Development of a Mab-based heterologous immunoassay for the broad-selective determination of organophosphorus pesticides

Hapten synthesis, monoclonal antibody production and immunoassay development for analyzing spiropidion residues

Spiropidion developed by Syngenta shows high insecticidal and acaricidal activity against a wide range of sucking pests. In this study, according to the structure of spiropidion, two haptens were synthesized by introducing carboxyl groups from the ester group. After cell fusion, a monoclonal antibody (mAb 8B5) of spiropidion was obtained. The IC50 of the established heterologous indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) was 7.36 ng/mL, and its working range was 1.75-34.92 ng/mL. The average recoveries were 76.05-124.78% in the Yangtze River and citrus samples. Moreover, the ic-ELISA results of 15 citrus samples agreed well with ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Overall, the established ic-ELISA could be applied for the spiropidion residue monitor in food and agricultural samples.

Preparation of spirodiclofen monoclonal antibody and establishment of indirect competitive enzyme-linked immunosorbent assay

Spirodiclofen, a spirocyclic tetronic acid derivative, has excellent acaricidal effect and is used worldwide to control the majority of important mite species. For monitoring its residue in food and environmental samples, two haptens containing different spacer arms were synthesized, a monoclonal antibody (mAb 5A4) against spirodiclofen was prepared, and a heterologous indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) was established. The 50% inhibition concentration (IC₅₀) of ic-ELISA was 25.46 ng/mL, and the working range was 5.59-133.85 ng/mL. The ic-ELISA showed no cross-reactivity with structural analogs of spirodiclofen and other commonly-used acaricides. The average recoveries from Shiranui citrus samples and Yangtze River water were 85.62%-97.74% and 85.95%-99.30%, respectively. In the analysis of 12 citrus samples, the results of the ic-ELISA were quite similar to those of ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Hence, the new immunosorbent assay provides a substitute method for the qualitative and quantitative of spirodiclofen in food and environmental samples.

Changing Cross-Reactivity for Different Immunoassays Using the Same Antibodies: Theoretical Description and Experimental Confirmation

Many applications of immunoassays involve the possible presence of structurally similar compounds that bind with antibodies, but with different affinities. In this regard, an important characteristic of an immunoassay is its cross-reactivity: the possibility of detecting various compounds in comparison with a certain standard. Based on cross-reactivity, analytical systems are assessed as either high-selective (responding strictly to a specific compound) or low-selective (responding to a number of similar compounds). The present study demonstrates that cross-reactivity is not an intrinsic characteristic of antibodies but can vary for different formats of competitive immunoassays using the same antibodies. Assays with sensitive detection of markers and, accordingly, implementation at low concentrations of antibodies and modified (competing) antigens are characterized by lower cross-reactivities and are, thus, more specific than assays requiring high concentrations of markers and interacting reagents. This effect was confirmed by both mathematical modeling and experimental comparison of an enzyme immunoassay and a fluorescence polarization immunoassay of sulfonamides and fluoroquinolones. Thus, shifting to lower concentrations of reagents decreases cross-reactivities by up to five-fold. Moreover, the cross-reactivities are changed even in the same assay format by varying the ratio of immunoreactants’ concentrations and shifting from the kinetic or equilibrium mode of the antigen-antibody reaction. The described patterns demonstrate the possibility of modulating immunodetection selectivity without searching for new binding reactants.

Preparation and Characterization of Monoclonal Antibodies with High Affinity and Broad Class Specificity against Zearalenone and Its Major Metabolites

