Detection of ricin and other ribosome-inactivating proteins by an immuno-polymerase chain reaction assay

Development and validation of streptavidin-biotin-based double antibody sandwich ELISA for ricin diagnosis

BACKGROUND

Ricin is a potential biowarfare agent. It is a phytotoxin isolated from castor seeds. At present there is no antidote available for ricin poisoning, patients only get supportive treatment based on their symptoms. This highlights the importance of early detection to avoid severity of accidents and reduce the risk factor. Considering this, our study aimed to develop a highly sensitive and specific sandwich ELISA for the detection of ricin.

METHODS

Ricin was purified from castor seeds. Anti-ricin polyclonal and monoclonal antibodies were generated from rabbit antisera and hybridoma cell (1H6F1) supernatant using a protein A/G column. Antibody titer estimation was done using Indirect ELISA. A streptavidin-biotin-based sandwich ELISA was developed and the limit of detection (LOD), linear range, intra and inter-assay coefficient of variation (CV), and cross-reactivity with other similar toxins were determined. Interference of human plasma samples spiked with ricin was also checked.

RESULTS

The LOD of the ELISA was found to be 0.45 ng/ml, with a linear range of 0.90-62 ng/ml, intra and inter-assay CV ranged from 3.34 % to 5 % and 5.17 % to 10.80 % respectively. The assay was not cross-reactive with other similar ribosome-inactivating protein (RIP) toxins. Ricin was detected in spiked plasma samples.

CONCLUSION

The developed assay is highly sensitive and specific for detecting ricin and is not cross-reactive with other similar types of toxins. The assay can detect ricin in spiked plasma samples, so it has the potential to be used for the analysis of clinical samples after ricin poisoning.

Medical Countermeasures against Ricin Intoxication

Ricin toxin is a disulfide-linked glycoprotein (AB toxin) comprising one enzymatic A chain (RTA) and one cell-binding B chain (RTB) contained in the castor bean, a Ricinus species. Ricin inhibits peptide chain elongation via disruption of the binding between elongation factors and ribosomes, resulting in apoptosis, inflammation, oxidative stress, and DNA damage, in addition to the classically known rRNA damage. Ricin has been used in traditional medicine throughout the world since prehistoric times. Because ricin toxin is highly toxic and can be readily extracted from beans, it could be used as a bioweapon (CDC B-list). Due to its extreme lethality and potential use as a biological weapon, ricin toxin remains a global public health concern requiring specific countermeasures. Currently, no specific treatment for ricin intoxication is available. This review focuses on the drugs under development. In particular, some examples are reviewed to demonstrate the proof of concept of antibody-based therapy. Chemical inhibitors, small proteins, and vaccines can serve as alternatives to antibodies or may be used in combination with antibodies.

A Highly Sensitive Fluorescence and Screen-Printed Electrodes—Electrochemiluminescence Immunosensor for Ricin Detection Based on CdSe/ZnS QDs with Dual Signal

A sensitive dual-readout immunosensor for fluorescence and electrochemiluminescence (ECL) detection of ricin was established, which was combined with a streptavidin–biotin signal amplification system. CdSe/ZnS quantum dots with fine fluorescence and ECL properties were used as the dual-signal function probes of the sandwich immunocomplex. Under the optimum experimental conditions, the dual signal intensity increased significantly with the rise in ricin concentration. The fluorescence intensity of the senor exhibited a good liner relationship toward the ricin concentrations with 0.1~100 ng/mL and the limit of detection (LOD) was 81.7 pg/mL; taking ECL as the detection signal, the sensor showed a linear relationship with the ricin concentrations ranging from 0.01 ng/mL to 100 ng/mL and the LOD was 5.5 pg/mL. The constructed sensor with high sensitivity had been successfully applied to the detection of ricin in complex matrices with satisfactory recoveries. The proposed immunosensor model can be extended to the analysis and detection of others target proteins.

