Nanoplasmonic multiplex biosensing for COVID-19 vaccines

The ongoing emergence of severe acute respiratory syndrome caused by the new coronavirus (SARS-CoV-2) variants requires swift actions in identifying specific antigens and optimizing vaccine development to maximize the humoral response of the patient. Measuring the specificity and the amount of antibody produced by the host immune system with high throughput and accuracy is critical to develop timely diagnostics and therapeutic strategies. Motivated by finding an easy-to-use and cost-effective alternative to existing serological methodologies for multiplex analysis, we develop a proof-of-concept multiplex nanoplasmonic biosensor to capture the humoral response in serums against multiple antigens. Nanoplasmonic sensing relies on the wavelength shift of the localized surface plasmon resonance (LSPR) peak of gold nanostructures upon binding interactions between the antibodies and the immobilized antigens. Here the antigens are first immobilized on different sensing areas by using a mono-biotinylation system based on the high affinity interaction between biotin and streptavidin. We then validate the multiplex platform by detecting the presence of 3 monoclonal antibodies against 3 antigens (2 different hemagglutinins (HAs) from influenza viruses, and the SARS-CoV-2 Spike RBD (receptor binding domain)). We also measure the humoral response in murine sera collected before and after its immunization with the SARS-CoV-2 Spike protein, in good agreement with the results obtained by the ELISA assay. Our nanoplasmonic assays have successfully demonstrated multiple serum antibody profiling, which can be further integrated with microfluidics as an effective high throughput screening platform in future studies for the ongoing SARS-CoV-2 vaccine development.

Production of a mono-biotinylated EGFR nanobody in the E. coli periplasm using the pET22b vector

OBJECTIVE

Our aim was to produce a mono-biotinylated single domain antibody ('nanobody') specific for the epidermal growth factor receptor (EGFR), which is overexpressed in many cancer cells. The binding of the nanobody and its function are tested in cancer cells. The construct could be used to carry variable therapeutic or diagnostic load using biotin-streptavidin bridging.

RESULTS

The EGFR-specific 7D12 nanobody was genetically fused to an IgA hinge linker and to a C-terminal biotin ligase acceptor sequence, allowing mono-biotinylation in E. coli. Expression was in strain BL21-DE3 from a T7 RNA polymerase driven pET22b vector. The biotinylated nanobody, isolated from the periplasm, was purified using streptavidin-mutein affinity chromatography. Final yields were up to 5 mg/l of cell culture. We showed that the construct could bind to EGFR expressing A431 epidermoid carcinoma cells, and to transiently transformed EGFR overexpressing HEK293T cells and not to EGFR negative control cells. The specificity for the EGFR was further demonstrated by immunoprecipitation. To test the functionality, PC9 non-small cell lung cancer cells were treated with mono-biotinylated nanobody or with streptavidin-coupled tetravalent nanobodies. Both were able to block mutant EGFR phosphorylation and slow down growth of PC9 cells. Tetravalent nanobodies were able to downregulate AKT phosphorylation.