Hapten synthesis, monoclonal antibody production and immunoassay development for direct detection of 4-hydroxybenzehydrazide in chicken, the metabolite of nifuroxazide

Advancements in the preparation technology of small molecule artificial antigens and their specific antibodies: a comprehensive review

Small molecules find extensive application in medicine, food safety, and environmental studies, particularly in biomedicine. Immunoassay technology, leveraging the specific recognition between antigens and antibodies, offers a superior alternative to traditional physical and chemical analysis methods. This approach allows for the rapid and accurate detection of small molecular compounds, owing to its high sensitivity, specificity, and swift analytical capabilities. However, small molecular compounds often struggle to effectively stimulate an immune response due to their low molecular weight, weak antigenicity, and limited antigenic epitopes. To overcome this, coupling small molecule compounds with macromolecular carriers to form complete antigens is typically required to induce specific antibodies in animals. Consequently, the preparation of small-molecule artificial antigens and the production of efficient specific antibodies are crucial for achieving precise immunoassays. This paper reviews recent advancements in small molecule antibody preparation technology, emphasizing the design and synthesis of haptens, the coupling of haptens with carriers, the purification and identification of artificial antigens, and the preparation of specific antibodies. Additionally, it evaluates the current technological shortcomings and limitations while projecting future trends in artificial antigen synthesis and antibody preparation technology.

Highly selective and sensitive immunoassays for flurogestone acetate analysis in goat milk: From rational hapten design and antibody production to assay development

The preparation of high specificity and affinity antibodies is challenging due to limited information on characteristic groups of haptens in traditional design strategy. In this study, we first predicted characteristic groups of flurogestone acetate (FGA) using quantitative analysis of molecular surface combined with atomic charge distribution. Subsequently, FGA haptens were rationally designed to expose these identified characteristic groups fully. As a result, seven monoclonal antibodies were obtained with satisfactory performance, exhibiting IC50 values from 0.17 to 0.45 μg/L and negligible cross-reactivities below 1% to other 18 hormones. The antibody recognition mechanism further confirmed hydrogen bonds and hydrophobic interactions involving predicted FGA characteristic groups and specific amino acids in the antibodies contributed to their high specificity and affinity. Finally, one selective and sensitive ic-ELISA was developed for FGA determination with a detection limit as low as 0.12 μg/L, providing an efficient tool for timely monitoring of FGA in goat milk samples.

Antibody Production and Immunoassay Development for Authenticating Chlorpheniramine Maleate Adulteration in Herbal Tea

Chlorphenamine maleate is a prohibited additive found in herbal teas and health foods. Excessive intake of this substance can result in adverse health effects. In this study, two novel haptens, PEM and bepotastine (PB1), mimicking chlorphenamine maleate structure were designed and synthesized based on molecular simulation for developing two corresponding polyclonal antibodies (PEM-Ab and PB1-Ab), respectively. Afterward, an indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) was developed to quickly and accurately detect chlorphenamine maleate in herbal teas using PB1-Ab, which has a high sensitivity and specificity. For chlorphenamine maleate, the half-maximal inhibitory concentration (IC50) and limit of detection (LOD) of PB1-Ab under ideal circumstances were found to be 1.18 µg/L and 0.07 µg/L, respectively. Besides, an environmentally friendly sample pre-treatment strategy was employed that allowed easy and effective elimination of complex matrices. The ic-ELISA method observed the average recovery rate from 87.7% to 94.0% with the variance coefficient (CV) ranging from 2.2% to 9.4%. Additionally, the identification of 25 commercially available herbal teas using liquid chromatography-tandem mass spectrometry (LC-MS/MS) further confirmed the validity of our detection. The results of the two methods are consistent. Overall, the proposed ic-ELISA could be an ultrasensitive and reliable method for chlorphenamine maleate adulterated in foods or exposure to the environment.

