Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session Y10: Emerging Biophysical Techniques |
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Sponsoring Units: DBIO Chair: Wolfgang Losert Room: 201 |
Friday, March 7, 2014 8:00AM - 8:12AM |
Y10.00001: Two-color super-resolution imaging of dendritic spines of hippocampal neurons using a custom STED microscope Stephanie Meyer, Kevin Woolfrey, Baris Ozbay, Diego Restrepo, Mark Dell'Acqua, Emily Gibson We built a 2-color STED microscope and imaged dendritic spines in mouse hippocampal neurons at sub-diffraction limit resolution. The microscope is designed similar to one developed by Johanna B\"uckers, et. al. (Opt. Exp. 2011) in the lab of Dr. Stefan Hell. The STED microscope images at Atto590/Atto647N wavelengths and is capable of doing so simultaneously. We characterized the resolution of the system by imaging 40nm fluorescent beads as $\sim$58nm (Atto590) and $\sim$44 nm (Atto647N). The microscope is part of the UC Denver Advanced Light Microscopy Core, primarily for use by neuroscientists. We then performed 2-color STED imaging on hippocampal neurons immuno-labeled at PSD-95 (a postsynaptic density marker) along with either the GluA1-subunit of the AMPA-type glutamate receptor or the signaling scaffold protein AKAP150 in order to visualize nm-scale compartmentalization of these proteins within single postsynaptic dendritic spines. Importantly, for both GluA1 and AKAP150, STED imaging visualized sub-diffraction dimension clusters in spines located at both synaptic (overlapping or proximal to PSD-95) and extrasynaptic locations. In the future 2-color STED imaging should be useful for studying changes in the localization of these proteins during synaptic plasticity. [Preview Abstract] |
Friday, March 7, 2014 8:12AM - 8:24AM |
Y10.00002: Single-cell Genomics using Droplet-based Microfluidics Anindita Basu, Evan Macosko, Alex Shalek, Steven McCarroll, Aviv Regev, Dave Weitz We develop a system to profile the transcriptome of mammalian cells in isolation using reverse emulsion droplet-based microfluidic techniques. This is accomplished by (a) encapsulating and lysing one cell per emulsion droplet, and (b) uniquely barcoding the RNA contents from each cell using unique DNA-barcoded microgel beads. This enables us to study the transcriptional behavior of a large number of cells at single-cell resolution. We then use these techniques to study transcriptional responses of isolated immune cells to precisely controlled chemical and pathological stimuli provided in the emulsion droplet. [Preview Abstract] |
Friday, March 7, 2014 8:24AM - 8:36AM |
Y10.00003: Sensitize hydration shells of ions by the dynamics of water with terahertz spectroscopy Deepu George, John Rahmani, Vinh Nguyen Comparison of the relaxation dynamics of water in bulk state to that in a confined state is of significant importance to the study of interaction of biomolecules with its environment. In relation to this, the ability of terahertz dielectric spectroscopy to probe intermolecular dynamics has been explored in the past decade to look at the dynamics of water molecules which forms a hydration shell around proteins. The change in dynamics of water when its molecules interact with different types of solute molecules forms the basis of water- bio-molecular interaction. There have been several studies in the past looking at the effects of ion interactions with water molecules. In this study we have employed a vector network analyzer based terahertz dielectric spectrometer operating over the frequency range from 0.5 GHz to 1.1 THz to examine the water dynamics in several alkali metal chloride solutions. The terahertz dielectric response of these solutions as a function of concentration as well as the ion size has been studied. We have confirmed that for all these solutions the dynamics can be best described by a three Debye relaxation process of water. The relaxation times does not seem to depend on salt concentrations but on the other hand strength of relaxation modes is dependent on the molarity. [Preview Abstract] |
Friday, March 7, 2014 8:36AM - 8:48AM |
Y10.00004: Co-regulation of cell behavior by electromagnetic stimulus and extracellular environment Toloo Taghian, Abdul Sheikh, Daria Narmoneva, Andrei Kogan Chronic wounds do not effectively respond to pharmacological treatments because of insufficient blood supply (Impaired angiogenesis) in the wound. Developing non-pharmacological treatments requires application of advanced technology to control natural cell signals to trigger desired cell responses. Application of external electric field (EF) has been shown to enhance angiogenesis through manipulation of naturally-generated EF in the ionic environment surrounding cells and across the cell membrane; however biophysical mechanisms of cell responses to EF remain unknown. EF-cell interactions may be affected by both the distribution of the induced EF within the cell and the properties of the extracellular matrix (ECM), which is known to regulate cell response to the external stimuli. We have developed a combined theoretical-experimental approach to study EF-cell interactions. Our theoretical 3D interaction model provides spatial distribution of the induced EF in cell and extracellular space and predicts a frequency specific cell response to EF. Experimentally measured responses of cells to EF including growth factor expression and capillary morphogenesis confirm this prediction. We show that natural versus synthetic ECM can differentially mediate cell response to EF. [Preview Abstract] |
