Polyclonal antibody-based noncompetitive immunoassay for small analytes developed with short peptide loops isolated from phage libraries

Application of Anti-Immune Complex Reagents in Small Molecule Analyte Immunoassays

The detection of small molecule analytes (SMAs) is of great significance for food and drug testing, environmental monitoring, and disease diagnosis. However, the performance of commercially available SMA immunoassays is limited by their low sensitivity and specificity due to the competitive format, leaving significant room for improvement. In recent years, the application of noncompetitive immunoassays for the detection of SMAs has become a hot topic, especially with the rapid evolution of antibody development technology. The remarkable development and application of anti-immune complex (anti-IC) reagents targeting antigen-specific antibodies have garnered significant interest from researchers and diagnostic companies, particularly in the field of SMA detection. The discovery and development history of anti-IC antibodies, the advantages and limitations of different anti-IC reagent preparation methods, and the mechanisms of interaction between ICs and anti-IC antibodies are reviewed. A comprehensive overview of the application of anti-IC antibodies in SMAs assay, including pesticide residue detection, mycotoxin detection, and clinical testing, as well as current challenges and potential solutions in noncompetitive immunoassays, is also summarized to provide a reference for the rapid and accurate detection of SMAs.

A breakthrough of immunoassay format for hapten: recent insights into noncompetitive immunoassays to detect small molecules

Immunoassay based on the antibodies specific for targets has advantages of high sensitivity, simplicity and low cost, therefore it has received more attention in recent years, especially for the rapid detection of small molecule chemicals present in foods, diagnostics and environments. However, limited by low molecular weight and only one antigenic determinant existed, immunoassays for these small molecule chemicals, namely hapten substances, were commonly performed in a competitive immunoassay format, whose sensitivities were obviously lower than the sandwich enzyme-linked immunosorbent assay generally adaptable for the protein targets. In order to break through the bottleneck of detection format, researchers have designed and established several novel noncompetitive immunoassays for the haptens in the past few years. In this review, we focused on the four representative types of noncompetitive immunoassay formats and described their characteristics and applications in rapid detection of small molecules. Meanwhile, a systematic discussion on the current technologies challenges and the possible solutions were also summarized. This review aims to provide an updated overview of the current state-of-the-art in noncompetitive immunoassay for small molecules, and inspire the development of novel designs for small molecule detection.

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.

Sensitive detection of the okadaic acid marine toxin in shellfish by Au@Pt NPs/horseradish peroxidase dual catalysis immunoassay

Based on the catalysis enhancement strategy of Au@Pt nanoparticles (Au@Pt NPs) and horseradish peroxidase (HRP) related to the TMB-H₂O₂ indicator, a sensitive colorimetric immunoassay was established for trace okadaic acid (OA) detection. The anti-OA monoclonal antibody (McAb) with a high K_aff constant was prepared and modified on Au@Pt NPs. Through grafting the HRP conjugated goat anti-mouse IgG antibody (IgG) on Au@Pt/McAb, bifunctional composites with Au@Pt-Ab and HRP were prepared and adopted. Characteristics including morphology, specificity and catalytic performance were evaluated. Under the optimal conditions, the sensitivity of the resultant enzyme immunoassay was significantly improved, and a low limit of detection (LOD) of OA was achieved at 0.04 ng mL^-1 (equivalent to 0.6 μg kg^-1 in mussel tissue), which was better than that of most HRP or Au/HRP enzyme-linked immunosorbent assays. When applied to fortified shellfish samples (e.g. oysters, mussels and clams), the recoveries ranging from 98.3 ± 2.3% to 106.0 ± 9.0% were acceptable and comparable with those of the LC-MS method. Acceptable precision was achieved with a variation coefficient (CV) of 2.3-8.4%. The method provides a promising alternative for the highly sensitive detection of the OA marine toxin at trace levels.

