A comprehensive review on the detection of Staphylococcus aureus enterotoxins in food samples

Staphylococcal enterotoxins (SEs), the major virulence factors of Staphylococcus aureus, cause a wide range of food poisoning and seriously threaten human health by infiltrating the food supply chain at different phases of manufacture, processes, distribution, and market. The significant prevalence of Staphylococcus aureus calls for efficient, fast, and sensitive methods for the early detection of SEs. Here, we provide a comprehensive review of the hazards of SEs in contaminated food, the characteristic and worldwide regulations of SEs, and various detection methods for SEs with extensive comparison and discussion of benefits and drawbacks, mainly including biological detection, genetic detection, and mass spectrometry detection and biosensors. We highlight the biosensors for the screening purpose of SEs, which are classified according to different recognition elements such as antibodies, aptamers, molecularly imprinted polymers, T-cell receptors, and transducers such as optical, electrochemical, and piezoelectric biosensors. We analyzed challenges of biosensors for the monitoring of SEs and conclude the trends for the development of novel biosensors should pay attention to improve samples pretreatment efficiency, employ innovative nanomaterials, and develop portable instruments. This review provides new information and insightful commentary, important to the development and innovation of further detection methods for SEs in food samples.

Automated detection of neutralizing SARS-CoV-2 antibodies in minutes using a competitive chemiluminescence immunoassay

The SARS-CoV-2 pandemic has shown the importance of rapid and comprehensive diagnostic tools. While there are numerous rapid antigen tests available, rapid serological assays for the detection of neutralizing antibodies are and will be needed to determine not only the amount of antibodies formed after infection or vaccination but also their neutralizing potential, preventing the cell entry of SARS-CoV-2. Current active-virus neutralization assays require biosafety level 3 facilities, while virus-free surrogate assays are more versatile in applications, but still take typically several hours until results are available. To overcome these disadvantages, we developed a competitive chemiluminescence immunoassay that enables the detection of neutralizing SARS-CoV-2 antibodies within 7 min. The neutralizing antibodies bind to the viral receptor binding domain (RBD) and inhibit the binding to the human angiotensin-converting enzyme 2 (ACE2) receptor. This competitive binding inhibition test was characterized with a set of 80 samples, which could all be classified correctly. The assay results favorably compare to those obtained with a more time-intensive ELISA-based neutralization test and a commercial surrogate neutralization assay. Our test could further be used to detect individuals with a high total IgG antibody titer, but only a low neutralizing titer, as well as for monitoring neutralizing antibodies after vaccinations. This effective performance in SARS-CoV-2 seromonitoring delineates the potential for the test to be adapted to other diseases in the future.

Emerging roles of the aptasensors as superior bioaffinity sensors for monitoring shellfish toxins in marine food chain

Shellfish toxins are derived from harmful algae and are easily accumulated in environment and marine food through the food chain, exposing high risks on human health. Preliminary rapid screening is one of the most effective monitoring ways to reduce the potential risks; however, the traditional methods encounter with many limitations, such as complicated procedures, low sensitivity and specificity, and ethical problems. Alternatively, bioaffinity sensors are proposed and draw particular attention. Among them, the aptasensors are springing up and emerging as superior alternatives in recent years, exhibiting high practicability to analyze shellfish toxins in real samples in the marine food chain. Herein, the latest research progresses of aptasensors towards shellfish toxins in the marine food chain in the past five years was reviewed for the first time, in terms of the aptamers applied in these aptasensors, construction principles, signal transduction techniques, response types, individual performance properties, practical applications, and advantages/disadvantages of these aptasensors. Synchronously, critical discussions were given and future perspectives were prospected. We hope this review can serve as a powerful reference to promote further development and application of aptasensors to monitor shellfish toxins, as well as other analytes with similar demands.

