Department of Chemistry

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Author: search.filters.author.Pande, SurojitSubject: search.filters.subject.Molecules

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    Dopamine Molecules on Aucore−Agshell Bimetallic Nanocolloids: Fourier Transform Infrared, Raman, and Surface-Enhanced Raman Spectroscopy Study Aided by Density Functional Theory
    (ACS, 2009) Pande, Surojit
    Adsorption of dopamine (DA) on a Aucore−Agshell bimetallic nanocolloidal surface has been investigated using surface-enhanced Raman spectroscopy (SERS). The normal Raman spectra (NRS) of DA molecules in bulk and in aqueous solution have been investigated in depth. The vibrational signatures, as observed from the Raman and FTIR spectra of the molecule, have been assigned from the potential energy distributions. The pH-dependent NRS of the DA molecule in aqueous solution has been recorded to elucidate the protonation effect and preferential existence of different forms of the molecule. The pH-dependent SERS spectra of the molecule adsorbed on the bimetallic Aucore−Agshell nanocolloidal surface are also reported. The enhancement of bands in the pH-dependent SERS spectra suggests that the molecules are adsorbed onto the bimetallic Aucore−Agshell surface with the molecular plane tilted with respect to the silver surface of Aucore−Agshell bimetallic nanoparticles. The model study authenticates the spectral disposition and orientation of the molecule. Thus, experiment and theory keep abreast of the variety of DA structures envisaged from SERS studies on a new substrate.
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    Understanding the Enhancement Mechanisms in the Surface-Enhanced Raman Spectra of the 1,10-Phenanthroline Molecule Adsorbed on a Au@Ag Bimetallic Nanocolloid
    (ACS, 2011-05-11) Pande, Surojit
    Adsorption of 1,10-phenanthroline (PHEN) on the Aucore–Agshell (Au@Ag) bimetallic nanocolloid surface has been investigated. Bimetallic nanocolloids have been synthesized using β-cyclodextrin (β-CD) in alkaline solution. Nanocolloids of different Aucore:Agshell ratio were synthesized keeping the same Aucore size. Again, for the preparation, the total metal concentrations were always kept constant. The structure and composition of the bimetallic particles were characterized by UV–vis and high-resolution transmission electron microscopy. Detailed normal Raman (NRS) and surface-enhanced Raman spectra (SERS) of PHEN in aqueous solution have been studied. The relative contributions of the electromagnetic (EM) and charge-transfer (CT) mechanism to the overall enhancement of the SERS bands of the PHEN molecule have been estimated. PHEN molecules are adsorbed on the Agshell surface through both the nitrogen atoms with the molecular plane almost perpendicular to the surface, which has been confirmed from Ag–N stretching vibration. The three-dimensional finite difference time domain (3D-FDTD) method has been applied to simulate the local electric field on the spherical Au@Ag nanocolloid for various core/shell ratios. Comparative spectral information revealed the highest SERS effect from the 1:4 Aucore–Agshell bimetallic nanocolloid of 29 nm size. This observation has also been supported by theory. Thus, experiment and theory keep abreast the attachment of PHEN molecules on a new substrate from SERS studies.