Rapid and sensitive detection of biological warfare agents using time-resolved fluorescence assays

Impact of different classification schemes on discrimination of proteins with noise-contaminated spectra using laboratory-measured fluorescence data

Biological agents are important to detect and identify with respect to environmental contamination and public health. Noise contamination in fluorescent spectra is one of the contributors to the uncertainties of identification. In order to investigate the noise-tolerant capability provided by laboratory-measured excitation-emission matrix (EEM) fluorescence spectra that are used as a database, fluorescence properties of four proteinaceous biotoxin samples and ten harmless protein samples were characterized by EEM fluorescence spectra, and the predicting performance of models trained by laboratory-measured fluorescence data was tested and verified from validation data with noise-contaminated spectra. By means of peak signal of noise (PSNR) as an indicator of noise levels, the potential impact of noise contaminations on the characterization and discrimination of these samples was evaluated quantitatively. Different classification schemes utilizing multivariate analysis techniques of Principal Component Analysis (PCA), Random Forest (RF), and Multi-layer Perceptron (MPL) coupled with feature descriptors of differential transform (DT), Fourier transform (FT) and wavelet transform (WT) were conducted under different PSNR values. We systematically analyzed the performance of classification schemes by the case study at 20 PSNR and by statistical analysis from 1-100 PSNR. The results show that the spectral features with EEM-WT decreased the demanding number of input variables while retaining high performances in sample classification. The spectral features with EEM-FT presented the worst performance although having the largest number of features. The distributions of feature importance and contribution were found sensitive to noise contaminations. The classification scheme of PCA prior to MPL with EEM-WT as input presented an improvement in lower PSNR. These results indicate that robust features extracted by corresponding techniques are critical to enhancing the spectral differentiation capabilities among these samples and play an important role in eliminating the noise effect. The study of classification schemes for discriminating protein samples with noise-contaminated spectra presents tremendous potential for future developments in the rapid detection and identification of proteinaceous biotoxins based on three-dimensional fluorescence spectrometry.

Complex PK-PD of an engineered IL-15/IL-15Rα-Fc fusion protein in cynomolgus monkeys: QSP modeling of lymphocyte dynamics

XmAb24306 is a lymphoproliferative interleukin (IL)-15/IL-15 receptor α (IL-15Rα) Fc-fusion protein currently under clinical investigation as an immunotherapeutic agent for cancer treatment. XmAb24306 contains mutations in IL-15 that attenuate its affinity to the heterodimeric IL-15 receptor βγ (IL-15R). We observe substantially prolonged pharmacokinetics (PK) (half-life ∼ 2.5 to 4.5 days) in single- and repeat-dose cynomolgus monkey (cyno) studies compared to wild-type IL-15 (half-life ∼ 1 hour), leading to increased exposure and enhanced and durable expansion of NK cells, CD8+ T cells and CD4-CD8- (double negative [DN]) T cells. Drug clearance varied with dose level and time post-dose, and PK exposure decreased upon repeated dosing, which we attribute to increased target-mediated drug disposition (TMDD) resulting from drug-induced lymphocyte expansion (i.e., pharmacodynamic (PD)-enhanced TMDD). We developed a quantitative systems pharmacology (QSP) model to quantify the complex PKPD behaviors due to the interactions of XmAb24306 with multiple cell types (CD8+, CD4+, DN T cells, and NK cells) in the peripheral blood (PB) and lymphoid tissues. The model, which includes nonspecific drug clearance, binding to and TMDD by IL15R differentially expressed on lymphocyte subsets, and resultant lymphocyte margination/migration out of PB, expansion in lymphoid tissues, and redistribution to the blood, successfully describes the systemic PK and lymphocyte kinetics observed in the cyno studies. Results suggest that after 3 doses of every-two-week (Q2W) doses up to 70 days, the relative contributions of each elimination pathway to XmAb24306 clearance are: DN T cells > NK cells > CD8+ T cells > nonspecific clearance > CD4+ T cells. Modeling suggests that observed cellular expansion in blood results from the influx of cells expanded by the drug in lymphoid tissues. The model is used to predict lymphoid tissue expansion and to simulate PK-PD for different dose regimens. Thus, the model provides insight into the mechanisms underlying the observed PK-PD behavior of an engineered cytokine and can serve as a framework for the rapid integration and analysis of data that emerges from ongoing clinical studies in cancer patients as single-agent or given in combination.

