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

Sensitive amperometric immunosensor for pathogen antigen based on MoS2@AuNPs assembling dual-peptide as bioprobes with significant dual signal amplification

It is crucial to timely and accurately identify the causative virus for early treatment and urgent prevention. Viral antigen detection can identify those people who are most likely at risk of spreading the disease, but most based on antibodies with limited stability and sensitivity. Peptides offer several advantages over antibodies, such as low cost, smaller size and good stability. The development of electrochemical immunoassay using specific peptide probes have the merits of good sensitivity and selectivity as well as good stability. Herein we report an amperometric immunosensor using peptides as capture probe and recognition probe. The molecular docking suggests that the two peptides of Pi (sequence: NFWISPKLAFALGGGKKKSC) and FK11 (sequence: WFLNDSELISML), bioscreened from phage display, bind to N-terminal domain of SARS-CoV-2 spike protein (SP). The peptide Pi is assembled on MoS2@AuNPs modified electrode to capture SARS-CoV-2 SP, which is recognized by peptide FK11-displayed phage to form Pi/SARS-CoV-2 SP/FK11-phage sandwich. Then anti-M13 phage conjugated horseradish peroxidase (HRP) (anti M13-HRP) was introduced to recognize the phage capsid protein pVIII to form M13 phage/anti M13-HRP to enrich thousands of HRP, which can further electrochemically catalyze H2O2 reduction at highly conductive MoS2@AuNPs at - 0.35 V. Then amperometric immunosensor was constructed with linear range of 0.1-5000 pg/mL SARS-CoV-2 SP and detection limit of 0.074 pg/mL. The sensor also has good selectivity, batch reproducibility and stability, capable of detecting down to 10 transducing units/mL SARS-CoV-2 pseudoviruses. This work represents the first example of dual-peptide probes based sandwich-type electrochemical immunosensor integrated with dual signal amplification, which may provide a cost-effective assay platform in detecting real SARS-CoV-2 viruses for early diagnosis. The flexible and modular strategy can be extended to develop other type biosensors for a wide range of applications.

Genetic engineering-powered dual-mode lateral flow immunosensor for colorimetric and fluorescent detection of ochratoxin A in pepper

Ochratoxin A (OTA) poses significant risks to both environment and human health, necessitating the development of rapid and sensitive detection methods. Lateral flow immunosensors (LFIs) typically use monoclonal antibodies and artificial antigens for mycotoxin detection; however, the preparation of these components is time-intensive, laborious, costly, and environmentally harmful. Herein, we developed an innovative genetic engineering-powered colorimetric/fluorescent dual-mode LFI (CM/FL-dLFI) using nanobodies and the mimotope peptide (MP) of OTA. Initially, a heptameric bifunctional fusion (sfGFP-C4bpα-Y4) containing the superfolder green fluorescent protein, the C4-binding protein α-chain, and the MP Y4 was constructed. The fusion was subsequently labeled on gold nanoflowers (AuNFs) to create the AuNFs@sfGFP-C4bpα-Y4 probe, which can be captured by the nanobody heptamer (Nb-C4bpα) and provides colorimetric/fluorescent signals. The optimized CM/FL-dLFI achieved a colorimetric limit of detection (LOD) of 0.01 ng/mL and a fluorescent LOD of 0.05 ng/mL. It exhibited high selectivity for OTA, good recovery rates of 82.85-102.81 % with relative standard deviations not exceeding 14 %, and excellent long-term stability. Moreover, it showed strong correlation with high-performance liquid chromatography in the analysis of 11 real pepper samples. Therefore, this study highlights the promising application potential of nanobodies and MPs in developing an economical and eco-friendly LFI for OTA detection in pepper.

