Bulletin of the American Physical Society
Joint Fall 2010 Meeting of the Texas Sections of the APS, AAPT, Zone 13 of SPS and the National Society of Hispanic Physicists
Volume 55, Number 11
Thursday–Saturday, October 21–23, 2010; San Antonio, Texas
Session FA3: Biological and Chemical Physics II |
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Chair: Robert Thomas, Air Force Research Laboratory Room: University Center I Pecan Room, 2nd floor |
Friday, October 22, 2010 3:00PM - 3:12PM |
FA3.00001: Automatic quantification of early transition points in biofilm formation Travis Thatcher, Samuel Bienvenu, Shinji Strain, Vernita Gordon Biofilms are multicellular, dynamic communities of interacting single-cell organisms, like bacteria. Biofilms are responsible for many infectious diseases as well as for significant damage in industrial settings, yet many aspects of biofilm formation are not well understood. Identifying and quantifying the interactions leading to biofilm formation will not only be important for understanding the basic science of these and other multicellular systems, but it will also be essential for designing targeted strategies to prevent or disrupt biofilms. In particular, it is not clear what physical interactions, and corresponding biological mechanisms, are responsible for the early steps in biofilm formation. Because of this, we are developing high-throughput software techniques to analyze micrograph movies of biofilm formation, from attachment to surfaces through the development of microcolonies. This work will focus on developing software tools to identify and quantify key steps in biofilm formation, first in non-chemotacting systems and later in chemotacting (and autotacting) systems. [Preview Abstract] |
Friday, October 22, 2010 3:12PM - 3:24PM |
FA3.00002: NanoSphere Lithography-Based Micro/Nano-patterning techniques of polymer brushes. Fernando Monjaraz, Dipika Patel, Soyeun Park The fabrication of micro/nano-patterned polymer brushes has been a challenge due to unique interfacial properties originated from the strong confinement and the dominant edge effects. We have developed unique bottom-up fabrication to synthesize polymer brushes grafted on the nanoparticle arrays created by NanoSphere Lithography (NSL). We used spin-coating and capillary action deposition to create the nano-particle arrays. Through UV-driven living radical polymerization, based on iniferters selectively coupled on nanoislands, the poly-DMA chains were grown from nano-particle arrays. The superimposed patterns were transferred using conventional photo-lithography. AFM topographic images showed the swelling behavior of polymer chains in good solvents, confirming the selective growth of polymers on nanoislands. We also found that the mechanical and kinetic properties of polymer brushes grafted on nanoislands are strongly governed by dominant edge effects by analyzing the AFM force spectroscopy. [Preview Abstract] |
Friday, October 22, 2010 3:24PM - 3:36PM |
FA3.00003: Utilizing E. coli Autotactic Responses to Understand Quorum Dependent Behaviors in P. aeruginosa Shinji Strain, Samuel Bienvenu, Travis Thatcher, Vernita Gordon Biofilms are multicellular, surface-bound communities of interacting unicellular organisms. In the initial stages of biofilm formation, cells populate the surface and eventually form microcolonies (dense surface-bound clusters of cells). How much these microcolonies arise from clonal growth and how much they arise from attraction and binding of non-clonal cells is not well-understood. A potentially important form of attraction is autotaxis, movement of cells toward like cells. Using microscopy and automated tracking and analysis algorithms, we will study how bacteria respond to each other in a spatially-dependent manner. We will determinine how variations in neighbor density and arrangement stimulate changes in cell motility. E. coli will be our initial model system, and later we will probe early biofilm formation in P. aeruginosa. We will also study chemotaxis (motility toward an attractive chemical), to understand how this drives, complements, or competes with autotaxis in different settings. [Preview Abstract] |
Friday, October 22, 2010 3:36PM - 3:48PM |
FA3.00004: Photo-Thermal Ablation of Single Neurons Using Gold Nanostars Zurab Kereselidze, Victor Romero, Waskar Egido, Christopher Valdes, Emmanuel Michaelides, Xomalin Peralta, Miguel Jose-Yacaman, Fidel Santamaria Nanoparticle mediated photo-thermal ablation therapy is a promising technique for the treatment of multiple illnesses. It has been characterized in bulk tissue, but little is known about its effects at the single-cell level. Photo-thermal ablation works by exciting the surface Plasmon resonance of metal nanoparticles to cause an amplification of the absorption of the incident electromagnetic field, which is transformed into heat through various processes. We have fabricated gold nanostars with a surface plasmon mode in the near infrared via a modified seed-mediated method. Neurons from mouse cerebellar slices internalize the bare nanostars during incubation periods of $<$ 3 hrs. Using a two-photon microscope, we imaged the tissue slices and excited the surface plasmon mode of the nanoparticles. Our results show that we are capable of destroying individual nanostar containing cells without affecting their neighbors. Therefore nanostars can provide a technique for single-cell photo-thermal ablation of neurons with no functionalization. [Preview Abstract] |
Friday, October 22, 2010 3:48PM - 4:00PM |
FA3.00005: Measuring Forces of Bacterial Biofilms on Substrates Benjamin Cooley, Vernita Gordon Biofilms are multicellular aggregates of microorganisms with distinct gene expression and often complex spatial structure. Understanding the forces exerted by bacterial biofilms on their substrates could help in understanding damage they cause in industrial settings and to living tissue in biofilm infections. Here we propose a series of experiments to study the forces between biofilms and substrates using rheological and micro-rheological techniques. Polystyrene tracer beads embedded in agar gels can be mapped over the course of biofilm development, and these timelapse motions will show the strain in the substrate. Meanwhile, measurements of the Brownian motion of selected tracer beads can yield information about the microstructure of the agar. For instance, the extent of the Brownian motion will be increased if the agar is stretched apart or broken down. Additionally, tracers in the biofilms themselves would permit the study of the rheology of the biofilms throughout their development. [Preview Abstract] |
