Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session B28: Experimental Techniques in Biomaterials Science |
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Sponsoring Units: DBP Chair: Kevin Hewitt, Dalhousie University Room: Baltimore Convention Center 325 |
Monday, March 13, 2006 11:15AM - 11:27AM |
B28.00001: Dual-beam Oscillating Optical Tweezers-Based 3-D Confocal Microrheometer Jing Wang, Chuan Pu, H. Daniel Ou-Yang Optical tweezers are widely used in the studies of complex fluids and biological cells and tissues. Confocal microscopy visualizes detailed structures of sample specimen with high resolution in 3-D. In this report, we present the setup, calibration and application of a new powerful microrheometer that integrates a novel high temporal and spatial resolution dual-beam oscillating optical tweezers cytorheometer (DOOTC) with spinning disk confocal microscopy. The DOOTC uses the less photodamaging 1064nm laser, and detects the forced oscillatory particle motions by a lock-in amplifier. It can operate at single oscillating beam mode or the orthogonally polarized dual-beam mode to get large deflected forward scattering signals at both high and low frequencies. The system is demonstrated to identify granular structures trapped by optical tweezers with confidence, and at the same time measure dynamic mechanical modulus in the frequency range of 0.1-3000Hz at up to 10 data point per second and with sub-nanometer spatial resolution, while monitoring the sample structure and its transformation \textit{in situ. } [Preview Abstract] |
Monday, March 13, 2006 11:27AM - 11:39AM |
B28.00002: Integrated Fiber-optic Dipping-probe Microfluorometer Robert W. Gammon, Vildana Hodzic, Christopher C. Davis An integrated fiber-optic device has been built that is with multimode fiber and found to exhibit exceptional performance as a dipping probe microfluorometer. This was discovered in the course of testing its performance using the device with simple, cleaved fibers. Thus the fiber both excites and collects fluorescence from the fluid along the axis direction in solutions of dye. The novel feature is that the light is restricted to coming from a region very near the end of the cleaved fiber. It then lends itself to testing very small volumes of sample fluid for fluorescence. Since the probe is a 200 micron diameter multimode fiber is can easily fit into small capillaries and also be stuck into small drops of sample fluid, i.e. drops sitting in microwell in multi-well test plates. Because the device uses an avalanche photodiode, the sensetivity is high and has a large dynamic range (4 to 6 orders of magnitude). The combination of small diameter, flexible fibers with high effeciency of exciting and collecting of fluorescence, and a sensitive detector makes this device unique. There is nothing on the commercial market or literature like it. Most devices that are called fiber-optic fluormeters use stiff fibers of diameter about 1 mm or larger (rods, really). They ususally excite through one of more fibers and collect through nearby fibers. The collection efficiency is low and the net diameters are far too large to allow use with microliter samples. [Preview Abstract] |
Monday, March 13, 2006 11:39AM - 11:51AM |
B28.00003: Characterization of RNase Immobilization at Surfaces by NEXAFS Xiaosong Liu, Chang-Hyun Jang, Fan Zheng, Astrid Jurgensen, Nicholas L. Abbott, F.J. Himpsel Immobilization of proteins at surfaces plays an increasingly-important role for applications in biosensors and biochips, bioelectronics, bio-compatible implants, and biomimetic devices. In this study, Ribonuclease A (RNase A) is immobilized on silver surfaces in oriented and random form via self-assembled monolayers (SAMs) of alkanethiols as described previously.$^{[1]}$ The immobilization process is characterized step by step using chemically-selective near edge x-ray absorption fine structure spectroscopy (NEXAFS) at the C, N, and S K-edges. Oriented protein layers exhibit a small, but distinct polarization dependence of the N1s to $\pi $* orbital that is delocalized over O=C-NH, which is not seen for random orientation. They also have higher coverage. Oxidation and partial desorption of the alkanethiol SAMs are found to be predominant causes of imperfect immobilization. The results show how NEXAFS is able to provide feedback for optimizing the immobilization of proteins. [1] Luk, Y.-Y.; Tingey, M. L.; Dickson, K. A.; Raines, R. T.; Abbott, N. L. \textit{Journal of the American Chemical Society }\textbf{2004,} 126, (29), 9024. [Preview Abstract] |
Monday, March 13, 2006 11:51AM - 12:03PM |
B28.00004: Surface-enhanced Raman scattering of a hydrophilic ligand (tiopronin) adsorbed on gold nanoparticles. Joel St.Aubin, Kevin Hewitt Surface enhancement of the Raman signal derived from tiopronin coated gold nanoparticles was observed. The gold nanoparticles were synthesized to mean diameters of 40 nm and 130 nm. Enhancement greater than 360 times was measured for the 40 nm gold nanoparticles and greater than 500 times for the 130 nm particles. New phonon modes appear that are possibly due to electric field gradient effects. Experiments to partially substitute tiopronin with a small fraction of hydrophobic thiols are underway. Surface-enhanced Raman scattering studies of these mixed (hydrophobic/hydrophilic) ligands will be reported. [Preview Abstract] |
Monday, March 13, 2006 12:03PM - 12:15PM |
