Detection of abrin in food using enzyme-linked immunosorbent assay and electrochemiluminescence technologies

Mass Spectrometric Detection and Differentiation of Enzymatically Active Abrin and Ricin Combined with a Novel Affinity Enrichment Technique

Abrin and ricin are toxic proteins produced by plants. Both proteins are composed of two subunits, an A-chain and a B-chain. The A-chain is responsible for the enzymatic activity, which causes toxicity. The B-chain binds to glycoproteins on the cell surface to direct the A-chain to its target. Both toxins depurinate 28S rRNA, making it impossible to differentiate these toxins based on only their enzymatic activity. We developed an analytical workflow for both ricin and abrin using a single method and sample. We have developed a novel affinity enrichment technique based on the ability of the B-chain to bind a glycoprotein, asialofetuin. After the toxin is extracted with asialofetuin-coated magnetic beads, an RNA substrate is added. Then, depurination is detected by a benchtop matrix-assisted laser desorption/ionization time-of-flight (MALDI TOF) mass spectrometer to determine the presence or absence of an active toxin. Next, the beads are subjected to tryptic digest. Toxin fingerprinting is done on a benchtop MALDI-TOF MS. We validated the assay through sensitivity and specificity studies and determined the limit of detection for each toxin as nanogram level for enzymatic activity and μg level for toxin fingerprinting. We examined potential cross-reactivity from proteins that are near neighbors of the toxins and examined potential false results in the presence of white powders.

Gaps in forensic toxicological analysis: The veiled abrin

Abrus precatorius is an herbaceous, flowering plant that is widely distributed in tropical and subtropical regions. Its toxic component, known as abrin, is classified as one of the potentially significant biological warfare agents and bioterrorism tools due to its high toxicity. Abrin poisoning can be utilized to cause accidents, suicides, and homicides, which necessitates attention from clinicians and forensic scientists. Although a few studies have recently identified the toxicological and pharmacological mechanisms of abrin, the exact mechanism remains unclear. Furthermore, the clinical symptoms and pathological changes induced by abrin poisoning have not been fully characterized, and there is a lack of standardized methods for identifying biological samples of the toxin. Therefore, there is an urgent need for further toxicopathologic studies and the development of detection methods for abrin in the field of forensic medicine. This review provides an overview of the clinical symptoms, pathological changes, metabolic changes, toxicologic mechanisms, and detection methods of abrin poisoning from the perspective of forensic toxicology. Additionally, the evidence on abrin in the field of forensic toxicology and forensic pathology is discussed. Overall, this review serves as a reference for understanding the toxicological mechanism of abrin, highlighting the clinical applications of the toxin, and aiding in the diagnosis and forensic identification of toxin poisoning.

A New Method for Abrin Detection Based on the Interaction between Target Molecules and Fluorescently Labeled Aptamers on Magnetic Microspheres

A quantitative structure-activity relationship (QSAR) model for the structure and affinity of abrin aptamers was established. A higher affinity abrin aptamer based on the established QSAR model was screened by site-directed mutagenesis. The fluorescence quenching effect between magnetic microspheres and fluorescent molecules was studied for the first time. A new method for abrin detection based on the interaction between target molecules and fluorescently labeled aptamers on magnetic microspheres was developed, with the detection limit of 5 ng mL^-1. This method can overcome the influence of complex environmental interferents in abrin detection and can meet the analysis requirements for simulated samples such as water, soil, and food.

