MEDICAL DEVICE INNOVATION - Medical Device Daily

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Thinnest, strongest material
molded into sensors, batteries
By LYNN YOFFEE
Medical Device Daily Staff Writer
Thin is in when it comes to building new medical
devices. But biomaterials don’t have to struggle with counting
calories to reach the desirable size. Instead, researchers
at Kansas State University (Manhattan, Kansas) are fabricating
graphene – carbon material that is only a single
atom thick – to then build an ultra-sensitive, bio-driven
DNA sensor and a high-efficiency bacteria-operated battery.
“It’s the strongest material in the world at that scale,”
KSU’s Vikas Berry, assistant professor of chemical engineering,
told Medical Device Daily. “All the carbon atoms are
connected to one another via hybridized bonds.”
Graphene was discovered just five years ago and biological
interfacing is now taking the material to the next
level of development. Berry and his team have to use an
atomic force microscope to see and manipulate the carbon
sheets that are no bigger than 100 microns across, about
the same size as a strand of hair.
What does this material look like “Black,” Berry said.
“We have been able to suspend graphene in solution and it
looks totally black.” Which makes sense because it’s exfoliated
from graphite (the mineral from which pencil lead is
extracted; it’s also considered the highest grade of coal).
And because graphite is an electrical conductor, the resulting
graphene, which also looks a bit like honeycomb or
chicken wire, may one day replace silicon as the choice
material for semiconductors.
But Berry’s team is focused on med-tech applications of
the 2-D, chemically modified graphene nanostructures.
The graphene-based invention that’s nearest to reality
is a DNA sensor for cancer detection. Most current sensors
are optical, but a graphene-based sensor would be electrical.
When electrons flow on the graphene, they tend to
change speed if they encounter DNA. The researchers
noticed this change by measuring the electrical conductivity.
“It should not take very long to develop,” Berry said.
“The preliminary tests have been done. We’ve measured the
sensitivity. We are further developing this to have a sensor
that has absolutely no noise. We want to see how sensitive
the system is. Our first set of experiments was 20 base
pairs. Now we want to see different lengths of DNA and if
we can hybridize complementary DNA to different regions
of graphene. In one to two years from now, we should see a
very sensitive DNA sensor.
“It’s a fascinating material to work with,” Berry said of
his work, which was published in Nano Letters. “The most
significant feature of graphene is that the electrons can
travel without interruptions at speeds close to that of light
MEDICAL DEVICE INNOVATION 2010
at room temperature. Usually you have to go near zero
Kelvin – that’s about 450 degrees below zero Fahrenheit to
get electrons to move at ultra high speeds.”
He’s using the same graphene to develop a bacteriaoperated
battery by loading the thin sheets of biomaterial
with antibodies and flowing bacteria across the surface.
“We have wrapped bacteria cells with graphene sheets,”
he said. “The idea, and it’s too early for this, is to use this as
a interface between bacterial cells and external nanodevice.
We want to ultimately have a very strong interfacing
with bacterium by a material which is very high in conductivity,
which is graphene. By doing this interfacing, electrons
produced on the surface can be extracted.”
Berry’s team found that the graphene, with tethered
antibodies, wraps itself around an individual bacterium and
remains alive for 12 hours. How does this translate into a
battery By specifically using geobacter, a type of bacteria
known to produce electrons, it can be wrapped with
graphene to produce electricity.
A resulting battery, he said, is “futuristic work.” He said
fellow researchers currently working with geobacter to
develop batteries have had little success because efficiency
is very low.
“But with graphene, you can extract more electrons,” he
said. “Engineering that into a battery would be the next
step.
“Materials science is an incredible field with several
exploitable quantum effects occurring at molecular scale,
and biology is a remarkable field with a variety of specific
biochemical mechanisms,” Berry said. “But for the most part
the two fields are isolated. If you join these two fields, the
possibilities are going to be immense. For example, one can
think of a bacterium as a machine with molecular scale
components and one can exploit the functioning of those
components in a material device.”
(This story originally appeared in the April 24, 2009,
edition of Medical Device Daily).
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