Detection of estradiol with a digital immunoassay using an anti-immunocomplex antibody and single-molecule observation of gold nanoparticles

Gold nanoparticles (AuNPs) have been widely applied to molecular sensors due to their optical properties. We previously reported a molecular detection by observing the scattered light of AuNPs at a single nanoparticle level using dark field microscopy (DFM). Recently, a molecular detection method using digital immunoassay has been reported, taking advantage of the characteristics of DFM. However, the digital immunoassays reported so far have been performed by a conventional sandwich immunoassay, which is difficult to apply to the detection of small molecules. In this study, with the aim of small molecule detection, we developed a digital immunoassay method using an anti-immunocomplex antibody that specifically recognizes immunocomplexes of small molecules with antibodies. The number of AuNPs modified with anti-immunocomplex antibody bound to immunocomplex of estradiol and anti-estradiol antibody was counted at a single nanoparticle level using DFM. We demonstrated for the first time that estradiol molecule can be detected by digital immunoassay using DFM and an anti-immunocomplex antibody with a detection sensitivity of 1 pg/mL.

Single-drop electrochemical immunosensor with 3D-printed magnetic attachment for onsite smartphone detection of amoxicillin in raw milk

Amoxicillin is a beta-lactam group of antibiotics used against bacterial infections. The growth of the antibiotic market and abuse of amoxicillin led to its accumulation in nature, especially in foods. Thus, rapid amoxicillin tests are needed to protect human health and increase food safety. In this study, a single drop, mobile electrochemical amoxicillin immunosensor was developed for the first time. The immunosensor platform is based on amoxicillin antibodies conjugated magnetic nanoparticles. A 3-Dimensional (3D) cell capable of accumulating amoxicillin molecules, which interact with antibody-conjugated magnetic nanoparticles on the electrode surface was designed and 3D-printed. A small potentiostat connected to an Android mobile phone was used to detect amoxicillin in a single-drop raw milk sample in a 3D-printed cell. Results demonstrated linearity between 0.5 and 100 µM with an LOD of 0.44 µM. Due to its rapid and portable application, the designed immunosensor shows good potential in on-site amoxicillin detection from milk samples.

CRISPR/Cas12a-Powered Competitive Immunosorbent Assay for Small Molecules

CRISPR/Cas systems are powerful tools for sensitive nucleic acid molecular diagnosis due to their specific nucleic acid recognition and high trans-cleavage activity and have also allowed for quantification of non-nucleic acid targets, relying on a strategy to convert the target detection to analysis of nucleic acids. Here, we describe a CRISPR/Cas12a-powered immunosorbent assay for sensitive small-molecule detection by using the antibody coated on the microplate to recognize the target and the small molecule-labeled active DNA (acDNA) to trigger the activity of CRISPR/Cas12a. In the absence of small-molecule targets, acDNA probes are captured by the antibody on the microplate and then activate Cas12a in catalytic trans-cleavage of fluorescent DNA reporters, generating strong fluorescence. The presence of small-molecule targets displaces the acDNA probes from the antibody, causing a decrease of acDNA probes on the microplate and reduction of activated Cas12a, so the fluorescence signal decreases, and small molecules can be detected by monitoring the fluorescence change. After systematically optimizing experimental conditions (e.g., Cas12a reaction), the proposed method achieved the detection of three model small molecules, biotin, digoxin, and folic acid, with low detection limits, and a flexible detection concentration range was obtained by simply changing the amount of acDNA probes and immobilized antibodies. The assay showed high selectivity and good applicability in complex media. The integration of the CRISPR/Cas12a system improves the analytical performance of immunoassay, broadening and facilitating its applications in rapid, simple, and sensitive small molecule analysis.

The Dawn of a New Era: Targeting the "Undruggables" with Antibody-Based Therapeutics

The high selectivity and affinity of antibodies toward their antigens have made them a highly valuable tool in disease therapy, diagnosis, and basic research. A plethora of chemical and genetic approaches have been devised to make antibodies accessible to more "undruggable" targets and equipped with new functions of illustrating or regulating biological processes more precisely. In this Review, in addition to introducing how naked antibodies and various antibody conjugates (such as antibody-drug conjugates, antibody-oligonucleotide conjugates, antibody-enzyme conjugates, etc.) work in therapeutic applications, special attention has been paid to how chemistry tools have helped to optimize the therapeutic outcome (i.e., with enhanced efficacy and reduced side effects) or facilitate the multifunctionalization of antibodies, with a focus on emerging fields such as targeted protein degradation, real-time live-cell imaging, catalytic labeling or decaging with spatiotemporal control as well as the engagement of antibodies inside cells. With advances in modern chemistry and biotechnology, well-designed antibodies and their derivatives via size miniaturization or multifunctionalization together with efficient delivery systems have emerged, which have gradually improved our understanding of important biological processes and paved the way to pursue novel targets for potential treatments of various diseases.

