Antibody-based surfaces: Rapid characterization using two complementary colorimetric assays

Sensitivity and reproducibility enhancement in enzyme immunosorbent assays based on half fragment antibodies

The free sulfhydryl groups of the hinge region of monovalent antibody fragments (rIgG) allow the orientation of rIgG on functionalized surfaces in immunosensors. To evaluate the contribution of reduction and orientation on signal enhancement we compared the performance of whole antibodies and their rIgG in ELISA performed on polystyrene or maleimide-functionalized microplates. Monoclonal anti-horseradish peroxidase (anti-HRP) and monoclonal anti-fPSA antibodies (1 mg/mL) were reduced with 2-mercaptoethylamine (53 mM). Western blot confirmed the presence of rIgG as a band at 75 kDa, detectable only by anti-heavy chain but not by anti-light chain antibodies, suggesting a possible folding rearrangement. Using anti-HRP we confirmed the retention of the antigen binding capacity of rIgG. Moreover, we observed a signal enhancement for rIgG even if randomly absorbed on polystyrene [linear regression slope (95%CI): rIgG 0.524 (0.434-0.614), IgG 0.370 (0.430-0.399); P = 0.0016] suggesting that chemical reduction might affect the antigen binding capacity of antibodies. ELISA with anti-fPSA rIgG coated on polystyrene confirmed these observations. Oriented anti-fPSA rIgG on a maleimide surface showed comparable signals to the assay performed on polystyrene for each analyzed concentration of antigen (P_ANOVA = 0.1980), anyway, with a significant improvement of the repeatability likely providing a more homogeneous capturing surface (SD rIgG_maleimide-rIgG_polystirene: fPSA 0.725 ng/mL:0.74-2.89; 1.45 ng/mL:1.56-8.69; 3.625 ng/mL:3.52-15.03; 7.25 ng/mL:7.78-18.44).

Photochemistry on the Space Station-Antibody Resistance to Space Conditions after Exposure Outside the International Space Station

Antibody-based analytical instruments are under development to detect signatures of life on planetary bodies. Antibodies are molecular recognition reagents able to detect their target at sub-nanomolar concentrations, with high affinity and specificity. Studying antibody binding performances under space conditions is mandatory to convince space agencies of the adequacy of this promising tool for planetary exploration. To complement previous ground-based experiments on antibody resistance to simulated irradiation, we evaluate in this paper the effects of antibody exposure to real space conditions during the EXPOSE-R2 mission outside the International Space Station. The absorbed dose of ionizing radiation recorded during the 588 days of this mission (220 mGy) corresponded to the absorbed dose expected during a mission to Mars. Moreover, samples faced, at the same time as irradiation, thermal cycles, launch constraints, and long-term storage. A model biochip was used in this study with antibodies in freeze-dried form and under two formats: free or covalently grafted to a solid surface. We found that antibody-binding performances were not significantly affected by cosmic radiation, and more than 40% of the exposed antibody, independent of its format, was still functional during all this experiment. We conclude that antibody-based instruments are well suited for in situ analysis on planetary bodies.

Oriented Immobilization of Fab Fragments by Site-Specific Biotinylation at the Conserved Nucleotide Binding Site for Enhanced Antigen Detection

Oriented immobilization of antibodies and antibody fragments has become increasingly important as a result of the efforts to reduce the size of diagnostic and sensor devices to miniaturized dimensions for improved accessibility to the end-user. Reduced dimensions of sensor devices necessitate the immobilized antibodies to conserve their antigen binding activity for proper operation. Fab fragments are becoming more commonly used in small-scaled diagnostic devices due to their small size and ease of manufacture. In this study, we used the previously described UV-NBS(Biotin) method to functionalize Fab fragments with IBA-EG11-Biotin linker utilizing UV energy to initiate a photo-cross-linking reaction between the nucleotide binding site (NBS) on the Fab fragment and IBA-Biotin molecule. Our results demonstrate that immobilization of biotinylated Fab fragments via UV-NBS(Biotin) method generated the highest level of immobilized Fab on surfaces when compared to other typical immobilization methods while preserving antigen binding activity. UV-NBS(Biotin) method provided 432-fold, 114-fold, and 29-fold improved antigen detection sensitivity than physical adsorption, NHS-Biotin, and ε-NH3(+), methods, respectively. Additionally, the limit of detection (LOD) for PSA utilizing Fab fragments immobilized via UV-NBS(Biotin) method was significantly lower than that of the other immobilization methods, with an LOD of 0.4 pM PSA. In summary, site-specific biotinylation of Fab fragments without structural damage or loss in antigen binding activity provides a wide range of application potential for UV-NBS immobilization technique across numerous diagnostic devices and nanotechnologies.

Site-specific fab fragment biotinylation at the conserved nucleotide binding site for enhanced Ebola detection

The nucleotide binding site (NBS) is a highly conserved region between the variable light and heavy chains at the Fab domains of all antibodies, and a small molecule that we identified, indole-3-butyric acid (IBA), binds specifically to this site. Fab fragment, with its small size and simple production methods compared to intact antibody, is good candidate for use in miniaturized diagnostic devices and targeted therapeutic applications. However, commonly used modification techniques are not well suited for Fab fragments as they are often more delicate than intact antibodies. Fab fragments are of particular interest for sensor surface functionalization but immobilization results in damage to the antigen binding site and greatly reduced activity due to their truncated size that allows only a small area that can bind to surfaces without impeding antigen binding. In this study, we describe an NBS-UV photocrosslinking functionalization method (UV-NBS(Biotin) in which a Fab fragment is site-specifically biotinylated with an IBA-EG11-Biotin linker via UV energy exposure (1 J/cm(2)) without affecting its antigen binding activity. This study demonstrates successful immobilization of biotinylated Ebola detecting Fab fragment (KZ52 Fab fragment) via the UV-NBS(Biotin) method yielding 1031-fold and 2-fold better antigen detection sensitivity compared to commonly used immobilization methods: direct physical adsorption and NHS-Biotin functionalization, respectively. Utilization of the UV-NBS(Biotin) method for site-specific conjugation to Fab fragment represents a proof of concept use of Fab fragment for various diagnostic and therapeutic applications with numerous fluorescent probes, affinity molecules and peptides.

Preparation of aqueous sol-gel silica and titania multi-layered thin films and their evaluation as biomolecular encapsulation hosts

Multi-layered silica and titania thin films were prepared via an aqueous sol-gel route. The titania layers could efficiently entrap anti-HRP antibodies and showed increase in stability upon ageing, up to 2 months. Specific activity of the entrapped antibodies could be monitored in a reliable manner over one week. The silica films showed lower performances, as a probable consequence of large pore size. Increase in the titania precursor (TiBALDH) concentration and addition of glycerol allowed the design of tri-enzymatic multi-layered systems for the detection of lactose. The multilayer approach showed higher robustness than the co-immobilization of the enzymes in a single layer. This process is simple, solvent-free and flexible, opening the route to multi-biofunctional materials at the nanoscale.