Friday, March 7, 2014 8:48AM - 9:00AM |
Y10.00005: Superparamagnetic nanoplatforms for theragnostic applications: a structural investigation Irena Milosevic, Laurence Motte, Marie-Louise Saboungi, Bachir Aoun, Tao Li, Chengjun Sun, Yang Ren Magnetic nanoplatforms are being developed for use in bioassays, diagnosis, therapy and nano-organocatalysis. The nanoparticle has two essential roles: to act as a probe owing to its specific magnetic properties and to carry on its surface antitumoral molecules, precursor groups for the covalent coupling of biological recognition molecules, or small organic catalysts such as amino acids and alkaloids. The nanoplatforms consist of a superparamagnetic iron oxide core and different coatings for surface passivation and stabilization. We report recent results obtained at the Advanced Photon Source on three kinds of nanoplatforms, differing in their coating molecules: shape and size determination by small-angle X-ray scattering, distribution of valences and chemical environments of the iron ions deduced from X-ray absorption near-edge structure measurements, and atomic structures determined by x-ray diffraction. [Preview Abstract] |
Friday, March 7, 2014 9:00AM - 9:12AM |
Y10.00006: High resolution electron microscopy and spectroscopy of ferritin in thin window liquid cells Canhui Wang, Qiao Qiao, Tolou Shokuhfar, Robert Klie In-situ transmission electron microscopy (TEM) has seen a dramatic increase in interest in recent years with the commercial development of liquid and gas stages. High-resolution TEM characterization of samples in a liquid environment remains limited by radiation damage and loss of resolution due to the thick window-layers required by the in-situ stages. We introduce thin-window static-liquid cells that enable sample imaging with atomic resolution and electron energy-loss (EEL) spectroscopy with 1.3 nm resolution. Using this approach, atomic and electronic structures of biological samples such as ferritin is studied via in-situ transmission electron microscopy experiments. Ferritin in solution is encapsulated using the static liquid cells with reduced window thickness. The integrity of the thin window liquid cell is maintained by controlling the electron dose rate. Radiation damage of samples, such as liquid water and protein, is quantitatively studied to allow precision control of radiation damage level within the liquid cells. Biochemical reactions, such as valence change of the iron in a functioning ferritin, is observed and will be quantified. Relevant biochemical activity: the release and uptake of Fe atoms through the channels of ferritin protein shell is also imaged at atomic resolution. [Preview Abstract] |
Friday, March 7, 2014 9:12AM - 9:24AM |
Y10.00007: Multiphoton-generated localized electron plasma for membrane permeability modification in single cells T. Merritt, M. LeBlanc, J. McMillan, J. Westwood, G.A. Khodaparast Successful incorporation of a specific macromolecule into a single cell would be ideal for characterizing trafficking dynamics through plasmodesmata or for studying intracellular localizations. Here, we demonstrate NIR femtosecond laser-mediated infiltration of a membrane impermeable dextran-conjugated dye into living cells of Arabidopsis thaliana seedling stems. Based on the reactions of fluorescing vacuoles of transgenic cells and artificial cell walls comprised of nanocellulose, laser intensity and exposure time were adjusted to avoid deleterious effects. Using these plant-tailored laser parameters, cells were injected with the fluorophores and long-term dye retention was observed, all while preserving vital cell functions. This method is ideal for studies concerning cell-to-cell interactions and potentially paves the way for introducing transgenes to specific cells. [Preview Abstract] |
Friday, March 7, 2014 9:24AM - 9:36AM |
