Detection of Campylobacter and Shigella Species in Food Samples Using an Array Biosensor

A novel SERS method for the detection of Staphylococcus aureus without immobilization based on Au@Ag NPs/slide substrate

Here, an aptamer-based SERS method for the detection of Staphylococcus aureus (S. aureus) without immobilization using Au@Ag NPs/slide as enhanced substrate was constructed. ROX-aptamer of S. aureus was modified on the surface of Au@Ag NPs/slide through electrostatic interaction. Based on the specific binding effect of the aptamer to S. aureus, the ROX-aptamer fell off from the surface of the substrate, resulting in a decrease of the SERS signal intensity of the substrate. Under the optimal experimental conditions, a good linear relationship was found between SERS intensity at 1500 cm^-1 and the logarithm of concentration of S. aureus in the range of 10² cfu/mL-10⁷ cfu/mL (y = 6623-796lgx, R² = 0.994) with a detection limit of 6 cfu/mL. The selectivity analysis revealed that the method had higher selectivity toward the corresponding target. The results for milk sample using the developed SERS method for the detection of S. aureus were similar to those of the plate counting method. The recovery ratio was from 90.60% to 107.26%, indicating the accuracy and reliability of the developed method. This method eliminates the need for bacterial immobilization and improves the convenience and efficiency of detection.

Recent Progress and Challenges on the Microfluidic Assay of Pathogenic Bacteria Using Biosensor Technology

Microfluidic technology is one of the new technologies that has been able to take advantage of the specific properties of micro and nanoliters, and by reducing the costs and duration of tests, it has been widely used in research and treatment in biology and medicine. Different materials are often processed into miniaturized chips containing channels and chambers within the microscale range. This review (containing 117 references) demonstrates the significance and application of nanofluidic biosensing of various pathogenic bacteria. The microfluidic application devices integrated with bioreceptors and advanced nanomaterials, including hyperbranched nano-polymers, carbon-based nanomaterials, hydrogels, and noble metal, was also investigated. In the present review, microfluid methods for the sensitive and selective recognition of photogenic bacteria in various biological matrices are surveyed. Further, the advantages and limitations of recognition methods on the performance and efficiency of microfluidic-based biosensing of photogenic bacteria are critically investigated. Finally, the future perspectives, research opportunities, potential, and prospects on the diagnosis of disease related to pathogenic bacteria based on microfluidic analysis of photogenic bacteria are provided.

Water-soluble ZnCuInSe quantum dots for bacterial classification, detection, and imaging

Bacteria are everywhere and pose severe threats to human health and safety. The rapid classification and sensitive detection of bacteria are vital steps of bacterial community research and the treatment of infection. Herein, we developed optical property-superior and heavy metal-free ZnCuInSe quantum dots (QDs) for achieving rapid discrimination of Gram-positive/Gram-negative bacteria by the naked eye; driven by the structural differences of bacteria, ZnCuInSe QDs are effective in binding to Gram-positive bacteria, especially Staphylococcus aureus (S. aureus), in comparison with Gram-negative bacteria and give discernable color viewed by the naked eye. Meanwhile, based on its distinctive fluorescence response, the accurate quantification of S. aureus was investigated with a photoluminescence system in the concentration ranges of 1 × 10³ to 1 × 10¹¹ CFU/mL, with a limit of detection of 1 × 10³ CFU/mL. Furthermore, we demonstrated the feasibility of ZnCuInSe QDs as a fluorescence probe for imaging S. aureus. This simple strategy based on ZnCuInSe QDs provides an unprecedented step for rapid and effective bacterial discrimination, detection, and imaging.

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.

