by Lina Zeldovich
In 2010, Ethel Cesarman, a pathologist at New York City’s Weill Cornell Medical Center, was working with scientists running clinical trials on Kaposi sarcoma (KS), a cancer of the connective tissue characterized by bluish-red or purple bumps on the skin.
In the Western world, KS affects mostly older men of Mediterranean heritage. In Africa, though, it’s common in young adults and children, and has a high mortality rate in people under 40. It also often occurs as a side effect of AIDS. “In Africa it’s a big problem,” says Cesarman, who had been a part of the team that in the mid-1990s discovered that KS, originally identified by dermatologist Moritz Kaposi over a century ago, is caused by a human herpesvirus.
“For some reason, KS is endemic in Africa.”
With early diagnosis and treatment, the cancer’s progress can be significantly slowed. The technique used to detect viruses responsible for the cancer in biopsy samples employs a thermal process called the polymerase chain reaction (PCR), which is expensive and requires complex equipment.
But in Africa, medical centers don’t have the necessary machinery to diagnose the disease. So Cesarman decided the test was due for a redesign, and sought help from cornelluniversity engineers to create something cheap and easy to use. “I realized it’s very hard to diagnose KS in Africa because they don’t have the right tools and resources,” Cesarman recalls. “So I contacted Dr. Erickson, who had all sorts of fascinating new technologies in his lab.”
Miniature solution for big problem
Four years later, the Cornell team took their diagnostic tool for a test run. The miniature device they built consists of a smartphone, an app, a lens and a tiny round chip. And it’s powered by the one nearly unlimited resource Africa has: the sun.
The standard PCR test uses a technique called DNA amplification. Double-helix viral DNA from a biopsy sample is combined with primers—lab-synthesized single DNA strands that mimic the sequence of the viral DNA. The mix is put through a three-step thermal process. First, it is heated to 95 degrees Celsius, at which point the double-stranded viral DNA breaks down. Then it’s cooled to 65 degrees C, which causes the single-stranded primers to link to the broken viral DNA. Finally, it’s brought up to 72 degrees C, when the DNA chain recombines, doubling its amount. If the amount of resulting DNA exceeds a certain threshold, the test is positive for KS.
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