Xiao, Manda = 金納米晶修飾的空心介孔二氧化矽微球在表面等離子體激元調製下的光散射行為 / 肖蔓達. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references. / Abstracts in English and Chinese. / Xiao, Manda = Jin na mi jing xiu shi de kong xin jie kong er yang hua xi wei qiu zai biao mian deng li zi ti ji yuan diao zhi xia de guang san she xing wei / Xiao Manda. / Abstract --- p.i / 摘要 --- p.iii / Acknowledgement --- p.iv / Table of Contents --- p.vi / List of Figures --- p.viii / List of Tables --- p.x / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Plasmonic Properties of Noble Metal Nanocrystals --- p.1 / Chapter 1.2 --- Light Scattering from Dielectric Spheres --- p.6 / Chapter 1.3 --- Motivations and Outline of the Thesis --- p.9 / Chapter 2 --- Characterization Techniques --- p.17 / Chapter 2.1 --- Instrumentation --- p.17 / Chapter 2.2 --- Extinction Measurement of Au Nanocrystals and the HMSMSs Decorated with the Au Nanocrystals --- p.17 / Chapter 2.3 --- Sample Preparation for the TEM and SEM Characterization --- p.18 / Chapter 2.4 --- Dark-Field Imaging and Spectroscopy of the Individual Microspheres --- p.19 / Chapter 3 --- Fabrication of Hollow Mesoporous Silica Microspheres Decorated with the Au Nanocrystals --- p.25 / Chapter 3.1 --- Preparation of the Hollow Mesoporous Silica Microspheres --- p.25 / Chapter 3.2 --- Growth of the Au Nanocrystals --- p.29 / Chapter 3.3 --- Assembly of the Au Nanocrystals onto the Hollow Mesoporous Silica Microspheres --- p.32 / Chapter 4 --- Resonant Scattering Properties of the Hollow Mesoporous Silica Microspheres --- p.38 / Chapter 4.1 --- Experimental Results --- p.38 / Chapter 4.2 --- Calculation of the Scattering Spectra by Mie Theory --- p.42 / Chapter 4.3 --- Summary --- p.46 / Chapter 5 --- Resonant Scattering Properties of the Au Nanocrystal-Decorated Hollow Mesoporous Silica Microspheres --- p.49 / Chapter 5.1 --- Effect of the Plasmon Resonances of the Au Nanocrystals on the Resonant Scattering Behaviors of the HMSMSs --- p.49 / Chapter 5.2 --- Estimation of the Scattering Enhancement Factors --- p.54 / Chapter 5.3 --- Summary --- p.59 / Chapter 6 --- Summary --- p.61

Current understanding of potential toxicity of engineered nanomaterials to aquatic microorganisms is limited for risk assessment and management. Here we evaluate if the MetPLATE™ test can be used as an effective and rapid screening tool to test for potential aquatic toxicity of various metal-based nanoparticles (NPs). The MetPLATE bioassay is a heavy metal sensitive test based on β-galactosidase activity in Escherichia coli. Five different types of metal-based NPs were screened for toxicity: (1) citrate coated nAg (Citrate-nanosilver), (2) polyvinylpyrrolidone coated nAg (PVP-nAg), (3) uncoated nZnO, (4) uncoated nTiO2 and (5) 1-Octadecylamine coated CdSe Quantum Dots (CdSe QDs); and compared with their corresponding ionic salt toxicity. Citrate-nAg was further fractionated into clean Citrate-nAg, unclean Citrate-nAg and permeate using a tangential flow filtration (TFF) system to eliminate residual ions and impurities from the stock Citrate-nAg suspension and also to differentiate between ionic- versus nano-specific toxicity. Our results showed that nAg, nZnO and CdSe QDs were less toxic than their corresponding ionic salts tested, while nano- or ionic form of TiO2 was not toxic as high as 2.5 g L− 1 to the MetPLATE™ bacteria. Although coating-dependent toxicity was noticeable between two types of Ag NPs evaluated, particle size and surface charge were not adequate to explain the observed toxicity; hence, the toxicity appeared to be material-specific. Overall, the toxicity followed the trend: CdCl2 > AgNO3 > PVP-nAg > unclean Citrate-nAg > clean Citrate-nAg > ZnSO4 > nZnO > CdSe QDs > nTiO2/TiO2. These results indicate that an evaluation of β-galactosidase inhibition in MetPLATE™ E. coli can be an important consideration for rapid screening of metal-based NP toxicity, and should facilitate ecological risk assessment of these emerging contaminants.

