Plant-produced recombinant SARS-CoV-2 receptor-binding domain; an economical, scalable biomaterial source for COVID-19 diagnosis.

The outbreak of the novel coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), spread rapidly causing a severe global health burden. The standard COVID-19 diagnosis relies heavily on molecular tests to detect viral RNA in patient samples; however, this method is costly, requires highly-equipped laboratories, multiple reagents, skilled laboratory technicians, and takes 3-6 hours to complete. To overcome these limitations, we developed a plant-based production platform for the SARS-CoV-2 receptor-binding domain as an economical source of detection reagents for a lateral-flow immunoassay strip (LFIA) which is suitable for detection of IgM/IgG antibodies in human samples. Further, we validated the plant-produced SARS-CoV-2 receptor-binding domain-based LFIA as a useful diagnostic tool for COVID-19. A total of 51 confirmed COVID-19 serum samples were tested using the LFIA, and the obtained results were consistent with those from polymerase chain reaction assays, while providing sensitivity and specificity of 94.1% and 98%, respectively. The developed LFIA is rapid, scalable, user-friendly, and relatively inexpensive with a simple test procedure, making it useful for the routine monitoring of COVID-19 in clinical settings. This study was approved on March 19, 2020 by the Ethics Committee of the Faculty of Medicine, Chulalongkorn University (COA No. 354/2020 and IRB No. 236/63).