1. The Push Pin Probe
The Au-NP acts as a local surface-plasmon
scatterer. Inducing a plasmonic shift in the
frequency of scattered light via dielectric
interactions at the surface.
The CNT serves two roles:
1) Scattering resonance will shift
due to the potential between the CNT and
Au-NP.
2) Strong tip enhancement for Raman
Spectroscopy or Plasmonic
Resonance Energy Transfer
(PRET).[2]
Intensity
Frequency (Hz)
Electrons removed from
free electron gas
+
-
++
+ +
V
Frequency (Hz)
ScatteringIntensityScatteringIntensity
Raman Shift (cm-1)
Raman
PRET
Figure 4: The expected frequency shift in the absorption intensity of the Au-NPs with a gate voltage.
Figure 5: An emphasis of the enhanced
electric field at the tip of the CNT.
Figure 6: The expected Raman scattering of the
probe and the PRET shifts as the CNT interacts with
a molecule.
Figure 3: The absorption coefficient, dielectric
function, and plasma frequency equations.
-
Electrons added to free
electron gas
V
+
No Applied Voltage
A Microfluidic Array of Plasmonic Push-Pin Carbon Nanotubes.
Nikhil Sthalekar, Gabriel Dunn B.A., and Alex Zettl Ph.D.
Department of Physics
UC Berkeley, 94720
Preliminary Results
Next Steps
Acknowledgments
Fabrication Method
1) Obtain a single crystalline quartz
substrate and make a horizontal
photoresist pattern with E-beam
lithography. Deposit 0.1nm-0.2nm of Fe
catalyst then lift off the photoresist and
oxidize the catalyst.
2) Using Chemical Vapor Deposition
(CVD), grow horizontally aligned Single-
Walled Carbon Nanotubes (SWCNT).[3]
3) Transfer the SWCNTs using a PDMS-
polymer stamp to a pre-patterned gold
substrate.
4) Utilize E-beam lithography,
electrochemical deposition and etchant
techniques to pattern Au-NPs and create
the array.
A
C
E F
D
Figure 7(A-F): A Schematic of the
Fabrication method. B and D show the
SEM images of steps 1 and 2 in the
fabrication method.
Difficulties:
• Non-uniform CNT
growth during CVD.
• Choosing the right
polymer for the transfer
between substrates.
• Gabriel Dunn
• Alex Zettl
• Jason Belling
• The Zettl Group
• Test the CNT push pins with cyclic voltammetry by
replicating the neural cell environment.
• Diffuse the probes into a sample of neurons to
measure the transmembrane voltage.
• test the array as a molecular assay (DNA
sequencing).
Au-NP
CNT
Introduction
Throughout the past decade, biosensing applications
using the plasmonic properties of metal nanoparticles
have become a prevalent technique in molecular
assays and observing the physical properties of
biological organisms.
Utilizing the sensitivity of the localized surface plasmon
resonance of gold nanoparticles (Au-NPs) along with
the biocompatibility and electrochemical properties of
carbon nanotubes (CNTs), this projects propose a AuNP
terminated CNT probe, henceforth known as CNT push
pins, as a transmembrane voltage indicator and
microfluidic molecular assay.
Figure 2: An ideal image of the CNT push
pin probe.
References:
1. Weissman et al. 2011
2. Lu et al. 2005
3. Rogers et al. 2007
Motivation
There are approximately 100
billion neurons in the average
human brain that vary in length
from four to 100 microns. These
neurons make thousands of
connections with each other,
forming a neural network. The
typical neural probe used in
measuring a membrane voltage
is on the order of microns in
length and diameter, making
them too large to resolve signals
on the level of individual
neurons, as well as restricting
them to measuring things locally
across the neural network.
Because of this, finding out the
macroscopic properties of the
brain is impossible.
Imagine taking a digital multimeter to measure each transistor
in a modern CPU. How long do you think it will take?
Figure 1: Fluorescently tagged nerve cells in a mouse
hippocampus.[1]
B
Figure 7: The fully fabricated plasmonic microfluidic array.
Intensity
Intensity
Frequency (Hz) Frequency (Hz)
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