Hapten synthesis, monoclonal antibody generation, and development of competitive immunoassays for the analysis of picoxystrobin in beer

Re-assessment of monoclonal antibodies against diclofenac for their application in the analysis of environmental waters

The non-steroidal anti-inflammatory drug (NSAID) diclofenac (DCF) is an important environmental contaminant occurring in surface waters all over the world, because, after excretion, it is not adequately removed from wastewater in sewage treatment plants. To be able to monitor this pollutant, highly efficient analytical methods are needed, including immunoassays. In a medical research project, monoclonal antibodies against diclofenac and its metabolites had been produced. Based on this monoclonal anti-DCF antibody, a new indirect competitive enzyme-linked immunosorbent assay (ELISA) was developed and applied for environmental samples. The introduction of a spacer between diclofenac and the carrier protein in the coating conjugate led to higher sensitivity. With a test midpoint of 3 μg L-1 and a measurement range of 1-30 μg L-1, the system is not sensitive enough for direct analysis of surface water. However, this assay is quite robust against matrix influences and can be used for wastewater. Without adjustment of the calibration, organic solvents up to 5%, natural organic matter (NOM) up to 10 mg L-1, humic acids up to 2.5 mg L-1, and salt concentrations up to 6 g L-1 NaCl and 75 mg L-1 CaCl2 are tolerated. The antibody is also stable in a pH range from 3 to 12. Cross-reactivity (CR) of 1% or less was determined for the metabolites 4'-hydroxydiclofenac (4'-OH-DCF), 5-hydroxydiclofenac (5-OH-DCF), DCF lactam, and other NSAIDs. Relevant cross-reactivity occurred only with an amide derivative of DCF, 6-aminohexanoic acid (DCF-Ahx), aceclofenac (ACF) and DCF methyl ester (DCF-Me) with 150%, 61% and 44%, respectively. These substances, however, have not been found in samples. Only DCF-acyl glucuronide with a cross-reactivity of 57% is of some relevance. For the first time, photodegradation products were tested for cross-reactivity. With the ELISA based on this antibody, water samples were analysed. In sewage treatment plant effluents, concentrations in the range of 1.9-5.2 μg L-1 were determined directly, with recoveries compared to HPLC-MS/MS averaging 136%. Concentrations in lakes ranged from 3 to 4.4 ng L-1 and were, after pre-concentration, determined with an average recovery of 100%.

Development of a Time-Resolved Fluorescent Microsphere Test Strip for Rapid, On-Site, and Sensitive Detection of Picoxystrobin in Vegetables

Picoxystrobin (PIC) is a fungicide extensively used for disease control in both crops and vegetables. Residues of PIC in vegetables pose a potential threat to human health due to their accumulation in the food chain. In this study, a specific PIC monoclonal antibody (mAb) was developed by introducing a carboxylic acid arm into PIC and subsequently preparing a hapten and an artificial antigen. A sensitive and rapid time-resolved fluorescence immunochromatographic assay (TRFICA) was established based on the mAb. Subsequently, using a time-resolved fluorescent microsphere (TRFM) as signal probe, mAbs and microspheres were covalently coupled. The activated pH, the mAb diluents, the mAb amount, and the probe amount were optimized. Under optimized conditions, the quantitative limits of detection (qLOD) of PIC in cucumber, green pepper, and tomato using TRFICA were established at 0.61, 0.26, and 3.44 ng/mL, respectively; the 50% inhibiting concentrations (IC50) were 11.76, 5.29, and 37.68 ng/mL, respectively. The linear ranges were 1.81-76.71, 0.80-35.04, and 8.32-170.55 ng/mL, respectively. The average recovery in cucumber, green pepper, and tomato samples ranged from 79.8% to 105.0%, and the corresponding coefficients of variation (CV) were below 14.2%. In addition, 15 vegetable samples were selected and compared with the results obtained using ultra-performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS). The results revealed a high degree of concordance between the proposed method and UPLC-MS/MS. In conclusion, the devised TRFICA method is a valuable tool for rapid, on-site, and highly sensitive detection of PIC residues in vegetables.