Phage Display Affibodies Combined with AuNPs@Ru(bpy)32+ for Ultra-Sensitive Electrochemiluminescence Detection of Abrin

Abrin is a cytotoxin with strong lethality, which is a serious threat to human health and public safety, and thus, highly sensitive detection methods are urgently needed. The phage display affibody has two major modules, among which, the affibody fragment, with small molecular weight, high affinity and easy preparation, can be used for the specific recognition of the target, and the phage shell, with numerous protein copies, can be used as a carrier for the massive enrichment of signal molecules, and thus is particularly suitable as a sensitive probe for signal amplification in high-sensitivity biosensors. In this study, with antibody-coated magnetic microspheres as capture probes, Ru(bpy)32+ and biotin dual-labeled phage display affibodies as the specific signal probes and AuNPs@Ru(bpy)32+ (Ru(bpy)32+-coated gold nanoparticles) as the signal amplification nanomaterials, a new electrochemiluminescence (ECL) biosensor with a four-level sandwich structure of “magnetic capture probe-abrin-phage display affibody-AuNPs@Ru(bpy)32+” was constructed for abrin detection. In this detection mode, AuNPs@Ru(bpy)32+, a gold nanocomposite prepared rapidly via electrical interaction, contained an extremely high density of signal molecules, and the phage display affibodies with powerful loading capacity were not only labeled with Ru(bpy)32+, but also enriched with AuNPs@Ru(bpy)32+ in large amounts. These designs greatly improved the detection capability of the sensor, ultimately achieving the ultra-sensitive detection of abrin. The limit of detection (LOD) was 4.1 fg/mL (3δ/S), and the quantification range was from 5 fg/mL to 5 pg/mL. The sensor had good reproducibility and specificity and performed well in the test of simulated samples. This study expanded the application of affibodies in the field of biosensing and also deeply explored the signal amplification potential of phage display technology, which is of high value for the construction of simple and efficient sensors with high sensitivity.

A highly sensitive electrochemiluminescence method for abrin detection by a portable biosensor based on a screen-printed electrode with a phage display affibody as specific labeled probe

Abrin is a highly toxic ribosome-inactivating protein, which could be used as a biological warfare agent and terrorist weapon, and thus needs to be detected efficiently and accurately. Affibodies are a new class of engineered affinity proteins with small size, high affinity, high stability, favorable folding and good robustness, but they have rarely played a role in biological detection. In this work, we establish a novel electrochemiluminescence (ECL) method for abrin detection with a phage display affibody as the specific probe for the first time, to our knowledge, and a portable biosensor based on a screen-printed electrode (SPE) as the testing platform. On the basis of the double antibody sandwich structure in our previous work, we used a phage display affibody instead of monoclonal antibody as a new specific labeled probe. Due to numerous signal molecules labeled on M13 phages, significant signal amplification was achieved in this experiment. Under optimized conditions, a linear dependence was observed from 0.005 to 100 ng/mL with a limit of detection (LOD) of 5 pg/mL. This assay also showed good reproducibility and specificity, and performed well in the detection of simulated samples. Considering its high sensitivity, interference resistance and convenience, this new biosensing system based on phage display affibodies and a portable ECL biosensor holds promise for in situ detection of toxins and pollutants in different environments.

Evaluation of an Electrochemiluminescence Assay for the Rapid Detection of Abrin Toxin

In this article, we detail a comprehensive laboratory evaluation of an immunoassay for the rapid detection of abrin using the Meso Scale Diagnostics Sector PR2 Model 1800. For the assay evaluation, we used inclusivity and exclusivity panels comprised of extracts of 11 Abrus precatorius cultivars and 35 near-neighbor plants, 65 lectins, 26 white powders, 11 closely related toxins and proteins, and a pool of 30 BioWatch filter extracts. The results show that the Meso Scale Diagnostics abrin detection assay exhibits good sensitivity and specificity with a limit of detection of 4 ng/mL. However, the dynamic range of the assay for the quantitation of abrin was limited. We observed a hook effect at higher abrin concentrations, which can lead to potential false negative results. A modification of the assay protocol that incorporates extra wash steps can decrease the hook effect and the potential for false negative results.

