AVS2004 Session NS-TuA: Nanostructures and Biology

Tuesday, November 16, 2004 1:20 PM in Room 213D

Tuesday Afternoon

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1:20 PM		NS-TuA-1 Virus & Biomolecule Detection Using Nanoelectromechanical Devices B. Ilic, Y. Yang, H.G. Craighead (Cornell University) We have used resonating mechanical cantilevers to detect binding of viruses and biomolecules captured from liquid. As a model virus, we used a nonpathogenic insect baculovirus to test the ability to immunospecifically bind and detect small numbers of virus particles. Arrays of surface micromachined antibody-coated polycrystalline silicon nanomechanical cantilever beams were used to detect binding from various concentrations of baculoviruses in a buffer solution, by observing the resonant frequency shift of the oscillators. Because of their small mass, the 0.5µm x 6µm cantilevers have mass sensitivities on the order of 10^-19 g/Hz, enabling the detection of an immobilized AcV1 antibody monolayer corresponding to a mass of about 3 x 10^-15g. With these devices we can detect the mass of a single virus to the cantilever. Resonant frequency shift, resulting from the adsorbed mass of the virus particles, distinguished solutions of virus concentrations varying between 10⁵ and 10⁷ pfu/ml. Single crystal silicon nanomechanical oscillators with spatially-defined chemical binding sites, with greater mass sensitivity, have similarly been used to detect the binding of specifically bound biomolecules at the attogram level. In both experiments careful controls were done to assure the detected mass resulted from the intended specifically bound biomaterial.
1:40 PM		NS-TuA-2 Electrokinetic Molecular Separation in Nanoscale Fluidic Channels A.L. Garcia (The University of New Mexico) We have developed an interferometric lithography technique to manufacture an integrated micro-nano-fluidic chip for use in bioseparations and sensing. Transport behavior of two dyes, one charged and one neutral, in these silica/silica oxide/Pyrex chips has been quantified. A mixture of the dyes was introduced into an array of nanoscale channels using electroosmosis through the microfluidic channels. Electrokinetic separations of the dyes in these nanochannels at various applied biases were examined in different chips with nanochannel widths ranging from 50-200 nm. Confocal laser scanning microscopy was used to observe the average velocities of the dyes in the array of nanochannels. The resulting velocities were in good agreement with theoretical predictions that take into account the wall surface potential overlap and electrolyte concentrations across the individual nanofluidic channels. Separations were also achieved in these channels by the application of pressure, utilizing the Poiseuille velocity distribution of fluid within the channels.
2:00 PM		NS-TuA-3 Fabrication of Nano-Structured Polymeric Surfaces for Bio-Sensing Devices A. Valsesia, P. Colpo, T. Meziani, M. Manso, D. Gilliland, G. Ceccone, F. Rossi (EU-JRC-IHCP, Italy) The interaction between material surfaces with specific chemical functionalities and bio-molecules has been widely investigated in order to modulate the performances of bio-sensors and medical devices. When the dimensions of the interacting surface structures are comparable with those of the single protein molecules or small clusters of proteins, the bio-molecules absorption is considerably influenced both from the morphological and chemical point of view. This can be exploited for the orientation of specific binding sites between antigens and antibodies. In this work we develop a reliable technique to produce chemical contrast at sub-micrometric level through the fabrication of nano-island from Poly Acrylic Acid (PAA) film deposited onto anti-fouling substrates. First, a thin layer of PAA is deposited on the substrate by PE-CVD. Then, a layer of polystyrene colloidal nano-particles (200-500 nm) is deposited by spin coating. The nano-particles are then partially removed by oxygen plasma etching of the surface. The etching process is stopped before the complete etching of the nano-particles and the residual ones are removed by ultrasonic bath. Whereas unmasked PAA film is completely etched, nano-domes of as deposited-PAA (located under the nano-mask) are created evenly on the surface. The shape and the 2-D geometry of the resulting PAA nano-domes (lateral distribution, surface density) is controlled by the parameters of the spin casting process and by the wetting characteristic of deposited PAA. The chemistry of the PAA films was characterized by XPS, whilst the resulting nano-structured surfaces have been studied using AFM, SEM, SPM and SIMS in imaging mode. Then protein absorption test have been performed on the nanostrucured surfaces: the SEM and AFM characterization revealed that nanometric proteins clusters are selectively bond on the top of the domes, and not between them where the anti-fouling matrix repels the biomolecules.