Preparing monoclonal antibodies and developing immunochromatographic assay strips for the determination of propamocarb levels

Propamocarb is a carbamate fungicide used to control Phytophthora disease. Frequent and large-scale use of propamocarb means that it poses a potential threat to the health of consumers. Monoclonal antibodies against propamocarb were prepared using a hapten of propamocarb that was generated by introducing a benzene ring and a carboxyl group into the structure of propamocarb. A lateral flow immunoassay strip was developed for the detection of propamocarb in tomato and cucumber samples using the gold nanoparticle-labeled antibody. The immunoassay strip was found to provide a visible limit of detection was 5 ng/g and the cut-off value was 250 ng/g for propamocarb in food samples. For quantitative analysis, the calculated limits of detection (LODs) of the immunoassay strip were 1.43 ng/g and 0.44 ng/g in cucumber and tomato, respectively. Using the immunoassay strip, the average recoveries ranged from 95.5 ± 5.4% to 108.8 ± 6.8%, with CVs of 3.1-6.2% for the cucumber, and the average recoveries were 95.1 ± 6.5%-111.9 ± 4.2%, with CVs ranging from 3.7% to 6.8% for tomato samples. All the results demonstrated that the immunoassay strip was suitable for the detection of propamocarb in fruits and vegetables.

Electrofusion preparation of anti-triazophos monoclonal antibodies for development of an indirect competitive enzyme-linked immunosorbent assay

Immunoassays have been widely used to detect small molecular contaminants due to the advantages of simplicity, high throughout and low-cost. Antibodies are essential reagents of immunoassays, their quality directly determines the characteristics of immunoassays. In this study, the monoclonal antibodies (mAbs) of triazophos were prepared by electrofusion, and used to develop an indirect competitive enzyme-linked immunosorbent assay (ic-ELISA). Under the optimal electrofusion conditions (cells treatment with pronase, the alternating electric field strength of 45 V cm^-1, the direct current voltage of 3 kV), the fusion efficiency was 1.104 ± 0.063‱, which was improved more than 4-fold compared with the chemical fusion method (0.255 ± 0.089‱). Three hybrid cell lines that can stably secrete the anti-triazophos mAbs were obtained. The cell line 4G6F10 showed the highest sensitivity, which was used to generate mAb and develop an ic-ELISA. After optimization, the 50% inhibition concentration (IC₅₀), limit of detection (LOD) and linear range (IC₁₀-IC₉₀) of the ic-ELISA were 0.32 ng mL^-1, 0.08 ng mL^-1 and 0.08-2.17 ng mL^-1, respectively. There was no significant cross-reactivity with the analogues of triazophos. The average recoveries of triazophos in spiked samples were 77.5%-89.3% with the relative standard deviations of 0.1%-9.2%. In addition, the ic-ELISA showed good repeatability, reproducibility and accuracy for the analysis of apple samples spiked with triazophos.

Synthesis of Zearalenone Immunogen and Comparative Analysis of Antibody Characteristics

Background

This study aimed to explore the zearalenone (ZEN) immunogen synthesis method, immunogenicity, and antibody characteristics and to lay a foundation for the establishment of immunoassay methods for ZEN single residue and ZEN and its analogs total residue.

Methods

Based on the molecular structure and active sites of ZEN, oxime active ester (OAE), condensation mixed anhydride (CMA), formaldehyde (FA), and 1,4-butanediol diglycidyl ether method (BDE) were designed and used for immunogen (ZEN-BSA) synthesis. The immunogens were identified by infrared (IR) and ultraviolet (UV) spectra and gel electrophoresis (SDS-PAGE) and were then used to immunize Balb/c mice to prepare ZEN polyclonal antibody (ZEN pAb). The titers and sensitivity of the ZEN pAb were determined by indirect noncompetitive ELISA (inELISA) and indirect competitive ELISA (icELISA), respectively, and its specificity was assessed by the cross-reaction test (CR).

Results

ZEN-BSA was successfully synthesized, and the molecular binding ratios of ZEN to BSA were 17.2 : 1 (OAE), 14.6 : 1 (CMA), 9.7 : 1 (FA), and 8.3 : 1 (BDE), respectively. The highest inELISA titers of ZEN pAb of each group were 1 : (6.4 × 10³) (OAE), 1 : (3.2 × 10³) (CMA), 1 : (1.6 × 10³) (FA), and 1 : (1.6 × 10³) (BDE), respectively. The 50% inhibition concentrations (IC50) for ZEN by icELISA of each group were 11.67 μg/L (OAE), 16.29 μg/L (CMA), 20.92 μg/L (FA) and 24.36 μg/L (BDE), respectively. ZEN pAb from the mice immunized with ZEN-BSA (OAE) and ZEN-BSA (CMA) had class broad specificity to ZEN and its analogs. The CRs of ZEN pAb with α-ZAL, β-ZAL, α-ZOL, β-ZOL, and ZON were 36.53%, 16.98%, 64.33%, 20.16%, and 10.66%, respectively. ZEN pAb from the mice immunized with ZEN-BSA (FA) and ZEN-BSA (BDE) had high specificity for ZEN. The CRs of ZEN pAb with its analogs were all less than 1.0%.