Framework-Directed Amino-Acid Insertions Generated over 55-Fold Affinity-Matured Antibody Fragments That Enabled Sensitive Luminescent Immunoassays of Cortisol

We generated three single-chain Fv fragments (scFvs) specific to cortisol according to our original affinity-maturation strategy and verified their utility in developing immunoassays. These scFv mutants (m-scFvs) had insertion of one, four, or six amino acid(s) in the framework region 1 of the VH-domain and showed >55-fold higher affinity (Ka, 2.0 - 2.2 × 1010 M-1) than the unmodified scFv (wt-scFv). Each m-scFv was fused with NanoLuc luciferase (NLuc) for the use in enzyme-linked immunosorbent assays (ELISAs). In these ELISA, the m-scFv-NLuc fusions were competitively reacted with immobilized cortisol residues and cortisol standards, and then the bound NLuc activity was monitored luminometrically. The luminescent ELISAs generated dose-response curves with extremely low midpoints (approx. 3 pg/assay) and were >150-fold more sensitive than the colorimetric ELISAs using wt-scFv and >8000-fold more sensitive than the ELISA using the parental native antibody. The luminescent ELISAs showed acceptable cross-reactivity patterns with related steroids, and the determination of control sera afforded cortisol levels in the reference range with satisfactory parallelism.

Retrieving Dissociation-Resistant Antibody Mutants: An Efficient Strategy for Developing Immunoassays with Improved Sensitivities

Previously, we generated high-affinity antibody mutants that enabled sensitive immunoassays by exploring diverse libraries of single-chain Fv fragments (scFvs) displayed on bacteriophage. To isolate rarely-occurring desirable clones, "panning" has commonly been performed but is often unsuccessful. Therefore, we previously developed a clonal array profiling (CAP) method, wherein scFv-displaying phage (scFv-Ph) clones in a library were examined individually regarding their ability to target antigens immobilized on microwells. Clones that showed strong reactivity were recovered via dissociation using an acidic treatment. The CAP successfully discovered cortisol-specific scFvs showing 17-31-fold improved K_a from libraries generated via site-directed insertions in a prototype anti-cortisol scFv (wt-scFv; K_a, 3.6 × 10⁸ M^-1), but their K_a did not exceed 1.1 × 10¹⁰ M^-1. In this study, to break this possible affinity ceiling, we devised a new system employing a dissociation-independent recovery. scFv-Phs were individually reacted to target antigen (cortisol) immobilized on microwells via a linker containing a disulfide bond. Following acidic and basic treatments to eliminate scFv-Phs with "ordinary affinities," dissociation-resistant scFv-Phs remaining on the microwells were retrieved via reductive cleavage of the disulfide bonds. This system allowed for a straightforward and efficient discovery of scFv mutants with 33-56-fold increased K_a (1.2-2.0 × 10¹⁰ M^-1), exceeding the previous affinity ceiling. These scFvs enabled an enzyme-linked immunosorbent assay for cortisol with 18-51-fold higher sensitivity than the assay performed using wt-scFv.

Derivatization-assisted immunoassays: application for group-specific detection of potent methamphetamine and amphetamine enantiomers

Reliable and feasible tools for detecting (S)-methamphetamine [(S)-MAP] and (S)-amphetamine [(S)-AP] are required for regulating their illicit circulation. Antibodies that react equally to these stimulants are desirable for this purpose, but have been difficult to generate because of the crucial difference between their characteristic structures: i.e., N-methylamino (MAP) and amino (AP) groups. Furthermore, their small molecular masses (M_r < 150) have hampered the generation of high-affinity antibodies. To overcome these problems, we converted (S)-MAP and -AP into their 2-(trimethylsilyl)ethyl carbamate forms, Teoc-(S)-MAP and -AP, respectively, as surrogate analytes. The Teoc-derivatization not only increases their molecular masses, but also masks their structural differences. We generated a novel monoclonal antibody that showed a satisfactory affinity to Teoc-(S)-MAP residues (K_d = 13 nM as the IgG form) and developed a competitive enzyme-linked immunosorbent assay (ELISA) using microplates containing immobilized Teoc-(S)-MAP residues. Almost overlapping dose-response curves were obtained for Teoc-(S)-MAP and -AP, with the limit of detection of 0.078 and 0.10 ng per assay, respectively. A fixed amount of test powder sample (1 mg) was derivatized with Teoc-O-succinimidyl for 5 min, and subjected to ELISA using Teoc-(S)-MAP as the calibration standard. Under this protocol, (S)-MAP and -AP were converted to their Teoc derivatives with 30% and 34% yield, respectively, determined using ELISA as "Teoc-(S)-MAP equivalent," being distinguished from the derivatization products of (R)-MAP, (R)-AP, ephedrine, (S)-methylenedioxymethamphetamine, tyramine, dopamine, and β-alanine. This ELISA detected as little as 10 μg of (S)-MAP and -AP, and (S)-MAP in urine obtained from (S)-MAP-administered rats. Immunochromatography devices were also developed using gold nanoparticles coated with the monoclonal antibody, with which 0.10 mg of (S)-MAP and -AP was detected by the naked eye. We conclude that the present derivatization-assisted immunoassays may be useful for the detection of (S)-MAP and/or -AP in early stage screening of suspicious substances.