Preparation of peptides against immunocomplex of deltamethrin and application in noncompetitive lateral flow immunoassay

Lateral flow immunoassay (LFIA) has the advantages of simplicity and rapidness, and is widely used for the rapid detection of pesticides and other analytes. However, small molecule compounds such as pesticides are often analyzed using competitive LFIA (CLFIA), whose sensitivity often does not meet the actual needs. In this study, a noncompetitive LFIA (NLFIA) for deltamethrin (DM) with high sensitivity was developed by using anti-immunocomplex peptides (AIcPs). A total of 21 unique AIcPs were identified through the screening of phage-displayed cyclic peptide libraries. The AIcP containing the CYFDGAWYAC sequence in noncompetitive phage enzyme-linked immunosorbent assays (P-ELISA) exhibited a half signal saturation concentration (SC50) of 1.49 ng/mL, achieving a remarkable 209-fold sensitivity enhancement compared to antigen-based competitive ELISA. The AIcP, in the form of CYFDGAWYACGGGSSK-biotin, was synthesized to prepare AIcP-conjugated gold nanoparticles (AuNPs) by reacting with streptavidin (SA)-labeled AuNPs and subsequently assembled into the NLFIA strip. After optimization, the NLFIA achieved a visual limit of detection (vLOD) of 6.25 ng/mL in Tris-HCl buffer and 0.5 mg/kg in wheat, Chinese cabbage, and celery within 8 min. Furthermore, NLFIA detection results for blind wheat samples matched those of a reference liquid chromatography method.

Development of targeted antimicrobial peptides for Escherichia coli: Combining phage display and rational design for food safety application

The growing demand for minimally processed foods has heightened the risk of pathogenic contamination. Balancing antimicrobial efficacy with the preservation of probiotic activity remains a significant challenge. In this study, we employed phage display peptide library screening, combined with next-generation sequencing to identify the HIMPIQA domain, which selectively targets pathogenic Escherichia coli (E. coli) in just one screening round. Using the yXy(PX)4yXy template, we designed antimicrobial peptides (AMPs) where 'y' represents hydrophobic amino acids, and 'X' represents positively charged residues. The peptide WK, combining HIMPIQA with a Trp/Lys-based antimicrobial domain, demonstrated high specificity and antibacterial activity. Molecular docking revealed WK's binding to FaeG and mechanistic studies showed its ability to disrupt E. coli membranes while maintaining probiotic viability. WK's application as a preservative enhanced the shelf life of yogurt and tomatoes. This innovative approach showcases the potential of phage display in developing targeted AMPs for food preservation and safety.

Recent Advances in Food Safety Detection: Split Aptamer-Based Biosensors Development and Potential Applications

Ensuring food safety is a shared responsibility across the entire food supply chain, encompassing manufacturers, processors, retailers, consumers, and regulatory bodies. However, traditional detection methods have several limitations, including slow processing times, high costs, limited sensitivity, and susceptibility to false positives or negatives. These shortcomings underscore the urgent need for faster, more accurate, and cost-effective detection technologies. Aptamers and aptasensors have emerged as promising alternatives. Aptamers offer advantages over traditional recognition probes due to their high affinity and specificity for diverse targets. The aptasensors enable rapid detection, cost reduction, shelf life extension, and minimal batch-to-batch variability, making them highly suitable for food safety applications. Detecting small molecules such as toxins, antibiotics, pesticides, contaminants, and heavy metals remains challenging due to steric hindrance, nonspecific binding, and reduced accuracy. Recent advancements in aptamer technology have focused on pre- and postmodifications to enhance detection performance. One of the most promising innovations is the development of split aptamers. These engineered aptamers, designed to operate in segments known as split aptamers, offer improved flexibility and binding specificity, effectively addressing the challenges of detecting small-sized targets. This review examines the evolution of aptamers and aptasensors, focusing on their application in detecting small molecules that are essential to food safety. It reported the strategies for modifying and optimizing selected aptamers, providing details on developing split aptamers as a promising approach to address the unique challenges of small-molecule detection. Additionally, recent advancements in split aptamer technology and its integration into aptasensor development are highlighted, showcasing how these innovations are revolutionizing the detection of food safety hazards by overcoming the limitations of traditional detection methods.

Mimotope peptides for nanobodies: A nontoxic alternative to ochratoxin A and its application in chemiluminescence immunoassays for analysis of pepper samples

Ochratoxin A (OTA) is a common food contaminant and poses a significant threat to human health, which requires rigorous monitoring. Mimotope peptides (MPs) are commonly used as non-toxic alternatives to toxic small molecules in eco-friendly immunoassays. Herein, with an anti-OTA nanobody as the target protein, cyclic 7-mer MPs of OTA were screened using phage display and immunomagnetic separation. The phage MPs (PMP) with the highest sensitivity and its alkaline phosphatase-tagged MP fusion (ALP-MP) were used to develop a PMP-based chemiluminescent immunoassay (PMP-CLIA) and an ALP-MP-based CLIA (AMP-CLIA). After optimization, PMP-CLIA and AMP-CLIA exhibited a limit of detection of 0.128 ng/mL and 0.232 ng/mL. Good accuracy and selectivity were confirmed for both CLIAs by recovery experiments and cross-reactions. Moreover, they were validated by high performance liquid chromatography in detecting real pepper samples. Thus, two CLIAs based on the nanobody and MPs were demonstrated as reliable tools for monitoring OTA in pepper.