Differentiation, Quantification and Identification of Abrin and Abrus precatorius Agglutinin

Abrin, the toxic lectin from the rosary pea plant Abrus precatorius, has gained considerable interest in the recent past due to its potential malevolent use. However, reliable and easy-to-use assays for the detection and discrimination of abrin from related plant proteins such as Abrus precatorius agglutinin or the homologous toxin ricin from Ricinus communis are sparse. To address this gap, a panel of highly specific monoclonal antibodies was generated against abrin and the related Abrus precatorius agglutinin. These antibodies were used to establish two sandwich ELISAs to preferentially detect abrin or A. precatorius agglutinin (limit of detection 22 pg/mL for abrin; 35 pg/mL for A. precatorius agglutinin). Furthermore, an abrin-specific lateral flow assay was developed for rapid on-site detection (limit of detection ~1 ng/mL abrin). Assays were validated for complex food, environmental and clinical matrices illustrating broad applicability in different threat scenarios. Additionally, the antibodies turned out to be suitable for immuno-enrichment strategies in combination with mass spectrometry-based approaches for unambiguous identification. Finally, we were able to demonstrate for the first time how the developed assays can be applied to detect, identify and quantify abrin from a clinical sample derived from an attempted suicide case involving A. precatorius.

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.

CCD Based Detector for Detection of Abrin Toxin Activity

Abrin is a highly potent and naturally occurring toxin produced in the seeds of Abrus precatorius (Rosary Pea) and is of concern as a potential bioterrorism weapon. There are many rapid and specific assay methods to detect this toxic plant protein, but few are based on detection of toxin activity, critical to discern biologically active toxin that disables ribosomes and thereby inhibits protein synthesis, producing cytotoxic effects in multiple organ systems, from degraded or inactivated toxin which is not a threat. A simple and low-cost CCD detector system was evaluated with colorimetric and fluorometric cell-based assays for abrin activity; in the first instance measuring the abrin suppression of mitochondrial dehydrogenase in Vero cells by the MTT-formazan method and in the second instance measuring the abrin suppression of green fluorescent protein (GFP) expression in transduced Vero and HeLa cells. The limit of detection using the colorimetric assay was 10 pg/mL which was comparable to the fluorometric assay using HeLa cells. However, with GFP transduced Vero cells a hundred-fold improvement in sensitivity was achieved. Results were comparable to those using a more expensive commercial plate reader. Thermal inactivation of abrin was studied in PBS and in milk using the GFP-Vero cell assay. Inactivation at 100 °C for 5 min in both media was complete only at the lowest concentration studied (0.1 ng/mL) while treatment at 63 °C for 30 min was effective in PBS but not milk.

Bio-barcode triggered isothermal amplification in a fluorometric competitive immunoassay for the phytotoxin abrin

Abrin is one of the most toxic phytotoxins to date, and is a potential biological warfare agent. A bio-barcode triggered isothermal amplification for fluorometric determination of abrin is described. Free abrin competes with abrin-coated magnetic microparticles (MMP) probes to bind to gold nanoparticle (AuNP) probes modified with abrin antibody and bio-barcoded DNA. Abundant barcodes are released from the MMP-AuNP complex via dithiothreitol treatment. This triggers an exponential amplification reaction (EXPAR) that is monitored by real-time fluorometry, at typical excitation/emission wavelengths of 495/520 nm. The EXPAR assay is easily operated, highly sensitive and specific. It was used to quantify abrin in spiked commercial samples. The detection limit (at S/N = 3; for n = 6) is 5.6 pg·mL^-1 which is considerably lower than previous reports. This assay provides a universal sensing platform and has great potential for determination of various analytes, including small molecules, proteins, DNA, and cells. Graphical abstract Schematic representation of the bio-barcode triggered exponential amplification reaction (EXPAR) for a fluorometric competitive immunoassay for abrin. The limit of detection is 5.6 pg mL^-1 with a large dynamic range from 10 pg mL^-1 to 1 µg mL^-1.

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.

