Development of sandwich dot-ELISA for specific detection of Ochratoxin A and its application on to contaminated cereal grains originating from India

Construction of dual-signal output sensing platform for different scene of rapid and sensitive ochratoxin A detection in corn

Photoelectrochemical (PEC) is a highly sensitive and fast analytical method that can be used at low concentrations, while photoelectrochromic is a simple and low-cost method primarily utilized for high concentration detection. Therefore, we have developed a dual-signal output sensing platform based on both PEC and photoelectrochromism for rapid and sensitive OTA detection. The sensing platform is divided into signal generation (SG) region and signal output (SO) region, which modified with WO3/BiVO4 photoactive nanocomposites and polyaniline (PANI), respectively. By irradiating the SG region, photogenerated electrons are generated and injected into the SO region through the conductive pathway, resulting in a decrease in surface blue polyaniline and a change to green. The smart device can accurately measure the RGB-Green values, enabling the construction of a photochromic visual sensing platform. After immobilizing the OTA aptamer in the SG region, a linear correlation was observed between the concentration of OTA and the RGB-Green value within the range of 20 ng/L ∼250 μg/L. The detection limit was determined to be 8.33 ng/L (S/N = 3). Furthermore, for a more sensitive OTA detection, a PEC sensing platform was developed utilizing the SG region as a photoanode, exhibiting a linear correlation in the range of 2 pg/L∼300 μg/L with a detection limit of 0.8 pg/L (S/N = 3). The detection of these two modes under the requirement of the international standard for the maximum limit realizes the sensitive OTA detection. The RGB-Green is verified to PEC signal, which improves the detection accuracy. The sensing platform has several advantages and is suitable for various application scenarios.

Development of an immunoassay for the detection of mycotoxins using xMAP technology and its evaluation in black tea samples

Mycotoxins, a natural food contaminant, are secondary metabolites of fungi. Aflatoxin B1 (AFB1) and ochratoxin A (OTA) are two major mycotoxins found in various food commodities. These mycotoxins are hepatotoxic, nephrotoxic, cytotoxic, mutagenic and carcinogenic, thus they are a public health concern and their monitoring in food commodities is necessary. There are several conventional techniques available for mycotoxin detection, such as HPLC, LCMS, and ELISA. However, extensive nature and huge cost allowances make it challenging to deploy these techniques for monitoring of mycotoxins in the large sample size. Therefore, a robust, responsive and high-throughput technique is required. Here, we aimed to develop a multiplexed Luminex suspension assay based on multi analyte profiling (xMAP) technology for the simultaneous detection of AFB1 and OTA in the black tea, which is found to be contaminated with these mycotoxins during the cultivation or processing steps. Limit of detection for AFB1 and OTA, was 0.06 ng/ml and 0.49 ng/ml, respectively without any cross-reactivity with other mycotoxins and this assay is suitable for simultaneous detection of AFB1 and OTA in the same sample. Collectively, based on the results, we suggest that the developed Luminex suspension assay is sensitive, accurate, rapid and suitable for high-throughput screening of multiple mycotoxins.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-023-05848-3.

Functionalized Parylene Films for Enhancement of Antibody Production by Hybridoma Cells

In this study, the influence of microenvironments on antibody production of hybridoma cells was analyzed using six types of functionalized parylene films, parylene-N and parylene-C (before and after UV radiation), parylene-AM, and parylene-H, and using polystyrene as a negative control. Hybridoma cells were cultured on modified parylene films that produced a monoclonal antibody against the well-known fungal toxin ochratoxin-A. Surface properties were analyzed for each parylene film, such as roughness, chemical functional groups, and hydrophilicity. The proliferation rate of the hybridoma cells was observed for each parylene film by counting the number of adherent cells, and the total amount of produced antibodies from different parylene films was estimated using indirect ELISA. In comparison with the polystyrene, the antibody-production by parylene-H and parylene-AM was estimated to be observed to be as high as 210-244% after the culture of 24 h. These results indicate that the chemical functional groups of the culture plate could influence antibody production. To analyze the influence of the microenvironments of the modified parylene films, we performed cell cycle analysis to estimate the ratio of the G0/G1, S, and G2/M phases of the hybridoma cells on each parylene film. From the normalized proportion of phases of the cell cycle, the difference in antibody production from different surfaces was considered to result from the difference in the proliferation rate of hybridoma cells, which occurred from the different physical and chemical properties of the parylene films. Finally, protein expression was analyzed using an mRNA array to determine the effect of parylene films on protein expression in hybridoma cells. The expression of three antibody production-related genes (CD40, Sox4, and RelB) was analyzed in hybridoma cells cultured on modified parylene films.

