Nanotubes and Nanowires as Chemical and Biological Sensors

1
Nanotubes and Nanowires as Chemical and
Biological Sensors R. Hamers, L.M. Smith, and D
.van der Weide, Univ. of Wisconsin,
DMR-0210806 http//hamers.chem.wisc.edu/
Education, Outreach, and Broader Impact
Through the EAGLE school science mentor program,
8th grade student Adam Schneider worked with
students Sarah Baker and Lu Shang to synthesize
and manipulate nanowires. We have mentored an
8th-grade EAGLE student for each of the last 5
years. We have also mentored a high school
student as part of the Madison Metropolitan
School Districts Summer Science Intern Program
for each of the last 4 years
Our NSF-funded scanning electron microscope
system has been used for many hands-on
demonstrations targeting students from
underrepresented groups. Here a middle-school
girl prepares to to operate the SEM while other
girls watch on a second monitor.
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Nanotubes and Nanowires as Chemical and
Biological Sensors R. Hamers, L.M. Smith, and D
.van der Weide, Univ. of Wisconsin,
DMR-0210806 http//hamers.chem.wisc.edu/
The top images shows Adam Schneider an 8th-grade
at Eagle School, standing beside graduate student
Sarah Baker and our home-built plasma chemical
vapor-deposition system for growing carbon
nanofibers. Adam conducted an 8-week science
project growing nanofibers and nanowires and then
manipulating them with electric fields. This year
we participated in day-long workshops done as
part of a Women of Science initiative on
campus. This initiative was targeted principally
toward middle-school girls but was open to
anyone. It included a number of different
workshops we hosted two workshops on scanning
electron microscopy. The bottom image shows
middle-school students in our laboratory. Every
participant was given the opportunity to operate
the controls of the SEM. This is one of many
demonstrations presented through the year.
Other demonstrations and workshop have targeted a
number of different sectors, principally (but not
exclusively) targeted toward underrepresented
groups.
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Nanotubes and Nanowires as Chemical and
Biological Sensors R. Hamers, L.M. Smith, and D
.van der Weide, Univ. of Wisconsin,
DMR-0210806 http//hamers.chem.wisc.edu/
Education, Outreach, and Broader Impact
Prof. Clark Miller organized a Citizens
Consensus Conference on Nanotechnology. Robert
Hamers participated an open panel discussion with
local citizens about nanotechnology and it
societal implications. A diverse group of
citizens was selected to participate in the
writing of a report summarizing their views on
nanotechnology, based upon selected reading
materials and what they learned in the forum with
Prof. Hamers and other nanotechnology experts.
The report of the consensus conference was
presented to local and state legislators in a
press conference at the Wisconsin State Capitol
and is on the web at http//www.lafollette.wisc.ed
u/research/Nano/nanoreport42805.pdf.
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Nanotubes and Nanowires as Chemical and
Biological Sensors R. Hamers, L.M. Smith, and D
.van der Weide, Univ. of Wisconsin,
DMR-0210806 http//hamers.chem.wisc.edu/
This slide shows photographs from the Citizens
Consensus Conference. The citizens engaged in a
series of three meeting. In the first one they
identified appropriate reading materials about
the field of nanotechnology. In a second
meeting, the citizens met with R. Hamers and
other UW-Madison scientists working on different
aspects of nanotechnology (physical science,
societal implications, medicine, etc) this was
open to all interested citizens and was well
attended. The photo at lower left shows the
expert panel (far side of room) and interested
citizens. The right panel shows R. Hamers and two
other panelists who participated as experts. In
a third meeting, the citizens wrote a report on
nanotechnology that was presented to our state
legislators at a press conference at the State
Capitol. The conference was organized primarily
by Professor Clark Miller. R. Hamers
participated as an expert and participated in the
press conference at the Capitol. More
information is at http//www.lafollette.wisc.edu/
research/Nano/index.htm
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Nanotubes and Nanowires as Chemical and
Biological Sensors R. Hamers, L.M. Smith, and D
.van der Weide, Univ. of Wisconsin,
DMR-0210806 http//hamers.chem.wisc.edu/
Semiconducting nanowires have the potential to
act as highly sensitive detector elements. We are
characterizing the electrical response of
semiconducting nanowire bridges, such as the
45-nanometer-diameter Si nanowire shown here. By
using two electrodes of different materials, an
inherent asymmetry can be built into the
junction. This asymmetry is clearly reflecting
the current voltage characteristics of the
junction when a silicon nanowire bridges across
the gap between electrodes. The optical and
electrical response of nanowire junctions are
currently being measured. The electrical
properties are expected to change in response to
chemical and/or biological molecules, leading to
new types of nanoscale biosensors.
Gold
Silver
2 mm
150
100
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Current, pA
0
-50
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Voltage, V
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Nanotubes and Nanowires as Chemical and
Biological Sensors R. Hamers, L.M. Smith, and D
.van der Weide, Univ. of Wisconsin,
DMR-0210806 http//hamers.chem.wisc.edu/
This slide shows a scanning electron microscopy
image of a 45-nanometer-diameter silicon nanowire
bridging across a pair of electrodes. The left
electrode is made from gold, and the on one the
right is made from silver. The difference in
work function between gold and silver creates a
built-in potential across the nanowire that
makes its current-voltage response asymmetric, as
shown by the curve in red. This asymmetric
behavior assists in separating the response of
the nanowire from other possible sources of
conduction. We are investigating the electrical
properties of these nanowires and how they change
in response to a variety of stimuli including
optical excitation and exposure to chemical
and/or biological molecules. Functionalization
of the nanowires with specific biomolecules of
interest is expected to provide selectivity
toward specific chemical or biological molecules
of interest, while the electrical response
provides a way to detect the binding of molecules
to the surface of the functionalized nanowires.
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Nanotubes and Nanowires as Chemical and
Biological Sensors R. Hamers, L.M. Smith, and D
.van der Weide, Univ. of Wisconsin,
DMR-0210806 http//hamers.chem.wisc.edu/
Carbon nanofibers are being used as the basis of
nanoscale electrodes. Carbon nanofiber growth
followed by deposition of a thin SiO2 coating
leads to insulated nanofiber electrodes that are
completely insulated except at the very ends,
where the nanofiber ends are exposed. Nanofiber
electrodes are being functionalized with
biomolecules such as horesradish peroxidase To
create new types of nanoscale biosensor systems.
CV in Hexaammine ruthenium (II/III) chloride
1 mm
8
Nanotubes and Nanowires as Chemical and
Biological Sensors R. Hamers, L.M. Smith, and D
.van der Weide, Univ. of Wisconsin,
DMR-0210806 http//hamers.chem.wisc.edu/
These images are top-view images showing carbon
nanofibers grown at precise locations on
molybenum electrodes, on a SiO2/Si substrate.
The position of the nanofibers was controlled
using electron-beam lithography to control the
spatial location of a nickel catalyst. When
placed in a plasma-enhanced chemical vapor
deposition system leads to nanofibers at these
predefined locations. The fibers shown here were
then insulated with a thin coating of SiO2,
leaving only the ends of the nanofibers exposed.
The carbon shows up as the small, bright spots
at the center of each nanofiber. The underlying
electrodes are completely insulated as well, but
this coating is partially transparent to the
scanning electron microscope electron beam,
making it possible to view the underlying
electrodes even though they are completely
insulated. When the nanofibers are placed in
solution, one can measure the electrochemical
response of the exposed nanofiber ends. We have
functionalized nanofiber electrodes with
molecules such as horeradish peroxidase and are
currently exploring their electrochemical
response as way to achieve nanoscale biosensing.