Development of a noncompetitive magnetic-phage anti-immunocomplex assay for detecting of organophosphorus pesticides with a thiophosphate group

Organophosphorus pesticides (OPs) are widely used in agriculture and the monitoring of their residues is very important to protect human health. Immunoassays are important tools for the analysis of small molecules. Generally, noncompetitive mode of immunoassay is considered to be more sensitive than competitive mode. In this study, peptides that can identify immunocomplex of OPs were screened from a phage display library. Subsequently, a second-generation peptide library was constructed and peptides with better performance were isolated. Then, a rapid and sensitive noncompetitive magnetic-phage anti-immunocomplex assay (MPHAIA) for OPs was developed based on the best phage-peptide and single chain antibody immunomagnetic beads. The MPHAIA showed broad specificity for OPs with a thiophosphate group. The half-saturated concentration (SC₅₀) values and limits of detection (LODs) of MPHAIA to 12 OPs were ranged from 15.04 to 105.48 ng/mL and 4.07-14.19 ng/mL, respectively. The accuracy and reliability of MPHAIA were verified by gas chromatography-tandem mass spectrometry (GC-MS/MS) parallel analysis of six kinds of OPs in spiked cucumber samples. The recovery rates were in range of 81.2-116.3% with coefficient of variation from 4.1% to 14.1%, which were consistent with the results of GC-MS/MS.

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.

Competitive immune-nanoplatforms with positive readout for the rapid detection of imidacloprid using gold nanoparticles

Two high-sensitivity competitive immune-nanoplatforms based on the inner filter effect (IFE-IN) and magnetic separation (MS-IN) with a positive readout were developed to rapidly detect imidacloprid (IMI) using gold nanoparticles (AuNPs). For IFE-IN, IMI competes with AuNPs-labeled IMI antigens (IMI-BSA-AuNPs) to bind with anti-IMI monoclonal antibody (mAb)-conjugated NaYF4:Yb,Er upconversion nanoparticles, which changes the fluorescence signal at excitation/emission wavelength of 980/544 nm. For MS-IN, the immunocomplex of IMI-BSA-AuNPs and magnetic-nanoparticles-labeled mAb (mAb-MNPs) dissociates in the presence of IMI, and the optical density of IMI-BSA-AuNPs at 525 nm increases with the IMI concentration after magnetic separation. Under the optimal conditions, the IMI concentration producing a 50% saturation of the signal (SC50) and linear range (SC10- SC90) were found to be 4.30 ng mL-1 and 0.47 - 21.37 ng mL-1 for IFE-IN, while 1.21 ng mL-1 and 0.07 - 10.21 ng mL-1 for MS-IN, respectively. Both IFE-IN and MS-IN achieved excellent accuracy for the detection of IMI in different matrices. The quantities of IMI in apple samples detected by IFE-IN and MS-IN were consistent with the high-performance liquid chromatography results. For IFE-IN, analyte competes with AuNPs-labeled-antigen to bind with the mAb-conjugated-UCNPs, which changes the fluorescence signal at 544 nm. For MS-IN, the immunocomplex of AuNPs-labeled-antigen and mAb-conjugated-MNPs dissociates in the presence of analyte, and the optical density of AuNPs-labeled-antigen at 525 nm increases with increasing analyte concentration after separation.

An enhanced open sandwich immunoassay by molecular evolution for noncompetitive detection of Alternaria mycotoxin tenuazonic acid

Open sandwich enzyme-linked immunosorbent assay (OS-ELISA), a novel noncompetitive immunoassay format, has shown great potential in rapid detection for small molecules compared with traditional competitive format. Here, an enhanced OS-ELISA towards the mycotoxin tenuazonic acid (TeA) was developed for the first time based on heavy chain variable region (V_H) and light chain variable region (V_L) from the hybridoma cells (3F10) producing anti-TeA monoclonal antibody (mAb). The established OS-ELISA exhibited a limit of detection of 0.08 ng/mL, and was 13 times more sensitive than mAb-based indirect competitive ELISA (ic-ELISA). The proposed assay was also applied to detect TeA contents in juice, flour and tomato ketchup samples with satisfactory recoveries of 87.6%-111.3%. Finally, the great accuracy of the established OS-ELISA method was validated by the standard ultra-performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS).

