Thesis (Ph. D.)--University of Canterbury, 2006. / Typescript (photocopy). "1st of February 2006." Includes bibliographical references (p. [217]-230). Also available via the World Wide Web.

This thesis describes the photochemical synthesis of silver nano particles, several ways to make these particles as well as control the size and shape of the colloidal particles. Understanding the primary reactions in photochemical nanoparticle formation has lead to important contributions to the overall mechanism of metal nanoparticle synthesis. The size and shape control of the particles is shown to have important implications for the Raman spectrum of surface bound molecules. The particles have also been used in antibacterial properties where it was shown that silver nanoparticles are more antibacterial than the corresponding silver cation, while remaining non-toxic to several common cell lines. The particles were also shown to have some interesting properties that can be exploited in lithography and optoelectronics.

Surface plasmons have been attracted extensive interests in recent decades due to the novel properties in nanometer sized dimensions. My work focused on the novel optical properties of metal nanostructures based on surface plasmons using theoretical simulation methods. In the first part, we investigated metal nanofilms and nanorods and demonstrated that extremely low scattering efficiency, high absorption efficiency and propagation with long distance could be obtained by different metal nanostructures. With a perforated silver film, we demonstrated that an extremely low scattering cross section with an efficiency of less than 1% can be achieved at tunable wavelengths with tunable widths. The resonance wavelength, width, and intensity are influenced by the shape, size and arrangement pattern of the holes, as well as the distance separating the holes along the polarization direction. The extremely low scattering could be used to obtain high absorption efficiency of a two-layer silver nanofilm. Using the discrete dipole approximation method, we achieved enhanced absorption efficiencies, which are close to 100%, at tunable wavelengths in a two-layer silver thin film. The film is composed of a 100 nm thick perforated layer facing the incident light and a 100 nm thick solid layer. Resonance wavelengths are determined by the distances between perforated holes in the first layer as well as the separation between two layers. The resonance wavelengths shift to red with increasing separation distance between two layers or the periodic distance of the hole arrays. Geometries of conical frustum shaped holes in the first layer are critical for the improved absorption efficiencies. When the hole bottom diameter equals the periodic distance and the upper diameter iv is about one-third of the bottom diameter, close to unit absorption efficiency can be obtained. We examined the electromagnetic wave propagation along a hollow silver nanorod with subwavelength dimensions. The calculations show that light may propagate along the hollow nanorod with growing intensities. The influences of the shape, dimension, and length of the rod on the resonance wavelength and the enhanced local electric field, |E|2 , along the rod were investigated. In the second part, a generalized electrodynamics model is proposed to describe the enhancement and quenching of fluorescence signal of a dye molecule placed near a metal nanoparticle (NP). Both the size of the Au NPs and quantum yield of the dye molecule are crucial in determining the emission intensity of the molecule. Changing the size of the metal NP will alter the ratio of the scattering and absorption efficiencies of the metal NP and consequently result in different enhancement or quenching effect to the dye molecule. A dye molecule with a reduced quantum yield indicates that the non-radiative channel is dominant in the decay of the excited dye molecules and the amplification of the radiative decay rate will be easier. In general, the emission intensity will be quenched when the size of metal NP is small and the quantum yield of dye molecule is about unity. A significant enhancement factor will be obtained when the quantum yield of the molecule is small and the particle size is large. When the quantum yield of the dye molecule is less than 10-5 , the model is simplified to the surface enhanced Raman scattering equation

The content of this thesis is based upon the interaction of light with metallic nanoparticles arranged in different array geometries. An incident electric field (light) can force the conduction electrons of a metallic nanoparticle to oscillate. At particular frequencies, in the optical regime for gold and silver particles, absorption and scattering of the light by the particle is enhanced, corresponding to the particle plasmon resonance. The spectral position and width of the particle plasmon resonance of an isolated single particle may be tuned by adjusting its size and shape, thus changing the surface charge distribution. Periodic arrays of particles offer additional control over the frequency and width of the resonance attributed to the re-radiating (scattering) property of plasmonic particles. By fabricating arrays with a pitch comparable to the wavelength of an isolated single particle plasmon resonance, a coherent interaction between particles may be produced, known as surface lattice resonances (SLRs). The electromagnetic coupling between in-plane particle plasmon modes for different particle array geometries is explored through experiment and theory. Firstly, SLRs in square, hexagonal and honeycomb arrays are investigated by normal-incidence extinction measurements and compared to a simple-coupled dipole model. Secondly, to verify the nature of the coupling between the scattered electric field associated with particle resonances, the incident electric field polarization-dependence of the extinction of rectangular arrays and chains is studied. Thirdly, the optical response of square arrays with a symmetric two-particle basis is investigated, particularly the retardation of the scattered electric field between particles in a pair. Fourthly, square arrays with an asymmetric two-particle basis are fabricated to explore the symmetric (dipole moments of both particles are parallel) and anti-symmetric (dipole moment of both particles anti-parallel) SLRs, excited by normal-incidence light.

