Hapten Design and Antibody Generation for Immunoanalysis of Spirotetramat and Spirotetramat-enol

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.

Development of immunoassay based on a specific antibody for sensitive detection of nicosulfuron in environment

Nicosulfuron, one of the most widely used selective herbicides in corn field, can effectively control annual and perennial grass weeds, sedges, and some broadleaf weeds. The residual phytotoxicity of nicosulfuron in soil and water has become increasingly prominent. Therefore, an efficient method for detection of nicosulfuron was critical to ensure the sustainable and healthy development of agriculture and the ecological environment. In this paper, five nicosulfuron haptens which contained carboxyl group or aldehyde groups were designed and synthesized, and an indirect competitive immunoassay was developed for the first time. The assay showed an IC50 of 8.42 ng/mL and had negligible cross reactivities toward other sulfonylurea herbicides. In the spike and recovery studies, the recovery rate from soil samples was 95 %-104 %, and that of wheat roots was 92 %-98 %, which showed a good correlation with LC-MS analysis for nicosulfuron. The immunoassay was then used to quantify nicosulfuron concentration which could cause the obvious phytotoxic symptoms to wheat. Obvious symptoms of nicosulfuron phytotoxicity in wheat root was observed at the concentration of 0.068 ± 0.006 mg/kg (ELISA result) which was consistent with 0.072 ± 0.007 mg/kg obtained by LC-MS. The developed immunoassay method is an effective tool for environment contamination monitoring.

Design of a novel hapten and development of a sensitive monoclonal immunoassay for dicamba analysis in environmental water samples

Weed resistance to glyphosate has been a driving force behind the increased use of alternative herbicides in agriculture. Recently, dicamba-tolerant recombinant plants were introduced to the market, which may result in residues of this agrochemical contaminating environmental waters. Given that restrictions on the use of dicamba have consequently been established by regulatory agencies, it is therefore also desirable to conduct extensive controls on dicamba residues. Immunoassays are currently the most powerful bioanalytical technology for the rapid monitoring of chemical residues and contaminants. In the present study, a novel hapten was designed maintaining unaltered all the antigenic moieties of the target molecule, and this was used to generate high-affinity monoclonal antibodies against dicamba for the first time. Additionally, a collection of haptens with different linker composition or linker tethering site was synthesized and conjugated to proteins. Using these novel immunoreagents, a direct competitive enzyme-linked immunosorbent assay with a limit of detection for dicamba of 0.24 ng/mL was developed and validated. Analysis of water samples from different origins afforded recovery values between 90 % and 120 %, and coefficients of variation below 20 % were obtained. These results indicate that the developed immunochemical assay is suitable for the rapid determination of dicamba residues in environmental water samples.

Highly specific nanobody against herbicide 2,4-dichlorophenoxyacetic acid for monitoring of its contamination in environmental water

2,4-dichlorophenoxyacetic acid (2,4-D), a widely used herbicide, is a small organic chemical pollutant in the environment. To develop a nanobody-based immunoassay for monitoring trace levels of 2,4-D, a step-wise strategy for the generation of nanobodies highly specific against this small chemical was employed. Firstly, we synthesized three novel haptens mimicking 2,4-D and assessed their influence on the sensitivity and specificity of the existing antibody-based assay. Polyclonal antibodies (pAb) from rabbits showed good sensitivity and moderate specificity for 2,4-D, pAb from llama based on selected haptens showed similar performance when compared to those from rabbits. Secondly, nanobodies derived from llama were generated for 2,4-D by an effective procedure, including serum monitoring and one-step library construction. One nanobody, NB3-9, exhibited good sensitivity against 2,4-D (IC₅₀ = 29.2 ng/mL) had better specificity than the rabbit pAb#1518, with no cross-reactivities against the 2,4-D analogs tested. Thirdly, one-step fluorescent enzyme immunoassay (FLEIA) for 2,4-D based on a nanobody-alkaline phosphatase (AP) fusion was developed with IC₅₀ of 1.9 ng/mL and a linear range of 0.4-8.6 ng/mL. Environmental water samples were analyzed by FLEIA and LC-MS/MS for comparison, and the results were consistent between both methods. Therefore, the proposed step-wise strategy from hapten design to nanobody-AP fusion production was successfully conducted, and the resulting nanobody based FLEIA was demonstrated as a convenient tool to monitor 2,4-D residuals in the environment.

Enzyme and lateral flow monoclonal antibody-based immunoassays to simultaneously determine spirotetramat and spirotetramat-enol in foodstuffs

Spirotetramat is employed worldwide to fight insect pests due to its high efficiency. This chemical is quickly metabolized by plants into spirotetramat-enol, so current regulations establish that both compounds must be determined in foodstuffs for monitoring purposes. Nowadays, immunochemical methods constitute rapid and cost-effective strategies for chemical contaminant analysis at trace levels. However, high-affinity binders and suitable bioconjugates are required. In this study, haptens with opposite functionalisation sites were synthesized in order to generate high-affinity monoclonal antibodies. A direct competitive enzyme-linked immunosorbent assay with an IC50 value for the sum of spirotetramat and spirotetramat-enol of 0.1 μg/L was developed using selected antibodies and a novel heterologous bioconjugate carrying a rationally-designed hapten. Studies with fortified grape, grape juice, and wine samples showed good precision and accuracy values, with limits of quantification well below the maximum residue limits. Excellent correlation of results was observed with a standard reference chromatographic method. As a step forward, a lateral flow immunoassay was developed for onsite screening analysis of spirotetramat in wine. This assay was successfully validated according to Regulation 519/2014/EU for semi-quantitative methods at concentrations in line with the legal levels of spirotetramat and spirotetramat-enol in grapes, with a satisfactory false suspect rate below 2%.

Hapten Synthesis, Antibody Development, and a Highly Sensitive Indirect Competitive Chemiluminescent Enzyme Immunoassay for Detection of Dicamba

Although dicamba has long been one of the most widely used selective herbicides, some U.S. states have banned the sale and use of dicamba because of farmers complaints of drift and damage to nonresistant crops. To prevent illegal use of dicamba and allow monitoring of nonresistant crops, a rapid and sensitive method for detection of dicamba is critical. In this paper, three novel dicamba haptens with an aldehyde group were synthesized, conjugated to the carrier protein via a reductive-amination procedure and an indirect competitive chemiluminescent enzyme immunoassay (CLEIA) for dicamba was developed. The assay showed an IC50 of 0.874 ng/mL which was over 15 times lower than that of the conventional enzyme immunoassay. The immunoassay was used to quantify dicamba concentrations in field samples of soil and soybean obtained from fields sprayed with dicamba. The developed CLEIA showed an excellent correlation with LC-MS analysis in spike-and-recovery studies, as well as in real samples. The recovery of dicamba ranged from 86 to 108% in plant samples and from 105 to 107% in soil samples. Thus, this assay is a rapid and simple analytical tool for detecting and quantifying dicamba levels in environmental samples and potentially a great tool for on-site crop and field monitoring.