Magnetic fields move microbeads

By Kimberly Patch, Technology Research News

Researchers from Harvard University have shown that it's possible to manipulate tiny magnetic beads using magnetic fields generated by microcircuits made of tiny gold wires.

The researchers closely controlled microbeads suspended in fluid-filled pathways etched into a polyurethane-coated silicon wafer, holding the beads stationary and moving them along s-shaped pathways.

The beads, at 4.5 microns, or a little smaller than a red blood cell in diameter, were dwarfed by the wires used to generate the current, which were 50 to 100 microns wide and stood 10 to 20 microns high. The paths were 10 to 50 microns thick.

Systems like these may eventually be used to transport small amounts of chemicals or cells for biotechnology, microanalysis and microsynthesis applications, according to Tao Deng, a graduate student at Harvard University. "They will be used for manipulating objects attached [to] magnetic particles, such as enzymes, cells, antibodies and even some chemical reagents," Deng said.

The researchers controlled the beads by varying the electrical current running along the wires, which in turn changed the electrical field around the wires generated by the current.

They did this by engineering the system of wires so that it generated local maxima, or concentrations of the magnetic field that attracted and trapped the microbeads. When the researchers changed the location of the maxima, the beads followed.

The researchers adapted a system for manipulating atoms to the magnetic microbeads, said Deng. "We [thought] magnetic microbeads should have similar behavior as atoms in a magnetic field so we tried it and it works," he said.

The researchers constructed the tiny systems using a microtransfer molding technique, curing micro patterns in a layer of polyurethane on a titanium-coated silicon wafer using ultraviolet light. They used electrodeposition and wet chemical etching to carve out the tiny gold wires that carried the current, according to Deng.

The fabrication process for making the pathways is compatible with microfluidic and microelectromechanical systems (MEMS), making integrating the manipulation process into existing microfluidic and MEMS devices easy, said Deng.

The group is currently trying to reduce the heat generated from the electrical current needed to manipulate the tiny beads. The researchers want to be able to keep the beads cool in order to eventually use them to manipulate living biological objects, Deng said.

Deng's research colleague was George M. Whitesides. They published the research in the March 19, 2001 issue of Applied Physics Letters. The research was funded by the National Science Foundation (NSF) and the Defense Advanced Research Projects Agency (DARPA).

Timeline:   5-10 years
Funding:   Government
TRN Categories:  MicroElectroMechanical Systems (MEMS); Applied Computing
Story Type:   News
Related Elements:  Technical paper, "Manipulation of Magnetic Microbeads in Suspension Using Micromagnetic Systems Fabricated with Soft Lithography," Applied Physics Letters March 19, 2001.


March 28/April 4, 2001

Page One

Programming goes quantum

Diversity trumps fitness

Nanotubes paint clear picture

Hitting the deck cools microdevices

Magnetic fields move microbeads


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