Practical use of tobravirus-based vector to produce SARS-CoV-2 antigens in plants.

A plant-based heterologous expression system is an attractive option for recombinant protein production because it is based on a eukaryotic system of high feasibility, and low biological risks. Frequently, binary vector systems are used for transient gene-expression in plants. However, plant virus vector-based systems offer advantages for higher protein yields due to their self-replicating machinery. In the present study, we show an efficient protocol using a plant virus vector based on a tobravirus, pepper ringspot virus, that was employed for transient expression of severe acute respiratory syndrome coronavirus 2 partial gene fragments of the spike (named S1-N) and the nucleocapsid (named N) proteins in Nicotiana benthamiana plants. Purified proteins yield of 40-60 µg/g of fresh leaves were obtained. Both proteins, S1-N and N, showed high and specific reactivities against convalescent patients' sera by the enzyme-linked immunosorbent assay format. The advantages and critical points in using this plant virus vector are discussed.

Detection of SARS-CoV-2 virus via dynamic light scattering using antibody-gold nanoparticle bioconjugates against viral spike protein.

Mass testing for the diagnosis of COVID-19 has been hampered in many countries owing to the high cost of genetic material detection. This study reports on a low-cost immunoassay for detecting SARS-CoV-2 within 30 min using dynamic light scattering (DLS). The immunosensor comprises 50-nm gold nanoparticles (AuNPs) functionalized with antibodies against SARS-CoV-2 spike glycoprotein, whose bioconjugation was confirmed using transmission electron microscopy (TEM), UV-Vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), and surface-enhanced Raman scattering spectroscopy (SERS). The specific binding of the bioconjugates to the spike protein led to an increase in bioconjugate size, with a limit of detection (LOD) 5.29 × 103 TCID50/mL (Tissue Culture Infectious Dose). The immunosensor was also proven to be selective upon interaction with influenza viruses once no increase in size was observed after DLS measurement. The strategy proposed here aimed to use antibodies conjugated to AuNPs as a generic platform that can be extended to other detection principles, enabling technologies for low-cost mass testing for COVID-19.