Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session Y39: Techniques in Biophysics |
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Sponsoring Units: DBP Chair: Andrea Liu, University of Pennsylvania Room: 411 |
Friday, March 20, 2009 8:00AM - 8:12AM |
Y39.00001: The Molecular Splash Test: when applied physics help stroke patients. Cedric Hurth, Lena van Nimwegen, Deepthi Jampala, Kris Vijay, Frederic Zenhausern The Molecular Splash Test (MST) stems from recent observations of a solid sphere producing a splash when impacting a liquid (Bocquet et al, 2007, \textit{Nature Physics}, \textbf{3}, 180). We have developed the experimental setup incorporating a high-speed camera operated at 8,000 frames/s to perform biologically-relevant experiments, e.g. rheology studies from the impact of a native glass bead and molecular recognition tests when the impacting bead is functionalized with biomarkers. We present preliminary results with millimeter-sized glass beads impacting water mixtures of increasing glycerol content, i.e. increasing viscosities, as well as biotin-modified glass beads impacting avidin solutions (0.1 -- 1 mg/mL). The viscosity increase of a human blood sample containing heparin, once heparinase II is added to re-induce coagulation, is monitored over time to assess the ability of MST to function on samples of medical interest. The beads can then be derivatized with an antibody for detection of C-reactive protein in blood serum. [Preview Abstract] |
Friday, March 20, 2009 8:12AM - 8:24AM |
Y39.00002: Surfaced-Enhanced Raman Scattering of $\lambda $-DNA Diane Alvarez, Jiandi Zhang, Hong Wei, Hongxing Xu The ability to engineer metal particles at the nanoscale in which plasmons can be excited, directed, and manipulated has led to the rapid development of the field of ``plasmonics''. Here we demonstrate that the Raman scattering of $\lambda $-DNA molecules with colloidal silver nanoparticles is drastically enhanced by surface plasmon excitations. Colloidal silver nanoparticles ($\sim $ 90 nm size) were assembled onto DNA molecules using the molecular combing method. Surface-enhanced Raman scattering (SERS) spectra were obtained and compared for different solution concentrations of the DNA/Ag system. It is evident that the SERS peaks were shifted to a lower or higher wavenumber, depending on the concentration of the solution. These different shifts of Raman frequencies may indicate that the different stretching states of DNA molecules in different concentrations probably influence the Raman frequencies. It is speculated that the coiling states of DNA molecules might be different in different concentrations, thus making it a promising method for the study of DNA functionalities and DNA-nanoparticle interactions. [Preview Abstract] |
Friday, March 20, 2009 8:24AM - 8:36AM |
Y39.00003: Sub-cellular structure studied by combined atomic force-fluorescence microscopy Andreea Trache A novel experimental technique that integrates atomic force microscopy (AFM) with fluorescence imaging was used to study the role of extracellular matrix proteins in cellular organization. To understand the mechanism by which living cells sense mechanical forces, and how they respond and adapt to their environment, we developed a new technology able to investigate cellular behavior at sub-cellular level that integrates an AFM with total internal reflection fluorescence (TIRF) microscopy and fast-spinning disk (FSD) confocal microscopy. Live smooth muscle cells exhibited differences in focal adhesions and actin pattern depending on the extracellular matrix used for substrate coating. Data obtained by using the AFM-optical imaging integrated technique offer novel quantitative information that allows understanding the fundamental processes of cellular reorganization in response to extracellular matrix modulation. The integrated microscope presented here is broadly applicable across a wide range of molecular dynamic studies in any adherent live cells. [Preview Abstract] |
Friday, March 20, 2009 8:36AM - 8:48AM |
