COVID-19 is threatening the world, and the World Health Organization (WHO) declared a pandemic 11 years after the H1N1 Flu. When such a highly contagious and lethal new epidemic occurs, preventive measures are needed, such as quickly locating the infected person and separating the infected person from others. The most important thing here is to diagnose the virus quickly.

POSTECH(Pohang University of Science and Technology) researchers have developed a diagnostic method that can determine whether a person is infected in 15 minutes using an aptamer (nucleic acid substance), which is a type of molecular capture. This method, which can be used for all new viruses, is expected to be used not only for examination but also for treatment.

▲ A diagram of viro-SELEX method (Image by POSTECH)

The POSTECH research team including Prof. Sung Key Jang, Dr. Jun Young Kwon, and Dr. Narayan developed a new aptamer discovery method ("viro-SELEX") with Aptamer Sciences Inc. By using the new method, viro-SELEX, the research team developed a rapid diagnostic method to determine whether an influenza virus had infected within 15 minutes with high sensitivity and specificity. This research achievement was published one after another in the related journals, "Journal of Biomedical Nanotechnology" and "Analyst."

The virus diagnostic methods include molecular, antigen/antibody, and cell culture diagnosis. The currently used method for COVID-19 is a molecular diagnosis, which is sensitive, but requires samples to be sent to a specialized analytical facility for analysis, takes more than 6 hours to analyze, and is expensive. Cell culture diagnostic method takes too long (2-4 weeks) and is not suitable for large-scale testing. In addition, the diagnosis method of the COVID-19 virus using antigen/antibody has not been developed yet. Unfortunately, in the case of COVID-19, a real-time diagnostic method for directly testing a sample is not developed.

Aptamers are nucleic acid materials composed of DNA or RNA. They are a kind of molecular captures that bind with high specificity and affinity to various targets ranging from simple low-molecular compounds to high-molecular substances such as proteins. DNA aptamers are highly stable and easy to transport and store. And, if only the base sequence is known, it can be synthesized in large quantities at a low production cost and is considered as a material to replace antibodies.

▲ A diagram of rapid diagnostic kit and a picture of showing the existence of virus through changes in color (Image by POSTECH)

Aptamers are discovered through a process called SELEX (Systematic Evolution of Ligands by EXponential Enrichment). In the case of viruses, it was difficult to find aptamers using the existing SELEX method because the envelope protein used as a target is a membrane protein. Therefore, instead of separating and purifying membrane proteins separately, the research team recombined baculovirus to target the spike protein of the virus. The team then separated and purified the recombined virus to invent viro-SELEX method, which is used for SELEX.

Based on this method, the team discovered a new aptamer that acts on the spike protein (hemagglutinin, HA) of the influenza virus. In addition, by using a pair of aptamers that bind to different parts of the spike protein (hemagglutinin, HA), it has succeeded in developing a diagnostic kit that can diagnose whether a virus infected with only changes of the color, like a pregnancy diagnostic kit. With this device, 15 minutes is enough to check for infection.

"Using the newly developed viro-SELEX method, aptamers with high specificity and binding ability to the spike protein of COVID-19 virus can be identified. With these aptamers, a quick diagnostic kit can be made immediately. When these aptamers bind to the spike protein of coronavirus, they can prevent the virus from infecting healthy cells. As such, it is expected to use aptamers as a therapeutic agent," said Prof. Sung Key Jang, Department of Life Sciences, POSTECH.



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