A novel sustainable immunoassay for sensitive detection of atrazine based on the anti-idiotypic nanobody and recombinant full-length antibody

Immunoassays have been widely used to determine small-molecule compounds in food and the environment, meeting the challenge of obtaining false positive or negative results because of the variance in the batches of antibodies and antigens. To resolve this problem, atrazine (ATR) was used as a target, and anti-idiotypic nanobodies for ATR (AI-Nbs) and a recombinant full-length antibody against ATR (ATR-rAb) were prepared for the development of a sustainable enzyme-linked immunosorbent assay (ELISA). AI-Nb-7, AI-Nb-58, and AI-Nb-66 were selected from an immune phage display library. ATR-rAb was produced in mammalian HEK293 (F) cells. Among the four detection methods explored, the assay using AI-Nb-66 as a coating antigen and ATR-rAb as a detection reagent yielded a half maximal inhibitory concentration (IC50) of 1.66 ng mL-1 for ATR and a linear range of 0.35-8.73 ng mL-1. The cross-reactivity of the assay to ametryn was 64.24%, whereas that to terbutylazine was 38.20%. Surface plasmon resonance (SPR) analysis illustrated that these cross-reactive triazine compounds can bind to ATR-rAb to varying degrees at high concentrations; however, the binding/dissociation kinetic curves and the response values at the same concentration are different, which results in differences in cross-reactivity. Homology modeling and molecular docking revealed that the triazine ring is vital in recognizing triazine compounds. The proposed immunoassay exhibited acceptable recoveries of 84.40-105.36% for detecting fruit, vegetables, and black tea. In conclusion, this study highlights a new strategy for developing sustainable immunoassays for detecting trace pesticide contaminants.

Enzyme Cascade Amplification-Based Immunoassay Using Alkaline Phosphatase-Linked Single-Chain Variable Fragment Fusion Tracer and MnO2 Nanosheets for Detection of Deoxynivalenol in Corn Samples

Deoxynivalenol (DON) is a common mycotoxin that contaminates cereals. Therefore, the development of sensitive and efficient detection methods for DON is essential to guarantee food safety and human health. In this study, an enzyme cascade amplification-based immunoassay (ECAIA) using a dual-functional alkaline phosphatase-linked single-chain fragment variable fusion tracer (scFv-ALP) and MnO2 nanosheets was established for DON detection. The scFv-ALP effectively catalyzes the hydrolysis of ascorbyl-2-phosphate (AAP) to produce ascorbic acid (AA). This AA subsequently interacts with MnO2 nanosheets to initiate a redox reaction that results in the loss of oxidizing properties of MnO2. In the absence of ALP, MnO2 nanosheets can oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to produce the blue oxidized product of TMB, which exhibits a signal at a wavelength of 650 nm for quantitative analysis. After optimization, the ECAIA had a limit of detection of 0.45 ng/mL and a linear range of 1.2-35.41 ng/mL. The ECAIA exhibited good accuracy in recovery experiments and high selectivity for DON. Moreover, the detection results of the actual corn samples correlated well with those from high-performance liquid chromatography. Overall, the proposed ECAIA based on the scFv-ALP and MnO2 nanosheets was demonstrated as a reliable tool for the detection of DON in corn samples.

