Nanobody stability engineering by employing the ΔTm shift; a comparison with apparent rate constants of heat-induced aggregation

Nanobody-based indirect competitive ELISA for the detection of aflatoxin M1 in dairy products

Aflatoxin M1 (AFM1) is known to be carcinogenic, mutagenic, and teratogenic and poses a serious threat to food safety and human health, which makes its surveillance critical. In this study, an indirect competitive ELISA (icELISA) based on a nanobody (Nb M4) was developed for the sensitive and rapid detection of AFM1 in dairy products. In our previous work, Nb M4 was screened from a Bactrian-camel-immunized phage-displayed library. It exhibits VH-like features, possesses higher thermal stability than monoclonal antibody (mAb 1E6) and tightly binds to AFM1-BSA with a KD value of 2.5 nM. Under the optimal conditions, its half-maximal inhibitory concentration was 0.338 ng/mL, the limit of detection was 0.051 ng/mL, and linearity was noted in the range of 0.168-0.679 ng/mL. Nb M4 displayed almost no cross-reactivity with other mycotoxins. No matrix effect was observed in milk and milk powder samples, and the matrix effect in yogurt samples could be weakened by 2-fold dilution. Furthermore, validation studies in spiked samples (milk, yogurt, and milk powder) resulted in good recoveries of 95.40-111.33%, with a low coefficient of variation (2.89-6.78%). High-performance liquid chromatography was used to evaluate the accuracy and reliability of the developed icELISA, which indicated a satisfactory consistent correlation (R2 = 0.9722). This study highlights the potential of Nb M4 as a promising component for detecting AFM1 in dairy products.

Phage-Displayed Nanobody as a Sensitive Nanoprobe to Enhance Chemiluminescent Immunoassay for Cronobacter sakazakii Detection in Dairy Products

The exploitation of stable, high-affinity, and low-cost nanoprobes is essential to develop immunoassays for real-time monitoring of foodborne pathogens, so as to safeguard human health. The possible interaction of the Fc fragment of antibodies with spA protein on Staphylococcus aureus will result in unexpected interference. To address this consideration, we described herein for the first time the development of nanobodies that by definition are devoid of the Fc fraction. These nanobodies directed against Cronobacter sakazakii (C. sakazakii) were retrieved from a dedicated immune phage-displayed nanobody library. The binders showed superiority of low cost, strong stability, high binding affinity, and adequate load capacity. Thereafter, a phage-mediated sandwich enzyme-linked immunosorbent assay (ELISA) was constructed by using Cs-Nb2 as an antigen-capturing antibody and phage-displayed Cs-Nb1 as a detection probe. To further enhance the sensitivity, a chemiluminescent enzyme immunoassay (CISA) was established by replacing the substrate from 3,3',5,5'-tetramethylbenzidine (TMB) to luminol, providing a limit of detection of 1.04 × 104 CFU/mL, with a recovery of 98.15-114.63% for the detection of C. sakazakii in dairy products. The proposed nanobody-based phage-mediated sandwich CLISA shows various advantages, including high sensitivity, cost effectiveness, enhanced loading capacity of the enzyme, and high resistance to the matrix effect, providing a strategy for the design of immunoassays toward foodborne pathogens.

A comprehensive comparison between camelid nanobodies and single chain variable fragments

By the emergence of recombinant DNA technology, many antibody fragments have been developed devoid of undesired properties of natural immunoglobulins. Among them, camelid heavy-chain variable domains (VHHs) and single-chain variable fragments (scFvs) are the most favored ones. While scFv is used widely in various applications, camelid antibodies (VHHs) can serve as an alternative because of their superior chemical and physical properties such as higher solubility, stability, smaller size, and lower production cost. Here, these two counterparts are compared in structure and properties to identify which one is more suitable for each of their various therapeutic, diagnosis, and research applications.

Contribution of Intrinsic Fluorescence to the Design of a New 3D-Printed Implant for Releasing SDABS

Single-domain antibodies (sdAbs) offer great features such as increased stability but are hampered by a limited serum half-life. Many strategies have been developed to improve the sdAb half-life, such as protein engineering and controlled release systems (CRS). In our study, we designed a new product that combined a hydrogel with a 3D-printed implant. The results demonstrate the implant’s ability to sustain sdAb release up to 13 days through a reduced initial burst release followed by a continuous release. Furthermore, formulation screening helped to identify the best sdAb formulation conditions and improved our understanding of our CRS. Through the screening step, we gained knowledge about the influence of the choice of polymer and about potential interactions between the sdAb and the polymer. To conclude, this feasibility study confirmed the ability of our CRS to extend sdAb release and established the fundamental role of formulation screening for maximizing knowledge about our CRS.