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

Development of a Sensitive Enzyme Immunoassay Using Phage-Displayed Antigen-Binding Fragments for Zearalenone Detection in Cereal Samples

Zearalenone (ZEN), a non-steroidal estrogenic mycotoxin, contaminates animal feed and grain crops, thereby entering the food chain and posing a significant threat to human health. Consequently, there is an urgent need for a sensitive and rapid method for detecting trace levels of ZEN. In this study, we developed a phage-displayed antigen-binding fragment (Fab-phage) and established a Fab-phage-based enzyme-linked immunosorbent assay (Fab-pELISA) for ZEN detection. Under optimal conditions, this method exhibits a half-maximal inhibitory concentration of 0.36 ng/mL, with a linear range from 0.07 to 3.89 ng/mL and a detection limit of 0.03 ng/mL. The method demonstrates high selectivity towards ZEN and good recovery rates of 97.35-122.66% with relative standard deviations not exceeding 3.5%. Furthermore, the detection results obtained using Fab-pELISA on real cereal samples are consistent with those from high-performance liquid chromatography, meeting practical application requirements. Therefore, the Fab-phage serves as a valuable biochemical reagent, and the established Fab-pELISA represents a promising analytical strategy for detecting ZEN and other trace toxic contaminants in cereals.

Enhanced nanobody-driven bioluminescent immunoassay for rapid parathion detection using engineered split-nanoluciferase

In this work, with parathion, a typical forbidden organophosphate pesticide as target drug, an enhanced nanobody-driven bioluminescent immunoassay based on the engineered split-nanoluciferase (NanoLuc) was proposed. Concretely, through labeling 11S and β10, two split-NanoLuc units onto the anti-parathion nanobody (Nb) VHH9 and the artificial antigen H1 coupled with carrier protein ovalbumin (H1-OVA) respectively, an NanoLuc Binary Technology (NanoBiT) system was firstly developed in the form of homogeneous immunoassay, in which the luminescence signal was produced by the reassembled NanoLuc after the combination of the 11S-fused VHH9 and β10-labeled H1-OVA. Subsequently, in order to enhance the signal-to-noise (S/N) ratio, a novel strategy of splitting 11S into two smaller subunits Δ11S and β9 was adopted so then an NanoLuc Ternary Technology (NanoTeT) system based on tri-part components of β9-fused VHH9, β10-labeled H1-OVA and Δ11S was successfully established. The results showed that the maximum half inhibition concentration (IC50) for parathion can be as low as 2.04 ng/mL, 3.2-fold and 4.2-fold improved than that of the NanoBiT system and indirect competitive enzyme-linked immunosorbent assay (ic-ELISA). Meanwhile, the detection range was from 0.19 ng/mL to 22.11 ng/mL. More importantly, this method required simply a one-step incubation with all reagents mixed together, and the total time used in detection was only 10 min, 7-fold faster than ic-ELISA. Finally, the average recoveries for vegetable samples were from 84.8% to 122% with the coefficient of variance (CV) below 15%. Overall, this study provides a new platform for homogeneous immunoassay of the small-molecule contaminants.

Engineering an Ag/Au bimetallic nanoparticle-based acetylcholinesterase SERS biosensor for in situ sensitive detection of organophosphorus pesticide residues in food

Developing simple, efficient, and inexpensive method for trace amount organophosphorus pesticides' (OPs) detection with high sensitivity and specificity is of significant importance for guaranteeing food safety. Herein, an Ag/Au bimetallic nanoparticle-based acetylcholinesterase (AChE) surface-enhanced Raman scattering (SERS) biosensor was constructed for in situ simple and sensitive detection of pesticide residues in food. The principle of this biosensor exploited 4-mercaptophenylboronic acid (4-MPBA)-modified Ag/Au bimetallic nanoprobes as SERS signal probe to improve sensitivity and stability. The combination of AChE and choline oxidase (CHO) can hydrolyze acetylcholine (ATCh) to generate H₂O₂. The product of H₂O₂ selectively oxidizes the boronate ester of 4-MPBA, decreasing the Raman intensity of the B-O symmetric stretching. In the presence of OPs, it could inhibit the production of H₂O₂ by destroying the AChE activity, so the reduction of the SERS signal was also alleviated. Based on the principle, an Ag/Au bimetallic nanoparticle-based AChE SERS sensor was established without any complicated pretreatments. Benefiting from the synergistic effects of Ag/Au bimetallic hybrids, a linear detection range from 5×10^-9 to 5×10^-4 M was achieved with a limit of detection down to 1.7×10^-9 M using parathion-methyl (PM) as the representative model of OPs. Moreover, the SERS biosensor uses readily available reagents and is simple to implement. Importantly, the proposed SERS biosensor was used to quantitatively analyze OP residues in apple peels. The levels of OPs detected in real samples by this method were consistent with those obtained using gas chromatography-mass spectrometry (GC-MS), suggesting the proposed assay has great potential applications for OPs in situ detection in food safety fields.