Enhanced detection of ATTR amyloid using a nanofibril-based assay

More than 30 proteins and peptides have been found to form amyloid fibrils in human diseases. Fibrils formed by transthyretin (TTR) are associated with ATTR amyloidosis, affecting many vital organs, including the heart and peripheral nervous system. Congo red staining is the gold standard method for detection of amyloid deposits in tissue. However, Congo red staining and amyloid typing methods such as immunofluorescence labelling are limited to relatively large deposits. Detection of small ATTR deposits present at an early stage of the disease could enable timely treatment and prevent severe tissue damage. In this study, we developed an enhanced ATTR amyloid detection method that uses functionalised protein nanofibrils. Using this method, we achieved sensitive detection of monomeric TTR in a microplate immunoassay and immunofluorescence labelling of ex vivo tissue from two patients containing ATTR aggregates. The system's utility was confirmed on sections from a patient with AA amyloidosis and liver sections from inflamed mouse. These results suggest that the detection system constitutes important new technology for highly sensitive detection of microscopic amounts of ATTR amyloid deposited in tissue.

Dianthin and Its Potential in Targeted Tumor Therapies

Dianthin enzymes belong to ribosome-inactivating proteins (RIPs) of type 1, i.e., they only consist of a catalytic domain and do not have a cell binding moiety. Dianthin-30 is very similar to saporin-S3 and saporin-S6, two RIPs often used to design targeted toxins for tumor therapy and already tested in some clinical trials. Nevertheless, dianthin enzymes also exhibit differences to saporin with regard to structure, efficacy, toxicity, immunogenicity and production by heterologous expression. Some of the distinctions might make dianthin more suitable for targeted tumor therapies than other RIPs. The present review provides an overview of the history of dianthin discovery and illuminates its structure, function and role in targeted toxins. It further discusses the option to increase the efficacy of dianthin by endosomal escape enhancers.

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

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

Detection of ricin by using gold nanoclusters functionalized with chicken egg white proteins as sensing probes

Ricin produced from the castor oil plant, Ricinus communis, is a well-known toxin. The toxin comprises A and B chains. Ricin A chain can cause toxicity by inhibiting protein synthesis, and ricin B can bind to the galactose ligand on the cell membrane of host cells. Inhalation or ingestion of ricin may even lead to death. Therefore, rapid and convenient sensing methods for detecting ricin in suspicious samples must be developed. In this study, we generated protein encapsulated gold nanoclusters (AuNCs@ew) with bright photoluminescence by using chicken egg white proteins as starting materials to react with aqueous tetrachloroaurate. The generated nanoclusters, which were mainly composed of chicken ovalbumin-encapsulated AuNCs, can recognize ricin B because of the presence of Galβ(1→4)GlcNAc ligands on chicken ovalbumin. The generated conjugates of AuNCs@ew and ricin B were heavy and readily settled down under centrifugation (13,000rpm, 60min). Thus, bright spots resulting from the conjugates at the bottom of the sample vials were easily visualized by the naked eye under ultraviolet light illumination. The limit of detection (LOD) was ~4.6µM. The LOD was reduced to ~400nM when fluorescence spectroscopy was used as the detection tool, while the LOD can be further improved to ~7.8nM when using matrix-assisted laser desorption/ionization mass spectrometry as the detection method. We also demonstrated the feasibility of using the proposed approach to selectively detect ricin B chain in complex samples.

Responsive Fluorescent PNA Analogue as a Tool for Detecting G-quadruplex Motifs of Oncogenes and Activity of Toxic Ribosome-Inactivating Proteins

Fluorescent oligomers that are resistant to enzymatic degradation and report their binding to target oligonucleotides (ONs) by changes in fluorescence properties are highly useful in developing nucleic-acid-based diagnostic tools and therapeutic strategies. Here, we describe the synthesis and photophysical characterization of fluorescent peptide nucleic acid (PNA) building blocks made of microenvironment-sensitive 5-(benzofuran-2-yl)- and 5-(benzothiophen-2-yl)-uracil cores. The emissive monomers, when incorporated into PNA oligomers and hybridized to complementary ONs, are minimally perturbing and are highly sensitive to their neighboring base environment. In particular, benzothiophene-modified PNA reports the hybridization process with significant enhancement in fluorescence intensity, even when placed in the vicinity of guanine residues, which often quench fluorescence. This feature was used in the turn-on detection of G-quadruplex-forming promoter DNA sequences of human proto-oncogenes (c-myc and c-kit). Furthermore, the ability of benzothiophene-modified PNA oligomer to report the presence of an abasic site in RNA enabled us to develop a simple fluorescence hybridization assay to detect and estimate the depurination activity of ribosome-inactivating protein toxins. Our results demonstrate that this approach with responsive PNA probes will provide new opportunities to develop robust tools to study nucleic acids.

