In this thesis we describe two separate experiments involving the use of gold nanoparticles. The first experiment looks at the use of gold nanoparticles as a localized heat source and the potential application as a cancer treatment. The second experiment, which is the real focus of this thesis, applies gold nanoparticles in the study of the free surface dynamics of glassy thin films. Gold nanoparticles have the ability to strongly absorb the energy in an incident laser beam and convert that energy into heat. Photothermal therapy is a proposed cancer treatment which exploits this ability to irreparably damage cancerous tissues surrounding gold nanoparticles. In the first chapter of this thesis we explain an experiment designed to probe the local temperatures achieved in such a process. Gold nanoparticles are used to stabilize the boundary of an inverse micelle system which contains an aqueous fluorescent dye solution on it's interior. A temperature dependent fluorescence intensity allows us to probe the temperature changes induced by laser irradiation. In the remainder of this thesis we describe a separate experiment involving the use of gold nanoparticles to study the free surface dynamics of thin glassy films. There is a growing body of evidence in the literature that thin polymer films in the glassy state exhibit heterogeneous dynamics; specifically that the first few nanometers from an air-polymer interface exhibit enhanced mobility relative to the interior of the film. The underlying mechanism responsible for this enhanced mobility remains elusive, however some believe it to be a direct consequence of the polymeric nature of these films. We describe in detail an experiment aimed at addressing this concern. We deposit gold nanoparticles onto the surface of a molecular (non-polymeric) glassy film and monitor their behaviour upon heating using atomic force microscopy. Our results clearly show the existence of enhanced surface mobility in the system studied and provide strong evidence that enhanced surface mobility should be expected in all glass forming systems.

<p>Expanding the role of plasmonics in tomorrow's technology requires a broader knowledge base from which to develop such applications today. Several limitations to the current plasmonics field limit progress to incremental advances within a narrow set of materials and techniques rather than developing non-traditional metals and flexible growth and characterization methods. The work described herein will provide an introduction to the burgeoning field of spectroscopic ellipsometry for plasmonic characterization; in particular, the power of its real-time monitoring capabilities and flexibility will be demonstrated. More importantly, a novel plasmonic metal, gallium, is investigated in detail. Critical characteristics of gallium for an array of applications include its tunability over a wide spectral range, phase stability across a wide temperature range, plasmon stability even after air exposure, and an ultra high vacuum evaporation growth process enabling simple, alloyed nanostructure development. Deeper scientific investigation of the underlying ripening mechanisms driving gallium nanoparticle formation and in concert with in situ alloying paves the way for future work contributing to the development of advanced nanostructured alloys. Finally, this work demonstrates the first example of gallium nanoparticle-enhanced Raman spectroscopy - an area craving materials innovation. While the specific application of gallium for SERS detection is interesting, the far-reaching implication lies in the demonstrated potential for plasmonic gallium nanoparticles' ultimate use in a wider variety of applications enhanced by nanoscale materials.</p> / Dissertation

<p>The refractive index sensitivity of plasmonic nanoparticles is utilized in the development of real-time, label-free biodetection. Analyte molecules that bind to receptor-conjugated nanoparticles cause an increase in local refractive index that in turn induces an energy shift in the optical resonance of the particle. Biomolecular binding is quantified by quantitatively measuring these resonance shifts. This work describes the application and optimization of a biomolecular detection system based on gold nanorods as an optical transducer.</p> <p>A microspectroscopy system was developed to collect scattering spectra of single nanoparticles, and measure shifts of the spectra as a function of biomolecular binding. The measurement uncertainty of LSPR peak shifts of the system was demonstrated to be 0.3 nm. An analytical model was also developed that provides the optimal gold nanorod geometry for detection with specified receptor-analyte pair. The model was applied to the model biotin-streptavidin system, which resulted in sensing system with a detection limit of 130 pM - an improvement by four orders of magnitude over any other single-particle biodetection previously presented in the literature.</p> <p>Alternative optical detection schemes were also investigated that could facilitate mulitplexed biosensing. A theoretical model was built to investigate the efficacy of using a multi-channel detector analogous to a conventional RGB camera. The results of the model indicated that even in the best case, the detection capabilities of such a system did not provide advantages over the microspectroscopic approach.</p> <p>We presented a novel hyperspectral detection scheme we term Dual-Order Spectral Imaging (DOSI) which is capable of simultaneously measuring spectra of up to 160 individual regions within a microscope's field of view. This technique was applied to measuring shifts of individual nanoparticles and was found to have a peak measurement uncertainty of 1.29 nm, at a measurement rate of 2-5 Hz.</p> / Dissertation

