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Author: search.filters.author.Basu, MrinmoyeeSubject: search.filters.subject.Raman spectroscopy

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    Exploration of Electrostatic Field Force in Surface-Enhanced Raman Scattering: An Experimental Investigation Aided by Density Functional Calculations
    (ACS, 2008-10-27) Basu, Mrinmoyee
    Surface chemical properties of metal nanoparticles must be tunable to create chemical specificity and are a key prerequisite for successful sensing and imaging platforms. To relate surface enhanced Raman scattering (SERS) to electrostatic field force, a simple colloidal chemistry approach has been deliberately exploited for syntheses of gold nanoparticles with negative and positive surface charges to study their interactions with charged analytes. We took up the challenge with sulfur-containing analytes because “Au−S” interaction is well-known. Thiocyanate ion, −SCN−, a well-known SERS analyte, has been proved to be chemically ligated/anchored on positively charged gold nanoparticles surface owing to favorable electrostatic attraction. The Au−S vibrational band at ∼240 cm−1 and blue-shifting of the −C≡N stretching frequency by ∼46 cm−1 in conjunction with its intensity enhancement by an order of ∼103 in the SERS spectrum clearly illustrate a chemisorption phenomenon. In contrast, physisorption of the −SCN− ion becomes evident on negatively charged colloid. Again, methylene blue has been shown to remain engrossed on the negatively charged gold surfaces. However, the electrostatic field force could not be accounted for from fluorescence quenching while methylaminopyrene was introduced because of the distance-dependence effect. The feasibility of such coordinative/chemical attachment also has been examined theoretically by density functional theory (DFT). Moreover, employment of this DFT calculation has been performed on five different metal−molecule interaction models to fruitfully interpret the experimental SERS findings and also the orientation of the SERS analyte. The observed Raman signals have been assigned from the potential energy distributions in terms of internal coordinates of adsorbate from the output of DFT calculations. The results thus provide a benchmark illustration of the value of DFT for aiding interpretation of adsorbate vibrational spectra attainable by using SERS.
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    A Green Chemistry Approach for the Synthesis of Flower-like Ag-Doped MnO2 Nanostructures Probed by Surface-Enhanced Raman Spectroscopy
    (ACS, 2009) Basu, Mrinmoyee
    Novel hierarchical flower-like nanostructures of Ag-doped MnO2 have been obtained by facile wet chemical and photochemical routes. UV−visible absorption spectroscopy measurement reveals that doping of Ag nanoparticles in MnO2 nanostructures leads to a red shift of the absorption edge and reduces the optical band gap energy from 2.68 to 2.51 eV while compared with undoped MnO2. Raman study reveals that the band broadens and shifts toward higher wavenumbers as the MnO6 octahedron is contorted by Ag doping and thus the loss of translational symmetry activates otherwise Raman-forbidden oxygen vibrations. Finally, SERS activity upsurges from Ag-doped MnO2 with Rhodamine 6G and 2-aminothiophenol as probe molecules.
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    Chelate Effect in Surface Enhanced Raman Scattering with Transition Metal Nanoparticles
    (ACS, 2009-12-17) Basu, Mrinmoyee
    Over the years, several protocols have been designed to achieve surface enhanced Raman scattering (SERS) from noble/coinage metal nanoparticles preferably with silver and gold owing to the local electromagnetic field enhancement near their surface. However, the higher value of the imaginary component of the dielectric constant and the coupling between conduction and interband electron transitions result in poor SERS intensity for transition metals. Therefore, a good number of approaches such as the development of various surface roughening procedures have been made to increase the SERS sensitivity involving transition metal nanoparticles. This letter reports that chelating ligands such as 1,10-phenanthroline, ethylenediammine, and so forth have been found to be superior alternatives to bring forth the SERS activity from “3d” block transition metal nanoparticles (nickel and cobalt). Thus, a comparative account of SERS efficiency derived from these materials as well as from coinage metal nanoparticles engaging chelating and nonchelating (e.g., pyridine) ligands becomes intriguing.
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    Selective and Sensitive Recognition of Cu2+ in an Aqueous Medium: A Surface-Enhanced Raman Scattering (SERS)-Based Analysis with a Low-Cost Raman Reporter
    (Wiley, 2012-04-04) Basu, Mrinmoyee
    In the present study, surface-enhanced Raman spectra of a bifunctional Raman reporter, 2-mercaptobenzimidazole, has been found to be responsive exclusively towards Cu(2+) ions while the reporter remains anchored on the Au nanoparticle surface. Thus a specific Cu(2+)-ion-detection protocol emerges. The simplicity, sensitivity, and reproducibility of the method allow routine and quantitative detection of Cu(2+) ions. An interference study involving a wide number of other metal ions shows the procedure to be uniquely selective and analytically rigorous. A theoretical study was carried out to corroborate the experimental results. Finally, the method is promising for real-time assessment of Cu(2+) ions in aqueous samples and also has the ability to discriminate Cu(I) and Cu(II) ions in solution.