Development of competitive and noncompetitive immunoassays for clothianidin with high sensitivity and specificity using phage-displayed peptides

Clothianidin is a widely used pesticide that has been banned from outdoor use by the European Union due to its toxicity. To improve the sensitivity and specificity of existing clothianidin immunoassays, we developed competitive and noncompetitive immunoassays for clothianidin based on phage-displayed peptides. Cyclic 8-, 9-, and 10-residue peptide libraries were constructed using an optimized phagemid pComb-pVIII to prevent the loss of theoretical library diversity. Twenty-eight peptidomimetics and two anti-immunocomplex peptides were isolated through a blended panning process and used to develop competitive and noncompetitive phage enzyme-linked immunosorbent assays (P-ELISAs), respectively. After optimization, the half inhibition concentration (IC₅₀) and half saturation concentration (SC₅₀) of competitive and noncompetitive P-ELISAs were 3.83 ± 0.23 and 0.45 ± 0.02 ng/mL, respectively. Competitive P-ELISA showed 2.6-18.2% cross-reactivity with imidaclothiz, nitenpyram and imidacloprid. Importantly, noncompetitive P-ELISA, which has the best specificity and great sensitivity for clothianidin, showed no cross-reactivity with the analogs. The average recoveries of competitive and noncompetitive P-ELISAs were 73.8-104.1% and 76.6-102.2%, respectively, while the relative standard deviations were ≤ 11.0%. In addition, the results of P-ELISAs in the analysis of blind samples were consistent with those of high-performance liquid chromatography.

Transparent and flexible AuNSs/PDMS-based SERS substrates for in-situ detection of pesticide residues

Herein, we developed a PDMS-based flexible SERS substrate modified with gold nanostars (AuNSs) for in-situ detection of pesticide residues on fruit surfaces. AuNSs with sharp branches were assembled on aminated PDMS membrane by chemical bonding effect. The AuNSs/PDMS substrate showed good signal uniformity, stability and sensitivity using the Raman signal molecule 4-MBA and the detection concentration of 4-MBA was as low as 10^-8 mol/L. Then the AuNSs/PDMS substrate was used to detect methyl parathion (MP) standard solution. A good linear relationship between SERS intensity at 1342 cm^-1 and MP concentration was established in the range of 4 μg/mL-100 μg/mL, and the limit of detection was down to 1.946 μg/mL. Moreover, the AuNSs/PDMS substrate was directly covered on the surface of MP contaminated apple, and the Raman laser was incident from the back of substrate to achieve in-situ detection of pesticide residues. The recovery ratio indicated that the fabricated SERS substrate was realized successfully in real sample detection. AuNSs/PDMS substrate eliminates the requirement for sample pre-processing steps before testing, which can be used as a method for rapid inspection of pesticide in agricultural products on site.

Application of phage-display developed antibody and antigen substitutes in immunoassays for small molecule contaminants analysis: A mini-review

Toxic small molecule contaminants (SMCs) residues in food threaten human health. Immunoassays are popular and simple techniques for SMCs analysis. However, immunoassays based on polyclonal antibodies, monoclonal antibodies and chemosynthetic antigens have some defects, such as complicated preparation of antibodies, risk of toxic haptens using for antigen chemosynthesis and so on. Phage-display technique has been proven to be an attractive alternative approach to producing antibody and antigen substitutes of SMCs, and opened up new realms for developing immunoassays of SMCs. These substitutes contain five types, including anti-idiotypic recombinant antibody (AIdA), anti-immune complex peptide (AIcP), anti-immune complex recombinant antibody (AIcA) and anti-SMC recombinant antibody (anti-SMC RAb). In this review, the principle of immunoassays based on the five types of substitutes, as well as their application and advantages are summarized and discussed.

