The electro-optical properties of the ZnO/Si heterojunction embedded with self-assembled gold nanoparticles on patterned silicon substrate are investigated in this master thesis. High quality n-type ZnO film is deposited on patterned p-type silicon substrate by radio-frequency sputtering to form a ZnO/Si pn junction. The patterned silicon substrates are prepared by ICP-RIE using self-assembled nickel metal dot and silicon dioxide as etching mask. The optimum ICP process conditions of silicon nanopillars are CF4/Ar ~ 40/40 sccm and bias/RF power 400/400 W. Silicon nanopillars of diameter ~ 50 nm and height 100~400 nm are formed on the substrate surface. ZnO film is then deposited of a growth rate ~ 12 nm/min at the substrate temperature = 200oC. The plasmonic effects on the electro-optical properties, including photoluminescence (PL), reflection, and electrical characteristics, are studied by adding self-assembled gold nanoparticles within the ZnO film. The self-assembled gold nanoparticles are formed by thermal deposition and rapid thermal annealing at 700oC. The gold nanoparticles are observed by scanning electron microscopy (SEM) and particles of diameter about 100 nm. The PL intensity of ZnO is enhanced more than ten times at the peak wavelength = 380 nm by adding the gold nanoparticles and silicon nanopillars. Strong blue emission light could be saw with the naked eyes. For the electric characteristics, self-assembled gold nanoparticles in patterned ZnO/Si heterojunction show photoelectric conversion phenomenon because of high electromagnetic absorption and plasmonic effects.

Understanding and manipulating nanosized particles is crucial for the advancement of nanotechnology research. Dependent light scattering of noble metals can be used to achieve new material responses that can be used in different applications. Dependent light scattering of nanoparticles allows the understanding of orientation and location of closely positioned particles. Besides, dependently scattering metallic particles create significantly enhanced near fields and high absorption rates when excited at their plasmon resonance. It is used for spectrally selective heating and melting of nanosized particles as a nanomanufacturing method. With numerical methods dependent scattering properties of particles can be obtained. In this study, the dependent optical absorption efficiencies of metallic nanoparticles are obtained with the newly developed Integrated Poynting Vector Approach (IPVA). This is used in conjunction with a numerical light scattering solution tool DDSCAT. Results indicate that IPVA and DDSCAT together can be used for the estimation of scattering and absorption of nanoparticles affected by the near field of other particles in their close vicinity. The method is suggested to be suitable for the understanding of physical mechanisms behind dependent scattering prior to experiments that require lots of effort and resources.

In order to gain insights into the electronic interactions between metallic gold and self-assembled monolayers composed of π-conjugated thiols, a series of thiol-containing molecules based on a stilbene backbone were synthesized and assembled on gold surface. The resulted monolayers were characterized with a variety of surface-sensitive techniques and the electronic properties of the obtained surfaces were studied with the use of ultraviolet photoelectron spectroscopy. Work-function changes and alignment of the molecular energy levels with respect to the Fermi level of the metal were investigated and important insights regarding the electronic properties of the metal / organic interfaces were obtained. Another aspect of interactions between organic dyes and metallic gold was studied in the context of spectroscopic properties of systems incorporating gold nanoparticles with organic fluorophores covalently attached to the nanoparticle surface. Ultrafast dynamics of the excited-state deactivation of the organic fluorophores attached to the surface of gold nanoparticles were studied with the use of a fs transient absorption technique. It was found that the close proximity of a gold nanoparticle had a profound impact on the excited-state lifetime of the studied organic fluorophore. The influence of the structure of the studied systems on the excited-state deactivation dynamics of the organic fluorophores was described.

A few computational models currently exist to predict heat production and dissipation in tissue when a tumor containing optically-tunable gold nanoparticles such as nanoshells or nanorods is illuminated with near infrared (NIR) laser. The validity of any computational model still needs to be established by experiments before its wide use for various future clinical applications. One of the possible ways to validate the model is through the heat measurements within a phantom made with tissue-equivalent heat-sensitive gel. Currently, there are a few recipes available for this type of gel and the majority of them use severely toxic ingredients. However, none of them seems to perfectly serve the current purposes. Therefore, the primary goal of this thesis work was to develop and characterize two new types of heat-sensitive gels, using relatively non-toxic substances for the in-phantom validation of computational models. Specifically, two novel agar based phantoms, TG1 and TG2, were developed and characterized. The basic optical response of these phantoms at 808 nm NIR light was determined to test their equivalency to human tissue. Thermal damage to the phantoms was quantified by heating them to specific temperatures and obtaining calibration curves to relate temperature and R2 relaxation rates. The phantoms were scanned with magnetic resonance imaging (MRI) to obtain T2 values. TG1 gel, agar and bovine serum albumin (BSA) mixture, was found not to be optically tissue-equivalent. However, TG1 gel demonstrated unambiguous digital response capable of distinguishing temperature of at least 70 °C compared to the sample receiving no heat. Additionally, TG1 gel produced high degree of linearity in the thermal therapy temperature regime (60 - 80 °C). TG2 gel containing agar mixed with BSA and Intralipid has exhibited tissue equivalency based on laser transmission measurements. TG2 gel exhibited heat damage based on T2 values, only when the temperature reaches 80 °C. This digital response is considered less sensitive in view of the fact that BSA starts to undergo denaturing and cause optical density change at approximately 70 °C. Both gels, however, have shown to be thermally stable at temperatures up to 80 °C with no evidence of gel melting being observed.

