Silver compounds have become popular for the treatment of arresting dental caries and dentine hypersensitivity. This study investigated the interaction of silver compounds in demineralised dentine under different conditions. Scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), ion chromatography (IC) and inductively coupled plasma-mass spectroscopy (ICP-MS) were used to analyse these interactions. A systematically-approached literature review was conducted on silver compounds in dentistry. They have been demonstrated to be effective for preventing and arresting caries, as well dentine desensitivity. The mode of action of silver compounds on carious teeth includes inhibition of demineralisation process and anti-bacterial effect. Reaction products of Silver Diammine Fluoride (SDF) on dentine in different saliva substitutes were determined. Dentine samples were stored in deionised water (DIW), non-protein artificial saliva (NPAS), basal medium mucin (BMM), and un-stimulated whole saliva (UWS). These samples were chemically demineralised. Afterwards 38 wt-% SDF was applied. Dentine surfaces were analysed by SEM and showed different surface deposits and coatings. EDX, XPS and XRD detected metallic silver and silver compounds (predominantly AgCl) were formed and the amount was highest in NPAS group. BMM and UWS groups showed similar reactions. Sulphur was detected only in BMM and UWS groups. Chemical composition of BMM and UWS were determined by IC. Dentine samples were pre-saturated with BMM, UWS and DIW and then chemically demineralised. Either of 42 wt-% AgNO3, 22 wt-% AgF and 38 wt-% SDF was applied. Treated samples were replaced in their respective “saliva”. The exposed surface and a cross-section of dentine was analysed by quantitative EDX. A precise linear relation of the silver standard wires (wt-%) according to EDX counts was obtained (R2 > 0.99). The amount of silver was concentrated between 0 to 60 μm in depth. BMM groups yielded the highest amount of silver for AgF and AgNO3 compounds (p < 0.06), which may be related to the greater concentration of salivary protein and chloride in BMM solution. ICP-MS was used to quantitatively determine silver present on SDF-treated dentine. Dentine samples were pre-saturated with BMM or UWS and chemically demineralised. Afterwards 10 wt-%, 24 wt-% or 38 wt-% of SDF was applied and the treated samples were re-placed with respective “saliva” daily for 5 days. Dentine samples were then digested in 70% HNO3 and silver concentration was determined by ICP. For UWS, silver was in proportion to the application of various concentrations of SDF. However, for BMM, the higher amount of silver at 10 wt-% and 38 wt-% SDF suggests an interaction effect with excessive salivary protein and chloride. Reaction products of silver compounds on dentine can be determined by the combined SEM-EDX, XPS and XRD techniques. Both modified SEM-EDX and ICP techniques are qualified for quantitative comparison of silver concentration between treatment groups. The interaction effects of silver with different in vitro salivary components should be considered in future investigations as this may affect the chemical reaction outcomes. / published_or_final_version / Dentistry / Doctoral / Doctor of Philosophy

Thesis (Ph. D.)--University of Hong Kong, 2000. / Includes bibliographical references (leaves 250-279).