The hapten rigidity improves antibody performances in immunoassay for rifamycins: Immunovalidation and molecular mechanism

The immunogenicity of haptens determines the performance of the resultant antibody for small molecules. Rigidity is one of the basic physicochemical properties of haptens. However, few studies have investigated the effect of hapten rigidity on the strength of an immune response and overall antibody performance. Herein, we introduce three molecular descriptors that quantify hapten rigidity. By using of these descriptors, four rifamycin haptens with varied rigidity were designed. The structural and physicochemical feasibility of the designed haptens was then assessed by computational chemistry. Immunization demonstrated that the strength of induced immune responses, i.e., the titer and affinity of antiserum, was significantly increased with increased rigidity of haptens. Furthermore, molecular dynamic simulations demonstrated conformation constraint of rigid haptens contributed to the initial binding and activation of naïve B cells. Finally, a highly sensitive indirect competitive enzyme-linked immunosorbent assay was developed for detection of rifaximin, with an IC50 of 1.1 μg/L in buffer and a limit of detection of 0.2-11.3 μg/L in raw milk, river water, and soil samples. This work provides new insights into the effect of hapten rigidity on immunogenicity and offers new hapten design strategies for antibody discovery and vaccine development of small molecules.

Generation of a highly specific recombinant full-length antibody for detecting ethirimol in fruit and environmental water

High-performance antibodies are core reagents for highly sensitive immunoassays. Herein, based on a novel hapten, a hybridoma secreting the high-affinity anti-ethirimol monoclonal antibody (mAb-14G5F6) was isolated with an IC50 value of 1.35 μg/L and cross-reactivity below 0.20% for 13 analogs. To further address the challenge of hybridoma preservation and antibody immortalization, a recombinant full-length antibody (rAb-14G5F6) was expressed using the HEK293(F) expression system based on the mAb-14G5F6 gene. The affinity, specificity, and tolerance of rAb-14G5F6, as characterized by indirect competitive enzyme-linked immunosorbent assay and noncompetitive surface plasmon resonance, exhibited high concordance with those of mAb-14G5F6. Further immunoassays based on rAb-14G5F6 were developed for irrigation water and strawberry fruit with limits of detection of 0.0066 and 0.036 mg/kg, respectively, recoveries of 80100%, and coefficients of variation below 10%. Furthermore, homology simulation and molecular docking revealed that GLU(L40), GLY(L107), GLY(H108), and ASP(H114) play important roles in forming hydrogen bonds and pi-anion ionic bonds between rAb-14G5F6 and ethirimol, resulting in the high specificity and affinity of rAb-14G5F6 for ethirimol, with a KD of 5.71 × 10-10 mol/L. Overall, a rAb specific for ethirimol was expressed successfully in this study, laying the groundwork for rAb-based immunoassays for monitoring fungicide residues in agricultural products and the environment.

Simultaneous identification of three emergent stimulant laxative adulterants in slimming foods using only one antibody

Stimulant laxatives were recently found to be abused in slimming foods, resulting in harmful effects on consumers. To ensure the safety of relative products, sensitive yet multiplex immunoassays are crucial in rapid screening of stimulant laxatives. However, there are few immunoassays for these substances, and even less for broad-specific recognition. Thus, in this work, four theoretically promising haptens of emerging stimulant laxative bisacodyl were rationally designed using molecular modeling and synthesized to immune animals, whose feasibility was confirmed by the obtained broad-specific antibody. Based on this unique antibody, a highly sensitive multiplex competitive indirect enzyme-linked immunosorbent assay (ciELISA) was established with low limits of detection for bisacodyl, sodium picosulfate, and BHPM (0.23, 13.68, and 0.11 ng/mL). In spiked sample recovery test and real sample detection, this ciELISA exhibited acceptable consistency with the validation method, demonstrating high accuracy and applicability of our method. This reliable multiplex ciELISA proceeds the rapid screening of stimulant laxatives in slimming foods.

Novel hapten design, highly sensitive monoclonal antibody production, and immunoassay development for rapid screening of illegally added chloramphenicol in cosmetics

Hapten design and synthesis have been regarded as the key factor to generate high-quality antibodies. In the present study, a novel hapten of chloramphenicol was synthesized, characterized and compared with two conventional haptens. The new hapten generated mAb 4B5 showed higher sensitivity and titer than the other two haptens-based mAbs. The haptens synthesized with the structure of chloramphenicol base generated more sensitive antibodies than the hapten with chloramphenicol succinate, and the spacer arm linked to the phenyl group hapten elicited the strongest antibody response. After optimization, a direct competitive enzyme-linked immunosorbent assay (dcELISA) and a lateral flow immunoassay (LFIA), both based on the mAb 4B5, were developed. The dcELISA had a half maximum inhibition concentration of 0.23 ng/mL and the LFIA showed a cutoff value of 5-10 ng/mL. The LFIA was applied to detect illegally-added chloramphenicol samples in anti-acne cosmetics, five out of 19 samples were tested chloramphenicol containing within 10 min, which result was confirmed with the dcELISA and HPLC. The LFIA has an adequate sensitivity and can be used as a point of care diagnostic device for rapidly screening chloramphenicol in cosmetics.

