Single domain antibodies in the development of immunosensors for diagnostics

Facile construction of sandwich ELISA based on double-nanobody for specific detection of α-hemolysin in food samples

α-hemolysin (Hla), a toxin secreted by Staphylococcus aureus (S. aureus), has been proved to be involved in the occurrence and aggravation of food poisoning. Hence, it is quite essential to establish its rapid detection methods to guarantee food safety. Sandwich ELISA based on nanobody is well known to be viable for toxins, but there is absence of nanobody against Hla, let alone a pair for it. Therefore, in this paper, we screened specific nanobodies by bio-panning and obtained the optimal nanobody pair for sandwich ELISA firstly. Then, RANbody, a novel nanobody owning both recognition and catalytic capability, is generated in a single step and at low cost through molecular recombination technology. Subsequently, sandwich ELISA was developed to detect Hla based on the nanobody and RANbody, that not only eliminated the use of secondary antibodies and animal-derived antibody, but also reduced detection time and cost, compared with traditional sandwich ELISA. Lastly, the performance has been evaluated, especially for specificity which showed no response to other hemolysins and a low limit of detection of 10 ng/mL. Besides, the proposed sandwich ELISA exhibits favorable feasibility and was successfully employed for the detection of Hla in milk and pork samples.

Nanobody engineering: computational modelling and design for biomedical and therapeutic applications

Nanobodies, the smallest functional antibody fragment derived from camelid heavy-chain-only antibodies, have emerged as powerful tools for diverse biomedical applications. In this comprehensive review, we discuss the structural characteristics, functional properties, and computational approaches driving the design and optimisation of synthetic nanobodies. We explore their unique antigen-binding domains, highlighting the critical role of complementarity-determining regions in target recognition and specificity. This review further underscores the advantages of nanobodies over conventional antibodies from a biosynthesis perspective, including their small size, stability, and solubility, which make them ideal candidates for economical antigen capture in diagnostics, therapeutics, and biosensing. We discuss the recent advancements in computational methods for nanobody modelling, epitope prediction, and affinity maturation, shedding light on their intricate antigen-binding mechanisms and conformational dynamics. Finally, we examine a direct example of how computational design strategies were implemented for improving a nanobody-based immunosensor, known as a Quenchbody. Through combining experimental findings and computational insights, this review elucidates the transformative impact of nanobodies in biotechnology and biomedical research, offering a roadmap for future advancements and applications in healthcare and diagnostics.

A multispecies competitive nanobody-based ELISA for the detection of antibodies against hepatitis E virus

The hepatitis E virus (HEV) is an emergent zoonotic virus causing viral hepatitis worldwide. Clinically, hepatitis E is not easily distinguished from other types of acute viral hepatitis. There is a need for HEV diagnostic assays to detect and prevent interspecies transmission among susceptible populations. Nanobodies (Nbs) are expressed recombinantly in different systems, produced with high yields, and have superior physicochemical properties compared with conventional antibodies (Ab). Several Nbs against ORF2, the capsid protein and main antigen, were selected and produced in E. coli. Nb39 and Nb74 specifically recognized HEV ORF2 (genotypes 3 and 4). A competitive ELISA (cELISA) was developed and validated using a reference panel of human (n = 86) and swine sera (n = 116) tested in comparison with a commercial kit. The optimal cutoff values determined by ROC analysis were 69.16% (human) and 58.76% (swine); the sensitivity and specificity were high: 97.4% (95% CI 86.5-99.5%) and 95.8% (95% CI 86.0-98.8%) for human vs. 100% (95% CI 93.5-100%) and 98.3% (95% CI 91.0-99.7%) for swine. Further, the cELISA detected total anti-HEV antibodies in wild boar, deer, and mice. To our knowledge, this is the first report of production of Nbs against HEV-3 ORF2 for diagnostic purposes.

Quantification of soluble epoxide hydrolase inhibitors in experimental and clinical samples using the nanobody-based ELISA

To ensure proper dosage of a drug, analytical quantification of it in biofluid is necessary. Liquid chromatography mass spectrometry (LC-MS) is the conventional method of choice as it permits accurate identification and quantification. However, it requires expensive instrumentation and is not appropriate for bedside use. Using soluble epoxide hydrolase (sEH) inhibitors (EC5026 and TPPU) as examples, we report development of a nanobody-based enzyme-linked immunosorbent assay (ELISA) for such small molecules and its use to accurately quantify the drug chemicals in human samples. Under optimized conditions, two nanobody-based ELISAs were successfully established for EC5026 and TPPU with low limits of detection of 0.085 ng/mL and 0.31 ng/mL, respectively, and two order of magnitude linear ranges with high precision and accuracy. The assay was designed to detect parent and two biologically active metabolites in the investigation of a new drug candidate EC5026. In addition, the ELISAs displayed excellent correlation with LC-MS analysis and evaluation of inhibitory potency. The results indicate that nanobody-based ELISA methods can efficiently analyze drug like compounds. These methods could be easily implemented by the bedside, in the field in remote areas or in veterinary practice. This work illustrates that nanobody based assays offer alternative and supplementary analytical tools to mass spectrometry for monitoring small molecule medicines during clinical development and therapy. Attributes of nanobody based pharmaceutical assays are discussed.