More than 370-Fold Increase in Antibody Affinity to Estradiol-17β by Exploring Substitutions in the VH-CDR3

Antibodies that specifically target biomarkers are essential in clinical diagnosis. Genetic engineering has assisted in designing novel antibodies that offer greater antigen-binding affinities, thus providing more sensitive immunoassays. We have succeeded in generating a single-chain Fv fragment (scFv) targeted estradiol-17β (E₂) with more than 370-fold improved affinity, based on a strategy focusing the complementarity-determining region 3 in the V_H domain (V_H-CDR3). Systematic exploration of amino acid substitutions therein, using a clonal array profiling, revealed a cluster of four substitutions, containing H99P and a serial substitution E100eN-I100fA-L100gQ that lead to a 90-fold increase in E₂-binding affinity. This substitution quartet in the V_H-CDR3, combined with the substitution cluster I29V/L36M/S77G in the V_L domain, resulted in a scFv fragment with a further increase in the affinity (K_a, 3.2 × 10¹⁰ M^-1). This enabled a highly sensitive enzyme-linked immunosorbent assay capable of detecting up to 0.78 pg/assay. The current study has, thus, focused on the significance of reevaluating the potential of mutagenesis targeting the V_H-CDR3, and encouraging the production and use of engineered antibodies that enable enhanced sensitivities as next-generation diagnostic tools.

Single-step noncompetitive immunocomplex immunoassay for rapid aflatoxin detection

Owing to the high carcinogenicity of aflatoxins, these toxic secondary metabolites pose a severe risk to human and animal health and can have major economic implications. Herein, we report the development of a noncompetitive immunoassay for aflatoxins based on a monoclonal capture antibody and a unique anti-immunocomplex (anti-IC) antibody fragment (scFv) isolated from a synthetic antibody repertoire. The anti-IC scFv recognizes the immunocomplex and enables the development of noncompetitive sandwich-type assays despite the small size of the analyte. The single-step assay developed in this work, with a detection limit of 70 pg mL^-1, could detect aflatoxins within 15 min. The assay was applied to the analysis of spiked food samples, and the results showed that the method could provide a rapid and simple tool for aflatoxin detection. Moreover, the work demonstrates the potential of anti-IC antibodies and non-competitive immunoassays for the analysis of small molecule contaminants.

Enhancing the detection sensitivity of nanobody against aflatoxin B1 through structure-guided modification

Nanobodies (Nbs) have shown great potential in immunodetection of small-molecule contaminants in food and environmental monitoring. However, the limited knowledge of the mechanism of Nbs binding to small molecules has hampered the development of high-affinity Nbs and assay improvement. We previously reported two homologous nanobodies Nb26 and Nb28 specific to aflatoxin B₁ (AFB₁), with the former exhibiting higher sensitivity in ELISA. Herein, Nb26 was selected as the model antibody to resolve its solution nuclear magnetic resonance (NMR) structure, and investigate its AFB₁ recognition mechanism. The results revealed that Nb26 exhibits a typical immunoglobulin fold and its AFB₁-binding interface is uniquely located in complementarity-determining region 3 (CDR3) and framework region 2 (FR2). This finding was applied to improve the binding activity of Nb28 against AFB₁ by constructing two Nb28-based mutants A⁵⁰V and S¹⁰²D, resulting in 2.3- and 3.3-fold sensitivity enhancement over the wild type, respectively. This study develops an NMR-based strategy to analyze the underlying mechanism of Nb against AFB₁, and successfully generated two site-modified Nbs with improved detection sensitivity. It is believed that this work could greatly expand the applications of Nbs by providing a way to enhance the binding activity.