Protein kinases: Role of their dysregulation in carcinogenesis, identification and inhibition

Protein kinases belong to the phosphor-transferases superfamily of enzymes, which "activate" enzymes via phosphorylation. The kinome of an organism is the total set of genes in the genome, which encode for all the protein kinases. Certain mutations in the kinome have been linked to dysregulation of protein kinases, which in turn can lead to several diseases and disorders including cancer. In this review, we have briefly discussed the role of protein kinases in various biochemical processes by categorizing cancer associated phenotypes and giving their protein kinase examples. Various techniques have also been discussed, which are being used to analyze the structure of protein kinases, and associate their roles in the oncogenesis. We have also discussed protein kinase inhibitors and United States Federal Drug Administration (USFDA) approved drugs, which target protein kinases and can serve as a counter to protein kinase dysregulation and mitigate the effects of oncogenesis. Overall, this review briefs about the importance of protein kinases, their roles in oncogenesis on dysregulation and how their inhibition via various drugs can be used to mitigate their effects.

Performance of feature extraction method for classification and identification of proteins based on three-dimensional fluorescence spectrometry

Three-dimensional excitation emission matrix (EEM) fluorescence spectroscopy was employed to discriminate protein samples comprising bovine serum albumin, neurotensin, ovalbumin, ricin, trypsin from bovine pancreas and trypsin from porcine pancreas. Two methods of feature extraction with and without parameterization were applied to the spectral data in order to evaluate their performance of discrimination between protein samples. The discrimination of protein samples was conducted by k-means clustering algorithm and eigenvalue extracting procedure based on principal component analysis (PCA). It was found that the method of feature extraction without parameterization performed best, correctly attributing 100% of the spectral data in the condition of two principal components (PCs) captured. Features extracted with spectral parameterization failed to separate ricin and trypsin from bovine pancreas in same condition. Without spectral parameterization, less dimensionality and unique principal components captured by PCA indicates the spectrally-resolved features of corresponding protein samples. By clustering using each spectrum at fixed excitation wavelength, excitation wavelengths matched with common intrinsic fluorophores were found to be more sensitive to the classification accuracy. Contributions of spectral features extracted from EEM to the principal components were discussed and demonstrated their feature differentiation capabilities among six protein samples. These results reveal that appropriate extraction approach of features in combination with PCA analysis could be used in discrimination of protein samples at species level as a spectroscopic diagnostic tool. Our study provides fundamental references about computational strategies when EEM are used to explore proteins in ambient environment.

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.

Rapid quantification of artemisinin derivatives in antimalarial drugs with dipstick immunoassays

Substandard antimalarial drugs will result in unsatisfied therapeutic efficacy and increase the risk of resistance development. The point-of-care, qualitative, or semi-quantitative dipstick immunoassays cannot differentiate the substandard drugs with confidence. A rapid and quantitative analytical method that can be used under field conditions is needed. Here, three lateral flow immunoassays (LFIAs) based on colloidal gold nanobeads (CGN) as labels were developed for quantification of artemether, dihydroartemisinin and artesunate contents in antimalarial drugs with the aid of a portable optical scanner. Also, time-resolved fluorescent nanobeads (TRFN)-LFIA, coupled with a portable fluorescent lateral flow reader, was developed for quantification of artesunate. Commercial antimalarial drugs were used to validate these LFIAs with comparison to the gold standard high-performance liquid chromatography (HPLC) method. The drug contents estimated with these CGN-LFIAs were in the range of 85.5-109.3% of the contents determined by HPLC with a coefficient of variation (CV) of 4.5-13.0%. The TRFN-LFIA results were in the range of 93.7-108.4% of contents determined by HPLC with a CV of 5.2-8.9%. There were no significant differences between the results of CGN-LFIA and TRFN-LIFA (P = 0.5277, t-test). Both types of LFIAs with portable readers may be used for quantitation of active ingredients in antimalarial drugs and for screening substandard antimalarial drugs in resource-limiting settings.

