Publications (11) View all
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Article: Tailoring plasmon resonances in the deep-ultraviolet by size-tunable fabrication of aluminum nanostructures
Applied Physics Letters 08/2012; 101(8):081110. · 3.84 Impact Factor -
Article: Deep ultraviolet resonant Raman imaging of a cell.
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ABSTRACT: We report the first demonstration of deep ultraviolet (DUV) Raman imaging of a cell. Nucleotide distributions in a HeLa cell were observed without any labeling at 257 nm excitation with resonant bands attributable to guanine and adenine. Obtained images represent DNA localization at nucleoli in the nucleus and RNA distribution in the cytoplasm. The presented technique extends the potential of Raman microscopy as a tool to selectively probe nucleic acids in a cell with high sensitivity due to resonance.Journal of Biomedical Optics 07/2012; 17(7):076001. · 3.16 Impact Factor -
Article: Simple and versatile route to high yield face-to-face dimeric assembly of Ag nanocubes and their surface plasmonic properties.
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ABSTRACT: We have demonstrated the higher yield dimerization of single-crystalline Ag nanocubes through preciously controlled face-selective functionalization. With the achievement of the higher yield dimerization, we could thus observe some interesting optical properties of the dimer. Both experimental and theoretical studies revealed that the 50-nm-diameter Ag nanocubes dimers with a ca. 3.3 nm gap at their junction exhibited two plasmon peaks centered at 446 nm and 600 nm, which contributed to transverse and longitudinal plasmon resonances, respectively. Elctromagnetic calculations based on the FDTD method clearly showed that a greater enhancement of the local field occurred, with an average amplitude of the electric field of 22, at the fractal space between the aggregated Ag nanocubes when the dimer was illuminated under longitudinally polarized light.Journal of Nanoscience and Nanotechnology 04/2011; 11(4):2890-6. · 1.56 Impact Factor -
Article: Deep UV resonant Raman spectroscopy for photodamage characterization in cells.
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ABSTRACT: We employed deep UV (DUV) Raman spectroscopy for characterization of molecular photodamage in cells. 244 nm light excitation Raman spectra were measured for HeLa cells exposed to the excitation light for different durations. In the spectra obtained with the shortest exposure duration (0.25 sec at 16 µW/µm(2) irradiation), characteristic resonant Raman bands of adenine and guanine at 1483 cm(-1) and tryptophan and tyrosine at 1618 cm(-1) were clearly visible. With increasing exposure duration (up to 12.5 sec), these biomolecular Raman bands diminished, while a photoproduct Raman band at 1611 cm(-1) grew. By exponential function fitting analyses, intensities of these characteristic three bands were correlated with sample exposure duration at different intensities of excitation light. We then suggest practical excitation conditions effective for DUV Raman observation of cells without photodamage-related spectral distortion.Biomedical Optics Express 01/2011; 2(4):927-36. · 2.33 Impact Factor -
Article: One-photon and two-photon excited fluorescence microscopies based on polarization-control: Applications to tip-enhanced microscopy
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ABSTRACT: One-photon and two-photon excited fluorescence microscopies using either radial or azimuthal polarization have been developed and applied to the imaging of quantum dots. In both cases (one-photon and two-photon excitations), the fluorescence image profile of each quantum dot is in good agreement with the electric field intensity distribution of a tightly focused spot using a high numerical aperture objective lens. While this polarization dependence of the absorption/emission of quantum dots (or other dye molecules) is useful for characterizing the orientation of the quantum dots, most of the biological applications that employ quantum dots or dye molecules as labels require the information describing not only the orientation but also the precise position of each dot. In order to improve the sensing accuracy of the dot’s position, we employ a modified near-field fluorescence microscopy system that utilizes a tip-enhancement technique and radially polarized two-photon excitations. For the tip enhancement, a commercially available silicon cantilever tip has been successfully utilized instead of metallic tips, as the latter tip can drastically quench the near-field fluorescence. Our tip-enhanced two-photon excited fluorescence microscopy technique enables visualization of the quantum dots distributed on a cover slip beyond the diffraction limit of light. We demonstrate that our approach is advantageous not only due to its high spatial resolution but also due to its high sensitivity by showing that the fluorescence signal is not detectable without the aid of the tip enhancement in some cases.Journal of Applied Physics 01/2010; · 2.17 Impact Factor
