Development of a SARS-CoV-2-specific biosensor for antigen detection using scFv-Fc fusion proteins

Coronavirus disease 2019 (COVID-19) is a newly emerged human infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In a global pandemic, development of a cheap, rapid, accurate, and easy-to-use diagnostic test is necessary if we are to mount an immediate response to this emerging threat. Here, we report the development of a specific lateral flow immunoassay (LFIA)-based biosensor for COVID-19. We used phage display technology to generate four SARS-CoV-2 nucleocapsid protein (NP)-specific single-chain variable fragment-crystallizable fragment (scFv-Fc) fusion antibodies. The scFv-Fc antibodies bind specifically and with high affinity to the SARS-CoV-2 NP antigen, but not to NPs of other coronaviruses. Using these scFv-Fc antibodies, we screened three diagnostic antibody pairs for use on a cellulose nanobead (CNB)-based LFIA platform. The detection limits of the best scFv-Fc antibody pair, 12H1 as the capture probe and 12H8 as the CNB-conjugated detection probe, were 2 ng antigen protein and 2.5 × 10⁴ pfu cultured virus. This LFIA platform detected only SARS-CoV-2 NP, not NPs from MERS-CoV, SARS-CoV, or influenza H1N1. Thus, we have successfully developed a SARS-CoV-2 NP-specific rapid diagnostic test, which is expected to be a simple and rapid diagnostic test for COVID-19.