2:20 PM		NS-TuA-4 Hairy Peptide Nanotubes M. Biesalski, J. Couet, J.D. Jeyaprakash S. Samuel, S. Santer (Institute for Microsystem Technology (IMTEK), Germany) A general theme in Nanotechnology is the development of novel materials with well-defined composition and nanometer scale structures. To this, materials scientists are increasingly deriving new lessons from naturally occurring "nanomaterials" about useful composition-structure property relationships that might be mimicked with synthetic materials.¹ An interesting example constitutes the bottom-up formation of hollow tubular structures by a spontaneous self-assembly of cyclic peptides. Cyclic peptides consisting of alternating D- and L-amino acids posses a flat conformation that allows the build-up of beta-sheet type assemblies, where the cyclic peptides are stacked onto each other forming a hollow tubular structure with a precisely defined inner diameter and all amino acid residues pointing outwards.² In order to construct functional polymeric nanotubes we have synthesized cyclic peptides that are modified with an ATRP initiator at distinct side groups ("CP-ini"). The CP-ini self-assembles into nanotubes that present these initiator moieties on the surface. The peptide nanotubes are subsequently coated with different functional polymers by using (living) radical polymerization initiated from the surface of the tubes. The so prepared functional nanotubes are characterized with respect to the dimensions, morphology and higher order assemblies using AFM, TEM and X-ray diffraction. The size of the polymeric shell of the nanotubes can be controlled by adjusting the graft density and the molecular mass of the surface-attached polymer chains. The concept of grafting polymer chains from cyclic peptide assemblies is highly modular with respect to the incorporation of a wide range of different functions. ¹ M. Tirrell, E. Kokkoli, M. Biesalski, Surface Science 500, 2002, p61-83. ² M.R. Ghadiri, J.R. Granja, R.A. Milligan, D.E. McRee, N. Khazanovich, Nature 366, 1993, p324-327.
2:40 PM		NS-TuA-5 Atomic Force Microscope Conductivity Measurements of Single Ferritin Molecules D. Xu, G.D. Watt, J.N. Harb, R.C. Davis (Brigham Young University) We will present electrical measurements on the conductivity of ferritin molecules by conductive atomic force microscope (c-AFM). The high structural stability of ferritin molecules, relative to other proteins, makes them attractive for nanotechnology applications such as nanoscale batteries. Ferritin is an iron-storage protein that functions as an iron reservoir in animals, plants, fungi and bacteria. Ferritin consists of 24 protein subunits that are arranged to form a spherical molecule with an external diameter of 12nm. The hollow ferritin interior with a diameter of ~8nm can hold up to 4500 iron atoms as Fe(OH)₃. For battery applications the electron transfer rate through the ferritins is a critically important parameter; it will affect the internal resistance and limit the maximum current. Ferritin molecules were self-assembled on gold surfaces to form sub-monolayer films and characterized by AFM prior to electrical measurements. Electrical conductivity measurements were performed on both single apoferritin and holoferritin molecules by c-AFM. The conductivity of monolayer films (~ 1 µm²) of ferritin molecules on atomically flat gold surfaces was measured for comparison. Holoferritin was 5-15 times more conductive than apoferritin, indicating that for holoferritin most electron transfer occurs through the ferrihydrite core. With 1 volt applied, the average electrical current through single holoferritins and single apoferritins was 2.58 pA and 0.188 pA respectively.
3:00 PM		NS-TuA-6 Friction Measurements of DMPC Phospholipidic Bilayers G. Oncins, S. Garcia-Manyes, F. Sanz (Universitat de Barcelona, Spain) Self-assembled phospholipid layers have been a matter of extensive research during last decades. The high content of these structures in cellular membranes has led to their use as models for the study of a wide bunch of biological, biochemical, biophysical and medical issues. Besides, the Supported Planar Bilayers (SPBs) have been very useful in the study of interaction and adhesion forces between cells, in the modelling of the diffusion kinetics of phospholipids and in the insertion of proteins in membranes. AFM has proved to be the most suitable technique to obtain molecular topographic resolution of these systems and to study the morphology of SPBs under various conditions. We have recently worked with such structures at a nanometric level, mostly performing studies based on AFM force spectroscopy measurements of 1,2-Dimyristoyl-sn-glycero-3-phosphocholine (DMPC) bilayers¹. The present work has used Lateral Force Microscopy (LFM) to mechanically test DMPC bilayers supported on mica, performing a series of experiments with laterally and vertically calibrated tips in aqueous environment and in which NaCl concentration has been ramped from 0M to 0.1M. Obtained friction results have been complemented with AFM height images of the same tested bilayer area, being able to relate each friction signal with its corresponding topography. Results have shown that the presence of NaCl modifies drastically the mechanical response of the DMPC bilayer, and, consequently, of the cellular phospholipidic membrane. ¹Garcia-Manyes, S. ;Oncins, G.; Sanz, F.; Effect of ionic solutions on the nanomechanics of a model lipid bilayer: a quantitative Force Spectroscopy contribution, submitted to JACS Communications.).