Development of a sensitive non-competitive immunoassay via immunocomplex binding peptide for the determination of ethyl carbamate in wine samples

Ethyl carbamate is a group of 2A carcinogen ubiquitously existed in fermented foods. The monitoring of its residues was important for evaluating the potential risk to human beings. Immunoassays with good accuracy and simplicity are great analytical tools for small molecule contaminants. However, it is typically confined in a competitive mode for small molecules with drawback of the sensitivity curbing. In this work, three different phages displayed peptides with capability of identifying the xanthyl ethyl carbamate immunocomplex were isolated from phage library. The binding mechanism of peptides and immunocomplex was studied by computer-assisted simulation. Results indicated that the xanthydrol group of xanthyl ethyl carbamate and the Asn-32 and Asn-92 residues of the antibody light chain were mainly responsible for binding. Simultaneously, a sensitive non-competitive immunoassay for detecting ethyl carbamate in wine samples was developed. The established method exhibited a limit of detection of 5.4 ng/mL and a linear range from 8.7 ng/mL to 32 ng/mL for wine samples. In comparison with the conventional competitive immunoassay, the sensitivity of the proposed non-competitive immunoassay was improved by 17-fold. The results of the immunoassay were validated by a standard ultra-performance liquid chromatography-quadrupole/orbitrap high-resolution mass spectrometry, which illustrated good reliability of the proposed assay.

Transcription Factor Based Small-Molecule Sensing with a Rapid Cell Phone Enabled Fluorescent Bead Assay

Recently, allosteric transcription factors (TFs) were identified as a novel class of biorecognition elements for in vitro sensing, whereby an indicator of the differential binding affinity between a TF and its cognate DNA exhibits dose-dependent responsivity to an analyte. Described is a modular bead-based biosensor design that can be applied to such TF-DNA-analyte systems. DNA-functionalized beads enable efficient mixing and spatial separation, while TF-labeled semiconductor quantum dots serve as bright fluorescent indicators of the TF-DNA bound (on bead) and unbound states. The prototype sensor for derivatives of the antibiotic tetracycline exhibits nanomolar sensitivity with visual detection of bead fluorescence. Facile changes to the sensor enable sensor response tuning without necessitating changes to the biomolecular affinities. Assay components self-assemble, and readout by eye or digital camera is possible within 5 minutes of analyte addition, making sensor use facile, rapid, and instrument-free.

Construction and characterization of a class-specific single-chain variable fragment against pyrethroid metabolites

Pyrethroids are insecticides that are widely used in rural and urban areas worldwide. After entering the environment, pyrethroids are rapidly metabolized or degraded by various biological or abiotic methods. In this study, a single-chain variable fragment (scFv) which could simultaneously detect three pyrethroid metabolites was constructed based on a hybridoma raised against 3-phenoxybenzoic acid (3-PBA). By molecular docking, it showed that there were hydrogen bonds, hydrophobic interactions, CH-π interaction, and cation-π interaction between 3-PBA and its scFv. All the contact residues contributing to hydrogen bonds are located in VH-CDR2 or its neighboring region, and two of them were mutants of the closest germline sequence. Based on competitive ELISA, the half maximal inhibitory concentration (IC₅₀) of the scFv for 3-PBA, 3-phenoxybenzaldehyde (PBAld), and 3-phenoxybenzyl alcohol (PBAlc) were calculated to be 0.55, 0.59, and 0.63 μgmL^-1, respectively. The scFv also showed 23.91%, 13.41%, 1.15%, 1.00%, and 0.56% cross-reactivity with phenothrin, deltamethrin, fenvalerate, beta-cypermethrin, and fenpropathrin. The broad specificity of the scFv may be due to its hapten design. The scFv could be employed in class-specific immunoassays for pyrethroid metabolites with phenoxybenzyl (PB) group. It is also potentially used for characterizing degradation of pyrethroids or detecting PBAlc (PBAld) alone, and the detection results should be confirmed by other selective methods. KEY POINTS: • A scFv which can simultaneously detect 3-PBA, PBAlc, and PBAld was constructed. • Antibody informatics and binding mode of the scFv were obtained. • The reason for its broad specificity was discussed. • It could be used to monitor single or multi-pyrethroid metabolites with PB group.