Friday, October 22, 2010 4:00PM - 4:12PM |
FA3.00006: Using a Microwave Resonant Cavity to Study Hydrogen Bonding at Phase Transition in H$_{2}$O and D$_{2}$O James Roberts, Jai Dahiya The resonant microwave cavity is a very sensitive device for detecting small changes in material properties as they are perturbed by temperature, electric and magnetic fields. In this laboratory all states of mater have studied with the resonant cavity, including the plasma state. In this paper we report on an experiment with water as it changes from liquid (disordered) to water ice (ordered) phase. In that hydrogen bonds are involved n this process, we are able to observe behavior in the dielectric response of H$_{2}$O as it is cycled from solid to liquid. The transition through the densest state of water near 4$^{\circ}$C indicates that the order of the water molecules in the ice phase is less than that experienced at the most dense temperature of water. If we associate this density with the interaction of the hydrogen bonds, it can be postulated that the distribution of the structure in snowflakes is a consequence of random processes in sharing the hydrogen bonds as the system cycles from the disordered state to the more ordered state. Phase transition from liquid to solid and solid to liquid was studied for H$_{2}$O and D$_{2}$O. It is expected that the bonding of the two molecules will behave the same during the transition from ordered to disordered states and in the reverse transition. The apparatus used in this investigation will be discussed. [Preview Abstract] |
Friday, October 22, 2010 4:12PM - 4:24PM |
FA3.00007: Chemotaxis in P. Aeruginosa Biofilm Formation Samuel Bienvenu, Shinji Strain, Travis Thatcher, Vernita Gordon Pseudomonas biofilms form infections in the lungs of Cystic Fibrosis (CF) patients that damage lung tissue and lead to death. Previous work shows chemotaxis is important for Pseudomonas in CF lungs. The work studied swimming bacteria at high concentrations. In contrast, medically relevant biofilms initiate from sparse populations of surface-bound bacteria. The recent development of software techniques for automated, high-throughput bacteria tracking leaves us well-poised to quantitatively study these chemotactic conditions. We will develop experimental systems for such studies, focusing on L-Arginine (an amino acid), D-Galactose (a sugar present in lungs), and succinate and glucose (carbon sources for bacteria). This suite of chemoattractants will allow us to study how chemoattractant characteristics--size and diffusion behavior--change bacterial response; the interaction of competing chemoattractants; and, differences in bacterial behaviors, like motility modes, in response to different types of chemoattractions and varying neighbor cell density. [Preview Abstract] |
Friday, October 22, 2010 4:24PM - 4:36PM |
FA3.00008: AFM-based nano-mechanical clues for cancer metastasis Lyndon Bastatas, Raul Martinez-Zaguilan, Soyeun Park We have evaluated if the nano-biomechanical properties of cells with distinct metastatic potential could provide a reliable indicator of cancer progression using lowly (LNCaP) and highly (CL1) metastatic prostate cancer cells. From the AFM force-distance curves, we determined the cellular elastic moduli and adhesiveness in the local nano-domain of cells by applying the standard Hertz model and the advanced models. Using the AFM force spectroscopy, the two dimensional topographic, elastic, adhesive maps of an individual cell were successfully delineated. We found that the elastic moduli in CL1 are higher than in LNCaP. These results are paradoxical since greater cell deformability -hence low elastic moduli- is needed for highly metastatic cells to intra/extra-vasate for metastasis to ensue. However, our result also showed that CL1 strongly adheres on the substrate while the LNCaP poorly adheres. We postulate that the tensional force originated from the enhanced adhesion generates higher cortical tension, elicit dynamic intracellular calcium transit, and lead to the highly metastatic behavior. [Preview Abstract] |
Friday, October 22, 2010 4:36PM - 4:48PM |
FA3.00009: Interactions and transitions in biofilm formation Vernita Gordon, Kelly Colvin, Jacinta Conrad, Maxsim Gibiansky, Fan Jin, Matthew Parsek, Gerard Wong Biofilms are multicellular, interacting communities of intrinsically-unicellular organisms that grow on surfaces. As such, they are fascinating model systems for multicellularity. They are also of great practical importance, since biofilms damage a variety of industrial infrastructure and are the cause of most persistent, antibiotic-resistant infections. In natural settings, most bacteria are found in biofilms. To initiate a biofilm, planktonic, free-swimming bacteria attach to a surface and then undergo a series of phenotypic changes as that adhesion becomes irreversible and the surface is populated, first by discrete bacteria, and then bacteria growing in dense clusters, ``microcolonies.'' Both adhesion to a surface and adhesion to other cells are associated with adhesive properties of cell-produced extracellular polysaccharides (EPSs). Using laser tweezers to test cell aggregation and aggregate stability, in combination with gene expression assays and gene-knockouts, we show the importance of one EPS, pel, for early cell aggregation. We also use automated bacteria-identification and --tracking software algorithims to identify and quantify key transitions early in biofilm formation. [Preview Abstract] |
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