Pixel-Based Machine Learning and Image Reconstitution for Dot-ELISA Pathogen Diagnosis in Biological Samples

Serological methods serve as a direct or indirect means of pathogen infection diagnosis in plant and animal species, including humans. Dot-ELISA (DE) is an inexpensive and sensitive, solid-state version of the microplate enzyme-linked immunosorbent assay, with a broad range of applications in epidemiology. Yet, its applicability is limited by uncertainties in the qualitative output of the assay due to overlapping dot colorations of positive and negative samples, stemming mainly from the inherent color discrimination thresholds of the human eye. Here, we report a novel approach for unambiguous DE output evaluation by applying machine learning-based pattern recognition of image pixels of the blot using an impartial predictive model rather than human judgment. Supervised machine learning was used to train a classifier algorithm through a built multivariate logistic regression model based on the RGB ("Red," "Green," "Blue") pixel attributes of a scanned DE output of samples of known infection status to a model pathogen (Lettuce big-vein associated virus). Based on the trained and cross-validated algorithm, pixel probabilities of unknown samples could be predicted in scanned DE output images, which would then be reconstituted by pixels having probabilities above a cutoff. The cutoff may be selected at will to yield desirable false positive and false negative rates depending on the question at hand, thus allowing for proper dot classification of positive and negative samples and, hence, accurate diagnosis. Potential improvements and diagnostic applications of the proposed versatile method that translates unique pathogen antigens to the universal basic color language are discussed.

A Novel Method for Antibiotic Detection in Milk Based on Competitive Magnetic Immunodetection

The misuse of antibiotics as well as incorrect dosage or insufficient time for detoxification can result in the presence of pharmacologically active molecules in fresh milk. Hence, in many countries, commercially available milk has to be tested with immunological, chromatographic or microbiological analytical methods to avoid consumption of antibiotic residues. Here a novel, sensitive and portable assay setup for the detection and quantification of penicillin and kanamycin in whole fat milk (WFM) based on competitive magnetic immunodetection (cMID) is described and assay accuracy determined. For this, penicillin G and kanamycin-conjugates were generated and coated onto a matrix of immunofiltration columns (IFC). Biotinylated penicillin G or kanamycin-specific antibodies were pre-incubated with antibiotics-containing samples and subsequently applied onto IFC to determine the concentration of antibiotics through the competition of antibody-binding to the antibiotic-conjugate molecules. Bound antibodies were labeled with streptavidin-coated magnetic particles and quantified using frequency magnetic mixing technology. Based on calibration measurements in WFM with detection limits of 1.33 ng·mL-1 for penicillin G and 1.0 ng·mL-1 for kanamycin, spiked WFM samples were analyzed, revealing highly accurate recovery rates and assay precision. Our results demonstrate the suitability of cMID-based competition assay for reliable and easy on-site testing of milk.

Recent Progress and Development of G-Quadruplex-Based Luminescent Assays for Ochratoxin A Detection

Ochratoxin A (OTA) is a mycotoxin that is widespread throughout the world. It contaminates foods such as vegetables, fruits, and rice. It harms human health and has potential carcinogenic effects. The G-quadruplex (G4) is a tetraplexed DNA structure generated from guanine-rich DNA that has found emerging use in aptamer-based sensing systems. This review outlines the status of OTA contamination and conventional detection methods for OTA. Various G4-based methods to detect OTA developed in recent years are summarized along with their advantages and disadvantages compared to existing approaches.

Inhibitory effect of C. zeylanicum, C. longa, O. basilicum, Z. officinale, and C. martini essential oils on growth and ochratoxin A content of A. ochraceous and P. verrucosum in maize grains

•

Essenetial oils (EOs) extrcated by hydrodistillation and chemical profile deduced by GC–MS.

•

EOs shown potential antioxidant activity by DPPH and ABTS assay.

•

EOs presented superlative antifungal activity against P. verrucosum related to A. ochraceus.

