Nanoscale glass conductors for new class of lab-on-chip devices
24 May 2010
Dr Alan Hunt of the University of Michigan has discovered a
new electrical phenomenon that only acts at the nanoscale and could lead
to faster, less expensive lab-on-a-chip diagnostic devices.
Dr Hunt, an associate professor in the Department of Biomedical
Engineering, 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. The finding has been published in the
journal Nature Nanotechnology.
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 the new
discovery "This is a new, truly nanoscale physical phenomenon," Hunt
said. "At larger scales, it doesn't work. You get extreme heating
"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
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
"We were surprised by this, as it runs counter to accepted
thinking about the behaviour 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,"
The university is pursuing patent protection for the intellectual
property, and is seeking commercialization partners to help bring
the technology to market.