<p>Nanomaterials often exhibit enhanced reactivity relative to their larger colloidal counterparts because of the high specific surface area and number of imperfections on the crystal lattice at the nanoscale. Management of ecosystems, remediation of contaminated waters, and assessment of the potential risks from the industrial use on nanomaterials requires an understanding of the environmental factors that control the reactivity and bioavailability of natural and manufactured nanomaterials. Dissolved organic matter (DOM) acts as a moderator of reactivity and bioavailability for dissolved and particulate moieties in natural waters. DOM consists of a range of low and high molecular weight species that are complex and heterogeneous. It has been historically categorized based on operational definitions, rather than physical properties. In order to understand the effect of DOM on nanomaterials, there is an urgent need for information regarding specific properties of DOM, such as ligand groups. </p><p>The goal of this research was to study how cysteine, a low molecular weight metal-binding ligand, affects the composition and reactivity of nanoparticulate zinc sulfide and metallic silver. Zinc sulfide was used as a representative of nanoparticulate metal sulfide which occurs naturally in sulfidic environments. Metallic silver nanoparticles were also studied because of its wide use in consumer products. Both types of nanomaterials contain metal constituents (zinc and silver) that are expected to strongly bind to sulfhydryl-containing ligands (such as cysteine) in the environment. Serine is structurally similar to cysteine, with the only difference of a hydroxyl group in the place of the sulfhydryl group of cysteine. Therefore, serine was used for comparison as a hydroxyl-containing analogue to cysteine. </p><p>The aggregation kinetics of zinc and other metal sulfide nanoparticles in the presence of cysteine and serine were investigated using dynamic light scattering. Cysteine decreased aggregation rates of the particles, while serine had no effect on their aggregation behavior. Further experiments revealed that the mechanism of stabilization occurred through the adsorption of cysteine on zinc sulfide, which induced electrostatic charge on the particles surface. A direct link was established between the amount of cysteine sorbed and attachment efficiency, an indicator of the tendency of particles to aggregate. These results shed light on discrepancies in the literature between metal sulfide precipitation experiments conducted in our lab and work on the formation and aggregation of zinc sulfide nanoparticles on biofilms of sulfate reducing bacteria. </p><p>The early-stage growth and aggregation kinetics of zinc sulfide nanoclusters in the presence of cysteine was studied in detail using a suite of complementary techniques. Growth and aggregation experiments have been traditionally difficult to conduct due to instrumental precision issues, but newly developed analytical tools and software products have made it possible to study the early-stage formation of nanoclusters. Experiments with small angle X-ray scattering, X-ray diffraction, dynamic light scattering, and X-ray absorption spectroscopy at the extended fine structure range showed that cysteine controlled the growth and aggregation of zinc sulfide nanoclusters. The molar ratio between zinc, sulfide, and cysteine was a determining factor in the precipitation process. When zinc and sulfide were in equimolar concentrations with cysteine, very small nanoclusters of about 2.5 nm formed within 12 hours and aggregated to structures with hydrodynamic diameter larger than 100 nm. When cysteine was in excess of zinc and sulfide, aggregation was held to a minimum, but monomer nanoclusters were able to grow to about 5 nm in 12 hours. Overall, these results indicate the importance of thiol ligands on the monomer size, extent of aggregation, and aggregate structure of zinc sulfides. </p><p>The effect of metal ligands on metal bearing particle surfaces is of particular interest for manufactured nanoparticles, because they are typically coated with an organic coating during the production process. These coatings are sorbed on the particles surface and are likely to interfere between the metallic surface and the ligand. Dissolution experiments using citrate and polyvinylpyrrolidone (PVP) coated zero valent silver nanoparticles in the presence of cysteine and serine showed that cysteine dissolved both types of particles, while serine did not. Dissolution rates depended on the aggregation state of the particles exposed to cysteine. As indicated by zeta potential and adsorption measurements, cysteine replaced the coating on the particles surface and altered their aggregation pattern. X-ray absorption spectroscopy near the absorption edge showed partial oxidation of silver and formation of Ag(+I)-sulfur bonds, indicating that the thiol group in cysteine formed chemical bonds with oxidized surface silver atoms. A comparison between the two coatings showed that citrate coated particles dissolved approximately three times faster than PVP coated particles. Overall, these results show that metal binding ligands can drastically change the fate of manufactured silver nanoparticles in the environment and that this effect is moderated by surface coatings. </p><p>The results of this study suggest that cysteine, a metal binding ligand was able to induce and control transformations, such as growth, aggregation, dissolution, and surface reactivity of zinc sulfide and metallic silver nanoparticles. Cysteine adsorbed on metal sites on both ZnS and Ag particles, inducing changes on their surface charge. Aggregation of ZnS particles was slowed because of a net decrease in zeta potential compared to the bare particles. On the contrary, cysteine enhanced the aggregation of Ag particles, by replacing the citrate and PVP coatings on the particles surface. Finally, the cysteine-Ag(+I) bonds caused strong polarization on the particles surface and lead to the oxidative dissolution of the particles. </p><p>Overall, this research provides a better understanding of the fate of natural and manufactured nanoparticles in anaerobic waters, where thiols are present in significant amounts. It may also be used for risk assessment of manufactured nanomaterials and the production of safer and environmentally responsible materials.</p> / Dissertation