•

C. zeylanicum and C. martini EOs presented superlative antifungal activity related to other EOs.

•

C. zeylanicum EO inhibited the growth and OTA of fungi at 1500 μg/g in maize grains.

In the study, antifungal and ochratoxin A (OTA) production inhibitory activities of essential oils (EOs) of Cinnamomum zeylanicum, Curcuma longa, Ocimum basilicum, Zingiber officinale, and Cymbopogon martini were reported on Aspergillus ochraceus and Penicillium verrucosum. EOs were obtained by hydrodistillation and GC–MS technique was chosen to deduce their chemical profile. Major chemical compounds in EOs of C. zeylanicum, C. longa, O. basilicum, Z. officinale, and C. martini were (E)-cinnamaldehyde (35.81 %), ar-turmerone (46.13 %), eugenol (36.58 %), geranyl proprionate (18.93 %), and geranyl acetate (14.88 %), respectively. The EOs shown potent antioxidant activity by DPPH and ABTS assays. The EOs presented superlative antifungal activity against P. verrucosum related to A. ochraceus. The C. zeylanicum and C. martini EOs shown superlative antifungal activity related to other EOs. The C. zeylanicum and C. martini EOs completely inhibited the growth and OTA production of P. verrucosum and A. ochraceous at 1500 and 2500 μg/g in maize grains, respectively.

Detection of Antibodies Against Canine Circovirus in Naturally and Experimentally Infected Canines by Recombinant Capsid Enzyme-Linked Immunosorbent Assay

Canine circovirus (CanineCV), a new pathogen, was found to be associated with canine hemorrhagic diarrhea, vasculitis, granulomatous lymphadenitis, and acute gastroenteritis. Although CanineCV was highly positive rate in diarrhea cases, its pathogenicity remains controversial. In this study, the seroprevalence and associated risk factors of CanineCV infection among domestic dogs in northeastern China was investigated by an indirect enzyme-linked immunosorbent assay (iELISA) based on recombinant capsid protein. Results revealed the proposed iELISA had no cross-reactivity with other related pathogens, and yielded good diagnostic values. Then, to evaluate the rCap iELISA, this study applied it to detect antibodies against CanineCV in 1,047 clinical serum samples obtained from northeastern China in 2016–2017. Results showed the positive rates in the five cities of Jilin, Liaoning, and Heilongjiang provinces ranged from 22.22 to 42.29%. Statistical analysis shows a significant difference in age between dogs <3 months old with respect to the >1-year-old dogs (p = 0.005), that is, the CanineCV infection was more frequently identified from older dogs. In the artificially infected experiment, the dogs developed seroconversion after 9 or 12 days and the main way of virus excretion was through feces. More interestingly, among the 32 ELISA-positive serum samples, 34.75% samples tested positive for the CanineCV DNA by qPCR, far higher than that in ELISA-negative serum samples (5.26%, 2/38). This report is the first to demonstrate that CanineCV infection is common in the dog population in northeastern China. The results showed obvious differences in the positive rate associated with diarrhea, age, but not with different cities. This study also provide basis for evaluating the pathogenic potential of CanineCV. But, the pathogenicity, the relationship between antibody level and immune protection, and the harmful effects of this virus remain to be established.

Development of ELISA and Lateral Flow Immunoassays for Ochratoxins (OTA and OTB) Detection Based on Monoclonal Antibody

Ochratoxins were important secondary metabolites secreted by fungi, and OTA and OTB are mainly significant mycotoxin, having toxic effects on humans and animals. Therefore, it is important to establish a rapid, sensitive, and precise method for ochratoxins detection and quantification in real samples. In this study, a stable monoclonal antibody (mAb) that recognizing both OTA and OTB toxins was employed for the establishment of indirect competitive ELISA (ic-ELISA), colloidal gold nanoparticles (CGNs), and nanoflowers gold strips (AuNFs) for detection of ochratoxins in real samples. A 6E5 hybridoma cell line stable secreting mAb against both OTA and OTB toxins was obtained by fusion of splenocytes with myeloma SP2/0 cells. The 6E5 mAb had a high affinity (3.7 × 10⁸ L/mol) to OTA, and also showed similar binding activity to OTB. The optimized ic-ELISA resulted in a linear range of 0.06–0.6 ng/mL for ochratoxins (OTA and OTB) detection. The IC50 was 0.2 ng/mL and the limit of detection (LOD) was 0.03 ng/mL. The mean recovery rate from the spiked samples was 89.315 ± 2.257%, with a coefficient variation of 2.182%. The result from lateral flow immunoassays indicated that the LOD of CGNs and AuNFs were 5 and 1 μg/mL, respectively. All these results indicated that the developed ic-ELISA, CGNs, and AuNFs in this study could be used for the analysis of the residual of ochratoxins (OTA and OTB) in food and agricultural products.