Development of a biotinylated nanobody for sensitive detection of aflatoxin B1 in cereal via ELISA

Aflatoxin B₁ (AFB₁) contamination is a severe threat to food safety and human health, and requires continuous monitoring. In this study, we developed a biotin-streptavidin-amplified enzyme-linked immunosorbent assay (BA-ELISA) by using biotinylated nanobody Nb26 and streptavidin-conjugated polymerized horseradish peroxide (SA-PolyHRP) for sensitive and rapid detection of AFB₁ in cereal. Under the optimal condition, the IC₅₀ value of the BA-ELISA was improved to 0.21 ng mL^-1 for AFB₁, satisfying the requirement of detection limit in practical applications. The total assay time of our strategy is reduced to 50 min from 2 h in conventional competitive ELISA. Additionally, the BA-ELISA saves as much as 98% of the antibody in comparison to the previous classic ELISA. Our work also demonstrated an interesting phenomenon that the biotinylated Nb26 achieved better selectivity to AFB₁, which could possibly result from the steric hindrance that interferes reaction between the Nb26 and the AFB₁ analogs. Furthermore, the assay was used to detect AFB₁ in two cereal samples, and the results were in good agreement with that obtained by high performance liquid chromatography. The developed BA-ELISA can be used for routine screening analysis of AFB₁, and offers a promising strategy for measuring low concentrations of food contaminants.

Derivatization-assisted enzyme-linked immunosorbent assay for identifying hallucinogenic mushrooms with enhanced sensitivity

A sensitive immunochemical method for identifying hallucinogenic mushrooms (magic mushrooms) is required for regulating their illicit use. We have previously generated a monoclonal antibody (mAb) that targets psilocin (Psi), the major psychoactive compound in hallucinogenic mushrooms, and developed an enzyme-linked immunosorbent assay (ELISA). However, this ELISA failed to achieve the expected low-picomole-range sensitivity, as a result of insufficient affinity of the mAb to Psi. It is recognized that haptenic antigens with a larger molecular mass tend to induce antibodies with higher affinities. Thus, we herein report a "derivatization-assisted ELISA," in which the "real analyte" Psi was determined as a "surrogate analyte," the tert-butyldimethylsilyl ether analog thereof (TBS/Psi) having a 1.6-fold greater molecular mass (M_r 318.53) than Psi. A novel mAb against TBS/Psi, prepared by immunizing mice with a TBS/Psi-albumin conjugate showed a 69-fold higher affinity to TBS/Psi residues (K_a = 3.6 × 10⁷ M^-1 as IgG) than that of our previous mAb against Psi. This mAb consequently enabled a competitive ELISA for measuring TBS/Psi with the desired sensitivity: the dose-response curve midpoint (12.1 pmol per assay) was >100-fold lower than that of the previous ELISA for determining Psi. Extracts of dried mushroom powders were mixed with TBS triflate for 30 min at room temperature, converting Psi into TBS/Psi in approximately 50% yield. The reaction mixture was then subjected to an ELISA using the anti-TBS/Psi mAb to determine TBS/Psi. Psilocybe cubensis, a species of hallucinogenic mushrooms, gave rise to positive signals, indicating the presence of Psi therein in the expected quantity, while no detectable response was observed for four kinds of edible mushrooms available in the markets.

The VH framework region 1 as a target of efficient mutagenesis for generating a variety of affinity-matured scFv mutants

In vitro affinity-maturation potentially generates antibody fragments with enhanced antigen-binding affinities that allow for developing more sensitive diagnostic systems and more effective therapeutic agents. Site-directed mutagenesis targeting “hot regions,” i.e., amino acid substitutions therein frequently increase the affinities, is desirable for straightforward discovery of valuable mutants. We here report two “designed” site-directed mutagenesis (A and B) targeted the N-terminal 1–10 positions of the V_H framework region 1 that successfully improved an anti-cortisol single-chain Fv fragment (K_a, 3.6 × 10⁸ M⁻¹). Mutagenesis A substituted the amino acids at the position 1–3, 5–7, 9 and 10 with a limited set of substitutions to generate only 1,536 different members, while mutagenesis B inserted 1–6 random residues between the positions 6 and 7. Screening the resulting bacterial libraries as scFv-phage clones with a clonal array profiling system provided 21 genetically unique scFv mutants showing 17–31-fold increased affinity with > 10⁹ M⁻¹K_a values. Among the mutants selected from the library A and B, scFv mA#18 (with five-residue substitutions) and mB_1-3#130 (with a single residue insertion) showed the greatest K_a value, 1.1 × 10¹⁰ M⁻¹.