Y39.00004: Expanding the applicability of multi-photon fluorescence recovery after photobleaching \textit{in vivo} by incorporating convective flow into the recovery model Kelley Sullivan, William Sipprell, Edward Brown, Jr., Edward Brown, III Multi-photon fluorescence recovery after photobleaching is a well-established microscopy technique used to study diffusion, with expanding applications \textit{in vivo}. We present a new model of fluorescence recovery that explicitly includes the effect of convective flows within a system, thereby improving the efficacy of the technique \textit{in vivo}, where convective flows are omnipresent. We test this ``flow'' model through both simulations and \textit{in vitro} experimentation, and demonstrate the effectiveness of the new model \textit{in vivo}. Our results show that the flow model significantly improves the capabilities of multi-photon fluorescence recovery after photobleaching \textit{in vivo}, by enabling an accurate determination of the diffusion coefficient, even when significant flows are present. [Preview Abstract] |
Friday, March 20, 2009 8:48AM - 9:00AM |
Y39.00005: Electrophoretic Migration of Branched DNA in Polymer Solutions Henry Lau, Lynden Archer The electrophoretic migration of large, star-branched DNA molecules has previously been studied in both neutral polymer solutions and gels, and the results have provided insight into the local interactions between the analytes and the sieving matrix during electrophoresis (Electrophoresis, 2006, 27, 3128). This talk focuses on using rigid-rod DNA molecules of complex shapes as model analytes in studying the effects of analyte architecture on mobility in polymer solutions. Electrophoresis of a series of Y-shaped DNA molecules that mimick the shapes of antibodies, was performed in polymer solutions above the overlap concentration and at electric fields up to 300V/cm. The location of the branch point as well as the arm sizes are varied in order to examine their influence on mobility. Our results point to novel, topology-based fractionation strategies for separating biological molecules using capillary electrophoresis with polymer sieving media. [Preview Abstract] |
Friday, March 20, 2009 9:00AM - 9:12AM |
Y39.00006: Time-resolved dielectric spectroscopy of protein aggregation performed on model system of hen lysozyme and beta-lactoglobulin Brian Mazzeo, Andrew Flewitt Time-resolved dielectric spectroscopy measurements of solutions containing hen lysozyme and beta-lactoglobulin reveal changes in electrical configuration and hydrodynamic parameters during their interaction. These measurements were performed in a temperature-controlled dielectric cell connected to an HP4194A impedance analyzer. The protein titrations were performed by sequential additions of reacting proteins. Differential spectra reveal the electrical contributions by each species. The computer-controlled measurements and relevant post-processing of the obtained spectra allow quantitative extraction of reaction parameters. This is demonstrated for a model system of proteins consisting of hen lysozyme and beta-lactoglobulin. Reorientation time constants, dielectric increments, and relaxation spread parameters are plotted against time and indicate binding processes. The technique is demonstrated to be a useful analytical tool for monitoring reactions in biological and colloidal systems. [Preview Abstract] |
Friday, March 20, 2009 9:12AM - 9:24AM |
Y39.00007: ``Shooting Bead'' Method with Filament Energy Loss Consideration for Finding the Flexural Rigidity of the Rodelike Biological Filaments Abdorreza Samarbakhsh, Jack Tuszynski Flexural rigidity is one of the important characteristics of flexible polymers including biological filaments. For elastic deformation it is analogous to the spring constant in the Hook's law for bending. In this work we propose a new method for experimentally evaluating the cantilever stiffness and flexural rigidity of semiflexible rodlike biological filaments based on the measurement of just two distances. The method is based on applying a force normal to the filament with a microsphere bead trapped in the laser tweezer followed by its sudden release. Through two simple measurements of the initial and final position of the bead, the cantilever stiffness and flexural rigidity of the filament can be found from the formula that has been provided. In the second part, the effect of filament radius has been taken into account and a new formula with filament energy loss consideration, for flexural rigidity and the cantilever stiffness has been found. [Preview Abstract] |
Friday, March 20, 2009 9:24AM - 9:36AM |
