Development of a sensitive enzyme-linked immunosorbent assay for the detection of fumonisin B1 in maize

Rapid and convenient screening method based on single-chain variable fragments for the detection of restricted monensin in chicken muscle

A colloidal gold immunochromatographic assay (CGIA) based on single-chain variable fragments (scFvs) has been successfully developed for the detection of monensin (MON). Colloidal gold probes were conjugated to anti-MON scFvs through electrostatic interaction, with the conjugated objects serving as the visual signals. The detection lines were formed by capturing the antibody with MON-OVA. This assay offers a rapid detection time of 15 min, a wide linear range from 2.19 to 10.76 ng mL-1, and boasts high accuracy, precision, and an absence of cross-reactivity. By homology modeling and molecular docking, we predicted the interaction patterns between the scFv and monensin, and the amino acid residues involved in the recognition of MON by the antibody were analyzed. These key amino acid sites are presumed integral to ligand recognition per current interaction models. This hypothesis was confirmed by computer-aided alanine scanning mutation, MM/P(G)BSA molecular dynamics simulation, and in vitro binding experiments. In this study, we successfully developed the scFvs-based CGIA system for rapid and easy quantification of monensin, providing a simple, efficient routine detection of chicken muscle samples.

Development of Fluorescence Polarization Immunoassay With scFv to Detect Fumonisin Bs in Maize and Simultaneous Study of Their Molecular Recognition Mechanism

In this study, a fluorescence polarization immunoassay (FPIA) was developed based on the single-chain variable fragments (scFvs) for fumonisin B_s (FB_s). The scFvs were prepared from FB_s-specific monoclonal antibody secreting hybridomas (4F5 and 4B9). The established FPIA could determine the sum of fumonisin B₁ (FB₁) and fumonisin B₂ (FB₂) within a short time. The IC₅₀ of FPIA for the detection of FB₁ and FB₂ were 29.36 ng/ml and 1,477.82 ng/ml with 4F5 scFv, and 125.16 ng/ml and 30.44 ng/ml with 4B9 scFv, so the 4B9 scFv was selected for detection of FB₁ and FB₂ in maize samples with a limit of detection of 441.54 μg/kg and 344.933 μg/kg. The recoveries ranged from 84.7 to 104.1% with a coefficient of variation less than 14.1% in spiked samples, and the result of the FPIA method was in good consistency with that of HPLC-MS/MS. To supply a better understanding of the immunoassay results, the interactions mechanism of scFvs-FB_s was further revealed by the homology modelling, molecular docking, and molecular dynamic simulation. It was indicated that six complementarity-determining regions (CDRs) were involved in 4B9 scFv recognition, forming a narrow binding cavity, and FB₁/FB₂ could be inserted into this binding cavity stably through strong hydrogen bonds and other interactions. While in 4F5 scFv, only the FB₁ stably inserted in the binding pocket formed by four CDRs through strong hydrogen bonds, and FB₂ did not fit the binding cavity due to the lack of hydroxyl at C10, which is the key recognition site of 4F5 scFv. Also, the binding energy of FB₂-4B9 scFv complex is higher than the FB₂-4F5 scFv complex. This study established a FPIA method with scFv for the detection of FB₁ and FB₁ in maize, and systematically predicted recognition mechanism of FB_s and scFvs, which provided a reference for the better understanding of the immunoassay mechanism.

A Sensitive Monoclonal-Antibody-Based ELISA for Forchlorfenuron Residue Analysis in Food Samples

In this study, forchlorfenuron (CPPU) was coupled with succinic anhydride to yield a CPPU hapten (CPPU-COOH), and a high-affinity monoclonal antibody (mAb) that can specifically recognize CPPU was produced. Using this mAb as a recognition reagent, a sensitive indirect competitive enzyme-linked immunosorbent assay (icELISA) for CPPU was optimized, which exhibits an IC50 of 1.04 ng/mL, a limit of detection of 0.16 ng/mL, and a linear range of 0.31–3.43 ng/mL for CPPU. Cross-reactivity percentages with six analogues were all below 6%. The average recovery rates for cucumber and orange samples were from 85.23% to 119.14%. The analysis results of this icELISA showed good consistency with those from liquid chromatography mass spectrometry. These results suggest that the proposed icELISA provides a sensitive, specific, and reliable strategy for CPPU detection in food samples.

