“…Nanobody is a single domain antibody and is derived from the Camelidae heavy chain-only antibodies (VHH) ( Vincke and Muyldermans, 2012 ), with some advantages including small molecular weight (∼15 kDa) and easy genetic engineering and expression ( Hamers-Casterman et al., 1993 ; Vanlandschoot et al., 2011 ). Therefore, the nanobody-horseradish peroxidase (HRP) fusion has been used as a probe for developing competitive ELISA (cELISA) for the diagnosis of viral infection ( Du et al., 2019 ; Ji et al., 2020 ; Lu et al., 2020 ). Compared with the ELISA assays based on the traditional antibodies, the ones using nanobody-HRP fusion protein showed advantages, such as short testing time, simple operation, and accessibility to commercial production ( Sheng et al., 2019 ).…”