Bulletin of the American Physical Society
2007 Joint Fall Meeting of the Texas Sections of the APS and AAPT; Zone 13 of SPS
Volume 52, Number 16
Thursday–Saturday, October 18–20, 2007; College Station, Texas
Session B5: GEN1: Biological, Chemical and General Physics |
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Chair: Alexei Sokolov, Texas A&M University Room: Rudder Tower 504 |
Friday, October 19, 2007 10:40AM - 10:52AM |
B5.00001: A Swept Wavelength Optical Resonant Raman Detector (SWOrRD) for Bio-detection. Charles Manka, Jacob Grun, Dan Zabetakis, Sergei Nikitin, Gelu Comanescu, Jeff Bowles, David Gillis A new device that sequentially illuminates bacteria with different ultraviolet wavelengths and obtains a spectrum at each wavelength has been developed and tested. The available wavelengths are spaced at $\sim $ 0.3 nm intervals from 210 to 280 nm. Tuning from one wavelength to another requires 20 to 60 seconds, depending on the wavelength region. Liquid samples are contained in a quartz cuvette, illuminated side-on and the scattered light is collected at 90 degrees. A double spectrograph and CCD camera record the resulting Raman Spectra. Spectra from the sequential illumination are assembled into a data ``cube'' for processing and analysis. Measurements of two-dimensional resonant-Raman spectra of bacteria are presented and the applicability of the method for the identification of bacteria, including differentiation of genetically similar species, is demonstrated. We anticipate that information within such two-dimensional spectra will allow identification of bacteria, as well as chemicals, in complex environments containing multiple organisms and chemicals. This device may lead to instruments that rapidly identify bacteria in hospital and food process settings, for screening large populations, and for biochemical-threat warning systems. [Preview Abstract] |
Friday, October 19, 2007 10:52AM - 11:04AM |
B5.00002: Towards Single-Shot Detection of Bacterial Endospores via Coherent Raman Spectroscopy Dmitry Pestov, Xi Wang, Gombojav Ariunbold, Robert Murawski, Vladimir Sautenkov, Alexei Sokolov, Marlan Scully Recent advances in coherent anti-Stokes Raman scattering (CARS) spectroscopy hold exciting promise to make the most out of now readily available ultrafast laser sources. Techniques have been devised to mitigate the nonresonant four-wave-mixing in favor of informative Raman-resonant signal. In particular, a hybrid technique for CARS (see \textit{Science} \textbf{316}, 265 (2007)) brings together the advantages of coherent broadband pump-Stokes excitation of molecular vibrations and their time-delayed but frequency-resolved probing via a spectrally narrowed and shaped laser pulse. We apply this technique to the problem of real-time detection of warfare bioagents and report single-shot acquisition of a distinct CARS spectrum from a small volume of \textit{B. subtilis} endospores ($\sim $10$^{4}$ spores), a harmless surrogate for \textit{B. anthracis}. We study the dependence of the CARS signal on the energy of the ultrashort preparation pulses and find the limit on the pulse energy fluence ($\sim $0.2 J/cm$^{2})$, imposed by the laser-induced damage of the spores. [Preview Abstract] |
Friday, October 19, 2007 11:04AM - 11:16AM |
B5.00003: Microfabricated Devices for Control of Electric and Magnetic Fields on Cellular Length Scales Daniel Stark, Laura Timmerman, Lisa Biswal, Robert Raphael, Thomas Killian Microfabrication techniques, such as photolithography and electroplating, are increasingly being used to create tools that, in combination with biological imaging, probe the physics of biological systems. With these devices one can exert control over electric and magnetic fields at the cellular length scale. We present here the design and development of two microscale devices. These devices can be used as magnetic micromanipulators that apply piconewtons of force to cells or as stimulators that apply electrical fields up kV/cm. Additionally, these devices can be utilized to probe cell membrane mechanics or to deliver genetic material to individual cells by electroporation. [Preview Abstract] |
Friday, October 19, 2007 11:16AM - 11:28AM |