NanoLuc luciferase as a suitable fusion partner of recombinant antibody fragments for developing sensitive luminescent immunoassays

Enzyme-linked immunosorbent assays (ELISAs) are essential for monitoring various biomarkers. Competitive and noncompetitive (sandwich) assay formats are used to determine hapten and macromolecule levels, respectively. Both formats require more sensitive detection of reporter enzymes for greater assay sensitivities. We previously reported the utility of wild-type Gaussia luciferase (wtGLuc) as a fusion partner with antibody single-chain Fv fragments (scFvs) for developing sensitive luminescent ELISAs. Here, we evaluated utility of NanoLuc luciferase (NLuc), a recently developed luciferase, as fusion partner with scFvs from the view of comparison with wtGLuc and a mutant of alkaline phosphatase (ALP'). Thyroxine (T₄) and T₄-labeled albumin were chosen as model haptenic and macromolecular antigens, respectively. An in-house-prepared anti-T₄ scFv was fused with NLuc, wtGLuc, or ALP'. The scFv-NLuc fusion protein showed 47-fold and 29-fold lower limit of detection [LOD; 59 zmol (per assay)] than the wtGLuc- and ALP'-fusions, respectively. In a competitive T₄ ELISA, the NLuc-fusion showed 9.3- and 6.3-fold lower LOD, (0.67 pg) than the wtGLuc- and ALP'-fusions, respectively, with a higher specificity in clinical applications. A typical colorimetric ELISA using a peroxidase-labeled second antibody showed 70-fold higher LOD than NLuc-based ELISA. Another advantage of the NLuc-fusion was shown in the sandwich assays; the LOD of T₄-labeled albumin (5.0 fmol) was >6-fold lower than that of the other luminescent ELISAs. In an additional sandwich assay developed to count bacteriophage particles, NLuc enabled more sensitive determination than wtGLuc, whereas ALP' showed nearly equivalent performance. Its slowest alteration rate for light intensity after starting the enzyme reaction should enable robust batch-by-batch assay operations. Thus, we concluded that scFv-NLuc fusions serve as suitable probes in various types of immunoassays and may facilitate higher sensitivities with practical specificities.

Immunochemical monitoring of psilocybin and psilocin to identify hallucinogenic mushrooms

Development of rapid and reliable immunochemical methods for monitoring psilocybin (4-phosphoryloxy-N,N-dimethyltryptamine; Pyb) and psilocin (dephosphorylated metabolite; Psi), the psychoactive compounds contained within hallucinogenic mushrooms (magic mushrooms), is desirable in order to identify these mushrooms and regulate their illicit use. Because no antibody was publicly available for this purpose, we generated two independent monoclonal antibodies (mAbs) against Pyb or Psi, and then developed enzyme-linked immunosorbent assays (ELISAs) by using them. To generate the specific antibodies, novel immunogenic conjugates were prepared by linking Pyb or Psi molecules to carrier proteins by modifying their 2-(N,N-dimethylamino)ethyl side chains. Spleen cells from mice immunized with these conjugates were fused with P3/NS1/1-Ag4-1 myeloma cells, and hybridoma clones secreting anti-Pyb and anti-Psi mAbs were established. These mAbs were characterized for their biochemical features and then applied to competitive ELISAs, which used microplates coated with Pyb or Psi linked with albumin. These ELISAs enabled the determination of Pyb or Psi with measurable ranges of ca. 0.20-20 or 0.040-2.0 μg/assay (limit of detection was 0.14 or 0.029 μg/assay), respectively. The related tryptamines were satisfactorily discriminated as exemplified by the cross-reactivity of the ELISA to determine Pyb (or Psi) with Psi (or Pyb) that were found to be 2.8 % (or <0.5 %), respectively. The Pyb and Psi contents in a dried powder of the hallucinogenic mushroom, Psilocybe cubensis, were determined to be 0.39 and 0.32 (w/w)%, respectively. The ELISAs developed using the current mAbs are promising tools for identifying illegal hallucinogenic mushrooms.

Clonal array profiling of scFv-displaying phages for high-throughput discovery of affinity-matured antibody mutants

"Antibody-breeding" approach potentially generates therapeutic/diagnostic antibody mutants with greater performance than native antibodies. Therein, antibody fragments (e.g., single-chain Fv fragments; scFvs) with a variety of mutations are displayed on bacteriophage to generate diverse phage-antibody libraries. Rare clones with improved functions are then selected via panning against immobilized or tagged target antigens. However, this selection process often ended unsuccessful, mainly due to the biased propagation of phage-antibody clones and the competition with a large excess of undesirable clones with weaker affinities. To break radically from such panning-inherent problems, we developed a novel method, clonal array profiling of scFv-displaying phages (CAP), in which colonies of the initial bacterial libraries are examined one-by-one in microwells. Progenies of scFv-displaying phages generated are, if show sufficient affinity to target antigen, captured in the microwell via pre-coated antigen and detected using a luciferase-fused anti-phage scFv. The advantage of CAP was evidenced by its application with a small error-prone-PCR-based library (~ 10⁵ colonies) of anti-cortisol scFvs. Only two operations, each surveying only ~ 3% of the library (9,400 colonies), provided five mutants showing 32–63-fold improved K_a values (> 10¹⁰ M⁻¹), compared with the wild-type scFv (K_a = 3.8 × 10⁸ M⁻¹), none of which could be recovered via conventional panning procedures operated for the entire library.

