Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session V27: Focus Session: Emerging Scanning Probe Microscopy Methods for Biological Applications |
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Sponsoring Units: GIMS Chair: Igor Sokolov, Clarkson University, Sergei Kalinin, Oak Ridge National Laboratory Room: 329 |
Thursday, March 19, 2009 8:00AM - 8:36AM |
V27.00001: Kinetic parameters of association and dissociation between single molecules measured by single-molecule force spectroscopy Invited Speaker: This presentation is focused on development of experimental scanning probe microscopy (SPM) approaches to quantify kinetic parameters of association and dissociation between receptor--ligand pairs. The potential of mean force (pmf) between interacting molecules is quantified by single molecule force spectroscopy (SMFS) approach. In SMFS molecules are allowed to interact and form molecular bond. Consequent measurements of rupture forces are used to characterize the attractive part of the pmf by extracting the distance from the equilibrium to the transition state, the rate of dissociation at no force and the activation energy. Factors affecting accuracy of the measured kinetic parameters are discussed including effects of the polymeric tether stiffening and possible contribution of non-single molecule events to the statistics of rupture forces. The developed SMFS method accounts for pertinent systematic errors and is tested using specific biotin-streptavidin interactions. The measured kinetic parameters show quantitative agreement with theoretical predictions. In addition, a new single-molecule approach to measure the activation energy of association is proposed. This approach uses the dependence of the probability to form molecular bonds on probe velocity when one of the interacting molecules is tethered by a flexible polymeric linker to the AFM probe. The application of the developed method to study interactions between biomolecules is demonstrated with measurements of the activation energy of biotin-streptavidin association. [Preview Abstract] |
Thursday, March 19, 2009 8:36AM - 8:48AM |
V27.00002: Coaxial and Triaxial Atomic Force Microscope Probes for Nanoassembly Keith A. Brown, Jonathan Aguilar, R.M. Westervelt We present a technique for the controlled three dimensional assembly of nanoscale objects using a modified atomic force microscope (AFM) probe. A conducting AFM probe is coated with alternating insulating and metal layers then etched at the tip to expose coaxial electrodes. The fabrication allows freedom to specify the size of the tip and therefore the length scale of objects to manipulate. An RF voltage is applied to the electrodes to trap objects at the tip with dielectrophoresis (DEP). The object may be released when it has been moved to the desired location by turning off the field. We present a two electrode coaxial configuration capable of positive DEP and a three electrode triaxial configuration for negative DEP which holds the trapped object away from the tip to overcome the ''sticky finger'' problem. The integration of three dimensional assembly with the nanometer precision and force-imaging capability of an AFM creates a platform for imaging and constructing structures at the nanoscale. We describe initial experiments and fabrication. [Preview Abstract] |
Thursday, March 19, 2009 8:48AM - 9:00AM |
V27.00003: Protein bond rupture measured by AFM and the energy landscape problem Peter Hoffmann, Essa Mayyas, Lindsay Runyan The measurement of protein interaction provides an intriguing opportunity for Atomic Force Microscopy (AFM)-based force measurements. The AFM has the advantage that it is relatively easy to use and widely available. However, the interpretation of the force data is lagging behind the experimental capabilities of the technique. In this talk, I will present some recent results of rupture force measurements between two proteins, and discuss our efforts to interpret the resulting data in terms of the underlying energy landscape. We performed measurements on matrix metalloproteases and their natural inhibitors at pulling speeds ranging over 3 orders of magnitude (30-48000 nm/s). However, we found that commonly used theory to interpret such data is inadequate and does not capture the physics of the problem. Consequently, data analysis based on such theories leads to highly erroneous results. We will discuss our attempts to improve the theory and present parameters extracted from the data that reflect the underlying energy landscape of the studied protein-protein interaction. [Preview Abstract] |