Sensitive Dual-Signal ELISA Based on Specific Phage-Displayed Double Peptide Probes with Internal Filtering Effect to Assay Monkeypox Virus Antigen

The global spread of monkeypox has become a worldwide public healthcare issue. Therefore, there is an urgent need for accurate and sensitive detection methods to effectively control its spreading. Herein, we screened by phage display two peptides M4 (sequence: DPCGERICSIAL) and M6 (sequence: SCSSFLCSLKVG) with good affinity and specificity to monkeypox virus (MPXV) B21R protein. To simulate the state of the peptide in the phage and to avoid spatial obstacles of the peptide, GGGSK was added at the C terminus of M4 and named as M4a. Molecular docking shows that peptide M4a and peptide M6 are bound to different epitopes of B21R by hydrogen bonds and salt-bridge interactions, respectively. Then, peptide M4a was selected as the capture probe, phage M6 as the detection probe, and carbonized polymer dots (CPDs) as the fluorescent probe, and a colorimetric and fluorescent double-signal capture peptide/antigen/signal peptide-displayed phage sandwich ELISA triggered by horseradish peroxidase (HRP) through a simple internal filtration effect (IFE) was constructed. HRP catalyzes H2O2 to oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to generate blue oxidized TMB, which can further quench the fluorescence of CPDs through IFE, enabling to detect MPXV B21R in colorimetric and fluorescent modes. The proposed simple immunoassay platform shows good sensitivity and reliability in MPXV B21R detection. The limit of detection for colorimetric and fluorescent modes was 27.8 and 9.14 pg/mL MPXV B21R, respectively. Thus, the established double-peptide sandwich-based dual-signal immunoassay provides guidance for the development of reliable and sensitive antigen detection capable of mutual confirmation, which also has great potential for exploring various analytical strategies for other respiratory virus surveillance.

Sequence-based design and construction of synthetic nanobody library

Nanobody (Nb), the smallest antibody fragments known to bind antigens, is now widely applied to various studies, including protein structure analysis, bioassay, diagnosis, and biomedicine. The traditional approach to generating specific nanobodies involves animal immunization which is time-consuming and expensive. As the understanding of the antibody repertoire accumulation, the synthetic library, which is devoid of animals, has attracted attention widely in recent years. Here, we describe a synthetic phage display library (S-Library), designed based on the systematic analysis of the next-generation sequencing (NGS) of nanobody repertoire. The library consists of a single highly conserved scaffold (IGHV3S65*01-IGHJ4*01) and complementary determining regions of constrained diversity. The S-Library containing 2.19 × 108 independent clones was constructed by the one-step assembly and rapid electro-transformation. The S-Library was screened against various targets (Nb G8, fusion protein of Nb G8 and green fluorescent protein, bovine serum albumin, ovalbumin, and acetylcholinesterase). In comparison, a naïve library (N-Library) from the source of 13 healthy animals was constructed and screened against the same targets as the S-Library. Binders were isolated from both S-Library and N-Library. The dynamic affinity was evaluated by the biolayer interferometry. The data confirms that the feature of the Nb repertoire is conducive to reducing the complexity of library design, thus allowing the S-Library to be built on conventional reagents and primers.

Generation of anti-idiotypic antibodies mimicking Cry2Aa toxin from an immunized mouse phage display library as potential insecticidal agents against Plutella xylostella

This study tried to generate anti-idiotypic antibodies (Ab2s) which mimic Cry2Aa toxin using a phage-display antibody library (2.8 × 107 CFU/mL). The latter was constructed from a mouse immunized with F (ab')2 fragments digested from anti-Cry2Aa polyclonal antibodies. The F (ab')2 fragments and Plutella xylostella (P. xylostella) brush border membrane vesicles (BBMV) were utilized as targets for selection. Eight mouse phage-display single-chain variable fragments (scFvs) were isolated and identified by enzyme-linked immunoassay (ELISA), PCR and DNA sequencing after four rounds of biopanning. Among them, M3 exhibited the highest binding affinity with F (ab')2, while M4 bound the best with the toxin binding region of cadherin of P. xylostella (PxCad-TBR). Both of these two fragments were chosen for prokaryotic expression. The expressed M3 and M4 proteins with molecular weights of 30 kDa were purified. The M4 showed a binding affinity of 29.9 ± 2.4 nM with the PxCad-TBR and resulted in 27.8 ± 4.3 % larvae mortality against P. xylostella. Computer-assisted molecular modeling and docking analysis showed that mouse scFv M4 mimicked some Cry2Aa toxin binding sites when interacting with PxCad-TBR. Therefore, anti-idiotypic antibodies generated by BBMV-based screening could be useful for the development of new bio-insecticides as an alternative to Cry2Aa toxin for pest control.

