The ELISA plate is coated (overnight) with Strep-Tactin XT. The sample and the RBD-bridge mix are added after blocking. The RBD-bridge mix contains two components, recombinant RBD with a Twin-Strep-tag, and recombinant RBD with a WASP peptide tag. Antibodies with specificity to RBD will bind RBD-Twin-Strep-tag with one binding site and RBD-WASP tag with the other, creating a bridge. The Twin-Strep-tag will bind to the coated Strep-Tactin XT, allowing the whole bridge-complex to be captured. The captured complex is detected by addition of Anti-WASP Antibodies (HRP). Addition of TMB substrate will result in a colored substrate product. The reaction is stopped with sulfuric acid and optical density determined using an ELISA plate reader.