Various solution-processed methods have been employed in this work. For the synthesis of graphene, a chemical exfoliation method has been used to generate large graphene flakes in the solution phase. In addition, chemical or electro polymerization has been used for synthesizing polyanthracene, which tends to form graphene nanoribbon through cyclodehydrogenation. For the device fabrication, graphene oxide (GO) thin films were deposited from solution phase on the vapor-silanzed aminosilane surface to make semiconducting active layer or conducting electrodes. Gold nanoparticles (AuNPs) were selectively self-assembled from solution phase to pattern nanowires.

The present thesis titled “Molecular Modulation of Material Properties: Stud- ies on Nanoparticles, Nanoassemblies and Low Molecular Mass Gelator” deals with the preparation, characterization, and investigations into the properties of gold nanoparticles coated with novel thiols. The coverage of nanoparticle surfaces with these thiols renders them with special characteristics that will be of interest in biological and sensor applications. Also, a novel low molecular mass tetrameric sugar-based hydrogelator was synthesized and its gelation properties were studied in detail. Chapter 1 gives a general introduction and an overview about Nanomaterials, with emphasis towards nanoparticles of gold, which form the basis of this work. It delves with the history of research in noble metal nanoparticles, their interesting electronic and optical properties, the present methods of synthesis of high quality nanoparticles of noble metals, numerous potential applications of these novel materials, as well as the challenges in their real-life applications, and ends with the future outlook of this field of research. Chapter 2 describes the synthesis and characterization of three cationic lipid-like disulfides whose molecular structures are shown in Fig. 2.1. Gold nanoparticles capped with these molecules were then synthesized in small size dispersion by a simple one-phase protocol. These particles exhibited remarkably different solubility properties that were dictated by the molecular structure of the capping agent. The nanoparticles were characterized by a variety of techniques like UV-visible spec- troscopy, Transmission Electron Microscopy (TEM), proton Nuclear Magnetic Resonance (1H NMR), Fourier Transform Infra-red (FTIR) spectroscopy, and Zeta Potential measurements. These nanoparticles were then examined for their interactions (structural formula) Figure 1: Chemical Structures of the cationic lipid-like thiols used for nanoparticle preparation with dipalmitoyl phosphatidyl choline (DPPC) vesicles as model biological membranes. TEM, UV-vis, and Differential Scanning Calorimetry (DSC) were employed to probe the interactions. It was found that the capping agent of the nanoparticle had a strong bearing upon the interactions of the nanoparticles with DPPC vesicles. Chapter 3 describes the assembly of hydrophilic cationic nanoparticles upon elec- trostatic interaction with a variety of anionic surfactants. The chemical structures of some of the anions employed in the study, as well as a schematic of cationic nanopar- ticle are shown in Fig. 2. Upon ion pairing with long-chain anionic surfactants, the hydrophilic cationic nanoparticles were completely hydrophobized. They could then be phase-transferred to organic layer. TEM showed that nanoparticles assemble in to a variety of mesostructures upon ion-pairing with anions. The aggregate formation was found to depend critically upon length of the hydrophobic alkyl chain as well as the head-group of the anion. Isothermal Titration Calorimetry (ITC) was employed to probe the interactions of these nanoparticles with anions. It was found that the anions that resulted in nanoparticle precipitation displayed exothermic interactions with the nanoparticle. Chapter 4 deals with the synthesis of -thiolated metal chelator derivatives whose structures are shown in Fig. 3. The molecules are based on well-known chelators viz. iminodiacetic acid and bis-(2-pyridylmethyl)amine. While the first one is carboxylic acid-based chelator, the second one is pyridine-based. Nanoparticles coated with these chelators were synthesized in a size-controlled manner. These nanoparticles exhibited pH-controlled reversible assembly. However, while S-IDA based nanoparticles aggregated at low pH values, the S-BPA based nanoparticles aggregated in high pH regimes. Mixed monolayer protected gold nanoparticles were synthesized by employing S-BPA and C12H25SH as capping agents. It resulted in the formation of nanoparticles in low size-dispersion. These nanoparticles were characterized by 1H NMR spectroscopy to infer the ratio of the two capping agents on the nanoparticle surface. These nanoparticles demonstrated metal-ion induced aggregation. It was found that the nanoparticles could differentiate Cu2+ ions from other ions, and immediately formed aggregates in presence of Cu2+ ions. Chapter 5 describes the synthesis of novel mono-thiolated “Gemini” surfactants for nanoparticle synthesis. Gemini surfactants with different spacers were prepared. These surfactants had a 12-n-12 kind of molecular structure as shown in the Fig. 4. Upon preparation of nanoparticles with these thiols, the resulting material was soluble in water in the case of rigid thiols like D2S and DBPS Chapter 6 deals with the synthesis and hydrogelation properties of a low molecular mass hydrogelator based on an azobenzene based tetrameric sugar derivative (Fig. 5). The pKa of carboxylic acids in the molecule were determined using 13C NMR. The trans-to-cis isomerization of the compound was probed by time-dependent UV-vis studies. The sugar derivative exhibited pronounced hydrogelation capacity, gelling water at micromolar concentration. The gel formed was characterized extensively (structural formula) Figure 2: Schematic of cationic nanoparticles and molecular structures of the anions employed for nanoparticle assembly (structural formula) Figure 3: Chemical structures of metal-chelator containing thiols employed for the pH-controlled and metal-ion mediated nanoparticle assembly (structural formula) Figure 4: Schematic of cationic nanoparticles and molecular structures of the anions employed for nanoparticle assembly (structural formula) Figure 5: Chemical Structure of azobenzene-based tetrameric sugar derivative exhibit- ing pronounced hydrogelation using melting temperature analysis, UV-vis, FT-IR, circular dichroism spectroscopy and scanning electron microscopy. The resultant gel exhibited impressive tolerance to the pH variation of the aqueous phase and gelated water in the pH range of 4 to 10. While UV-vis and CD spectroscopy indicated that pronounced aggregation of the azobenzene chromophores in the gelator was responsible for gelation, FT-IR studies showed that hydrogen bonding is also a contributing factor in the gelation process. The melting of gel was found to depend upon the pH of the aqueous medium in which gel was formed. The gel showed considerable photostability to UV irradiation indicating tight intermolecular packing inside gelated state that render azobenzene groups in the resultant aggregate refractory to photoisomerization. The electron micrographs of the aqueous gels thus formed showed the existence of spongy globular aggregates in such gelated materials. Addition of salts to the aqueous medium led to a delay in the gelation process and also caused remarkable morphological changes in the microstructure of the gel. Appendix A describes the employment of ligand-free palladium nanoparticles towards efficient catalysis of Heck and Suzuki reactions in aqueous medium. Hexadecyl trimethylammonium bromide was employed as the surfactant to achieve solubilization of organic compounds in aqueous medium. UV-vis and TEM investigations into the formation of nanoparticles in the reaction media were undertaken. These studies indicate that the nanoparticles were formed by reduction of potassium tetrachloropalladinate by methyl acrylate used as one of the reactants. TEM investigation indicated the formation of nanoparticle assemblies upon solvent drying. Efficient and catalytic synthesis of a number of organic compounds could be achieved in high yield.