Evaluation of Mass Sensitive Micro-Array biosensors for their feasibility in multiplex detection of low molecular weight toxins using mycotoxins as model compounds

Mycotoxins produced by Fusarium species including trichothecenes, zearalenone and fumonisins, can co-contaminate food and feed throughout the supply chain, including cereal grains and animal feeds. There is an increasing demand to enhance global food security by improving the monitoring of mycotoxins throughout our food supply chain. For time and cost-efficient analysis, rapid tests capable of detecting multiple toxins from a single sample are ideal. Considering these current trends in mycotoxin testing, this project examined the feasibility of using both a portable and non-portable mass-based biosensor for multiplex mycotoxin detection. The biosensor was a mass sensitive microarray (MSMA) which consisted of 4 × 16 miniaturized mass sensitive transducer pixels based on solidly mounted resonator (SMR) technology. Functionalisation of individual pixels on the sensor surface using nano-spotting technology for the simultaneous and semi-quantitative detection of three regulated mycotoxins: T2-toxin (T2) zearalenone (ZEN), and fumonisin B1 (FumB1) was examined. With the integration of portable and non-portable microfluidic devices for antibody and standard sample injections, competitive inhibition assays were developed followed by singleplex and multiplex calibration curves. The characteristics and performance of the MSMA were evaluated including sensitivity which was determined as the concentration causing 50% inhibition. Sensitivity of singleplex assays using the portable microfluidic device (PMD) were 1.3 ng/ml, 2.0 ng/ml and 6.8 ng/ml for T2, FumB1 and ZEN, respectively. Sensitivity of the multiplex assay again using the PMD was 6.1 ng/ml, 3.6 ng/ml and 2.4 ng/ml for T2, FumB1 and ZEN, respectively. The PMD was an easy to use and highly sensitive screening tool which has been demonstrated for the multiplex detection of three regulated mycotoxins. Analysis was in real time and results were fully digital. Since detection of analytes was by mass it was both a label-free and cost-efficient method proposed method of analysis for mycotoxins.

Development of an IgY-based lateral flow immunoassay for detection of fumonisin B in maize

Fumonisin is one of the most prevalent mycotoxins in maize, causing substantial economic losses and potential health risks in human and animals. In the present study, in-house polyclonal IgY antibody against fumonisin group B (FB) was applied for the development of a competitive lateral flow immunoassay detecting these mycotoxins in maize grains with the limit of detection of 4000 µg/kg, which corresponds to the maximum residue limit adopted by The International Codex Alimentarius Commission. To this end, factors affecting the test performance including nitrocellulose membrane type, dilution factor of maize homogenates in running buffer, amount of detection conjugate, and incubation time between detection conjugate and samples were optimized. Under the optimal condition (UniSart ^®CN140 nitrocellulose membrane, FB ₁-BSA immobilized at 1 µg/cm, 1:10 dilution factor, 436 ng of gold nanoparticle conjugate, 30 minutes of incubation), the developed test could detect both FB ₁ and FB ₂ in maize with limit of detection of 4000 µg/kg, and showed no cross-reactivity to deoxynivalenol, ochratoxin A, aflatoxin B1 and zearalenone. When applied to detect FB ₁ and FB ₂ in naturally contaminated maize samples, results obtained from the developed assay were in good agreement with those from the high-performance liquid chromatography method. This lateral flow immunoassay is particularly suitable for screening of fumonisins in maize because of its simplicity and cost-effectiveness.