Review of phage display: A jack-of-all-trades and master of most biomolecule display

Phage display was first described by George P. Smith when it was shown that virus particles were capable of presenting foreign proteins on their surface. The technology has paved the way for the evolution of various biomolecules presentation and diverse selection strategies. This unique feature has been applied as a versatile platform for numerous applications in drug discovery, protein engineering, diagnostics, and vaccine development. Over the decades, the limits of biomolecules displayed on phage particles have expanded from peptides to proteomes and even alternative scaffolds. This has allowed phage display to be viewed as a versatile display platform to accommodate various biomolecules ranging from small peptides to larger proteomes which has significantly impacted advancements in the biomedical industry. This review will explore the vast array of biomolecules that have been successfully employed in phage display technology in biomedical research.

Development of competitive and noncompetitive lateral flow immunoassays for pendimethalin using synthetic peptides

Peptidomimetic and anti-immunocomplex peptides can be easily isolated from phage display libraries, and can be used as alternatives to chemical competing haptens to improve the sensitivity of small molecule immunoassay. In this work, 16 peptidomimetics and 7 anti-immunocomplex peptides of pendimethalin (PND) were obtained from cyclic 7-, 8-, 9-, and 10-residue peptide phage libraries. Peptidomimetic EJ-2 (CMFTGTDFPC) with the highest sensitivity in competitive phage enzyme-linked immunosorbent assay (ELISA) and immunocomplex peptide EF-30 (CNPGWPPIPC) with the highest sensitivity in noncompetitive phage ELISA were selected to prepare phage-free peptides with GGGSSK-biotin at the C-terminus. Competitive and noncompetitive lateral flow immunoassays (CLFIA and NLFIA) were developed by using the phage-free peptides. After optimization, the CLFIA and NLFIA showed visual limit of detections (vLODs) of 5 ng/mL and 2.5 ng/mL, respectively, which were improved two- and fourfold compared with a LFIA based on chemical hapten. The NLFIA showed better sensitivity than CLFIA in the detection of spiked samples, and can meet the detection requirements for agro-products regulated by EU and China. The detection results of CLFIA and NLFIA for blind samples were consistent with that of ultra performance liquid chromatography/tandem mass spectrometry.

Isolation, Characterization, and Comparative Genomic Analysis of Bacteriophage Ec_MI-02 from Pigeon Feces Infecting Escherichia coli O157:H7

The most significant serotype of Shiga-toxigenic Escherichia coli that causes foodborne illnesses is Escherichia coli O157:H7. Elimination of E. coli O157:H7 during food processing and storage is a possible solution. Bacteriophages have a significant impact on bacterial populations in nature due to their ability to lyse their bacterial host. In the current study, a virulent bacteriophage, Ec_MI-02, was isolated from the feces of a wild pigeon in the United Arab Emirates (UAE) for potential future use as a bio-preservative or in phage therapy. Using a spot test and an efficiency of plating analysis, Ec_MI-02 was found to infect in addition to the propagation host, E. coli O157:H7 NCTC 12900, five different serotypes of E. coli O157:H7 (three clinical samples from infected patients, one from contaminated green salad, and one from contaminated ground beef). Based on morphology and genome analysis, Ec_MI-02 belongs to the genus Tequatrovirus under the order Caudovirales. The adsorption rate constant (K) of Ec_MI-02 was found to be 1.55 × 10^-8 mL/min. The latent period was 50 min with a burst size of almost 10 plaque forming units (pfu)/host cell in the one-step growth curve when the phage Ec_MI-02 was cultivated using the propagation host E. coli O157:H7 NCTC 12900. Ec_MI-02 was found to be stable at a wide range of pH, temperature, and commonly used laboratory disinfectants. Its genome is 165,454 bp long with a GC content of 35.5% and encodes 266 protein coding genes. Ec_MI-02 has genes encoding for rI, rII, and rIII lysis inhibition proteins, which supports the observation of delayed lysis in the one-step growth curve. The current study provides additional evidence that wild birds could also be a good natural reservoir for bacteriophages that do not carry antibiotic resistance genes and could be good candidates for phage therapy. In addition, studying the genetic makeup of bacteriophages that infect human pathogens is crucial for ensuring their safe usage in the food industry.