Nanochannel-driven rapid capture of sub-nanogram level biomarkers for painless preeclampsia diagnosis

Preeclampsia (PE) is a pregnancy-specific hypertensive syndrome recognized as the leading cause of maternal and fetal morbidity and mortality worldwide. Painful blood-collection procedures or low accuracy of non-invasive approaches require faster, patient-friendly, and more sensitive diagnostic technologies. Here we report a painless, highly sensitive detection platform using nanoporous microneedles (nMNs) that enables rapid capture of biomarkers present at sub-nanogram levels. The highly porous nanostructures on the nMN surface were prepared by anodization of aluminum MN and then functionalized by immobilization of capture antibodies to detect target biomarkers based on an immunoassay method. The immuno-functionalized nMN array demonstrated rapid capture of an estrogen (E2) biomarker for PE following a 1-min incubation and exhibited a concentration-dependent change in fluorescence intensity over the E2 range of 0.5 ng mL^-1 to 1000 ng mL^-1 after treatment with fluorescence-detection antibodies. Remarkably, the nMN patch selectively detected sub-nanogram-levels of E2 in subcutaneous interstitial fluid from rats with increased diagnostic accuracy as compared with commercial immunoassay kits. This bio-functionalized nMN platform showed improved biosensing capability for multiple PE-related biomarkers, including hormones and proteins. Furthermore, this painless method demonstrated efficacy as a point-of-need diagnostic platform using portable smartphone-based fluorescence microscope to obtain fluorescence images of biomarker-captured nMN arrays.

Fluorescent "Turn off-on" Small-Molecule-Monitoring Nanoplatform Based on Dendrimer-like Peptides as Competitors

Peptides isolated from phage display libraries are powerful reagents for small-molecule immunoassay; however, their application as phage-borne peptides is significantly limited by the biological nature of the phage. Here, we present the use of lysine scaffold to prepare a series of different valence peptides to serve as replacements for phage-borne peptides. Benzothiostrobin was selected as a model analyte, the cyclic benzothiostrobin-peptidomimetic in the form of monomer, dendrimer-like dimer, and tetramer were designed and synthesized. Compared with the monomer, the affinity of dendrimer-like dimer and tetramer increased 1.87 and 13.6 times, respectively, as determined by isothermal titration calorimetry (ITC). A novel inner filter effect immunoassay (IFE-IA) with positive readout was developed for benzothiostrobin detection utilizing the peptidomimetics attached to upconversion nanoparticles (UCNPs) as energy donor and monoclonal antibody (mAb)-labeled urchin-like gold nanoflowers (AuNFs) as energy absorber, respectively. The sensitivity of the assay based on dendrimer-like tetramer was approximately 6 and 3 times higher than monomer and dendrimer-like dimer, respectively. After optimization, 50% saturation of the signal (SC50) and detection range (SC10 to SC90) of the IFE-IA based on dendrimer-like tetramer were 11.81 ng mL-1 and 2.04-106.17 ng mL-1, respectively. The IFE-IA also shows good accuracy for the detection of benzothiostrobin in authentic samples.

Noncompetitive Homogeneous Detection of Small Molecules Using Synthetic Nanopeptamer-Based Luminescent Oxygen Channeling

Our group has previously developed immunoassays for noncompetitive detection of small molecules based on the use of phage borne anti-immunocomplex peptides. Recently, we substituted the phage particles by biotinylated synthetic anti-immunocomplex peptides complexed with streptavidin and named these constructs nanopeptamers. In this work, we report the results of combining AlphaLisa, a commercial luminescent oxygen channeling bead system, with nanopeptamers for the development of a noncompetitive homogeneous assay for the detection of small molecules. The signal generation of AlphaLisa assays relies on acceptor-donor bead proximity induced by the presence of the analyte (a macromolecule) simultaneously bound by antibodies immobilized on the surface of these beads. In the developed assay, termed as nanoAlphaLisa, bead proximity is sustained by the presence of a small model molecule (atrazine, MW = 215) using an antiatrazine antibody captured on the acceptor bead and an atrazine nanopeptamer on the donor bead. Atrazine is one of the most used pesticides worldwide, and its monitoring in water has relevant human health implications. NanoAlphaLisa allowed the homogeneous detection of atrazine down to 0.3 ng/mL in undiluted water samples in 1 h, which is 10-fold below the accepted limit in drinking water. NanoAlphaLisa has the intrinsic advantages for automation and high-throughput, simple, and fast homogeneous detection of target analytes that AlphaLisa assay provides.

