京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19724号 / 工博第4179号 / 新制||工||1644(附属図書館) / 32760 / 京都大学大学院工学研究科材料化学専攻 / (主査)教授 平尾 一之, 教授 三浦 清貴, 教授 田中 勝久 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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The polymeric gel-forming mucins provide the structural framework of saliva and the mucus barriers that cover the mucosal surfaces of the alimentary canal. Dietary compounds may influence the barrier properties of these protective layers. The effects of green tea polyphenols, which have many health benefits but have low bioavailability and contribute to the astringency of green tea, on the structural properties of the mucins in the alimentary canal are investigated here. Using well characterised, highly purified salivary mucins MUC5B and MUC7, and porcine gastric mucins, the effects of the green tea polyphenol epigallocatechin-3-gallate (EGCG) on mucins were studied here. Using rate-zonal centrifugation coupled to agarose gel electrophoresis, atomic force microscopy and particle tracking microrheology, EGCG, at concentrations found in a cup of green tea, caused increased aggregation of MUC5B in human whole saliva, and increased aggregation and viscosity of purified MUC5B. It was revealed using recombinant proteins of the N- and C-terminal regions of MUC5B that EGCG had these effects by aggregating the terminal globular protein domains of MUC5B. In contrast, MUC5B trypsin-resistant high molecular weight glycopeptides were not aggregated by EGCG, demonstrating that the oligosaccharide-rich, highly-glycosylated regions of mucins are not involved in the EGCG-induced aggregation of mucins. EGCG also caused the majority of MUC7 in human whole saliva to aggregate, and purified MUC7 also showed substantial aggregation in the presence of EGCG.Porcine gastric mucins were also used in order to model human gastric mucins. First, the identity of the porcine gastric mucins was explored using tandem mass spectrometry and immunohistochemistry. This revealed that Muc5ac was expressed by the surface epithelium and was the prominent mucin in porcine gastric mucus. Muc6 was expressed by gastric submucosal glands, but was not a major component of the secreted mucus barrier. Porcine Muc5ac and Muc6 were shown to be aggregated by EGCG. These data demonstrate that mucins from both saliva and the stomach are substantially altered by EGCG. This may contribute to the astringency and low bioavailability of EGCG. In contrast, the green tea polyphenol epicatechin (EC) did not cause aggregation of salivary mucins or porcine gastric mucins, suggesting that the galloyl ring of EGCG (which is absent in EC) is important for its aggregation of mucins, and that EC has different mechanisms of astringency. The structure of the mucins in the alimentary canal was studied using Raman spectroscopy, Raman optical activity (ROA) and Tip-enhanced Raman spectroscopy (TERS). The secondary structure of the oligosaccharide-rich regions of mucins was shown to be largely disordered, with some contribution of poly-proline II helix. The N- and C-terminal regions of MUC5B were largely β-sheet in structure, with some disordered structure also present in the C-terminal region. Raman spectroscopy could reliably distinguish between MUC5B glycoforms, demonstrating the sensitivity of this technique to mucin glycosylation and secondary structure. The first TERS spectra along the length of a MUC5B chain are reported, and suggest that patterns may exist in the glycosylation of MUC5B. Therefore, Raman spectroscopies are novel tools that shed new light on mucin structure and in future may be useful for studying the changes to mucin structure during interactions, such as those with polyphenols.