Thursday, March 19, 2009 9:00AM - 9:12AM |
V27.00004: AFM method to detect differences in adhesion of silica bids to cancer and normal epithelial cells Igor Sokolov, Swaminathan Iyer, Ravi Gaikwad, Craig Woodworth To date, the methods of detection of cancer cells have been mostly based on traditional techniques used in biology, such as visual identification of malignant changes, cell growth analysis, specific ligand-receptor labeling, or genetic tests. Despite being well developed, these methods are either insufficiently accurate or require a lengthy complicated analysis. A search for alternative methods for the detection of cancer cells may be a fruitful approach. Here we describe an AFM study that may result in a new method for detection of cancer cells in vitro. Here we use atomic force microscopy (AFM) to study adhesion of single silica beads to malignant and normal cells cultured from human cervix. We found that adhesion depends on the time of contact, and can be statistically different for malignant and normal cells. Using these data, one could develop an optical method of cancer detection based on adhesion of various silica beads. [Preview Abstract] |
Thursday, March 19, 2009 9:12AM - 9:24AM |
V27.00005: Rapid Cellular Identification by Dynamic Electromechanical Response Vladimir Reukov, Maxim Nikiforov, Alexei Vertegel, Gary Thompson, Stephen Jesse, Sergei Kalinin Quick and reliable identification of individual prokaryotic organisms and cellular types is of utmost importance for various applications. A number of strategies for cellular identification are currently used to meet this challenge. All of the existing techniques require culturing bacteria prior to measurement, which increases the time needed for experimentation and analysis considerably. Here, we report on a method for rapid cellular identification and mapping using the detection of broadband electromechanical response. Electromechanical spectra from \textit{M. Lysodeikticus} and \textit{P. Fluorescens} deposited on PLL-coated mica were collected over wide frequency range. Principal component analysis of the spectra bundled with neural network analysis provides a robust algorithm for identification of the cellular organisms based on their electromechanical properties. [Preview Abstract] |
Thursday, March 19, 2009 9:24AM - 10:00AM |
V27.00006: Simultaneous Nanomechanical and 3d Optical Microscopy: Cellular Distortions and Structural Dynamics Invited Speaker: Combined SPM and Optical systems are increasingly used to study biological structures, including living cells. Here, an AFM is employed to expose cells to foreign bodies and biochemicals, and to measure the resulting attractive and repulsive forces exerted by the cell. 3d optical fluorescence measurements are simultaneously performed revealing distortions and/or restructuring of the cell, membrane, actin cystoskeleton, etc. The work focuses primarily on MH-S cells (mouse lung macrophages) transfected with GAP-43 GFP to identify cell membranes and/or mCherry Actin to identify cytoskeleton dynamics. During standard AFM, optical-cross sections reveal drastic cell distortions up to 50 percent. The viscoelastic response of the cells to nanoNewton induced forces by Silica and Polystyrene beads is also quantified via Structural Recovery After Probing (STrAP), which monitors the rate of cellular recovery following nanoindentation. [Preview Abstract] |
Thursday, March 19, 2009 10:00AM - 10:12AM |
V27.00007: Spectral Oscillations in Backscattering of Light from a Biological Cell Alexander Heifetz, Alexander Patashinski, Vadim Backman Based on general electrodynamics principles, we provide an explanation for spectral oscillations in the intensity of visible light elastic backscattering from a live epithelial biological cell. We suggest that the source of spectral oscillations in backscattering from a cell is the nucleus, which is a spheroidal particle several times larger then the incident wavelength, and has a sharp boundary. Because of the small optical contrast of the nucleus relative to surrounding cytoplasm, contribution of single scattering to the overall signal is comparable to that of multiple scattering. We show that the high frequency spectral oscillations in backscattering are due to single scattering, which can be obtained in the first Born approximation. Multiple scattering effects result in slow envelope spectral oscillations. We expand the Mie backscattering cross-section of a uniform sphere in power series to show that the equivalence between the first order Mie backscattering and first order in Born series. [Preview Abstract] |