Detection of Abrin by Electrochemiluminescence Biosensor Based on Screen Printed Electrode

For the convenience of fast measurement in the outdoor environment, a portable electrochemiluminescence biosensor with the screen-printed electrode as the reaction center was developed, which possesses the characteristics of high sensitivity, small scale, simplified operation and so on, and has been used for in situ detection of abrin. First, combining with magnetic separation technique, the "biotin-avidin" method was used to immobilize the polyclonal antibody (pcAb) on the magnetic microspheres surface as the capture probe. Secondly, the Ru(bpy)₃²⁺-labeled monoclonal antibody (mcAb) was used as the specific electrochemiluminescence signal probe. Then, the "mcAb-toxin-pcAb" sandwich model was built to actualize the quantitative detection of abrin on the surface of the screen-printed electrode. The linear detection range was 0.5-1000 ng/mL; the regression equation was Y = 89.251lgX + 104.978 (R = 0.9989, n = 7, p < 0.0001); and the limit of detection (LOD) was 0.1 ng/mL. The sensing system showed high sensitivity, excellent specificity and good anti-interference ability, and could be used for the analysis of trace abrin in various environmental samples with good recovery and reproducibility. Compared with the traditional electrochemiluminescence sensing device, its miniaturization and portability gives it potential to satisfy the requirement of in situ detection.

Detection of Abrin Holotoxin Using Novel Monoclonal Antibodies

Abrin, a member of the ribosome-inactivating protein family, is produced by the Abrus precatorius plant. Having the potential to pose a severe threat to both human and animal health, abrin is classified as a Select Agent by the U.S. Department of Health and Human Services. However, an immunoassay that is specific for intact abrin holotoxin has not yet been reported. In this study, seven new monoclonal antibodies (mAbs), designated as Abrin-1 through Abrin-7 have been developed. Isotyping analyses indicate these mAbs have IgG1, IgG2a, or IgG2b heavy-chains and kappa light-chains. Western blot analyses identified two abrin A-chain specific mAbs, Abrin-1 and Abrin-2, and four B-chain specific mAbs (Abrin-3, -5, -6, and -7). A sandwich enzyme-linked immunosorbent assay (ELISA), capable of detecting a mixture of abrin isoforms and agglutinins was developed using B-chain specific Abrin-3 for capture and A-chain specific Abrin-2 as detector. The ELISA is highly sensitive and detects 1 ng/mL of the abrin holotoxin in phosphate-buffered saline, nonfat milk, and whole milk, significantly below concentrations that would pose a health concern for consumers. This ELISA also detects native abrin in plant extracts with a very low background signal. The new abrin mAbs and ELISA should be useful for detecting this potent toxin in the milk supply chain and other complex matrices.

Rapid detection of abrin in foods with an up-converting phosphor technology-based lateral flow assay

Abrin is a natural plant toxin found in the seeds of Abrus precatorius. It may be used for food poisoning or bioterrorism, seriously endangering public health. In this study, a reliable method for the rapid detection of abrin in foods was developed, based on an up-converting phosphor technology-based lateral flow assay (abrin-UPT-LFA). Nine high-affinity monoclonal antibodies (mAbs) against abrin were prepared, and the optimum mAbs (mAb-6F4 and mAb-10E11) were selected for use in the assay in double-antibody-sandwich mode. The assay was confirmed to be specific for abrin, with a detection sensitivity of 0.1 ng mL-1 for standard abrin solutions. Good linearity was observed for abrin quantitation from 0.1 to 1000 ng mL-1 (r = 0.9983). During the analysis of various abrin-spiked food samples, the assay showed strong sample tolerance and a satisfactory limit of detection for abrin (0.5-10 ng g-1 for solid and powdered samples; 0.30-0.43 ng mL-1 for liquid samples). The analysis of suspected food samples, from sample treatment to result feed-back, could be completed by non-professionals within 20 min. Therefore, the abrin-UPT-LFA is a rapid, sensitive, and reliable method for the on-site detection of abrin in foods.