Mineral dust aerosol plays an important role in determining the physical and chemical equilibrium of the atmosphere. The radiative balance of the Earth's atmosphere can be affected by mineral dust through both direct and indirect means. Mineral dust can directly scatter or absorb incoming visible solar radiation and outgoing terrestrial IR radiation. Dust particles can also serve as cloud condensation nuclei, thereby increasing albedo, or provide sites for heterogeneous reactions with trace gas species, which are indirect effects. Unfortunately, many of these processes are poorly understood due to incomplete knowledge of the physical and chemical characteristics of the particles including dust concentration and global distribution, as well as aerosol composition, mixing state, and size and shape distributions. Much of the information about mineral dust aerosol loading and spatial distribution is obtained from remote sensing measurements which often rely on measuring the scattering or absorption of light from these particles and are thus subject to errors arising from an incomplete understanding of the scattering processes. The light scattering properties of several key mineral components of atmospheric dust have been measured at three different wavelengths in the visible. In addition, measurements of the scattering were performed for several authentic mineral dust aerosols, including Saharan sand, diatomaceous earth, Iowa loess soil, and palagonite. These samples include particles that are highly irregular in shape. Using known optical constants along with measured size distributions, simulations of the light scattering process were performed using both Mie and T-Matrix theories. Particle shapes were approximated as a distribution of spheroids for the T-Matrix calculations. It was found that the theoretical model simulations differed markedly from experimental measurements of the light scattering, particularly near the mid-range and near backscattering angles. In many cases, in the near backward direction, theoretical models predicted scattering intensities for near spherical particles that were up to 3 times higher than the experimentally measured values. It was found that better agreement between simulations and experiments could be obtained for the visible scattering by using a much wider range of more eccentric particle shapes.

The mechanisms linking deposits of insoluble fibrils of amyloid proteins to the debilitating neuronal cell death characteristic of neurodegenerative diseases remain enigmatic. Recent findings suggest that transiently formed intermediate aggregates, and not the prominent neuronal plaques, represent the principal toxic agent. Evaluating the neurotoxicity of intermediate aggregates, however, requires unambiguous characterization of all aggregate structures present, their relative distributions, and how they evolve in time. Hen-egg white lysozyme represents an attractive model for studying intermediate aggregate formation since it is an extensively characterized globular protein, and its human variants can lead to systemic amyloidosis. Combining in-situ dynamic light scattering (DLS) with atomic force microscopy (AFM), we have characterized the morphologies and growth kinetics of intermediate aggregates formed during lysozyme fibrillogenesis. Upon incubation at elevated temperatures, small uniform oligomers form with their numbers increasing for several hours. After a variable lag period protofibrils spontaneously nucleate. The heights and widths of protofibrils closely match those of oligomers. This match in physical dimensions, combined with the delayed onset of protofibril nucleation vs. the continuous formation of oligomers, suggest that protofibrils both nucleate and grow from oligomers. Protofibril morphologies and structures, visualized with AFM, are quite distinct from subsequently emerging mature fibrils. Overall, the evolution of aggregate morphologies during lysozyme fibrillogenesis follows a clear hierarchical pathway: amyloid monomers initially coalesce into oligomers of uniform size. Their steadily increasing numbers eventually induce nucleation and growth of protofibrils. Protofibrils, in turn, nucleate and grow via oligomer addition until they start to self-assemble into micron-sized double-stranded fibrils.