This study aimed to detect and monitor total Zearalenone (ZEN) and its five homologs (ZENs) in cereals and feed. The monoclonal antibodies (mAbs) with a high affinity and broad class specificity against ZENs were prepared, and the conditions of a heterologous indirect competitive ELISA (icELISA) were preliminarily optimized based on the ZEN mAbs. The immunogen ZEN-BSA was synthesized using the oxime active ester method (OAE) and identified using infrared (IR) and ultraviolet (UV). The coating antigen ZEN-OVA was obtained via the 1,4-butanediol diglycidyl ether method (BDE). Balb/c mice were immunized using a high ZEN-BSA dose with long intervals and at multiple sites. A heterologous indirect non-competitive ELISA (inELISA) and an icELISA were used to screen the suitable cell fusion mice and positive hybridoma cell lines. The ZEN mAbs were prepared by inducing ascites in vivo. The standard curve was established, and the sensitivity and specificity of the ZEN mAbs were determined under the optimized icELISA conditions. ZEN-BSA was successfully synthesized at a conjugation ratio of 17.2:1 (ZEN: BSA). Three hybridoma cell lines, 2D7, 3C2, and 4A10, were filtered, and their mAbs corresponded to an IgG1 isotype with a κ light chain. The mAbs titers were between (2.56 to 5.12) × 10² in supernatants and (1.28 to 5.12) × 10⁵ in the ascites. Besides, the 50% inhibitive concentration (IC50) values were from 18.65 to 31.92 μg/L in the supernatants and 18.12 to 31.46 μg/L in the ascites. The affinity constant (Ka) of all of the mAbs was between 4.15 × 10⁹ and 6.54 × 10⁹ L/mol. The IC50 values of mAb 2D7 for ZEN, α-ZEL, β-ZEL, α-ZAL, β-ZAL and ZAN were 17.23, 16.71, 18.27, 16.39, 20.36 and 15.01 μg/L, and their cross-reactivities (CRs, %) were 100%, 103.11%, 94.31%, 105.13%, 84.63%, and 114.79%, respectively, under the optimized icELISA conditions. The limit of detection (LOD) for ZEN was 0.64 μg/L, and its linear working range was between 1.03 and 288.55 μg/L. The mAbs preparation and the optimization of icELISA conditions promote the potential development of a rapid test ELISA kit, providing an alternative method for detecting ZEN and its homologs in cereals and feed.

Monitoring of the Organophosphate Pesticide Chlorpyrifos in Vegetable Samples from Local Markets in Northern Thailand by Developed Immunoassay

Chlorpyrifos is an organophosphate pesticide that is wildly used among farmers for crop protection. However, there are concerns regarding its contamination in the environment and food chain. In the present study, an in-house indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) specific for detecting chlorpyrifos is developed and validated against gas chromatography–flame photometric detection (GC-FPD) as the conventional method. The developed ic-ELISA was used for detecting chlorpyrifos residue in vegetable samples. The developed ic-ELISA showed good sensitivity to chlorpyrifos at an IC₅₀ of 0.80 µg/kg, with low cross-reactivity to other organophosphate pesticides. The 160 samples were collected from local markets located in the Chiang Rai, Chiang Mai, and Nan provinces in northern Thailand. The positive rate of chlorpyrifos residues in the vegetable samples was 33.8%, with the highest levels found in cucumbers, coriander, and morning glory, at 275, 145, and 35.3 µg/kg, respectively. The highest median levels of chlorpyrifos found in the detected samples were Chinese cabbage (332 μg/kg), cucumber (146.3 μg/kg) and Chinese Kale (26.95 μg/kg). The developed ic-ELISA is suitable for the rapid quantitation of chlorpyrifos residues.

Simultaneous detection of imidacloprid and parathion by the dual-labeled time-resolved fluoroimmunoassay

A highly sensitive direct dual-labeled time-resolved fluoroimmunoassay (TRFIA) to detect parathion and imidacloprid simultaneously in food and environmental matrices was developed. Europium (Eu(3+)) and samarium (Sm(3+)) were used as fluorescent labels by coupling separately with L1-Ab and A1P1-Ab. Under optimal assay conditions, the half-maximal inhibition concentration (IC50) and limit of detection (LOD, IC10) were 10.87 and 0.025 μg/L for parathion and 7.08 and 0.028 μg/L for imidacloprid, respectively. The cross-reactivities (CR) were negligible except for methyl-parathion (42.4 %) and imidaclothiz (103.4 %). The average recoveries of imidacloprid ranged from 78.9 to 104.2 % in water, soil, rice, tomato, and Chinese cabbage with a relative standard deviation (RSD) of 2.4 to 11.6 %, and those of parathion were from 81.5 to 110.9 % with the RSD of 3.2 to 10.5 %. The results of TRFIA for the authentic samples were validated by comparison with gas chromatography (GC) analyses, and satisfactory correlations (parathion: R (2) = 0.9918; imidacloprid: R (2) = 0.9908) were obtained. The results indicate that the dual-labeled TRFIA is convenient and reliable to detect parathion and imidacloprid simultaneously in food and environmental matrices.