This work demonstrates the pretilt angle controllable photo-alignment effect in nanoparticles and azo-dye doped liquid crystal film. Followed by increasing the absorbed azo-dye, the vertical alignment induced by nanoparticles of polyhedral oligomeric silsesquioxanes (POSS) can be changed from high pretilt to low pretilt angle. Competition between the homogeneously aligned azo-dye and POSS-induced spontaneous vertical alignment domain generated the variable pretilt angle. The pretilt angle is a function of the pumping intensity and can be controlled continuously within the range of 0¢X~90¢X. With the sufficient absorption of photo excited azo-dye, The POSS induced vertical alignment can be switch to homogeneous alignment. The pretilt angle and surface energy are also examined to confirm the alignment effect. Both nanoparticles and azo-dye induced vertical and homogeneous alignment are non contact methods, and suitable for low temperature plastic process.

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This study presents a simple process for producing resistance-based humidity sensors utilizing dopamine (DA) coated gold nano-particles (AuNPs) as the sensing material. The sensing material for typical humidity sensors are solid state metal oxides, graft-polymers or salt-doped polymers. However, these humidity sensors may suffer from low sensing response or slow time response since water molecules have to diffuse into the sensing materials to induce the electrical property changes. Alternatively, AuNPs have large surface area for water molecule absorption and can be potentially for high performance humidity sensing. Nevertheless, the surface property of AuNPs is hydrophobic and needs to be modified. In this regards, this work uses a highly hydrophilic molecule of dopamine to modify the surface of AuNP into hydrophilic to enhance the humidity sensing performance. Highly hydrophilic bio-molecule of dopamine is physically bonded onto 4-6 nm AuNPs to enhance the humidity sensing performance. Results show that the DA coated AuNPs have nice humidity sensing responses in the measuring range of 20-90%RH. The measured resistance response shows >1500 times greater than the sensor using the same AuNPs without DA coating. The developed humidity sensor shows rapid time responses for water absorption (13 s) and desorption (30 s), respectively. Moreover, a 3-day long-term measurement at low, medium and high humidity ranges also shows the good stability of the developed sensor. The method developed in this study provides a simple and low-cost method to produce high-performance humidity sensors with DA-coated AuNPs.

The chemical characterization of individual nanoparticles (NPs) </= 100 nm in diameter is one of the current frontiers in analytical chemistry. We present here, a methodology for the characterization of individual NPs by obtaining molecular information from single massive cluster impacts. The clusters used in this secondary ion mass spectrometry (SIMS) technique are Au4004+ and C60+. The ionized ejecta from each impact are recorded individually which allows to identify ions emitted from a surface volume of ~10 nm in diameter and 5-10 nm in depth. The mode of analyzing ejecta individually from each single cluster impact gives insight into surface homogeneity, in our case NPs and their immediate surroundings. We show that when the NPs (50 nm Al) are larger than the size of the volume perturbed by the projectile, the secondary ion emission (SI) resembles that of a bulk surface. However, when the NP (5 nm Ag) is of the size range of the volume perturbed by projectile the SI emission is different from that of a bulk surface. As part of this sub-assay volume study, the influence of neighboring NP on the SI emission was examined by using a mixture of different types of NPs (5 nm Au and 5 nm Ag). The methodology of using cluster SIMS via a sequence of stochastic single impacts yield information on the surface coverage of the NPs, as well as the influence of the chemical environment on the type of SI emission. We also present a case of soft landing NPs for laser desorption ionization mass spectrometry. NPs enhance the SI emission in a manner that maintains the integrity of the spatial distribution of molecular species. The results indicate that the application can be extended to imaging mass spectrometry.

