Proposal of De Novo Antigen Test for COVID-19: Ultrasensitive Detection of Spike Proteins of SARS-CoV-2

• Main Authors: Yuta Kyosei, Mayuri Namba, Sou Yamura, Rikiya Takeuchi, Noriko Aoki, Kazunari Nakaishi, Satoshi Watabe, Etsuro Ito
• Format: Article
• Language: English
• Published: MDPI AG 2020-08-01
• Series: Diagnostics
• Subjects: COVID-19; SARS-CoV-2; spike protein; thio-NAD cycling; ultrasensitive ELISA
• Online Access: https://www.mdpi.com/2075-4418/10/8/594

Polymerase chain reaction (PCR)-based antigen tests are technically difficult, time-consuming, and expensive, and may produce false negative results requiring follow-up confirmation with computed tomography. The global coronavirus disease 2019 (COVID-19) pandemic has increased the demand for accurate, easy-to-use, rapid, and cost-effective antigen tests for clinical application. We propose a de novo antigen test for diagnosing COVID-19 using the combination of sandwich enzyme-linked immunosorbent assay and thio-nicotinamide adenine dinucleotide (thio-NAD) cycling. Our test takes advantage of the spike proteins specific to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus. The limit of detection of our test was 2.3 × 10⁻¹⁸ moles/assay. If the virus has ~25 spike proteins on its surface, our method should detect on the order of 10⁻²⁰ moles of virus/assay, corresponding to ~10⁴ copies of the virus RNA/assay. The detection sensitivity approaches that of PCR-based assays because the average virus RNA load used for PCR-based assays is ~10⁵ copies per oro- or naso-pharyngeal swab specimen. To our knowledge, this is the first ultrasensitive antigen test for SARS-CoV-2 spike proteins that can be performed with an easy-to-use microplate reader. Sufficient sensitivity can be achieved within 10 min of thio-NAD cycling. Our antigen test allows for rapid, cost-effective, specific, ultrasensitive, and simultaneous multiple measurements of SARS-CoV-2, and has broad application for the diagnosis for COVID-19.