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4 Jun 2007

Volume 90, Issue 23, Articles (23xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 233105 (2007); http://dx.doi.org/10.1063/1.2747052 (3 pages)

Youhui Gao, Daisuke Shindo, Yuping Bao, and Kannan Krishnan
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In situ assembled diffraction grating for biomolecular detection

Chun-Li Chang, Ghanashyam Acharya, and Cagri A. Savran

Appl. Phys. Lett. 90, 233901 (2007); http://dx.doi.org/10.1063/1.2746409 (3 pages) | Cited 10 times

Online Publication Date: 5 June 2007

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The authors report experiments with a diffraction-based biosensor based on self-assembly of target-containing nanobeads that form optical diffraction gratings. They demonstrate that the diffraction signal is a function of the bead size, and that noise is minimized by normalizing the intensities of the diffraction modes. They characterize the dependence of the diffraction signal on equivalent bead size and demonstrate the potential of the scheme in detecting biologically significant molecules.
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87.85.Qr Nanotechnologies-design
87.85.Rs Nanotechnologies-applications
87.80.-y Biophysical techniques (research methods)
87.15.-v Biomolecules: structure and physical properties
42.79.Gn Optical waveguides and couplers
42.79.Dj Gratings
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Hydration dynamics of oriented DNA films investigated by time-domain terahertz spectroscopy

C. Kistner, A. André, T. Fischer, A. Thoma, C. Janke, A. Bartels, T. Gisler, G. Maret, and T. Dekorsy

Appl. Phys. Lett. 90, 233902 (2007); http://dx.doi.org/10.1063/1.2743401 (3 pages) | Cited 11 times

Online Publication Date: 6 June 2007

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The B to A conformational transition of highly oriented DNA films due to a hydration change is observed with time-domain terahertz spectroscopy. Wet-spun films of calf thymus and salmon DNA are investigated for different film thicknesses and for different polarizations of the terahertz radiation relative to the DNA orientation. A clear polarization dependence is observed. Asynchronous optical sampling allows recording of terahertz absorption and background spectra in a few 10 s, permitting the tracking of the dehydration dynamics on a time scale of minutes. The observation of a phase transition is corroborated by Raman spectroscopy.
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87.15.M- Spectra of biomolecules
87.14.G- Nucleic acids
33.20.Bx Radio-frequency and microwave spectra
33.20.Fb Raman and Rayleigh spectra (including optical scattering)

Highly sensitive sensors for alkali metal ions based on complementary-metal-oxide-semiconductor-compatible silicon nanowires

Guo-Jun Zhang, Ajay Agarwal, Kavitha D. Buddharaju, Navab Singh, and Zhiqiang Gao

Appl. Phys. Lett. 90, 233903 (2007); http://dx.doi.org/10.1063/1.2746962 (3 pages) | Cited 8 times

Online Publication Date: 6 June 2007

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Highly sensitive sensors for alkali metal ions based on complementary-metal-oxide- semiconductor-compatible silicon nanowires (SiNWs) with crown ethers covalently immobilized on their surface are presented. A densely packed organic monolayer terminated with amine groups is introduced to the SiNW surface via hydrosilylation. Amine-modified crown ethers, acting as sensing elements, are then immobilized onto the SiNWs through a cross-linking reaction with the monolayer. The crown ether–functionalized SiNWs recognize Na+ and K+ according to their complexation ability to the crown ethers. The SiNW sensors are highly selective and capable of achieving an ultralow detection limit down to 50 nM, over three orders of magnitude lower than that of conventional crown ether–based ion-selective electrodes.
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85.30.-z Semiconductor devices
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