Discovery of sandwich type COVID-19 nucleocapsid protein DNA aptamers.

Here, we report for the first time DNA aptamers targeted toward the COVID-19 nucleocapsid protein (Np). Np is one of the most abundant structural proteins and it serves as a diagnostic marker for the accurate and sensitive detection of COVID-19. After five rounds of selection, we obtained four DNA sequences with an affinity below 5 nM. The best one displayed a superb binding performance toward Np with a Kd value of 0.49 nM. Interestingly, we found that the four pairs of aptamers could bind to Np successively, suggesting a sandwich-type interaction. Using these sandwiched aptamers in ELISA and colloidal gold immunochromatographic strips, we were able to detect Np at the tens of pM level. The results demonstrate that aptamers are powerful molecular tools for virus detection, diagnosis, and antiviral therapy.