A standard bicycle pump is all that’s required to power a DNA purifying kit, designed by Catherine Klapperich and her students at Boston University. The thermos-size device, dubbed SNAP (System for Nucleic Acid Preparation), extracts genetic material from blood and other bodily fluids by pumping fluid through a polymer-lined straw designed to trap DNA. A user can then pop the straw out and mail it to the nearest lab, where the preserved DNA can be analyzed for suspicious bacteria, viruses, and genetic diseases.
A DNA extraction device that requires no power, such as the SNAP prototype, would have tremendous value in rural communities, says Paul Yager, a professor and acting chair of the University of Washington’s Department of Bioengineering, who was not involved in the research. “This would be the front end for a lot of potential instruments people could use,” he says.
To test for diseases like HIV, clinicians typically take blood samples from patients, which then must be refrigerated and transported to the nearest laboratory. Technicians then extract and analyze the DNA. In areas where electricity is scarce, blood may not be adequately refrigerated, potentially degrading a sample’s quality. Isolated DNA, on the other hand, remains relatively stable at room temperature, so extracting DNA from blood before shipping it to a laboratory may eliminate the need for expensive refrigeration.
“Instead of taking blood samples and keeping them cold, with our technology, they would be able to prepare all the samples at the point of care,” says Klapperich, an assistant professor of mechanical and biomedical engineering at Boston University. “They would also have a longer period of time to get a much more preserved sample to a central lab someplace else.”
The conventional method of extracting DNA from blood involves a number of instruments: researchers first break open blood cell walls, either with chemicals or by shaking the blood, in order to get at genetic material inside cells. They then add a detergent to wash away the fatty cell walls, and spin the DNA out of solution with a centrifuge. The SNAP prototype performs a similar series of events with a bicycle pump, some simple chemicals, and a specialized straw lined with a polymer designed to attract and bind DNA.
A clinician first takes a fluid sample, such as blood or saliva from a patient, and injects it into the disposable straw within the device. A large cap on the device contains two small packets: a lysis buffer and an ethanol wash. Pressure from the pump releases the lysis buffer, which breaks open cells in the fluid, releasing DNA. A second pump of air releases ethanol, which washes out everything but the DNA.
So far, Klapperich has used the prototype to isolate DNA from nasal wash samples infected with influenza A. Compared with traditional DNA extraction kits in the laboratory, Klapperich says, the SNAP prototype isolates less DNA. “But in general, our data show that the nucleic acid we get back is cleaner,” she says. The DNA can also be amplified using the polymerase chain reaction, or PCR, one of the most common methods of amplifying DNA in the lab. In the near future, the group plans to experiment with other human fluids that contain different viruses; DNA from various bacteria and viruses may behave differently at room temperature.
Jose Gomez-Marquez, program director for the Innovations in International Health Initiative at MIT, first learned of Klapperich’s invention at a recent meeting about medical technology for the developing world. Since then, he and Klapperich have worked together to refine the prototype. Gomez-Marquez will soon be bringing a model to Nicaragua, where he hopes to get feedback on its effectiveness and user friendliness from local clinicians and patients. “This device doesn’t wait for a cold system to be in place for diagnostic samples to be transferred from one place to another,” says Gomez-Marquez. “You can take five days or two weeks to get a sample out there–you don’t have to worry about refrigerating it.”
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