Exonuclease III-assisted graphene oxide amplified fluorescence anisotropy strategy for ricin detection

Graphene oxide (GO) is an excellent fluorescence anisotropy (FA) amplifier. However, in the conventional GO amplified FA strategy, one target can only induce the FA change of one fluorophore on probe, which limits the detection sensitivity. Herein, we developed an exonuclease III (Exo III) aided GO amplified FA strategy by using aptamer as an recognition element and ricin B-chain as a proof-of-concept target. The aptamer was hybridized with a blocker sequence and linked onto the surface of magnetic beads (MBs). Upon the addition of ricin B-chain, blocker was released from the surface of MBs and hybridized with the dye-modified probe DNA on the surface of GO through the toehold-mediated strand exchange reaction. The formed blocker-probe DNA duplex triggered the Exo III-assisted cyclic signal amplification by repeating the hybridization and digestion of probe DNA, liberating the fluorophore with several nucleotides (low FA value). Thus, ricin B-chain could be sensitively detected by the significantly decreased FA. The linear range was from 1.0μg/mL to 13.3μg/mL and the limit of detection (LOD) was 400ng/mL. This method improved the sensitivity of FA assay and it could be generalized to any kind of target detection based on the use of an appropriate aptamer.

A facile label-free colorimetric aptasensor for ricin based on the peroxidase-like activity of gold nanoparticles

A facile colorimetric aptasensor for ricin based on the peroxidase-like activity of gold nanoparticles was demonstrated for the first time.

Anti-idiotypic nanobody-phage based real-time immuno-PCR for detection of hepatocarcinogen aflatoxin in grains and feedstuffs

Aflatoxins are a group of extremely toxic small molecules that have been involved in human hepatic and extrahepatic carcinogenesis as causative agents. Herein, we developed a real-time immuno polymerase chain reaction (IPCR) assay for the accurately quantitative detection of aflatoxins in agri-products base on a M13 phage containing aflatoxin anti-idiotypic nanobody and its encoding DNA which was used to design the specific primers. The limit of detection (LOD) of the assay is 0.02 ng/mL, which exhibits a 4-fold improvement over traditional phage ELISA. The developed method was successfully validated with the samples of corn, rice, peanut, and feedstuff, which are major aflatoxin-contaminated agri-products. And the recoveries were from 77.05 to 122.16%. For further validation, the developed assay was also compared with a reference HPLC method for the analysis of aflatoxins in corn and peanuts, and concordant results (R(2) = 0.991) were obtained. In this context, this study provides a novel opportunity to analyze aflatoxins in agri-products.

Highly sensitive and rapid visual detection of ricin using unmodified gold nanoparticle probes

A sensitive aptamer-based colorimetric biosensor for the detection of ricin using unmodified gold nanoparticles as probe was developed.

Localized surface plasmon resonance detection of biological toxins using cell surface oligosaccharides on glyco chips

We have detected biological toxins using localized surface plasmon resonance (LSPR) and synthetic glycosyl ceramides (β-lactoside, globosyl trisaccharide (Gb3), or GM1 pentasaccharide) attached to gold (Au) nanoparticles. The particle diameters ranged from 5-100 nm. The detection sensitivity for three toxins (ricin, Shiga toxin, and cholera toxin) was found to depend not only on the attached glycoside but also on the diameter of the Au nanoparticles. For the detection of ricin, the 20-nm β-lactoside-coated Au nanoparticle exhibited the highest LSPR response, whereas 40-nm Gb3- and GM1-coated Au nanoparticles gave the best results for Shiga toxin and cholera toxin, respectively. In addition, a blocking process on the nanoparticle surface greatly improved the detection sensitivity for cholera toxin. The LSPR system enabled us to detect ricin at 30 ng/mL, Shiga toxin at 10 ng/mL, and the cholera toxin at 20 ng/mL.