Conclusion

This study demonstrated that the preparation of the class broad-specificity antibodies of ZEN and its analogs can be achieved by immunizing animals with the immunogen ZEN-BSA prepared by the OAE method, while the preparation of highly specific antibodies can be achieved by immunizing animals with the immunogen ZEN-BSA prepared by the FA method. These findings lay the material and technical foundation for immunoassay of ZEN single residue and ZEN and its analogs total residue.

Rationally designed haptens for highly sensitive monoclonal antibody-based immunoanalysis of fenhexamid

Immunochemical methods have been consolidated during the last few years as complementary analytical strategies for chemical contaminant and residue determination. However, generation of suitable immunoreagents for small organic molecules demands adequate hapten design. In this study, fenhexamid was considered as a model compound and novel haptens were designed and synthesized in order to evaluate the influence of the linker tethering site on antibody binding properties and immunoassay parameters. Haptens were conceived with the spacer arm at different positions, while the more antigenic aromatic moiety was kept free. The synthesis of these functionalized compounds was accomplished by total construction of the molecule through several steps. This strategy afforded very high-affinity monoclonal antibodies specific of fenhexamid, with IC50 values around or below 0.1 nM. Using these novel immunoreagents, a direct competitive enzyme-linked immunosorbent assay with a remarkably low limit of detection (4 ng L-1) was developed for the determination of fenhexamid residues. The selected immunoassay was investigated in terms of trueness, precision, repeatability, and robustness. The QuEChERS extraction methodology was applied to fortified samples and recoveries between 83% and 113%, with relative standard deviations below 20%, were observed. Moreover, contaminated and blind spiked samples were measured by the developed immunoassay and by ultra-performance liquid chromatography coupled to tandem mass spectrometry, showing statistically comparable results.

Biodegradation of pyraclostrobin by two microbial communities from Hawaiian soils and metabolic mechanism

Pyraclostrobin has been widely and long-termly applicated to agricultural fields. The removal of pyraclostrobin from ecological environment has received wide attention. In this study, using sequential enrichments with pyraclostrobin as a sole carbon source, two microbial communities (HI2 and HI6) capable of catabolizing pyraclostrobin were obtained from Hawaiian soils. The microfloras analysis indicated that only Proteobacteria and Bacteroides could survive in HI2-soil after acclimatization, whereas the number of Proteobacteria in HI6-soil accounted for more than 99%. The percentages of Pseudomonas in the HI2 and HI6 microfloras were 69.3% and 59.3%, respectively. More than 99% of pyraclostrobin (C₀ = 100 mg L^-1) was degraded by the HI2 and HI6 microorganisms within five days. A unique metabolite was identified by high performance liquid chromatography tandem quadrupole time-of-flight mass spectrometry (HPLC-QTOF-MS/MS). A metabolic pathway involving carbamate hydrolysis was proposed. The tertiary amine group of pyraclostrobin was hydrolyzed to primary amine group with the decarboxylation, which facilitated pyraclostrobin detoxification because carboxylester was an important functional group. The metabolic mechanism suggested that Pseudomonas expressing carboxylesterase might be able to degrade carbamate chemicals. Therefore, Pseudomonas might be an ideal candidate for expression and cloning of carbamate-degrading gene in genomics studies. The current study would have important implications in detoxification and bioremediation of carbamates through the CN bond cleavage of methyl carbamate.

Protein-Free Hapten-Carbon Nanotube Constructs Induce the Secondary Immune Response

Carbon nanotubes are novel technological tools with multiple applications. The interaction between such nanoparticles and living organisms is nowadays a matter of keen research by academic and private institutions. In this study, carbon nanotube constructs were investigated as delivery vehicles for immunostimulation and induction of the secondary immune response to a small organic molecule, namely, a hapten. Two types of nanoconstructs were prepared: on one hand, carbon nanotubes carrying a protein bioconjugate of a hapten covalently linked to the carbon surface, and on the other hand, covalent carbon nanotube constructs of the same model chemical compound without the carrier protein. Nanotube vehicles carrying a hapten-protein bioconjugate were demonstrated to stimulate the immune system and to induce a strong primary immune response against the hapten with as low as 0.1 μg of the model chemical. The influence of the different elements of those nanoconstructs over the immune response was investigated to better understand the molecular mechanisms that are involved. As expected, the presence of the carrier protein was shown to be necessary in order to trigger the immune response. Interestingly, we found that a remarkable secondary immune response to the model organic compound occurred in the absence of a carrier protein. Additionally, a satisfactory adjuvant effect of carbon nanotubes was observed and a potent immune response was elicited without employing an oil-based adjuvant.