Detection and functional characterization of sigma class GST in Phlebotomus argentipes and its role in stress tolerance and DDT resistance

Several Glutathione S-transferases (GSTs) enzymes, in insects, have previously been implicated in resistance developed against DDT and other insecticides. The GST enzyme particularly sigma class have important physiological role in detoxification of lipid peroxidation by-products in insects. Phlebotomus argentipes has been intensely exposed to DDT over years due to Indoor Residual Spray (IRS) programme for Kala-azar elimination in Bihar, India. However, in P. argentipes, role of GSTs in DDT resistance have not been elucidated. Here, sigma class GST of P. argentipes (Parg-GSTσ) was successfully cloned, expressed and purified by affinity chromatography. The recombinant Parg-GSTσ was found to be highly active towards cumene hydroperoxide and 4-HNE having specific activity 92.47 & 203.92 µM/min/mg of protein, respectively and exhibited low activity towards universal substrate CDNB i.e., 8.75 µM/min/mg of protein. RT-PCR and immunoblot analysis showed at least 2 and 1.8 fold overexpression of Parg-GSTσ in the single exposed and non exposed DDT resistant P. argentipes as compared to susceptible, implicating Parg-GSTσ also involved in DDT resistance probably by imparting enhanced stress tolerance. The DDT, H₂O₂ and temperature induction assays demonstrated stress-dependent induction of Parg-GSTσ expression indicating its important role in oxidative stress redressal.

Evaluation of in vitro neutralization of epoxyscillirosidine by antibodies raised in sheep

Intoxication by Moraea pallida Bak. (yellow tulp) in livestock is of great importance in South Africa, ranking top among all plant-induced cardiac glycoside toxicosis. The toxic principle, a bufadienolide, is 1α, 2α-epoxyscillirosidine. Treatment of poisoning is challenging and affected livestock often succumbs due to the stress of handling. Manipulating animals to resist poisoning is a potential management strategy. The goal of this study was to explore the potential to develop a vaccine against epoxyscillirosidine by raising antibodies against epoxyscillirosidine in sheep and to assess the neutralization ability of the antibodies in vitro. Epoxyscillirosidine was successfully conjugated to keyhole limpet haemocyanin (KLH) and bovine serum albumin (BSA) rendering them immunogenic. The sheep, vaccinated with epoxyscillirosidine-KLH conjugate (n = 4) and KLH (n = 2) with Montanide, developed antibodies as determined with an indirect enzyme linked immunosorbent assay (ELISA). Total immunoglobulins from sera of vaccinated and control sheep that were purified and concentrated using ammonium sulphate precipitation were 11,940 and 7850 μg, respectively. The in vitro neutralization assay using the methyl blue tetrazolium bromide (MTT) cell viability assay indicated no significant difference (p > 0.05) between anti-epoxyscillirosidine-KLH and KLH antibodies. Rather, the antibodies seemed to enhance the cytotoxicity of epoxyscillirosidine in H9c2 cells. Thus, it is necessary to develop improved vaccination methods to generate antibodies capable of neutralizing the functional group responsible for epoxyscillirosidine toxicity.

Current methods for mycotoxins analysis and innovative strategies for their reduction in cereals: an overview

Mycotoxins are secondary metabolites produced by moulds in food that are considered a substantial issue in the context of food safety, due to their acute and chronic toxic effects on animals and humans. Therefore, new accurate methods for their identification and quantification are constantly developed in order to increase the performance of extraction, improve the accuracy of identification and reduce the limit of detection. At the same time, several industrial practices have shown the ability to reduce the level of mycotoxin contamination in food. In particular, a decrease in the amount of mycotoxins could result from standard processes naturally used for food processing or by procedures strategically introduced during processing, with the specific aim of reducing the amount of mycotoxins. In this review, the current methods adopted for accurate analyses of mycotoxins in cereals (aflatoxins, ochratoxins, trichothecenes, fumonisins) are discussed. In addition, both conventional and innovative strategies adopted to obtain safer finished products from common cereals intended for human consumption will be explored and analysed. © 2018 Society of Chemical Industry.

