Browsing by Author "Wattanavichean, Nungnit"

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Detection of Metal-Molecule-Metal Junction Formation by Surface Enhanced Raman Spectroscopy
(2019-02-19)
Wattanavichean, Nungnit
;
Gilby, Matthew
;
Nichols, Richard J.
;
Arnolds, Heike
;
應用化學系
Vibrational modes play a key role in characterizing metal-molecule-metal junctions, but their detection currently either requires single-molecule sensitivity or the generation of defect-free large-scale junctions. Here we demonstrate that surface-enhanced Raman scattering (SERS) on nonideal surfaces can provide a significant amount of information despite many defects in the layer. We determine the vibrational signature of the molecular electronic junction for palladium ions complexed and reduced on 4-mercaptopyridine adsorbed on rough gold and gold nanoparticles using SERS and density functional theory. We show that these nonideal surfaces can be used to probe kinetics of metal ion complexation and establish the success of electrochemical metallization. SERS on nonideal surfaces is thus revealed as a useful tool to rapidly establish the key process parameters in making molecular electronic junctions before embarking on more detailed studies on single molecules or single crystal surfaces.
Organelle specific simultaneous Raman/green fluorescence protein microspectroscopy for living cell physicochemical studies
(1970-01-01)
Wattanavichean, Nungnit
;
Nishida, Ikuhisa
;
Ando, Masahiro
;
Kawamukai, Makoto
;
Yamamoto, Tatsuyuki
We demonstrate a novel bio-spectroscopic technique, "simultaneous Raman/GFP microspectroscopy". It enables organelle specific Raman microspectroscopy of living cells. Fission yeast, Schizosaccharomyces pombe, whose mitochondria are green fluorescence protein (GFP) labeled, is used as a test model system. Raman excitation laser and GFP excitation light irradiate the sample yeast cells simultaneously. GFP signal is monitored in the anti-Stokes region where interference from Raman scattering is negligibly small. Of note, 13 568 Raman spectra measured from different points of 19 living yeast cells are categorized according to their GFP fluorescence intensities, with the use of a two-component multivariate curve resolution with alternate least squares (MCR-ALS) analysis in the anti-Stokes region. This categorization allows us to know whether or not Raman spectra are taken from mitochondria. Raman spectra specific to mitochondria are obtained by an MCR-ALS analysis in the Stokes region of 1389 strongly GFP positive spectra. Two mitochondria specific Raman spectra have been obtained. The first one is dominated by protein Raman bands and the second by lipid Raman bands, being consistent with the known molecular composition of mitochondria. In addition, the second spectrum shows a strong band of ergosterol at 1602 cm(-1), previously reported as "Raman spectroscopic signature of life of yeast."