Noble metal nanostructures possess unique properties including large near-field enhancement and strong light scattering and absorption due to their plasmon resonance - the collective coherent oscillation of the metal free electrons in resonance with the electromagnetic field of light. The effect of nanostructure size, shape, composition, and environment on the plasmon resonance frequency and plasmonic enhancement is well known. In this thesis, we describe the effect of inter-particle coupling in assembled plasmonic nanostructures on their radiative and non-radiative properties. When metal nanoparticles assemble, plasmon oscillations of neighboring particles couple, resulting in a shift in the plasmon resonance frequency. Our investigation of plasmon coupling in gold nanorods shows that the coupling between the plasmons is "bonding" in nature when the plasmon oscillations are polarized along the inter-particle axis, whereas an "anti-bonding" interaction results when the polarization is perpendicular. We studied the distance-dependence of plasmon coupling using electrodynamic simulations and experimental plasmon resonances of lithographically fabricated gold nanoparticle pairs with systematically varying inter-particle separations. The strength of plasmon bonding, reflected by the fractional plasmon shift, decays near-exponentially with the inter-particle separation (in units of particle size) according to a universal trend independent of the nanoparticle size, shape, metal type, or medium. From the universal scaling model, we obtain a "plasmon ruler equation" which calculates (in good agreement with the experiments of Alivisatos and Liphardt) the inter-particle separation in a gold nanosphere pair from its plasmon resonance shift, making it applicable to the determination of inter-site distances in biological systems. Universal size-scaling is valid also in the metal nanoshell structure, a nanosphere trimer, and pairs of elongated nanoparticles, thus making it a generalized fundamental model, which is useful in optimizing plasmon coupling for achieving tunable plasmon resonances, enhanced plasmonic sensitivities, and large SERS cross-sections. Ultrafast laser pump-probe studies of non-radiative electronic relaxation in coupled metal nanospheres in aggregates and in gold nanospheres conjugated to thiol SAMs are also reported. We also show that the relative contribution of scattering (radiative) to absorption (non-radiative) part of the plasmon relaxation, respectively useful in optical and photothermal applications, can be increased by increasing the nanostructure size.

Ce document présente les notions de base permettant la conception d'un système de biodétection reposant sur la résonance des plasmons de surface. Il expose ensuite les grandes étapes de la conception du système, sa caractérisation, de même que son application à la mesure de l'activité cellulaire. Plus particulièrement, un système de biodétection basé sur la résonance des plasmons de surface a été conçu et réalisé.Ce système, intégrant deux types de détection, soit la modulation de l'angle de couplage aux plasmons de surface ainsi que la modulation de l'intensité d'un laser réfléchi sur le substrat, a été fabriqué sous la forme d'un goniomètre vertical. Un prisme sur lequel était déposé le substrat assurait le couplage de ce dernier avec un laser, permettant la mesure de la résonance des plasmons de surface.Ce système a été caractérisé quant à sa fidélité, sa sensibilité, sa plage dynamique et sa résolution. Finalement, le système a été appliqué à la mesure de l'activité de cellules vivantes induite par l'injection d'agents reconnus pour leur effet sur la morphologie des cellules. Cette application démontre qu'un biocapteur à large plage de détection peut être formé par la combinaison de la résonance des plasmons de surface et d'une monocouche de cellules vivantes.Ce biocapteur permet de détecter en temps réel des agents chimiques ou biologiques induisant des changements morphologiques dans la cellule.

