Browsing by Author "Tanwar, S."

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    DNA Origami Directed Au Nanostar Dimers for Single-Molecule Surface-Enhanced Raman Scattering
    (American Chemical Society, 2017) Tanwar, Swati; Haldar, Krishna Kanta; Sen, Tapasi; Tanwar, S.; Haldar, K.K.; Sen, T.
    We demonstrate the synthesis of Au nanostar dimers with tunable interparticle gap and controlled stoichiometry assembled on DNA origami. Au nanostars with uniform and sharp tips were immobilized on rectangular DNA origami dimerized structures to create nanoantennas containing monomeric and dimeric Au nanostars. Single Texas red (TR) dye was specifically attached in the junction of the dimerized origami to act as a Raman reporter molecule. The SERS enhancement factors of single TR dye molecules located in the conjunction region in dimer structures having interparticle gaps of 7 and 13 nm are 2 ? 1010 and 8 ? 109, respectively, which are strong enough for single analyte detection. The highly enhanced electromagnetic field generated by the plasmon coupling between sharp tips and cores of two Au nanostars in the wide conjunction region allows the accommodation and specific detection of large biomolecules. Such DNA-directed assembled nanoantennas with controlled interparticle separation distance and stoichiometry, and well-defined geometry, can be used as excellent substrates in single-molecule SERS spectroscopy and will have potential applications as a reproducible platform in single-molecule sensing. ? 2017 American Chemical Society.
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    One-Pot Synthesis of Au Embedded ZnO Nanorods Composite Heterostructures with Excellent Photocatalytic Properties
    (Wiley-Blackwell, 2018) Haldar, K.K.; Biswas, R.; Tanwar, S.; Sen, T.; Lahtinen, J.
    Here, we have designed a noble composite nanostructure by embedding gold (Au) nanoparticles into zinc oxide (ZnO) nanorods surface in one pot synthesis as a photocatalyst. The formation the composite nanostructure was confirmed by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy and transmission electron microscopy investigations. Microscopic studies suggest that spherical Au nanoparticles are nucleated on the ZnO nanorods surface. XPS shows shifting of peak positions towards higher binding energy which indicates charge transfer from ZnO to Au in the composite nanostructures. This is unambiguously confirmed by the steady state spectroscopic studies. It was found that 95.7% (1.8 × 10?5 mM) of Methylene blue dye is degraded by the composite nanostructure after 140 min under UV light illumination and the apparent rate constant was found to be 0.015 min?1. This new class of Au nanoparticles embedded ZnO nanorods composite nanostructure opens up new possibilities in photocatalytic, solar energy conversion, photovoltaic, and other new emerging applications.