A sensitive monoclonal antibody-based enzyme-linked immunosorbent assay for the detection of bifenthrin in a chemical soil barrier

A sensitive monoclonal antibody-based enzyme monoclonal antibody-based enzyme-linked immunosorbent assay (ELISA) was developed to detect bifenthrin in a chemical soil barrier for termite control. LBc ((2-methyl[1,1-biphenyl]-3-methoxy) carbonyl propionic acid) was conjugated to bovine serum albumin (BSA) for producing monoclonal antibody. After optimization, the IC50 and limit of detection (LOD, IC10) were 0.05 mg L(-1) and 0.004 mg L(-1), respectively. The sensitivity was improved 40-fold compared to polyclonal antibody-based ELISA reported earlier. No cross-reactivity was measured for the other analogues such as cyhalothrin, cyhalothric acid, cypermethrin, deltamethrin, fenpropathrin, fenvalerate, ethofenprox and tetramethrin except 2-methyl-3-biphenylmethyanol. Spiked recoveries were between 83.5% and 104.7% for the detection of bifenthrin in loess, red soil and black soil. All the relative standard deviations (RSDs) were less than or equal to 15.0%. Moreover, the ELISA for authentic samples showed reliability and high correlation with gas chromatography. The developed ELISA is an alternative tool for simple, sensitive and accurate monitoring of bifenthrin in chemical soil barriers.

Immunodiagnostics and immunosensor design (IUPAC Technical Report)

This work compiles information on the principles of diagnostic immunochemical methods and the recent advances in this field. It presents an overview of modern techniques for the production of diagnostic antibodies, their modification with the aim of improving their diagnostic potency, the different types of immunochemical detection systems, and the increasing diagnostic applications for human health that include specific disease markers, individualized diagnosis of cancer subtypes, therapeutic and addictive drugs, food residues, and environmental contaminants. A special focus lies in novel developments of immunosensor techniques, promising approaches to miniaturized detection units and the associated microfluidic systems. The trends towards high-throughput systems, multiplexed analysis, and miniaturization of the diagnostic tools are discussed. It is also made evident that progress in the last few years has largely relied on novel chemical approaches.

Development of a heterologous enzyme-linked immunosorbent assay for organophosphorus pesticides with phage-borne peptide

An enzyme-linked immunosorbent assay (ELISA) was developed to detect organophosphorus pesticides using a phage-borne peptide that was isolated from a cyclic 8-residue peptide phage library. The IC₅₀ values of the phage ELISA ranged from 1.4 to 92.1 μg L^-1 for eight organophosphorus pesticides (parathion-methyl, parathion, fenitrothion, cyanophos, EPN, paraoxon-methyl, paraoxon, fenitrooxon). The sensitivity was improved 120- and 2-fold compared to conventional homologous and heterologous ELISA, respectively. The selectivity of the phage ELISA was evaluated by measuring its cross-reactivity with 23 organophosphorus pesticides, among which eight were the main cross-reactants. The spike recoveries were between 66.1% and 101.6% for the detection of single pesticide residues of parathion-methyl, parathion and fenitrothion in Chinese cabbage, apple and greengrocery, and all of the coefficient of variation were less than or equal to 15.9%. Moreover, the phage ELISA results were validated by gas chromatography. The results indicate that isolating phage-borne peptides from phage display libraries is an alternative method for the development of a heterologous immunoassay and that the developed assay has a lower limit of detection than the chemically synthesized competitor assay.