Label-free electrochemiluminescent detection of transcription factors with hybridization chain reaction amplification

Label-free and efficient ECL strategy for detection of NF-κB based on the HCR signal amplification.

Development of ELISA and Colloidal Gold-PAb Conjugate-Based Immunochromatographic Assay for Detection of Abrin-a

When abrin-a was combined with several polyclonal antibodies (PAb), the detection limit could be increased. In this way, a monoclonal antibody (capture) and polyclonal antibody (detection) sandwich enzyme-linked immunosorbent assay (ELISA) and a colloidal gold-PAb conjugate-based immunochromatographic assay for detection of abrin-a were developed. The ELISA had a detection limit of 3.9 ng/mL for abrin-a in standard solution and 7.8 ng/mL in soybean milk, and was more sensitive than polyclonal antibody (capture) and monoclonal antibody (detection) ELISA, which had a detection limit of 15.6 ng/mL. The test strip had a detection range of 50 to 500 ng/mL for abrin-a and a detection limit in standard solution or soybean milk samples of 50 ng/mL. However, the test strip had a reduced detection capability compared with a colloidal gold-monoclonal antibody conjugate-based immunochromatographic assay test strip, which had a lower detection limit of 10 ng/mL. The developed ELISAs and test strip show the specificity towards abrin-a and have no cross-reactivity towards abrin-b, -c, -d, ricin, or the agglutinins from either castor beans or rosary peas.

Aptamer-based colorimetric biosensing of abrin using catalytic gold nanoparticles

In this study we propose a simple and sensitive colorimetric aptasensor for the quantitative analysis of abrin by using catalytic AuNPs for the first time. AuNPs possess the peroxidase-like activity that can catalyse 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2, leading to color change of the solution. It is interesting to find that the peroxidase-like activity of AuNPs can be improved by surface activation with a target-specific aptamer. However, with a target molecule, the aptamer is desorbed from the AuNPs surface, resulting in a decrease of the catalytic abilities of AuNPs. The color change of the solution is relevant to the target concentration, and this can be judged by the naked eye and monitored by using a UV-vis spectrometer. The linear range for the current analytical system was from 0.2 nM to 17.5 nM. The corresponding limit of detection (LOD) was 0.05 nM. Some other proteins such as thrombin (Th), glucose oxidase (GOx), and bovine serum albumin (BSA) all had a negligible effect on the determination of abrin. Furthermore, several practical samples spiked with abrin were analyzed using the proposed method with excellent recoveries. This aptamer-based colorimetric biosensor is superior to other conventional methods owing to its simplicity, low cost, and high sensitivity.

Rapid method using two microbial enzymes for detection of L-abrine in food as a marker for the toxic protein abrin

Abrin is a toxic protein produced by the ornamental plant Abrus precatorius, and it is of concern as a biothreat agent. The small coextracting molecule N-methyl-l-tryptophan (l-abrine) is specific to members of the genus Abrus and thus can be used as a marker for the presence or ingestion of abrin. Current methods for the detection of abrin or l-abrine in foods and other matrices require complex sample preparation and expensive instrumentation. To develop a fast and portable method for the detection of l-abrine in beverages and foods, the Escherichia coli proteins N-methyltryptophan oxidase (MTOX) and tryptophanase were expressed and purified. The two enzymes jointly degraded l-abrine to products that included ammonia and indole, and colorimetric assays for the detection of those analytes in beverage and food samples were evaluated. An indole assay using a modified version of Ehrlich's/Kovac's reagent was more sensitive and less subject to negative interferences from components in the samples than the Berthelot ammonia assay. The two enzymes were added into food and beverage samples spiked with l-abrine, and indole was detected as a degradation product, with the visual lower detection limit being 2.5 to 10.0 μM (∼0.6 to 2.2 ppm) l-abrine in the samples tested. Results could be obtained in as little as 15 min. Sample preparation was limited to pH adjustment of some samples. Visual detection was found to be about as sensitive as detection with a spectrophotometer, especially in milk-based matrices.