Characterization of micron and sub-micron size particles requires the simultaneous measurement of the joint particle property distribution (JPPD). The JPPD is comprised of particle size, shape, orientation, composition, optical properties, and surface properties. Measurement of each of the particle properties independently is a difficult task and it has been only partially successful. To determine as many particle properties as possible using optical methods it is necessary to simultaneously measure all aspects of the interaction of the incident light with the particles of interest. This approach leads to the concept of multidimensional spectroscopy suggested by Prof. Garcia-Rubio. Dr. Bacon proved the proposition by developing and testing a prototype multianglemultiwavelength (MAMW) spectrometer proposed by Prof. Garcia-Rubio. However, the prototype MAMW spectrometer has limitations in the amount of information it can obtain because of strong absorption of deep UV light and detector saturation due to the use of optical fibers and single integration time for the CCD detector. The Integrated UV-VIS MAMW spectrometer has been developed to overcome the limitations of the prototype MAMW spectrometer. Improvements have become possible through the use of UV lenses and integration time multiplexing (ITM). The Integrated UV-VIS MAMW spectrometer has the capabilities to perform low angle scattering measurements starting from 4o with simultaneous detection of multiwavelength light from 200 nm to 820 nm, UV-VIS transmission spectroscopy, and frequency domain fluorescence spectroscopy. Following the development, possible sources of errors were analyzed and data calibration procedures have been established to ensure the validity and reproducibility of the measurement results. The capabilities of the Integrated UV-VIS MAMW spectrometer were tested by measuring UV-VIS MAMW spectra of polystyrene standards. The measured UV-VIS MAMW spectra clearly show differences due to particle size, shape, and compositional changes. Measurements of the UV-VIS MAMW spectra of sickled whole blood samples demonstrate that particle shape and compositional changes can be detected simultaneously. These results confirmed that the Integrated UV-VIS MAMW spectrometer could be a powerful tool for the characterization of micron and sub-micron size particles. Alternate approaches to enhance these capabilities further, i.e., the development of a new multidimensional MAMW spectrometer, are also described.

A blue sky, a white cloud or a red sunset are explained by classical multiple scattering theory of light. However, these phenomena neglect interference occurrence. Once it is taken into account, interference in a disordered medium may actually put a halt to the propagation of light, an effect known as Anderson Localization. Until now, experimental reports of Anderson Localization of light in 3D systems have not been conclusive. Our goal is to understand what are the underlying obstacles, and look for new insights from a theoretical point of view. In this dissertation, the properties of a cloud of two-level atoms scattering light are investigated. The dipole-dipole interaction generates collective modes, some of them, being localized. We found that finite-size effects dominate the lifetime of the localized modes, specifically by the ratio of localization length to their distance to the system boundaries. Localized modes saturates at maximum of 20% even above phase transition. Studying the steady-state regime, the coupling between localized modes and light is weak. Both results agrees with the difficulty of experimental evidence of light localization and promote the link of experiments and theory. / Um céu azul, uma nuvem branca ou um por do sol vermelho são explicados pela teoria clássica de espalhamento múltiplo da luz. No entanto, esses fenômenos negligenciam a ocorrência de interferências. Uma vez levada em conta, a interferência em um meio desordenado pode interromper a propagação da luz, um efeito conhecido como Localização de Anderson. Até agora, relatos experimentais de Anderson Localização de luz em sistemas 3D não foram conclusivos. Nosso objetivo é entender quais são os obstáculos fundamentais, e buscar novos insights do ponto de vista teórico. Nesta dissertação, as propriedades de uma nuvem de átomos de dois níveis espalhando luz de é investigado. A interação dipolo-dipolo gera modos coletivos, alguns deles, sendo localizados. Descobrimos que os efeitos de tamanho finito dominam o tempo de vida dos modos localizados, especificamente pela razão entre o comprimento da localização e sua distância até os limites do sistema. Os modos localizados saturam no máximo 20%, mesmo acima da transição de fase. Estudando o regime de estado estacionário, o acoplamento entre modos localizados e luz é fraco. Ambos os resultados concordam com a dificuldade da evidência experimental da localização da luz e promovem a ligação entre experimentos e teoria.