Rapid Detection of Botulinum Neurotoxins-A Review

A toxin is a poisonous substance produced within living cells or organisms. One of the most potent groups of toxins currently known are the Botulinum Neurotoxins (BoNTs). These are so deadly that as little as 62 ng could kill an average human; to put this into context that is approximately 200,000 × less than the weight of a grain of sand. The extreme toxicity of BoNTs leads to the need for methods of determining their concentration at very low levels of sensitivity. Currently the mouse bioassay is the most widely used detection method monitoring the activity of the toxin; however, this assay is not only lengthy, it also has both cost and ethical issues due to the use of live animals. This review focuses on detection methods both existing and emerging that remove the need for the use of animals and will look at three areas; speed of detection, sensitivity of detection and finally cost. The assays will have wide reaching interest, ranging from the pharmaceutical/clinical industry for production quality management or as a point of care sensor in suspected cases of botulism, the food industry as a quality control measure, to the military, detecting BoNT that has been potentially used as a bio warfare agent.

Advances in Molecular Diagnostic Approaches for Biothreat Agents

The advancement in Molecular techniques has been implicated in the development of sophisticated, high-end diagnostic platform and point-of-care (POC) devices for the detection of biothreat agents. Different molecular and immunological approaches such as Immunochromatographic and lateral flow assays, Enzyme-linked Immunosorbent assays (ELISA), Biosensors, Isothermal amplification assays, Nucleic acid amplification tests (NAATs), Next Generation Sequencers (NGS), Microarrays and Microfluidics have been used for a long time as detection strategies of the biothreat agents. In addition, several point of care (POC) devices have been approved by FDA and commercialized in markets. The high-end molecular platforms like NGS and Microarray are time-consuming, costly, and produce huge amount of data. Therefore, the future prospects of molecular based technique should focus on developing quick, user-friendly, cost-effective and portable devices against biological attacks and surveillance programs.

Sample processing approach for detection of ricin in surface samples

With several ricin contamination incidents reported over the past decade, rapid and accurate methods are needed for environmental sample analysis, especially after decontamination. A sample processing method was developed for common surface sampling devices to improve the limit of detection and avoid false negative/positive results for ricin analysis. Potential assay interferents from the sample matrix (bleach residue, sample material, wetting buffer), including reference dust, were tested using a Time-Resolved Fluorescence (TRF) immunoassay. Test results suggested that the sample matrix did not cause the elevated background fluorescence sometimes observed when analyzing post-bleach decontamination samples from ricin incidents. Furthermore, sample particulates (80mg/mL Arizona Test Dust) did not enhance background fluorescence or interfere with ricin detection by TRF. These results suggested that high background fluorescence in this immunoassay could be due to labeled antibody quality and/or quantity issues. Centrifugal ultrafiltration devices were evaluated for ricin concentration as a part of sample processing. Up to 30-fold concentration of ricin was observed by the devices, which serve to remove soluble interferents and could function as the front-end sample processing step to other ricin analytical methods. The procedure has the potential to be used with a broader range of environmental sample types and with other potential interferences and to be followed by other ricin analytical methods, although additional verification studies would be required.

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.

Sacrificial conversion of layered rare-earth hydroxide (LRH) nanosheets into (Y1−xEux)PO4 nanophosphors and investigation of photoluminescence

Sacrificial conversion of LRH nanosheets has led to (Y,Eu)PO₄ red-emitting nanophosphors.

Prospects for point-of-care pathogen diagnostics using surface-enhanced Raman scattering (SERS)

This review highlights recent advances in the application of surface-enhanced Raman scattering (SERS) in pathogen detection and discusses many of the challenges in moving this technology to the point-of-care (POC) arena.

Self-assembled lanthanum hydroxide microspheres within a reaction–diffusion framework: synthesis, characterization, control and application

The reaction–diffusion framework is used to synthesize lanthanum hydroxide microspheres with controlled particle size and fascinating surface topology and adsorption capacity.

Nanopore sensing of botulinum toxin type B by discriminating an enzymatically cleaved Peptide from a synaptic protein synaptobrevin 2 derivative

Botulinum neurotoxins (BoNTs) are the most lethal toxin known to human. Biodefense requires early and rapid detection of BoNTs. Traditionally, BoNTs can be detected by looking for signs of botulism in mice that receive an injection of human material, serum or stool. While the living animal assay remains the most sensitive approach, it is costly, slow and associated with legal and ethical constrains. Various biochemical, optical and mechanical methods have been developed for BoNTs detection with improved speed, but with lesser sensitivity. Here, we report a novel nanopore-based BoNT type B (BoNT-B) sensor that monitors the toxin's enzymatic activity on its substrate, a recombinant synaptic protein synaptobrevin 2 derivative. By analyzing the modulation of the pore current caused by the specific BoNT-B-digested peptide as a marker, the presence of BoNT-B at a subnanomolar concentration was identified within minutes. The nanopore detector would fill the niche for a much needed rapid and highly sensitive detection of neurotoxins, and provide an excellent system to explore biophysical mechanisms for biopolymer transportation.