Methods and Advances in the Design, Testing and Development of In Vitro Diagnostic Instruments

With the continuous improvement of medical testing and instrumentation engineering technologies, the design, testing and development methods of in vitro diagnostic instruments are developing rapidly. In vitro diagnostic instruments are also gradually developing into a class of typical high-end medical equipment. The design of in vitro diagnostic instruments involves a variety of medical diagnostic methods and biochemical, physical and other related technologies, and its development process involves complex system engineering. This paper systematically organizes and summarizes the design, testing and development methods of in vitro diagnostic instruments and their development in recent years, focusing on summarizing the related technologies and core aspects of the R&D process, and analyzes the development trend of the in vitro diagnostic instrument market.

Application of Molecularly Imprinted Electrochemical Biomimetic Sensors for Detecting Small Molecule Food Contaminants

Environmental chemical contaminants in food seriously impact human health and food safety. Successful detection methods can effectively monitor the potential risk of emerging chemical contaminants. Among them, molecularly imprinted polymers (MIPs) based on electrochemical biomimetic sensors overcome many drawbacks of conventional detection methods and offer opportunities to detect contaminants with simple equipment in an efficient, sensitive, and low-cost manner. We searched eligible papers through the Web of Science (2000-2022) and PubMed databases. Then, we introduced the sensing mechanism of MIPs, outlined the sample preparation methods, and summarized the MIP characterization and performance. The classification of electrochemistry, as well as its advantages and disadvantages, are also discussed. Furthermore, the representative application of MIP-based electrochemical biomimetic sensors for detecting small molecular chemical contaminants, such as antibiotics, pesticides, toxins, food additives, illegal additions, organic pollutants, and heavy metal ions in food, is demonstrated. Finally, the conclusions and future perspectives are summarized and discussed.

Small Peptides in the Detection of Mycotoxins and Their Potential Applications in Mycotoxin Removal

Mycotoxins pose significant risks to humans and livestock. In addition, contaminated food- and feedstuffs can only be discarded, leading to increased economic losses and potential ecological pollution. Mycotoxin removal and real-time toxin level monitoring are effective approaches to solve this problem. As a hot research hotspot, small peptides derived from phage display peptide libraries, combinatorial peptide libraries, and rational design approaches can act as coating antigens, competitive antigens, and anti-immune complexes in immunoassays for the detection of mycotoxins. Furthermore, as a potential approach to mycotoxin degradation, small peptides can mimic the natural enzyme catalytic site to construct artificial enzymes containing oxidoreductases, hydrolase, and lyase activities. In summary, with the advantages of mature synthesis protocols, diverse structures, and excellent biocompatibility, also sharing their chemical structure with natural proteins, small peptides are widely used for mycotoxin detection and artificial enzyme construction, which have promising applications in mycotoxin degradation. This paper mainly reviews the advances of small peptides in the detection of mycotoxins, the construction of peptide-based artificial enzymes, and their potential applications in mycotoxin control.

Identification and Application of Two Promising Peptide Ligands for the Immunodetection of Imidacloprid Residue

As the most widely used neonicotinoid insecticide, it is of great significance to explore the immunoreagents and immunoassays for imidacloprid (IMI) residue. In immunoassays, specific peptide ligands, such as peptidomimetic and anti-immunocomplex peptides, are regarded as promising substitutes for chemical haptens. In the present work, we identified thirty sequences of peptidomimetics and two sequences of anti-immunocomplex peptides for IMI from three phage pVIII display cyclic peptide libraries, in which the anti-immunocomplex peptides are the first reported noncompetitive reagents for IMI. The peptidomimetic 1-9-H and anti-immunocomplex peptide 2-1-H that showed the best sensitivity were utilized to develop competitive and noncompetitive phage enzyme-linked immunosorbent assays (P-ELISAs), with a half inhibition concentration of 0.55 ng/mL for competitive P-ELISA and a half-saturation concentration of 0.35 ng/mL for noncompetitive P-ELISA. The anti-immunocomplex peptide was demonstrated to greatly improve the specificity compared with competitive P-ELISA. In addition, the accuracy of proposed P-ELISAs was confirmed by recovery analysis and HPLC verification in agricultural and environmental samples. These results show that the peptide ligands identified from phage display library can replace chemical haptens in the immunoassays of IMI with the satisfactory performance.

