ANN ARBOR, Mich.—At
the scale of the very small, physics can get peculiar. A University of
Michigan biomedical engineering professor has discovered a new instance
of such a nanoscale phenomenon—one that could lead to faster, less
expensive portable diagnostic devices and push back frontiers in
building micro-mechanical and "lab on a chip" devices.
In
our macroscale world, materials called conductors effectively transmit
electricity and materials called insulators or dielectrics don't, unless
they are jolted with an extremely high voltage. Under such "dielectric
breakdown" circumstances, as when a bolt of lightening hits a rooftop,
the dielectric (the rooftop in this example) suffers irreversible
damage.
This isn't the case at the nanoscale, according to a new discovery byAlan Hunt,
an associate professor in the Department of Biomedical Engineering.
Hunt and his research team were able to get an electric current to pass
nondestructively through a sliver of glass, which isn't usually a
conductor.
A paper on the research is newly published online in Nature Nanotechnology.
"This
is a new, truly nanoscale physical phenomenon," Hunt said. "At larger
scales, it doesn't work. You get extreme heating and damage.
"What
matters is how steep the voltage drop is across the distance of the
dielectric. When you get down to the nanoscale and you make your
dielectric exceedingly thin, you can achieve the breakdown with modest
voltages that batteries can provide. You don't get the damage because
you're at such a small scale that heat dissipates extraordinarily
quickly."
These
conducting nanoscale dielectric slivers are what Hunt calls liquid
glass electrodes, fabricated at the U-M Center for Ultrafast Optical
Science with a femtosecond laser, which emits light pulses that are only
quadrillionths of a second long.
The
glass electrodes are ideal for use in lab-on-a-chip devices that
integrate multiple laboratory functions onto one chip just millimeters
or centimeters in size. The devices could lead to instant home tests for
illnesses, food contaminants and toxic gases. But most of them need a
power source to operate, and right now they rely on wires to route this
power. It's often difficult for engineers to insert these wires into the
tiny machines, Hunt said.
"The
design of microfluidic devices is constrained because of the power
problem," Hunt said. "But we can machine electrodes right into the
device."
Instead
of using wires to route electricity, Hunt's team etches channels
through which ionic fluid can transmit electricity. These channels, 10
thousand times thinner than the dot of this "i," physically dead-end at
their intersections with the microfluidic or nanofluidic channels in
which analysis is being conducted on the lab-on a-chip (this is
important to avoid contamination). But the electricity in the ionic
channels can zip through the thin glass dead-end without harming the
device in the process.
This
discovery is the result of an accident. Two channels in an experimental
nanofluidic device didn't line up properly, Hunt said, but the
researchers found that electricity did pass through the device.
"We
were surprised by this, as it runs counter to accepted thinking about
the behavior of nonconductive materials," Hunt said. "Upon further study
we were able to understand why this could happen, but only at the
nanometer scale."
As for electronics applications, Hunt said that the wiring necessary in integrated circuits fundamentally limits their size.
"If
you could utilize reversible dielectric breakdown to work for you
instead of against you, that might significantly change things," Hunt
said.
The paper is called "Liquid glass electrodes for nanofluidics." This research is funded by the National Institutes of Health.
The
university is pursuing patent protection for the intellectual property,
and is seeking commercialization partners to help bring the technology
to market.
Related Link: Center for Ultrafast Optical Science Biomedical Lab
