Investigation of the Small Size of Nanobodies for a Sensitive Fluorescence Polarization Immunoassay for Small Molecules: 3-Phenoxybenzoic Acid, an Exposure Biomarker of Pyrethroid Insecticides as a Model

Streptavidin-biotin system-mediated immobilization of a bivalent nanobody onto magnetosomes for separation and analysis of 3-phenoxybenzoic acid in urine

The compound 3-phenoxybenzoic acid (3-PBA) is frequently utilized as a biomarker to detect exposure to various pyrethroids. In this study, a bivalent nanobody (Nb2) specifically targeting 3-PBA was biotinylated and immobilized onto streptavidin (SA)-modified bacterial magnetic nanoparticles (BMPs), resulting in the formation of BMP-SA-Biotin-Nb2 complexes. These complexes demonstrated remarkable stability when exposed to strongly acidic solutions (4 M HCl), methanol (80%), and high ionic strength (1.37 M NaCl). An immunoassay was subsequently developed utilizing BMP-SA-Biotin-Nb2 as the capture agent and 3-PBA-horseradish peroxidase as the detection probe. The immunoassay exhibited an IC50 value (half-maximum signal inhibition concentration) of 1.11 ng mL-1 for 3-PBA. To evaluate the accuracy of the assay, spiked sheep and cow urine samples (ranging from 3.0 to 240 ng mL-1) were analyzed. The quantitative recoveries ranged from 82.5% to 113.1%, which agreed well with the findings obtained using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Overall, the BMP-SA-Biotin-Nb2-based immunoassay holds great promise for rapid monitoring of 3-PBA following acid dissociation.

Enhanced sandwich immunoassay based on bivalent nanobody as an efficient immobilization approach for foodborne pathogens detection

BACKGROUND

Nanobodies (Nbs), which consist of only antigen-binding domains of heavy chain antibodies, have been used in a various range of applications due to their excellent properties. Nevertheless, the size of Nbs is so small that their antigen binding sites may be sterically hindered after random fixation as capture antibodies, thus leading to poor detection performance in immunoassays. To address this problem, we have focused on the multivalent modification of Nbs, wanted to retain the advantage of good stability through enlarging the size of Nbs to a certain extent, while improve its affinity and reduce its influence by spatial orientation.

RESULTS

Here, we designed homo- and heterodimeric Nbs based on Nb413 and Nb422 which recognize different epitopes of Salmonella. The affinity of engineered bivalent nanobodies for S. Enteritidis were 2 orders of magnitude higher compared to monovalent Nbs and low to sub-nM KD, as calculated by Scatchard analysis. To further explore the potential of bivalent Nbs for the detection of Salmonella, we established a sandwich ELISA based on bivalent and phage-displayed Nbs (BNb-ELISA) for multiplex Salmonella determination. Compared with monovalent Nb-based ELISA, the limit of detection (LOD) of the BNb-ELISA was shown to increase 7.5-fold to 2.364 × 103 CFU mL-1 for S. Enteritidis. In addition, the feasibility of this approach for S. Enteritidis detection in real samples was evaluated, with recoveries ranging from 73.0 % to 125.6 % and coefficients of variation (CV) below 7.68 %.

SIGNIFICANCE AND NOVELTY

In this study, we developed for the first time bivalent Nbs against Salmonella and examined their improved affinity and impact on the performance of ELISA assay. It confirmed the high binding affinity and good ability of dimeric Nbs to reduce the occupation of the binding sites of immobilized antibodies. Thus, the multivalent modification of Nbs was demonstrated to be a promising means to enhance the performance of Nbs-based immunoassays for foodborne pathogens.

Design of an Antigen-Triggered Nanobody-Based Fluorescence Probe for PET Immunoassay to Detect Quinalphos in Food Samples

Photoinduced electron-transfer (PET) immunoassay based on a fluorescence site-specifically labeled nanobody, also called mini Quenchbody (Q-body), exhibits extraordinary sensitivity and saves much time in the homogeneous noncompetitive mode and is therefore regarded as a valuable method. However, limited by the efficiency of both quenching and dequenching of the fluorescence signal before and after antigen binding associated with the PET principle, not all original nanobodies can be used as candidates for mini Q-bodies. Herein, with the anti-quinalphos nanobody 11A (Nb-11A) as the model, we, for the first time, adopt a strategy by combining X-ray structural analysis with site-directed mutagenesis to design and produce a mutant Nb-R29W, and then successfully generate a mini Q-body by labeling with ATTO520 fluorescein. Based on this, a novel PET immunoassay is established, which exhibits a limit of detection of 0.007 μg/mL with a detection time of only 15 min, 25-fold improved sensitivity, and faster by 5-fold compared to the competitive immunoassay. Meanwhile, the recovery test of vegetable samples and validation by the standard ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) both demonstrated that the established PET immunoassay is a novel, sensitive, and accurate detection method for quinalphos. Ultimately, the findings of this work will provide valuable insights into the development of triggered PET fluorescence probes by using existing antibody resources.