New colorimetric aptasensor for rapid on-site detection of Campylobacter jejuni and Campylobacter coli in chicken carcass samples

Campylobacter is the most common cause of infectious intestinal disease, with nearly all cases caused by two species: C. jejuni and C. coli. We recently reported a gold nanoparticle-based two-stage aptasensing platform, which was improved in the present study for the rapid and on-site detection of both C. jejuni and C. coli in food samples. Compared to the previous platform, the improved platform yielded a more obvious colour change from red to purple due to the aggregation of gold nanoparticles, and does not require additional time or a pH optimization step for the aptamers to be adsorbed onto the gold nanoparticles. Using a highly specific aptamer that binds to live C. jejuni and C. coli, the improved aptasensor was highly effective for testing pure culture samples. The accuracy of the newly developed platform was comparable (p = 0.688) to that of the gold-standard detection method of tazobactam-supplemented culture, whereas it was superior to the official agar-based detection method (p = 0.016) in a validation study with 50 naturally contaminated chicken carcass samples. This is the first study on a colorimetric sensor that targets both live C. coli and C. jejuni in naturally contaminated samples. In addition, we provide the first evidence that both morphological status and the amount of Campylobacter present play key roles in the effectiveness of colorimetric detection. Thus, suitable selection of an antibody or aptamer with consideration of the morphological status of pathogens in samples is essential for direct detection without enrichment. Our data suggest that the sensor developed in this study can provide an excellent screening method, with a reduction in the detection time from 48 h to 30 min after enrichment, thus saving time, labour, and cost.

Colorimetric Fingerprints of Gold Nanorods for Discriminating Catecholamine Neurotransmitters in Urine Samples

Catecholamine neurotransmitters, generally including dopamine (DA), epinephrine (EP) and norepinephrine (NE) are known as substantial indicators of various neurological diseases. Simultaneous detection of these compounds and their metabolites is highly recommended in early clinical diagnosis. To this aim, in the present contribution, a high performance colorimetric sensor array has been proposed for the detection and discrimination of catecholamines based on their reducing ability to deposit silver on the surface of gold nanorods (AuNRs). The amassed silver nanoshell led to a blue shift in the longitudinal localized surface plasmon resonance (LSPR) peak of AuNRs, creating a unique pattern for each of the neurotransmitters. Hierarchical cluster analysis (HCA) and linear discriminate analysis (LDA) pattern recognition techniques were employed to identify DA, EP and NE. The proposed colorimetric array is able to differentiate among individual neurotransmitters as well as their mixtures, successfully. Finally, it was shown that the sensor array can identify these neurotransmitters in human urine samples.

A Potentiometric Addressable Photoelectrochemical Biosensor for Sensitive Detection of Two Biomarkers

It is a great challenge to fabricate multiplex and convenient photoelectrochemical biosensors for ultrasensitive determination of biomarkers. Herein, a fascinating potentiometric addressable photoelectrochemical biosensor was reported for double biomarkers' detection by varying the applied bias in the detection process. In this biosensor, the nanocomposite of cube anatase TiO₂ mesocrystals and polyamidoamine dendrimers modified a dual disk electrode as an excellent photoelectrochemical sensing matrix. Subsequently, two important biomarkers in serum for prostate cancer, prostate-specific antigen and human interleukin-6, were immobilized onto the different disks of modified electrode via glutaraldehyde bridges. Then another two photosensitizers, graphitic-carbon-nitride-labeled and CS-AgI-labeled different antibodies, were self-assembled onto the electrode surface by a corresponding competitive immune recognition reaction. The change in photocurrent with the target antigen concentration at different critical voltages enables us to selectively and quantitatively determine targets. The results demonstrated that this potentiometric addressable photoelectrochemical biosensing strategy not only has great promise as a new point-of-care diagnostic tool for early detection of prostate cancer but also can be conveniently expanded to multiplex biosensing by simply change biomarkers. More importantly, this work provides an unambiguous operating guideline of multiplex photoelectrochemical immunoassay.

