Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session P21: Nanotubes, Nanowire and Nanoparticles in Biology |
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Sponsoring Units: DBP Chair: Robert Austin, Princeton University Room: LACC 409A |
Wednesday, March 23, 2005 11:15AM - 11:27AM |
P21.00001: Electrical Detection of ssDNA by Single Wall Carbon Nanotubes Chih-kuan Tung, Yuexing Zhang, Phuan Ong, Edward Cox, Robert Austin We report conductance measurements of single-walled carbon nanotubes (SWNT) in the presense of single-stranded DNA (ssDNA). The characteristic I-V curves of our metallic SWNT samples changed from linear (ohmic) to non-ohmic in the presence of ssDNA dissolved in DI water, and remained so when the sample was dried. The results imply possible applications of SWNT in the electronic detection of ssDNA, detection of hybridization of ssDNA, and sequencing of DNA. [Preview Abstract] |
Wednesday, March 23, 2005 11:27AM - 11:39AM |
P21.00002: Sturdier DNA nanotubes via ligation Patrick O'Neill Self-assembly of DNA nanotubes from double crossover tiles results in cylindrical lattices of tiles joined by overlapping sticky ends. We show that nicks formed at overlapping sticky ends can be successfully ligated in the tube geometry, resulting in increased thermal and mechanical stability of the nanotubes. We compare the melting temperature and persistence length of ligated and unligated nanotubes. [Preview Abstract] |
Wednesday, March 23, 2005 11:39AM - 11:51AM |
P21.00003: Interaction between proteins and carbon nanotubes field effect transistors. Mikhail Briman, Keith Bradley, Alex Star, George Gruner The interaction between proteins and carbon nanotube network field effect transistors in a biological buffer environment has been investigated. In general, chemical or biological species can affect conduction through the network either by charge transfer or by introduction of a scattering potential on the nanotubes. A method employing the real-time analysis of transistor transfer characteristics allows us to distinguish between these two effects. Based on the available experimental data, we argue that the mechanism by which proteins influence carbon nanotubes is the charge transfer from --NH$_{2}$ groups. [Preview Abstract] |
Wednesday, March 23, 2005 11:51AM - 12:03PM |
P21.00004: Self-Assembled Gold Nanowires from Nanoparticles Lifeng Zheng, Shengdong Li, J. Brody, Peter Burke We present a new technique for fabricating gold nanowires using carbon nanotubes as the template. By applying an ac voltage to an electrically contacted single walled carbon nanotube, we generate highly non-uniform ac electric fields in the vicinity of the nanotubes. These ac electric fields serve to polarize 2 nm gold nanoparticles dispersed in solution. The induced dipole moment in the nanoparticles is attracted to the high-intensity field regions at the surface of the nanotube, thus causing a gold nanowire to grow on the surface of the nanotube[1]. Interestingly, we find gold nanowires grow even on nanotubes that are not electrically contacted but in close proximity to the electrodes. This process is also visualized using fluorescently labeled nanoparticles. Future applications of this work include DNA sensors based on functionalized Au nanoparticles. Additional work on the electronic trapping of proteins and DNA[2] using AC electric fields will also be presented. [1] L. Zheng, S. Li, J. Brody, and P. J. Burke, ``Manipulating nanoparticles in solution with electrically contacted nanotubes using dielectrophoresis'', Langmuir, 20, 8612-8619, 2004; [2] Zheng, L.; Brody, J. P.; Burke, P. J. "Electronic Manipulation of DNA, Proteins, and Nanoparticles for Potential Circuit Assembly", Biosens. Bioelectron., 20, 606-619 (2004). [Preview Abstract] |
Wednesday, March 23, 2005 12:03PM - 12:15PM |