Quantitative SERS-based DNA detection assisted by magnetic microspheres

We report a quantitative SERS measurement scheme based on the magnetic microsphere–Ag nanoparticles to detect target DNA.

Mechanoluminescence and thermoluminescence characterization of Tb3+doped CaAl2O4: a theoretical and experimental study

Mechanoluminescence and thermoluminescence of Tb in CaAl₂O₄prepared by a solution combustion method has been reported.

Development of an ELISA microarray assay for the sensitive and simultaneous detection of ten biodefense toxins

Plant and microbial toxins are considered bioterrorism threat agents because of their extreme toxicity and/or ease of availability. Additionally, some of these toxins are increasingly responsible for accidental food poisonings. The current study utilized an ELISA-based protein antibody microarray for the multiplexed detection of ten biothreat toxins, botulinum neurotoxins (BoNT) A, B, C, D, E, F, ricin, shiga toxins 1 and 2 (Stx), and staphylococcus enterotoxin B (SEB), in buffer and complex biological matrices. The multiplexed assay displayed a sensitivity of 1.3 pg mL(-1) (BoNT/A, BoNT/B, SEB, Stx-1 and Stx-2), 3.3 pg mL(-1) (BoNT/C, BoNT/E, BoNT/F) and 8.2 pg mL(-1) (BoNT/D, ricin). All assays demonstrated high accuracy (75-120 percent recovery) and reproducibility (most coefficients of variation <20%). Quantification curves for the ten toxins were also evaluated in clinical samples (serum, plasma, nasal fluid, saliva, stool, and urine) and environmental samples (apple juice, milk and baby food) with overall minimal matrix effects. The multiplex assays were highly specific, with little cross-reactivity observed between the selected toxin antibodies. The results demonstrate a multiplex microarray that improves current immunoassay sensitivity for biological warfare agents in buffer, clinical, and environmental samples.

Application of time-resolved fluorescence for imaging-based multisample and multianalyte detection in single microtiter wells

Enzyme-linked immunosorbent assays are routinely used in laboratories around the world and ensure highly specific protein detection. Often, more than one analyte needs to be determined in a single sample and numerous protein arrays for multianalyte detection of a single sample have been developed to address this problem. They have the potential to analyze several dozen or even more analytes in an assay volume of usually around 100 μL. However, due to the presence of numerous different antibodies, these multianalyte sandwich immunoassays suffer from undesired cross-reactivities between the antibodies which lead to a loss of assay specificities. Here, we present an assay principle which allows, e.g., a detection of an analyte in a sample volume of only 1 μL in a normal 96-microtiter well plate, so that up to 100 analytes can be determined from a 100 μL sample volume, but in separate wells. This eliminates antibody cross-reactivities. The assay is based on the biotinylated time-resolved fluorophore EuLH used as a PEG11-dye conjugate in combination with ExtrAvidin® to ensure high signal-to-background ratios. The model protein epidermal growth factor (EGF) was detected with the established sandwich immunoassay and showed assay parameters comparable to commercially available ones. Furthermore, the assay principle enables a spatial resolution of the assay signal. Here, we demonstrated the application of the new detection system for universal imaging-based analysis of individual spots in one single 96-microtiter well by applying it to multisample and also multianalyte detections. In the case of the multisample analysis approach, a considerable reduction of the required sample volume to only 1 μL in a single 96 microtiter well could be achieved.