Microfluidic biosensor array with integrated poly(2,7-carbazole)/fullerene-based photodiodes for rapid multiplexed detection of pathogens

A multiplexed microfluidic biosensor made of poly(methylmethacrylate) (PMMA) was integrated into an array of organic blend heterojunction photodiodes (OPDs) for chemiluminescent detection of pathogens. Waterborne Escherichia coli O157:H7, Campylobacter jejuni and adenovirus were targeted in the PMMA chip, and detection of captured pathogens was conducted by poly(2,7-carbazole)/fullerene OPDs which showed a responsivity over 0.20 A/W at 425 nm. The limits of chemiluminescent detection were 5 × 10⁵ cells/mL for E. coli, 1 × 10⁵ cells/mL for C. jejuni, and 1 × 10⁻⁸ mg/mL for adenovirus. Parallel analysis for all three analytes in less than 35 min was demonstrated. Further recovery tests illustrated the potential of the integrated biosensor for detecting bacteria in real water samples.

Capillary Array Waveguide Amplified Fluorescence Detector for mHealth

Mobile Health (mHealth) analytical technologies are potentially useful for carrying out modern medical diagnostics in resource-poor settings. Effective mHealth devices for underserved populations need to be simple, low cost, and portable. Although cell phone cameras have been used for biodetection, their sensitivity is a limiting factor because currently it is too low to be effective for many mHealth applications, which depend on detection of weak fluorescent signals. To improve the sensitivity of portable phones, a capillary tube array was developed to amplify fluorescence signals using their waveguide properties. An array configured with 36 capillary tubes was demonstrated to have a ~100X increase in sensitivity, lowering the limit of detection (LOD) of mobile phones from 1000 nM to 10 nM for fluorescein. To confirm that the amplification was due to waveguide behavior, we coated the external surfaces of the capillaries with silver. The silver coating interfered with the waveguide behavior and diminished the fluorescence signal, thereby proving that the waveguide behavior was the main mechanism for enhancing optical sensitivity. The optical configuration described here is novel in several ways. First, the use of capillaries waveguide properties to improve detection of weak florescence signal is new. Second we describe here a three dimensional illumination system, while conventional angular laser waveguide illumination is spot (or line), which is functionally one-dimensional illumination, can illuminate only a single capillary or a single column (when a line generator is used) of capillaries and thus inherently limits the multiplexing capability of detection. The planar illumination demonstrated in this work enables illumination of a two dimensional capillary array (e.g. x columns and y rows of capillaries). In addition, the waveguide light propagation via the capillary wall provides a third dimension for illumination along the axis of the capillaries. Such an array can potentially be used for sensitive analysis of multiple fluorescent detection assays simultaneously. The simple phone based capillary array approach presented in this paper is capable of amplifying weak fluorescent signals thereby improving the sensitivity of optical detectors based on mobile phones. This may allow sensitive biological assays to be measured with low sensitivity detectors and may make mHealth practical for many diagnostics applications, especially in resource-poor and global health settings.

Hybridization chain reaction engineered DNA nanopolylinker for amplified electrochemical sensing of biomarkers

A DNA nanopolylinker was designed as a three dimensional nanoprobe with high loading of signal molecules for amplifying the biosensing signal. The nanoprobe was prepared by hybridization chain reaction engineering dsDNA polymerization on initiator DNA modified Au nanoparticle with two kinds of small molecule, for example, FITC-labeled DNA hairpins. The core-shell conjugate that was formed contained approximately 320 FITC molecules for further binding of signal molecules. With a sandwich-type immunoreaction and a biotin-streptavidin affinity reaction, the biotinylated core-shell nanoprobe was immobilized on the immunosensor surface, and the FITC molecules then bound enzyme labeled anti-FITC antibody to catalyze a silver deposition process, leading to a novel cascade signal amplification strategy. By combining the proposed strategy with stripping analysis of the deposited silver, an ultrasensitive immunoassay method for biomarker detection was developed. Under optimal conditions, this method showed a linear detection range over 5 orders of magnitude for carcinoembryonic antigen with a detection limit of 1.2 fg mL(-1) (about 18 molecules in 5.0 μL sample). The preparation of DNA nanopolylinker was simple and economic, and it could be used as a universal and multifarious probe for different bioanalytical techniques and showed the promising potential of the signal amplification strategy in the future design of biosensing methodology.