Thursday, March 19, 2009 10:12AM - 10:24AM |
V27.00008: Single-molecule detection of near-infrared phthalocyanine dyes You Li, Brian Canfield, Lloyd Davis The major advantage associated with near-IR monitoring is the fact that few compounds show intrinsic fluorescence in this region of the spectrum. Phthalocyanine dyes provide excellent photostability and hence are an attractive candidate for fluorescence bioassay applications. However, because of their small Stokes shifts, non-standard methods are needed for separation of fluorescence from scattered laser light. We have developed a custom confocal microscope that uses a low-cost laser diode operating at 665.8 nm for sample excitation and an angle-tuned Raman notch filter to block scattered laser radiation and provide high-throughput of fluorescence. Also, a diffraction grating is used to isolate the laser excitation wavelength from the block broadband luminescence of the laser. We have used the system to observe photon bursts from single molecules of zinc phthalocyanine fluorophores in an ethanol solution. The autocorrelation function of the photon trace provides a measure of the signal-to-noise ratio. We also discuss ongoing experiments to characterize the limits of detection of near-infrared fluorophores in aqueous solution using the microscope. [Preview Abstract] |
Thursday, March 19, 2009 10:24AM - 10:36AM |
V27.00009: Chemical Recognition Tunneling via Hydrogen Bond Jin He, Shuai Chang, Lisha Lin, Shuo Huang, Ashley Kibel, Myeong Lee, Peiming Zhang, Otto Sankey, Stuart Lindsay Hydrogen bonds enhance electron tunneling rates over vacuum tunneling as well as making chemically selective attachments to target molecules when patterns of donors and acceptors match. This raises the possibility of a completely new approach to transducing chemical information into electrical signals, based on forming an electrical circuit via a target molecule that bridges a gap between two electrodes by means of hydrogen bonding. Hydrogen-bond sensitive contrast has recently been demonstrated in scanning-tunneling microscope (STM) images of DNA bases. In this presentation, I will first show that the tunnel-current vs. distance decay curves acquired by STM change shape with the number of hydrogen bonds mediating an interaction. [1] Base composition of DNA oligomers can be resolved by this method. Further studies demonstrate that these tunnel-current decay signals can be used to count the number of hydrogen bonds in interactions between DNA bases and related compounds. The signals are partially mechanical in origin, reflecting the tensile strength of a tunnel junction held together with hydrogen bonds. \\[4pt] [1] He, J., Lin, L., Zhang, P. {\&} Lindsay, S. M. \textit{Nano Letters} \textbf{7}, 3854-3858 (2007). [Preview Abstract] |
Thursday, March 19, 2009 10:36AM - 10:48AM |
V27.00010: Nanoscale Properties of Neural Cell Prosthetic and Astrocyte Response D.A. Flowers, V.M. Ayres, R. Delgado-Rivera, I. Ahmed, S.A. Meiners Preliminary data from in-vivo investigations (rat model) suggest that a nanofiber prosthetic device of fibroblast growth factor-2 (FGF-2)-modified nanofibers can correctly guide regenerating axons across an injury gap with aligned functional recovery. Scanning Probe Recognition Microscopy (SPRM) with auto-tracking of individual nanofibers is used for investigation of the key nanoscale properties of the nanofiber prosthetic device for central nervous system tissue engineering and repair. The key properties under SPRM investigation include nanofiber stiffness and surface roughness, nanofiber curvature, nanofiber mesh density and porosity, and growth factor presentation and distribution. Each of these factors has been demonstrated to have global effects on cell morphology, function, proliferation, morphogenesis, migration, and differentiation. The effect of FGF-2 modification on the key nanoscale properties is investigated. Results from the nanofiber prosthetic properties investigations are correlated with astrocyte response to unmodified and FGF-2 modified scaffolds, using 2D planar substrates as a control. [Preview Abstract] |
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