Effects of thiram exposure on liver metabolism of chickens

Pesticides are widely used to control crop diseases, which have made an important contribution to the increase of global crop production. However, a considerable part of pesticides may remain in plants, posing a huge threat to animal safety. Thiram is a common pesticide and has been proven that its residues in the feed can affect the growth performance, bone formation, and intestinal health of chickens. However, there are few studies on the liver metabolism of chickens exposed to thiram. Here, the present study was conducted to investigate the effect of thiram exposure on liver metabolism of chickens. Metabolomics analysis shows that 62 metabolites were down-regulated (ginsenoside F5, arbekacin, coproporphyrinogen III, 3-keto Fusidic acid, marmesin, isofumonisin B1, 3-Hydroxyquinine, melleolide B, naphazoline, marmesin, dibenzyl ether, etc.) and 35 metabolites were up-regulated (tetrabromodiphenyl ethers, deoxycholic acid glycine conjugate, L-Palmitoylcarnitine, austalide K, hericene B, pentadecanoylcarnitine, glyceryl palmitostearate, quinestrol, 7-Ketocholesterol, tetrabromodiphenyl ethers, etc.) in thiram-induced chickens, mainly involved in the metabolic pathways including glycosylphosphatidylinositol (GPI)-anchor biosynthesis, porphyrin and chlorophyll metabolism, glycerophospholipid metabolism, primary bile acid biosynthesis and steroid hormone biosynthesis. Taken together, this research showed that thiram exposure significantly altered hepatic metabolism in chickens. Moreover, this study also provided a basis for regulating the use and disposal of thiram to ensure environmental quality and poultry health.

Dual-Wavelength Fluorescence Polarization Immunoassay for Simultaneous Detection of Sulfonamides and Antibacterial Synergists in Milk

Combinations of sulfonamides (SAs) and antibacterial synergists (ASGs) are frequently used for treating infectious diseases and promoting growth for animals, which cause potential hazards to food safety and human health. To realize the simultaneous detection of SAs and ASGs in food, a homogeneous and high-throughput screening dual-wavelength fluorescence polarization immunoassay (DWFPIA) was developed. In this study, three SAs tracers and three ASGs tracers were synthesized by fluoresceins with different linkers and paired with their corresponding monoclonal antibodies (mAbs), respectively. To achieve a high sensitivity and broad specificity, the combination of tracers SADMPM-HDF with the longest linker paring mAb 10E6 for SAs and tracer HaptenA-DSCA paring mAb 9C9 for ASGs were chosen for the development of DWFPIA, achieving surprising IC₅₀ values for 23 SAs below 100 μg L^-1 and 5 ASGs below 50 μg L^-1. The accuracy of DWFPIA was applied in real milk samples by typical sulfamethazine (SMZ) and trimethoprim (TMP), with recoveries of 81.7-97.2% and 78.6-103.6%, and coefficient of variations (CVs) below 18.9%, which could be completed within 15 min, including sample pretreatment. We firstly developed a simultaneous screening DWFPIA, covering all of the SAs and ASGs used in clinic and providing a great application potential in food safety analysis.

Multivalent nanobody-biotin amplified enzyme-linked immunosorbent assay for the environmental detection of 3-phenoxybenzoic acid

The 3-phenoxybenzoic acid (3-PBA) metabolized from pyrethroids is more toxic and has a longer half-life to degradation in a natural environment compared to its parent compounds. Few reports have focused on the environmental detection of 3-PBA. In this study, anti-3-PBA nanobodies in trivalent form (Nb3) were biotinylated. A sensitive enzyme-linked immunosorbent assay (ELISA) based on the combination of Nb3-biotin and streptavidin-horseradish peroxidase (SA-HRP) was developed for the environmental detection of 3-PBA. After optimization, the ELISA showed a half-maximum signal inhibition concentration (IC₅₀) of 0.39 ng mL^-1 in phosphate-buffered saline (pH 7, 20% MeOH) and a limit of detection (LOD) of 0.02 ng mL^-1, which was more sensitive than the parent Nb-based ELISAs with IC₅₀ and LOD values of 1.4 ng mL^-1 and 0.1 ng mL^-1, respectively. The Nb3-biotin amplified assay showed negligible cross-reactivity with its structural analogues (<0.1%). The average recoveries of 3-PBA from spiked canal water and soil samples ranged from 86.54-109.25% at 0.5-50 ng mL^-1 (or ng g^-1 (dw)). The 3-PBA residues in canal water and soil samples determined using this assay were in the ranges <LOD-1.46 ng mL^-1 and <LOD-4.35 ng g^-1 (dw), respectively, which correlated well with the results obtained using liquid chromatography tandem mass spectrometry. The results suggest that multivalent Nb-biotin-SA amplified ELISA is a promising tool for the routine environmental screening of 3-PBA.

