Tiny pumps drive liquid circuits
Technology Research News
Many research teams are working to make
labs-on-a-chip that manipulate tiny amounts of fluids. A second major
research effort is geared toward making cheap and flexible organic, or
plastic, electric components. And other researchers are looking for better
ways to control, or tune, compact optical devices like fibers, waveguides
and photonic crystals.
Researchers from the University of Illinois at Urbana-Champaign
and Lucent Technologies' Bell Laboratories have combined microfluidics
and organic electronics to make a tunable plastic transistor that could
enable low-cost methods to drive, control and monitor labs-on-a-chip.
The device can also use tiny amounts of fluid to adjust optical devices.
The idea is to use the microfluidic organic transistors to drive
fluid motion, said John Rogers, a professor of materials science and engineering
at the University of Illinois at Urbana-Champaign. Such motion can be
harnessed to change circuit properties in order to drive pumps, detect
fluid motion, and control microvalves, he said. "It is the marriage and
direct integration of electronics with microfluidics," he said.
Electric transistors turn on when electricity flows from a source
electrode through a central channel to a drain electrode, and off when
the flow of electricity is blocked. Transistors usually use a gate electrode
to generate an electric field that controls the flow of electricity through
the central channel.
The researchers' microfluidic transistor contains channels filled
with short plugs of a conducting liquid like mercury that act as source
and drain electrodes. The transistor's electrical properties depend on
geometries like the amount the electrodes overlap with one another and
with the semiconductor.
And the position of the mercury in the channels adjusts the electrical
response of the transistor, said Rogers. "As the plugs move through these
channels, the geometries of these electrodes change, thereby altering
the electrical properties of the transistor," he said.
This type of transistor provides a flexible way to drive a device
and to sense its operation and amplify the output, said Rogers. This opens
the way to building active power supplies and control circuitry for microfluidic
pumps directly into the chip structure of a device in a low-cost and convenient
way, he said.
Key to the concept is the use of an elastomeric, or rubbery, material
to form the channels, and surface chemistries that allow the material
to instantly bond to an organic semiconductor once they come in contact,
said Rogers. "Because they're soft and rubbery it is possible to achieve
leakage-free seals... against a range of organic semiconductors without
application of external pressure... heating [or] adhesives," he said.
The process doesn't affect the organic semiconductor, said Rogers.
This is important because "nearly all organic semiconductors are very
fragile from a chemical and mechanical standpoint -- it's easy to degrade
them by doing any kind of processing on top of them," he said.
The elastomeric material is inexpensive, cheap and quick to process,
and structures can be built over large areas, said Rogers. These characteristics
make the material practical for new types of active, low-cost plastic
microfluidic devices in addition to the tunable transistors, he said.
The next step is demonstrating microfluidic pumps that are capable
of reconfiguring tunable microfluidic photonic systems, said Rogers.
The researchers are working on ways to use tunable microfluidic
transistors or transistor arrays to build self-starting microfluidic pumps
that can move liquids around in microfluidic systems, said Rogers. They
are also looking to use the method to make active components like valves
and fluid motion sensors, he said.
The researchers' test device shows that it may be possible to
make tunable organic transistors, said Chang-Jin Kim, a professor of mechanical
aerospace engineering at the University of California at Los Angeles.
The device is "an important step" toward the goal of demonstrating such
transistors. The approach is novel because it uses mercury as a part of
a transistor, said Kim.
Tunable microfluidic transistors could be used practically in
three to six years, according to Rogers.
Rogers's research colleagues were George Maltezos, Robert Nortrup
and Jana Zaumseil of Lucent Technologies' Bell Laboratories, and Seokwoo
Jeon of the University of Illinois at Urbana-Champaign. The work appeared
in the September 8, 2003 issue of Applied Physics Letters. The
research was funded by Lucent Technologies and the University of Illinois.
Timeline: 3-6 years
Funding: Corporate, University
TRN Categories: Microfluidics and BioMEMS; Integrated Circuits
Story Type: News
Related Elements: Technical paper, "Tunable Organic Transistors
that use Microfluidic Source and Drain Electrodes," Applied Physics Letters,
September 8, 2003
March 10/17, 2004
Red wine mends solar cells
Search tool aids browsing
Tiny pumps drive
X-shape pulses hold together
makes tiny scope
Atom spouts photons
Charges make micro
Research News Roundup
Research Watch blog
View from the High Ground Q&A
How It Works
News | Blog
Buy an ad link