Bulletin of the American Physical Society
Joint Fall 2009 Meeting of the Texas Sections of the APS, AAPT, and SPS
Volume 54, Number 13
Thursday–Saturday, October 22–24, 2009; San Marcos, Texas
Session B2: Biological and Chemical Physics, Medical Physics |
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Chair: Charles Allen, Angelo State University Room: LBJ Student Center 3-13.1 |
Friday, October 23, 2009 10:00AM - 10:12AM |
B2.00001: AFM Bio-Mechanical Investigation of the Taxol Treatment of Breast Cancer Cells Dylan Smith, Dipika Patel, Fernando Monjaraz, Soyeun Park Cancerous cells are known to be softer and easier to deform than normal cells. Changes in mechanical properties originate from the alteration of the actin cytoskeleton. The mechanism of cancer treatment using Taxol is related to the stabilization of microtubules. It has been shown that Taxol binds to polymerized tublin, stabilizes it against disassembly, and consequently inhibits cell division. An accurate quantitative study still lacks to relate the microtubule stabilizing effect with the cellular mechanical properties. We utilized our AFM to study changes in elastic properties of treated breast cancer cells. The AFM has several advantages for precise force measurements on a localized region with nanometer lateral dimension. In previous AFM studies, measurable contributions from the underlying hard substrate have been an obstacle to accurately determine the properties on thin samples. We modified our AFM tip to obtain the exact deformation profile as well as reducing the high stresses produced. We have probed depth profiles of mechanical properties of the taxol-treated and untreated cells by varying the indentation depth of the AFM-nanoindenting experiments. [Preview Abstract] |
Friday, October 23, 2009 10:12AM - 10:24AM |
B2.00002: Single-Molecule Manipulation Studies of a Mechanically Activated Protein Eric Botello, Nolan Harris, Huiwan Choi, Angela Bergeron, Jing-fei Dong, Ching-Hwa Kiang Plasma von Willebrand factor (pVWF) is the largest multimeric adhesion ligand found in human blood and must be adhesively activated by exposure to shear stress, like at sites of vascular injury, to initiate blood clotting. Sheared pVWF (sVWF) will undergo a conformational change from a loose tangled coil to elongated strings forming adhesive fibers by binding with other sVWF. VWF's adhesion activity is also related to its length, with the ultra-large form of VWF (ULVWF) being hyper-actively adhesive without exposure to shear stress; it has also been shown to spontaneously form fibers. We used single molecule manipulation techniques with the AFM to stretch pVWF, sVWF and ULVWF and monitor the forces as a function of molecular extension. We showed a similar increase in resistance to unfolding for sVWF and ULVWF when compared to pVWF. This mechanical resistance to forced unfolding is reduced when other molecules known to disrupt their fibril formation are present. Our results show that sVWF and ULVWF domains unfold at higher forces than pVWF, which is consistent with the hypothesis that shear stress induces lateral association that alters adhesion activity of pVWF. [Preview Abstract] |
Friday, October 23, 2009 10:24AM - 10:36AM |
B2.00003: Nano-Optical Properties of Noble Metal Nano-Arrays Fernando Monjaraz, Dipika Patel, Soyeun Park NanoSphere Lithography (NSL) is a relatively inexpensive versatile, and high throughput technique which allows us to create two dimensional (2D) periodic nanoparticle arrays. Using NSL, we successfully fabricated size-variable gold nanoparticles. We controlled sizes (16 nm to 610 nm) and spacing (115 nm to 1 $\mu $m) of patterns by varying sizes of the nano-spheres (200 nm to 1 micron). The size and spacing of the pattern can be independently controlled by adjusting the sphere deposition parameters such as deposition speed and humidity to form either a monolayer/bilayer. The heights of the nanoislands are also controlled by the deposition of gold particles. The obtained 2D gold nano-arrays are known to display the size-dependent nanoparticle optical properties. We have examined the size-dependent nano-optical properties of 2D gold nanoarrays by measuring the Localized Surface Plasmon Resonance Spectroscopy using the UV-VIS spectrometer. This systematic investigation will provide the fundamental information to use the 2D nanoarrays as nanosensors to detect the chemical and biological events. [Preview Abstract] |
Friday, October 23, 2009 10:36AM - 10:48AM |