Y10.00008: Comparative study on the biodegradation and biocompatibility of silicate bioceramic coatings on biodegradable magnesium alloy as biodegradable biomaterial M. Razavi, M.H. Fathi, O. Savabi, S.M. Razavi, B. Hashemibeni, M. Yazdimamaghani, D. Vashaee, L. Tayebi Many clinical cases as well as in vivo and in vitro assessments have demonstrated that magnesium alloys possess good biocompatibility. Unfortunately, magnesium and its alloys degrade too quickly in physiological media. In order to improve the biodegradation resistance and biocompatibility of a biodegradable magnesium alloy, we have prepared three types of coating include diopside (CaMgSi2O6), akermanite (Ca2MgSi2O6) and bredigite (Ca7MgSi4O16) coating on AZ91 magnesium alloy through a micro-arc oxidation (MAO) and electrophoretic deposition (EPD) method. In this research, the biodegradation and biocompatibility behavior of samples were evaluated in vitro and in vivo. The in vitro analysis was performed by cytocompatibility and MTT-assay and the in vivo test was conducted on the implantation of samples in the greater trochanter of adult rabbits. The results showed that diopside coating has the best bone regeneration and bredigite has the best biodegradation resistance compared to others. [Preview Abstract] |
Friday, March 7, 2014 9:36AM - 9:48AM |
Y10.00009: Mechanics and optics of stretchable microlenses for artificial compound eye camera Zhengwei Li, Jianliang Xiao Due to the wide-angle field of view, low aberrations, high acuity to motion and infinite depth of field, insect eye-inspired imaging devices have attracted more and more interest. Recently, researchers have developed an imaging device that resembles the structure and functions of insects' apposition eyes. Elastomeric microlens array that can be mechanically stretched to very large extent without deteriorating the optics is critical to this development. The stretchable microlens array is composed of a number of hemispherical microlenses each sitting on top of a pedestal and connected through a continuous elastomeric film. Here we present our study on mechanical and optical aspects of stretchable microlens. Our results show that proper designs of the hemispherical microlens, pedestal and film are critically important to meet both mechanical and optical requirements simultaneously. Our study can have important implications in not only the design of artificial compound eye cameras, but also other developments that require stretchable optical elements. [Preview Abstract] |
Friday, March 7, 2014 9:48AM - 10:00AM |
Y10.00010: Systems with High Diffusivity Contrast: Treatment of Stochastic Force Matters Zheng Ma, Gary W. Slater It has been suggested, based on computer simulations, that systems containing regions with drastically different diffusivity could be used for controlled drug delivery. However, these studies neglect the fact that for particles diffusing in inhomogeneous media, the particular interpretation of the stochastic force has a significant impact. We present systematic investigations of several such systems using Lattice Monte-Carlo (LMC) methods based on Ito, Stratonovich and isothermal calculus. We find that even for moderate diffusivity contrast ($\sim 100$), different calculi predict distinct distributions of particles among regions. Results of previous work that implicitly use Ito calculus (without physical justification) crucially rely on particles accumulating in the low diffusivity medium, which is not observed for all choices of calculi. We argue that a proper choice of calculus, depending on the microscopic origin of the diffusivity contrast, must be made before any convincing conclusion can be drawn about what might constitute a promising candidate system for controlled drug delivery. [Preview Abstract] |
Friday, March 7, 2014 10:00AM - 10:12AM |
Y10.00011: Photothermal Mid-Infrared Microscopy: a new tool for hyperspectral chemical imaging Alket Mertiri, Mi Hong, Michelle Sander, Shyamsunder Erramilli We describe a method for label free microscopy in the mid-infrared region of the electromagnetic spectrum based on the photothermal effect. A Quantum Cascade Laser (QCL) tuned to an infrared active vibrational molecular normal mode is used as the pump laser. A low-phase noise Erbium-doped fiber (EDF) laser (1.5$\mu$m) is used as the probe. We demonstrate the method using a patterned image target with liquid crystal 4-cyano-4'-octylbiphenyl (8CB) as the mid-infrared absorber. The QCL is tuned across the C-H scissoring band, with a peak absorption at 1607cm$^{-1}$. Absorption of the modulated pump beam results in a change in the dielectric function and the refractive index at the probe beam frequency. The resultant scatter of the probe is observed in heterodyne lock-in detection. The combination of heterodyne detection, high brightness mid-infrared QCLs and low-phase noise stable EDF lasers provides an ultra-sensitive method for obtaining mid-infrared microscope images using short-wavelength optical detectors, whose performance far exceeds those of cryogenically cooled broadband mid-infrared detectors. The method provides a powerful new tool for hyperspectral label-free mid-infrared imaging. [Preview Abstract] |
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