Highly sensitive MALDI-MS measurement of active ricin: insight from more potential deoxynucleobase-hybrid oligonucleotide substrates

Herein, we report an improved MALDI-MS method for active ricin to contribute toward countermeasures against its real threat to the public. Compared with commonly used DNA or RNA substrates, the deoxynucleobase-hybrid oligonucleotide (RNA_dA, Rd) substrate containing functional Gd[combining low line]A[combining low line]GA loop was revealed as a substrate with more potential and used for the first time in ricin measurement via MALDI-MS. The Rd sequence greatly prompted ricin to exhibit its catalytic activity as rRNA N-glycosylase in ex vitro condition, which was supported by molecular docking simulation and enzymatic parameters depicted in MALDI-MS. Furthermore, we discovered that a highly pure matrix was the most crucial parameter for enhancing the sensitivity, which addressed the major obstacle encountered in the oligo(deoxy)nucleotide measurement, i.e., the interfering alkali metal ion-adducted signals in MALDI-MS. After the optimization of pH and enzymatic reaction buffer composition in this ex vitro condition, this method can provide a wide linearity of up to three orders of magnitude, i.e., 1-5000 ng mL-1, and a high sensitivity of 1 ng mL-1 without any enrichment. Denatured and active ricin could be distinctly differentiated, and the application to practical samples from one international exercise and a soft drink proved the feasibility of this new method. We believe this MALDI-MS method can contribute to the first response to ricin occurrence events in public safety and security, as well as pave a new way for a deep understanding of ricin and other type II ribosome inactivating proteins involved toxicology.

Enhanced Non-Toxic Immunodetection of Alternaria Mycotoxin Tenuazonic Acid Based on Ferritin-Displayed Anti-Idiotypic Nanobody-Nanoluciferase Multimers

The non-toxic immunoassay for mycotoxins is being paid more attention due to its advantages of higher safety and cost savings by using anti-idiotype antibodies to substitute toxins. In this study, with tenuazonic acid (TeA), a kind of highly toxic Alternaria mycotoxin as the target, an enhanced non-toxic immunoassay was developed based on the ferritin-displayed anti-idiotypic nanobody-nanoluciferase multimers. First, three specific β-type anti-idiotype nanobodies (AId-Nbs) bearing the internal image of TeA mycotoxin were selected from an immune phage display library. Then, the AId-Nb 2D with the best performance was exploited to generate a nanoluciferase (Nluc)-functionalized fusion monomer, by which a one-step non-toxic immunodetection format for TeA was established and proven to be effective. To further improve the affinity of the monomer, a ferritin display strategy was used to prepare 2D-Nluc fusion multimers. Finally, an enhanced bioluminescent enzyme immunoassay (BLEIA) was established in which the half maximal inhibitory concentration (IC₅₀) for TeA was 6.5 ng/mL with a 10.5-fold improvement of the 2D-based enzyme-linked immunosorbent assay (ELISA). The proposed assay exhibited high selectivities and good recoveries of 80.0-95.2%. The generated AId-Nb and ferritin-displayed AId-Nb-Nluc multimers were successfully extended to the application of TeA in food samples. This study brings a new strategy for production of multivalent AId-Nbs and non-toxic immunoassays for trace toxic contaminants.

Naphthalimide-gold-based nanocomposite for the ratiometric detection of okadaic acid in shellfish

Okadaic acid (OA) is one of the known marine biotoxins produced by various dinoflagellates and exists in seafood such as shellfish. The consumption of contaminated shellfish with OA leads to diarrheic shellfish poisoning (DSP), which results in the inhibition of protein phosphatase enzymes in humans. This poisoning can cause immunotoxicity and tumor promotion due to the accumulation of okadaic acid in more than the allowed limit in bivalve molluscs. The reported methods for the detection of okadaic acid include mouse bioassays, immunoassays, chromatography coupled with spectroscopic techniques, electrochemical sensors and immunosensors. We have developed a naphthalimide-gold-based nanocomposite for the detection of okadaic acid. Individually, the organic nanoparticles (ONPs) of synthesized naphthalimide-based receptors and gold-coated ONPs are less sensitive for detection. However, fabrication of the composite of Au@ONPs and ONPs enhance the sensing properties and selectivity. The composite shows a ratiometric response in the UV-Vis absorption spectrum and quenching in the fluorescence profile with a detection limit of 20 nM for OA in aqueous medium. In cyclic voltammetry, a shift was observed in the cathodic peak (-0.532 V to -0.618 V) as well as in the anodic peak (-0.815 V to -0.847 V) with the addition of okadaic acid. To study the quick binding of the composite with OA, a time response experiment was performed. Also, the developed sensor retains its sensing ability in the pH range of 5-9 and in high salt conditions. Our developed composite can be used for the detection of OA in real applications.

