Transcript Slide 1

NIRT: Hierarchical Bionanomanufacturing
Co-PIs: Ashutosh
Mechanical Engineering and Materials
Abstract
Here we report on progress on our NIRT on hierarchical nanomanufacturing. I) First we
report on a holographic technique we adopted that provides a noninvasive laser-based
approach for adaptable, real-time nanofabrication and nanomodification of (bio)polymeric materials substrates. II) We then discuss a technique we are developing in
which optically addressable metal nanoparticles display large spectral shifts as a function
of subtle changes in distance from conductive films, and hence, represent a promising
way to measure angstrom-scale distances in potential biosensor applications. III) Finally
we report on a process we developed for the chemical modification of protein resistant
polymer brushes for the fabrication of protein arrays by field-induced scanning probe
lithography.
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Science ,
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Chilkoti ,
Biomedical
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Engineering ,
Au
I) Three-dimensional Dynamic Mask-Less
Holographic Lithography
Single NP, TIR Illumination
(SPP + LSP)
SPP and LSP Deconvolution
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SPP (from TIR)
LSP (from DF)
Wavelength (nm)
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Au-coated glass slide
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Right
prism
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Dielectric Layer Height (nm)
SPR
measurement
Duke University
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DF Illumination
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SPR Collection
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Chemistry ,
Highly controlled patterning of polymeric and biomolecular nanostructures on surfaces is a
critical step in the fabrication of biomolecular devices and sensors. We use field-induced
scanning probe lithography (FISPL) to chemically modify polymer brushes to allow conjugation of
biomolecules. Surface-confined, non-fouling (i.e., protein resistant) poly(oligo(ethylene glycol)
methyl methacrylate) (p(OEGMA)) brushes were prepared on silicon substrates by surfaceinitiated atom transfer radical polymerization (SI-ATRP) in a “grafting-from” approach. These
p(OEGMA) brushes were then patterned directly on the nanoscale by FISPL, generating
chemical functionalities that allowed for subsequent protein conjugation (Schematic and AFM
images below). Although our approach works, we do not yet have a complete physical-chemical
understanding of the process. We hypothesize that -CH3 groups are oxidized in the presence of
high electric fields and converted to -COOH groups. After chemical modification, protein
conjugation is achieved on the patterned areas via biotin-streptavidin coupling. With this
approach we were able to create periodic BSA protein arrays with a feature width of ~130 nm.
Non-specific adsorption of protein was dramatically reduced due to the non-fouling nature of the
polymer.
Spectroscopy of Nanoparticles near Gold Films
A method is presented for dynamic, computer-controlled, maskless beam-steering, by spatial light
modulators (SLMs), to address specific locations on arrays with large spatial and temporal
selectivity. The dynamic maskless holographic lithography (DMHL) approach is ideally suited to
trigger and direct nanofabrication in the optical near-field through easily controllable far-field,
broad beam illumination sources. The beam from the laser is centered on the computer-controlled
SLM, reflected into the microscope and directed upwards through the objective to illuminate the
specimen plane. The optical system ensures the plane of the SLM is imaged to and completely
fills the rear aperture of the microscope objective. Beam propagation from the rear aperture
through the objective results in reconstruction of the original image on the micro/nanoscale.
and Stefan
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Zauscher
III) Fabrication of Bioconjugated and Hybrid
Polymeric Nanostructures by Field-Induced
Scanning Probe Lithography
We are currently developing a novel and highly sensitive method of
sensing nanometer-scale distances between single nanoparticles (NPs)
and conductive surfaces. Once characterized, this method will be used
to indicate thermally responsive polymer actuation that is localized to
specific regions in-between metal nanoparticles and a conductive
film. Here, the high-energy focusing capabilities of nanoparticles in
proximity to metal films upon laser irradiation will cause a temperature
increase, and likely trigger polymer actuation, in a highly localized
manner.
Au-coated glass
Image/Specimen
Plane
Eric
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Toone ,
II) Localized Actuation of Thermally Responsive
Polymers and Polypeptides
Wavelength (nm)
PI: Robert L.
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Clark .
