Results were obtained which illustrated the use of tip-enhance Raman spectroscopy (TERS) and imaging in a novel top illumination geometry. A radially polarized beam was used to generate an electric field component in the direction of beam propagation, normal to the surface, resulting in a five times enhancement compared to a linearly polarized beam. This multiplicative enhancement facilitates a discrimination of the near-field signal from the far-field Raman background. The top illumination configuration allows the application of TERS for investigating molecules on a variety of surfaces, such as gold, glass and silicon. The near field Raman spectra of a variety of materials, including single wall carbon nanotubes, were examined. Sufficient enhancement was obtained to permit the obtaining of a sub-diffraction resolution hyperspectral Raman imaging cube of the surface distribution of large bundles of carbon nanotubes of varying diameter. To further facilitate nanoparticle enhanced Raman imaging of complex biological specimens, the use of higher laser order modes with radial and azimuthal polarizations focused onto a gold nanoparticle AFM tip was explored using a back-scattering microscope configuration. In particular, the radial polarized configuration provided enhanced spatial resolution. This is a consequence of the direction of the induced electron oscillation in the metal nanoparticle, which is oriented by the electromagnetic field at the laser focus. Specifically, the directionality of the electromagnetic enhancement is critical such that the molecule under observation experiences the greatest enhanced field at the apex of the nanostructure tip. These results indicate the potential for TERS to provide insights in molecular distributions on the nanoscale, as, for example, those systems representative of diseased states.

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Howard, Frank B; Levin, Ira W (2010) Lipid vesicle aggregation induced by cooling. Int J Mol Sci 11:754-61
Chen, Tsoching; Schultz, Zachary D; Levin, Ira W (2009) Infrared spectroscopic imaging of latent fingerprints and associated forensic evidence. Analyst 134:1902-4
Schultz, Zachary D; Pazos, Ileana M; McNeil-Watson, Fraser K et al. (2009) Magnesium-induced lipid bilayer microdomain reorganizations: implications for membrane fusion. J Phys Chem B 113:9932-41
Schultz, Zachary D; Stranick, Stephan J; Levin, Ira W (2009) Advantages and artifacts of higher order modes in nanoparticle-enhanced backscattering Raman imaging. Anal Chem 81:9657-63
Chen, Tsoching; Lee, Min-Jung; Kim, Yeong Sang et al. (2008) Pharmacodynamic assessment of histone deacetylase inhibitors: infrared vibrational spectroscopic imaging of protein acetylation. Anal Chem 80:6390-6
Crane, Nicole J; Pinto, Peter A; Hale, Douglas et al. (2008) Non-invasive monitoring of tissue oxygenation during laparoscopic donor nephrectomy. BMC Surg 8:8
Crane, Nicole J; McHone, Ben; Hawksworth, Jason et al. (2008) Enhanced surgical imaging: laparoscopic vessel identification and assessment of tissue oxygenation. J Am Coll Surg 206:1159-66
Schultz, Zachary D; Stranick, Stephan J; Levin, Ira W (2008) Tip-enhanced Raman spectroscopy and imaging: an apical illumination geometry. Appl Spectrosc 62:1173-9
Schultz, Zachary D; Levin, Ira W (2008) Lipid microdomain formation: characterization by infrared spectroscopy and ultrasonic velocimetry. Biophys J 94:3104-14