Large-Scale Production of Anti-RNase A VHH Expressed in pyrG Auxotrophic Aspergillus oryzae

Nanobodies, also referred to as VHH antibodies, are the smallest fragments of naturally produced camelid antibodies and are ideal affinity reagents due to their remarkable properties. They are considered an alternative to monoclonal antibodies (mAbs) with potential utility in imaging, diagnostic, and other biotechnological applications given the difficulties associated with mAb expression. Aspergillus oryzae (A. oryzae) is a potential system for the large-scale expression and production of functional VHH antibodies that can be used to meet the demand for affinity reagents. In this study, anti-RNase A VHH was expressed under the control of the glucoamylase promoter in pyrG auxotrophic A. oryzae grown in a fermenter. The feature of pyrG auxotrophy, selected for the construction of a stable and efficient platform, was established using homologous recombination. Pull-down assay, size exclusion chromatography, and surface plasmon resonance were used to confirm the binding specificity of anti-RNase A VHH to RNase A. The affinity of anti-RNase A VHH was nearly 18.3-fold higher (1.9 nM) when expressed in pyrG auxotrophic A. oryzae rather than in Escherichia coli. This demonstrates that pyrG auxotrophic A. oryzae is a practical, industrially scalable, and promising biotechnological platform for the large-scale production of functional VHH antibodies with high binding activity.

Nanobody-Based Sandwich Immunoassay for Pathogenic Escherichia coli F17 Strain Detection

Rapid and specific detection of pathogenic bacteria in fecal samples is of critical importance for the diagnosis of neonatal diarrhea in veterinary clinics. Nanobodies are a promising tool for the treatment and diagnosis of infectious diseases due to their unique recognition properties. In this study, we report the design of a nanobody-based magnetofluorescent immunoassay for the sensitive detection of pathogenic Escherichia coli F17-positive strains (E. coli F17). For this, a camel was immunized with purified F17A protein from F17 fimbriae and a nanobody library was constructed by phage display. Two specific anti-F17A nanobodies (Nbs) were selected to design the bioassay. The first one (Nb1) was conjugated to magnetic beads (MBs) to form a complex capable of efficiently capturing the target bacteria. A second horseradish peroxidase (HRP)-conjugated nanobody (Nb4) was used for detection by oxidizing o-phenylenediamine (OPD) to fluorescent 2,3-diaminophenazine (DAP). Our results show that the immunoassay recognizes E. coli F17 with high specificity and sensitivity, with a detection limit of 1.8 CFU/mL in only 90 min. Furthermore, we showed that the immunoassay can be applied to fecal samples without pretreatment and remains stable for at least one month when stored at 4 °C.

Nanobodies: a new potential for prostate cancer treatment

BACKGROUND

The current progressive increase in the cancer burden of prostate cancer requires the exploration of new diagnostic and therapeutic approaches. Nanobodies are single-domain antibodies with the advantages of small size, high stability, easy processing and modification, which are increasingly used in the treatment of many types of cancer.

METHODS

This review analyzed the relevant literature in PubMed and other databases.

RESULT

In the retrieved literature, nanobodies are widely used in the treatment of prostate cancer. The preparation of nanobodies targeting PSA or PSMA is straightforward. For diagnostic purposes, nanobodies can be used in the preparation of biosensors for more sensitive identification of prostate cancer; for therapeutic purposes, nanobodies are used in the preparation of immunotoxic and ADC drugs. Preclinical in vivo and in vitro experiments have shown that this therapeutic approach is feasible. This article is a review of the above to provide new ideas for the treatment of prostate cancer.

CONCLUSION

Compared with traditional antibodies, nano-antibodies have the advantages of small size, high stability, and high penetration. These advantages make nano-antibodies worthy to be widely used. Current studies have shown that nanobodies have advantages and future in the diagnosis and treatment of prostate cancer.