It is of fundamental significance to differentiate an enantiomer from its mirror image (i.e., enantiodifferentiation), through monitoring optical activity (OA) of enantiomers that is typically characterized by electronic circular dichroism (ECD or CD) in the UV-visible region. However, sub-wavelength molecular dimensions substantially prevent enantiomers from effectively perceiving the different circular polarization states, leading to low enantiomeric OA and weak enantiodifferentiation. Some approaches have been developed to amplify the enantiomeric OA; alternatively, on the basis of the emerging chiral metamaterials of metallic helical nanoparticles (HNPs) I devise two methods to enhance the enantiodifferentiation. First, I employ glancing angle deposition (GLAD) to deposit Ag HNPs with a helical pitch (P) larger than wire diameter (d) of the helical, i.e., Ag nanohelices (AgNHs). AgNHs exhibit strong plasmonic CD composed of a broadband longitudinal mode (i.e., L-mode) in the visible region, a transverse mode (i.e., T-mode) at a wavelength of ~370 nm, and a dielectric mode in the deep UV region (at a wavelength shorter than 320 nm). Adsorption of alkyl ligands on the AgNHs markedly weakens the two plasmonic CD modes, and the T-mode is weakened more seriously than the L-mode. The deterioration of the plasmonic CD is exacerbated with increasing the bonding energy of the Ag-alkyl ligand contacts, attributed to the increase of the dielectric constant of the medium of the AgNHs (εr) and the electron withdrawal from the AgNHs towards the alkyl ligands. Derived from the ligand-induced weakening of the plasmonic CD, enantiodifferentiation of L-Glutathione (L-GSH) from D-GSH is dramatically enhanced. The chiroptical weakening sensitively varies with the absolute configuration of GSH, resulting in an enantiodifferentiation anisotropic g factor of ~0.5 that is independent on the AgNH helicity. The AgNH-induced anisotropy g factor is superior to those obtained by other methods, by 2 - 4 orders of magnitude. It is the largest achieved up-to-date, as high as one-fourth of the theoretical maximum. Second, I operate GLAD with fast substrate rotation to reduce P less than d, to generate AgHNPs that exhibit negligible dielectric CD in the deep UV region, offering a helical substrate to directly amplify the OA of enantiomers grafted on the AgHNPs. The anchoring of enantiomers on AgHNPs with the sub-5 nm P leads to the enantioselective amplification of the enantiomeric OA in roughly ten folds; the LH- and RH-AgHNPs give rise to amplify the OA of (S)- and (R)-enantiomers, respectively. It is ascribed to the change of the dihedral angle of an enantiomer adsorbed on AgHNPs. Such the enantioselective amplification tends not to occur as long as P > 5 nm. Moreover, given the enantiodifferentiation of biomolecules that are typically dissolved in an aqueous solution, the effect of water on the plasmonic CD of AgHNPs is investigated and compared with that of AgNHs. Hydrophobic AgNHs with high structural porosity give rise to the irreversible water effect on the plasmonic CD; and hydrophilic AgHNPs with low structural porosity lead to the reversible water effect. At the end, I devise a new methodology to generate plasmonic CD through chirality transfer from chiral host to achiral guest, owing to the helicity duplication of the achiral guest from the chiral host. It leads to inducing chiroptical activity of the achiral guest made of some plasmonic materials that aren't facilely sculptured in the helical. The new methodology effectively broadens the range of materials made from the chiral nanostructures, which is on demand to develop diverse chirality-related bioapplications.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

