Project Summary Funds are requested to apply technologies being developed in a current NIGMS award to generate recombinant antibody-like affinity reagents to the spike protein of the SARS-CoV-2 virus. As a proof-of-principle experiment, we have already isolated four fibronectin type III (FN3) monobodies that bind with low nanomolar affinity to the receptor binding domain (RBD) of the viral spike protein. An administrative supplement will permit continuation and expansion of this work to generate affinity reagents that bind with picomolar affinity and can be used in sensitive, robust diagnostic assays (homogenous assays, lateral flow assays) for virus particles in saliva. Separately, these monobodies will be reformatted as bivalent Fc fusions and overexpressed in CHO cells. Such reagents have the potential to serve as therapeutic agents that lower or block viral entry into patients ACE2-expressing cells. 1