Klotho: An Elephant in Aging Research

The year 2017 marked the 20th anniversary of the first publication describing Klotho. This single protein was and is remarkable in that its absence in mice conferred an accelerated aging, or progeroid, phenotype with a dramatically shortened life span. On the other hand, genetic overexpression extended both health span and life span by an impressive 30%. Not only has Klotho deficiency been linked to a number of debilitating age-related illnesses but many subsequent reports have lent credence to the idea that Klotho can compress the period of morbidity and extend the life span of both model organisms and humans. This suggests that Klotho functions as an integrator of organ systems, making it both a promising tool for advancing our understanding of the biology of aging and an intriguing target for interventional studies. In this review, we highlight advances in our understanding of Klotho as well as key challenges that have somewhat limited our view, and thus translational potential, of this potent protein.

Seeking high-priority mutations enabling successful antibody-breeding: systematic analysis of a mutant that gained over 100-fold enhanced affinity

"Antibody-breeding" has provided therapeutic/diagnostic antibody mutants with greater performance than native antibodies. Typically, random point mutations are introduced into the VH and VL domains of parent antibodies to generate diverse libraries of single-chain Fv fragments (scFvs), from which evolved mutants are selected. We produced an scFv against estradiol-17β with 11 amino acid substitutions and a >100-fold improved affinity constant (Ka = 1.19 × 1010 M-1) over the parent scFv, enabling immunoassays with >30-fold higher sensitivity. We systematically analyzed contributions of these substitutions to the affinity enhancement. Comparing various partial scFv revertants based on their Kas indicated that a revertant with four substitutions (VH-L100gQ, VL-I29V, -L36M, -S77G) exhibited somewhat higher affinity (Ka = 1.46 × 1010 M-1). Finally, the VH-L100gQ substitution, occurring in VH complementarity-determining region (CDR) 3, was found to be the highest-priority for improving the affinity, and VL-I29V and/or VL-L36M cooperated significantly. These findings encouraged us to reconsider the potential of VH-CDR3-targeting mutagenesis, which has been frequently attempted. The substitution(s) wherein might enable a "high rate of return" in terms of selecting mutants with dramatically enhanced affinities. The "high risk" of generating a tremendous excess of "junk mutants" can be overcome with the efficient selection systems that we developed.

A rapid and specific bacterial detection method based on cell-imprinted microplates

Bacterial detection has attracted substantial interest in recent years owing to its importance in biology, medical care, drug discovery, and public health. For such applications, bacterial cell-imprinting technologies are regarded as potential methods, as they can fabricate artificial tailor-made receptors for cellular recognition. In comparison to conventional methods, which generally require a few days for bacterial determination, cell-imprinted polymers can save a substantial amount of time. Here, we report a high-throughput bacterial detection method based on a cell-imprinted 96-well microplate. The fabrication of the bacterial cell-imprinted polypyrrole and nafion complex was accomplished on a gold nanoparticle-coated microplate. The cell-imprinted polymer complex on the microplate can spontaneously rebind and specifically detect target cells with high selectivity in a short time frame (within 30 min). Furthermore, the microplates could discriminate particular target Escherichia coli O157:H7 cells from bacterial mixtures. This simple method may be used for a variety of applications such as clinical testing, food safety, and continuous environmental monitoring.

Antibodies and Engineered Antibody Fragments against M13 Filamentous Phage to Facilitate Phage-Display-Based Molecular Breeding

Antibodies are essential for characterizing various analytes. "Molecular-breeding" approaches enable rapid generation of antibody mutants with desirable antigen-binding abilities. Typically, prototype antibodies are converted to single-chain Fv fragments (scFvs), and random mutations are genetically introduced to construct molecular libraries with a vast diversity. Improved species therein are then isolated via phage display genotype-phenotype-connecting systems to separate them from a large excess of nonspecific scFvs. During these experiments, counting of phage particles is routinely performed. However, current methods depend on the time-consuming overnight cultivation of phage-infected bacteria on agar plates to estimate phage numbers as plaque-forming units (pfu) or colony-forming units, the results of which fluctuate considerably. Immunochemical systems capturing phage particles should be a more convenient and robust alternative. We therefore generated monoclonal antibodies against M13 filamentous phage, which is commonly used for phage display, by employing hybridoma technology. Combinatorial use of two such antibodies (Ab-M13#53 and #71; both specific to the major coat protein pVIII) enabled development of a sandwich enzyme-linked immunosorbent assay (ELISA) that could measure ca. 10⁷-10¹⁰ phage pfu/mL. To construct a more convenient system, Ab-M13#71 was converted to the scFv form and further fused with an alkaline phosphatase variant. Using this fusion protein, the sandwich ELISA enabled rapid (within 90 min) and reliable phage counting without reducing the sensitivity, and the results were reasonably consistent with those of infection-based methods. The present anti-phage antibodies and scFvs might also enable visualization of individual phage particles by combining them with sensitive fluorescent staining.

