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					                                                               NIRT: Hierarchical Bionanomanufacturing
               PI: Robert L.                                    Clark 1.                      Co-PIs: Ashutosh                                                            Chilkoti 2,                                 Eric                 Toone 3,        and Stefan                                Zauscher 1
                           Mechanical Engineering and Materials                                                                         Science1,                         Biomedical                            Engineering2,                       Chemistry 3,                   Duke University
                                         Abstract                                                                   II) Localized Actuation of Thermally Responsive                                                                                       III) Fabrication of Bioconjugated and Hybrid
Here we report on progress on our NIRT on hierarchical nanomanufacturing. I) First we                                          Polymers and Polypeptides                                                                                                  Polymeric Nanostructures by Field-Induced
report on a holographic technique we adopted that provides a noninvasive laser-based
approach for adaptable, real-time nanofabrication and nanomodification of (bio)-                                                                                                                                                                                   Scanning Probe Lithography
polymeric materials substrates. II) We then discuss a technique we are developing in                                                                              We are currently developing a novel and highly sensitive method of
which optically addressable metal nanoparticles display large spectral shifts as a function                                                                       sensing nanometer-scale distances between single nanoparticles (NPs)               Highly controlled patterning of polymeric and biomolecular nanostructures on surfaces is a
of subtle changes in distance from conductive films, and hence, represent a promising                                                                             and conductive surfaces. Once characterized, this method will be used              critical step in the fabrication of biomolecular devices and sensors. We use field-induced
way to measure angstrom-scale distances in potential biosensor applications. III) Finally                                                                         to indicate thermally responsive polymer actuation that is localized to            scanning probe lithography (FISPL) to chemically modify polymer brushes to allow conjugation of
we report on a process we developed for the chemical modification of protein resistant                                                          Au                specific regions in-between metal nanoparticles and a conductive                   biomolecules. Surface-confined, non-fouling (i.e., protein resistant) poly(oligo(ethylene glycol)
polymer brushes for the fabrication of protein arrays by field-induced scanning probe                                                                             film. Here, the high-energy focusing capabilities of nanoparticles in              methyl methacrylate) (p(OEGMA)) brushes were prepared on silicon substrates by surface-
lithography.                                                                                                                                                      proximity to metal films upon laser irradiation will cause a temperature           initiated atom transfer radical polymerization (SI-ATRP) in a “grafting-from” approach. These
                                                                                                                                       Au-coated glass            increase, and likely trigger polymer actuation, in a highly localized              p(OEGMA) brushes were then patterned directly on the nanoscale by FISPL, generating
                                                                                                                                                                  manner.                                                                            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
      I) Three-dimensional Dynamic Mask-Less                                                                                                                                                                                                         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
               Holographic Lithography                                                                                                                                                                                                               conjugation is achieved on the patterned areas via biotin-streptavidin coupling. With this
                                                                                                                       Spectroscopy of Nanoparticles near Gold Films                                                                                 approach we were able to create periodic BSA protein arrays with a feature width of ~130 nm.
A method is presented for dynamic, computer-controlled, maskless beam-steering, by spatial light                                                                                                                      Single NP, TIR Illumination    Non-specific adsorption of protein was dramatically reduced due to the non-fouling nature of the
                                                                                                                                                                     SPP and LSP Deconvolution                                                       polymer.
modulators (SLMs), to address specific locations on arrays with large spatial and temporal                                                                                                                                   (SPP + LSP)
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,                    DF Illumination
                                                                                                                             And
broad beam illumination sources. The beam from the laser is centered on the computer-controlled                        SPR Collection
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.                                       Au-coated glass slide




                                                                                                                               Right
                                                                                                                               prism

                                                                                                         SPR                                         TIR
                                                                                    Image/Specimen                                                                              26 nm   22 nm 18 nm   14 nm   10 nm   6 nm   2 nm   0 nm
                                                                                                         measurement                                 Illumination
                                                                                         Plane
                                                                                                                                                                                                                                           60-nm
                                                                                                                                                                                                                                           Au NP

                                                         SLM
                                                                                                                                                                               glass slide                              45-nm Au film
                                                                                                                                                                                                                                                    We also found that both (a) raised features and (b) trenches can be created on the p(OEGMA)
                                                                           Fourier Lens
                                                                                                                                                                                                polyelectrolyte layer                               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
                                                                                                          Layer-by-layer (LBL) assembly of oppositely charged polyelectrolytes (PELs) was used to control the distance
                                                                                                                                                                                                                                                    voltage, relative humidity and tip velocity. We note that if a negative tip bias or no bias is applied
                                                                                                          between NPs and gold films. The surface plasmon polariton (SPP) resonance propagating along the gold film red
                                                                                                                                                                                                                                                    with respect to the substrate, no appreciable changes are observed. This highlights the
                                                                                                          shifts as the number of PEL layers increases (left plot, green trend). Single NP spectra can be acquired using two
                                                                                                                                                                                                                                                    directionality of the electrochemical process and shows that physical interactions between the tip
                                                                                                          different methods of illumination: i) dark field (DF) or ii) total internal reflectance (TIR) illumination. Dark field
                                                                                                                                                                                                                                                    and the sample alone cannot be responsible for the formation of the patterns.
                                                                                                          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                                      a)                                                   b)
                                                                                                          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!

                Image                   Phase Hologram         Reconstructed Image
                                                                                                                                       Localized Optothermal ELP Actuation                                                                           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
                   Micro/Nano Patterning with                                                                                100x 1.25 NA
                                                                                                                                                                                                                                                     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
                         Photopolymer                                                                                        oil immersion
                                                                                                                                objective                                                                                                            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
                                                                                                                                                            cover glass
                                                      Initial system testing was performed using                                                                                                                                                     approach into a massively parallel, anodization stamping process.
                        a)                       b)   an optically responsive epoxy (Norland                           H2O

                                                      Photopolymer 63). (a)        CAD-generated                                                                 ELP
                                                      pattern (b) SEM image taken normal to the                                         Au-coated glass slide
                                                      substrate surface showing 880 nm to 2.5
                                                      m feature widths. Note the letter „L‟ has
                                                      fallen over due to post-processing after
                                                                                                                                                                                                                                                                                  Acknowledgments
                                                      patterning. (c) SEM images taken at a 40˚
                                                                                                                                          dove prism                                                                                                 We acknowledge support through NSF-NIRT 0609265. We also acknowledge the substantial
                                                      and (d) 60˚ from the surface show the
                                                      height of the features ranging between 3-5                                                                                                                                                     contributions to the optothermal NP interrogation by Prof. David Smith and Jack Mock at Duke
                      c)                         d)                                                                                                                                                                                                  University.
                                                      microns. With an optimized system and
                                                                                                          Preliminary experiments are aimed at localized actuation of elastin-like polypeptides (ELP, is a thermally responsive
                                                      improved feedback control, resolution could
                                                                                                          polypeptide) sandwiched between single NPs and a gold film, using laser heating. The schematic experimental setup
                                                      be improved to at least the diffraction limit of
                                                                                                          is shown above; the plot (above right) shows a shift of ~30 nm in the SPR response of a single nanoparticle after 1
                                                      ~ 250 nm.
                                                                                                          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.

				
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posted:11/19/2011
language:English
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