B5.00004: Vibratonal Spectra and DFT calculations of dipicolinic acid and its calcium salt Kathleen McCann, Jaan Laane The infrared and Raman spectra of dipicolinic acid (DPA) and calcium dipicolinate have been recorded in the solid phase and their vibrations have been assigned. DFT calculations using B3LYP/6-311++G** have been used to calculate the spectra of the free dipicolinic acid molecule and its ion in an environment free of intermolecular interactions. Calculations have also been carried out to better understand the effects of intermolecular hydrogen bonding and the interactions between water and DPA. The calculated frequencies agree well with the experimental values after scaling. [Preview Abstract] |
Friday, October 19, 2007 11:28AM - 11:40AM |
B5.00005: Surface Engineering for Microtubule Manipulation John Noel, Winfried Teizer, Wonmuk Hwang Microtubule filaments act as dynamic structures inside cells for cargo transport and cell motility. We have used self-assembled monolayers and lithographic techniques to control surface interactions between microtubules and synthetic substrates. Switchable protein adsorption has been achieved using an electrode coated with a non-fouling polyethylene glycol self-assembled silane monolayer (SAM). Novel integration of the SAM into current electron-beam lithography techniques has allowed for the underlying electrode to be patterned with much freedom of geometry while preventing permanent adsorption of the protein. In this configuration, microtubules assemble on top of the patterned electrode but are blocked from the surrounding regions. The reversible adsorption permits study of microtubules under spatially controlled electric fields. Furthermore, such active test surfaces can be used to study microtubule assembly and to simulate kinesin motor transport in neurons. This method is also compatible with DNA and other biomolecules and, unlike soft lithography, can be scaled down to tens of nanometers in a straightforward manner. [Preview Abstract] |
Friday, October 19, 2007 11:40AM - 11:52AM |
B5.00006: Conformation transition of betaA in solution and on surface of lipid bilayer Liming Qiu, Andrew Reay, Qing Zhu, Mark Vaughn, Kwan Cheng Beta amyloid (betaA) is a 39 to 43 residue peptide generated by a proteolytic cleavage of a large transmembrane amyloid precursor protein in neuronal membranes. The misfolding and self-aggregation of betaA, as well as its interactions with neuronal membranes, have been linked to the early onset of pathogenesis of Alzheimer disease. The secondary structure conformational transition of betaA from an alpha-helix to beta-sheet in some key regions of the peptide represents an important signature of the complex misfolding behavior of betaA. Using all-atom molecular dynamics simulations, the conformation changes of betaA in solution and on the surface of lipid bilayer containing nanodomains of cholesterol have been studied. Our results indicated that the appearance of beta-sheet structures depends strong on the initial structures of betaA and the arrangement of cholesterol molecules in the lipid bilayer. [Preview Abstract] |
Friday, October 19, 2007 11:52AM - 12:04PM |
B5.00007: Emergence of Alpha and Gamma Like Rhythms in a Large Scale Simulation of Interacting Neurons Philipp Gaebler, Bruce Miller In the normal brain, at first glance the electrical activity appears very random. However, certain frequencies emerge during specific stages of sleep or between quiet wake states. This raises the question of whether current mathematical and computational models of interacting neurons can display similar behavior. A recent model developed by Eugene Izhikevich appears to succeed. However, early dynamical simulations used to detect these patterns were possibly compromised by an over-simplified initial condition and evolution algorithm. Utilizing the same model, but a more robust algorithm, here we present our initial results, showing that these patterns persist under a wide range of initial conditions. We employ spectral analysis of the firing patterns of a system of interacting excitatory and inhibitory neurons to demonstrate a bimodal spectrum centered on two frequencies in the range characteristic of alpha and gamma rhythms in the human brain. [Preview Abstract] |
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