P21.00005: Accurate and efficient modeling for carbon nanotubes in biological applications Yan Li, Deyu Lu, Klaus Schulten, Umberto Ravaioli Carbon nanotubes (CNTs) hold great promise for applications in biomedicine and biotechnology, in particular, as biosensors. For such applications, it is essential to understand the interaction of CNTs and water and/or other biomolecules in the aqueous environment. In this regard, the short-ranged van der Waals interaction together with the Coulomb interaction arising from atomic partial charges and dielectrically induced charges on the CNT play an important role. We have developed an accurate, yet computationally efficient, empirical method to model the electrostatics of finite-length single-walled armchair CNTs. Atomic partial charges are fitted to electrostatic potentials computed at a B3LYP/6-31G* level of density functional theory. The dielectric properties are calculated self-consistently from a third-nearest-neighbor tight-binding Hamiltonian, and are found to be in good agreement with density functional theory results. We demonstrate our description for water transport through a finite-length CNT channel. The atomic partial charges on the edges are found to greatly contribute to the total interaction energy and may influence water entering the CNT, while the polarizability of the CNT significantly lowers the electrostatic energy in the tube center. [Preview Abstract] |
Wednesday, March 23, 2005 12:15PM - 12:27PM |
P21.00006: Importance of specific magnetic moment and size monodispersity of magnetic nanoparticles for biomedical applications You Qiang, Joe Nutting, Jiji Antony, Sweta Pendyala, Amit Sharma, Daniel Meyer Magnetic nanoparticles with suitable biocompatible coatings are becoming increasingly important recentlt in biomedical applications. In most cases people just use nanoparticles but don't pay much attention to their magnetic properties and size effects, which could improve greatly the applications. There are very few publications dealing with underlying physics and discussing how the magnetic properties and size distribution of nanoparticles influence the applications. Most magnetic particles or beads used currently are based on ferromagnetic iron oxides with low magnetic moment and large size distribution. In this paper we will discuss the important role of high magnetic moment and monodispersity of magnetic nanoparticles from physics point review. Physics of hyperthermia treatments of nanoparticles, and biomolecule detection using Brownian rotation dynamics will be discussed in detail. As an example we will show how we produce monodispersive core-shell iron nanoparticles with ultrahigh magnetic moment and the significant results in biomedical applications. [Preview Abstract] |
Wednesday, March 23, 2005 12:27PM - 12:39PM |
P21.00007: Incorporation and release of materials into/from nanohorns used as drug delivery systems Masako Yudasaka, Jing Fan, Jin Miyawaki, Sumio Iijima We have established methods of incorporating organic materials into nanohorns in the liquid phase at room temperature in a quality-controlled manner. The methods are classified into two types: quasi-equilibrium or non-equilibrium. We can choose a suitable type depending on the affinity between guest molecules and nanohorns. When nanohorns are used as drug carriers in drug delivery systems, the incorporated materials must be released, ideally over controllable period of time. We found that the release process included fast components that release 50--70{\%} of the materials quickly as a result of the weak binding among the molecules in the central region inside the hollow spaces of the nanohorns. We also found methods of slowing down the quick release, which should improve the applicability of nanohorns as drug carriers in drug delivery systems. [Preview Abstract] |
Wednesday, March 23, 2005 12:39PM - 12:51PM |
P21.00008: Drug-loaded single-wall carbon nanohorns: adsorption and release of dexamethasone in vitro Tatsuya Murakami, Kumiko Ajima, Jin Miyawaki, Masako Yudasaka, Sumio Iijima, Kiyotaka Shiba Oxidized single-wall carbon nanohorns (SWNHox) are spherical aggregates (80-100 nm) of elongated graphitic tubes and have holes of $<$2 nm on the surface that enable incorporation of small guest molecules into them. Here we evaluate the \textit{in vitro} capacity of SWNHox to adsorb and release an anti-inflammatory drug, dexamethasone (DEX). The total amount of DEX adsorbed to SWNHox was determined to be 200 mg/g using [$^{3}$H]-labeled DEX. Kinetic analysis showed DEX slowly released from the complexes into PBS: about a half of DEX adsorbed was released in two weeks. Experiments with mammalian cells indicated that functional DEX was released from the complex. The results obtained here showed that SWNHox is an attractive candidate for a controlled drug carrier. [Preview Abstract] |
Wednesday, March 23, 2005 12:51PM - 1:03PM |