Development of an IgY-based lateral flow immunoassay for detection of fumonisin B in maize

Fumonisin is one of the most prevalent mycotoxins in maize, causing substantial economic losses and potential health risks in human and animals. In the present study, in-house polyclonal IgY antibody against fumonisin group B (FB) was applied for the development of a competitive lateral flow immunoassay detecting these mycotoxins in maize grains with the limit of detection of 4000 µg/kg, which corresponds to the maximum residue limit adopted by The International Codex Alimentarius Commission. To this end, factors affecting the test performance including nitrocellulose membrane type, dilution factor of maize homogenates in running buffer, amount of detection conjugate, and incubation time between detection conjugate and samples were optimized. Under the optimal condition (UniSart ®CN140 nitrocellulose membrane, FB 1-BSA immobilized at 1 µg/cm, 1:10 dilution factor, 436 ng of gold nanoparticle conjugate, 30 minutes of incubation), the developed test could detect both FB 1 and FB 2 in maize with limit of detection of 4000 µg/kg, and showed no cross-reactivity to deoxynivalenol, ochratoxin A, aflatoxin B1 and zearalenone. When applied to detect FB 1 and FB 2 in naturally contaminated maize samples, results obtained from the developed assay were in good agreement with those from the high-performance liquid chromatography method. This lateral flow immunoassay is particularly suitable for screening of fumonisins in maize because of its simplicity and cost-effectiveness.

Rapid screening of flonicamid residues in environmental and agricultural samples by a sensitive enzyme immunoassay

A fast and sensitive polyclonal antibody-based enzyme-linked immunosorbent assay (ELISA) was developed for the analysis of flonicamid in environmental and agricultural samples. Two haptens of flonicamid differing in spacer arm length were synthesized and conjugated to proteins to be used as immunogens for the production of polyclonal antibodies. To obtain most sensitive combination of antibody/coating antigen, two antibodies were separately screened by homologous and heterologous assays. After optimization, the flonicamid ELISA showed that the 50% inhibitory concentration (IC50 value) was 3.86mgL(-1), and the limit of detection (IC20 value) was 0.032mgL(-1). There was no cross-reactivity to similar tested compounds. The recoveries obtained after the addition of standard flonicamid to the samples, including water, soil, carrot, apple and tomato, ranged from 79.3% to 116.4%. Moreover, the results of the ELISA for the spiked samples were largely consistent with the gas chromatography (R(2)=0.9891). The data showed that the proposed ELISA is an alternative tool for rapid, sensitive and accurate monitoring of flonicamid in environmental and agricultural samples.

Development of a sensitive, competitive, indirect ELISA for the detection of fumonisin B1 in corn originating from Anhui province, China

Fumonisin B₁ (FB₁) is a secondary metabolite produced by Fusarium verticillioides or Fusarium proliferatum, which present in food and feed. It causes hazardous effects on human and animal health. A monoclonal antibody (mAb) against FB₁ was produced and a simple, reliable and sensitive, competitive, indirect enzyme-linked immunosorbent assay (ci-ELISA) for detection of FB₁ was developed and the experiment conditions were optimized. The coating concentration of FB₁-ovalbumin (FB₁-OVA) was 500 ng mL^-1, the action concentrations of anti-FB₁ mAb and goat anti-mouse IgG were 1.28 × 10⁴ and 1:5000, respectively. The 50% inhibitory concentration (IC₅₀) was 11 ng mL^-1, with a detectable range of 1.25-250 ng mL^-1, and a limit of determination (LOD) of 1.15 ng mL^-1. The cross-reactivity (CR) of the antibody against fumonisin B₂ (FB₂) was 60.4, and <1% against deoxynivalenol (DON), aflatoxin B₁ (AFB₁), ochratoxin A (OTA) or zearalenone (ZEN). In spiked samples (250 ng g^-1, 500 ng g^-1, 1000 ng g^-1), the mean recoveries ranged from 86.7 ± 5% to 102 ± 4%, and the coefficient of variation (CV) ranged from 3% to 10%. A survey of 96 corn samples from Bozhou, Fuyang, Bengbu, and Hefei, in Anhui province, China, was performed. Frequencies of FB₁ contamination were 83.3%, 95.8%, 20.8% and 91.7%, and the mean concentrations of positive samples were 0.702 μg kg^-1, 0.883 μg kg^-1, 0.074 μg kg^-1, and 0.276 μg kg^-1, respectively. The results of this study suggest that the ci-ELISA developed in this study can be used to identify FB₁ in corn, furthermore, further study is needed to investigate FB₁ contamination in food and feed to prevent its harmful health effects.