Campylobacter spp. detection in the 21st century: a review of the recent achievements in biosensor development

Campylobacter spp. are an important cause of acute bacterial diseases in humans worldwide. Many bacterial species in the Campylobacter genus are considered harmful and may cause several infectious diseases. Currently, there are no commercial biosensors available to detect Campylobacter spp. in food matrices, and little to no testing has been done in research laboratories with actual food matrices. Biosensors potentially provide a powerful means to detect Campylobacter spp. with the advantages of high sensitivity (low limits of detection with a high signal to noise ratio), high specificity (able to selectively detect the target among several similar targets), real time sensing, and in-site monitoring. This review summarizes the latest research in biosensing technologies for detection of Campylobacter spp. based on a variety of transducers and recognition elements. Finally, a comparison is made among all recently reported biosensors for the detection of Campylobacter spp.

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.

Virus hybrids as nanomaterials for biotechnology

The current review describes advances in the field of bionanotechnology in which viruses are used to fabricate nanomaterials. Viruses are introduced as protein cages, scaffolds, and templates for the production of biohybrid nanostructured materials where organic and inorganic molecules are incorporated in a precise and a controlled fashion. Genetic engineering enables the insertion or replacement of selected amino acids on virus capsids for uses from bioconjugation to crystal growth. The variety of nanomaterials generated in rod-like and spherical viruses is highlighted for tobacco mosaic virus (TMV), M13 bacteriophage, cowpea chlorotic mottle virus (CCMV), and cowpea mosaic virus (CPMV). Functional biohybrid nanomaterials find applications in biosensing, memory devices, nanocircuits, light-harvesting systems, and nanobatteries.

Specific detection of unamplified mycobacterial DNA by use of fluorescent semiconductor quantum dots and magnetic beads

Here we present the development of a specific DNA detection method using fluorescent semiconductor quantum dots (QDs) and magnetic beads (MBs) for fast detection of Mycobacterium spp., dispensing with the need for DNA amplification. Two biotinylated oligonucleotide probes were used to recognize and detect specific complementary mycobacterial target DNA through a sandwich hybridization reaction. Cadmium selenite QDs conjugated with streptavidin and species-specific probes were used to produce a fluorescent signal. MBs conjugated with streptavidin and a genus-specific probe were used to isolate and concentrate the DNA targets. The application of the proposed method to isolated bacteria produced the expected result in all cases. The minimum detection limit of the assay was defined as 12.5 ng of DNA diluted in a sample volume of 20 microl. In order to obtain an indication of the method's performance with clinical samples, we applied the optimized assay to the detection of Mycobacterium tuberculosis in DNA isolated from bronchoalveolar lavage specimens from patients with tuberculosis and Mycobacterium avium subsp. paratuberculosis in DNA isolated from feces and paraffin-embedded tissues in comparison with culture, Ziehl-Neelsen staining, and real-time PCR. The concordance of these methods compared to the proposed method with regard to positive and negative samples varied between 53.84% and 87.23% and between 84.61% and 100%, respectively. The overall accuracy of the QD assay compared to real-time PCR was 70 to 90% depending on the type of clinical material. The proposed diagnostic assay offers a simple, rapid, specific, and cost-effective method for direct detection and identification of mycobacterial DNA in clinical samples.

An electrochemical impedimetric immunosensor for label-free detection of Campylobacter jejuni in diarrhea patients' stool based on O-carboxymethylchitosan surface modified Fe3O4 nanoparticles

