fields move microbeads
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
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
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
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
TRN Categories: MicroElectroMechanical Systems (MEMS); Applied
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.
28/April 4, 2001
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