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.

Identifying fungicide difenoconazole as illegal growth regulator in vegetable: Computer-aided hapten similarity to enhance immunoassay sensitivity

Difenoconazole, a fungicide with broad-spectrum properties, has recently been found to have been used illegally used as a plant growth regulator in Brassica campestris, with the intent of inducing thick stems and dark green leaves. However, analysts have encountered challenges in implementing a rapid surveillance screening approach for this purpose. In this study, a novel hapten was designed to improve the analytical performance of difenoconazole immunoassay. Specifically, the triazole of the original hapten was replaced with a benzene ring, guided by molecular simulation. This led to the development of a very sensitive antibody and the subsequent development of a competitive indirect enzyme linked immunosorbent assay (ciELISA) for the detection of difenoconazole in vegetable samples. The assay exhibited a working range of 0.16 ng mL^-1 to 9.64 ng mL^-1, with a detection limit of 0.05 ng mL^-1. Upon analysis of blind samples, a strong correlation was observed between the ciELISA and HPLC-MS/MS methods. As a result, the proposed technique may prove to be an excellent tool for the rapid detection of difenoconazole overuse and adulteration in vegetables.

Heterologous-coating antigen enhancing the sensitivity of enzyme-linked immunosorbent assay for detection of mebendazole residues

The heterologous strategy could improve the sensitivity of competitive enzyme-linked immunosorbent assay (ELISA) for detection of chemical contaminants in food samples. In this study, the heterologous coating antigen ELISA was developed to evaluate its sensitivity for mebendazole (MBZ). Results showed that the heterologous ELISA had a linear range of (IC₂₀-IC₈₀) 0.34-10.54 ng/mL, an IC₅₀ value of 1.83 ng/mL, and a limit of detection (LOD) of 0.13 ng/mL, in which the sensitivity of ELISA improved 1.7- and 2-fold (IC₅₀ value dropping from 7.41 and 3.65 ng/mL to 4.27 and 1.83 ng/mL) than that of rabbit IgG- and chicken IgY-based homologous ELISA for MBZ, respectively. The heterologous coating antigen ELISA showed negligible cross reactivity (<0.2%) with its structural analogues, including hydroxy-MBZ, albendazole, oxfendazole, fenbendazole, and flubendazole, except the value of 72.6% for amino-MBZ. The average recoveries of MBZ spiked in pork and chicken muscle samples by the assay ranged from 83.7% to 109.8% and agreed well with those of high-performance liquid chromatography. The results suggested that using heterologous coating antigen could distinctly improve the sensitivity of ELISA for routine screening of MBZ residues in food samples.

Hapten designs based on aldicarb for the development of a colloidal gold immunochromatographic quantitative test strip

The common carbamate insecticide aldicarb is considered one of the most acutely toxic pesticides. Herein, rational design was used to synthesize two haptens with spacers of different carbon chain lengths. The haptens were then used to immunize mice. The antibodies obtained were evaluated systematically, and a colloidal gold immunochromatographic strip was developed based on an anti-aldicarb monoclonal antibody. The 50% inhibition concentration and linear range of anti-aldicarb monoclonal antibody immunized with Hapten 1 were 0.432 ng/mL and 0.106–1.757 ng/mL, respectively. The cross-reactivities for analogs of aldicarb were all <1%. The limit of detection of the colloidal gold immunochromatographic strip was 30 μg/kg, and the average recoveries of aldicarb ranged from 80.4 to 110.5% in spiked samples. In the analysis of spiked samples, the test strip could accurately identify positive samples detected by the instrumental method in the GB 23200.112-2018 standard but produced some false positives for negative samples. This assay provides a rapid and accurate preliminary screening method for the determination of aldicarb in agricultural products and environments.

