Phage-mediated double-nanobody sandwich immunoassay for detecting alpha fetal protein in human serum

Scalable, robust, high-throughput expression & purification of nanobodies enabled by 2-stage dynamic control

Nanobodies are single-domain antibody fragments that have garnered considerable use as diagnostic and therapeutic agents as well as research tools. However, obtaining pure VHHs, like many proteins, can be laborious and inconsistent. High level cytoplasmic expression in E. coli can be challenging due to improper folding and insoluble aggregation caused by reduction of the conserved disulfide bond. We report a systems engineering approach leveraging engineered strains of E. coli, in combination with a two-stage process and simplified downstream purification, enabling improved, robust, soluble cytoplasmic nanobody expression, as well as rapid cell autolysis and purification. This approach relies on the dynamic control over the reduction potential of the cytoplasm, incorporates lysis enzymes for purification, and can also integrate dynamic expression of protein folding catalysts. Collectively, the engineered system results in more robust growth and protein expression, enabling efficient scalable nanobody production, and purification from high throughput microtiter plates, to routine shake flask cultures and larger instrumented bioreactors. We expect this system will expedite VHH development.

Development of a double antibody sandwich ELISA method for the quantitative detection of serum C-reactive protein based on nanobody

In this study, we successfully developed a nanobody-based double antibody sandwich ELISA kit for the detection of clinical serum C-reactive protein (CRP) by using two novel CRP specific nanobodies. The developed method exhibited a linear detection range of approximately 6-200 ng/mL, with a detection limit of 1 ng/mL. Furthermore, the method demonstrated excellent specificity, as there was no cross-reactivity with interfering substances such as total bilirubin and hemoglobin and so on. To assess reproducibility, independent measurements of the samples were conducted under experimental conditions, resulting in intra- and inter-batch coefficients of variation below 10% and a recovery rate of 93%-102%. These results indicate robust reproducibility of the method. To evaluate the performance of the developed kit, we collected 90 clinical samples for correlation analysis with commercial kits. The results showed a high correlation coefficient value (R2) of 0.98, indicating accurate concordance between the developed and commercial kits. In conclusion, our study successfully developed a nanobody-based double antibody sandwich ELISA kit to detect clinical serum CRP. The utilization of nanobodies represents a significant advancement in the field of CRP immunoassay development. The developed kit demonstrates excellent performance characteristics and holds promise for clinical applications.

Advanced detection of cervical cancer biomarkers using engineered filamentous phage nanofibers

Cervical cancer is a major global health concern, characterized by its high incidence and mortality rates. The detection of tumor markers is crucial for managing cancer, making treatment decisions, and monitoring disease progression. Vascular endothelial growth factor (VEGF) and programmed death-ligand 1 (PDL-1) are key targets in cervical cancer therapy and valuable biomarkers in predicting treatment response and prognosis. In this study, we found that combining the measurement of VEGF and soluble PDL-1 can be used for diagnosing and evaluating the progression of cervical cancer. To explore a more convenient approach for detecting and assessing cervical cancer, we designed and prepared an engineered fd bacteriophage, a human-safe viral nanofiber, equipped with two peptides targeting VEGF and PD-L1. The dual-display phage nanofiber specifically recognizes and binds to both proteins. Utilizing this nanofiber as a novel capture agent, we developed a new enzyme-linked immunosorbent assay (ELISA) method. This method shows significantly enhanced detection sensitivity compared to conventional ELISA methods, which use either anti-VEGF or anti-PD-L1 antibodies as capture agents. Therefore, the phage dual-display nanofiber presents significant potential in detecting cancer markers, evaluating medication efficacy, and advancing immunotherapy drug development. KEY POINTS: • The combined measurement of VEGF and soluble Programmed Death-Ligand 1(sPD-L1) demonstrates an additive effect in the diagnosis of cervical cancer. Fd phage nanofibers have been ingeniously engineered to display peptides that bind to VEGF and PD-L1, enabling the simultaneous detection of both proteins within a single assay • Genetically engineered phage nanofibers, adorned with two distinct peptides, can be utilized for the diagnosis and prognosis of cancer and can be mass-produced cost-effectively through bacterial infections • Employing dual-display fd phage nanofibers as capture probes, the phage ELISA method exhibited significantly enhanced detection sensitivity compared to traditional sandwich ELISA. Furthermore, phage ELISA facilitates the detection of a single protein or the simultaneous detection of multiple proteins, rendering them powerful tools for protein analysis and diagnosis across various fields, including cancer research.