Supersandwich-type electrochemiluminescenct aptasensor based on Ru(phen)3(2+) functionalized hollow gold nanoparticles as signal-amplifying tags

An electrochemiluminescent (ECL) aptasensor was fabricated and used for the amplified detection of thrombin (TB) based on DNA supersandwich structure. Herein, hollow gold nanospheres (HGNPs) were firstly employed as effective tag-carriers for the immobilization of detection aptamer (TBA 2) to form the HGNPs labeled TBA 2 (HGNPs-TBA 2). Subsequently, streptavidin (SA) was used to block the non-specific binding sites of HGNPs-TBA 2 as well as to supply binding sites, which could further introduce numerous initiator DNA strands (bio-S1) via biotin-streptavidin specific interaction. Next, bio-S1 could in situ trigger hybridization chain reaction (HCR) to create a long nicked double helices analogous (dsDNA) in the present of ssDNA S2 and ssDNA S3 (S3 is partially complementary to the S2) to obtain the DNA supersandwich structure. Furthermore, Ru(phen)3(2+), a well-known ECL luminophore, could be intercalated into the grooves of dsDNA (Ru-dsDNA) to form the Ru-dsDNA-SA-HGNPs-TBA 2 bioconjugate. As a result, the target of TB was sandwiched between Ru-dsDNA-SA-HGNPs-TBA 2 and TBA 1. In this strategy, numerous Ru(phen)3(2+) could be immobilized on the electrode based on the supersandwich structure, resulting in an increased ECL signal output. A supersandwich ECL assay for TB detection was developed with excellent sensitivity of a large concentration variation from 5fM to 50pM and a detection limit of 1.6fM.

Development of a monoclonal antibody-based sandwich-type enzyme-linked immunosorbent assay (ELISA) for detection of abrin in food samples

Abrin is a plant toxin, which can be easily isolated from the seeds of Abrus precatorius. It may be used as a biological warfare agent. In order to detect abrin in food samples, a two-layer sandwich format enzyme-linked immunosorbent assay based on the monoclonal antibody (mAb) (as capture antibody) and rabbit polyclonal serum (as detecting antibody) was developed and applied for the determination of abrin in some food matrices. The linear range of the mAb was 1-100 μg L(-1) with a detection limit of 0.5 μg L(-1) for abrin in phosphate buffered saline (PBS). The recoveries of abrin from sausage, beer and milk samples ranged 97.5-98.6%, 95.8-98.4% and 94.8-9.6%, respectively, with a coefficient of variation (CV) of 3.7% or less. The newly developed sandwich ELISA using the mAb appears to be a reliable and useful method for detection of abrin in sausage, beer and milk.

Llama-derived single domain antibodies specific for Abrus agglutinin

Llama derived single domain antibodies (sdAb), the recombinantly expressed variable heavy domains from the unique heavy-chain only antibodies of camelids, were isolated from a library derived from llamas immunized with a commercial abrin toxoid preparation. Abrin is a potent toxin similar to ricin in structure, sequence and mechanism of action. The selected sdAb were evaluated for their ability to bind to commercial abrin as well as abrax (a recombinant abrin A-chain), purified abrin fractions, Abrus agglutinin (a protein related to abrin but with lower toxicity), ricin, and unrelated proteins. Isolated sdAb were also evaluated for their ability to refold after heat denaturation and ability to be used in sandwich assays as both capture and reporter elements. The best binders were specific for the Abrus agglutinin, showing minimal binding to purified abrin fractions or unrelated proteins. These binders had sub nM affinities and regained most of their secondary structure after heating to 95 °C. They functioned well in sandwich assays. Through gel analysis and the behavior of anti-abrin monoclonal antibodies, we determined that the commercial toxoid preparation used for the original immunizations contained a high percentage of Abrus agglutinin, explaining the selection of Abrus agglutinin binders. Used in conjunction with anti-abrin monoclonal and polyclonal antibodies, these reagents can fill a role to discriminate between the highly toxic abrin and the related, but much less toxic, Abrus agglutinin and distinguish between different crude preparations.