Simultaneous allergen inactivation and detoxification of castor bean cake by treatment with calcium compounds

Ricinus communis L. is of great economic importance due to the oil extracted from its seeds. Castor oil has been used for pharmaceutical and industrial applications, as a lubricant or coating agent, as a component of plastic products, as a fungicide or in the synthesis of biodiesel fuels. After oil extraction, a castor cake with a large amount of protein is obtained. However, this by-product cannot be used as animal feed due to the presence of toxic (ricin) and allergenic (2S albumin) proteins. Here, we propose two processes for detoxification and allergen inactivation of the castor cake. In addition, we establish a biological test to detect ricin and validate these detoxification processes. In this test, Vero cells were treated with ricin, and cell death was assessed by cell counting and measurement of lactate dehydrogenase activity. The limit of detection of the Vero cell assay was 10 ng/mL using a concentration of 1.6 x 10(5) cells/well. Solid-state fermentation (SSF) and treatment with calcium compounds were used as cake detoxification processes. For SSF, Aspergillus niger was grown using a castor cake as a substrate, and this cake was analyzed after 24, 48, 72, and 96 h of SSF. Ricin was eliminated after 24 h of SSF treatment. The cake was treated with 4 or 8% Ca(OH)2 or CaO, and both the toxicity and the allergenic properties were entirely abolished. A by-product free of toxicity and allergens was obtained.

Synthesis and photophysical characterisation of a fluorescent nucleoside analogue that signals the presence of an abasic site in RNA

The synthesis and site-specific incorporation of an environment-sensitive fluorescent nucleoside analogue (2), based on a 5-(benzofuran-2-yl)pyrimidine core, into DNA oligonucleotides (ONs), and its photophysical properties within these ONs are described. Interestingly and unlike 2-aminopurine (a widely used nucleoside analogue probe), when incorporated into an ON and hybridised with a complementary ON, the emissive nucleoside 2 displays significantly higher emission intensity than the free nucleoside. Furthermore, photophysical characterisation shows that the fluorescence properties of the nucleoside analogue within ONs are significantly influenced by flanking bases, especially by guanosine. By utilising the responsiveness of the nucleoside to changes in base environment, a DNA ON reporter labelled with the emissive nucleoside 2 was constructed; this signalled the presence of an abasic site in a model depurinated sarcin/ricin RNA motif of a eukaryotic 28S rRNA.

Ricin poisoning causing death after ingestion of herbal medicine

Ricin intoxication is a fatal and an uncommon medical condition. We report a case of ricin poisoning in a 42-year-old Saudi male patient who ingested a herbal medicine mixture containing ricin bean powder, after which he presented with gastrointestinal symptoms followed by gastrointestinal bleeding and hypotension. The patient then passed into a state of shock with respiratory failure followed by cardiac arrest and death. Public health awareness of self-prescribed herbal medications is necessary.

A novel xyloglucan film-based biosensor for toxicity assessment of ricin in castor seed meal

Oil from the seed of the castor plant (Ricinus communis L.) is an important commodity for a number of industries, ranging from pharmaceuticals to renewable energy resources. However, the seed and subsequent seed meal contain ricin (RCA60), a potent cytotoxin, making it an unusable product for animal feed. In order to investigate the efficiency of reducing the toxicity of the seed meal, a biosensor is proposed by exploring the lectin-carbohydrate binding. A gold electrode was assembled with a film of Xyloglucan (XG) extracted from Hymenaea courbaril L. The analytical response to RCA60 was obtained using a polyclonal antibody against RCA60 conjugated to peroxidase. The current responses were generated by reaction with H2O2 and amplified with hydroquinone as chemical mediator. Voltammetric studies showed that the XG film was tightly bound to the gold electrode. This biosensor allows discriminate lectins in native and denatured forms. The limit of detection of native RCA60 was 2.1 μg mL(-1). This proposed biosensor showed to be a potential and accurate method for toxicity assessment of the ricin in castor seed meal by simple polysaccharide film-electrode strategy.

