NEWS OF THE WEEK MICROFLUIDICS
FLOATING DROPLETS Magnetic lévitation technique could have uses in crystallization, synthesis
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crofluidics, tiny droplets and particles are levitated magnetically and then moved, merged, and rotated in open channels on chip surfaces in a highly controllable manner. The technique could make it possible to take precise physical measurements, perform chemical syntheses, and crystallize substances in droplets and particles of pico- to femMOVING EXPERIENCE toliter size. Droplet (circle) is levitated magnetically between two fixed Developed by physicists Igor magnets and moved by current F. Lyuksyutov, pulses through electrodes Donald G. Nauembedded in substrate. gle,andK.D.D. Rathnayaka of Texas A&M University {Appl. Phys. Lett., 85,1817 (2004)}, the method is the latest step in efforts to develop microfluidic devices in which discrete droplets or particles can
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be manipulated on planar surfaces or in open channels. Such techniques can enable better control of reagents and operations than can be achieved with conventional microfluidic devices that use solutions flowing in closed channels. The new technique uses magnetism to levitate droplets in shallow channels between tiny, permanent magnets. The droplets are also moved magnetically using induced forces from current pulses in electrodes beneath the channels. The Texas A&M team has used the devices to levitate and manipulate a range of items, including aqueous and alcohol solutions, oils, polystyrene microspheres, inorganic microparticles, nanotube powders, and red blood cells. T h e devices, which the researchers call magnetic micromanipulation chips, "open the way to perform chemical and biochemical reactions with only one pair of molecules confined in
LIABILITY
Pfizer To Pay $835 Million In Asbestos Claims
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rugmaker Pfizer says it will pay $430 million to settle asbestos personal injury claims against a subsidiary, Quigley Co. In addition, Pfizer will contribute $405 million to a trust intended to compensate future claimants. To account for the cost, Pfizer plans to take a $229 million after-tax charge against earnings in the third quarter—the first of several charges to come. Acquired in 1968 when Pfizer was a more diversified company, Quigley made powdered insulation containing what Pfizer says were small amounts of chrysotile asbestos. The insulation, which the company stopped selling in the early 1970s, was used on pipes, boilers, and furnaces. As of the end of July, Pfizer and Quigley were 8
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named as defendants in 171,611 lawsuits, Pfizer says. Quigley's business since 1982 has been to manage its asbestos litigation. Quigley will file a reorganization plan in U.S. Bankruptcy Court for the Southern District of New York. That plan contains an agreement, between Pfizer and attorneys representing more than 80% of individuals with claims, that provides the $430 million settlement. The plan will also establish a trust for future claims. If the court and 75% of claimants approve, the reorganization plan calls fora permanent injunction that will channel all future asbestos claims to the trust. Pfizer will fund the trust over a 40-year period through a note and $100 million in insurance.-MARC REISCH
femtoliter droplets," Lyuksyutov says. Other possible applications include Crystallizations, measurements of tiny forces (in the femtonewton range), and incorporation of specific compounds into cells, he notes. In previous studies of droplet microfluidics, groups such as those of Richard B. Fair at Duke University and David Quéré at the College of France, Paris, have used electrical manipulation or particle coatings to ease the handling of droplets on solid surfaces. Other groups —such as those of Peter R. C. Gascoyne at the University of Texas M. D. Anderson Cancer Center, Houston, and Orlin D. Velev at North Carolina State University—have controlled tiny droplets suspended in immiscible liquids by polarizing them electrically The new technique eliminates contact with both solid and liquid media. Magnetic lévitation of droplets "is an interesting phenomenon," Fair comments. But he believes that some of the claimed applications maybe impractical, that tiny levitated droplets might evaporate too rapidly to be useful, and that it's better in any case for droplets to be moved around freely on surfaces instead of being confined to channels. Quéré and Gascoyne, on the other hand, believe the lack of droplet-surface contact is a key advantage. Contacts can have unwanted effects on small droplets, and lévitation avoids such problems, Quéré says. "Velev notes that "droplets have to be maintained in saturated vapor" to prevent rapid evaporation, and that could interfere with biological applications. Nevertheless, he believes the technique "is going to make a difference in microfluidics and could be specifically important for biomolecular crystallization." Photos, videos, and descriptions of the Texas A&M work are at http://levitation.physics.tamu. edu.—STU B0RMAN HTTP://WWW.CEN-ONLINE.ORG