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).

Enzyme immunoassays as screening tools for catalysts and reaction discovery

This feature article summarizes the development and use of immunoassay techniques (ELISA) as screening tools for fast identification of efficient catalysts in libraries and for the discovery of new chemical reactions.

Recombinant streptavidin nanopeptamer anti-immunocomplex assay for noncompetitive detection of small analytes

Short peptide loops selected from phage libraries can specifically recognize the formation of hapten-antibody immunocomplexes and can thus be used to develop phage anti-immunocomplex assays (PHAIA) for noncompetitive detection of small molecules. In this study, we generated recombinant chimeras by fusing anti-immunocomplex peptides selected from phage libraries to the N- or C-termini of core streptavidin and used them to setup phage-free noncompetitive assays for the herbicide clomazone (MW 240 Da). The best conditions for refolding were optimized by a high throughput screening allowing to obtain tens of mg of purified protein per liter of culture. The noncompetitive assay developed with these chimeras performed with a 50% saturating concentration (SC50) of 2.2 ± 0.3 ng/mL and limit of detection (LOD) of 0.48 ng/mL. Values that are 13- and 8-fold better that those obtained for the SC50 and LOD of the competitive assay setup with the same antibody. Apart from the first demonstration that recombinant peptide-streptavidin chimeras can be used for sensitive immunodetection of small molecules with a positive readout, this new assay component is a highly standardized reagent with a defined stoichiometry, which can be used in combination with the broad option of existing biotinylated reagents offering a great versatility for the development of conventional immunoassay and biosensors. The utility of the test was demonstrated analyzing the clomazone runoff during the rice growing season in northern Uruguay.

Development of a highly sensitive noncompetitive electrochemical immunosensor for the detection of atrazine by phage anti-immunocomplex assay

The development of immunosensors for the detection of small molecules is of great interest because of their simplicity, high sensitivity and extended analytical range. Due to their size, small compounds cannot be simultaneously recognized by two antibodies impeding their detection by noncompetitive two-site immunoassays, which are superior to competitive ones in terms of sensitivity, kinetics, and working range. In this work, we combine the advantages of magneto-electrochemical immunosensors with the improved sensitivity and direct proportional signal of noncompetitive immunoassays to develop a new Phage Anti-Immunocomplex Electrochemical Immunosensor (PhAIEI) for the detection of the herbicide atrazine. The noncompetitive assay is based on the use of recombinant M13 phage particles bearing a peptide that specifically recognizes the immunocomplex of atrazine with an anti-atrazine monoclonal antibody. The PhAIEI performed with a limit of detection (LOD) of 0.2 pg mL(-1), which is 200-fold better than the LOD obtained using the same antibody in an optimized conventional competitive ELISA, with a large increase in working range. The developed PhAIEI was successfully used to assay undiluted river water samples with no pretreatment and excellent recoveries. Apart from the first demonstration of the benefits of integrating phage anti-immunocomplex particles into electrochemical immunosensors, the extremely low and environmentally relevant detection limits of atrazine attained with the PhAIEIS may have direct applicability to fast and sensitive detection of this herbicide in the environment.

Enhanced sensitive immunoassay: noncompetitive phage anti-immune complex assay for the determination of malachite green and leucomalachite green

To develop a more sensitive immunoassay for malachite green (MG) and leucomalachite green (LMG), we identified the immunocomplex binding phage-borne peptides for use in the noncompetitive phage anti-immunocomplex assay (PHAIA). An anti-LMG monoclonal antibody (mAb) was used to select immunocomplex binding peptides from a circular random eight-amino-acid phage-displayed library. After three rounds of panning-elution, five peptides that bound the LMG-mAb immunocomplex were obtained. One of the phage-borne peptide clones that resulted in an assay with the highest sensitivity was chosen for further research. The concentration of LMG producing 50% of the saturated signal and the limit of detection of the assay were 7.02 and 0.55 ng/mL, respectively, with a linear range of 1.35 to 21.56 ng/mL. The PHAIA based on the same antibody was 16 times more sensitive compared to the competitive immunoassay. PHAIA was used to analyze LMG, MG, and two mixtures of spiked fish samples, with validation by high-performance liquid chromatography (HPLC) with fluorescence detector. Results showed a good correlation (R(2)LMG = 0.9841; R(2)MG = 0.993; R(2)Mixture = 0.9903) between the data of PHAIA and HPLC, thus the assay was an efficient method for monitoring food safety.