Single-chain fragment variable produced by phage display technology: Construction, selection, mutation, expression, and recent applications in food safety

Immunoassays are reliable, efficient, and accurate methods for the analysis of small-molecule harmful substances (such as pesticides, veterinary drugs, and biological toxins) that may be present in food. However, traditional polyclonal and monoclonal antibodies are limited by animal hosts and hinder further development of immunoassays. With the gradual application of phage display technology as an efficient in vitro selection technology, the single-chain fragment variable (scFv) now provides an exciting alternative to traditional antibodies. Efficiently constructed scFv source libraries and specifically designed biopanning schemes can now yield scFvs possessing specific recognition capabilities. A rational mutation strategy further enhances the affinity of scFv, and allows it to reach a level that cannot be achieved by immunization. Finally, appropriate prokaryotic expression measures ensure stable and efficient production of scFv. Therefore, when developing excellent scFvs, it is necessary to focus on three key aspects of this process that include screening, mutation, and expression. In this review, we analyze in detail the preparation and affinity improvement process for scFv and provide insights into the research progress and development trend of scFv-based immunoassay methods for monitoring small-molecule harmful substances.

Biotin-labelled peptidomimetic for competitive time-resolved fluoroimmunoassay of benzothiostrobin

In recent years, more and more functional peptide ligands have been identified from phage display libraries and served the immunoassay of small molecules. After the identification, the phage particle instead limits further application of peptide ligands, so it is of great significance to explore the peptide ligand as an independent detection reagent. In this work, the identified peptidomimetic of benzothiostrobin was synthesized and labelled with biotin, which was combined with Eu³⁺-labelled streptavidin to develop the peptide-based time-resolved fluoroimmunoassay (P-TRFIA). Under the optimal conditions, the half-maximum inhibitory concentration (IC₅₀) of proposed P-TRFIA is 3.63 ng mL^-1, which is similar to the TRFIA using phage-borne peptidomimetic and Eu³⁺-labelled anti-phage antibody (IC₅₀: 4.55 ng mL^-1), also more sensitive than previously reported immunoassays for benzothiostrobin. In addition, the proposed P-TRFIA shows excellent specificity and accuracy for analysis of spiked samples, and its detection results shows good consistency with high-performance liquid chromatography for the detection of environment and agro-products samples with unknown benzothiostrobin concentrations.

"Ready-to-use" immunosensor for the detection of small molecules with fast readout

Immunoassays are commonly used methods for detection of small molecules that typically require numerous steps of the labeling between immune-recognition reagents and tracers, immobilization and recurrent washing, making them time consuming and difficult to adapt into point of care formats. Here we describe a "ready-to-use" homogeneous competitive immunosensor with an assay time of 10 min that is based exclusively on recombinant reagents. The signal is produced when the split fragments of the nano luciferase (Nluc) are brought together by the interaction of a heavy chain only variable domain (VHH) with a peptidomimetic of the target small molecule. A VHH to 2,4-dichlorophenoxyacetic acid (2,4-D) was used to isolated the peptidomimetic (NGFFEPWQVVYV) from phage display libraries using six panning conditions. Then the peptidomimetic and VHH were fused with the larger (LgN) and smaller piece (SmN) of split fragments of Nluc, respectively. In order to optimize the signal and sensitivity of the immunosensor, we explored the effects of the spacer between the peptidomimetic and LgN, the copy number of peptidomimetics, and the spacer between SmN and VHH, generating 24 combinations that allowed to conclude on their respective roles. Eventually, the developed "ready-to-use" immunosensor performed excellent signal-to-noise ratio and sensitivity, and could be applied to the detection of 2,4-D in real samples. Meanwhile, the immunosensor totally realizes labeling-free, immobilization-free and washing-free, also can be produced in a highly cost effective way.

Identification of single domain antibodies with insect cytotoxicity using phage-display antibody library screening and Plutella xylostella ATP-binding cassette transporter subfamily C member 2 (ABCC2) -based insect cell expression system