基於局域表面等離子體共振極其敏感于金屬納米結構的尺寸和形貌的特性，貴金屬納米晶體在近些年來受到了研究人員的極大注意。而膠體金屬納米顆粒在共振時表現出極大的光散射和光吸收截面，且存在于金屬表面的電磁場強度也遠遠高於入射光的電磁場強度。膠體顆粒的各種應用已被發掘並廣泛應用於生物醫學領域，比如表面增強拉曼散射、表面增強螢光、基於等離子的傳感及光熱治療等。然而由於金材料的損耗係數大於銀，金納米材料對電磁場的增強效果弱于銀納米材料。傳統的銀納米膠體顆粒的局域表面等離子體共振峰多局限於420~500 nm，而常見的商業雷射器多在500~660 nm範圍內，目前對膠體銀納米顆粒的大小和形狀的可控性研究的報到還很有限，且將銀納米顆粒的共振調控到常用雷射器的波長範圍內對實際的應用有著重大的意義。本篇論文將系統地研究利用光化學方法製備銀納米十面體和相關納米結構，以及他們的等離子體增強效果。 / 首先，我們將介紹各種化學試劑及光源在銀納米顆粒的形成過程中的作用，以及一種能較好的控制銀納米十面體（LSPR：420~660 nm）的大小的方法。我們發現化學試劑和光源對最終納米顆粒的純度和形狀均有影響。比如通過調節硝酸銀和檸檬酸鈉的摩爾比例可以有效的控制被硼氫化鈉還原出來的金屬納米顆粒的晶體結構。465nm的光照能有效地將聚乙烯吡咯烷酮穩定的小金屬銀納米顆粒轉變成納米十面體。如果我們再使用與十面體種子顆粒的LSPR接近的LED作為光源，並用含有大量的金屬銀納米小顆粒溶液做為前驅液，更大的金屬納米十面體顆粒（LSPR：490~590 nm）可以獲得。而另一方面，使用通過離心的方法提純出來的銀十面體作為種子，更大範圍的金屬十面體（LSPR：490~660 nm）可以被生長出來，即使我們只使用了一種光源（500nm LED）。 / 之後，我們研究了銀十面體的光學性質，及它們基於表面增強拉曼散射的低濃度分子探測的應用。相比于其他形狀的金屬納米顆粒，銀納米十面體能得到更強的拉曼信號，這表明銀納米十面體對局域場的增強效果優於其他的顆粒。實驗結果表明，單個金屬納米顆粒的拉曼平均增強係數能達到10⁶。爲了能將銀納米十面體應用於生物傳感和成像領域，我們製備出具有高穩定性和強拉曼信號的表面增強拉曼探針。另一方面，通過表面增強拉曼光譜，銀納米十面體修飾的矽片能靈敏地探測出10⁻⁸ M的4-MBA分子。我們並通過模擬計算的方法證明，在十面體和襯底之間加入介質和導體薄膜能進一步增加其拉曼靈敏度。 / 最後，我們通過光化學方法在襯底上製備出金屬銀納米結構，並得到一些初步的實驗結果。在633nm鐳射的照射下，組裝在玻璃襯底上的小納米顆粒將會轉變由銀納米片組成的納米結構。通過測量，存在于金屬納米結構中的週期只有幾個微米，這也充分的表明通過光化學的方法，我們可以在襯底上製備出由銀納米顆粒組成的任意結構。拉曼光譜可以作為一種實時觀測銀納米結構生長和表面增強拉曼“熱點形成的有效手段。 / Noble-metal nanocrystals have received considerable attention in recent years for their size and shape dependent localized surface Plasmon resonances (LSPR). Various applications based on colloidal nanoparticles, such as surface enhanced Raman scattering (SERS), surface enhanced fluorescence (SEF), plasmonic sensing, photothermal therapy etc., have been broadly explored in the field of biomedicine, because of their extremely large optical scattering and absorption cross sections, as well as giant electric field enhancement on their surface. However, despite its high chemical stability, gold exhibits quite large losses and electric field enhancement is comparatively weaker than silver. Silver nanoparticles synthesized by the traditional technique only cover an LSPR ranged from 420~500 nm. On the other hand, the range of 500~660 nm, which is covered by several easily available commercial laser lines, very limited colloidal silver nanostructures with controllable size and shape have been reported, and ealization of tuning the resonance to longer wavelengths is very important for the practical applications. In this thesis, a systematic study on photochemical synthesis of silver nanodecahedrons (NDs) and related nanostructures, and their plasmonic field enhancements are presented. / First, the roles of chemicals and the light source during the formation of silver nanoparticles have been studied. We have also developed a preparation route for the production size-controlled silver nanodecahedrons (LSPR range 420~660 nm) in high purity. Indeed our experiments indicate that both the chemicals and the light sources can affect the shape and purity of final products. Adjusting the molar ratio between sodium citrate and silver nitrate can help to control the crystal structure following rapid reduction from sodium borohydride. Light from a blue LED (465 nm) can efficiently transform the polyvinylpyrrolidone stabilized small silver nanoparticles into silver NDs through photo excitation. These silver NDs acting as seeds can be re-grown into larger silver NDs with LSPR ranging from 490 nm to 590 nm, upon receiving LED irradiation with emission close to the LSPR of silver ND seeds, which are suspended in a precursor solution containing small silver nanoparticles. With the aid of centrifugation, silver NDs with high purity can be obtained. Furthermore, silver ND with a broad tuning range (LSPR 490~660 nm) can be synthesized from these seeds using irradiation from a 500 nm LED. / Second, the optical properties of silver NDs and their SERS application for sensitive molecular detection are presented. Raman signal obtained from silver NDs show remarkable advantage over noble nanoparticles of other shaped, thus revealing their strong localized field enhancement. Experimental results demonstrate that average enhancement factor from individual silver ND may be as high as 10⁶. In order to explore their application for biosensing and bioimaging, stable silica coated SERS tags based on silver ND producing high Raman intensity have been studied. Our experiment results indicate that 10⁻⁸ M 4-MBA in solution can be detected by silver NDs modified silicon chip through SERS. Simulation result