X-ray diffraction from protein crystals remains the most reliable way to determine the molecular structure of proteins, and how this structure relates to biological function. However, we still lack the ability to predict solution conditions that support the nucleation and growth of high-quality protein crystals for X-ray diffraction studies. The overall goal of this thesis is two-fold: (a) determine the nucleation behavior and solubilities for lysozyme crystals with two distinct crystal structures (orthorhombic vs. tetragonal) and (b) investigate whether these changes in crystal habit and crystal solubility correlate with any discontinuities in the liquid-liquid phase boundary of lysozyme that occurs under the same solution conditions. We measured lysozyme crystal solubility by nucleating and subsequently dissolving very small lysozyme crystals in highly supersaturated solutions. The presence of crystals in our samples is detected and monitored by measuring the light scattered off the micron-sized crystals. These "turbidity measurements" are repeated across a range of protein concentrations, for pH 4.6 and 5.6, thereby yielding the crystal solubility boundary. Changes in crystal structure are assessed at the end of the experiments by microscopic inspection of the distinct crystal habits. Attractive protein interactions in solution also induce liquid-liquid phase separation. Similar to the crystal solubility measurement, we use the turbidity increase associated with liquid-liquid phase separation to map out this phase boundary. Since both crystal formation and liquid-liquid phase separation are driven by attractive protein interactions, we investigated whether the dramatic changes in crystal solubility associated with different protein crystal structures lead to any discernable “discontinuities” in the liquid-liquid phase boundaries.

The effect of shear on the evolution of floc properties was investigated to analyse the flocculation mechanisms. Little fundamental attention has been given to the shear influence that often creates compact aggregates, while the floc characteristics might differ in other aggregating conditions. It is thus crucial to understand how flocs evolve to steady state, if their properties are to be 'tailored' to suit subsequent solids-liquid separation processes. In this work, flocculation of monodisperse latex particles of various sizes (60, 380, and 810 nm diameter) via electrolyte addition was carried out in a couette-flow and also in shear fields generated by an axial-flow impeller (Fluid foil A310) and a radial-flow impeller (Rushton R100) in standard mixing tanks. A small-angle light scattering technique was used to acquire information regarding the time variation of floc properties in a non-intrusive manner. The structure was quantified by a measure of fractal dimension, signifying the degree of floc compactness. Estimates of the average floc mass were also obtained from the aggregate scattering patterns. By monitoring the changes in floc structure and mass, corresponding to the size evolution; mechanisms of floc formation, fragmentation, and restructuring were identified. Aggregates of 60 and 380 nm particles were observed to grew larger initially, before decreasing to their equilibrium sizes at moderate shear rates (32 - 100 s-1) in a homogeneous shear environment. Floc restructuring at large length scales occurred extensively, and was responsible for the drop in size, particularly at the early stage of the process. Aggregates of 810 nm particles did not, however, display this behaviour. Flocs of larger primary particles were presumably susceptible to breakage rather than deformation, as they were weaker under comparable conditions. Denser aggregates were found when restructuring transpired, while comparatively tenuous flocs were observed when formation and breakage kinetics were the governing mechanisms. The disparity in floc behaviour at higher shear rates (246 s-1 - 330 s-1) was less apparent. The intense hydrodynamic stresses in those instances inevitably caused fragmentation, regardless of the intrinsic particle properties; hence the observed floc compaction was the product of break-up and re-aggregation. A population balance model, incorporating variation in floc structure, displayed comparable trends in size evolution; verifying that restructuring indeed took an important role under certain flocculation conditions. Similar phenomena were likewise observed with the flocculation in stirred tanks. The results reinforced findings in literature; that while circulation time controlled the process kinetics; the floc size was determined by the turbulent stresses. In addition, the maximum shear levels also influenced the floc structures, with denser aggregates produced in a shear field generated using the radial-flow impeller at equivalent energy dissipation per-unit mass. A correlation between non-dimensional floc factor that embodied the aggregate size and structure, and aggregation factor comprising the significant parameters from flocculation conditions, was proposed. The proposed relationship takes into account aspects such as the aggregate structure, interparticle forces, and particle concentration that are often overlooked in existing relationships, which usually only relate the maximum floc size to the applied energy dissipation rate. It thus provides an improved manner of presenting general flocculation data, as well as a means to predict floc properties produced under a specific aggregation condition. Future studies with increasingly complex systems that resemble real conditions are recommended in order to establish a practical understanding of the flocculation mechanisms, for the purpose of optimising the aggregate properties.