Glycotechnology for decontamination of biological agents: a model study using ricin and biotin-tagged synthetic glycopolymers

Two types of biotin-tagged glycopolymers carrying lactose or glucose in clusters along the polyacrylamide backbone were prepared and subjected to decontamination analyses with the plant toxin ricin. A buffer solution containing the toxin was treated with one glycopolymer followed by streptavidin-magnetic particles. Supernatant solutions were analyzed with surface plasmon resonance and capillary electrophoresis, and revealed that the lactose glycopolymer "captured" this toxin more effectively than the glucose polymer. Free toxin was not detectable in the supernatant after treatment with the glycopolymer and magnetic particles; >99% decontamination was achieved for this potentially fatal biological toxin.

Understanding ricin from a defensive viewpoint

The toxin ricin has long been understood to have potential for criminal activity and there has been concern that it might be used as a mass-scale weapon on a military basis for at least two decades. Currently, the focus has extended to encompass terrorist activities using ricin to disrupt every day activities on a smaller scale. Whichever scenario is considered, there are features in common which need to be understood; these include the knowledge of the toxicity from ricin poisoning by the likely routes, methods for the detection of ricin in relevant materials and approaches to making an early diagnosis of ricin poisoning, in order to take therapeutic steps to mitigate the toxicity. This article will review the current situation regarding each of these stages in our collective understanding of ricin and how to defend against its use by an aggressor.

Ricinus communis intoxications in human and veterinary medicine-a summary of real cases

Accidental and intended Ricinus communis intoxications in humans and animals have been known for centuries but the causative agent remained elusive until 1888 when Stillmark attributed the toxicity to the lectin ricin. Ricinus communis is grown worldwide on an industrial scale for the production of castor oil. As by-product in castor oil production ricin is mass produced above 1 million tons per year. On the basis of its availability, toxicity, ease of preparation and the current lack of medical countermeasures, ricin has gained attention as potential biological warfare agent. The seeds also contain the less toxic, but highly homologous Ricinus communis agglutinin and the alkaloid ricinine, and especially the latter can be used to track intoxications. After oil extraction and detoxification, the defatted press cake is used as organic fertilizer and as low-value feed. In this context there have been sporadic reports from different countries describing animal intoxications after uptake of obviously insufficiently detoxified fertilizer. Observations in Germany over several years, however, have led us to speculate that the detoxification process is not always performed thoroughly and controlled, calling for international regulations which clearly state a ricin threshold in fertilizer. In this review we summarize knowledge on intended and unintended poisoning with ricin or castor seeds both in humans and animals, with a particular emphasis on intoxications due to improperly detoxified castor bean meal and forensic analysis.

Purification, characterization and toxicity profile of ricin isoforms from castor beans

The castor seed contains the toxin ricin, one of the most poisonous naturally occurring toxins. The whole of the plant is poisonous, however the seeds are considered the major source of ricin. Ricin exists in different forms in beans of different origin. We investigated the presence of ricin in different isoforms and elucidate some of their structural and biological features isolated from the castor seeds. The isoforms were sub fractionated into ricin I, II and III by chromatography. Their molecular weights lie between 60-65 kDa with difference in their relative electrophoretic mobility. An acidic native PAGE of ricin isoforms at pH 2.9 was performed. Ricin I, II and III are highly cytotoxic against Vero cell line with IC(50) values of 60, 30 and 8 ng/ml respectively. Difference in cytotoxicity of isoforms was confirmed through hemagglutination assay, ricin III caused high degree of hemolysis. The preliminary in vivo toxicity studies showed that ricin III is highly toxic. Immunological studies revealed that anti-ricin I and II antibodies are cross reactive with all the ricin variants, whereas the anti-ricin III antibody is highly specific. The present study shows that anti-ricin I and II antibodies can be used for detection of entire ricin isoforms.

AB toxins: a paradigm switch from deadly to desirable

To ensure their survival, a number of bacterial and plant species have evolved a common strategy to capture energy from other biological systems. Being imperfect pathogens, organisms synthesizing multi-subunit AB toxins are responsible for the mortality of millions of people and animals annually. Vaccination against these organisms and their toxins has proved rather ineffective in providing long-term protection from disease. In response to the debilitating effects of AB toxins on epithelial cells of the digestive mucosa, mechanisms underlying toxin immunomodulation of immune responses have become the focus of increasing experimentation. The results of these studies reveal that AB toxins may have a beneficial application as adjuvants for the enhancement of immune protection against infection and autoimmunity. Here, we examine similarities and differences in the structure and function of bacterial and plant AB toxins that underlie their toxicity and their exceptional properties as immunomodulators for stimulating immune responses against infectious disease and for immune suppression of organ-specific autoimmunity.