Research on nanofluids has been undertaken for several years because of the reported enhancements of thermal properties such as thermal conductivity and enhanced heat transfer performance in laminar flow. Nanofluid is the fluid where nanoparticles are dispersed in a base fluid. Thermal conductivity and viscosity are considered to be the most prominent factors in the efficient use of nanofluids. A change in thermal conductivity and viscosity also changes the convective heat transfer coefficient. Nanoparticles can be metallic or non-metallic and also can have different shapes. In this study, Poly-Alpha-Olefin (PAO) has been used as a base fluid with Alumina (Al2O3) nanoparticles. Poly-Alpha-Olefin is commonly used for engine lubrication in military applications and cooling in electronic and industrial devices. Several nanofluid samples were made by METSS Corp. in Ohio, USA using different dispersants, different base fluids and different morphology of alumina nanoparticles. The mass fraction of nanoparticles is from 2.5 to 20 percent. The thermal properties of each sample such as thermal conductivity and viscosity have been measured. Thermal conductivity of nanofluids and pure base fluids were both measured and the thermal conductivity enhancement has been calculated. Also, the heat transfer coefficient has been determined for laminar flow under constant heat flux conditions. Results indicate that all the tested nanofluids and base fluid samples show a Newtonian behavior. Among the nanofluid samples, NF-048, which contains non-spherical Alumina nanoparticles exhibits the greatest thermal conductivity enhancement when compared to pure PAO. Heat transfer tests were conducted with pure PAO and NF-048, and an enhancement in convective heat transfer coefficient was observed. The thermal conductivity of NF-048 increases with temperature, which is consistent with heat transfer results. Furthermore, the percentage enhancement in convective heat transfer coefficient was shown to increase non-linearly with the axial distance in the heat transfer section. NF-048 exhibits a lower Re (Reynolds number)*Ra (Rayleigh number) than pure PAO under laminar flow constant heat flux conditions indicating that nanoparticle morphology and composition are the two main factors responsible for convective heat transfer enhancement at low Reynolds number.

The aim of this project was to design an intelligent controlled release system based on thermoresponsive nanoparticles for cancer therapy and to evaluate the efficiencies of these systems with in vitro cell culture. Poly(Nisopropylacrylamide), an important thermoresponsive polymer, was selected for this study to prepare the responsive nanoparticles. This polymer has an lower critical solution temperature (LCST) of 32 oC, below which it is hydrophilic and above this temperature, it shows hydrophobic behavior. Controlling drug release with this property was the objective of this study. Nanoparticles were prepared by nanoprecipitation method. By using different solvent:non-solvent ratios and polymer concentrations, different samples were prepared. The particle size was decreased when solvent:non-solvent ratio was increased and polymer concentration was decreased. This was found to be related with the solution viscosity. Nanoparticles prepared from polymers prepared with different initiatoraccelarator amounts had significantly different sizes and release rates, and additionally the size of particles prepared from polymers with various crosslinker amounts were decreased with increased croslinker amount. In situ release experiments were performed both below and above polymer&amp / #8216 / s LCST degree. Uncrosslinked nanoparticles demonstrated higher release rate of Celecoxib above LCST. However, there was no significant difference with the crosslinked nanoparticles. Crosslinked and uncrosslinked nanoparticles were tested on Saos-2 cells to assess their toxicity. Both Celecoxib loaded and free crosslinked particles were found to be cytotoxic. Uncrosslinked nanoparticles showed an increased toxicity upon loading with the bioactive agent, Celecoxib. In conclusion, uncrosslinked particles would be a proper drug carrier for cancer therapy with enhanced drug loading.