Remote sensing is the collection of information about an object from a distance without physically being in contact with it. The type of remote sensing of interest here is in the form of digital images of water bodies acquired by satellite. The advantage over traditional sampling techniques is that data can be gathered quickly over large ranges, and be available for immediate analysis. Remote sensing is a powerful technique for the monitoring of water bodies. To interpret the remotely sensed data, however, knowledge of the optical properties of the water constituents is needed. One of the most important of these is the volume scattering function, which describes the angular distribution of light scattered by a sample. This thesis presents the first measurements of volume scattering functions for Australian waters. Measurements were made on around 40 different samples taken from several locations in the Gippsland lakes and the Great Barrier Reef. The measurements were made by modifying an existing static light scattering spectrometer in order to accurately measure the volume scattering functions. The development of the apparatus, its calibration and automation, and the application of a complex series of post-acquisition data corrections, are all discussed. In order to extrapolate the data over the full angular range, the data was analysed using theoretical curves calculated for multi-modal size distributions using Mie light scattering theory applied to each data set. From the Mie fits the scattering and backscattering coefficients were calculated. These were compared with scattering coefficients measured using in situ sensors ac-9 and Hydroscat-6, and with values from the literature. The effect of chlorophyll a concentrations on the scattering coefficients was examined, and a brief investigation of the polarisation properties of the samples was also undertaken. Finally the angular effects on the relationship between the backscattering coefficient and the volume scattering function were investigated. This is important as in situ backscattering sensors often assume that measuring at a single fixed-angle is a good approximation for calculating the backscattering coefficient. This assumption is tested, and the optimal measurement angle determined.

Virus-like particles (VLPs) are elegant functional architectures formed by the self-assembly of viral structural proteins. VLPs have been developed as vaccines against hepatitis B and cervical cancer, and have recently been shown in animal studies to provide protection against both seasonal and avian influenza following intranasal administration. This new class of vaccines offers unprecedented immunoprotection, inherent safety, and a simple route of administration. To realize the full potential of VLP technology as an efficient and responsive vaccine platform, this project exploits the parallel advancements in recombinant technology, analytical techniques and colloidal science to facilitate the swift and economical delivery of candidate VLP vaccines from laboratory to clinical trials, and ultimately into commercial production. Three areas of VLP production are specifically targeted in this work, i.e., VLP subunit production, particle characterisation and assembly. The major research outcomes in this work are: (i) establishment of a simple and economical VLP subunit production method which eliminates inefficient and complicated purification procedures necessitated by the current in vivo production methods; (ii) development of a high-resolution and high-throughput analytical method for rapid and reliable quality control check of VLP products; and (iii) establishment of the foundation to predict optimal VLP self-assembly conditions through molecular thermodynamics. These research outcomes collectively enhance the quantitative knowledge base in VLP assembly and may ultimately enable the development of a mechanistic and descriptive modelling approach to optimize VLP production. From a fundamental perspective, this work introduces the first experimental technique to measure protein interactions of viral subunits undergoing rapid, irreversible assembly reaction. Such information, when correlated with molecular details and assembly conditions may provide unique insights into the molecular switches responsible for viral assembly, unveiling the fundamental mechanism underpinning viral self-assembly.