Multiplex Immunoassay Techniques for On-Site Detection of Security Sensitive Toxins

Biological toxins are a heterogeneous group of high molecular as well as low molecular weight toxins produced by living organisms. Due to their physical and logistical properties, biological toxins are very attractive to terrorists for use in acts of bioterrorism. Therefore, among the group of biological toxins, several are categorized as security relevant, e.g., botulinum neurotoxins, staphylococcal enterotoxins, abrin, ricin or saxitoxin. Additionally, several security sensitive toxins also play a major role in natural food poisoning outbreaks. For a prompt response to a potential bioterrorist attack using biological toxins, first responders need reliable, easy-to-use and highly sensitive methodologies for on-site detection of the causative agent. Therefore, the aim of this review is to present on-site immunoassay platforms for multiplex detection of biological toxins. Furthermore, we introduce several commercially available detection technologies specialized for mobile or on-site identification of security sensitive toxins.

Ratiometric fluorescent sensing system for drug residue analysis: Highly sensitive immunosensor using dual-emission quantum dots hybrid and compact smartphone based-device

Immunoassays such as the enzyme-linked immunosorbent assay (ELISA) are utilized extensively for detecting protein biomarkers and small molecules in healthcare, environmental monitoring, and food analysis. Unfortunately, the current strategies for immunoassays often require sophisticated apparatus such as a microplate reader, which might not be available in resource-limited areas. To mitigate this problem, we designed a compact smartphone based-device and a multicolor response immunosensor. First, we designed a compact and cost-effective 3D-printed attachment, where a light-emitting diode was used as a light excitation source and a smartphone captured the fluorescent emission signals. Second, by combining quantum dots hybrid and chemical redox reaction, multiple color responses were displayed in the presence of the analyte at different concentrations. Third, solutions with distinct tonality could be readily distinguished by the naked eye and they were suitable for quantitative analysis using the hue-saturation-lightness color space based on a smartphone application. The versatility of the proposed sensing system was demonstrated by implementing an indirect competitive ELISA for analyzing trace drug residues in foodstuffs. The multicolor response of this sensing strategy allows us to visually quantify drug residues in foodstuffs. Moreover, the smartphone-based immunosensor can assess the exact concentration of the analyte by using a self-designed mobile application. The proposed assay provides a highly sensitive performance that the limit of detection was 0.37 ng/mL by visual detection and 0.057 ng/mL using the compact device. Due to its advantages in terms of portability, straightforward visual detection, high sensitivity, and cost effectiveness, the proposed immunosensor has great potential for applications in areas without access to laboratories or expensive infrastructure.

An Electrochemical Fiveplex Biochip Assay Based on Anti-Idiotypic Antibodies for Fast On-Site Detection of Bioterrorism Relevant Low Molecular Weight Toxins