Protein structures (cytochrome c) were visualized by TERS measurements on whole mitochondria referring to specific spectral features describing the electronic state of the heme moiety. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Surface- and tip-enhanced resonant Raman scattering (resonant SERS and TERS) by optical phonons in a monolayer of CdSe quantum dots (QDs) is demonstrated. The SERS enhancement was achieved by employing plasmonically active substrates consisting of gold arrays with varying nanocluster diameters prepared by electron-beam lithography. The magnitude of the SERS enhancement depends on the localized surface plasmon resonance (LSPR) energy, which is determined by the structural parameters. The LSPR positions as a function of nanocluster diameter were experimentally determined from spectroscopic micro-ellipsometry, and compared to numerical simulations showing good qualitative agreement. The monolayer of CdSe QDs was deposited by the Langmuir–Blodgett-based technique on the SERS substrates. By tuning the excitation energy close to the band gap of the CdSe QDs and to the LSPR energy, resonant SERS by longitudinal optical (LO) phonons of CdSe QDs was realized. A SERS enhancement factor of 2 × 10³ was achieved. This allowed the detection of higher order LO modes of CdSe QDs, evidencing the high crystalline quality of QDs. The dependence of LO phonon mode intensity on the size of Au nanoclusters reveals a resonant character, suggesting that the electromagnetic mechanism of the SERS enhancement is dominant. Finally, the resonant TERS spectrum from CdSe QDs was obtained using electrochemically etched gold tips providing an enhancement on the order of 10⁴. This is an important step towards the detection of the phonon spectrum from a single QD. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Surface- and tip-enhanced resonant Raman scattering (resonant SERS and TERS) by optical phonons in a monolayer of CdSe quantum dots (QDs) is demonstrated. The SERS enhancement was achieved by employing plasmonically active substrates consisting of gold arrays with varying nanocluster diameters prepared by electron-beam lithography. The magnitude of the SERS enhancement depends on the localized surface plasmon resonance (LSPR) energy, which is determined by the structural parameters. The LSPR positions as a function of nanocluster diameter were experimentally determined from spectroscopic micro-ellipsometry, and compared to numerical simulations showing good qualitative agreement. The monolayer of CdSe QDs was deposited by the Langmuir–Blodgett-based technique on the SERS substrates. By tuning the excitation energy close to the band gap of the CdSe QDs and to the LSPR energy, resonant SERS by longitudinal optical (LO) phonons of CdSe QDs was realized. A SERS enhancement factor of 2 × 10³ was achieved. This allowed the detection of higher order LO modes of CdSe QDs, evidencing the high crystalline quality of QDs. The dependence of LO phonon mode intensity on the size of Au nanoclusters reveals a resonant character, suggesting that the electromagnetic mechanism of the SERS enhancement is dominant. Finally, the resonant TERS spectrum from CdSe QDs was obtained using electrochemically etched gold tips providing an enhancement on the order of 10⁴. This is an important step towards the detection of the phonon spectrum from a single QD. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

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Raman spectroscopy is a powerful analytical method that allows deposited and/or immobilized cells to be evaluated without complex sample preparation or labeling. However, a main limitation of Raman spectroscopy in cell analysis is the extremely weak Raman intensity that results in low signal to noise ratios. Therefore, it is important to seize any opportunity that increases the intensity of the Raman signal and to understand whether and how the signal enhancement changes with respect to the substrate used. Our experimental results show clear differences in the spectroscopic response from cells on different surfaces. This result is partly due to the difference in spatial distribution of electric field at the substrate/cell interface as shown by numerical simulations. We found that the substrate also changes the spatial location of maximum field enhancement around the cells. Moreover, beyond conventional flat surfaces, we introduce an efficient nanostructured silver substrate that largely enhances the Raman signal intensity from a single yeast cell. This work contributes to the field of vibrational spectroscopy analysis by providing a fresh look at the significance of the substrate for Raman investigations in cell research.

Nanomaterials have the remarkable characteristic of displaying physical properties different from their bulk counterparts. An additional degree of complexity and functionality arises when oxide nanoparticles interact with metallic nanostructures. In this context the Raman spectra due to plasmonic enhancement of iron oxide nanocrystals are here reported showing the activation of spin-waves. Iron oxide nanoparticles on gold and silver tips are found to display a band around 1584 cm−1 attributed to a spin-wave magnon mode. This magnon mode is not observed for nanoparticles deposited on silicon (111) or on glass substrates. Metal–nanoparticle interaction and the strongly localized electromagnetic field contribute to the appearance of this mode. The localized excitation that generates this mode is confirmed by tip-enhanced Raman spectroscopy (TERS). The appearance of the spin-waves only when the TERS tip is in close proximity to a nanocrystal edge suggests that the coupling of a localized plasmon with spin-waves arises due to broken symmetry at the nanoparticle border and the additional electric field confinement. Beyond phonon confinement effects previously reported in similar systems, this work offers significant insights on the plasmon-assisted generation and detection of spin-waves optically induced. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.