Evaluation of trapping parameters of γ-rays irradiated Dy3+ -doped LaPO4 phosphors

Thermoluminescence (TL) materials are widely used in radiation measurements. The best-known applications of TL materials are in the dosimetry of ionizing radiation, and in CTV screen phosphors, scintillators, X-ray laser materials, etc. The TL glow curve and its kinetic parameters for annealed LaPO4 at different constant temperatures and for Dy(3+) -doped LaPO4 phosphors irradiated by gamma-rays are reported here. The samples were irradiated using a (60) Co gamma-ray source at a dose of 10 Gy and the heating rate used for TL measurements was 5 ºC/s. The samples were characterized using X-ray diffraction (XRD), Fourier transform infrared, transmission electron microscopy and TL techniques. The XRD pattern shows that the prepared phosphor has a good crystalline structure with an average crystallite size of ~ 18 nm. The samples show good TL peaks for 0.05, 0.1 and 0.2 mole % doping concentrations of Dy(3+) ions and anneal above 400 ºC. The TL glow curve characteristics of annealed LaPO4 and Dy(3+) -doped LaPO4 were analyzed and trapping parameters calculated using various methods. All TL glow curves obey the second-order kinetics with a single glow peak, which reveals that only one set of trapping parameter is set for a particular temperature. The TL sensitivity was found to depend upon the annealing temperature and Dy(3+) doping concentration. The prepared sample may be a new nano phosphor and be useful in TL dosimetry.

Selective cultivation and rapid detection of Staphylococcus aureus by computer vision

In this paper, we developed a selective growth medium and a more rapid detection method based on computer vision for selective isolation and identification of Staphylococcus aureus from foods. The selective medium consisted of tryptic soy broth basal medium, 3 inhibitors (NaCl, K2 TeO3 , and phenethyl alcohol), and 2 accelerators (sodium pyruvate and glycine). After 4 h of selective cultivation, bacterial detection was accomplished using computer vision. The total analysis time was 5 h. Compared to the Baird-Parker plate count method, which requires 4 to 5 d, this new detection method offers great time savings. Moreover, our novel method had a correlation coefficient of greater than 0.998 when compared with the Baird-Parker plate count method. The detection range for S. aureus was 10 to 10(7) CFU/mL.

PRACTICAL APPLICATION

Our new, rapid detection method for microorganisms in foods has great potential for routine food safety control and microbiological detection applications.

Sensitive Detection ofBacillus anthracisUsing a Binding Protein Originating from γ-Phage

Detection of biological weapons is a primary concern in force protection, treaty verification, and safeguarding civilian populations against domestic terrorism. One great concern is the detection of Bacillus anthracis, the causative agent of anthrax. Therefore, there is a pressing need to develop novel methods for rapid, simple, and precise detection of B. anthracis. Here, we report that the C-terminal region of gamma-phage lysin protein (PlyG) binds specifically to the cell wall of B. anthracis and the recombinant protein corresponding to this region (positions, 156-233), PlyGB, is available as a bioprobe for detection of B. anthracis. Our detection method, based on a membrane direct blot assay using recombinant PlyGB, was more rapid and sensitive than the gamma-phage test and was simpler and more inexpensive than genetic methods such as PCR, or immunological methods using specific antibodies. Furthermore, its specificity was comparable to the gamma-phage test. PlyGB is applicable in conventional methods instead of antibodies and could be a potent tool for detection of B. anthracis.

Minimizing nonspecific protein adsorption in liquid crystal immunoassays by using surfactants

In this paper, we report the role of surfactants in minimizing nonspecific protein adsorption in liquid crystal (LC)-based immunoassays in which LC is used as a readout system. Among all surfactants tested, only nonionic surfactant such as Tween 20 can effectively reduce the nonspecific protein adsorption, while maintaining the selectivity of the LC-based immunoassay. We also show that to minimize nonspecific protein adsorption, Tween 20 can be added directly into the antibody solution to a final concentration of 0.8 mM. After the addition of Tween 20, better correlations between the antibody concentrations and the interference colors of LCs can therefore be obtained. For example, when Cy3 antibiotin was used, black, yellow, red, and green interference colors correspond to a concentration of 5, 25, 50, and 100 μg/mL, respectively. This feature gives LC immunoassay a unique advantage over the fluorescence-based immunoassay.

