SARS-CoV-2 Spike and RBD ELISA Assay

RBD and spike ELISAs were modified from Amanat et al. and conducted as previously described [6 (link),8 (link)]. ELISA plates were coated either with RBD (Sino Biological, Wayne, PA, USA), nucleocapsid (Gift from B. Geiss Lab) or spike protein (Sino Biological, Wayne, PA, USA). Samples and controls were added after 1 h of blocking (1X PBS, 3% milk powder, 0.1% tween). Positive controls included convalescent patient serum (gift of R. Goodrich) and monoclonal antibody CR3022 (Absolute Antibody, Boston, MA, USA). Negative control serum was charcoal inactivated pooled human serum collected in 2015 (Jackson Immuno Research, West Grove, PA, USA). Secondary antibody was added followed by development and reading via spectrophotometer (Thermo Fisher, Dallas, TX, USA).