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Taking Blood Cells for a Spin

A principle elucidated by Albert Einstein in 1926 is the driving force behind a new technique for rapidly separating red blood cells from plasma. The concept, which explains why stirred tea leaves accumulate at a container's bottom rather than its sides, could allow quicker and cheaper tests for illnesses from anemia to kidney disease.

The goal is to purify plasma, the fluid that transports vital substances, such as blood cells, carbon dioxide, glucose, and vitamins. Many medical tests require samples of plasma without components like red and white blood cells, including those for cholesterol and glucose levels and immune deficiencies. Smaller and easier-to-use machines for blood separation have begun to replace older ones such as the spinning centrifuge. Because they require less blood, these tests are easier for patients. In addition, these so-called microfluidic devices differ from other separators because they contain no moving parts, which could increase reliability.

The new device was designed by mechanical engineer Leslie Yeo of Monash University in Clayton, Australia, and colleagues. They electrified a needle hovering over a sample of blood. The resulting electric field tugged at ions in the plasma, triggering enough collisions that the sample's surface layer began to circulate. As a miniature tornado ensued, the red blood cells swirled to the bottom and settled below the plasma. Adhering to Einstein's "tea leaf paradox," the red blood cells collected at the center of the container's bottom because of friction that minimized centrifugal force. The researchers describe their findings in the January to March quarterly issue of Biomicrofluidics.

Such a device could have wide-ranging applications, Yeo says, such as miniaturizing bioterror sensors that concentrate harmful bacteria or viruses. In a few years, he says, the technology could be placed on a credit-card-sized chip, which could be manufactured cheaply.

"The concept is pretty good," says Sung Yang, a biomedical engineer at Pennsylvania State University in State College. But he cautions that the concentration of red blood cells was much lower in the samples than in the body. "They need to test in real conditions," he says.

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