Development of a Novel Immuno-PCR Assay for Detection of Ricin in Ground Beef, Liquid Chicken Egg, and Milk

Reliable, sensitive, and high-throughput methods are essential for food defense, to detect foodborne contaminants and to facilitate remediation and recovery from potential toxin-related incidents. Ricin is a protein toxin that has been used for intentional contamination of foods in the past. In this study, we developed procedures for quantification of ricin in foods using immuno-PCR (IPCR). The direct adsorption of ricin onto the wells of a microtitration plate was compared with indirect immobilization via a capture antibody (sandwich IPCR). The latter procedure provided much greater sensitivity. We also compared a protocol with the immunoassay and PCR conducted in a single plate to a two-step procedure in which the PCR was conducted in a second plate, following release and transfer of the DNA marker. The two-step procedure proved 1,000-fold more sensitive for ricin detection, so this format was used to detect ricin in spiked samples of ground beef, chicken egg, and milk, and the results were compared with those obtained from enzyme-linked immunosorbent assay (ELISA). The IPCR had a limit of detection of 10 pg/ml in chicken egg and milk samples and 100 pg/ml in ground beef extracts. Comparable ELISA results were in the 1 to 10 ng/ml range. Thus, IPCR affords sensitivity that is 10-fold greater in the ground beef matrix, 100-fold greater in the milk, and 1,000-fold greater in the egg matrix than the sensitivity obtained by ELISA. Further optimization of the sandwich IPCR was performed by comparing various antibody combinations. Among the four formats investigated, the pAb-pAb combination yielded the lowest limit of detection (10 fg/ml).

Use of lactose against the deadly biological toxin ricin

Developing a technology for detecting and decontaminating biological toxins is needed. Ricin from Ricinus communis is a highly poisonous toxin; it was formerly used for an assassination in London and in postal attacks in the United States. Ricin is readily available from castor beans and could be used as a biological agent. We propose using glycotechnology against the illegal use of ricin. Lactose (a natural ligand of this toxin) was incorporated into polyacrylamide-based glycopolymers at variable sugar densities (18-100%) and evaluated with surface plasmon resonance (SPR) spectroscopy and the real agent, ricin. Glycopolymers (18-65% lactose densities) effectively interfered with the toxin-lactoside adhesion event (>99% efficiency within 20 min). This supported the notion of using the mammary sugar lactose against a deadly biological toxin.

Population-level variation of the preproricin gene contradicts expectation of neutral equilibrium for generalist plant defense toxins

The preproricin gene encodes ricin, the highly toxic, type II ribosome-inactivating protein of castor bean (Ricinus communis L.). As a generalist plant defense gene, preproricin is expected to exhibit population-level variation consistent with the neutral equilibrium model and to comprise few functionally different alleles. We first test the hypothesis that the preproricin gene family should comprise six to eight members by searching the publicly available draft genome sequence of R. communis and analyzing its ricin-like loci. We then test the neutral equilibrium expectation for the preproricin gene by characterizing its allelic variation among 25 geographically diverse castor bean plants. We confirm the presence of six ricin-like loci that share with the preproricin gene 62.9-96.3% nucleotide identity and intact A-chains. DNA sequence variation among the preproricin haplotypes significantly rejects tests of the neutral equilibrium model. Replacement mutations preserve the 12 amino acids known to affect catalytic and electrostatic interactions of the native protein toxin, which suggests functional divergence among alleles has been minimal. Nucleotide polymorphism is maintained by purifying selection (omega < 0.3) yet includes an excess of rare silent mutations greater than predicted by the neutral equilibrium model. Development of robust detection methods for ricin contamination must account for the presence of these other ricin-like molecules and should leverage the specificity provided by the numerous single nucleotide polymorphisms in the preproricin gene.