Development of immunoassay based on rational hapten design for sensitive detection of pendimethalin in environment

Pendimethalin (PND) is one of the most widely used selective herbicides, but it is considered a potential human carcinogen and persistent bioaccumulative toxic chemical. Herein, five haptens with carboxylic groups were synthesized based on rational design and used to immunize mice, respectively. Then the antibodies obtained were evaluated systematically, and an indirect competitive ELISA (ic-ELISA) was developed based on an anti-PND monoclonal antibody. The 50% inhibition concentration and limit of detection of ic-ELISA were 0.53 ng/mL and 0.07 ng/mL, respectively. The cross-reactivities of ic-ELISA for the analogs of PND were ≤ 1.1%. The average recoveries of PND ranged from 79.5% to 107.4% in spiked samples. A good correlation was achieved between the ic-ELISA results and UPLC-MS/MS results in the analysis of blind samples. Thus, this assay provides a rapid and accurate tool for the determination of PND in the agro-products and agricultural producing environment.

An aggregation-induced emission immunoassay for broad detection of polychlorinated biphenyls in chicken and crab

Polychlorinated biphenyls (PCBs) are persistent organic pollutants (POPs) with multiple variants, which may be harmful to human health by absorption and bioaccumulation. To ensure food safety, it is necessary to develop multi-residue immunoassays for broad recognition of PCBs. In this study, by mimicking the generic core structure of PCBs, three haptens have been designed and synthesized for monoclonal antibody (mAb) generation. A carboxylic acid derivative of PCB80 was a hapten that induced a mAb with broad recognition of PCBs. The results of ELISA further identified that the mAb could recognize 11 different kinds of PCBs; half-maximal inhibition concentrations (IC₅₀) ranged from 33.12 to 476.42 ng/mL. Subsequently, using aggregation-induced emission luminogen (AIEgen) nanobeads as the tracer for the output signal, the IC₅₀ value of the various PCBs was improved to 6.38-252.1 ng/mL. The limit of detection (LOD) varied from 0.32 to 42.15 ng/mL. Recoveries of 76.90-95.74% and intra-assay coefficients of variation of 8.5-14.4% were obtained with spiked chicken and crab meat samples. Matrix interference was eliminated by dilution, and no false-positive and false-negative results were observed. The developed assay provides a simple, broad-spectrum, and sensitive tool for detecting PCBs, with high-throughput possibilities for large-scale screening of PCBs in food.

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.

Development of a New Monoclonal Antibody against Brevetoxins in Oyster Samples Based on the Indirect Competitive Enzyme-Linked Immunosorbent Assay

The consumption of shellfish contaminated with brevetoxins, a family of ladder-frame polyether toxins formed during blooms of the marine dinoflagellate Karenia brevis, can cause neurotoxic poisoning, leading to gastroenteritis and neurotoxic effects. To rapidly monitor brevetoxin levels in oysters, we generated a broad-spectrum antibody against brevetoxin 2 (PbTx-2), 1 (PbTx-1), and 3 (PbTx-3) and developed a rapid indirect competitive enzyme-linked immunosorbent assay (icELISA). PbTx-2 was reacted with carboxymethoxylamine hemihydrochloride (CMO) to generate a PbTx-2-CMO hapten and reacted with succinic anhydride (HS) to generate the PbTx-2-HS hapten. These haptens were conjugated to keyhole limpet hemocyanin (KLH) and bovine serum albumin (BSA) to prepare immunogen and coating antigen reagents, respectively, using the active ester method. After immunization and cell fusion, a broad-spectrum monoclonal antibody (mAb) termed mAb 1D3 was prepared. The 50% inhibitory concentration (IC₅₀) values of the icELISA for PbTx-2, PbTx-1, and PbTx-3 were 60.71, 52.61, and 51.83 μg/kg, respectively. Based on the broad-spectrum mAb 1D3, an icELISA was developed to determine brevetoxin levels. Using this approach, the limit of detection (LOD) for brevetoxin was 124.22 μg/kg and recoveries ranged between 89.08% and 115.00%, with a coefficient of variation below 4.25% in oyster samples. These results suggest that our icELISA is a useful tool for the rapid monitoring of brevetoxins in oyster samples.