Rapid Multi-Residue Detection Methods for Pesticides and Veterinary Drugs

The excessive use or abuse of pesticides and veterinary drugs leads to residues in food, which can threaten human health. Therefore, there is an extremely urgent need for multi-analyte analysis techniques for the detection of pesticide and veterinary drug residues, which can be applied as screening techniques for food safety monitoring and detection. Recent developments related to rapid multi-residue detection methods for pesticide and veterinary drug residues are reviewed herein. Methods based on different recognition elements or the inherent characteristics of pesticides and veterinary drugs are described in detail. The preparation and application of three broadly specific recognition elements-antibodies, aptamers, and molecular imprinted polymers-are summarized. Furthermore, enzymatic inhibition-based sensors, near-infrared spectroscopy, and SERS spectroscopy based on the inherent characteristics are also discussed. The aim of this review is to provide a useful reference for the further development of rapid multi-analyte analysis of pesticide and veterinary drug residues.

Competitive Bio-Barcode Immunoassay for Highly Sensitive Detection of Parathion Based on Bimetallic Nanozyme Catalysis

A competitive sensitive bio-barcode immunoassay based on bimetallic nanozyme (Au@Pt: gold@platinum) catalysis has been designed for the detection of the pesticide parathion. Gold nanoparticles (AuNPs) were modified with single-stranded thiol oligonucleotides (ssDNAs) and monoclonal antibodies (mAbs) to form AuNP probes; magnetic nanoparticles (MNPs) were coated with ovalbumin (OVA)-parathion haptens as MNP probes, and bimetallic nanozyme (Au@Pt) nanoparticles functionalized with the complementary thiolated ssDNA were used as Au@Pt probes. The Au@Pt probes reacted with the AuNP probes through complementary base pairing. Further, parathion competed with MNP probes to bind the mAbs on the AuNP probes. Finally, the complex system was separated by a magnetic field. The released Au@Pt probes catalyzed a chromogenic system consisting of teramethylbenzidine (TMB). The bimetallic nanozyme-based bio-barcode immunoassay was performed on rice, pear, apple, and cabbage samples to verify the feasibility of the method. The immunoassay exhibited a linear response from 0.01 to 40 μg·kg^-1, and the limit of detection (LOD) was 2.13 × 10^-3 μg·kg^-1. The recoveries and relative standard deviations (RSDs) ranged from 73.12 to 116.29% and 5.59 to 10.87%, respectively. The method was found to correlate well with data obtained by liquid chromatography-tandem mass spectrometry (LC-MS/MS). In conclusion, this method exhibits potential as a sensitive alternative method for the detection of a variety of pesticides, ensuring the safety of fruits and vegetables in agriculture.

Improvement of High Affinity and Selectivity on Biosensors Using Genetically Engineered Phage by Binding Isotherm Screening

The genetically engineered M13 bacteriophage (M13 phage), developed via directed evolutionary screening process, can improve the sensitivity of sensors because of its selective binding to a target material. Herein, we propose a screening method to develop a selective and sensitive bioreporter for toxic material based on genetically engineered M13 phage. The paraquat (PQ)-binding M13 phage, developed by directed evolution, was used. The binding affinities of the PQ-binding M13 phage to PQ and similar molecules were analyzed using isothermal titration calorimetry (ITC). Based on the isotherms measured by ITC, binding affinities were calculated using the one-site binding model. The binding affinity was 5.161 × 10⁻⁷ for PQ, and 3.043 × 10⁻⁷ for diquat (DQ). The isotherm and raw ITC data show that the PQ-binding M13 phage does not selectively bind to difenzoquat (DIF). The phage biofilter experiment confirmed the ability of PQ-binding M13 bacteriophage to bind PQ. The surface-enhanced Raman scattering (SERS) platform based on the bioreporter, PQ-binding M13 phage, exhibited 3.7 times the signal intensity as compared with the wild-type-M13-phage-coated platform.

Isolation of Bactrian Camel Single Domain Antibody for Parathion and Development of One-Step dc-FEIA Method Using VHH-Alkaline Phosphatase Fusion Protein

A heavy chain variable fragment of heavy chain only antibodies derived from camelids termed VHH shows beneficial characteristics for immunoassay in terms of high sensitivity, outstanding stability and ease in expression. In the present study, we isolated six VHHs from phage display library against parathion, which is a widely used organophosphorus pesticide with high toxicity and persistence. One of six selected VHHs named VHH9, showed highest specificity and superior thermo-stability. A VHH9-alkaline phosphatase (AP) fusion was constructed and used to establish a one-step direct competitive fluorescence enzyme immunoassay (dc-FEIA) with a half maximal inhibitory concentration (IC50) of 1.6 ng/mL and a limit of detection of 0.2 ng/mL which was 4-fold or 3-fold higher sensitivity than direct competitive enzyme-linked immunoassay (dc-ELISA) and indirect competitive enzyme-linked immunoassay (ic-ELISA) for parathion. Furthermore, our assay indicated a 50% reduction on operation time compared with the ic-ELISA method. The presented immunoassay was validated with spiked Chinese cabbage, cucumber, and lettuce samples, and confirmed by UPLC-MS/MS. The results indicated that the VHH-AP-based dc-FEIA is a reproducible detection assay for parathion residues in vegetable samples.

