Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session N35: Nanophotonic Materials, Nonlinear Optics and Spectroscopy III |
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Sponsoring Units: DCP Chair: Joe Perry, Georgia Institute of Technology Room: LACC 511B |
Wednesday, March 23, 2005 8:00AM - 8:36AM |
N35.00001: Sub-cellular and Multi-cellular Signaling Mechanisms Revealed by Quantitative Laser Microscopies Invited Speaker: Newly developed instrumentation and optical probes allows us to image quantitatively dynamic processes within ever more complicated biological systems. Using methods such as fluorescence recovery after photobleaching (FRAP) and F\"{o}rster resonance energy transfer (FRET) of GFPs fused to the glucose sensing enzyme glucokinase (GK), we have discovered that the location and activity of beta cell GK is acutely regulated by insulin. These findings provide a mechanism whereby the glucose sensing ability of the beta cell is tightly coupled to insulin signaling. We have also measured pancreatic $\beta $-cell metabolism during glucose stimulation by quantitative two-photon NAD(P)H imaging. We have developed methods to delineate quantitatively the NAD(P)H signals from the cytoplasm and mitochondria, and show that the metabolic response of these two compartments are differentially stimulated by glucose and other metabolites. Absolute levels of NAD(P)H were determined using two-photon excited fluorescence lifetime imaging (FLIM). These findings elucidate the relative contributions of glycolytic and citric acid cycle metabolism in normal and diabetic cells. [Preview Abstract] |
Wednesday, March 23, 2005 8:36AM - 9:12AM |
N35.00002: Multimodal nonlinear imaging and manipulation of biomaterials Invited Speaker: Multiphoton microscopy is quickly becoming a multimodal image contrast tool. Initially, multiphoton microscopy was essentially the domain of two-photon absorption fluorescence microscopy, but with the discovery of third- harmonic microscopy and the renaissance of second-harmonic microscopy, it is becoming increasingly interesting to simultaneously exploit all of these contrast mechanisms (and more!). As the image content explodes, so too does the ability to manipulate materials within the image using these same lasers. Multicontrast, three-dimensional images and manipulation will be presented in this talk. [Preview Abstract] |
Wednesday, March 23, 2005 9:12AM - 9:48AM |
N35.00003: Experimental and Theoretical Investigation of Conformational Dynamics and Dynamic Disorder of Single Enzyme Molecules Invited Speaker: We investigate conformational fluctuation and dynamic disorder of proteins by conducting single-molecule electron-transfer and enzymatic turnover experiments. Our findings lead to new insights on how enzymes work. [Preview Abstract] |
Wednesday, March 23, 2005 9:48AM - 10:00AM |
N35.00004: Tunable resonance hyper-Raman spectroscopy of nonlinear optical chromophores Anne M. Kelley, Lian C. T. Shoute Two-photon-resonant hyper-Raman spectra have been obtained for several dipolar and octupolar donor-acceptor substituted conjugated organic chromophores that have large first hyperpolarizabilities. The excitation source is an unamplified picosecond mode-locked Ti:sapphire laser tunable from 710 to 950 nm. The hyper-Raman spectra are compared to the linear resonance Raman spectra measured at the laser second harmonic. Excitation into regions that appear to contain more than one electronic transition gives rise to different intensity patterns in the resonance Raman and hyper-Raman spectra, indicating that different transitions contribute differently to the one-photon and two-photon oscillator strength. Hyper-Raman excitation profiles have been measured on an absolute scale by using the hyper-Rayleigh from acetonitrile as an external standard, and simulated using time-dependent wavepacket propagation techniques to obtain the geometric parameters and one- and two-photon transition strengths for both states. Hyper-Raman is a promising technique for probing electronic transitions that are both one- and two-photon allowed and for examining the origins of molecular first hyperpolarizabilities. [Preview Abstract] |
Wednesday, March 23, 2005 10:00AM - 10:12AM |
N35.00005: Surface Enhanced Raman Scattering from a molecule adsorbed on a single cluster of nano metal particles Karamjeet Arya Very large enhancement up to 14 orders of magnitude in the Raman cross section from a molecule adsorbed on a single cluster of a few nano metal particles has been reported recently. The enhancement is believed mainly due to the enhanced electric field because of the excitation of the localized surface modes. We have developed a diagrammatic Green's function theory in the wave-vector space to solve the Maxwell equation for the enhanced electric field near a spherical metal particle cluster. The large enhancement in the field is due to the multiple scattering of the localized modes of the individual metal particles that has been included exactly. The advantage of working in the wave-vector space is that one does not need the use of complicated translational addition theorem required in the real space as used in earlier calculations. Therefore our approach can be easily extended to any shape or size of the metal particle cluster. We find the enhancement in the Raman cross section can reach up to 10 orders of magnitude for silver particle cluster. The enhancement is in a broad frequency range and is below the Mie resonance of the single metal sphere. The results for gold particle cluster are also presented. [Preview Abstract] |