A universal multi-wavelength fluorescence polarization immunoassay for multiplexed detection of mycotoxins in maize

Multi-analyte immunoassays have attracted increasing attention due to their short assay times, low sample consumption, and reduced detection costs per assay. In this work, we describe a homologous and high-throughput multi-wavelength fluorescence polarization immunoassay (MWFPIA) for the multiplexed detection of mycotoxins. Three typical Fusarium mycotoxins, deoxynivalenol (DON), T-2 toxin and fumonisin B1 (FB1), were labeled with different dyes. Tracers and specific monoclonal antibodies (mAbs) were employed in the MWFPIA to simultaneously detect the three mycotoxins. Under optimal conditions, the limits of detection using MWFPIA were 242.0 μg kg(-1) for DON, 17.8 μg kg(-1) for T-2 toxin and 331.5 μg kg(-1) for FB1, providing sufficient sensitivity to meet the action levels of these three contaminants in maize as set by the European Union. The use of a methanol/water (2:3, v/v) mixture for sample pretreatment allowed recoveries ranging from 76.5-106.3%, with coefficients of variation less than 21.7%. The total time of analysis, including sample preparation, was less than 30 min. Twenty naturally contaminated maize samples were tested using MWFPIA and HPLC-MS/MS, with correlation coefficients (R(2)) of 0.97 for DON and 0.99 for FB1. By changing the targets of interest, homologous MWFPIA, a method with high sensitivity, a simple procedure and a short analysis time, can easily be extended to other chemical contaminants. Thus, MWFPIA represents a versatile strategy for food safety analysis.

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.

Development of a screening fluorescence polarization immunoassay for the simultaneous detection of fumonisins B₁ and B₂ in maize

This paper reports the development of a screening fluorescence polarization immunoassay (FPIA) for the simultaneous detection of fumonisins B1 (FB1) and B2 (FB2) in maize. Three FB1 tracers including FB1-fluorescein isothiocyanate isomer I (FB1-FITC), FB1-5-([4,6-dichlorotriazine-2-yl]amino)-fluorescein (FB1-5-DTAF), and FB1-Texas Red-X succinimidyl ester (FB1-TRX) were synthesized and studied to select appropriate tracer-antibody pairs using seven previously produced monoclonal antibodies (mAbs). An FPIA employing the pair of FB1-FITC and mAb 4B9 showing 98.9% cross-reactivity (CR) toward FB2 was used to simultaneously detect FB1 and FB2. Maize flour samples were extracted with methanol/water (2:3, v/v). After optimization, the FPIA revealed a limit of detection (LOD) of 157.4 μg/kg for FB1 and an LOD of 290.6 μg/kg for FB2, respectively. Recoveries were measured for spiked samples of FB1 or FB2 separately, ranging from 84.7 to 93.6%, with a coefficient of variation (CV) of <9.9%. Total time needed for FPIA including sample pretreatment was <30 min. The FPIA was used to screen naturally contaminated maize samples. Results detected by FPIA showed good agreement with that of HPLC-MS/MS with a fit of R(2) = 0.99 for the simultaneous detection of FB1 and FB2. The established method offered a rapid, simple, sensitive, and high-throughput screening tool for the detection of fumonisins in maize.