Virus outbreaks in chemical and biological sensors

Filamentous bacteriophages have successfully been used to detect chemical and biological analytes with increased selectivity and sensitivity. The enhancement largely originates not only from the ability of viruses to provide a platform for the surface display of a wide range of biological ligands, but also from the geometric morphologies of the viruses that constitute biomimetic structures with larger surface area-to-volume ratio. This review will appraise the mechanism of multivalent display of the viruses that enables surface modification of virions either by chemical or biological methods. The accommodation of functionalized virions to various materials, including polymers, proteins, metals, nanoparticles, and electrodes for sensor applications will also be discussed.

Shiga-like toxin B subunit of Escherichia coli as scaffold for high-avidity display of anti-immunocomplex peptides

Small compounds cannot bind simultaneously to two antibodies, and thus, their immunodetection is limited to competitive formats in which the analyte is indirectly quantitated by measuring the unoccupied antibody binding sites using a competing reporter. This limitation can be circumvented by using phage-borne peptides selected for their ability to specifically react with the analyte–antibody immunocomplex, which allows the detection of these small molecules in a noncompetitive format (PHAIA) with increased sensitivity and a positive readout. In an effort to find substitutes for the phage particles in PHAIA, we explore the use of the B subunit of the Shiga-like toxin of Escherichia coli, also known as verotoxin (VTX), as a scaffold for multivalent display of anti-immunocomplex peptides. Using the herbicides molinate and clomazone as model compounds, we built peptide–VTX recombinant chimeras that were produced in the periplasmic space of E. coli as soluble pentamers, as confirmed by multiangle light scattering analysis. These multivalent constructs, which we termed nanopeptamers, were conjugated to a tracer enzyme and used to detect the herbicide–antibody complex in an ELISA format. The VTX–nanopeptamer assays performed with over a 10-fold increased sensitivity and excellent recovery from spiked surface and mineral water samples. The carbon black-labeled peptide–VTX nanopeptamers showed great potential for the development of a lateral-flow test for small molecules with a visual positive readout that allowed the detection of up to 2.5 ng/mL of clomazone.

Nanopeptamers for the development of small-analyte lateral flow tests with a positive readout

There is a great demand for rapid tests that can be used on-site for the detection of small analytes, such as pesticides, persistent organic pollutants, explosives, toxins, medicinal and abused drugs, hormones, etc. Dipsticks and lateral flow devices, which are simple and provide a visual readout, may be the answer, but the available technology for these compounds requires a competitive format that loses sensitivity and produces readings inversely proportional to the analyte concentration, which is counterintuitive and may lead to potential misinterpretation of the result. In this work, protein-multipeptide constructs composed of anti-immunocomplex peptides selected from phage libraries and streptavidin/avidin as core protein were used for direct detection of small compounds in a noncompetitive two-site immunoassay format that performs with increased sensitivity and positive readout. These constructs that we termed "nanopeptamers" allow the development of rapid point-of-use tests with a positive visual end point of easy interpretation. As proof of concept, lateral flow assays for the herbicides molinate and clomazone were developed and their performance was characterized with field samples.

Immunoassays and biosensors for monitoring environmental and human exposure to pyrethroid insecticides

This paper describes some of the early work on pyrethroid insecticides in the Casida laboratory and briefly reviews the development and application of immunochemical approaches for the detection of pyrethroid insecticides and their metabolites for monitoring environmental and human exposure. Multiple technologies can be combined to enhance the sensitivity and speed of immunochemical analysis. The pyrethroid assays are used to illustrate the use of some of these immunoreagents such as antibodies, competitive mimics, and novel binding agents such as phage-displayed peptides. The paper also illustrates reporters such as fluorescent dyes, chemiluminescent compounds, and luminescent lanthanide nanoparticles, as well as the application of magnetic separation, and automatic instrumental systems, biosensors, and novel immunological technologies. These new technologies alone and in combination result in an improved ability to both determine if effective levels of pyrethroids are being used in the field and evaluate possible contamination.

