Schematic presentation of screening nanobodies, SARS-CoV-2 spike pseudovirus production and neutralization assay. a Screening specific nanobodies against S and RBD protein from naïve VHH library, and the expression of nanobody-hFc fusions. b Production of SARS-CoV-2 spike pseudovirus using HEK293T cells as the host cells. c Determination the neutralizing activity of multivalent nanobodies