Schematic representation of screening the nanobodies and detection porcine parvovirus with reporter-nanobody fusions. a Screening the nanobodies from an immunized phage display library. b The platform for expressing nanobody-HRP and nanobody-EGFP fusion proteins. c Detection porcine parvovirus with nanobody-HRP fusions. d Detection porcine parvovirus with nanobody-EGFP fusions