Modern threats of bioterrorism force the need for multiple detection of biothreat agents to determine the presence or absence of such agents in suspicious samples. Here, we present a rapid electrochemical fiveplex biochip screening assay for detection of the bioterrorism relevant low molecular weight toxins saxitoxin, microcystin-LR, T-2 toxin, roridin A and aflatoxin B1 relying on anti-idiotypic antibodies as epitope-mimicking reagents. The proposed method avoids the use of potentially harmful toxin-protein conjugates usually mandatory for competitive immunoassays. The biochip is processed and analyzed on the automated and portable detection platform pBDi within 13.4 min. The fiveplex biochip assay revealed toxin group specificity to multiple congeners. Limits of detection were 1.2 ng/mL, 1.5 ng/mL, 0.4 ng/mL, 0.5 ng/mL and 0.6 ng/mL for saxitoxin, microcystin-LR, T-2 toxin, roridin A or aflatoxin B1, respectively. The robustness of the fiveplex biochip for real samples was demonstrated by detecting saxitoxin, microcystin-LR, HT-2 toxin, roridin A and aflatoxin B1 in contaminated human blood serum without elaborate sample preparation. Recovery rates were between 52–115% covering a wide concentration range. Thus, the developed robust fiveplex biochip assay can be used on-site to quickly detect one or multiple low molecular weight toxins in a single run.

Electrochemical Biochip Assays Based on Anti-idiotypic Antibodies for Rapid and Automated On-Site Detection of Low Molecular Weight Toxins

Phycotoxins and mycotoxins, such as paralytic shellfish poisoning toxins, type A trichothecenes, and aflatoxins are among the most toxic low molecular weight toxins associated with human poisoning incidents through the consumption of naturally contaminated food. Therefore, there is an utmost need for rapid and sensitive on-site detection systems. Herein, an electrochemical biochip for fast detection of saxitoxin, T-2 toxin as well as aflatoxin M1 and their corresponding congeners, respectively, using a portable and fully automated detection platform (pBDi, portable BioDetector integrated) was developed. Toxin analysis is facilitated upon the biochip via an indirect competitive immunoassay using toxin-specific antibodies combined with anti-idiotypic antibodies. The developed biochips enable detection in the low ng/mL-range within 17 min. Moreover, the assays cover a wide linear working range of 2–3 orders of magnitude above the limit of detection with an inter-chip coefficient of variation lower than 15%. The broad specificity of the employed antibodies which react with a large number of congeners within the respective toxin group allows efficient screening of contaminated samples for the presence of these low molecular weight toxins. With respect to the analysis of human urine samples, we focused here on the detection of saxitoxin, HT-2 toxin, and aflatoxin M1, all known as biomarkers of acute toxin exposure. Overall, it was proved that the developed biochip assays can be used to rapidly and reliably identify severe intoxications caused by these low molecular weight toxins.

Study of the binding way between saxitoxin and its aptamer and a fluorescent aptasensor for detection of saxitoxin

Aptamers could be used to construct simple and effective biosensor because the conformational switch of aptamer upon target binding is easy to be transferred to optical or electrochemical signals. Nevertheless, we found that the binding between saxitoxin (STX) and aptamer (M-30f) is not accompanied with conformational switch. Here, the circular dichroism spectra, fluorophore and quencher labeled aptamer, and crystal violet-based assays were used to identify the binding way between STX and aptamer. The results show that the conformation of aptamer is stabilized in PBS buffer (10 mM phosphate buffer, 2.7 mM KCl, 137 mM NaCl, pH 7.4) and this conformation may provide an exactly suitable cave for STX binding. Through the analysis of UV-melting curves and circular dichroism-melting curves, it is found that different concentrations of STX produce different unfolding extents of the aptamer under high temperature. Then, a simple temperature-assisted "turn-on" fluorescent aptasensor was developed to detect STX and the application in real sample detection demonstrates its feasibility. The proposed method provides not only an alternative for STX detection but also a strategy for simple aptasensor design using aptamers that do not switch conformation upon targets binding.

The effects of antigen size, binding site valency, and flexibility on fab-antigen binding near solid surfaces

Next generation antibody microarray devices have the potential to outperform current molecular detection methods and realize new applications in medicine, scientific research, and national defense. However, antibody microarrays, or arrays of antibody fragments ("fabs"), continue to evade mainstream use in part due to persistent reliability problems despite improvements to substrate design and protein immobilization strategies. Other factors could be disrupting microarray performance, including effects resulting from antigen characteristics. Target molecules embody a wide range of sizes, shapes, number of epitopes, epitope accessibility, and other physical and chemical properties. As a result, it may not be ideal for microarray designs to utilize the same substrate or immobilization strategy for all of the capture molecules. This study investigates how three antigen properties, such as size, binding site valency, and molecular flexibility, affect fab binding. The work uses an advanced, experimentally validated, coarse-grain model and umbrella sampling to calculate the free energy of ligand binding and how this energy landscape is different on the surface compared to in the bulk. The results confirm that large antigens interact differently with immobilized fabs compared to smaller antigens. Analysis of the results shows that despite these differences, tethering fabs in an upright orientation on hydrophilic surfaces is the best configuration for antibody microarrays.

