New blood-separation technique

inspired by Einstein’s tea leaves. Many medical diagnostic tests, including those for cholesterol levels, blood chemistry, and liver and thyroid function, are performed on blood plasma—the liquid part of the blood that’s left after all cells and cellular components are removed. Obtaining purified blood plasma usually requires a lab with a large centrifuge, but scientists at Australia’s Monash University have developed a new process based on the same principle that causes stirred tea leaves to accumulate at the bottom center of a teacup, a phenomenon first explained by Albert Einstein in the 1920s. A tiny amount of blood enters a microfluidic chamber, and a needle tip is placed at an angle just above the surface of the blood. With a sufficient voltage applied to the needle, air near the tip is ionized and the resulting “ionic wind” sweeps across the surface of the blood, causing it to circulate. To satisfy the boundary conditions, a secondary bulk meridional flow arises that carries the microscopic particles—red blood cells in the Monash experiments—in a downward spiral along the chamber’s sides and radially inward at the bottom to a stagnation point at the center. The figure shows the separated cells collecting at the bottom after just a few minutes. The scientists say the technology could be incorporated into a low-cost, credit-card-sized device, but it may still be 5–10 years away from mass production. (D. R. Arifin, L. Y. Yeo, J. R. Friend, Biomicrofluidics 1 , 014103, 2007; http://bmf.aip.org .)