A single thiolated-phage displayed nanobody-based biosensor for label-free detection of foodborne pathogen

Rapid and sensitive detection of bacterial pathogens present in food and environmental samples is of crucial importance to ensure human health and safety. Here, we present a one-step label-free colorimetric strategy based on M13 bacteriophage-displayed nanobody (phage-Nb) derived from camelid heavy-chain antibodies specific to Vibrio parahaemolyticus (V. parahaemolyticus). The thiolation of phage-Nb (Phage-Nb-SH) on pVIII shell proteins induces the aggregation of gold nanoparticles (AuNPs), whereas the specific interaction between nanobody and bacteria prevents the aggregation of AuNPs, resulting in visible color change due to alteration of surface plasmon resonance properties. Based on this phenomenon, a simple and sensitive colorimetric immunosensor for V. parahaemolyticus was developed. The assay can be accomplished within 100 min, and exhibits a visual detection limit of 10⁴ cfu/mL and a quantitative detection limit of 10³ cfu/mL, with no cross-reactivity towards other bacterial species. This strategy takes full advantages of both the high specificity of phage-Nbs and the optical properties of AuNPs, enabling simple and rapid detection of bacterial pathogens.

M13 bacteriophage as biometric component for orderly assembly of dynamic light scattering immunosensor

The ordered assembly of nanostructure is an effective strategy used to manipulate the hydrodynamic diameter (D_H) of nanoparticles. Herein, a versatile dynamic light scattering (DLS) immunosensing platform is presented to sensitively detect small molecules and biomacromolecules by using the M13 phage as the building module to order the assembly of gold nanoflowers and gold-coated magnetic nanoparticles, respectively. After the directional assembly of M13 phage, the D_H of the probes was significantly increased due to its larger filamentous structure, thus improving the detection sensitivity of the DLS immunosensor. The designed M13 assembled DLS immunosensor with competitive and sandwich formats showed high sensitivities for ochratoxin A and alpha-fetoprotein in real corn and undiluted serum samples, with the detection limits of 1.37 and 57 pg/mL, respectively. These values are approximately 15.8 and 164.9 times lower than those of traditional phage-based enzyme-linked immunosorbent assays. Collectively, this work provides a promising strategy to manipulate the D_H of nanoparticles by highly evolved biomaterials such as engineered M13 phages and opens upon a new direction for developing DLS immunosensors to detect various targets by the fusion expression of special peptide or nanobody on the pIII or pVIII protein of M13 phage.

VHH Structural Modelling Approaches: A Critical Review

VHH, i.e., VH domains of camelid single-chain antibodies, are very promising therapeutic agents due to their significant physicochemical advantages compared to classical mammalian antibodies. The number of experimentally solved VHH structures has significantly improved recently, which is of great help, because it offers the ability to directly work on 3D structures to humanise or improve them. Unfortunately, most VHHs do not have 3D structures. Thus, it is essential to find alternative ways to get structural information. The methods of structure prediction from the primary amino acid sequence appear essential to bypass this limitation. This review presents the most extensive overview of structure prediction methods applied for the 3D modelling of a given VHH sequence (a total of 21). Besides the historical overview, it aims at showing how model software programs have been shaping the structural predictions of VHHs. A brief explanation of each methodology is supplied, and pertinent examples of their usage are provided. Finally, we present a structure prediction case study of a recently solved VHH structure. According to some recent studies and the present analysis, AlphaFold 2 and NanoNet appear to be the best tools to predict a structural model of VHH from its sequence.

Generation of a nanobody-alkaline phosphatase heptamer fusion for ratiometric fluorescence immunodetection of trace alpha fetoprotein in serum

Alpha fetoprotein (AFP) is an important biomarker for diagnosis of hepatocellular carcinoma (HCC). Whereas, it is always a challenge to detect trace AFP in serum. In this work, a ratiometric fluorescence enzyme immunoassay (RFEIA) was developed using nanobody-alkaline phosphatase (Nb-AP) heptamer and MnFe layered double hydroxides nanoflakes (MnFe LDH) for ultrasensitive detection of AFP. The Nb-AP heptamer (Nb-C4bpα-AP) was constructed by fusion expression of Nb, AP, and α-chain of C4 binding protein (C4bpα), where the C4bpα contributed to multimerization through self-assembly. The dual functional Nb-C4bpα-AP can recognize AFP, dephosphorylate ascorbic acid-2-phosphate (AAP) into ascorbic acid (AA), and thus tune the MnFe LDH-mediated ratiometric fluorescence, which was generated from the oxidization of MnFe LDH on o-phenylenediamine (OPD) and the catalyzation of MnFe LDH on the cyclization reaction between AA and OPD. By integration of Nb-C4bpα-AP, MnFe LDH, AAP, and OPD, the RFEIA showed a limit of detection of 0.013 ng/mL with good selectivity, accuracy and precision. Furthermore, results of clinical serum samples tested by the RFEIA were well confirmed by the automated chemiluminescence immunoassay analyzer. Thus, this work demonstrated that the Nb-C4bpα-AP is a robust immunoreagent and the developed RFEIA could be a very promising tool for diagnosis of HCC.