Analysis of active ricin and castor bean proteins in a ricin preparation, castor bean extract, and surface swabs from a public health investigation

In late February 2008, law enforcement officials in Las Vegas, Nevada, discovered in a hotel room, a copy of The Anarchist Cookbook, suspected castor beans and a "white powder" thought to be a preparation of ricin. Ricin is a deadly toxin from the seed of the castor bean plant (Ricinus communis). The United States regulates the possession, use, and transfer of ricin and it is the only substance considered a warfare agent in both the Chemical and the Biological Weapons Conventions. Six samples obtained from the hotel room were analyzed by laboratories at the Centers for Disease Control and Prevention using a panel of biological and mass spectrometric assays. The biological assays (real time-PCR, time resolved fluorescence and cytotoxicity) provided presumptive evidence of active ricin in each of the samples. This initial screen was followed by an in-depth analysis using a novel, state-of-the-art mass spectrometry-based ricin functional assay and high sensitivity tandem mass spectrometry for protein identification. Mass spectrometric analysis positively identified ricin and confirmed that in each of the samples it was enzymatically active. The tandem mass spectrometry analysis used here is the most selective method available to detect ricin toxin. In each sample, ricin was unequivocally identified along with other R. communis plant proteins, including the highly homologous protein RCA120. Although database searches using tandem mass spectra acquired from the samples indicated that additional controlled substances were not present in these samples, the mass spectrometric results did provide extensive detail about the sample contents. To the best of our knowledge following a review of the available literature, this report describes the most detailed analysis of a white powder for a public health or forensic investigation involving ricin.

Analysis of staphylococcal enterotoxin A in milk by matrix-assisted laser desorption/ionization-time of flight mass spectrometry

Staphylococcal enterotoxin A (SEA) is an exotoxin excreted mainly by Staphylococcus aureus and nowadays is the most prevalent compound in staphylococcal food poisoning worldwide. SEA is highly heat-resistant, and usual cooking times and temperatures are unlikely to completely inactivate it. A procedure for extraction of this toxin based on protein precipitation with a mixture of dichloromethane and acidified water was used before SDS-PAGE separation of soluble proteins. Finally, bands of interest were excised from the gel and in-gel enzymatic digestion was done. SEA from pasteurized milk was detected with matrix-assisted laser-desorption/ionization-time of flight (MALDI-TOF) mass spectrometry. Nineteen peptides (range 800-2400 Da) were identified as products of trypsin cleavage of the SEA standard with a score of 204 and 73% coverage of the protein sequence, whereas thirteen peptides were revealed for SEA extracted from milk with a score of 148 and 58% sequence coverage obtained. This procedure has been applied successfully for identification of SEA in milk.

Highly sensitive microplate chemiluminescence enzyme immunoassay for the determination of staphylococcal enterotoxin B based on a pair of specific monoclonal antibodies and its application to various matrices

A highly specific and sensitive microplate chemiluminescent enzyme immunoassay (CLEIA) was established and validated for the detection of staphylococcal enterotoxin B (SEB). A pair of monoclonal antibodies (mAbs) that recognizes different epitopes of SEB was selected from 20 SEB-specific mAbs, and the experimental conditions were examined and optimized for the development of the CLEIA. This method exhibited high performance with a dynamic range of 0.01-5 ng/mL, and the measured limit of detection (LOD) was 0.01 ng/mL. Intra- and interassay coefficient variations were all lower than 13% at three concentrations (0.2, 0.4, and 2 ng/mL). For specificity studies, when this method was applied to test staphylococcal enterotoxins A, C1, and D, no cross-reactivity was observed. It has been successfully applied to the analysis of SEB in a variety of environmental, biological and humoral matrices such as sewage, tap water, river water, roast beef, peanut butter, cured ham, 10% nonfat dry milk, milk, orange juice, and human urine and serum. The aim of this article is to show that the highly sensitive, specific, and simple microplate CLEIA, based on a pair of highly specific monoclonal antibodies, has potential applications for quantifying SEB in public health and military reconnaissance.

Nucleation sequence on the cation exchange process between Y0.95Eu0.05PO4 and CePO4 nanorods