Development of an indirect competitive enzyme-linked immunosorbent assay for screening ethopabate residue in chicken muscle and liver

Development of an indirect competitive enzyme-linked immunosorbent assay for screening ethopabate residue in chicken muscle and liver.

Assessment of strobilurin fungicides' content in soya-based drinks by liquid micro-extraction and liquid chromatography with tandem mass spectrometry

Seven strobilurin fungicides were pre-concentrated from soya-based drinks using dispersive liquid-liquid micro-extraction (DLLME) with a prior protein precipitation step in acid medium. The enriched phase was analysed by liquid chromatography (LC) with dual detection, using diode array detection (DAD) and electrospray-ion trap tandem mass spectrometry (ESI-IT-MS/MS). After selecting 1-undecanol and methanol as the extractant and disperser solvents, respectively, for DLLME, the Taguchi experimental method, an orthogonal array design, was applied to select the optimal solvent volumes and salt concentration in the aqueous phase. The matrix effect was evaluated and quantification was carried out using external aqueous calibration for DAD and matrix-matched calibration method for MS/MS. Detection limits in the 4-130 and 0.8-4.5 ng g(-1) ranges were obtained for DAD and MS/MS, respectively. The DLLME-LC-DAD-MS method was applied to the analysis of 10 different samples, none of which was found to contain residues of the studied fungicides.

Pharmacokinetics and bioavailability of tuftsin-derived T peptide, a promising antitumor agent, in beagles

Tuftsin, a natural phagocytosis-stimulating tetrapeptide, had aroused much interest in tumor immunotherapy, but the poor pharmacokinetics hampered its clinical developments, for that it was extremely susceptible to degradation by enzymolysis in vivo. T Peptide (TP) was a newly designed tuftsin derivative aimed to enhance stability and was proved to have significant antitumor activity. In this study, the pharmacokinetics and bioavailability of TP was first clarified in beagles with subcutaneous administration, by using a simple and robust competitive ELISA method. Dose-dependency and non-linear dynamics of TP after single-dose (2, 6 and 18 mg kg(-1), respectively) were found, and the half-time of TP was proved to reach 1.3-2.8 h. Multiple dosing of 6 mg kg(-1) once a day for 7 days resulted in a slight accumulation (accumulation index was 1.92 ± 0.43), indicating that the dosing interval in the following clinical trial needs to be extended. The absolute bioavailability of TP was 31.1 ± 6.2% after subcutaneous administration. These results first demonstrated the pharmacokinetics and bioavailability data of TP in vivo, which illustrated the potential druggability of TP and provided useful information for the dosage regimen design in the following clinical trials, as well as a simple and feasible analytical method for clinical sample analysis.

Haptens, bioconjugates, and antibodies for penthiopyrad immunosensing

Haptens, bioconjugates, and antibodies for highly sensitive immunochemical analysis of the new-generation fungicide penthiopyrad are described. Two haptens with equivalent carboxylated linkers were prepared, and the purified active esters were efficiently coupled to proteins. The results revealed slightly different antibody-eliciting capacities for the two synthetic derivatives. All of the produced antibodies were specific for penthiopyrad, and showed affinity values in the nanomolar range.

Ready Access to Proquinazid Haptens via Cross-Coupling Chemistry for Antibody Generation and Immunoassay Development

Bioconjugate preparation is a fundamental step for antibody generation and immunoassay development to small chemical compounds. For analytical targets holding in their structure an aryl halogen atom, cross-coupling reactions may be a simple and efficient way to obtain functionalized derivatives; thus offering great potential to elicit robust and selective immune responses after being coupled to immunogenic carrier proteins. However, substitution of the halogen atom by an aliphatic chain might eventually compromise the affinity and specificity of the resulting antibodies. In order to address this issue, proquinazid, a new-generation fungicide with outstanding performance, was chosen as model analyte. Two functionalized derivatives differing in spacer arm rigidity were synthesized by Sonogashira cross-coupling chemistry. These haptens were covalently coupled to bovine serum albumin and the resulting immunoconjugates were employed for rabbit vaccination. Antibodies were tested for proquinazid recognition by direct and indirect competitive immunoassay, and IC50 values in the low nanomolar range were found, thus demonstrating the suitability of this straightforward synthetic strategy for the generation of immunoreagents to compounds bearing an aryl halide. Following antibody characterization, competitive immunoassays were developed and employed to determine proquinazid residues in grape musts, and their analytical performance was satisfactorily validated by comparison with GC-MS. Besides having described the development of the first immunochemical method for proquinazid analysis, an efficient functionalization approach for analytes comprising aryl halides is reported.