Preparation and identification of monoclonal antibody against abrin-a

BALB/c mice were immunized four times with formalin-prepared abrin-a. Using the polyethylene glycol method, immunized splenocytes were isolated and fused with SP2/0 cells. An indirect ELISA was established and used to detect positive clones secreting monoclonal antibodies (mAbs) against abrin-a. After analysis, three hybridoma clones secreting IgG-subtype mAbs were obtained. The antibodies were purified from the hybridoma growth medium using protein A or G affinity chromatography. Western blot analysis was used to analyze the antigenic epitopes on abrin-a recognized by the mAbs. The mAbs were specific for abrin-a, with no detectable cross-reactivity with several homologous toxins and associated agglutinins. Sandwich ELISA was then developed using these mAbs, which had a detection limit for abrin-a of 7.8 ng/mL.

Simultaneous multiplex detection and confirmation of the proteinaceous toxins abrin, ricin, botulinum toxins, and Staphylococcus enterotoxins a, B, and C in food

Detection of proteinaceous toxins in complex heterogeneous mixtures requires highly specific and sensitive methods. Multiplex technology employing multiple antibodies that recognize different epitopes on a toxin provides built-in confirmatory analysis as part of the initial screen and thereby increases the reliability associated with both presumptive positive and negative results. Polyclonal and monoclonal antibodies were obtained for abrin, botulinum toxins, ricin, and Staphylococcus enterotoxins A, B, and C (SEA, SEB, and SEC). Food samples were spiked with the toxins either individually or mixed and analyzed following 40-fold dilution. Abrin, botulinum toxin A complex, ricin, and SEB displayed limits of detection in the original food samples ranging from 0.03 to 1.3 microg/mL, from 0.03 to 0.07 microg/mL, from 0.01 to 0.1 microg/mL, and from <0.01 to 0.03 microg/mL, respectively. Redundancy, that is, multiple antibodies for each toxin, some recognizing different epitopes or displaying different binding affinities, provided a "fingerprint" for the presence of the toxins and built-in confirmation, thus reducing the likelihood of false-positive and false-negative results. Inclusion of internal controls, including a unique protein, helped control for variations in dilution. Paramagnetic microspheres facilitated the detection of analyte in foods containing particulate matter incompatible with the use of filter plates normally used in the wash steps of assays employing standard polystyrene microspheres.

Application of deadenylase electrochemiluminescence assay for ricin to foods in a plate format

A recently developed bead-based deadenylase electrochemiluminescence assay for ricin is simple and sensitive in its ability to detect ricin, based on the catalytic activity of the toxin subunit, ricin A chain. The assay was modified to work in a 96-well plate format and evaluated by using juice samples. The plate-based assay, unlike the bead-based assay, includes wash steps that enable the removal of food particles. These steps minimize matrix effects and improve the signal-to-noise ratios and limits of detection (LOD). The LOD values for ricin in apple juice, vegetable juice, and citrate buffer by using the bead-based assay were 0.4, 1, and 0.1 microg/ml, respectively. In contrast, the LOD values for ricin by using the plate-based assay were 0.04, 0.1, and 0.04 microg/ml in apple juice, vegetable juice, and citrate buffer, respectively. The plate-based assay displayed three- to 10-fold lower LOD values than did the bead-based assay. Signal-to-noise ratios for the plate-based assay were comparable to those for the bead-based assay for ricin in citrate buffer, but 2- to 4.5-fold higher when the plate-based assay was used for analysis of juice samples.