Detection of trace elements such as organic contaminants, explosive residues, and metal ions is an intellectually challenging task in science and engineering. It is also a topic of increasing importance due to its impact on society and the environment. Designing molecularly imprinted materials is one of the most promising approaches to explore sensing and detection applications. “Stimuli-sensitive” polymer materials are ideal candidates for these imprinted sensors as they are able to respond to changes in their environment and can be tailored by cross-linking the polymer chains. The responses can be amplified and transduced into measurable signals due to macromolecular properties provided by the use of a polymer. The purpose of the research in this project is to combine organic polymers with inorganic constituents to tailor the binding properties and the responses of the composite material for detection of metals ions in aqueous solutions. The research, here, is based on a thermally responsive polymer such as poly(Nisopropylacrylamide) (PNIPAM), which exhibits a well-known reversible volume phase transition in aqueous media around approximately 32°C. Combining cross-linked microgels formed from PNIPAM and its copolymers with gold nanoparticles (GNP) imparts the composite material with optical properties such as intense visible absorption due to the unique surface plasmon absorption of these small nanoparticles. The use of copolymers allows incorporation of functional groups, such as carboxylic acid, that are potential sites for binding metal ions. Cross-linking of the metal ion binding polymer imprints the metal ion in the PNIPAM microgel network. In this research, design of the composite material was investigated using copolymers of NIPAM and acrylic acid (AA), copolymers of NIPAM and glycidyl methacrylate (GMA), and interpenetrating networks of PNIPAM and PAA. A broad spectrum of polymerization conditions were studied such as changes in cross-linking density as well as changes in the synthetic procedure. Techniques such as turbidometry, ultraviolet visible spectroscopy (UV-VIS), transmission electron microscopy (TEM), and dynamic light scattering (DLS) were employed to characterize the microgels as well as their composites with GNP. Preliminary investigation of imprinting the microgels with heavy metal ions such as copper was also performed. The novel polymer-metal nanocomposites explored here will serve as an important contribution for the current ongoing research efforts in designing materials in the nano-scale capable of sensing and detecting metal ions in solution with high selectivity.