Novel haptens and monoclonal antibodies with subnanomolar affinity for a classical analytical target, ochratoxin A

Ochratoxin A is a potent toxic fungal metabolite whose undesirable presence in food commodities constitutes a problem of public health, so it is strictly regulated and controlled. For the first time, two derivatives of ochratoxin A (OTAb and OTAd) functionalized through positions other than the native carboxyl group of the mycotoxin, have been synthesized in order to better mimic, during the immunization process, the steric and conformational properties of the target analyte. Additionally, two conventional haptens making use of that native carboxyl group for protein coupling (OTAe and OTAf) were also prepared as controls for the purpose of comparison. The immunological performance in rabbits of protein conjugates based on OTAb and OTAd overcome that of conjugates employing OTAe and OTAf as haptens. After immunization of mice with OTAb and OTAd conjugates, a collection of high-affinity monoclonal antibodies to ochratoxin A was generated. In particular, one of those antibodies, the so-called OTAb#311, is very likely the best antibody produced so far in terms of selectivity and affinity to ochratoxin A.

Development of Hybrid IgG-Aptamer Sandwich Immunoassay Platform for Aflatoxin B1 Detection and Its Evaluation Onto Various Field Samples

The present study was aimed to develop a novel antibody-aptamer based hybrid detection strategy for specific and sensitive detection of aflatoxin B1 (AFB1) from contaminated food grains. The study comprises generation of ssDNA aptamers and anti-AFB1 IgG against AFB1 toxin. The generated bio-probes (aptamers and antibodies) were further characterized for their specificity and sensitivity using indirect ELISA. The generated aptamers namely AFB1a and AFB1b showed prominent reactivity and selectivity against AFB1 toxin. These aptamers were further characterized for their secondary structures and dG values were determined as -4.6 and -2.75 Kcal/mol, respectively. The detection limit (LOD) of AFB1a and anti-AFB1 IgG was determined as 5 and 10 ng/mL, respectively. The characterized aptamers and antibodies against AFB1 were used to develop the sandwich immunoassay. Anti AFB1 IgG was used as a capturing antibody whereas anti-AFB1a aptamer was used as its revealing partner in the assay. The limit of detection (LOD) of the immunoassay was determined to be 5 ng/mL of AFB1 standard toxin and showed no cross-reactivity with closely related mycotoxins. To assess the reliability of the developed method, several field samples contaminated with aflatoxin B1 was included in the study and results were validated with commercial AFB1-ELISA Kit. Additionally, the spiking studies were also carried out to demonstrate the consistency and dependability of the developed hybrid sandwich immunoassay wherein the toxins recovered were found to be ranging between 73 and 98.80% with the LOD at 5 ng/mL. In conclusion, the developed method may find the better utility in routine food testing laboratories for assessment of AFB1.

A Novel Nano Magnetic Beads Dot ELISA Immunoassay and Its Application on the Detection of Giardia lamblia Coproantigen

BACKGROUND

The traditional basis of diagnosis is identification of Giardia lamblia trophozoites or cysts in the stool of infected patients. Recently the advent of more objective techniques like antigen detection methods has led to an increase in their use versus those that rely on subjective microscopic examination of fecal specimens for Giardia cysts may facilitate diagnosis of G. lamblia in stool specimens.

METHODS

This cross-sectional study was carried out from Oct 2015 to Feb 2016 on patients admitted to Benha University Hospitals (Benha, Egypt) and outpatients of Theodor Bilharz Research Institute (TBRI) (Giza, Egypt). Purified G. lamblia cysts antigen was prepared by two-phase sucrose gradient technique. Polyclonal antibody against purified G. lamblia cysts antigen was prepared and labeled with horseradish peroxidase and Nano Magnetic Beads (NMB) to be used as detecting antibody. A total of 72 stool samples, 32 samples positive for giardiasis, 20 samples positive for other parasitic infections in addition to 20 negative samples were examined using dot ELISA and NMB dot-ELISA.

RESULTS

The sensitivity of the traditional dot-ELISA was 81.3 % and it increased by using the NMB-dot-ELISA to be 96.9% in stool samples. Specificity of both techniques was 97.5%.