Development and comparative study of chemosynthesized antigen and mimotope-based immunoassays for class-specific analysis of O,O-dimethyl organophosphorus pesticides

The multi-residue determination of organophosphorus pesticides (OPs) is an important task due to the wide application and high toxicity of OPs. However, there is no promising immunoassay to monitor the multi-residue of O,O-dimethyl OPs. In this study, a monoclonal antibody (mAb) against a generic hapten of O,O-dimethyl OPs (O,O-dimethyl O-(3-carboxyphenyl)phosphorothioate) was prepared. To develop an effective class-specific immunoassay, two strategies were performed to select the appropriate coating antigen or competing antigen. On the one hand, a total of 20 haptens were chemosynthesized, attached to ovalbumin for use as coating antigen candidates, and selected by direct competitive ELISA (dcELISA). As a second strategy, mimotopes of the mAb were selected from a random phage-display peptide library by panning, and the optimum mimotope was expressed as a fusion protein and biotinylated in vitro. Based on the selected chemosynthesized coating antigen and the biotinylated mimotope fusion protein, two sensitive broad-specificity dcELISAs were developed. The sensitivity, selectivity and practicability of the two immunoassays were compared. The results demonstrated that both methods showed similar selectivity and sensitivity and were reliable for O,O-dimethyl OP residues screening. However, the screening operation of mimotopes was much simpler and safer compared to the preparation of chemosynthesized coating antigens.

Competitive and noncompetitive phage immunoassays for the determination of benzothiostrobin

Twenty-three phage-displayed peptides that specifically bind to an anti-benzothiostrobin monoclonal antibody (mAb) in the absence or presence of benzothiostrobin were isolated from a cyclic 8-residue peptide phage library. Competitive and noncompetitive phage enzyme linked immunosorbent assays (ELISAs) for benzothiostrobin were developed by using a clone C3-3 specific to the benzothiostrobin-free mAb and a clone N6-18 specific to the benzothiostrobin immunocomplex, respectively. Under the optimal conditions, the half maximal inhibition concentration (IC50) of the competitive phage ELISA and the concentration of analyte producing 50% saturation of the signal (SC50) of the noncompetitive phage ELISA for benzothiostrobin were 0.94 and 2.27 ng mL(-1), respectively. The noncompetitive phage ELISA showed higher selectivity compared to the competitive. Recoveries of the competitive and the noncompetitive phage ELISAs for benzothiostrobin in cucumber, tomato, pear and rice samples were 67.6-119.6% and 70.4-125.0%, respectively. The amounts of benzothiostrobin in the containing incurred residues samples detected by the two types of phage ELISAs were significantly correlated with that detected by high-performance liquid chromatography (HPLC).

Development of an enzyme-linked immunosorbent assay for thiacloprid in soil and agro-products with phage-displayed peptide

A monoclonal antibody (3A5) that can recognize thiacloprid was produced, and a linear 8-residue peptide phage library was constructed. Six phage-displayed peptides were isolated from the linear 8-residue peptide phage library and a cyclic 8-residue peptide phage library. A phage enzyme-linked immunosorbent assay (ELISA) was developed to detect thiacloprid using a phage-displayed peptide. Under the optimal conditions, the half-maximal inhibition concentration (IC50) and the limit of detection (IC10) of the developed phage ELISA were 8.3 and 0.7 μg/L, respectively. Compared with the conventional ELISA, the sensitivity was improved more than 3-fold. The cross-reactivity (CR) was less than 0.08% for the tested structural analogues and was regarded as negligible. The recoveries of thiacloprid ranged from 80.3% to 116.3% in environmental and agricultural samples, which conformed to the requirements for residue detection. The amount of thiacloprid detected by phage ELISA in the samples was significantly correlated with that detected by high-performance liquid chromatography. The current study indicates that isolating phage-displayed peptides from phage display libraries is an alternative method for the development of a sensitive immunoassay and that the developed assay is a potentially useful tool for detecting thiacloprid in environmental and agricultural samples.