[Slashdot] - How the Rapid FDA-Approved Coronavirus Testing System Works

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Tekla Perry writes: In 2001, a rapid, easy-to-use, PCR-based testing system for biological testing was still in prototype form when letters containing anthrax spores started arriving in the mailboxes of journalists and senators. Its creators at startup Cepheid quickly adapted it to test for anthrax, and now it is used to run that test as part of U.S. mail sorting systems. The tool, now called GeneXpert, is also installed in health care facilities around the world. And cartridges to allow these systems to test for COVID-19 -- the first rapid such test approved in the U.S. -- are rolling out. The technology relies on microfluidics, and takes about 45 minutes to run an extremely accurate and sensitive test. Cepheid co-founder Kurt Petersen, now an angel investor, explains how it works. "The test cartridge contains microfluidic channels; these are made out of plastic using high-precision injection molding," explains Petersen. "All the chemicals needed for the process are stored in chambers within the system. In the center of the cartridge, a rotary valve turns to open different pathways, while a tiny plunger -- like a syringe -- moves fluids in and out as needed. So, the plunger pulls the sample into the center, the valve rotates, and the plunger pushes it into another region of the cartridge to do an operation on it. The system can do that multiple times, moving the sample to different regions with different chemicals, extracting RNA, mixing it with the reverse transcriptase that synthesizes complementary DNA that matches the RNA, and eventually pushing it into PCR reaction tube, where rapid heating and cooling speeds up the process of copying the DNA. Each new copy of the DNA gets a fluorescent molecule attached, which allows an optical system to determine whether or not the targeted gene sequence is in the sample."

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