CONCLUSION

Diagnosis of G. lamblia by NMB-Dot-ELISA technique is sensitive, specific, rapid and easy to perform and interpret. In this study, using the nano-magnetic beads increased the sensitivity of the applied technique.

Determination of Ochratoxin A in Rye and Rye-Based Products by Fluorescence Polarization Immunoassay

A rapid fluorescence polarization immunoassay (FPIA) was optimized and validated for the determination of ochratoxin A (OTA) in rye and rye crispbread. Samples were extracted with a mixture of acetonitrile/water (60:40, v/v) and purified by SPE-aminopropyl column clean-up before performing the FPIA. Overall mean recoveries were 86 and 95% for spiked rye and rye crispbread with relative standard deviations lower than 6%. Limits of detection (LOD) of the optimized FPIA was 0.6 μg/kg for rye and rye crispbread, respectively. Good correlations (r > 0.977) were observed between OTA contents in contaminated samples obtained by FPIA and high-performance liquid chromatography (HPLC) with immunoaffinity cleanup used as reference method. Furthermore, single laboratory validation and small-scale collaborative trials were carried out for the determination of OTA in rye according to Regulation 519/2014/EU laying down procedures for the validation of screening methods. The precision profile of the method, cut-off level and rate of false suspect results confirm the satisfactory analytical performances of assay as a screening method. These findings show that the optimized FPIA is suitable for high-throughput screening, and permits reliable quantitative determination of OTA in rye and rye crispbread at levels that fall below the EU regulatory limits.

Ochratoxin A Concentrations in a Variety of Grain-Based and Non-Grain-Based Foods on the Canadian Retail Market from 2009 to 2014

The extent of ochratoxin A (OTA) contamination of domestically produced foods sold across Canada was determined from 2009 to 2014 with sampling and testing occurring each fiscal year. Cereal-based, fruit-based, and soy-based food samples (n = 6,857) were analyzed. Almost half of the samples (3,200; 47%) did not contain detectable concentrations of OTA. The remaining 3,657 samples contained OTA at 0.040 to 631 ng/g. Wheat, oats, milled products of other grains (such as rye and buckwheat), and to a lesser extent corn products and their derived foods were the most significant potential sources of OTA exposure for the Canadian population. Wine, grape juice, soy products, beer, dairy-based infant formula, and licorice candy were not significant contributors to OTA consumption. Spices had the highest OTA concentrations; but because so little is ingested, these foods are not considered to be a significant source of OTA. In contrast, infant formulas and cereals can be important dietary sources of OTA. Infant cereals containing oats and infant formulas containing soy had detectable concentrations of OTA, some of which exceeded the proposed Canadian guidelines. The prevalence and concentrations of OTA in major crops (wheat, corn, and oats) varied widely across years. Because these foods were purchased at retail stores, no information was available on the OTA concentrations in the raw materials, the storage conditions before purchase of the samples, or the origin of the ingredients (may include blends of raw materials from different years and/or different geographical regions of Canada); therefore, impact of these factors could not be assessed. Overall, 2.3% of the samples exceeded the proposed Canadian OTA regulatory limits and 2.7% exceeded the current European Union (EU) OTA regulatory limits. These results are consistent with a Health Canada exposure assessment published in 2010, despite the inclusion of a wider range of products and confirm the safety of foods widely available across Canada.

Immuno Affinity SELEX for Simple, Rapid, and Cost-Effective Aptamer Enrichment and Identification against Aflatoxin B1

Aflatoxins are naturally occurring mycotoxins that contaminate food and agro commodities, leading to acute and chronic health conditions in human and animals. In the present work, an attempt was made to generate high-affinity single stranded DNA aptamers that specifically bind to Aflatoxin B1 (AFB1) by a modified Systemic Evolution of Ligands by Exponential Enrichment (SELEX) procedure with the aid of Immunoaffinity columns. Ten rounds of SELEX and alternating three counter SELEX rounds with a cocktail of related and other mycotoxins were performed to enhance the specificity. Resultant 105 aptamers were clustered into 12 groups according to their primary sequence homology. Candidates with lowest Gibbs free energy (dG value) and unique stem loop structures were selected for further characterization. Aptamers, AFLA5, AFLA53, and AFLA71 exhibiting lower K_d values (50.45 ± 11.06, 48.29 ± 9.45, and 85.02 ± 25.74 nM) were chosen for development of ELONA and determination of purification ability of toxin. The detection limit (LOD) of AFLA5 and AFLA71 was 20 and 40 ng/ml, respectively. HPLC analysis implied that selected aptamers were able to recover and quantify 82.2 to 96.21% (LOQ – 53.74 ng) and 78.3 to 94.22% (LOQ – 66.75 ng) of AFB1 from spiked corn samples, respectively. These findings indicate, immunoaffinity based SELEX can pave an alternative approach to screen aptamers against mycotoxin detection and purification.