Enantioselective Monoclonal Antibodies for Detecting Ketamine to Crack Down on Illicit Use

Ketamine (KT) is a chiral anesthetic agent, (R)- and (S)-enantiomers of which differ in their pharmacological properties. KT has become one of the most commonly used illicit drugs in the world, thus, rapid and feasible on-site testing is required to crack down on the illicit use. Although immunochemical approach with specific antibodies is promising for this purpose, in practice anti-KT antibodies are difficult to obtain. We here disclose generation of monoclonal antibodies against KT. Mice were immunized with either (a) commercially-available or (b) in-house-prepared KT-albumin conjugates. Splenocytes from these mouse groups (a and b) were separately fused with P3/NS1/1-Ag4-1 myeloma cells. After standard screening and cloning, we established 5 hybridoma clones: 2 were derived from group-a mice [generating Ab-KT(a)#2 and #37] and 3 were from group-b mice [generating Ab-KT(b)#9, #13, and #45]. These antibodies exhibited practical performance in competitive enzyme-linked immunosorbent assay systems. When (±)-KT·hydrochloride (HCl) was used as the competitor, dose-response curves showed midpoint values of 30 and 70 ng/assay (a-series antibodies) and 2.0-3.0 ng/assay (b-series antibodies). Remarkably, the a-series antibodies were specific for (S)-KT·HCl, while the b-series antibodies were specific for (R)-KT·HCl. Ab-KT(a)#2 (K_a, 7.5×10⁷ M^-1) and Ab-KT(b)#45 (K_a, 7.7×10⁸ M^-1) exhibited the highest enantioselectivity for each group, and cross-reactivity with the (R)- and (S)-antipodes was 1.3 and 1.7%, respectively. The hybridomas established here are also valuable as a source of genetic information for the anti-KT antibodies, which is required for progressing to next-generation technologies using genetically engineered antibodies.

A Single-Step "Breeding" Generated a Diagnostic Anti-cortisol Antibody Fragment with Over 30-Fold Enhanced Affinity

Cortisol levels in bodily fluids represent a useful index for pituitary-adrenal function, and thus practical anti-cortisol antibodies are required. We have studied "antibody-breeding" approaches, which involve in vitro evolution of antibodies to improve their antigen-binding performances. Here, we produced an antibody fragment to measure serum cortisol levels with over 30-fold enhanced affinity after single mutagenesis and selection steps. A mouse anti-cortisol antibody, Ab-CS#3, with insufficient affinity for practical use, was chosen as the prototype antibody. A "wild-type" single-chain Fv fragment (wt-scFv; K_a, 3.4×10⁸ M^-1) was prepared by bacterial expression of a fusion gene combining the V_H and V_L genes for this antibody. Then, random point mutations were generated separately in V_H or V_L by error-prone PCR, and the resulting products were used to assemble scFv genes, which were displayed on filamentous phages. Repeated panning of the phage library identified a mutant scFv (scFv#m1-L10) with an over 30-fold enhanced affinity (K_a 1.2×10¹⁰ M^-1). Three amino acid substitutions (Cys49Ser, Leu54Pro, and Ser63Gly) were observed in its V_L sequence. In a competitive enzyme-linked immunosorbent assay (ELISA), the mutant scFv generated dose-response curves with measuring range ca. 0.03-0.6 ng/assay cortisol, midpoint of which (0.15 ng/assay) was 7.3-fold lower than that of wt-scFv. Although cortisone, 11-deoxycortisol, and prednisolone showed considerable cross-reactivity, the mutant scFv should enable sensitive routine cortisol assays, except for measurement after metyrapone or high-dose of prednisolone administrations. Actually, cortisol levels of control sera obtained with the scFv-based ELISA were in the reference range.

Chromatographic immunoassays: strategies and recent developments in the analysis of drugs and biological agents

A chromatographic immunoassay is a technique in which an antibody or antibody-related agent is used as part of a chromatographic system for the isolation or measurement of a specific target. Various binding agents, detection methods, supports and assay formats have been developed for this group of methods, and applications have been reported that range from drugs, hormones and herbicides to peptides, proteins and bacteria. This review discusses the general principles and applications of chromatographic immunoassays, with an emphasis being given to methods and formats that have been developed for the analysis of drugs and biological agents. The relative advantages or limitations of each format are discussed. Recent developments and research in this field, as well as possible future directions, are also considered.