A novel electrochemical impedimetric immunosensor based on O-carboxymethylchitosan surface modified Fe(3)O(4) nanoparticles (denoted as OCMCS-Fe(3)O(4) nanoparticles) was developed for rapid detection of Campylobacter jejuni, which is becoming the most common cause of gastroenteritis in developed countries and raising major public health concerns worldwide. In the present study, anti-FlaA monoclonal antibodies 2D12 (denoted as 2D12McAbs) were immobilized on OCMCS-Fe(3)O(4) nanoparticles. The detection was performed by measuring relative change in impedance before and after 2D12McAbs-Campylobacter jejuni reaction with the technique of electrochemical impedance spectroscopy. Under the optimized conditions, the relative change in impedance was proportional to the logarithmic value of Campylobacter jejuni concentrations in the range of 1.0x10(3) to 1.0x10(7) CFU/mL (r=0.991). The advantages of the OCMCS-Fe(3)O(4) nanoparticle-based immunosensor are simplicity of use, fast response, wide linear range, acceptable reproducibility and long stability. Moreover, the immunosensor could be regenerated by being treated with glycine-HCl buffer solution (pH 2.8). We demonstrate the convenient application of the novel immunosensor for the detection of Campylobacter jejuni in diarrhea patients' stool samples.

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.

Immobilization of biomolecules onto silica and silica-based surfaces for use in planar array biosensors

Several methods are described in which a biological recognition molecule--a critical element in any biosensor--is immobilized onto a silica or silica-based sensing substrate. Although several variations are described, the methods for covalent immobilization share a common theme and are generally composed of three steps: modification of the surface to add specific functional groups (using appropriate silanes or an amine or carboxyl-containing hydrogel), covalent attachment of a crosslinker through one of its reactive moieties, and finally, covalent linking of the biomolecule (recognition element) to the remaining reactive moiety of the crosslinker. One final method is presented in which the surface is modified with a highly hydrophobic silane and a glycolipid recognition element immobilized, essentially irreversibly, by hydrophobic interactions. All of the methods described have been successfully used to immobilize biological recognition molecules onto sensing surfaces, with full functionality in biosensor-binding assays.

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.

Channel and Substrate Zone Two-Dimensional Resolution for Chemiluminescent Multiplex Immunoassay

A two-dimensional resolution system of channels and substrate zones was proposed for multiplex immunoassay performed with a designed multichannel chemiluminescent (CL) detection device coupled with a single photomultiplier. Using carcinoma antigen 125 (CA 125), carcinoma antigen 153 (CA 153), carcinoma antigen 199 (CA 199), and carcinoembryonic antigen (CEA) as two couples of model analytes, two couples of capture antibodies were immobilized in two channels, respectively. With a sandwich format, the CL substrates for alkaline phosphatase and horseradish peroxidase were delivered into the channels sequentially to perform a multiplex immunoassay after the sample and tracer antibodies were introduced into the channels for on-line incubation. CA 125, CA 153, CA 199, and CEA could be assayed in the ranges of 0.50-80, 2.0-100, and 5.0-150 U/mL and 1.0-70 ng/mL with limits of detection of 0.15, 0.80, and 2.0 U/mL and 0.65 ng/mL at 3sigma, respectively. The whole assay process including regeneration of the device could be completed in 37 min. The proposed system showed acceptable detection and fabrication reproducibility, and the results obtained were in acceptable agreement with those from parallel single-analyte test of practical clinical sera. This technique provides a new strategy for a simple, automated, and near-simultaneous multianalyte immunoassay.

Preparation and characterization of functional poly(ethylene glycol) surfaces for the use of antibody microarrays

Protein microarrays serve as measurement platforms for multianalytical applications. Small molecules, DNA, proteins, and cells are determined quantitatively. Amino-PEG surfaces can be a smart functional platform for protein microarrays with high signal-to-noise ratios. An effective step-by-step chemistry is developed for uniform presentation of terminal functional groups at each monolayer. Poly(ethelene glycol diamine) 2000 (DAPEG, 2000 g/mol) films were prepared onto silanized glass slides presenting epoxy groups. The uniformity of the grafted DAPEG monolayer is characterized by a chemiluminescence reaction using a chemiluminescence microarray reader with automated reagent supply and a horseradish peroxidase (HRP)/luminol reporter system. An intensity line plot on the horizontal axis was generated. The chemiluminescence intensities vary in a range of 2.6%. Antibodies against HRP as model system were immobilized on N-hydroxysuccinimide activated DAPEG layers by means of a microcontact roboter system. Chemiluminescence signals of bound HRP are detected at each spot with a standard deviation of 2.9%. The maximum antibody concentration that can be immobilized at the surface is determined with 1 mg/mL. Additives for an optimal spotting buffer are also studied. The use of the block-copolymer Pluronic F127 as antibody stabilizer is as well investigated as trehalose for the prevention of spot evaporation. The lowest detectable HRP concentration is 0.08 ng/mL determined on anti-HRP antibody microarrays. This study demonstrates how surfaces and analytical parameters for protein microarray applications can be characterized with a chemiluminescence readout system using a HRP reporter system.