Noncompetitive phage anti-immunocomplex real-time polymerase chain reaction for sensitive detection of small molecules

Immuno polymerase chain reaction (IPCR) is an analytical technology based on the excellent affinity and specificity of antibodies combined with the powerful signal amplification of polymerase chain reaction (PCR), providing superior sensitivity to classical immunoassays. Here we present a novel type of IPCR termed phage anti-immunocomplex assay real-time PCR (PHAIA-PCR) for the detection of small molecules. Our method utilizes a phage anti-immunocomplex assay (PHAIA) technology in which a short peptide loop displayed on the surface of the M13 bacteriophage binds specifically to the antibody-analyte complex, allowing the noncompetitive detection of small analytes. The phagemid DNA encoding this peptide can be amplified by PCR, and thus, this method eliminates hapten functionalization or bioconjugation of a DNA template while providing improved sensitivity. As a proof of concept, two PHAIA-PCRs were developed for the detection of 3-phenoxybenzoic acid, a major urinary metabolite of some pyrethroid insecticides, and molinate, a herbicide implicated in fish kills. Our results demonstrate that phage DNA can be a versatile material for IPCR development, enabling universal amplification when the common element of the phagemid is targeted or specific amplification when the real time PCR probe is designed to anneal the DNA encoding the peptide. The PHAIA-PCRs proved to be 10-fold more sensitive than conventional PHAIA and significantly faster using magnetic beads for rapid separation of reactants. The assay was validated with both agricultural drain water and human urine samples, showing its robustness for rapid monitoring of human exposure or environmental contamination.

A clomazone immunoassay to study the environmental fate of the herbicide in rice (Oryza sativa) agriculture

The environmental impact of rice agriculture is poorly studied in developing countries, mainly due to limitations of the analytical capacity. Here, we report the development of a clomazone enzyme-linked immunosorbent assay as a fast and cost-effective tool to monitor the dissipation of this herbicide along the harvest. Antibodies were prepared using different strategies of hapten conjugation, and the best hapten/antibody pair was selected. It proved to be a reliable tool to measure the herbicide in the 2.0-20 ng/mL range in field samples, with excellent correlation with high-performance liquid chromatography results. The assay was used to study the dissipation of the herbicide in the floodwater of experimental rice paddies in Uruguay. Large differences in the residual amounts of herbicide were observed depending on the flooding practices. Because of its robustness and simplicity, the assay may be useful to delineate and monitor management practices that can contribute to minimizing the release of the herbicide in the environment.

Development of a noncompetitive phage anti-immunocomplex assay for brominated diphenyl ether 47

We present a new application of the noncompetitive phage anti-immunocomplex assay (PHAIA) by converting an existing competitive assay to a versatile noncompetitive sandwich-type format using immunocomplex binding phage-borne peptides to detect the brominated flame retardant, brominated diphenyl ether 47 (BDE 47). Three phage-displayed 9-mer disulfide-constrained peptides that recognize the BDE 47-polyclonal antibody immunocomplex were isolated. The resulting PHAIAs showed variable sensitivities, and the most sensitive peptide had a dose-response curve with an SC(50) (concentration of analyte producing 50% saturation of the signal) of 0.7ng/ml BDE 47 and a linear range of 0.3-2ng/ml, which was nearly identical to the best heterologous competitive format (IC(50) of 1.8ng/ml, linear range of 0.4-8.5/ml). However, the PHAIA was 1400-fold better than homologous competitive assay. The validation of the PHAIA with extracts of house furniture foam as well as human and calf sera spiked with BDE 47 showed overall recovery of 80-113%. The PHAIA was adapted to a dipstick format (limit of detection of 3.0ng/ml), and a blind test with six random extracts of local house furniture foams showed that the results of the PHAIA and dipstick assay were consistent, giving the same positive and negative detection.