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.

Aptamers and Aptasensors for Highly Specific Recognition and Sensitive Detection of Marine Biotoxins: Recent Advances and Perspectives

Marine biotoxins distribute widely, have high toxicity, and can be easily accumulated in water or seafood, exposing a serious threat to consumer health. Achieving specific and sensitive detection is the most effective way to prevent emergent issues caused by marine biotoxins; however, the previous detection methods cannot meet the requirements because of ethical or technical drawbacks. Aptamers, a kind of novel recognition element with high affinity and specificity, can be used to fabricate various aptasensors (aptamer-based biosensors) for sensitive and rapid detection. In recent years, an increasing number of aptamers and aptasensors have greatly promoted the development of marine biotoxins detection. In this review, we summarized the recent aptamer-related advances for marine biotoxins detection and discussed their perspectives. Firstly, we summarized the sequences, selection methods, affinity, secondary structures, and the ion conditions of all aptamers to provide a database-like information; secondly, we summarized the reported aptasensors for marine biotoxins, including principles, detection sensitivity, linear detection range, etc.; thirdly, on the basis of the existing reports and our own research experience, we forecast the development prospects of aptamers and aptasensors for marine biotoxins detection. We hope this review not only provides a comprehensive summary of aptamer selection and aptasensor development for marine biotoxins, but also arouses a broad readership amongst academic researchers and industrial chemists.

Detecting Nonvolatile Life- and Nonlife-Derived Organics in a Carbonaceous Chondrite Analogue with a New Multiplex Immunoassay and Its Relevance for Planetary Exploration

Potential martian molecular targets include those supplied by meteoritic carbonaceous chondrites such as amino acids and polycyclic aromatic hydrocarbons and true biomarkers stemming from any hypothetical martian biota (organic architectures that can be directly related to once living organisms). Heat extraction and pyrolysis-based methods currently used in planetary exploration are highly aggressive and very often modify the target molecules making their identification a cumbersome task. We have developed and validated a mild, nondestructive, multiplex inhibitory microarray immunoassay and demonstrated its implementation in the SOLID (Signs of Life Detector) instrument for simultaneous detection of several nonvolatile life- and nonlife-derived organic molecules relevant in planetary exploration and environmental monitoring. By utilizing a set of highly specific antibodies that recognize D- or L- aromatic amino acids (Phe, Tyr, Trp), benzo[a]pyrene (B[a]P), pentachlorophenol, and sulfone-containing aromatic compounds, respectively, the assay was validated in the SOLID instrument for the analysis of carbon-rich samples used as analogues of the organic material in carbonaceous chondrites or even Mars samples. Most of the antibodies enabled sensitivities at the 1-10 ppb level and some even at the ppt level. The multiplex immunoassay allowed the detection of B[a]P as well as aromatic sulfones in a water/methanol extract of an Early Cretaceous lignite sample (c.a., 140 Ma) representing type IV kerogen. No L- or D-aromatic amino acids were detected, reflecting the advanced diagenetic stage and the fossil nature of the sample. The results demonstrate the ability of the liquid extraction by ultrasonication and the versatility of the multiplex inhibitory immunoassays in the SOLID instrument to discriminate between organic matter derived from life and nonlife processes, an essential step toward life detection outside Earth.