Denatured ricin can be detected as native ricin by immunological methods, but nontoxic in vivo

Ricin is a glycoprotein from Ricinus communis seeds. It is known to have diverse toxic effects on cells of different visceral organs. In the present study, we purified and denatured ricin in a boiling water bath for different time intervals. We further made an attempt to identify native and denatured ricin by immunobased detection systems. All the antigen/antibody-based assays identified native and denatured ricin. On SDS-PAGE, only native ricin was observed. In western blotting, ricin boiled for 3.75 min gave a strong band on X-ray film. On native polyacryl amide gel electrophoresis, native and denatured ricin gave ricin band in 60-kDa region. The denatured ricin did not [corrected] cause mortality up to 25 mg/kg, while 5 and 10 microg/kg of native ricin caused 50% and 100% mortality, respectively. Detection of native and denatured ricin is very difficult, and the investigating agencies, forensic scientists, and analysts should be very careful while interpreting the results.

Detection of trace anthracene in soil samples with real-time fluorescence quantitative immuno-PCR using a molecular beacon probe

We developed a highly sensitive and robust real-time fluorescence quantitative immuno-PCR (RTFQ-IPCR) method which uses molecular beacon (MB) probe to detect trace anthracene in the environment. This method was performed on serial dilutions of known anthracene concentrations equivalent to 10-fold dilutions of 10fg/mL to 100pg/mL. We obtained a linear relationship between 10fg/mL and 100pg/mL, with y=0.684x+13.221. A correlation coefficient of 0.994 was also identified, with a detection limit of 4.5fg/mL. After investigating the presence of anthracene in soil samples via RTFQ-IPCR, the obtained concentrations were confirmed by ELISA to be correct and believable, with the recovery ratio ranging from 82% to 112.5%. Based on its sensitivity and reproducibility, MB-based RTFQ-IPCR was found to be acceptable for use in on-site field tests to provide rapid, quantitative, and reliable test results for making environmental decisions.

Simple, clickable protocol for atomic force microscopy tip modification and its application for trace ricin detection by recognition imaging

A simple two-step protocol for modification of atomic force microscopy (AFM) tip and substrate by using a "click reaction" has been developed. The modified tip and substrate would be applied to detect trace amounts of ricin by using atomic force microscopy. A key feature of the approach is the use of a PEG (polyethylene glycol) derivative functionalized with one thiol and one azide ending group. One end of the PEG was attached to the gold-coated AFM tip by a strong Au-thiol bond. The azide group hanging at the other end of the immobilized PEG was used for the attachment of an antiricin antibody modified with an alkyne group using a "click reaction". The latter reaction is highly efficient, compatible with the presence of many functional groups and could proceed under mild reaction conditions. In a separate step, ricin was immobilized on the gold substrate surface that was modified by active esters. For this process, a novel bifunctional reagent was employed containing an active ester and a thioctic acid moiety. By these modification processes, AFM recognition imaging was used to detect the toxin molecules and the results show fg/mL detection sensitivity, surpassing the existing detection techniques. With measurement of the unbinding force between the antiricin antibody and ricin, which was statistically determined to be 64.89 +/- 1.67 pN, the single molecular specificity of this sensing technique is realized.

Detection of naphthalene by real-time immuno-PCR using molecular beacon

A rapid and quantitative technique is urgently needed in detecting toxicological and carcinogenic polycyclic aromatic hydrocarbons (PAHs) in the environment. Using a molecular beacon (MB), this study aimed at detecting the presence of naphthalene through an assay developed via a highly sensitive and robust, real-time fluorescent quantitative immuno-PCR (FQ-IPCR), which was then performed on serial dilutions of known naphthalene concentrations equivalent to 10-fold dilutions of 1-10(4) fg/mL. A correlation coefficient of 0.996 was identified, and a linear relationship between 1 fg/mL and 10 pg/mL, with y = 1.392x + 11.188, was obtained. A trace amount (1 fg/mL) of naphthalene congeners could be detected using this method. Five water samples were then used for validation, the results of which were further confirmed through a conventional enzyme-linked immuno sorbent assay (ELISA). Based on sensitivity and reproduction, the MB-based FQ-IPCR technique is a promising tool for monitoring environmental endocrine disruptors.