New biorecognition molecules in biosensors for the detection of toxins

Biological and synthetic recognition elements are at the heart of the majority of modern bioreceptor assays. Traditionally, enzymes and antibodies have been integrated in the biosensor designs as a popular choice for the detection of toxin molecules. But since 1970s, alternative biological and synthetic binders have been emerged as a promising alternative to conventional biorecognition elements in detection systems for laboratory and field-based applications. Recent research has witnessed immense interest in the use of recombinant enzymatic methodologies and nanozymes to circumvent the drawbacks associated with natural enzymes. In the area of antibody production, technologies based on the modification of in vivo synthesized materials and in vitro approaches with development of "display "systems have been introduced in the recent years. Subsequently, molecularly-imprinted polymers and Peptide nucleic acid (PNAs) were developed as an attractive receptor with applications in the area of sample preparation and detection systems. In this article, we discuss all alternatives to conventional biomolecules employed in the detection of various toxin molecules We review recent developments in modified enzymes, nanozymes, nanobodies, aptamers, peptides, protein scaffolds and DNazymes. With the advent of nanostructures and new interface materials, these recognition elements will be major players in future biosensor development.

Comparison of Fluorescent Microspheres and Colloidal Gold as Labels in Lateral Flow Immunochromatographic Assays for the Detection of T-2 Toxin

A new highly specific and sensitive monoclonal antibody (MAb) to T-2 toxin (T-2) was produced, providing an IC50 value of 1.02 ng/mL and negligible cross-reactivity (CR) to other related mycotoxins. Based on the new MAb, a lateral-flow immunochromatographic assay (LFIA) using colloidal gold (CG) and fluorescent microspheres (FMs) as labels was proposed for T-2. Under the optimized conditions, in rapid qualitative assay, the cut-off values of the CG-LFIA were 400 μg/kg in rice and 50 μg/L in fresh milk, and the cut-off values of the FMs-LFIA were 100 μg/kg in both rice and chicken feed. For the quantitative assay with the FMs-LFIA, the limit of detection (LOD) were 0.23 μg/kg and 0.41 μg/kg in rice and chicken feed, respectively, and the average recoveries ranged from 80.2% to 100.8% with the coefficient of variation (CV) below 10.8%. In addition, we found that the CG-LFIA could tolerate the matrix effect of fresh milk better than the FMs-LFIA, while the FMs-LFIA could tolerate the matrix effect of chicken feed better than CG-LFIA under the same experimental conditions. These results provide a certain reference for the selection of appropriate labels to establish a rapid LFIA in various biological samples.

Identification of a high-affinity monoclonal antibody against ochratoxin A and its application in enzyme-linked immunosorbent assay

Ochratoxin A (OTA) is one of the most commonly occurring mycotoxins produced by some species of Aspergillus and can contaminate cereal and cereal products. A high-affinity anti-OTA monoclonal antibody (mAb) was generated from a hybridoma cell line 2D8 using splenocytes from a BALB/c mouse immunized with synthesized OTA-bovine serum albumin conjugate. The mAb 2D8 is specific with high affinity (3.75 × 10(9) L/M). An indirect competitive ELISA (ic-ELISA) was then developed using this mAb for quantitative determination of OTA in corn and feed samples. Using the optimized conditions, there was good linearity between OTA concentration and competitive inhibition (y = -0.6076x + 0.2441, R(2) = 0.9923) with the working range from 2.4 to 23.6 μg/kg, IC50 at 7.6 μg/kg and lower limit of detection at 1.4 μg/kg. The recovery rates in spiked samples were 91.2-110.3%. Of the 56 corn and feed samples, this ic-ELISA and a commercial kit both found the same 13 samples positive for OTA with good linear correlation between the two methods in OTA quantification (R(2) = 0.9706). We conclude that this ic-ELISA can be used for rapid and quantitative screening of corn and feed samples for the presence of OTA.