B28.00005: Employing Grating Couplers in Biosensors Amal Kasry, Wolfgang Knoll Grating couplers have become very important tool in developing optical biosensors. In this work, surface plasmon polaritons excited by a dye molecule on the surface of a grating were studied. These polaritons can couple out to bulk radiation by scattering from the grating, and the emitted light comes off in certain well-defined directions. We focused here in studying how the coupling between the emitted light of a chromophore at the surface of a metallic grating and the scattered surface plasmons depends on the chromophore-metal separation. This was done using a protein layer-by-layer system as a spacer between the metal and the dye. The results show that the back coupling efficiency is maximum at distance about 30-50 nm, which is also the optimum distance for the fluorescence intensity. These results agree with the results determined on a planar metallic surface, and the behavior of the fluorescence was proved to be the same in different media (air or liquid). It was also proved that the back coupling could still be seen at the high distance reached here (106 nm), where the surface plasmon can scatter till this high distance. [Preview Abstract] |
Monday, March 13, 2006 12:15PM - 12:27PM |
B28.00006: 15nm diameter upconversion nanophosphors as bio-labels. Shuang Fang Lim, Robert Riehn, Chih-kuan Tung, Robert H. Austin, Nora Khanarian, William S. Ryu, David Tank We have synthesized 15 nm diameter yttrium oxide based nanophosphors that are capable of visible to infrared upconversion. We show that these phosphors can be used for dual-mode imaging of biological systems by observing visible emission under both infrared excitation, and electron excitation in a scanning electron microscope. We have investigated the optical properties, confirmed the 2-photon nature of the upconversion process, and verified that similar narrow band emission spectra are obtained under electron and infrared excitation. We will also report on progress in surface functionalization for targeted bio-labeling . We demonstrate that biocompatibility is sufficient for in-vivo imaging in the nematode worm C. Elegans, and locate phosphors with high spatial resolution using energy dispersive X-ray imaging in scanning electron microscope. [Preview Abstract] |
Monday, March 13, 2006 12:27PM - 12:39PM |
B28.00007: Thermal Stability, and Curvature Dependence of Bovine Serum Albumin on Gold Nanoparticles Using Localized Surface Plasmon Resonance Jonathan Teichroeb, James Forrest, Valentina Ngai Gold nanoparticles exhibit Surface Plasmon Resonance (SPR), whose absorption peak is strongly dependent on the index of refraction, and coating thickness of the near surface region. A macromolecule bound to the nanoparticle will typically undergo a shift in index of refraction as its conformation changes, leading to a shift in the peak wavelength. Nanospheres can be made with a large variety of diameters, and present a novel method of looking at curvature dependencies of stability. In this study, Bovine Serum Albumin (BSA) was conjugated to Au nanospheres. Using a visible absorption spectrometer, the peak wavelength vs. temperature for eight diameters from 5nm to 60nm, was collected. Diameters above 20nm exhibited a continual increase in peak wavelength with temperature. Theoretical calculations indicate that this is a thickening of the protein layer. Below 20nm, peak wavelength shifts indicated a thinning of the BSA layer, and possible a decrease in index of refraction, followed by thickening at higher temperatures. Additionally, the study indicates that the peak shifts are highly time dependent, and a kinetic study has been performed at several temperatures. [Preview Abstract] |
Monday, March 13, 2006 12:39PM - 12:51PM |
B28.00008: High Q RF Resonant Cavity for Detecting Biological Tissue Nonlinearities Vildana Hodzic, Robert W. Gammon, Quirino Balzano, Christopher C. Davis To investigate whether biological cells exhibit nonlinearity in the radiofrequency (RF) region, a high quality factor resonant cavity has been built. The cavity is fitted with two loop antennas, one transmitting at 880-890 MHz and a second one receiving at 1760-1790 MHz. The antenna operating at the low frequency (LF) band actively excites the TE$_{111}$ cavity mode; the high frequency antenna must receive the energy of the TE$_{113}$ mode at twice the frequency of the LF antenna. The cavity and the two antennas have been built. The Q of the cavity is over 6000 for both the frequencies of operation. Experiments to detect nonlinear RF frequency conversion by biological tissue can be performed using this high quality factor device. [Preview Abstract] |
Monday, March 13, 2006 12:51PM - 1:03PM |
B28.00009: Micromachined piconewton force sensor for biophysics investigations Steven Koch, Gayle Thayer, Alex Corwin, George Bachand, Maarten de Boer We describe a polysilicon surface-micromachined force sensor that is able to measure forces as small a few pN in both air and water. The simple device consists of compliant springs with force constants as low as 0.3 mN/m and Moire patterns for nanometer-scale optical displacement measurement. First, we measured the force field produced by an electromagnet on individual 2.8 micron magnetic beads glued to the force sensor. Forces matched predictions from finite element magnetic modeling and provided a calibration for future biophysical applications of the magnet. By repeating with several different beads, we measured a 9 percent standard deviation in saturation magnetization. We also demonstrated that the force sensor was fully functional when immersed in aqueous buffer and when performing the kinesin inverted motility assay on the sensor surfaces. These results show the force sensors can be useful for calibrating magnetic forces on magnetic beads and also for direct measurement of biophysical forces on-chip. [Preview Abstract] |
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