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A scanning electron microscope image shows the stepped
microelectrodes in an experimental realization of Prof.
Martin Bazant's 3D ACEO array (by J.P. Urbanski from
the lab of Prof. Todd Thorsen). This new design greatly
increases the flow rate per voltage compared to traditional
planar ACEO arrays. |
Micropumps create a “fluid conveyor belt”
CAMBRIDGE, Mass., September 20, 2006 – Employing a
novel three-dimensional alternating-current electro-osmotic
(3D ACEO) pump, a group of MIT researchers led by Prof. Martin
Z. Bazant may have just taken a substantial leap forward
in the development of microfluidics, a leap that could enable
portable, or even implantable, biomedical lab-on-a-chip devices.
Existing ACEO pumps move fluids over a planar microelectrode
array applying an AC voltage. “However,” says
Prof. Bazant, “this design is inefficient, since it
involves opposing surface flows, where one direction slightly ‘wins’ over
the other due unequal electrode widths.” Prof.
Bazant theoretically predicted that dramatic increases in
flow rate could be achieved – by more than order of
magnitude – by using electrodes with raised steps.
His 3D design actually turns what was previously considered
a drawback of ACEO into a means of increasing flow speed. “The
basic idea,” says Bazant, “is to recess the reverse
flows to form ‘rollers’ for the raised pumping
flow, thus forming a ‘fluid conveyor belt.’”
Bazant’s collaborators in the lab of Prof. Todd Thorsen
have demonstrated that the concept really works. Using
the new 3D design, the team has fabricated, by far, the fastest
low voltage (<10 Volt) AC electrokinetic pumps. They expect
to achieve mm/second velocities after design optimization.
To reach similar flow speeds, standard DC electro-osmotic
pumps require a high voltage power supply (> 100
Volt) and produce undesirable electrochemical reactions.
By working at battery voltages with low power consumption
(< 10 milliWatt), the team foresees the possibility of
portable lab-on-a-chip devices, where fluids are pumped and
mixed at the micron scale by 3D ACEO and other phenomena
of induced-charge electro-osmosis (ICEO), also springing
from Bazant’s theoretical work.
Research in ICEO flows is ongoing, with the goal of being
able to manipulate common electrolytes, such as blood and
other biological fluids, through microchannels. Current pressure-driven
systems, many of which require substantial external plumbing,
are not very sensitive to the fluid, but they offer little
local flow control and require extraordinary – even
unfeasible – pressures when channel sizes approach
the micron scale. ICEO can generate fast, tunable flows
in microchannels, but seems limited to relatively dilute
electrolytes (< 10 mM), for reasons currently under investigation. Nevertheless,
Jeremy Levitan (Bazant's postdoc) has successfully demonstrated
rapid DNA hydridization microarrays and ELISA immunoassays
using ICEO flows in 10x diluted buffer solutions. These are
important milestones for Prof. Thorsen’s vision of
a portable ICEO-based microfluidic device for early detection
of exposure to toxic warfare agents. Similar devices
could also be used for point-of-care diagnostics in civilian
medical applications.
A paper on Bazant’s theoretical work (with former
postdoc, Yuxing Ben) is published online and in press at
the journal Lab on a Chip. A related paper on the team’s
experimental progress will appear in an upcoming edition
of Applied Physics Letters (coauthored by graduate student,
J. P. Urbanski, postdoc, Jeremy Levitan, and Profs. Thorsen
and Bazant). A company, ICEO, Inc., has been created to commercialize
the technology.
The new pumping devices are being developed as part of a
broader effort to increase the safety of Soldiers and first
responders at MIT's Institute for Soldier Nanotechnologies.
For more information on Prof. Martin Bazant and his research
click here.
Contact:
Franklin Hadley
617-324-6413
fhadley@mit.edu
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