Moreover, the concentrations of analytes in fetal calf serum were measured and quantified using the developed sensing system. The array biosensor showed good specificity for the simultaneous analysis of multiple samples for multianalytes without obvious cross-interference. The analytical ranges of the four analytes were between 0.01 and 10mM with detection limits of 2.5-80 microM. High precision with relative standard deviations of 3.8-9.2% (n=45) was also demonstrated. The reproducibility of array-to-array in 3 consecutive months was 5.4% (n=3). Moreover, the concentrations of analytes in fetal calf serum were 5.9 mM for urea, 0.13 mM for creatinine, 3.3mM for glucose, and 0.15 mM for uric acid, which were in good agreement with results obtained using the traditional spectroscopic methods. These results demonstrate the first use of a sol-gel-derived optical array biosensor for simultaneous analysis of multiple samples for the presence of multiple clinically important renal analytes.