Rational design of a fluopyram hapten and preparation of bioconjugates and antibodies for immunoanalysis

A fluopyram mimicking hapten was designed, immunochemically active bioconjugates were produced and high-affinity and specific antibodies to fluopyram were generated.

Sensitive time-resolved fluoroimmunoassay for quantitative determination of clothianidin in agricultural samples

Europium (Eu(3+))-labeled antibody was used as a fluorescent label to develop a highly sensitive time-resolved fluoroimmunoassay (TRFIA) for determination of clothianidin residues in agricultural samples. Toward this goal, the Eu(3+)-labeled polyclonal antibody and goat anti-rabbit antibody were prepared for developing and evaluating direct competitive TRFIA (dc-TRFIA) and indirect competitive TRFIA (ic-TRFIA). Under optimal conditions, the half-maximal inhibition concentration (IC50) and the limit of detection (LOD, IC10) of clothianidin were 9.20 and 0.0909 μg/L for the dc-TRFIA and 2.07 and 0.0220 μg/L for the ic-TRFIA, respectively. The ic-TRFIA has no obvious cross-reactivity with the analogues of clothianidin except for dinotefuran. The average recoveries of clothianidin from spiked water, soil, cabbage, and rice samples were estimated to range from 74.1 to 115.9 %, with relative standard deviations of 3.3 to 11.7 %. The results of TRFIA for the blind samples were largely consistent with gas chromatography (R (2) = 0.9902). The optimized ic-TRFIA might become a sensitive and satisfactory analytical method for the quantitative monitoring of clothianidin residues in agricultural samples.

Immunoreagents and competitive assays to fludioxonil

Fludioxonil is a new-generation fungicide widely used for postharvest fruit protection. The aim of this study was to produce hitherto unreported immunoreagents for Fludioxonil analysis by immunoassay. Derivatives of this agrochemical were synthesized with different linker tethering sites. Those functionalized haptens were activated, and the purified active esters were efficiently conjugated to different carrier proteins for immunogen and assay antigen preparation. Antibodies to Fludioxonil were raised in rabbits, and their selectivity and affinity were characterized, revealing the significance of the linker. Those antibodies were evaluated using homologous and heterologous conjugates by direct and indirect competitive ELISA formats. Finally, a pair of immunoreagents was identified showing an IC50 value for Fludioxonil of 5.7 μg/L.

Design and development of heterologous competitive immunoassays for the determination of boscalid residues

Antibodies and protein–hapten conjugates from novel boscalid derivatives were used to set up competitive immunoassays enabling sensitive detection of this modern fungicide.

Immunoassays for trifloxystrobin analysis. Part I. Rational design of regioisomeric haptens and production of monoclonal antibodies

Trifloxystrobin is one of the main active principles belonging to the strobilurin family of crop protection compounds. In this article, the synthesis of a battery of regioisomeric functionalized derivatives of trifloxystrobin is described. The same aliphatic linear carboxylated chain was introduced as spacer arm in all of the synthesized haptens, but it was located at different positions of the parent molecule. N,N'-Disuccinimidyl carbonate was employed for hapten activation, so the resulting N-hydroxysuccinimyl ester could be readily purified and efficiently coupled to proteins. After immunization and hybridoma generation, a collection of 20 mouse monoclonal antibodies from different immunizing haptens was obtained. The analytical performance of these immunoreagents was evaluated in terms of affinity and selectivity with the aim to develop rapid and practical immunochemical procedures for trifloxystrobin determination.

Immunoreagent generation and competitive assay development for cyprodinil analysis

Cyprodinil is an anilinopyrimidine fungicide applied worldwide for the prevention and treatment of highly destructive plant diseases in a large variety of crops, including cereals, fruits, and vegetables. This paper describes the development of the first reported immunoassays for cyprodinil. Two original haptens have been synthesized and conjugated to different carrier proteins, and polyclonal antibodies have been produced. Moreover, competitive enzyme-linked immunosorbent assays have been developed and characterized for the analysis of this widely used pesticide. The influence of organic solvents and buffer conditions over the assay analytical parameters was studied. The IC(50) values of the optimized immunoassays were 1.6 and 2.8 ng/mL for the direct and indirect formats, respectively. Quantitative recoveries were found using spiked apple and grape juice samples after a simple direct dilution, and a limit of quantification of 20 ng/mL for both fruit matrices was achieved. These immunoreagents could be very valuable for the sensitive, straightforward, and rapid monitoring of cyprodinil residues in foodstuffs.