A Nanobody‐on‐Quantum Dot Displacement Assay for Rapid and Sensitive Quantification of the Epidermal Growth Factor Receptor (EGFR)

Biosensing approaches that combine small, engineered antibodies (nanobodies) with nanoparticles are often complicated. Here, we show that nanobodies with different C‐terminal tags can be efficiently attached to a range of the most widely used biocompatible semiconductor quantum dots (QDs). Direct implementation into simplified assay formats was demonstrated by designing a rapid and wash‐free mix‐and‐measure immunoassay for the epidermal growth factor receptor (EGFR). Terbium complex (Tb)‐labeled hexahistidine‐tagged nanobodies were specifically displaced from QD surfaces via EGFR‐nanobody binding, leading to an EGFR concentration‐dependent decrease of the Tb‐to‐QD Förster resonance energy transfer (FRET) signal. The detection limit of 80±20 pM (16±4 ng mL⁻¹) was 3‐fold lower than the clinical cut‐off concentration for soluble EGFR and up to 10‐fold lower compared to conventional sandwich FRET assays that required a pair of different nanobodies.

Identification of Serum Ferritin-Specific Nanobodies and Development towards a Diagnostic Immunoassay

Serum ferritin (SF) is an iron-rich protein tightly connected with iron homeostasis, and the variations are frequently observed in diseased states, including iron-deficiency anemia, inflammation, liver disease, and tumors, which renders SF level an indicator of potential malignancies in clinical practice. Nanobodies (Nbs) have been widely explored and developed into theranostic reagents. Surprisingly, no reports stated the identification of anti-SF Nbs, nor the potential of such Nbs as a diagnostic tool. In this study, we generated SF-specific Nbs and provided novel clinical diagnostic approaches to develop an immunoassay. An immune library was constructed after immunizing an alpaca with SF, and five Nbs specifically targeting human SF were retrieved. The obtained Nbs exhibited robust properties including high stability, affinity, and specificity. Then, an ELISA-based test using a heterologous Nb-pair was developed. The calibration curve demonstrated a linear range of SF between 9.0 to 1100 ng/mL, and a limit of detection (LOD) of 1.01 ng/mL. The detecting recovery and coefficient variation (CV) were determined by spiking different concentrations of SF into the serum sample, to verify the successful application of our selected Nbs for SF monitoring. In general, this study generated SF-specific Nbs and demonstrated their potential as diagnostic immunoassay tools.

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.

Antibodies as Biosensors' Key Components: State-of-the-Art in Russia 2020-2021

The recognition of biomolecules is crucial in key areas such as the timely diagnosis of somatic and infectious diseases, food quality control, and environmental monitoring. This determines the need to develop highly sensitive display devices based on the achievements of modern science and technology, characterized by high selectivity, high speed, low cost, availability, and small size. Such requirements are met by biosensor systems—devices for reagent-free analysis of compounds that consist of a biologically sensitive element (receptor), a transducer, and a working solution. The diversity of biological material and methods for its immobilization on the surface or in the volume of the transducer and the use of nanotechnologies have led to the appearance of an avalanche-like number of different biosensors, which, depending on the type of biologically sensitive element, can be divided into three groups: enzyme, affinity, and cellular/tissue. Affinity biosensors are one of the rapidly developing areas in immunoassay, where the key point is to register the formation of an antigen–antibody complex. This review analyzes the latest work by Russian researchers concerning the production of molecules used in various immunoassay formats as well as new fundamental scientific data obtained as a result of their use.

Oriented immobilization of antibodies through different surface regions containing amino groups: Selective immobilization through the bottom of the Fc region

Amino groups on the antibody surface (amino terminus and Lys) are very interesting conjugation targets due to their substantial quantities and selectivity toward various reactive groups. Oriented immobilization of antibodies via amino moieties on the Fc region instead of the antigen-binding fragment (Fab) is highly appreciated to conserve antigen-binding capacity. In this paper, targeting amino moieties on distinct regions, three antibody immobilization strategies were compared with the recognition ability of corresponding adsorbents. Our results demonstrate that oriented immobilization of antibodies onto heterofunctional chelate-epoxy support selectively involving Lys residues placed at the bottom of the Fc region, thus preserved the highest antigen recognition capacity (over 75% functionality). For homofunctional aldehyde support, immobilization at pH 10 demonstrates 50% remaining functionality due to the random orientation of tethered antibodies; while only 10% functionality remained when N-terminus were specifically conjugated at pH 8.5. With the rationalization of moieties density onto heterofunctional support, 2-fold recognition capacity was exhibited over randomly immobilization for antigens with higher size (β-galactosidase, 425 kDa vs. horseradish peroxidase, 40 kDa). Meanwhile, at least 97% of antigens with a varied concentration in diluted human serum were efficiently captured by the optimized chelate-epoxy support. Therefore, our antibody immobilization protocol proved the potential to be utilized as a promising candidate to capture voluminous antigens (large proteins and cells) in real samples.