Prevention of nonspecific bacterial cell adhesion in immunoassays by use of cranberry juice

The ability of Vaccinum macrocarpon, the North American cranberry, to prevent bacterial adhesion has been used to advantage in the prevention of urinary tract infections and has recently been described for the prevention of adhesion of bacteria responsible for oral infections and stomach ulcers. This report documents the ability of cranberry juice to reduce nonspecific adhesion of bacteria to the borosilicate glass microscope slides used in an immunoarray biosensor format. Nonspecific binding of analytes in the array sensor leads to high background signals that cause increased detection limits and false positives. Reduction in background-to-signal ratios can be seen as the juice concentration is increased from 0 to 50% of the sample. This impact cannot be duplicated with grape, orange, apple, or white cranberry juice. Sugar content and pH have been eliminated as the agents in the juice responsible for the anti-adhesive activity.

Development of a surface plasmon resonance biosensor for the identification of Campylobacter jejuni

The purpose of this study was to develop a biosensor based on surface plasmon resonance (SPR) for the rapid identification of C. jejuni in broiler samples. We examined the specificity and sensitivity of commercial antibodies against C. jejuni with six Campylobacter strains and six non-Campylobacter bacterial strains. Antigen-antibody interactions were studied using enzyme-linked immunosorbent assay (ELISA) and a commercially available SPR biosensor platform (Spreeta). Campylobacter cells killed with 0.5% formalin had significant lower antibody reactivity when compared to live cells, or cells inactivated with 0.5% thimerosal or heat (70 degrees C for 3 min) using ELISA. The SPR biosensor showed a good sensitivity with commercial antibodies against C. jejuni at 10(3) CFU/ml and a low cross reactivity with Salmonella serotype typhimurium. The sensitivity of the SPR was similar when testing spiked broiler meat samples. However, research is still needed to reduce the high background observed when sampling meat products.

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.

Pathogen detection: A perspective of traditional methods and biosensors

The detection of pathogenic bacteria is key to the prevention and identification of problems related to health and safety. Legislation is particularly tough in areas such as the food industry, where failure to detect an infection may have terrible consequences. In spite of the real need for obtaining analytical results in the shortest time possible, traditional and standard bacterial detection methods may take up to 7 or 8 days to yield an answer. This is clearly insufficient, and many researchers have recently geared their efforts towards the development of rapid methods. The advent of new technologies, namely biosensors, has brought in new and promising approaches. However, much research and development work is still needed before biosensors become a real and trustworthy alternative. This review not only offers an overview of trends in the area of pathogen detection but it also describes main techniques, traditional methods, and recent developments in the field of pathogen bacteria biosensors.

Array biosensor for detection of ochratoxin A in cereals and beverages

Contamination of food by mycotoxins occurs in minute quantities, and therefore, there is a need for a highly sensitive and selective device that can detect and quantify these organic toxins. We report the development of a rapid and highly sensitive array biosensor for the detection and quantitation of ochratoxin A (OTA). The array biosensor utilizes a competitive immunoassay format. Immobilized OTA derivatives compete with toxin in solution for binding to fluorescent anti-OTA antibody spiked into the sample. This competition is quantified by measuring the formation of the fluorescent immunocomplex on the waveguide surface. The fluorescent signal is inversely proportional to the concentration of OTA in the sample. Analyses for OTA in buffer and a variety of food and beverage samples were performed. Samples were extracted with methanol, without any sample cleanup or preconcentration step prior to analysis. The limit of detection for OTA in several cereals ranged from 3.8 to 100 ng/g, while in coffee and wine, detection limits were 7 and 38 ng/g, respectively.