Detection of ricin in complex samples by immunocapture and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Ricin, the toxin component of Ricinus communis is considered as a potential chemical weapon. Several complementary techniques are required to confirm its presence in environmental samples. Here, we report a method combining immunocapture and analysis by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for the accurate detection of different species of R. communis. Liquid environmental samples were applied to magnetic particles coated with a monoclonal antibody directed against the B-chain of the toxin. After acidic elution, tryptic peptides of the A- and B-chains were obtained by accelerated digestion with trypsin in the presence of acetonitrile. Of the 20 peptides observed by MALDI-TOF MS, three were chosen for detection ( m/ z 1013.6, m/ z 1310.6 and m/ z 1728.9, which correspond to peptides 161-LEQLAGNLR-169, 150-YTFAFGGNYDR-160, and 233-SAPDPSVITLENSWGR-248, respectively). Their selection was based on several parameters such as detection sensitivity, specificity toward ricin forms and absence of isotopic overlap with unrelated peptides. To increase assay reproducibility, stable isotope-labeled peptides were incorporated during the sample preparation phase. The final assay has a limit of detection estimated at approximately 50 ng/mL ( approximately 0.8 nM) of ricin in buffer. No interference was observed when the assay was applied to ricin-spiked milk samples. In addition, several varieties of R. communis or from different geographical origins were also shown to be detectable. The present assay provides a new tool with a total analytical time of approximately 5 h, which is particularly relevant in the context of a bioterrorist incident.

Evaluation of an in vitro bioassay for the detection of purified ricin and castor bean in beverages and liquid food matrices

The potential use of ricin as a biological weapon in food highlights the necessity for the development of food-specific detection methods. Current methods for the detection of ricin consist of various immunoassays, which detect only one subunit of the ricin toxin and therefore may not be indicative of a biologically active molecule. An in vivo assay, such as a mouse bioassay, can indicate the biological activity of the toxin; however, this method is not feasible for laboratories that do not have animal testing facilities. The purpose of this study was to develop an in vitro assay for the detection of biologically active ricin in beverages and liquid foods. Acidic and high-protein beverages were spiked with either purified ricin or ground castor beans and added to cultured human Jurkat cells. After an overnight incubation, the supernatant was tested for lactate dehydrogenase (LDH) activity with a colorimetric assay. LDH was released from the cytosol upon cell damage and was positively correlated with cell death. Ricin was detectable in all the matrices tested, with a sensitivity of 10 to 100 pg/ml. Biologically active ricin was detectable in all the matrices incubated with ground castor bean material. This method provides a confirmatory way to detect biologically active ricin that can be utilized by laboratories lacking animal facilities.

Comparison of an electrochemiluminescence assay in plate format over a colorimetric ELISA, for the detection of ricin B chain (RCA-B)

An electrochemiluminescence (ECL) assay for the detection of the B chain of ricin (RCA-B) in a 96-well plate format was developed in parallel with a colorimetric ELISA utilizing the same pair of antibodies. Sensitivity results were interpreted with the ANOVA and Tukey statistical tests, allowing a direct comparison between the two technologies, that can probably be extended to other protein antigens such as toxins. Reproducibility, repeatability and rapidity of the two techniques were also compared. The ELISA assay utilized an alkaline phosphatase conjugate for signal generation. After optimization, its limit of detection was 400 pg of RCA-B per ml buffer, with an intra-day standard deviation (SD) of 2.2% of the mean and an inter-day SD of 5.1%. The ECL assay utilized ruthenylated antibodies for detection. The ECL measurement was carried out using a Sector PR 400 plate reader. After optimization, its limit of detection was 50 pg of RCA-B per ml buffer, with an intra-day SD of 4.1% of the mean and an inter-day SD of 4.3%. Starting from a pre-coated plate, the ELISA assay was completed in 7 h and the ECL assay took 2.5 h. While reproducibility and repeatability of the two assays were equivalent, this ECL assay in plate format had an 8-fold better sensitivity for RCA-B detection than the colorimetric ELISA in buffer and in various matrices. The ECL assay was also three times faster, and retained the robustness and convenience of the 96-well plate format.