Y39.00008: Electrostatic Force Microscopy Identification of Different Peptide Structures Casper Hyttel Clausen In this work electrostatic force microscopy (EFM) was used to distinguish between different dipeptides tubes, silver filled peptides, spheres and silver wires, all the samples were placed on pre fabricated SiO$_{2}$ surfaces with a backgate under ambient conditions. The EFM method used for the experiments was force gradient signal, which uses a dual scan approach in order to minimize the atomic force interactions. The investigation shows that it is possible to distinguish between the three types of structures. Further an agreement between the detected signal and the structure of the hollow peptide was demonstrated. These measurements only show qualitative agreement with the mathematical expressing for the peptide tubes. Further during EFM mapping of the silver filled peptide structures showed a changing effect between the tip and the sample. Investigations of this effect were carried out in order to get a better understanding of the physical properties of the peptide structures. [Preview Abstract] |
Friday, March 20, 2009 9:36AM - 9:48AM |
Y39.00009: Specific Detection of Vascular Endothelial Growth Factor Using Microcantilever Resonators. Jason Francis, Stephanie Archer, Lisa Holland, David Lederman We demonstrate the specific detection of vascular endothelial growth factor, a protein indicated in tumor angiogenesis, using resonant frequency shifts in microcantilevers due to mass loading, avoiding the need to use tagged antibodies and multiple reagents as is needed with enzyme linked immunosorbent assays (ELISA). Cantilever surfaces were functionalized using F(ab') fragments linked to gold surfaces via their native thiol groups, eliminating the need for complex linking processes. The cantilever surfaces were then passivated with bovine serum albumin to minimize shifts due to nonspecific binding. This technique allows the detection of pg/mL-level concentrations of analyte. [Preview Abstract] |
Friday, March 20, 2009 9:48AM - 10:00AM |
Y39.00010: Positioning and guidance of neurons on Au by directed assembly of proteins using Atomic Force Microscopy. Cristian Staii, Chris Viesselmann, Jason Ballweg, Justin Williams, Erik Dent, Susan Coppersmith, Mark Eriksson The specific interactions between neurons and guidance factors as well as the mechanism of axonal navigation toward a target in the developing brain are not well understood. To address this problem we present a new approach for controlling the adhesion, growth and interconnectivity of cortical neurons on Au surfaces. Specifically, we use AFM nanolithography to immobilize extracellular matrix proteins at well-defined locations on Au surfaces, and show that these protein patterns can confine neuronal cells and control their growth and interconnectivity. We will compare this method with other nanofabrication techniques and discuss its main advantages: 1) the procedure is carried out in aqueous solutions, so that the proteins retain their bioactivity, 2) a high degree of control over location and shape of the protein patterns can be achieved, and 3) the minimum protein feature size can be as small as 50nm. [Preview Abstract] |
Friday, March 20, 2009 10:00AM - 10:12AM |
Y39.00011: Determination of Frank-Oseen parameters in collagen using polarization modulated second harmonic signal. Clayton Bratton, Karen Reiser, Andre Knoesen, Diego Yankelevich, Mingshi Wang, Israel Rocha - Mendoza A method is presented for determining the Frank-Oseen parameters for the elastic modulus of collagen based on analysis of polarization-modulated second harmonic signal (PM-SHG). The liquid crystal structure of collagen and its associated order parameter, the director field, were characterized in samples of tendon and annulus fibrosus.~ Deformation of the director field caused by controlled stress loading or heating was assessed. Three distinct curvature strains--splay, twist, and bend---were determined, using the PM-SHG data. This optical technique permits highly localized determination of the three major elastic deformations. [Preview Abstract] |
Friday, March 20, 2009 10:12AM - 10:24AM |
Y39.00012: Direct measurement of the non-conservative force field generated by optical tweezers Pinyu Wu, Rongxin Huang, Christian Tischer, Alexandr Jonas, Ernst-Ludwig Florin Optical tweezers have been widely used in soft condensed matter physics and biophysics to measure forces in molecular processes on the single molecule level. The usual assumption is that the force applied to a particle confined with the tweezers is directly proportional to the displacement of the particle from the trapping center, which would imply that the force field of the tweezers is conservative. However, the Gaussian beam model indicates that this force field is actually non-conservative, yet no experiments have measured this effect. We developed a new experimental method that can directly measure the force field with femtonewton precision without assuming its conservative character. We successfully obtained the 3-D force field for an optically trapped Rayleigh particle with 10~nm resolution by analyzing its Brownian motion. We found a non-conservative contribution that increases as the trapped particle moves away from the optical axis. In the light of this finding, optical trapping experiments that assumed a conservative force field may need careful reevaluation. [Preview Abstract] |