Proteomic Methods of Detection and Quantification of Protein Toxins

Biological toxins are a heterogeneous group of compounds that share commonalities with biological and chemical agents. Among them, protein toxins represent a considerable, diverse set. They cover a broad range of molecular weights from less than 1000 Da to more than 150 kDa. This review aims to compare conventional detection methods of protein toxins such as in vitro bioassays with proteomic methods, including immunoassays and mass spectrometry-based techniques and their combination. Special emphasis is given to toxins falling into a group of selected agents, according to the Centers for Disease Control and Prevention, such as Staphylococcal enterotoxins, Bacillus anthracis toxins, Clostridium botulinum toxins, Clostridium perfringens epsilon toxin, ricin from Ricinus communis, Abrin from Abrus precatorius or control of trade in dual-use items in the European Union, including lesser known protein toxins such as Viscumin from Viscum album. The analysis of protein toxins and monitoring for biological threats, i.e., the deliberate spread of infectious microorganisms or toxins through water, food, or the air, requires rapid and reliable methods for the early identification of these agents.

A graphene oxide-based strand displacement amplification platform for ricin detection using aptamer as recognition element

The toxic plant protein ricin is a potential agent for criminal or bioterrorist attacks due to the wide availability and relative ease of preparation. Herein, we developed a novel strategy for the detection of ricin B-chain (RTB) based on isothermal strand-displacement polymerase reaction (ISDPR) by using aptamer as a recognition element and graphene oxide (GO) as a low background platform. In this method, ricin-binding aptamer (RBA) hybridized with a short blocker firstly, and then was immobilized on the surface of streptavidin-coated magnetic beads (MBs). The addition of RTB could release the blocker, which could hybridize with the dye-modified hairpin probe and trigger the ISDPR, resulting in high fluorescence intensity. In the absence of RTB, however, the fluorescence of the dye could be quenched strongly by GO, resulting in the extremely low background signal. Thus, RTB could be sensitively detected by the significantly increased fluorescence signal. The linear range of the current analytical system was from 0.75μg/mL to 100μg/mL and the limit of detection (3σ) was 0.6μg/mL. This method has been successfully utilized for the detection of both the RTB and the entire ricin toxin in real samples, and it could be generalized to any kind of target detection based on an appropriate aptamer.

Experimental Protocol for Detecting Cyanobacteria in Liquid and Solid Samples with an Antibody Microarray Chip

Global warming and eutrophication make some aquatic ecosystems behave as true bioreactors that trigger rapid and massive cyanobacterial growth; this has relevant health and economic consequences. Many cyanobacterial strains are toxin producers, and only a few cells are necessary to induce irreparable damage to the environment. Therefore, water-body authorities and administrations require rapid and efficient early-warning systems providing reliable data to support their preventive or curative decisions. This manuscript reports an experimental protocol for the in-field detection of toxin-producing cyanobacterial strains by using an antibody microarray chip with 17 antibodies (Abs) with taxonomic resolution (CYANOCHIP). Here, a multiplex fluorescent sandwich microarray immunoassay (FSMI) for the simultaneous monitoring of 17 cyanobacterial strains frequently found blooming in freshwater ecosystems, some of them toxin producers, is described. A microarray with multiple identical replicates (up to 24) of the CYANOCHIP was printed onto a single microscope slide to simultaneously test a similar number of samples. Liquid samples can be tested either by direct incubation with the antibodies (Abs) or after cell concentration by filtration through a 1- to 3-μm filter. Solid samples, such as sediments and ground rocks, are first homogenized and dispersed by a hand-held ultrasonicator in an incubation buffer. They are then filtered (5 - 20 μm) to remove the coarse material, and the filtrate is incubated with Abs. Immunoreactions are revealed by a final incubation with a mixture of the 17 fluorescence-labeled Abs and are read by a portable fluorescence detector. The whole process takes around 3 h, most of it corresponding to two 1-h periods of incubation. The output is an image, where bright spots correspond to the positive detection of cyanobacterial markers.