Generation of a nanobody-alkaline phosphatase fusion and its application in an enzyme cascade-amplified immunoassay for colorimetric detection of alpha fetoprotein in human serum

Sensitive detection of liver disease biomarkers can facilitate the diagnosis of primary hepatoma and other benign liver diseases, and the alpha fetoprotein (AFP) was selected as the model macromolecule in this work. Herein an enzyme cascade-amplified immunoassay (ECAIA) based on the nanobody-alkaline phosphatase fusion (Nb-ALP) and MnO₂ nanoflakes was developed for detecting AFP. The bifunctional biological macromolecule Nb-ALP serves as the detection antibody and the reporter molecule. The MnO₂ nanoflakes mimic the oxidase for catalyzing the 3,3',5,5'-tetramethylbenzidine (TMB) into the blue oxidized TMB, which has a quantitative signal at the wavelength of 650 nm. Moreover, the Nb-ALP could dephosphorylate the ascorbic acid-2-phosphate (AAP) to form the ascorbic acid (AA) that can disintegrate the nanoflakes to reduce their oxidation capacity with the content decrease of the oxidized TMB. Using the constructed TMB-MnO₂ colorimetric sensing system for Nb-ALP and the optimized experimental parameters, the ECAIA has a limit of detection (LOD) of 0.148 ng/mL which is 18.7-fold lower than that of the p-nitrophenylphosphate (pNPP)-based method (LOD = 2.776 ng/mL). The ECAIA showed good selectivity for AFP with observed negligible cross-reactions with several common cancer biomarkers. The recovery rate for AFP spiked in human serum ranged from 94.8% to 113% with the relative standard deviation from 0.3% to 6.5%. For analysis of the actual human serum samples, a good linear correlation was found between the results tested by the ECAIA and the automatic chemiluminescence analyzer. Thus, the ECAIA was demonstrated to be a promising tool for highly sensitive and selective detection of AFP, providing a reference for analysis of other macromolecule biomarkers.

Enzyme cascade-amplified immunoassay based on the nanobody-alkaline phosphatase fusion and MnO2 nanosheets for the detection of ochratoxin A in coffee

Ochratoxin A (OTA) is a common food contaminant with multiple toxicities and thus rapid and accurate detection of OTA is indispensable to minimize the threat of OTA to public health. Herein a novel enzyme cascade-amplified immunoassay (ECAIA) based on the mutated nanobody-alkaline phosphatase fusion (mNb-AP) and MnO2 nanosheets was established for detecting OTA in coffee. The detection principle is that the dual functional mNb-AP could specifically recognize OTA and dephosphorylate the ascorbic acid-2-phosphate (AAP) into ascorbic acid (AA), and the MnO2 nanosheets mimicking the oxidase could be reduced by AA into Mn2+ and catalyze the 3,3',5,5'-tetramethyl benzidine into blue oxidized product for quantification. Using the optimal conditions, the ECAIA could be finished within 132.5 min and shows a limit of detection of 3.38 ng mL-1 (IC10) with an IC50 of 7.65 ng mL-1 and a linear range (IC20-IC80) of 4.55-12.85 ng mL-1. The ECAIA is highly selective for OTA. Good recovery rates (84.3-113%) with a relative standard deviation of 1.3-3% were obtained and confirmed by high performance liquid chromatography with a fluorescence detector. The developed ECAIA was demonstrated to be a useful tool for the detection of OTA in coffee which provides a reference for the analysis of other toxic small molecules.

Selection and characterization of a novel affibody peptide and its application in a two-site ELISA for the detection of cancer biomarker alpha-fetoprotein

Alpha-fetoprotein (AFP) is one of the most important biomarkers associated with primary liver cancer, and the main approaches for diagnosis are based on immunoassay. Affibody is a 58 amino acids peptide derived from the Z domain of staphylococcal protein A and generally applied in imaging diagnosis, clinical therapeutics and biotechnology research. The aim of this study was therefore to develop a novel affibody-based ELISA for detection of AFP. After three rounds of biopanning, six AFP-binding affibody peptides were selected using phage display technology, among them affibody Z_AFPD2 showed high and specific binding affinity to AFP. An affibody dimer of Z_AFPD2 was created, named (Z_{AFP D2})₂, expressed in E.coli and the purified (Z_{AFP D2})₂ recombinant protein showed higher binding affinity to AFP, as well as high thermal stability. A novel affibody-based two-site ELISA method using Z_AFPD2 or (Z_{AFP D2})₂ and polyclonal antibody to detect AFP was developed, the detection limit of the immunoassay using (Z_{AFP D2})₂ was 2 ng mL^-1 that was 4 times lower than Z_AFPD2, which meets the requirements for practical application. Therefore, this concept of affibody-based ELISA may provide a new method for the detection of various cancer biomarkers.