Bulletin of the American Physical Society
2008 Joint Fall Meeting of the Texas and Four Corners Sections of APS, AAPT, and Zones 13 and 16 of SPS, and the Societies of Hispanic & Black Physicists
Volume 53, Number 11
Friday–Saturday, October 17–18, 2008; El Paso, Texas
Session H2: Biological and Chemical Physics |
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Chair: Karine Chesnel, Brigham Young University Room: Union East, 3rd Floor Templeton |
Saturday, October 18, 2008 10:30AM - 10:54AM |
H2.00001: Emergence and Evolution of Order in Physical, Chemical, and Biological Systems Invited Speaker: Do the Great Red Spot of Jupiter and the spirals in a frog egg have anything in common? The sizes are vastly different and the biology of even a simple frog egg is far more complicated than the physics of a fluid. Yet the patterns formed in such systems, differing widely in scale and in the underlying molecular mechanisms, can in many cases be understood from a common approach. [Preview Abstract] |
Saturday, October 18, 2008 10:54AM - 11:06AM |
H2.00002: Nanoscale High Aspect Ratio Structures Jonathan Abbott, Robert Davis, Richard VanFleet, Hiram Conley Nanoscale high aspect ratio structures have possible applications in microfluidic channels, batteries, and fuel cells, among others. We present methods we have been trying to create 3:1 aspect ratio structures in transparent materials that will withstand temperatures needed for CVD or ALD processes; including contact molding, spin and etch back, and replica molding. [Preview Abstract] |
Saturday, October 18, 2008 11:06AM - 11:18AM |
H2.00003: Toward Nanoscale Fluorescence Microscopy of Biological Systems Jordan Gerton, Ben Mangum, Chun Mu, Eyal Shafran Fluorescence microscopy is a very powerful imaging technique in the biological sciences because of its ability to detect and identify individual molecules. The spatial resolution of traditional optical microscopy, however, is limited to $\sim $250 nm (in the visible spectrum) due to light diffraction. Thus, traditional optical microscopy is of limited utility for studying the molecular-scale architecture of biological systems where the fundamental length scale is on the order of 10 nm, the size of the constituent proteins. We have developed a technique that uses the enhanced optical intensity at the tip of an illuminated needle to surpass the diffraction limit with the goal of elucidating the relationship between the structure and function of protein networks embedded in biological membranes. We have used this microscope to image nanocrystal quantum dots and end-labeled DNA oligomers with spatial resolution of $\sim $10 nm. We are now working to improve the microscope contrast so that it can be applied to dense networks of biological molecules where the background signal will be high. We are also investigating single-wall carbon nanotubes as potential nano-optical probes to study energy transfer between fluorophores in molecular networks of importance for photovoltaic applications. [Preview Abstract] |
Saturday, October 18, 2008 11:18AM - 11:42AM |
H2.00004: Regulating gene-expression by mechanical force Invited Speaker: Initiation of transcription is an attractive target for controlling gene expression. Initiation typically involves binding of RNA polymerase to the DNA, followed by a rapid transition into a ``closed'' complex, and a subsequent transition into the ``open'' complex in which the DNA is locally melted. Nature makes good use of this target, for example in the form of repressor proteins that bind DNA and inhibit transcription. Here we will show that initiation of transcription is also dependent upon DNA tension and thus may be controlled by force alone, without the need for any accessory proteins. Using a three-bead assay in conjunction with optical tweezers we have shown that transient interactions of T7 RNA polymerase with the DNA promoter site shorten significantly, by up to a factor of $\sim$20, when DNA tension is increased. Experiments in the presence and absence of nucleotides have allowed us to conclude that force is likely to affect the rate constants into and/or out of the open complex, rather than the off-rate from the closed complex. [Preview Abstract] |
Saturday, October 18, 2008 11:42AM - 11:54AM |
H2.00005: Fluorescence decay dynamics of surface-functionalized nanoparticles Jacob Ajimo, Lun Ma, Mingzhen Yao, Xing Zhang, John Como, Louisa Hope-weeks, Juyang Huang, Wei Chen, Kwan Cheng We report the fluorescence decay dynamics of surface-functionalized nanoparticles (NPs), poly(ethylene glycol) bis(carboxymethyl) ether coated LaF$_{3}$: Ce,Tb and thioglycolic acid coated ZnS:Mn, in solution and also in the surface-bound phase. The NPs exhibited high quantum yield and multi-component decays, and of average lifetime of 20-130 microseconds in solution, but 10-60 microseconds in the bound phase depending on the solid substrates. Our results suggest that the coated ZnS:Mn nanoparticles hold great promise as a non-toxic labeling agent for ultra-sensitive, time-gated, trace biomaterials detections in nano-forensic applications. [Preview Abstract] |
Saturday, October 18, 2008 11:54AM - 12:06PM |
H2.00006: In-Situ Laser Tagging of $^{136}$Ba$^{+ }$Ions in a Liquid $^{136}$Xe Detector Kendy Hall, Cesar Benitez, William Fairbank Our group is working in partnership with the Enriched Xenon Observatory (EXO) collaboration to measure the effective Majorana mass of neutrinos with a sensitivity of 0.01eV in a ton size liquid $^{136}$Xe detector. The only way to achieve such sensitivity is by neutrinoless double beta decay (00$\nu \beta )$ with tagging of the $^{136}$Ba$^{+}$ daughter ion at the decay site. At CSU, we are developing a new fluorescence technique for in-situ laser tagging of a single $^{136}$Ba$^{+}$ ion in liquid Xe. Laser ablation is used to implant approximately 10$^{8}$ Ba$^{+}$ ions per pulse into a liquid xenon cell. In the past we have been troubled with inconsistencies in our fluorescence spectra, which may be due to impurities or unknown particles within our liquid Xe. To understand these problems, a liquid xenon recirculation system and purity monitor has been built. Purity levels of ppb can now be measure in our liquid xenon system. I will present possible emission spectra of Ba$^{+}$ ions in liquid xenon and discuss how they correlate with the liquid xenon purity. [Preview Abstract] |
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