on the geometry of silver ND/silica spacer/gold film/substrate shows that the Raman sensitivity of the NDs modified chip can be further improved with the insertion of a dielectric/conductor film between them. / Finally, we present a photochemical method for the preparation of silver nanostructures preparation with the use of 633 nm laser. Silver nanostructures composed of silver nanoplates could be grown from small silver nanoparticles deposited on a glass substrate. The periodicity of the silver nanostructures is several micrometers, revealing that this photochemical method has the potential for “writing“ silver pattern on a solid substrate. Raman spectroscopy has also been explored for real-time monitoring of silver nanostructure growth and SERS hotspots formation. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Lu, Haifei. / "December 2012." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 122-140). / Abstract also in Chinese. / Chapter Chapter 1. --- Introduction --- p.1 / Chapter 1.1 --- Chemical synthesis of noble nanoparticles --- p.1 / Chapter 1.1.1 --- Nucleation --- p.4 / Chapter 1.1.2 --- Evolution from Nuclei to Seeds --- p.5 / Chapter 1.1.3 --- Evolution from Seeds to Nanocrystals --- p.9 / Chapter 1.2 --- Theoretical background of localized surface plasmon (LSP) --- p.14 / Chapter 1.2.1 --- Determination of the dielectric constant --- p.15 / Chapter 1.2.2 --- Maxwell equations --- p.20 / Chapter 1.2.3 --- Quasi static approximation --- p.21 / Chapter 1.2.4 --- Gans Theory --- p.22 / Chapter 1.2.5 --- Mie theory --- p.23 / Chapter 1.2.6 --- Numerical methods --- p.25 / Chapter 1.3 --- Structure of this thesis --- p.29 / Chapter Chapter 2. --- Optical properties of noble nanoparticles and their biomedical applications --- p.30 / Chapter 2.1 --- Introduction --- p.30 / Chapter 2.2 --- LSPR of nanoparticles with different shapes and different material composition --- p.30 / Chapter 2.4 --- Local field enhancement of nanoparticles and their effects to Raman and fluorescence --- p.35 / Chapter 2.5 --- Noble nanoparticles for biomedical applications --- p.38 / Chapter 2.5.1 --- Noble nanocrystals for diagnostics --- p.38 / Chapter 2.5.2 --- Noble nanocrystals for cellular and in vivo bioimaging --- p.41 / Chapter 2.5.3 --- Noble metal nanocrystals in medicine --- p.43 / Chapter Chapter 3. --- Photochemical synthesis of size controlled silver nanodecahedrons (NDs) --- p.46 / Chapter 3.1 --- Introduction --- p.46 / Chapter 3.2 --- Seed mediated plasmon driven regrowth of silver nanodecahedrons . --- p.47 / Chapter 3.3 --- Chemical roles of reagents in the process and mechanism for photogrowth of silver nanodecahedrons --- p.55 / Chapter 3.4 --- Light wavelength effect to the regrowth of silver NDs --- p.63 / Chapter 3.5 --- Control on the crystal defects of small silver nanoparticles and effect of precursor to the regrowth of various size silver NDs --- p.67 / Chapter 3.6 --- Summary --- p.77 / Chapter Chapter 4. --- SERS assessment of silver nanodecahedrons and their application for sensitive detection based on SERS --- p.78 / Chapter 4.1 --- Introduction --- p.78 / Chapter 4.2 --- Investigation on SERS of silver NDs and other nanoparticles --- p.79 / Chapter 4.3 --- Silica coated SERS tags with silver NDs as the core --- p.85 / Chapter 4.4 --- Silver nanodecahedrons for biosensing --- p.93 / Chapter 4.5 --- Summary --- p.101 / Chapter Chapter 5. --- Photochemical growth of Plasmonic nanostructures on solid substrate --- p.103 / Chapter 5.1 --- Introduction --- p.103 / Chapter 5.2 --- Experimental --- p.104 / Chapter 5.3 --- Result and discussion --- p.105 / Chapter 5.3.1 --- Photochemical growth of silver nanostructures by laser irradiation through a single slit --- p.105 / Chapter 5.3.2 --- SERS characterization of silver nanostructures --- p.110 / Chapter 5.3.3 --- Observation of photochemical growth of silver nanostructures --- p.112 / Chapter 5.4 --- Summary --- p.115 / Chapter Chapter 6. --- Conclusion and outlook --- p.117 / References --- p.122

Includes bibliographical references (p. 149-179).

Thesis (Ph. D.)--University of Hong Kong, 1997. / Includes bibliographical references (leaf 306-329).

Thesis (M.S.)--Texas State University--San Marcos, 2009. / Vita. Appendices: leaves 38-39. Includes bibliographical references (leaves 40-41). Also available on microfilm.

No description available.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy