A colloidal gold probe-based silver enhancement immunochromatographic assay for the rapid detection of abrin-a

An improved clenbuterol detection by immunochromatographic assay with bacteria@Au composite as signal amplifier

Immunochromatographic assays (ICAs) are most frequently used for on-site rapid screening of clenbuterol. To improve sensitivity, a novel probe with bacteria as signal carriers was developed. Bacteria can load a great deal of gold nanoparticles (AuNPs) on their surface, meaning much fewer antibodies are needed to produce clearly visible results, although low concentrations of antibody could also trigger fierce competition between free analyte and the immobilized antigen. Thus, a limited number of antibodies was key to significantly improved sensitivity. Analytical conditions, including bacterial species, coupling method, and concentration, were optimized. The visual detection limit (VDL) for clenbuterol was 0.1 ng/mL, a 20-fold improvement in sensitivity compared with traditional strips. This work has opened up a new route for signal amplification and improved performance of ICAs. Furthermore, inactivated bacteria could also be environment-friendly and robust signal carriers for other biosensors.

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.

Multiplexed Detection of Foodborne Pathogens from Contaminated Lettuces Using a Handheld Multistep Lateral Flow Assay Device

This paper presents a handheld device that is capable of simplifying multistep assays to perform sensitive detection of foodborne pathogens. The device is capable of multiplexed detection of Escherichia coli (E. coli) O157:H7, Salmonella Typhimurium (S. Typhimurium), Staphylococcus aureus, and Bacillus cereus. The limit of detection for each bacterium was characterized, and then, the detection of bacteria from contaminated fresh lettuces was demonstrated for two representative foodborne pathogens. We employed a sample pretreatment protocol to recover and concentrate target bacteria from contaminated lettuces, which can detect 1.87 × 104 CFU of E. coli O157:H7 and 1.47 × 104 CFU of S. Typhimurium/1 g of lettuce without an enrichment process. Lastly, we demonstrated that the limit of detection can be reduced to 1 CFU of E. coli O157:H7 and 1 CFU of S. Typhimurium/1 g of lettuce by including a 6 h enrichment of contaminated lettuces in growth media before pretreatment.

Platinum-Decorated Gold Nanoparticles with Dual Functionalities for Ultrasensitive Colorimetric in Vitro Diagnostics

Au nanoparticles (AuNPs) as signal reporters have been utilized in colorimetric in vitro diagnostics (IVDs) for decades. Nevertheless, it remains a grand challenge to substantially enhance the detection sensitivity of AuNP-based IVDs as confined by the inherent plasmonics of AuNPs. In this work, we circumvent this confinement by developing unique dual-functional AuNPs that were engineered by coating conventional AuNPs with ultrathin Pt skins of sub-10 atomic layers (i.e., Au@Pt NPs). The Au@Pt NPs retain the plasmonic activity of initial AuNPs while possessing ultrahigh catalytic activity enabled by Pt skins. Such dual functionalities, plasmonics and catalysis, offer two different detection alternatives: one produced just by the color from plasmonics (low-sensitivity mode) and the second more sensitive color catalyzed from chromogenic substrates (high-sensitivity mode), achieving an "on-demand" tuning of the detection performance. Using lateral flow assay as a model IVD platform and conventional AuNPs as a benchmark, we demonstrate that the Au@Pt NPs could enhance detection sensitivity by 2 orders of magnitude.

Preparation and evaluation of Salmonella Enteritidis antigen conjugated with nanogold for screening of poultry flocks

Aim:

The present work aimed to develop lateral flow immunochromatographic strip (ICS) test for detection of Salmonella Enteritidis (SE) specific antibodies in chicken sera.

Materials and Methods:

A rapid lateral flow immunochromatographic test (LFIT) has been developed, in which SE Group D antigen labeled with the gold chloride molecules laid on the conjugate pad. Staphylococcus aureus protein A was used as capture antibody at the test line (T) of a nitrocellulose (NC) membrane and anti-SE antigen-specific rabbit antibodies were used as capture antibody at the control line (C) of the NC strip in the lateral flow layout device.

Results:

Using the developed LFIT, the minimal amount of SE-specific antibodies that can be detected in chicken serum sample was 1427 enzyme-linked immunosorbent assay (ELISA) unit/100 µl that was equal to 0.1 µg (Ab)/100 µl sample. 100 suspected serum samples collected from a poultry flock were tested with the prepared SE-LFIT kits and the locally prepared stained Salmonella antigen, and the results were compared with those obtained from examination of these samples with Salmonella Group D antibody ELISA kit as the gold standard test. The sensitivity, specificity, and accuracy of the prepared SE-LFIT antigen kits were 94.4%, 90%, and 94%, respectively, while those obtained with stained Salmonella antigen were 88.8%, 90%, and 89%, respectively.

Conclusion:

The developed test is a simple field rapid test of high sensitivity, specificity, and accuracy that can improve and facilitates rapid field surveillance of salmonellosis among chickens.

Recent advancements in lateral flow immunoassays: A journey for toxin detection in food

Biotechnology embraces various physical and chemical phenomena toward advancement of health diagnostics. Toward such advancement, detection of toxins plays an important role. Toxins produce severe health impacts on consumption with high mortality associated in acute cases. The most prominent route of infection and intoxication is through food matrices. Therefore, rapid detection of toxins at low concentrations is the need of modern diagnostics. Lateral flow immunoassays are one of the emergent and popularly used rapid detection technology developed for detecting various kinds of analytes. This review thus focuses on recent advancements in lateral flow immunoassays for detecting different toxins in agricultural food. Appropriate emphasis was given on how the labels, recognition elements, or detection strategy has laid an impact on improvement in immunochromatographic assays for toxins. The paper also discusses the gradual change in sensitivities and specificities of assays in accordance with the method of food processing used. The review concludes with the major challenges faced by this technology and provides an outlook and insight of ideas to improve it in the future.

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.

Development of a Calibration Strip for Immunochromatographic Assay Detection Systems

With many benefits and applications, immunochromatographic (ICG) assay detection systems have been reported on a great deal. However, the existing research mainly focuses on increasing the dynamic detection range or application fields. Calibration of the detection system, which has a great influence on the detection accuracy, has not been addressed properly. In this context, this work develops a calibration strip for ICG assay photoelectric detection systems. An image of the test strip is captured by an image acquisition device, followed by performing a fuzzy c-means (FCM) clustering algorithm and maximin-distance algorithm for image segmentation. Additionally, experiments are conducted to find the best characteristic quantity. By analyzing the linear coefficient, an average value of hue (H) at 14 min is chosen as the characteristic quantity and the empirical formula between H and optical density (OD) value is established. Therefore, H, saturation (S), and value (V) are calculated by a number of selected OD values. Then, H, S, and V values are transferred to the RGB color space and a high-resolution printer is used to print the strip images on cellulose nitrate membranes. Finally, verification of the printed calibration strips is conducted by analyzing the linear correlation between OD and the spectral reflectance, which shows a good linear correlation (R² = 98.78%).

An aptamer based lateral flow strip for on-site rapid detection of ochratoxin A in Astragalus membranaceus

An aptamer based lateral flow strip based on competitive format was developed for on-site rapid detection of ochratoxin A (OTA) in Astragalus membranaceus. Some crucial parameters that might influence the sensitive detection, such as the characterization of the colloidal gold, size and shape of gold nanoparticles (AuNPs), amount of AuNPs-aptamer conjugate, migration rate and the addition amount of methanol, were investigated to provide the optimum assay performance. To perform the test, 1g sample was extracted with 2.5mL of methanol-water (80:20, v/v) and diluted by 4-fold running buffer to eliminate the matrix and methanol interferences. Under optimized conditions, the aptamer-based assay showed a visual limit of detection (LOD) of 1ngmL(-1), and with no significant cross-reactivity with several homologous toxins. The whole detection could be completed within 15min without special equipment because of available visual results. One out of nine A. membranaceus samples was found to be positive of OTA, which was in a good agreement with those obtained from LC-MS/MS analysis. The results demonstrated that the aptamer-based lateral flow assay could be used as a rapid, reliable, cost-effective and robust on-site screening technique for mycotoxins at trace level in complex matrices without special instrumentation.

Development of the sensitive lateral flow immunoassay with silver enhancement for the detection of Ralstonia solanacearum in potato tubers

Ralstonia solanacearum is a dangerous and economically important pathogen of potatoes and other agricultural crops. Therefore, rapid and sensitive methods for its routine diagnostics are necessary. The aim of this study was to develop a rapid control method for R. solanacearum with a low limit of detection (LOD) based on a lateral flow immunoassay (LFIA) with silver enhancement. To minimize the LOD, the membrane type, antibody amount for conjugation with gold nanoparticles, conjugate concentration and antibody concentration in the analytical zone were optimized. Silver enhancement was used to decrease the LOD of the LFIA. For silver enhancement, release fiberglass membranes with pre-absorbed silver lactate and hydroquinone were placed on the analytical zone, and a drop of silver lactate was added. The LFIA with silver enhancement was found to be 10-fold more sensitive (LOD 2×10(2) CFU/mL; 20 min) in comparison with the common analysis (LOD 2×10(3) CFU/mL; 10 min). The specificity of the developed LFIA was studied using different strains of R. solanacearum (54 samples) and other widespread bacterial pathogens (18 samples). The LFIA detected all tested strains, whereas non-specific reactions were not observed. The developed tests were used for the control of bacteria in extracts of infected and non-infected potato tubers, and the quantitative analysis results (based on the densitometry of line colouration) were confirmed by ELISA with a correlation coefficient equal to 0.965.

Chromatographic immunoassays: strategies and recent developments in the analysis of drugs and biological agents

A chromatographic immunoassay is a technique in which an antibody or antibody-related agent is used as part of a chromatographic system for the isolation or measurement of a specific target. Various binding agents, detection methods, supports and assay formats have been developed for this group of methods, and applications have been reported that range from drugs, hormones and herbicides to peptides, proteins and bacteria. This review discusses the general principles and applications of chromatographic immunoassays, with an emphasis being given to methods and formats that have been developed for the analysis of drugs and biological agents. The relative advantages or limitations of each format are discussed. Recent developments and research in this field, as well as possible future directions, are also considered.

Silver and gold enhancement methods for lateral flow immunoassays

Sensitivity is the main concern at the development of rapid test by lateral flow immunoassays. On the other hand, low limits of detection are often required at medical diagnostics and other field of analysis. To overcome this drawback, several enhancement protocols have been described. In this paper, we have selected different silver enhancement methods and one dual gold conjugation, and we critically compared the amplification produced when applied to a gold-nanoparticle based lateral flow immunoassay for the detection of prostate specific antigen (PSA). The highest amplification was obtained by using an immersion method based on a solution of silver nitrate and hydroquinone/citrate buffer in proportion 1:1. Under these conditions, the system is capable of detecting PSA within 20 min at levels as low as 0.1 ng/mL, with a 3-fold sensitivity improvement.

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.

Development of a colloidal gold immunochromatographic strip for the rapid detection of soft-shelled turtle systemic septicemia spherical virus

A colloidal gold immunochromatographic strip (ICS) test based on a competitive format was developed for the rapid detection of soft-shelled turtle systemic septicemia spherical virus (STSSSV) in turtle and fecal samples. Specific egg yolk antibodies (IgY) against STSSSV were labeled with colloidal gold and used as probes in the one-step test strip. Antigen (STSSSV) and goat anti-chicken IgY were drawn on the nitrocellulose membrane as the test line and control line, respectively. When STSSSV standard samples (0-100μg/mL) were detected by the strips, the visual limit of detection (LOD) was found to be 50.0μg/mL. The ICS test showed high stability; the strips were stable for at least 3 months at 4°C without significant loss of activity. There was no obvious cross-reactivity with other aquatic pathogens. The assay can be performed within 5-10min. Analysis of STSSSV in turtle samples revealed that data obtained from the ICS test were in a good agreement with those obtained by ELISA. The positive results of fecal samples suggested that this method could be used to detect STSSSV while protecting the animals' welfare. The ICS assay does not need specialized equipment or a technician and can be used as a reliable, rapid, cost-effective and convenient qualitative tool for on-site diagnosis.

Novel strategies to enhance lateral flow immunoassay sensitivity for detecting foodborne pathogens

Food contaminated by foodborne pathogens causes diseases, affects individuals, and even kills those affected individuals. As such, rapid and sensitive detection methods should be developed to screen pathogens in food. One current detection method is lateral flow immunoassay, an efficient technique because of several advantages, including rapidity, simplicity, stability, portability, and sensitivity. This review presents the format and principle of lateral flow immunoassay strip and the development of conventional lateral flow immunoassay for detecting foodborne pathogens. Furthermore, novel strategies that can be applied to enhance the sensitivity of lateral flow immunoassay to detect foodborne pathogens are presented; these strategies include innovating new label application, designing new formats of lateral flow immunoassay, combining with other methods, and developing signal amplification systems. With these advancements, detection sensitivity and detection time can be greatly improved.