ENTEROBACTERIA ISOLATION IN BROILER CARCASSES FROM COMMERCIAL ESTABLISHMENTS IN FORTALEZA, CEARÁ STATE, BRAZIL

ABSTRACT Processing of poultry products requires a severe microbiological quality control, considering they are one of the main sources of foodborne infections. The objective of this research was to perform the isolation of enterobacteria in broiler carcasses from commercial establishments in the Metropolitan Region of Fortaleza in Ceará State, Brazil. Broiler carcasses were collected and selected as fresh (n = 14), refrigerated (n = 18) and frozen (n = 19). Carcasses were submitted to a rinsing method, followed by pre-enrichment and enrichment with Rappaport-Vassiliadis and Selenite-Cystine, streaked on plates with Brilliant Green, MacConkey and Salmonella-Shigella agars, and to a presumptive biochemical identification. It was verified that all broiler carcasses categories presented enterobacteria contamination, with the following frequency of isolation: Proteus sp., 66.7%; Enterobacter sp., 15.7%; Citrobacter sp., 2%; Escherichia coli, 47.1%; Klebsiella sp., 11.8%; Shigella sp., 5.9%, and Salmonella sp. 11.8%. It was observed that no combination of culture media was able to detect all enterobacteria contamination in the broiler carcasses. Thus, it may be necessary the use of several combinations of culture media to determine the real microbiological quality of broiler carcasses.

Quantitative and simultaneous detection of four foodborne bacterial pathogens with a multi-channel SPR sensor

We report the quantitative and simultaneous detection of four species of bacteria, Escherichia coli O157:H7, Salmonella choleraesuis serotype typhimurium, Listeria monocytogenes, and Campylobacter jejuni, using an eight-channel surface plasmon resonance (SPR) sensor based on wavelength division multiplexing. Detection curves showing SPR response versus analyte concentration were established for each species of bacteria in buffer at pH 7.4, apple juice at native pH 3.7, and apple juice at an adjusted pH of 7.4, as well as for a mixture containing all four species of bacteria in buffer. Control experiments were performed to show the non-fouling characteristics of the sensor surface as well as the specificity of the amplification antibodies used in this study. The limit of detection (LOD) for each of the four species of bacteria in the tested matrices ranges from 3.4 x 10(3) to 1.2 x 10(5) cfu/ml. Detection curves in buffer of an individual species of bacteria in a mixture of all four species of bacteria correlated well with detection curves of the individual species of bacteria alone. SPR responses were higher for bacteria in apple juice at pH 7.4 than in apple juice at pH 3.7. This difference in sensor response could be partly attributed to the pH dependence of antibody-antigen binding.

Shigellaas a Foodborne Pathogen and Current Methods for Detection in Food

Shigella, the causative agent of shigellosis or "bacillary dysentery," has been increasingly involved in foodborne outbreaks. According to the Centers for Disease Control and Prevention's Emerging Infections Program, Foodborne Diseases Active Surveillance Network (FoodNet), Shigella was the third most reported foodborne bacterial pathogen in 2002. Foods are most commonly contaminated with Shigella by an infected food handler who practices poor personal hygiene. Shigella is acid resistant, salt tolerant, and can survive at infective levels in many types of foods such as fruits and vegetables, low pH foods, prepared foods, and foods held in modified atmosphere or vacuum packaging. Survival is often increased when food is held at refrigerated temperatures. Detection methods for Shigella include conventional culture methods, immunological methods, and molecular microbiological methods. Conventional culture of Shigella in foods is often problematic due to the lack of appropriate selective media. Immunological methods for Shigella have been researched, yet there is only one commercially available test kit. Molecular microbiological methods such as PCR, oligonucleotide microarrays, and rep-PCR have also been developed for the detection and identification of Shigella. This manuscript reviews the general characteristics, prevalence, growth and survival, and methods for detection of Shigella in food.