Progress in the development of immunoanalytical methods incorporating recombinant antibodies to small molecular weight biotoxins

Rapid immunoanalytical screening of food and environmental samples for small molecular weight (hapten) biotoxin contaminations requires the production of antibody reagents that possess the requisite sensitivity and specificity. To date animal-derived polyclonal (pAb) and monoclonal (mAb) antibodies have provided the binding element of the majority of these assays but recombinant antibodies (rAb) isolated from in vitro combinatorial phage display libraries are an exciting alternative due to (1) circumventing the need for experimental animals, (2) speed of production in commonly used in vitro expression systems and (3) subsequent molecular enhancement of binder performance. Short chain variable fragments (scFv) have been the most commonly employed rAb reagents for hapten biotoxin detection over the last two decades but antibody binding fragments (Fab) and single domain antibodies (sdAb) are increasing in popularity due to increased expression efficiency of functional binders and superior resistance to solvents. rAb-based immunochromatographic assays and surface plasmon resonance (SPR) biosensors have been reported to detect sub-regulatory levels of fungal (mycotoxins), marine (phycotoxins) and aquatic biotoxins in a wide range of food and environmental matrices, however this technology has yet to surpass the performances of the equivalent mAb- and pAb-based formats. As such the full potential of rAb technology in hapten biotoxin detection has yet to be achieved, but in time the inherent advantages of engineered rAb are set to provide the next generation of ultra-high performing binder reagents for the rapid and specific detection of hapten biotoxins.

Development and application of a quantitative fluorescence-based immunochromatographic assay for fumonisin b1 in maize

A fluorescence-based immunochromatographic assay (ICA) for fumonisin B1 (FB1) that employs conjugates of fluorescent microspheres and monoclonal antibodies (FM-mAbs) as detection reporters is described. The ICA is based on the competitive reaction between FB1-bovine serum albumin (BSA; test line) and the target FB1 for binding to the FM-mAb conjugates. A limit of detection (LOD) for FB1 of 0.12 ng/mL was obtained, with an analytical working range of 0.25-2.0 ng/mL (corresponding to 250-2000 μg/kg in maize flour samples, according to the extraction procedure). The recoveries of the ICA to detect FB1 in maize samples ranged from 91.4 to 118.2%. A quantitative comparison of the fluorescence-based ICA and HPLC-MS/MS analysis of naturally contaminated maize samples indicated good agreement between the two methods (r(2) = 0.93). By replacing the target of interest, the FM-based ICA can easily be extended to other chemical contaminants and thus represents a versatile strategy for food safety analysis.

Developments in mycotoxin analysis: an update for 2012-2013

This review highlights developments in mycotoxin analysis and sampling over a period between mid-2012 and mid-2013. It covers the major mycotoxins: aflatoxins, Alternaria toxins, ergot alkaloids, fumonisins, ochratoxins, patulin, trichothecenes and zearalenone. A wide range of analytical methods for mycotoxin determination in food and feed were developed last year, in particular immunochemical methods and liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS)-based methods. After a section on sampling and sample preparation, due to the rapid spread and developments in the field of LC-MS/MS multimycotoxin methods, a separate section has been devoted to this area of research. It is followed by a section on mycotoxins in botanicals and spices, before continuing with the format of previous reviews in this series with dedicated sections on method developments for the individual mycotoxins.

Au NPs driven electrochemiluminescence aptasensors for sensitive detection of fumonisin B1

A simple gold nanoparticles–Ir complex driven electrochemiluminescence aptasensors was fabricated for the sensitive detection of fumonisin B1.

Cross-reactivity of rapid immunochemical methods for mycotoxins detection towards metabolites and masked mycotoxins: the current state of knowledge

The cross-reactivity of antibodies employed within immunochemistry-based analytical methods may lead to overestimation of the results. Under certain conditions, specifically when controlling mycotoxin maximum limits serious problems can be encountered. Not only the structurally related mycotoxins, such as their masked (conjugated) forms, but also the unidentified matrix components are responsible for concentration overestimation of respective target analytes. The cross-reactivity phenomenon may also pose a risk of miss-interpretation of the proficiency tests results, when the assigned value becomes influenced by over-estimated results reported by users of immunochemical tests. In this paper, the current state of the knowledge on trueness problems associated with the rapid screening immunochemical methods have been reviewed. Special attention is focused on discussion of cross-reactivity in the ELISA tests, because this rapid test dominates the routine screening practice. However, the cross-reactions reported in lateral flow test strips, fluorescence polarisation immunoassay, or immunosensors have also been addressed.