B2.00004: Geometric Structure and Desorption Kinetics of CO on Cr$_{2}$O$_{3}$(0001)/Cr(110) Gabriel Arellano, Sy Redding, Jennifer Walters, Nicholas Clark, Simona Rieman, Heike Geisler, Carl Ventrice The Cr(110) surface is unique in that its native oxide grows epitaxially. Since understanding the adsorption and desorption kinetics of simple molecules on transition metal oxides is important for understanding catalytic phenomena, we have studied the adsorption geometry and desorption kinetics of CO on the epitaxial Cr$_{2}$O$_{3}$(0001) surface. The adsorption of CO was performed at 120 K and produced a weak ($\surd $3 x $\surd $3) R 30$^{\circ}$ reconstruction, as monitored by low energy electron diffraction (LEED). To determine the activation energy and desorption kinetics, temperature programmed desorption (TPD) measurements have been performed at heating rates of 5, 10, 25, and 50 $^{\circ}$C/min. The results of the TPD measurements indicate that the desorption is approximately 1$^{st}$ order and has an activation energy of 0.52 eV/molecule (50 kJ/mol). [Preview Abstract] |
Friday, October 23, 2009 10:48AM - 11:00AM |
B2.00005: Investigating Docking Predictions for Beta-Lactoglobulin-Porphyrin IX Complexes in Monomer and Diamer Forms James Parker Molecular docking of protein-ligand complexes are largely focused upon filtering a large database of ligands. Our goal is to determine the exact binding site(s) of a known binding ligand, porphyrin IX (PPIX), to beta-lactoglobulin (BLG) to enable better descriptions of conformational changes that occur during the binding of the ligand-protein complex as well as physical/chemical changes that occur in the presence of other stimuli such as laser-tissue heating. The first step involved examining four conformations of BLG (1 diamer, 1BEB and 3 monomers, 1BEB chain A, 1BEB chain B, and 1DV9) for use in docking with PPIX. The computed bound state for the diamer configuration placed the ligand over the gap between the two monomers. For the monomer, the ligand bound along the exposed face of the polypeptide. The relative binding strengths of the two configurations differ by 2 parts in 100. This result was verified by experiment in which the ligand bound to a diamer configuration of BLG did not precipitate out of solution when a denaturing agent was added to divide the diamer. [Preview Abstract] |
Friday, October 23, 2009 11:00AM - 11:12AM |
B2.00006: Nanoparticle Self-Lighting Photodynamic Therapy For Deep Cancer Treatment Marius Hossu, Wei Chen Photodynamic therapy (PDT) has been designated as a ``promising new modality in the treatment of cancer'' since the early 1980s. Light must be delivered in order to activate photodynamic therapy. Most photosensitizers have strong absorption in the ultraviolet (UV) -- blue range, therefore, UV -blue light is needed for their activation. Unfortunately, UV-blue light has minimal penetration into tissue and its application for \textit{in vivo} activation is a problem. Here, we introduce a new PDT system in which the light is generated by afterglow nanoparticles with attached photosensitizers. When the nanoparticle-photosensitizer conjugates are targeted to tumor, the light from afterglow nanoparticles will activate the photosensitizers for photodynamic therapy. Therefore, no external light is required for treatment. More importantly, it can be used to treat deep tumor such as breast cancer because the light source is attached to the photosensitizers and are delivered to the tumor cells all together. This new modality is refereed as \textbf{\textit{Nanoparticle Self-Lighting Photodynamic Therapy}} (NSLPDT). [Preview Abstract] |
Friday, October 23, 2009 11:12AM - 11:24AM |
B2.00007: Altering Beamline Components to Reduce the Cost of Prostate Cancer Treatment T. Jones, A. Geibler, R. Zhang, W.D. Newhauser Proton beam therapy is an advanced technique used for the control of localized cancers. Currently it is one of the most cutting edge treatment options for prostate cancer but is still scarce and expensive. The expense is due, in part, to the unique beam collimators and range compensators that are manufactured for each treatment beam. The purpose of this study is to determine whether the custom collimator could be replaced by a reusable multileaf collimator and by eliminating the range compensator. Treatment plans were retrospectively selected for 10 patients who were treated for prostate cancer with 69 Gy delivered by two proton treatment fields. The originals were altered to include the multileaf collimator and to eliminate the range compensators. The dose distributions for each plan were calculated using a treatment planning system, which uses an analytical dose algorithm. They were then verified with Monte Carlo simulations, which are able to take into account individual particle trajectories and calculate dose resulting from stray neutron exposure. The calculated dose distributions for the altered treatments were dosimetrically equal or superior to the original plans. Our findings suggest that the proton-beam treatment technique for prostate cancer could be substantially simplified, thus yielding substantial cost savings. [Preview Abstract] |
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