Nanorods of Y0.95Eu0.05PO4@CePO4 (Y0.95Eu0.05PO4 phase was nucleated first and then a CePO4 phase was nucleated) and CePO4@Y0.95Eu0.05PO4 (CePO4 phase was nucleated first and then Y0.95Eu0.05PO4 phase was nucleated) were prepared at a relatively low temperature of 140 °C in ethylene glycol medium. Based on XRD, TEM and Raman studies it has been inferred that Y0.95Eu0.05PO4@CePO4 sample consists of a mixture of bigger (length around 800-1000 nm and width around of 80-100 nm) and smaller (length around 70-100 nm and width around 10-20 nm) nanorods, having monoclinic CePO4 and tetragonal YPO4 structure, whereas CePO4@Y0.95Eu0.05PO4 sample consists of mainly small nanorods having a single phase CePO4 structure. From the detailed luminescence studies it has been established that there exists significant incorporation of Y3+/Eu3+ ions in the CePO4 phase in CePO4@Y0.95Eu0.5PO4 sample. This has been attributed to the cation exchange taking place between Ce3+ ions in CePO4 host and Eu3+ and Y3+ ions in solution during the synthesis stage. Unlike this, such an exchange is not possible for Y0.95Eu0.05PO4@CePO4 sample synthesized under identical conditions due to the higher solubility product (Ksp) value of YPO4 compared to CePO4. Incorporation of Eu3+ in the CePO4 lattice of CePO4@Y0.95Eu0.5PO4 sample is confirmed by the significant reduction in the lifetime of 5D0 level of Eu3+ and the luminescence intensity from Eu3+, arising due to the electron transfer between the Ce3+/Ce4+ and Eu3+/Eu2+ species. These results are further supported by the non-radiative decay rates and quantum yields calculated from the emission spectrum.

Sensing the deadliest toxin: technologies for botulinum neurotoxin detection

Sensitive and rapid detection of botulinum neurotoxins (BoNTs), the most poisonous substances known to date, is essential for studies of medical applications of BoNTs and detection of poisoned food, as well as for response to potential bioterrorist threats. Currently, the most common method of BoNT detection is the mouse bioassay. While this assay is sensitive, it is slow, quite expensive, has limited throughput and requires sacrificing animals. Herein, we discuss and compare recently developed alternative in vitro detection methods and assess their ability to supplement or replace the mouse bioassay in the analysis of complex matrix samples.

Sensing the deadliest toxin: technologies for botulinum neurotoxin detection

Sensitive and rapid detection of botulinum neurotoxins (BoNTs), the most poisonous substances known to date, is essential for studies of medical applications of BoNTs and detection of poisoned food, as well as for response to potential bioterrorist threats. Currently, the most common method of BoNT detection is the mouse bioassay. While this assay is sensitive, it is slow, quite expensive, has limited throughput and requires sacrificing animals. Herein, we discuss and compare recently developed alternative in vitro detection methods and assess their ability to supplement or replace the mouse bioassay in the analysis of complex matrix samples.

Lab-on-a-chip for botulinum neurotoxin a (BoNT-A) activity analysis

A Lab-on-a-chip (LOC) was designed, fabricated and tested for the in vitro detection of botulinum neurotoxin serotype A (BoNT-A) activity using an assay that measures cleavage of a fluorophore-tagged peptide substrate specific for BoNT-A (SNAP-25) by the toxin light chain (LcA). LcA cleavage was detected by Förster Resonance Energy Transfer (FRET) fluorescence. FRET fluorescence was measured by a newly developed portable charge-coupled device (CCD) fluorescent detector equipped with multi-wavelength light-emitting diodes (LED) illumination. An eight V-junction microchannel device for BoNTs activity assays was constructed using Laminated Object Manufacturing (LOM) technology. The six-layer device was fabricated with a Poly(methyl methacrylate (PMMA) core and five polycarbonate (PC) layers micromachined by CO2 laser. The LOC is operated by syringe and is equipped with reagents, sample wells, reaction wells, diffusion traps (to avoid cross contamination among channels) and waste reservoirs. The system was detected LcA at concentrations as low as 0.5 nM, which is the reported sensitivity of the SNAP-25 in vitro cleavage assay. Combined with our CCD detector, the simple point of care system enables the detection of BoNTs activity and may be useful for the performance of other complex medical assays without a laboratory. This approach may realize the potential to enhance the quality of health care delivery for underserved populations.

Multiplexed detection of bacteria and toxins using a microflow cytometer

A microfabricated flow cytometer was used to demonstrate multiplexed detection of bacteria and toxins using fluorescent coded microspheres. Antibody-coated microspheres bound biothreat targets in a sandwich immunoassay format. The microfluidic cytometer focused the microspheres in three dimensions within the laser interrogation region using passive groove structures to surround the sample stream with sheath fluid. Optical analysis at four different wavelengths identified the coded microspheres and quantified target bound by the presence of phycoerythrin tracer. The multiplexed assays in the microflow cytometer had performance approaching that of a commercial benchtop flow cytometer. The respective limits of detection for bacteria (Escherichia coli, Listeria, and Salmonella) were found to be 10(3), 10(5), and 10(4) cfu/mL for the microflow cytometer and 10(3), 10(6), and 10(5) cfu/mL for the commercial system. Limits of detection for the toxins (cholera toxin, staphylococcal enterotoxin B, and ricin) were 1.6, 0.064, and 1.6 ng/mL for the microflow cytometer and 1.6, 0.064, and 8.0 ng/mL for the commercial system.