Validation Procedure for Multiplex Antibiotic Immunoassays Using Flow-Based Chemiluminescence Microarrays

Small molecules like antibiotics or other pharmaceuticals can be detected and quantified, among others, with indirect competitive immunoassays. With regard to multiplex quantification, these tests can be performed as chemiluminescence microarray immunoassays, in which, in principle, the analyte in the sample and the same substance immobilized on the chip surface compete for a limited number of specific antibody binding sites. The amount of the specific primary antibody that has been bound to the surface is visualized by means of a chemiluminescence reaction.Validated quantitative confirmatory methods for the detection of contaminants, for example drug residues, in food samples usually comprise chromatographic analysis and spectrometric detection, e.g., HPLC-MS, GC-MS, or GC with electron capture detection. Here, we describe a validation procedure (according to the Commission Decision of the European Communities 2002/657/EC) for multiplex immunoassays performed as flow-through chemiluminescence microarrays, using the example of a small molecule microarray for the simultaneous detection of 13 antibiotics in milk. By this means, we suggest to accept multianalyte immunoassays as confirmatory methods as well, to benefit from the advantages of a fast automated method that does not need any pretreatment of the sample. The presented microarray chip is regenerable, so an internal calibration is implemented. Therefore, the analytical results are highly precise, combined with low costs (the aim for commercialization is less than 1 € per analyte per sample, this is significantly less than HPLC-MS).

Detection of Legionella-contaminated aerosols in the vicinity of a bio-trickling filter of a breeding sow facility - A pilot study

The urbanization of agricultural areas results in a reduction of distances between residential buildings and livestock farms. In the public debate, livestock farming is increasingly criticized due to environmental disturbance and odor nuisance originating from such facilities. One method to reduce odor and ammonia is by exhaust air treatment, for example, by biological exhaust air purification processes with bio-trickling filters filled with tap water. Higher temperatures in the summer time and the generation of biofilms are ideal growth conditions for Legionella. However, there are no studies on the presence of Legionella in the water of bio-trickling filters and the release of Legionella-containing aerosols. Therefore, the aim of this study was to investigate Legionella in wash water and emitted bioaerosols of a bio-trickling filter system of a breeding sow facility. For this purpose, measurements were carried out using a cyclone sampler. In addition, samples of wash water were taken. Legionella were not found by culture methods. However, using molecular biological methods, Legionella spp. could be detected in wash water as well as in bioaerosol samples. With antibody-based methods, Legionella pneumophila were identified. Further studies are needed to investigate the environmental health relevance of Legionella-containing aerosols emitted by such exhaust air purification systems.

Integrating scFv into xMAP Assays for the Detection of Marine Toxins

Marine toxins, such as saxitoxin and domoic acid are associated with algae blooms and can bioaccumulate in shell fish which present both health and economic concerns. The ability to detect the presence of toxin is paramount for the administration of the correct supportive care in case of intoxication; environmental monitoring to detect the presence of toxin is also important for prevention of intoxication. Immunoassays are one tool that has successfully been applied to the detection of marine toxins. Herein, we had the variable regions of two saxitoxin binding monoclonal antibodies sequenced and used the information to produce recombinant constructs that consist of linked heavy and light variable domains that make up the binding domains of the antibodies (scFv). Recombinantly produced binding elements such as scFv provide an alternative to traditional antibodies and serve to "preserve" monoclonal antibodies as they can be easily recreated from their sequence data. In this paper, we combined the anti-saxitoxin scFv developed here with a previously developed anti-domoic acid scFv and demonstrated their utility in a microsphere-based competitive immunoassay format. In addition to detection in buffer, we demonstrated equivalent sensitivity in oyster and scallop matrices. The potential for multiplexed detection using scFvs in this immunoassay format is demonstrated.