Type 2 diabetes or adult onset diabetes, has been a global epidemic for the past two decades, and the number of new cases accelerates every year. Insulin resistance is one of the major factors behind this, wherein the insulin receptor, which signals to regulate glucose levels, based on the hormone insulin, loses its sensitivity. Obesity is one other major concern which is caused due to the improper balance between the caloric intake and the energy utilized. Gastric bypass surgeries (GBP) are performed to avert obesity. However, a beneficial side-effect is that the state of insulin resistance is reset to near baseline levels within a few days after the procedure. The reason behind this remains unexplained, with possible humoral effects, hypothesized to occur after the bariatric procedure. In this work, high-five insect cell line was utilized to recombinantly produce full length insulin receptors (IR). However commercially sourced IR ectodomains (eIR – soluble version of the full length IR with the completely extracellular α subunits along with extracellular and transmembrane regions of the β subunit), were used to study the interaction. Measuring the kinetics of IR-insulin interactions is critical to improving our understanding of this disease. In this study, a multiplex surface plasmon resonance (SPR) assay was developed for studying the interaction between insulin and the eIR. A scaffold approach was used in which anti-insulin receptor monoclonal antibody 83–7 (Abcam, Cambridge, UK) was first immobilized on the SPR sensorchip by amine coupling, followed by eIR capture. The multiplex SPR system (ProteOn XPR36TM, Bio-Rad Laboratories, Hercules, CA) enabled measurement of replicate interactions with a single, parallel set of analyte injections, whereas repeated regeneration of the scaffold between measurements caused variable loss of antibody activity. The main approach was to replicate the physiological IR-insulin interaction using this assay. It was also observed that insulin at higher concentrations tend to form dimers and hexamers in solution. This was tested using size exclusion chromatography analysis and proved to be true. Therefore an alternative analyte with the similar binding properties and affinity of insulin and at the same time with reduced self- association characteristics was explored. Lispro, the analogue of insulin with reduced self-association properties (generated by swapping of residue 28 and 29 with Lys and Pro respectively) was finally used to study the interaction with eIR. Interactions between recombinant human insulin with eIR-A (A isoform of the insulin receptor ectodomain) followed a two-site binding pattern (consistent with the literature), with a high-affinity site (dissociation constant KD1 = 38.1 ± 0.9 nM) and a low-affinity site (KD2 = 166.3 ± 7.3 nM). The predominantly monomeric insulin analogue Lispro had corresponding dissociation constants KD1 =73.2 ± 1.8 nM and KD2 =148.9 ± 6.1 nM, but the fit to kinetic data was improved when conformational change factor was included in which the high-affinity site was converted to the low-affinity site. Kinetics of interaction of insulin with eIR-A and eIR-B isoforms were then compared. eIR-A bound insulin with apparently higher affinity (with both the binding sites) when compared with eIR-B. This was again consistent with literature that IR-A had two-fold higher affinity for binding insulin than IR-B. The assay was further extended to study the effect of external factors such as glucose, visfatin on this interaction. Glucose (the main biomolecule which is regulated by the IR-insulin interaction) was tested, if it had any direct effect on the interaction. It was observed that glucose did not have any effect on eIR-insulin interactions. Visfatin, an adipocytokine which has been highly debated in literature for its insulin mimetic effects and IR binding properties, was then tested. The standard assay did not provide much insights as the reference channel immobilized with 83-7 monoclonal antibody to the receptor had much affinity for visfatin, leading to non-specific binding and negative responses. Therefore, in an alternative methodology was used - visfatin, Lispro and insulin were immobilized on separate channels along with bovine serum albumin immobilized on reference channel and eIR isoforms used as analyte to study the effect of visfatin on IR. This study showed that visfatin, a higher molecular weight protein compared to insulin, bound both the eIR isoforms. This is consistent with literature that visfatin binds IR at a site distinct from insulin, but the assay described here could not confirm the fact that it mimicked the signalling carried out by IR-insulin binding. Further studies are required to interpret the kinetics of visfatin-eIR interaction. To my knowledge, this is the first SPR assay developed to study eIR-insulin interactions in real-time. This could potentially be extended to study the interaction of insulin with full length insulin receptors and the effect of humoral and other external factors on the interaction, without the need for insulin labelling.

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The production of an efficient and low cost device has been the ultimate goal in the photovoltaic cell development. The fabrication and application of nanostructured materials in the field of energy conversion has been attracting a lot of attention. In this work, applications of surface plasmons (SPs) and photonic nanostructures to the field of energy conversion, specifically in the area of silicon solar cells and lanthanide energy upconversion (UC) luminescence applications were studied. Enhanced power conversion efficiency in bulk (single crystalline) silicon solar cells was demonstrated using an optimized mixture of the silver and gold nanoparticles (NPs) on the front of the cell to tackle the negative effect in the Au NPs plasmonic application. Then, a comparison of identically shaped metallic (Al, Au and Ag) and nonmetallic (SiO2) NPs integrated to the back contact of amorphous thin film silicon solar cells were investigated to solve a controversy issue in literature. The result indicates that parasitic absorption from metallic NPs might be a drawback to the SPs enhancement. A cost-effective fabrication of large area (5x5 cm2) honeycomb patterned transparent electrode for “folded” thin film solar cell application by combining the nanosphere lithography and electrodeposition were realized. Furthermore, the SPs enhanced tunable energy upconversion from NaYF4:Yb3+/Er3+ NPs in nanoslits were also demonstrated, our results shows that the relative red/green emission can be controlled by different plasmonic mode coupling. / Graduate / phwang@uvic.ca