Simultaneous quantification of five bacterial and plant toxins from complex matrices using a multiplexed fluorescent magnetic suspension assay

Proteotoxins such as ricin, abrin, botulinum neurotoxins type A and B (BoNT/A, BoNT/B) and staphylococcal enterotoxin B (SEB) are regarded as potential biological warfare agents which could be used for bioterrorism attacks on the food chain. In this study we used a novel immunisation strategy to generate high-affinity monoclonal and polyclonal antibodies against native ricin, BoNT/A, and BoNT/B. The antibodies were used along with antibodies against SEB and abrin to establish a highly sensitive magnetic and fluorescent multiplex bead array with excellent sensitivities between 2 ng/L and 546 ng/L from a minimal sample volume of 50 microL. The assay was validated using 20 different related analytes and the assay precision was determined. Advancing the existing bead array technology, the novel magnetic and fluorescent microbeads proved amenable to enrichment procedures, by further increasing sensitivity to 0.3-85 ng/L, starting from a sample volume of 500 microL. Furthermore, the method was successfully applied for the simultaneous identification of the target toxins spiked into complex food matrices like milk, baby food and yoghurt. On the basis of our results, the assay appears to be a good tool for large-scale screening of samples from the food supply chain.

Time-resolved fluorescent resonance energy transfer assay for simple and rapid detection of anti-Brucella antibodies in ruminant serum samples

Brucellosis is a globally significant zoonosis, the control of which is difficult and resource intensive. Serological tests form a vital part of a multifactorial approach to control and are often performed in large numbers. The aim of the present study was to develop a new assay to improve the efficiency, ease, and effectiveness of serological testing. An existing competitive enzyme-linked immunosorbent assay (cELISA) was adapted to a completely homogeneous time-resolved fluorescent resonance energy transfer (TR-FRET) assay. This was achieved by labeling an anti-Brucella monoclonal antibody with a long-lifetime donor fluorophore and Brucella smooth lipopolysaccharide with a compatible acceptor and optimizing the reading conditions. The assay was performed in a 96-well plate with a single 30-min incubation period and no separation (wash) steps and was concluded by a single plate-reading step. The performance of the assay was evaluated with a panel of serum samples from infected (n = 73) and uninfected (n = 480) sources and compared to the performance of the parent cELISA, an indirect ELISA (iELISA), and fluorescence polarization assay (FPA). The performance of the TR-FRET assay matched the performance of the iELISA, which had 100% diagnostic sensitivity and specificity, and surpassed the performance of the cELISA and the FPA. The results also demonstrated that the TR-FRET technique is effective with poor-quality serum samples from the field. To the knowledge of the authors, this is the first homogeneous TR-FRET assay to detect antibodies raised against an infectious disease. The technique appears to be sufficiently adaptable to meet the needs of many other similar testing requirements to identify infectious diseases.

Evanescent wave fiber optic biosensor for salmonella detection in food

Salmonella enterica is a major food-borne pathogen of world-wide concern. Sensitive and rapid detection methods to assess product safety before retail distribution are highly desirable. Since Salmonella is most commonly associated with poultry products, an evanescent wave fiber-optic assay was developed to detect Salmonella in shell egg and chicken breast and data were compared with a time-resolved fluorescence (TRF) assay. Anti-Salmonella polyclonal antibody was immobilized onto the surface of an optical fiber using biotin-avidin interactions to capture Salmonella. Alexa Fluor 647-conjugated antibody (MAb 2F-11) was used as the reporter. Detection occurred when an evanescent wave from a laser (635 nm) excited the Alexa Fluor and the fluorescence was measured by a laser-spectrofluorometer at 710 nm. The biosensor was specific for Salmonella and the limit of detection was established to be 10³ cfu/mL in pure culture and 10⁴ cfu/mL with egg and chicken breast samples when spiked with 10² cfu/mL after 2–6 h of enrichment. The results indicate that the performance of the fiber-optic sensor is comparable to TRF, and can be completed in less than 8 h, providing an alternative to the current detection methods.