Multivalent nanobody as capture antibody-based enzyme linked immunosorbent assay for detection of 3-phenoxybenzoic acid in urine

Nanobodies (Nbs) as capture antibodies in enzyme-linked immunosorbent assays (ELISAs) is greatly hampered by their poor performance after attaching onto polystyrene microplates. Reasons behind those phenomena remain unknown. One of possible explanation is that Nbs with a single domain might lose their accessibility of paratope when adsorbed on the plates. Increasing their binding sites might improve performance in capture Nbs-based ELISA. In this study, anti-3-phenoxybenzoic acid (3-PBA) Nbs was assembled to trivalent form (Nb3) in tandem with flexible linkers (G₄S)₃. Direct competitive ELISA on the basis of Nb3 and 3-PBA-horseradish peroxidase was developed for detection of 3-PBA in livestock urine. The ELISA had a half-maximum (IC₅₀) inhibition concentration of 0.51 ng/mL, with a limit of detection of 0.02 ng/mL, which was more sensitive than that of the parental Nb with a IC₅₀ of 2.39 ng/mL. The average recoveries of 3-PBA spiked in swine, sheep and dairy cow urine samples by the assay ranged from 89.52% to 114.25% and agreed well with those of liquid chromatography mass spectrometry (LC-MS). The above results indicated that multivalent Nbs could be treated as the capture antibody in ELISA for routine screening analysis of 3-PBA residues in urine.

Development of nanobody-based flow-through dot ELISA and lateral-flow immunoassay for rapid detection of 3-phenoxybenzoic acid

As a major metabolite of pyrethroid pesticides, 3-phenoxybenzoic acid (3-PBA) can be an indicator of health risk and human exposure assessment. Based on nanobodies (Nbs), we have developed a rapid flow-through dot enzyme linked immunosorbent assay (dot ELISA) and gold nanoparticle (GNP) lateral-flow immunoassay for detecting 3-PBA. The limit of detection (LOD) values for detecting 3-PBA by flow-through dot ELISA and GNP lateral-flow immunoassay were 0.01 ng mL-1 and 0.1 ng mL-1, respectively. The samples (urine and lake water) with and without 3-PBA were detected by both nanobody-based flow-through dot ELISA and GNP lateral-flow immunoassay, as well as liquid chromatography-mass spectrometry (LC-MS) for validation. There was good consistency between the results of the immunoassays. This demonstrated that the two developed nanobody-based immunoassays are suitable for rapid detection of 3-PBA.

Interaction standards for biophysics: anti-lysozyme nanobodies

There is a significant demand in the molecular biophysics community for robust standard samples. They are required by researchers, instrument developers and pharmaceutical companies for instrumental quality control, methodological development and in the design and validation of devices, diagnostics and instrumentation. To-date there has been no clear consensus on the need and type of standards that should be available and different research groups and instrument manufacturers use different standard systems which significantly hinders comparative analysis. One of the major objectives of the Association of Resources for Biophysical Research in Europe (ARBRE) is to establish a common set of standard samples that can be used throughout the biophysics community and instrument developers. A survey was circulated among ARBRE members to ascertain the requirements of laboratories when using standard systems and the results are documented in this article. In summary, the major requirements are protein samples which are cheap, relatively small, stable and have different binding strengths. We have developed a panel of sdAb’s or ‘nanobodies’ against hen-egg white lysozyme with different binding strengths and suitable stability characteristics. Here we show the results of the survey, the selection procedure, validation and final selection of a panel of nanobody interaction standards.

Competitive Immunoassay of SARS-CoV-2 Using Pig Sera-Derived Anti-SARS-CoV-2 Antibodies

Anti-severe acute respiratory syndrome coronavirus 2 (anti-SARS-CoV-2) nucleoprotein (NP) antibodies were isolated from pig sera using human SARS-CoV-2 NP-immobilized magnetic beads. The binding properties of the isolated antibodies against SARS-CoV-2 NP were tested via flow cytometry using SARS-CoV-2 NP-immobilized magnetic beads. A competitive immunoassay was developed for detecting SARS-CoV-2 NP as well as SARS-CoV-2 in the culture fluid using magnetic beads with immobilized anti-SARS-CoV-2 NP antibodies. Selectivity tests were carried out during the competitive immunoassay for SARS-CoV, MERS-CoV, and CoV strain 229E in the culture fluid.