Wednesday, March 23, 2005 10:12AM - 10:24AM |
N35.00006: SERS of DNA bases with carbohydrate stabilized silver and gold nanoparticles Vijayalakshmi Kattumuri, Meera Chandrasekhar, Suchi Guha, Kattesh Katti, Raghuraman Kannan The phenomenon of SERS using silver and gold nanoparticles has boosted single molecule spectroscopy research in recent years. Among the various techniques available for synthesizing nanoparticles, generation of carbohydrate stabilized nanoparticles has two advantages: 1) carbohydrate, a biologically benign medium, ensures non- degradation of probe molecules and 2) its gelation property facilitates easy film formation for on-chip bio-sensor applications. We studied the effect of carbohydrate stabilized silver and gold nanoparticles on SERS of DNA bases. Films of probe molecules with and without nanoparticles were casted on a silicon wafer. Comparing with the known Raman scattering cross-section of silicon, relative SERS scattering cross- sections of DNA bases are obtained. The dependence of relative strengths of SERS of DNA bases on the excitation wavelength will be discussed. This work was supported by a grant (RB03-080) from the University of Missouri Research Board, Department of Physics and Radiology. [Preview Abstract] |
Wednesday, March 23, 2005 10:24AM - 10:36AM |
N35.00007: Profiling the Near field of Nanoshells Using Surface Enhanced Raman Spectroscopy Surbhi Lal, Naomi J. Halas There is tremendous interest in the enhancement of electromagnetic fields near metal surfaces. The spatial extent of the near field as a function of distance from the metal surface is of particular interest for applications such as surface enhanced Raman spectroscopy. By using specially designed molecular scaffolds with Raman-active constituents, we measure the profile of this fringing field at a nanoshell surface. Nanoshells are colloidal particles composed of a silica core covered by a gold shell, which exhibit a tunable plasmon resonance; close to this resonance there is a strong enhancement of the electromagnetic near field. The molecular scaffolds consist of polyadenine DNA strands as tethers with a terminal fluorescein molecule. By varying the length of the DNA strand, the fluorescein molecule is placed at controlled distances from the nanoshell surface. Both the DNA scaffold and the terminal fluorescein molecule provide us with independent SERS Stokes modes whose relative intensities permit us to map the average spatial decay length of the near field of the nanoparticle at its plasmon resonance. [Preview Abstract] |
Wednesday, March 23, 2005 10:36AM - 10:48AM |
N35.00008: Single molecule sensitivity in near field tip enhanced Raman scattering Catalin C. Neacsu, Markus B. Raschke The local-field enhancement at a sharp metallic tip in combination with resonance Raman spectroscopy provides an optical scanning probe method with ultrahigh spatial resolution. Here we report on achieving sensitivity down to the single molecule level. Illuminating the apex of a Au wire tip at variable tip-sample distances down to nm proximity results in a strong field confinement and near field coupling. This provides a highly localized light source and a controlled degree of field enhancement for Raman scattering. In the tip-scattered resonance Raman response of malachite green and rhodamine 6G molecules spectral line narrowing compared to the ensemble average and spectral diffusion are seen. Temporal fluctuations of spectral position and relative peak intensities as well as transient line splitting in time series of sequentially recorded spectra are observed. The results illustrate that single molecule Raman spectroscopy can be achieved in scattering-type near-field microscopy. This approach provides the degrees of freedom necessary for a systematic investigation and understanding of the underlying mechanisms of surface-enhanced Raman spectroscopy. [Preview Abstract] |
Wednesday, March 23, 2005 10:48AM - 11:00AM |
N35.00009: Manipulating Surface Plasmons at Nanoscales for Enhancing Raman Scattering Q.-H. Wei, J. Gu, C.F. Chou, F. Zenhausern The excitation of surface plasmon resonances (SP) of noble metal nanoparticles and nanostructures results in extraordinary scattering at resonant wavelengths and local field enhancement at certain nano ``hotspots.'' Especially, when molecules are attached to these nano hotspots, the Raman signals of these molecules can be significantly enhanced, a phenomenon called surface-enhanced Raman scattering (SERS). Recent experiments revealed that at certain conditions, the Raman enhancement factor can reach 12 orders, allowing for single molecule detection. While large scale practical applications of SERS for biomolecular sensing have been prohibited by the poor reproducibility and controllability of SERS active substrates, this paper will report our recent efforts on manipulating surface plasmons on nanostructures such as nanoparticle arrays (1D and 2D), and nanotip arrays. Both experimental and numerical data will be reported on surface plasmons and SERS on these nanostructures. [Preview Abstract] |
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