Heterologous antigen selection of camelid heavy chain single domain antibodies against tetrabromobisphenol A

Tetrabromobisphenol A (TBBPA) is a ubiquitous flame retardant. A high-throughput immunoassay would allow for monitoring of human and environmental exposures as a part of risk assessment. Naturally occurring antibodies in camelids that are devoid of light chain, show great promise as an efficient tool in monitoring environmental contaminants, but they have been rarely used for small molecules. An alpaca was immunized with a TBBPA hapten coupled to thyroglobulin and a variable domain of heavy chain antibody (VHH) T3-15 highly selective for TBBPA was isolated from a phage displayed VHH library using heterologous coating antigens. Compared to the VHHs isolated using homologous antigens, VHH T3-15 had about a 10-fold improvement in sensitivity in an immunoassay. This assay, under the optimized conditions of 10% methanol in the assay buffer (pH 7.4), had an IC50 for TBBPA of 0.40 ng mL(-1) and negligible cross reactivity (<0.1%) with other tested analogues. After heating the VHH at 90 °C for 90 min about 20% of the affinity for coating antigen T3-BSA remained. The recoveries of TBBPA from spiked soil and fetal bovine serum samples ranged from 90.3% to 110.7% by ELISA and agreed well with a liquid chromatography-tandem mass spectrometry method. We conclude the many advantages of VHH make them attractive for the development of immunoassays to small molecules.

Enzyme-linked immunosorbent assay for the determination of five organophosphorus pesticides in camellia oil

A matrix solid-phase dispersion and direct competitive enzyme-linked immunosorbent assay (MSPD-ELISA) was developed for five organophosphorus pesticides (OPs) in camellia oil. Seven haptens with different substituents in the aromatic ring were used to prepare different competitors; the ELISA showed highest sensitivity and specificity to OPs when the competitor had moderate heterology to the immunizing hapten. Several assay conditions were optimized to increase the ELISA sensitivity. The optimized ELISA for five OPs had 50% inhibitory concentrations of 6.3 ng/ml (parathion), 18.9 ng/ml (methyl parathion), 120.7 ng/ml (fenitrothion), 110.4 ng/ml (fenthion), and 20.7 ng/ml (phoxim). The average recoveries of five OPs in camellia oil ranged from 75.7 to 105.3%, with the interassay coefficient of variations ranging from 6.0 to 13.4%. Compared with the results previously reported, the ELISA that was developed in the present study showed a much higher sensitivity. Additionally, MSPD was used in the sample preparation to minimize the matrix effect. Recoveries from the method developed here were in agreement with those obtained by gas chromatography, which indicated that the detection performance of the MSPD-ELISA could meet the regulatory requirements of different governments and international organizations.

Heterologous screening of hybridomas for the development of broad-specific monoclonal antibodies against deoxynivalenol and its analogues

Hapten heterology was introduced into the steps of hybridoma selection for the development of monoclonal antibodies (MAbs) against deoxynivalenol (DON). Firstly, a novel heterologous DON hapten was synthesised and covalently coupled to proteins (i.e. bovine serum albumin (BSA), ovalbumin and horseradish peroxidase) using the linkage of cyanuric chloride (CC). After immunisation, antisera from different DON immunogens were checked for the presence of useful antibodies. Next, both homologous and heterologous enzyme-linked immunosorbent assays were conducted to screen for hybridomas. It was found that heterologous screening could significantly reduce the proportion of false positives and appeared to be an efficient approach for selecting hybridomas of interest. This strategy resulted in two kinds of broad-selective MAbs against DON and its analogues. They were quite distinct from other reported DON-antibodies in their cross-reactivity profiles. A unique MAb 13H1 derived from DON-CC-BSA immunogen could recognise DON and its analogues in the order of HT-2 toxin ≯ 15-acetyl-DON ≯ DON ≯ nivalenol, with IC50 ranging from 1.14 to 7.69 μg/ml. Another preferable MAb 10H10 generated from DON-BSA immunogen manifested relatively similar affinity to DON, 3-acetyl-DON and 15-acetyl-DON, with IC50 values of 22, 15 and 34 ng/ml, respectively. This is the first broad-specific MAb against DON and its two acetylated forms and thus it can be used for simultaneous detection of the three mycotoxins.

A molecularly imprinted electrochemical enzymeless sensor based on functionalized gold nanoparticle decorated carbon nanotubes for methyl-parathion detection

Schematic of MP MIP sensor and the possible mechanism.