Cancer has become one of the leading causes of death today. The early detection of cancer may lead to desired therapeutic management of cancer and to decrease the mortality rate through effective therapeutic strategies. Advances in materials science have enabled the use of nanoparticles for added contrast in various imaging techniques. More recently there has been much interest in the use of gold nanoparticles as optical contrast agents because of their strong absorption and scattering properties at visible and near-infrared wavelengths. Highly proliferative cancer cells overexpress molecular markers such as epidermal growth factor receptor (EGFR). When specifically targeted gold nanoparticles bind to EGFR they tend to cluster thus leading to an optical red-shift of the plasmon resonances and an increase in absorption in the red region. These changes in optical properties provide the foundation for photoacoustic imaging technique to differentiate cancer cells from surrounding benign cells. In photoacoustic imaging, contrast mechanism is based on the optical absorption properties of the tissue constituents. Studies were performed on tissue phantoms, ex-vivo and in-vivo tumor models to evaluate molecular specific photoacoustic imaging technique. The results indicate that highly sensitive and selective detection of cancer cells can be achieved by utilizing the plasmon resonance coupling effect of EGFR targeted gold nanoparticles and photoacoustic imaging. In conclusion, the combined ultrasound and photoacoustic imaging technique has the ability to image molecular signature of cancer using bioconjugated gold nanoparticles. / text

Current methods to diagnose and treat cancer often involve expensive, time-consuming equipment and materials that may lead to unwanted side effects and may not even increase a patient’s chance of survival. Thus, for a while now, a large part of the research community has focused on developing improved methods to detect, diagnose, and treat cancer on the molecular scale. One of the most recently discovered methods of cancer therapy is targeted therapy. These targeted therapies have potential to provide a patient with a form of personalized medicine because these therapies are biological molecules that specifically target other molecules involved with a cancer’s growth. Past trials using these therapeutic molecules, however, have led to controversial results, where certain patients responded better than others to the therapy for unknown reasons. Elucidating the reason behind these mixed results can be accomplished using metal nanoparticle technologies which could provide a bright signal to monitor the path that these therapeutic molecules take in vivo as well as enhance the molecule’s efficacy. Literature has shown that presenting targeting molecules in a dense manner to their target will increase these molecules’ binding affinity. This concept has been explored here to increase binding affinity of therapeutic molecules by attaching these molecules in a dense manner on the surface of gold nanoparticles, and correlating this increased affinity with therapeutic efficacy. Additionally, gold nanoparticles provide an easy surface for molecules to be functionalized on and have shown to be effective imaging, x-ray, and photothermal therapy agents. A major roadblock to using these gold nanoparticles clinically is their non-degradability and thus potential to cause long-term negative side effects in vivo. A platform for developing biodegradable gold nanoparticles is also explored here to take advantage of the gold nanoparticles’ excellent imaging and drug delivery capabilities while still allowing them to be used safely in the long term. / text

Gold nanoparticles attain an intense focus in biomedical imaging applications due to their unique optical properties, facile conjugation with biomolecules, and biocompatibility. Although a considerable amount of work towards the development of gold nanoparticles has been completed, these promising contrast agents have not yet reached the clinic due to several challenges including efficient accumulation at the diseased site, sensitivity of detection in vivo, potential adverse effects, and clearance from the body. High signal-to-background ratio is required to enhance sensitivity of detection. Because near infrared (near-IR) light has the best tissue penetration, contrast agents designed to work in this range can significantly increase imaging sensitivity. Moreover, efficient targeting of the molecular biomarkers on diseased cells can decrease the required dosage, increase the site-specific accumulation, and enhance the imaging sensitivity. Molecular-specific contrast agents developed in this project use directional attachment of antibody molecules to the nanoparticle surface, enhancing the targeting efficacy. Additionally, cell-based delivery of diagnostic and therapeutic agents is gaining much interest due to the immune cells’ special access to the avascular, diseased regions. The contrast agents developed in this project enable detection of just a few cells per unit of imaging volume, enable multiplex imaging, and open up a possibility for tracking different cell populations with noninvasive photoacoustic and ultrasound imaging. Finally, the clearance of nanoparticles from the body dictates their clinical translation. The in vivo pharmacokinetics study along with the proposed in vitro model explored in this project will enable fast, reliable, and cost-efficient screening of promising agents and facilitate quick optimization of nanoparticles for their potential use in the clinic. / text