Monoclonal antibody production and the development of an indirect competitive enzyme-linked immunosorbent assay for screening spiramycin in milk

To monitor spiramycin (SP) residue in milk, a monoclonal antibody (mAb)-based indirect competitive enzyme-linked immunosorbent assay (icELISA) was developed. This study described the preparation of three immunogens and the production of a high-affinity mAb. After optimization, the 50% inhibition concentration (IC50) for the developed icELISA was estimated as 0.97 ng/mL in the assay buffer, and the limit of detection and limit of quantitation were 2.51 and 4.40 μg/L in the milk matrix. The newly developed assay demonstrated negligible cross-reactivity with 15 other macrolide antibiotics, but not with kitasamycin (23.4%). The mean recoveries ranged from 81 to 103% for the spiked samples (5, 10, and 50 μg/L), and the coefficient of variation ranged from 5.4 to 9.6%. The icELISA was validated by LC-MS/MS method, and all results demonstrated that it was a suitable screening method for detecting SP residue in milk without requiring a cleanup process.

Simultaneous screening analysis of 3-methyl-quinoxaline-2-carboxylic acid and quinoxaline-2-carboxylic acid residues in edible animal tissues by a competitive indirect immunoassay

Immunoassays contribute greatly to food safety. Yet there are no reported immunoassays that simultaneously detect MQCA and QCA, the marker residues for olaquindox and carbadox, respectively. Here, a broad-specificity mAb was successfully produced, and the mAb showed good cross-reactivity with both MQCA and QCA, having IC50 values in buffer of 4.8 and 9.6 ng/mL, respectively. The calibration curves ranged from 0.3 to 81 μg/kg. The average recoveries ranged from 76% to 108% at different spiked levels (2, 4, and 8 μg/kg for MQCA; and 4, 10, and 20 μg/kg for QCA), and the intra-/interday coefficients of variation were 4.2-13.3%. The limits of detection of MQCA and QCA in chicken, fish, pork, and shrimp were 1.76, 1.32, 1.90, and 1.18 μg/kg, respectively. This method was verified by LC-MS/MS, with a correlation coefficient above 0.98. The immunoassay was rapid and reliable for simultaneous screening analysis of MQCA and QCA residues.

Application of mimotope peptides of fumonisin b1 in Peptide ELISA

Anti-fumonisin B(1) (FB(1)) McAb 1D11 was used as the target for biopanning from a phage random loop-constrained heptapeptide library. After three cycles of panning, seven phages with three mimotope peptides were selected to mimic the binding of FB(1) to 1D11. After the identification of phage ELISA, the phage clone that showed the best linear range of detection was chosen for further research. One peptide with the inserted peptide sequence of the phage was synthetized, named CT-452. An indirect competitive ELISA (peptide ELISA) for detecting FB(1) was established using the CT-452-bovine serum albumin conjugate as coating antigen. The linear range of the inhibition curve was 1.77-20.73 ng/mL. The half inhibitory concentration (IC50) was 6.06 ng/mL, and the limit of detection was 1.18 ng/mL. This method was compared with conventional indirect ELISA (commercial ELISA kit) and high-performance liquid chromatography (HPLC), and the results showed the reliability of the peptide ELISA for the determination of FB(1) in cereal samples. The relationship between the CT-452 and FB(1) standard concentrations in peptide ELISA was evaluated. The results indicated that synthetic peptide CT-452 can replace the FB(1) standard to establish an immunoassay free of FB(1).