Development of colloidal gold immunochromatographic signal-amplifying system for ultrasensitive detection of Escherichia coli O157:H7 in milk

A colloidal gold immunochromatographic signal-amplifying test strip with a sandwich format was successfully developed to detect Escherichia coli O157:H7.

A portable and chromogenic enzyme-based sensor for detection of abrin poisoning

A first of its kind portable, colorimetric detection system has been developed for the rapid diagnosis of abrin poisoning. Abrin, a natural biotoxin that is homologous to ricin yet more lethal, has high potential for becoming a weapon of bioterrorism given its ease of production. Using an immobilization strategy that implements non-natural amino acids for site-specific conjugation, we have created a reusable N-methyltryptophan oxidase based magnetic bead system that is capable of detecting L-abrine, a marker for abrin poisoning, at concentrations as low as 4 μM in mock urine. Furthermore, we propose that this detection strategy may be readily adaptable for sensing other targets of interest. This unique diagnostic test for abrin poisoning has demonstrated key benefits of portability and simple visual readout. These significant advantages can thus provide the potential for more rapid assessment and corresponding poison management if dedicated toxicology laboratories are not an option.

Increased sensitivity of lateral flow immunoassay for ochratoxin A through silver enhancement

Silver nucleation on gold has been exploited for signal amplification and has found application in several qualitative and quantitative bio-sensing techniques, thanks to the simplicity of the method and the high sensitivity achieved. Very recently, this technique has been tentatively applied to improve the performance of gold-based immunoassays. In this work, the exploitation of the signal amplification due to silver deposition on gold nanoparticles has been first applied to a competitive lateral flow immunoassay (LFIA). The signal enhancement due to silver allowed us to strongly reduce the amount of the competitor and of specific antibodies employed to build an LF device for measuring ochratoxin A (OTA), thus permitting the attainment of a highly sensitive assessment of OTA contamination, with a sensitivity gain of more than 10-fold compared to the gold-based LFIA that used the same immunoreagents and to all previously reported LFIA for measuring OTA. In addition, a less sensitive "quantitative" LFIA could be established, by suitably tuning competitor and antibody amounts, which was characterized by reproducible and accurate OTA determinations (RSD% 6-12%, recovery% 82-117%). The quantitative system allowed a reliable OTA quantification in wines and grape musts at the microgram per liter level requested by the European legislation, as demonstrated by a highly results obtained through the quantitative silver-enhanced LFIA and a reference HPLC-FLD on 30 samples.

Comparison of the lateral flow immunoassays (LFIA) for the diagnosis of Helicobacter pylori infection

Helicobacter pylori infection is the most common human infection where approximately 50% of the world populations are infected. The diagnosis of such infection is mainly done by endoscopy where gastric biopsies are examined for the presence of H. pylori. Such invasive approach is costly, time consuming and generally requires more than one test to confirm the infection. Serology on the other hand is a non-invasive approach that can detect H. pylori exposure. The lateral flow immunoassays (LFIA) support the serological approach and have the advantage of being fast, economic and require no additional equipment or experience. In this review the principles, components of the LFIA, sensitivities and specificities of the commercially available H. pylori test strips were compared and discussed.

Signal enhancement in a lateral flow immunoassay based on dual gold nanoparticle conjugates

OBJECTIVE

In order to amplify signal of lateral flow immunoassay for specific detection of thrombin.

DESIGN AND METHODS

A new, simple method of amplifying signals using two gold nanoparticle conjugates (GNP) in gold-nanoparticle-based lateral flow immunoassay without an additional step was developed. The first conjugates were prepared by labeling DNA1 with 30 nm GNPs, and the second conjugates were prepared by immobilizing both DNA2 and thrombin aptamer on the surfaces of 16 nm GNPs.

RESULTS

The detection limit was improved 30 times. The lateral flow immunoassay developed in this study was applied to detect thrombin concentration in the range of 0.5-120 nM with a detection limit of 0.25 nM.

CONCLUSIONS

The lateral flow immunoassay developed in this study was used to detect thrombin concentrations within a range of 0.5-120 nM with a detection limit of 0.25 nM. This assay is very versatile and can be easily extended to other proteins.