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.

Simultaneous detection of Escherichia coli O157∶H7 and Salmonella Typhimurium using quantum dots as fluorescence labels

In this study, we explored the use of semiconductor quantum dots (QDs) as fluorescence labels in immunoassays for simultaneous detection of two species of foodborne pathogenic bacteria, Escherichia coli O157:H7 and Salmonella Typhimurium. QDs with different sizes can be excited with a single wavelength of light, resulting in different emission peaks that can be measured simultaneously. Highly fluorescent semiconductor quantum dots with different emission wavelengths (525 nm and 705 nm) were conjugated to anti-E. coli O157 and anti-Salmonella antibodies, respectively. Target bacteria were separated from samples by using specific antibody coated magnetic beads. The bead-cell complexes reacted with QD-antibody conjugates to form bead-cell-QD complexes. Fluorescent microscopic images of QD labeled E. coli and Salmonella cells demonstrated that QD-antibody conjugates could evenly and completely attach to the surface of bacterial cells, indicating that the conjugated QD molecules still retain their effective fluorescence, while the conjugated antibody molecules remain active and are able to recognize their specific target bacteria in a complex mixture. The intensities of fluorescence emission peaks at 525 nm and 705 nm of the final complexes were measured for quantitative detection of E. coli O157:H7 and S. Typhimurium simultaneously. The fluorescence intensity (FI) as a function of cell number (N) was found for Salmonella and E. coli, respectively. The regression models can be expressed as: FI = 60.6 log N- 250.9 with R(2) = 0.97 for S. Typhimurium, and FI = 77.8 log N- 245.2 with R(2) = 0.91 for E. coli O157:H7 in the range of cell numbers from 10(4) to 10(7) cfu ml(-1). The detection limit of this method was 10(4) cfu ml(-1). The detection could be completed within 2 hours. The principle of this method could be extended to detect multiple species of bacteria (3-4 species) simultaneously, depending on the availability of each type of QD-antibody conjugates with a unique emission peak and the antibody coated magnetic beads specific to each species of bacteria.

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.

A cowpea mosaic virus nanoscaffold for multiplexed antibody conjugation: application as an immunoassay tracer

Cowpea mosaic virus (CPMV), an icosahedral 30 nm virus, offers a uniquely programmable biological nanoscaffold. This study reports initial optimization of the simultaneous modification of two CPMV mutants with AlexaFluor 647 fluorescent dyes and either IgG proteins or antibodies at specific sites on the virus scaffold. The capacity of CPMV as a simultaneous carrier for different types of molecules was demonstrated, specifically, when applied as a tracer in direct and sandwich immunoassays. The ability to label the virus capsid with antibody and up to 60 fluorescent dyes resulted in an improved limit of detection in SEB sandwich immunoassays, when used as a tracer, relative to a mole equivalent of dye-labeled antibody.

Current and developing technologies for monitoring agents of bioterrorism and biowarfare

Recent events have made public health officials acutely aware of the importance of rapidly and accurately detecting acts of bioterrorism. Because bioterrorism is difficult to predict or prevent, reliable platforms to rapidly detect and identify biothreat agents are important to minimize the spread of these agents and to protect the public health. These platforms must not only be sensitive and specific, but must also be able to accurately detect a variety of pathogens, including modified or previously uncharacterized agents, directly from complex sample matrices. Various commercial tests utilizing biochemical, immunological, nucleic acid, and bioluminescence procedures are currently available to identify biological threat agents. Newer tests have also been developed to identify such agents using aptamers, biochips, evanescent wave biosensors, cantilevers, living cells, and other innovative technologies. This review describes these current and developing technologies and considers challenges to rapid, accurate detection of biothreat agents. Although there is no ideal platform, many of these technologies have proved invaluable for the detection and identification of biothreat agents.

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.