Magnetic bead-based phage anti-immunocomplex assay (PHAIA) for the detection of the urinary biomarker 3-phenoxybenzoic acid to assess human exposure to pyrethroid insecticides

Noncompetitive immunoassays are advantageous over competitive assays for the detection of small molecular weight compounds. We recently demonstrated that phage peptide libraries can be an excellent source of immunoreagents that facilitate the development of sandwich-type noncompetitive immunoassays for the detection of small analytes, avoiding the technical challenges of producing anti-immunocomplex antibody. In this work we explore a new format that may help to optimize the performance of the phage anti-immunocomplex assay (PHAIA) technology. As a model system we used a polyclonal antibody to 3-phenoxybenzoic acid (3-PBA) and an anti-immunocomplex phage clone bearing the cyclic peptide CFNGKDWLYC. The assay setup with the biotinylated antibody immobilized onto streptavidin-coated magnetic beads significantly reduced the amount of coating antibody giving identical sensitivity (50% saturation of the signal (SC(50))=0.2-0.4ng/ml) to the best result obtained with direct coating of the antibody on ELISA plates. The bead-based assay tolerated up to 10 and 5% of methanol and urine matrix, respectively. This assay system accurately determined the level of spiked 3-PBA in different urine samples prepared by direct dilution or clean-up with solid-phase extraction after acidic hydrolysis with overall recovery of 80-120%.

Magnetic bead-based phage anti-immunocomplex assay (PHAIA) for the detection of the urinary biomarker 3-phenoxybenzoic acid to assess human exposure to pyrethroid insecticides

Noncompetitive immunoassays are advantageous over competitive assays for the detection of small molecular weight compounds. We recently demonstrated that phage peptide libraries can be an excellent source of immunoreagents that facilitate the development of sandwich-type noncompetitive immunoassays for the detection of small analytes, avoiding the technical challenges of producing anti-immunocomplex antibody. In this work we explore a new format that may help to optimize the performance of the phage anti-immunocomplex assay (PHAIA) technology. As a model system we used a polyclonal antibody to 3-phenoxybenzoic acid (3-PBA) and an anti-immunocomplex phage clone bearing the cyclic peptide CFNGKDWLYC. The assay setup with the biotinylated antibody immobilized onto streptavidin-coated magnetic beads significantly reduced the amount of coating antibody giving identical sensitivity (50% saturation of the signal (SC(50))=0.2-0.4ng/ml) to the best result obtained with direct coating of the antibody on ELISA plates. The bead-based assay tolerated up to 10 and 5% of methanol and urine matrix, respectively. This assay system accurately determined the level of spiked 3-PBA in different urine samples prepared by direct dilution or clean-up with solid-phase extraction after acidic hydrolysis with overall recovery of 80-120%.

Phage-borne peptidomimetics accelerate the development of polyclonal antibody-based heterologous immunoassays for the detection of pesticide metabolites

Competitive immunoassays for the detection of small analytes, such as pesticides and their metabolites, use haptens that compete with the target compounds for binding to the antibody. This competing hapten can be either the same as the immunizing hapten (homologous assay) or structurally modified mimics of the immunizing hapten (heterologous assay). Polyclonal antibody-based heterologous immunoassays have shown superior sensitivities to homologous ones, butthe synthesis of heterologous haptens may be time-consuming, requiring expertise in synthetic chemistry. In this work we demonstrate that phage display peptide libraries can be used as a source of phage-borne peptidomimetics to facilitate the development of sensitive heterologous assays. Different strategies for the isolation of these peptides were explored using two metabolites of pyrethroid insecticides. The sensitivities of the best competitive phage heterologous enzyme-linked immunosorbent assays were 13 fold and 100 fold better than the homologous assay, for the glycine conjugate of trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane-1-carboxylic acid and 3-phenoxybenzoic acid, respectively. The phage particles were highly versatile as tracer reagents, allowing the use of enzymatic, chemiluminescent, or immuno-polymerase chain reaction detection. The data presented here shows a new systematic procedure that enables the fast generation of several competing haptens for the rapid development of sensitive heterologous immunoassays.