P21.00009: Cell Structure Assembly with Magnetic Nanowires E. J. Felton, A. Hultgren, M. Tanase, D. H. Reich, C. S. Chen The ability to precisely position and organize mammalian cells plays a significant role in numerous biological applications, including the assembly of multi-dimensional cell structures. Ferromagnetic nanowires, used in conjunction with patterned micromagnets, are shown to provide a highly effective tool for cell manipulation. The nanowires are fabricated by electrodeposition, allowing for precise control of their dimensions and magnetic properties. Their high aspect ratio and large remanent magnetization allow suspensions of cells bound to nanowires to be controlled with low magnetic fields through the alignment of the wires' moments. We have shown that these characteristics enable self-assembly and patterning of 3T3 mouse fibroblast cells with Ni nanowires in one and two dimensions in the presence of an applied horizontal field. Vertical orientation of the applied field promotes the creation of vertical cell columns which can be organized to form more complex structures. The geometry of these structures is controlled through selection of different micromagnet patterns, and the resulting three-dimensional structures can be made permanent by stabilization in hydrogel. These methods are potentially useful in the synthesis of engineered tissues. [Preview Abstract] |
Wednesday, March 23, 2005 1:03PM - 1:15PM |
P21.00010: Imaging of DNA/Nanosphere Condensates R. Krishnan, T. Jaleel, T. Nordlund DNA forms condensates in a variety of environments. In chromatin, DNA is condensed around 10-nm-diameter, positively-charged histone complexes. To model chromatin formation in cells, lambda-phage (16 microns long) and herring sperm (0.03 to1 micron) DNAs were mixed with polystyrene nanospheres of diameter 40nm and 930nm containing 1.8x10$^{4}$ and 2.6x10$^{8}$ positive surface charges, respectively, to form condensates. Sphere concentrations were 1-2 times the isoelectric concentration. Condensation vs time was imaged at various concentrations, pH's, viscosities, and ionic strengths. Bright-field and fluorescence (YOYO-1 dye bound to DNA) images were recorded. In general HS DNA aggregate size increased with time. Except in 0.5-0.8 M KCl, herring sperm DNA formed one huge aggregate (100's of microns) and depleted other areas, both in 10{\%} and 20{\%} glycerol. Phage DNA samples rapidly formed longer, fiber-like aggregates. Within 2 hours it formed ordered structures and in most samples, empty, apparently depleted regions were found in the viewing area. Shapes of the phage-DNA aggregates in 20{\%} glycerol, in contrast, formed small clumps like HS DNA. [Preview Abstract] |
Wednesday, March 23, 2005 1:15PM - 1:27PM |
P21.00011: Theory of Excluded Volume Effects in Tethered Particle Experiments Darren Segall, Rob Phillips Tethered particle motion is a class of single molecule experimental techniques that has been used to explore numerous macromolecular properties including the motion of kinesin and RNA polymerase; proteins synthesis of DNA and protein mediated loop formation in DNA. In this experimental technique an imagining bead is attached to the macromolecule of interest. Despite the diversity of experimental studies theoretical work regarding the relationship between the motion of the bead and that of the molecule is lacking. In this work we present a theoretical analysis of tethered particle motion. Our theoretical analysis reveals that the nature of the experimental protocol gives rise to a volume exclusion effect resulting in an effective force acting on the molecule. This effective force causes the molecule to swell changing its statistical properties and in some cases it biological functionality. Statistical properties of the tethered bead (experimentally measurable) are then related to that of the molecule (not observed). We then apply this theory to the analysis of dynamical macromolecular interactions. In particular, we demonstrate how the rate of loop formation of dsDNA generated by the lac-repressor protein is decreased due to the volume exclusion effect. Finally, we apply this theory to the analysis of protein digestion of DNA, revealing a simple manner in which tethered particle motion can be used to the study of such interactions. [Preview Abstract] |
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