Multiplex SARS-CoV-2 RBD Protein Coupling

RBD proteins described above (Supplemental Table 3) were covalently coupled onto magnetic multiplex beads as previously described (65 (link)). Briefly, each respective RBD protein was coupled to a distinct magnetic carboxylated bead region (Bio-Rad), using a 2-step carbodiimide reaction at a ratio of 1 million beads to 10 μg of each RBD protein. Recombinant influenza hemagglutinin from H1N1 (A/Cali/07/2009) (11085-V08H, Sino Biological) and SARS-CoV-2 Spike S1 (40591-V08H, Sino Biological) were also coupled using identical protocols as control proteins. Coupling efficiency of the recombinant RBD was assessed using an anti-His Tag antibody (A00174, GenScript Corporation). A complete list of the magnetic bead regions and respective RBD variants is in Supplemental Table 3.