Friday, March 20, 2009 10:24AM - 10:36AM |
Y39.00013: SERS-Active Nanoinjector for Intracellular Spectroscopy Elina Vitol, Zulfiya Orynbayeva, Michael Bouchard, Jane Azizkhan-Clifford, Gary Friedman, Yury Gogotsi We developed a multifunctional nanopipette which allows simultaneous cell injection and intacellular surface-enhanced Raman spectroscopy (SERS) analysis. SERS spectra contain the characteristic frequencies of molecular bond vibrations. This is a unique method for studying cell biochemistry and physiology on a single organelle level. Unlike the fluorescence spectroscopy, it does not require any specific staining. The principle of SERS is based on very large electromagnetic field enhancement localized around a nano-rough metallic surface. Gold colloids are widely used SERS substrates. Previously, the colloidal nanoparticles were introduced into a cell by the mechanism of endocytosis. The disadvantage of this method is the uncontrollable aggregation and distribution of gold nanoparticles inside a cell which causes a significant uncertainty in the origin of the acquired data. At the same time, the nanoparticle uptake is irreversible. We present a SERS-active nanoinjector, coated with gold nanoparticles, which enables selective signal acquisition from any point-of-interest inside a cell. The nanoinjector provides a highly localized SERS signal with sub-nanometer resolution in real time. [Preview Abstract] |
Friday, March 20, 2009 10:36AM - 10:48AM |
Y39.00014: Evaluating Epithelial Mechanics with Laser Hole-drilling M. Shane Hutson, David N. Mashburn, Xiaoyan Ma, Holley E. Lynch During the development of an organism, sheets of epithelial cells expand, contract and bend due to intra- and intercellular forces. We have previously developed laser hole-drilling as a technique to probe such epithelial mechanics -- with a focus on the ms-to-s dynamic recoil of single, directly adjacent cell edges. Here we extend the analysis to consider ablation-induced deformations for the entire field of surrounding cells. We treat each epithelium as a homogeneous, linearly elastic, thin sheet. This simplification provides analytical solutions for the expected strain relaxation after hole-drilling (under either plane stress or plane strain). We have developed routines that use these analytic mappings (plus potential rigid body motions) to warp and match pre- and post-drilling images. These mappings account for the majority of the observed deformations and allow one to estimate the epithelium's Poisson ratio and pre-drilling average strain tensor (which yields the anisotropy and direction of principle stress/strain). The unaccounted, residual displacements provide clues to how each epithelium deviates from a homogeneous sheet. [Preview Abstract] |
Friday, March 20, 2009 10:48AM - 11:00AM |
Y39.00015: Top-Down Fabricated Silicon Nanochannel Field-Effect Transistors for Biosensing Applications Yu Chen, Xihua Wang, Shyamsunder Erramilli, Pritiraj Mohanty Silicon nanochannel field-effect transistors have great promise for biomolecular sensing. The sensitivity is enhanced at the nanoscale due to the large surface-to-volume ratio. Specificity is achieved by functionalizing the devices with selected antibodies or complimentary target molecules. These devices are important as building blocks for high density bionanoelectronics. Top-down fabrication of these devices is compatible with advanced microfabrication processes. We show top-down fabricated silicon nanochannel devices with 3-dimensional relief can serve as a platform for biosensing applications. Three sides of the silicon nanowire are covered with a thin Al2O3 layer using Atomic Layer Deposition to form an insulating layer. When the surface is modified for binding to specific biomarkers, the device conductance change can be used to detect binding events through a field effect. Applications include building immunosensors to detect the breast cancer antigen 15-3 and other protein biomarkers, and constructing enzyme-based sensors to detect metabolites like glucose and urea. [Preview Abstract] |
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