TIR
Illumination
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glass slide
polyelectrolyte layer
Fourier Lens
Layer-by-layer (LBL) assembly of oppositely charged polyelectrolytes (PELs) was used to control the distance
between NPs and gold films. The surface plasmon polariton (SPP) resonance propagating along the gold film red
shifts as the number of PEL layers increases (left plot, green trend). Single NP spectra can be acquired using two
different methods of illumination: i) dark field (DF) or ii) total internal reflectance (TIR) illumination. Dark field
illumination primarily excites the localized surface plasmon (LSP) resonance of the NP. Single NP spectra, obtained
using DF illumination, are increasingly blue-shifted as the NPs are spaced further away from the high-dielectric gold
film (left plot, blue trend). While TIR illumination primarily excites the SPP resonance of the gold film, LSP
resonances of NPs in close proximity to the film are also excited via an evanescent field. For this reason, single NP
spectra, obtained using TIR illumination, show a convoluted dependence on layer height that is dominated by the
blue-shifting LSP when NPs are less than 14 nm away from the gold film, and by red-shifting (SPP-dominated) when
NPs are further than 14 nm from the gold film (right plot). These data suggest that the SPR of NPs is shifted by ~12
nm for every 1-nm change in distance from 0 – 6 nm and ~7 nm for every 1-nm change in distance from 6 – 14 nm.
With a high resolution grating this experimental design is potentially capable of sensing distance changes on the
order of Ångstroms!
Phase Hologram
Reconstructed Image
Localized Optothermal ELP Actuation
Micro/Nano Patterning with
Photopolymer
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Initial system testing was performed using
an optically responsive epoxy (Norland
Photopolymer 63). (a)
CAD-generated
pattern (b) SEM image taken normal to the
substrate surface showing 880 nm to 2.5
m feature widths. Note the letter ‘L’ has
fallen over due to post-processing after
patterning. (c) SEM images taken at a 40˚
and (d) 60˚ from the surface show the
height of the features ranging between 3-5
microns. With an optimized system and
improved feedback control, resolution could
be improved to at least the diffraction limit of
~ 250 nm.
100x 1.25 NA
oil immersion
objective
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H2O
ELP
Au-coated glass slide
Intensity
Image
pre-laser
post-laser
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b)
We have made use of the chemical changes on the brush surface that occur due to the oxidative
nature of the electrochemical patterning process and demonstrate that they can be used to
create bioconjugated nanostructures. Our unique patterning approach can potentially form the
basis for the fabrication of a large range of novel polymeric and biomolecular nanostructures that
may find application as biosensors or substrates for the precise presentation of biomolecular
queues to cells. We are currently developing the tools and procedures to expand the lithographic
approach into a massively parallel, anodization stamping process.
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Acknowledgments
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dove prism
We also found that both (a) raised features and (b) trenches can be created on the p(OEGMA)
brushes by controlling the contact force between the tip and the substrate. While the feature size
of the patterns could be controlled by adjusting the patterning parameters such as applied
voltage, relative humidity and tip velocity. We note that if a negative tip bias or no bias is applied
with respect to the substrate, no appreciable changes are observed. This highlights the
directionality of the electrochemical process and shows that physical interactions between the tip
and the sample alone cannot be responsible for the formation of the patterns.
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Wavelength (nm)
Preliminary experiments are aimed at localized actuation of elastin-like polypeptides (ELP, is a thermally responsive
polypeptide) sandwiched between single NPs and a gold film, using laser heating. The schematic experimental setup
is shown above; the plot (above right) shows a shift of ~30 nm in the SPR response of a single nanoparticle after 1
min of laser exposure. Although a spectral shift of this magnitude would indicate a change in distance between the
NP and the gold film, it cannot yet be concluded that this shift is due to thermally induced changes in ELP
conformation. Current studies are focused on characterizing spectral properties of NPs in close proximity to gold films
with water as the surrounding medium to provide a distance calibration for localized ELP actuation experiments.
We acknowledge support through NSF-NIRT 0609265. We also acknowledge the substantial
contributions to the optothermal NP interrogation by Prof. David Smith and Jack Mock at Duke
University.