Development of an enzyme linked immunosorbent assay and an immunochromatographic assay for detection of organophosphorus pesticides in different agricultural products

Objective

Organophosphorus (OP) pesticides are considered hazardous substances because of their high toxicity to nontarget species and their persistence in the environment and agricultural products. Therefore, it is important to develop a rapid, sensitive, and economical method for detecting OP pesticides and their residues in food and the environment.

Methods

A broad, selective monoclonal antibody (MAb) for organophosphorus pesticides was produced. Based on the MAb, an enzyme linked immunosorbent assay (ELISA) and an immunochromatography assay (ICA) for detecting OP pesticides in different agricultural products were developed using a binding inhibition format on microtiter plates and a membrane strip, respectively.

Results

Under the optimized conditions, the IC₅₀ values of the ELISA ranged from 3.7 to 162.2 ng mL^–1 for the 8 OP pesticides. The matrix interferences of Apple, Chinese cabbage, and greengrocery were removed by 40-fold dilution, the recoveries from spiked samples ranged from 79.1% to 118.1%. The IC₅₀ values of ICA for the 8 OP pesticides ranged from 11.8 to 470.4 ng mL⁻¹. The matrix interference was removed from the Chinese cabbage and Apple samples with 5-fold dilution, and the interference was removed from the greengrocery samples with 20-fold dilution. The recoveries from the spiked samples ranged between 70.6 and 131.9%. The established ELISA and ICA were specific selectivity for the 8 OP pesticides.

Conclusions

The established ELISA is a sensitive screening method for the detection of OP pesticides, but the ELISA detection method depends on a laboratory platform and requires a relative long assay time and several steps operation. The established ICA is very useful as a screening method for the quantitative, semi-quantitative or qualitative detection of OP pesticides in agricultural products, and it has advantages over ELISA methods with regard to factors such as the testing procedure, testing time, and matrix interferences, among others.

Development of a monoclonal antibody-based competitive indirect enzyme-linked immunosorbent assay for furaltadone metabolite AMOZ in fish and shrimp samples

A monoclonal antibody-based competitive indirect enzyme-linked immunosorbent assay (ELISA) with improved sensitivity and specificity for the determination of furaltadone metabolite 5-methylamorpholino-3-amino-2-oxazolidone (AMOZ) was described. AMOZ was derivatized with 2-(3-formylphenoxy)acetic acid and coupled with bovine serum albumin to form a novel immunogen. BABL/c mice were immunized and monoclonal antibody specific to the nitrophenyl derivative of AMOZ (NP-AMOZ) was produced and characterized. Four other haptens with different heterology to the immunizing hapten were synthesized and coupled to ovalbumin as coating antigens to study the effect of heterologous coating on assay sensitivity. Under the optimized heterologous coating format, the competitive indirect ELISA showed very high sensitivity to NP-AMOZ, with an IC(50) of 0.14 μg/L and limit of detection of 0.01 μg/L. The assay showed high specificity toward NP-AMOZ, and negligible cross-reactivity with analogous compounds was observed. The average recoveries of AMOZ from spiked fish and shrimp samples were estimated to range from 81.0 to 104.0%, with coefficients of variation below 20%. Good correlation was obtained between the results of ELISA analysis and of standard liquid chromatography-tandem mass spectrometry analysis. These results indicated that the proposed ELISA is ideally suited as a monitoring method for AMOZ residues at trace level.

Comparison of homologous and heterologous formats in nanocolloidal gold-based immunoassays for parathion residue determination

The effectiveness of homologous and heterologous formats in a nanocolloidal gold-based immunoassay for pesticide residue determination was investigated. Parathion, one of the most toxic organophosphorus pesticides, was used as the target analyte. One-step homologous and heterologous test strips based on a nanocolloidal gold-labeled monoclonal antibody were developed for the rapid detection of parathion residues. The results showed that the heterologous format was more effective than the homologous format, being more sensitive, more specific to parathion and more tolerant of matrix interferences. The best competitive hapten was found to have a moderate heterology and the opposite electronic distribution to the immunizing hapten. The detection limits for parathion using the preferred heterologous strip were 1 μg/L in water samples and 5 μg/kg in soil and food samples.