Coronavirus disease 2019 (COVID-19) is newly emerging human infectious diseases, which is caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2, also previously known as 2019-nCoV). Within two months of the outbreak, more than 80,000 cases of COVID-19 have been confirmed worldwide. Since the human to human transmission occurred easily and the human infection is rapidly increasing, the sensitive and early diagnosis is essential to prevent the global outbreak. Recently, World Health Organization (WHO) announced various primer and probe sets for SARS-CoV-2 previously developed in China, Germany, Hong Kong, Japan, Thailand, and USA. In this study, we compared the ability to detect SARS-CoV-2 RNA among the seven primer-probe sets for N gene and the three primer-probe sets for Orf1 gene. The result of the comparative analysis represented that the ‘2019-nCoV_N2, N3’ of USA and the ‘ORF1ab’ of China are the most sensitive primer-probe sets for N and Orf1 genes, respectively. Therefore, the appropriate combination from ORF1ab (China), 2019-nCoV_N2, N3 (USA), and NIID_2019-nCOV_N (Japan) sets should be selected for the sensitive and reliable laboratory confirmation of SARS-CoV-2.

Since the beginning of the COVID-19 pandemic, accumulating mutations have led to marked changes in the genetic sequence of SARS-CoV-2. Of these, mutations in the spike (S) protein can alter the properties of the virus, particularly transmissibility and antigenicity. However, it is difficult to detect antigenic variants of the SARS-CoV-2 S protein by immunoassay. Here, we developed an ACE2-based biosensor designed to detect both SARS-CoV-2 S1 mutations and neutralizing antibodies. In “binding mode”, the biosensor works by detecting binding of the S protein to an immobilized ACE2 receptor. The ACE2-based biosensor was able to detect S1 proteins of the alpha (500 pg/mL) and beta variants (10 ng/mL), as well as wild-type S1 (10 ng/mL), of SARS-CoV-2. The biosensor distinguished wild-type SARS-CoV-2 S1 from the S1 alpha and beta variants via color differences. In addition, a slight modification to the protocol enabled the ACE2-based biosensor to operate in “blocking mode” to detect neutralizing antibodies in serum samples from COVID-19 patients. Therefore, the ACE2-based biosensor is a versatile test for detecting wild-type S1, S1 mutants, and neutralizing antibodies against SARS-CoV-2. This approach to targeting both the mechanism by which SARS-CoV-2 enters host cells and the subsequent adaptive immune response will facilitate the development of various biosensors against SARS-CoV-2.