Progress in the development of immunoanalytical methods incorporating recombinant antibodies to small molecular weight biotoxins

Rapid immunoanalytical screening of food and environmental samples for small molecular weight (hapten) biotoxin contaminations requires the production of antibody reagents that possess the requisite sensitivity and specificity. To date animal-derived polyclonal (pAb) and monoclonal (mAb) antibodies have provided the binding element of the majority of these assays but recombinant antibodies (rAb) isolated from in vitro combinatorial phage display libraries are an exciting alternative due to (1) circumventing the need for experimental animals, (2) speed of production in commonly used in vitro expression systems and (3) subsequent molecular enhancement of binder performance. Short chain variable fragments (scFv) have been the most commonly employed rAb reagents for hapten biotoxin detection over the last two decades but antibody binding fragments (Fab) and single domain antibodies (sdAb) are increasing in popularity due to increased expression efficiency of functional binders and superior resistance to solvents. rAb-based immunochromatographic assays and surface plasmon resonance (SPR) biosensors have been reported to detect sub-regulatory levels of fungal (mycotoxins), marine (phycotoxins) and aquatic biotoxins in a wide range of food and environmental matrices, however this technology has yet to surpass the performances of the equivalent mAb- and pAb-based formats. As such the full potential of rAb technology in hapten biotoxin detection has yet to be achieved, but in time the inherent advantages of engineered rAb are set to provide the next generation of ultra-high performing binder reagents for the rapid and specific detection of hapten biotoxins.

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.

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.

A new approach for quantitative analysis of L-phenylalanine using a novel semi-sandwich immunometric assay

Here, we describe a novel method for L-phenylalanine analysis using a sandwich-type immunometric assay approach for use as a new method for amino acid analysis. To overcome difficulties of the preparation of high-affinity and selectivity monoclonal antibodies against L-phenylalanine and the inability to use sandwich-type immunometric assays due to their small molecular weight, three procedures were examined. First, amino groups of L-phenylalanine were modified by "N-Fmoc-L-cysteine" (FC) residues and the derivative (FC-Phe) was used as a hapten. Immunization of mice with bovine serum albumin/FC-Phe conjugate successfully yielded specific monoclonal anti-FC-Phe antibodies. Second, a new derivatization reagent, "biotin linker conjugate of FC-Phe N-succinimidyl ester" (FC(Biotin)-NHS), was synthesized to convert L-phenylalanine to FC-(Biotin)-Phe as a hapten structure. The biotin moiety linked to the thiol group of cysteine formed a second binding site for streptavidin/horseradish peroxidase (HRP) conjugates for optical detection. Third, a new semi-sandwich-type immunometric assay was established using pre-derivatized L-phenylalanine, the monoclonal anti-FC-Phe antibody, and streptavidin/HRP conjugate (without second antibody). Using the new "semi-sandwich" immunometric assay system, a detection limit of 35 nM (60 amol per analysis) and a detection range of 0.1-20 μM were attained using a standard L-phenylalanine solution. Rat plasma samples were analyzed to test reliability. Intra-day assay precision was within 6% of the coefficient of variation; inter-day variation was 0.1%. The recovery rates were from 92.4 to 123.7%. This is the first report of the quantitative determination of L-phenylalanine using a reliable semi-sandwich immunometric assay approach and will be applicable to the quantitative determination of other amino acids.

A novel method to assay molecular chaperone activity of HSP70: evaluation of drug resistance in cancer treatment

In this work, we have proposed a novel method to specifically assay the molecular chaperone activity of HSP70 based on the HSP70-substrate peptide interaction. By selectively labeling the substrate peptide of HSP70 via host-guest interaction with two different cucurbituril species, the HSP70-substrate peptide interaction can be transduced into detectable signal readout. By using the signal readout, assay of the molecular chaperone activity of HSP70 can be achieved. Moreover, by using our method, chaperone activity of HSP70 can serve as a reliable indicator of drug resistance in cancer treatment. The experimental results reveal that enhanced chaperone activity of HSP70 is observed in both drug-resistant cancer cell line and the serum of cancer victim subject to anti-cancer therapy. Therefore, the proposed method to assay the molecular chaperone activity of HSP70 can be a tool of efficiency in evaluating therapeutic response in HSP70-targeted cancer treatment.

Molecular engineering of antibodies for therapeutic and diagnostic purposes

During the past ten years, monoclonal antibodies (mAbs) have taken center stage in the field of targeted therapy and diagnosis. This increased interest in mAbs is due to their binding accuracy (affinity and specificity) together with the original molecular and structural rules that govern interactions with their cognate antigen. In addition, the effector properties of antibodies constitute a second major advantage associated with their clinical use. The development of molecular and structural engineering and more recently of in vitro evolution of antibodies has opened up new perspectives in the de novo design of antibodies more adapted to clinical and diagnostic use. Thus, efforts are regularly made by researchers to improve or modulate antibody recognition properties, to adapt their pharmacokinetics, engineer their stability, and control their immunogenicity. This review presents the latest molecular engineering results on mAbs with therapeutic and diagnostic applications.