Antibodies binding kinetics and competitive binding assay measured by Biolayer interferometry (BLI)

The affinity between SARS-CoV-2 RBD and antibodies were measured by BLI using GatorTM Label-Free Bioanalysis System (GatorBio). All experiments were performed at 25°C with shaking at 1,000 r.p.m, and anti-human IgG Fc biosensors were pre-equilibrated in Q buffer containing PBS (10mM pH7.4), 0.02%Tween-20, and 0.2%BSA for at least 300 s before use in experiments. 10 μg/mL antibody was loaded onto anti-human IgG Fc biosensors for 120 s and flowed the difference in concentrations of SARS-CoV-2 RBD-His recombinant protein (Sino biological) or buffer as control) for 120 s. Then the both dissociate in Q buffer for 300s. The competitive binding between two antibodies was also measured using the GatorTM Label-Free Bioanalysis System (GatorBio). Anti-His biosensors were pre-equilibrated in Q buffer, then 2 μg/mL SARS-CoV-2 RBD-His recombinant protein (Sino biological, China) was loaded onto anti-His biosensors for 120s, and flowed 10 μg/mL of the first antibody for 300 s and 10 µg/mL of the second antibody (or buffer as control) for 300 s. We analysed the data by using Gator™ System Analysis.