It is extremely imminent to study a new strategy to manage agricultural pest like Plutella xylostella (P. xylostella) which is currently resistant to most of pesticides, including three domain-Cry toxins from Bacillus thuringiensis (Bt). In this study, we reported a phage displayed single domain antibody screening from human domain antibody (DAb) library targeted on Spodoptera frugiperda 9 (Sf9) cells expressed Cry1Ac toxin receptor, ATP-dependent binding cassette transporter C2 in P. xylostella (PxABCC2). After three rounds of panning, three cytotoxic antibodies (1D2, 2B7, 3C4) were obtained from thirty-eight antibodies and displayed high binding ability towards PxABCC2-expressed Sf9 cells. Through homology modeling and molecular docking, the interaction mode indicated that the most cytotoxic 1D2 of the three antibodies presented the lowest binding free energy required and had the most hydrogen bond formed with PxABCC2 in molecular docking analysis. Functional assay of key regions in 1D2 via Alanine replacement indicated that complementarity-determining region (CDR) 3 played a crucial role in antibody exerts binding activity and cytotoxicity. This study provides the first trial for discovering of potential cytotoxic antibodies from the human antibody library via specific receptor-expressed insect cell system biopanning.

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.

An Overview for the Nanoparticles-Based Quantitative Lateral Flow Assay

The development of the lateral flow assay (LFA) has received much attention in both academia and industry because of their broad applications to food safety, environmental monitoring, clinical diagnosis, and so forth. The user friendliness, low cost, and easy operation are the most attractive advantages of the LFA. In recent years, quantitative detection has become another focus of LFA development. Here, the most recent studies of quantitative LFAs are reviewed. First, the principles and corresponding formats of quantitative LFAs are introduced. In the biomaterial and nanomaterial sections, the detection, capture, and signal amplification biomolecules and the optical, fluorescent, luminescent, and magnetic labels used in LFAs are described. The invention of dedicated strip readers has drawn further interest in exploiting the better performance of LFAs. Therefore, next, the development of dedicated reader devices is described and the usefulness and specifications of these devices for LFAs are discussed. Finally, the applications of LFAs in the detection of metal ions, biotoxins, pathogenic microorganisms, veterinary drugs, and pesticides in the fields of food safety and environmental health and the detection of nucleic acids, biomarkers, and viruses in clinical analyses are summarized.

Recognition elements based on the molecular biological techniques for detecting pesticides in food: A review

Excessive use of pesticides can cause contamination of the environment and agricultural products that are directly threatening human life and health. Therefore, in the process of food safety supervision, it is crucial to conduct sensitive and rapid detection of pesticide residues. The recognition element is the vital component of sensors and methods for fast testing pesticide residues in food. Improper recognition elements may lead to defects of testing methods, such as poor stability, low sensitivity, high economic costs, and waste of time. We can use the molecular biological technique to address these challenges as a good strategy for recognition element production and modification. Herein, we review the molecular biological methods of five specific recognition elements, including aptamers, genetic engineering antibodies, DNAzymes, genetically engineered enzymes, and whole-cell-based biosensors. In addition, the application of these identification elements combined with biosensor and immunoassay methods in actual detection was also discussed. The purpose of this review was to provide a valuable reference for further development of rapid detection methods for pesticide residues.

Sortase-Mediated Phage Decoration for Analytical Applications

Phage-borne peptides and antibody fragments isolated from phage display libraries have proven to be versatile and valuable reagents for immunoassay development. Due to the lack of convenient and mild-condition methods for the labeling of the phage particles, isolated peptide/protein affinity ligands are commonly removed from the viral particles and conjugated to protein tracers or nanoparticles for analytical use. This abolishes the advantage of isolating ready-to-use affinity binders and creates the risk of affecting the polypeptide activity. To circumvent this problem, we optimized the phage display system to produce phage particles that express the affinity binder on pIII and a polyglycine short peptide fused to pVIII that allows the covalent attachment of tracer molecules employing sortase A. Using a llama heavy chain only variable domain (VHH) against the herbicide 2,4-D on pIII as the model, we showed that the phage can be extensively decorated with a rhodamine-LPETGG peptide conjugate or the protein nanoluciferase (Nluc) equipped with a C-terminal LPETGG peptide. The maximum labeling amounts of rhodamine-LPETGG and Nluc-LPETGG were 1238 ± 63 and 102 ± 16 per phage, respectively. The Nluc-labeled dual display phage was employed to develop a phage bioluminescent immunoassay (P-BLEIA) for the detection of 2,4-D. The limit of detection and 50% inhibition concentration of P-BLEIA were 0.491 and 2.15 ng mL^-1, respectively, which represent 16-fold and 8-fold improvement compared to the phage enzyme-linked immunosorbent assay. In addition, the P-BLEIA showed good accuracy for the detection of 2,4-D in spiked samples.