Fig. 1

A naïve VHH library construction and screening the SARS-CoV-2 S and RBD specific nanobodies. a Amplification of VHH genes (~ 400 bp) by nest-PCR from PBLs, and estimation the correct insertion rate of VHH library. b Expression and purification of recombinant S and RBD protein were detected using SDS-PAGE. M: Marker; lane 1: purified S protein; lane 2: purified RBD protein. c Analysis of the enrichment of phage particles against S and RBD specific nanobodies with polyclonal indirect ELISA. d and e Identification of the recombinant VHH-gpIII protein from the 96 clones specifically binding with S protein (17 clones) and its RBD domain (40 clones), respectively. f Alignment of the amino acid sequences of specific nanobodies against S and RBD protein. The sequences were classified into four groups according to their CDRs. g Phylogenetic tree of the isolated S and RBD-directed VHHs based on the neighbor joining method by using DNASTAR software