A Review of the Methods for Detection of Staphylococcus aureus Enterotoxins

Food safety has attracted extensive attention around the world, and food-borne diseases have become one of the major threats to health. Staphylococcus aureus is a major food-borne pathogen worldwide and a frequent contaminant of foodstuffs. Staphylococcal enterotoxins (SEs) produced by some S. aureus strains will lead to staphylococcal food poisoning (SFP) outbreaks. The most common symptoms caused by ingestion of SEs within food are nausea, vomiting, diarrhea and cramps. Children will suffer SFP by ingesting as little as 100 ng of SEs, and only a few micrograms of SEs are enough to cause SPF in vulnerable populations. Therefore, it is a great challenge and of urgent need to detect and identify SEs rapidly and accurately for governmental and non-governmental agencies, including the military, public health departments, and health care facilities. Herein, an overview of SE detection has been provided through a comprehensive literature survey.

Glycan Arrays: From Basic Biochemical Research to Bioanalytical and Biomedical Applications

A major branch of glycobiology and glycan-focused biomedicine studies the interaction between carbohydrates and other biopolymers, most importantly, glycan-binding proteins. Today, this research into glycan-biopolymer interaction is unthinkable without glycan arrays, tools that enable high-throughput analysis of carbohydrate interaction partners. Glycan arrays offer many applications in basic biochemical research, for example, defining the specificity of glycosyltransferases and lectins such as immune receptors. Biomedical applications include the characterization and surveillance of influenza strains, identification of biomarkers for cancer and infection, and profiling of immune responses to vaccines. Here, we review major applications of glycan arrays both in basic and applied research. Given the dynamic nature of this rapidly developing field, we focus on recent findings.

A combination of positive dielectrophoresis driven on-line enrichment and aptamer-fluorescent silica nanoparticle label for rapid and sensitive detection of Staphylococcus aureus

Staphylococcus aureus (S. aureus) is an important human pathogen that causes several diseases ranging from superficial skin infections to life-threatening diseases. Here, a method combining positive dielectrophoresis (pDEP) driven on-line enrichment and aptamer-fluorescent silica nanoparticle label has been developed for the rapid and sensitive detection of S. aureus in microfluidic channels. An aptamer, having high affinity to S. aureus, is used as the molecular recognition tool and immobilized onto chloropropyl functionalized fluorescent silica nanoparticles through a click chemistry approach to obtain S. aureus aptamer-nanoparticle bioconjugates (Apt(S.aureus)/FNPs). The pDEP driven on-line enrichment technology was used for accumulating the Apt(S.aureus)/FNP labeled S. aureus. After incubating with S. aureus, the mixture of Apt(S.aureus)/FNP labeled S. aureus and Apt(S.aureus)/FNPs was directly introduced into the pDEP-based microfluidic system. By applying an AC voltage in a pDEP frequency region, the Apt(S.aureus)/FNP labelled S. aureus moved to the electrodes and accumulated in the electrode gap, while the free Apt(S.aureus)/FNPs flowed away. The signal that came from the Apt(S.aureus)/FNP labelled S. aureus in the focused detection areas was then detected. Profiting from the specificity of aptamer, signal amplification of FNP label and pDEP on-line enrichment, this assay can detect as low as 93 and 270 cfu mL(-1)S. aureus in deionized water and spiked water samples, respectively, with higher sensitivities than our previously reported Apt(S.aureus)/FNP based flow cytometry. Moreover, without the need for separation and washing steps usually required for FNP label involved bioassays, the total assay time including sample pretreatment was within 2 h.

Label and Label-Free Detection Techniques for Protein Microarrays

Protein microarray technology has gone through numerous innovative developments in recent decades. In this review, we focus on the development of protein detection methods embedded in the technology. Early microarrays utilized useful chromophores and versatile biochemical techniques dominated by high-throughput illumination. Recently, the realization of label-free techniques has been greatly advanced by the combination of knowledge in material sciences, computational design and nanofabrication. These rapidly advancing techniques aim to provide data without the intervention of label molecules. Here, we present a brief overview of this remarkable innovation from the perspectives of label and label-free techniques in transducing nano-biological events.

Synthesis of magnetic Fe3O4–Au hybrids for sensitive SERS detection of cancer cells at low abundance

A facile and rapid SERS-based immunoassay for living cancer cells using magnetic Fe₃O₄–Au hybrid nanoparticles is reported.