Gold immunochromatographic strips for enhanced detection of avian influenza and Newcastle disease viruses

A new technique that uses gold immunochromatographic strips enhances the detection sensitivity by inducing the clustering of additional gold nanoparticles (AuNPs) around the immunogold particles immobilized on nitrocellulose strips. The additional AuNPs provide an intense signal that can be detected by the naked eye. The AuNPs were synthesized and conjugated to monoclonal antibodies using self-assembly. Other antibodies were immobilized in a defined detection zone on the nitrocellulose membrane. The detection principle is based on a "sandwich" immunoreaction, where gold-labeled antibodies serve as signal vehicles. To improve the sensitivity of the strips, we use a mixture of 1% HAuCl4 and 10 mmol L(-1) NH2OH·HCl to "enlarge" the gold nanoparticles. The detecting limits of Avian influenza virus (AIV) and Newcastle disease virus (NDV) are significantly increased. Compared with commercial test strips, this method is 100-fold more sensitive. This method is easy to perform and can be carried out on-site in test laboratories.

Development of an immunochromatographic assay based on carbon nanoparticles for the determination of the phytoregulator forchlorfenuron

Rapid analytical methods enabling the determination of diverse targets are essential in a number of research areas, from clinical diagnostics to feed and food quality and safety. Herein, the development of a quantitative immunochromatographic assay for the detection of the synthetic phytoregulator forchlorfenuron (CPPU) is described. The competitive lateral flow immunoassay (LFIA) was based on the immobilization onto a nitrocellulose membrane of an ovalbumin-CPPU conjugate (test line) and on the use of an immunodetection ligand consisting of carbon nanoparticles labeled with an anti-CPPU monoclonal antibody through interaction with a secondary antibody. The presence of CPPU in horticultural samples was visually interpreted by the decrease in the black signal intensity of the test line, according to the competitive character of the format. The quantitative determination of the analyte was easily performed by a two-step procedure consisting of flatbed scanning of the strips followed by computer-based image analysis of the pixel gray volumes of the test lines. Under optimized conditions, the immunochromatographic test afforded a limit of quantification in buffer of 89 ng/L. The accuracy of the strip test was assessed by the analysis of fruit samples with incurred residues, and the obtained results were compared with those derived from two reference methods, ELISA and HPLC. The LOQ of the CPPU-specific LFIA in kiwifruits and grapes was established at 33.4 μg/kg. The excellent analytical performance of the developed strip test demonstrates the potential of immunochromatographic assays for the quantitative monitoring of small organic molecules in complex matrices.

MicroRNA detection using lateral flow nucleic acid strips with gold nanoparticles

In this study, the tested microRNA and the detection probe perfectly match with the capture probe instead of the traditional sandwich methods in which the tested oligonucleotide matches with the detection and capture probes. To avoid non-specific signals, mung-bean nuclease, a single-strand-specific nuclease, catalyzes the degradation of the capture probe if there is no tested miRNA in the samples. The gold nanoparticles conjugate the thiol-DNA as the detection probe and the biotin-single strand DNA serves as the capture probe. The avidin-biotin-Au-sample complex is captured by the anti-avidin antibody immobilized on a flow strip. The detection and quantification of the gold nanoparticle signal indicate the existence and quantity of the target miRNA. One fmol and five amol of the synthetic microRNA were detected without and with the silver enhancement, respectively. This highly sensitive and specific assay takes about 70 min after the RNA purification and preparation. It is simple, convenient, fast, and suitable for point-of-care.

Lateral-flow immunoassays for mycotoxins and phycotoxins: a review

Natural toxin (for example mycotoxin and phycotoxin) contamination of food is of safety and economic concern, so much effort is devoted to the development of screening methods which enable the toxins to be continuously and widely monitored in food and feed. More generally speaking, rapid and non-instrumental assays for detection of a variety of food contaminants are generating ever-increasing scientific and technological interest because they enable high-throughput, economical, on-site monitoring of such contaminants. Among rapid methods for first-level screening of food contaminants, lateral-flow immunoassay (LFIA), also named immunochromatographic assay or immune-gold colloid immunoassay, has recently attracted scientific and industrial interest because of its attractive property of enabling very rapid, one-step, in-situ analysis. This review focuses on new aspects of the development and optimization of lateral-flow devices for mycotoxin and phycotoxin detection, including strategies for management of matrix interference and, particularly, for investigation of the improvements achieved by signal-enhancing strategies or by application of non-gold nanoparticle signal reporters.

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.