<p> This thesis describes the synthesis of water-soluble dendron-conjugated gold nanoparticles (Den-AuNPs) with various average core sizes and the evaluation of stability, cytotoxicity, and cell permeability and uptake of these materials. The characterization of Den-AuNPs using various instruments including transmission electron microscopy (TEM), matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF-MS), 1H NMR, FT-IR, and UV-vis spectroscopy confirms the dendron conjugation to the glutathione-capped gold nanoparticles (AuNPs). The stability of AuNPs and Den-AuNPs in solutions of different pH and salt concentration was determined by monitoring changes in surface plasmon bands of gold using UV-vis spectroscopy. The Den-AuNPs were found to be more stable than the precursor AuNPs maintaining their solubility at the pHs higher than 4 and with the salt concentrations of up to 100 mM. The improved stability of Den-AuNPs suggests that the post-functionalization of thiol-capped gold nanoparticle surfaces with dondrons can further improve the physiological stability and biocompatibility of gold nanoparticle-based materials. Cytotoxicity studies with AuNPs and Den-AuNPs with and without flourophores were also performed by examining cell viability for 3T3 fibroblasts using a MTT cell proliferation assay. The conjugation of dendrons to the AuNPs with flourophores was able to decrease the cytotoxicity brought about by the flourophores. The successful uptake of Den-AuNPs in mouse fibroblast 3T3 cells shows the physiological viability of the hybrid materials.</p>

<p> Nanoscopic pores in biological systems &ndash; cells, for example &ndash; are responsible for regulating the transport of ionic and molecular species between physiologically distinct compartments maintained by thin plasma membranes. These biological pores are proteinaceous structures: long, contorted chains of chemical building blocks called amino acids. Protein pores have evolved to span a staggering range of shapes, sizes and chemical properties, each crucial to a pore's unique functionality. </p><p> Protein pores have extremely well-defined jobs. For instance, pores called ion channels only transport ions. Within this family, there are pores designated to selectively transport specific ions, such as sodium channels for sodium, chloride channels for chloride and so on. Further subdivisions exist within each type of ion channel, resulting in a pantheon of specialized proteins pores. </p><p> Specificity and selectivity are bestowed upon a pore through its unique incorporation and arrangement of its amino acids, which in turn have their own unique chemical and physical properties. With hundreds of task-specific pores, deciphering the precise relationship between form and function in these protein channels is a critical, but daunting task. In this thesis, we examine an alternative for probing the fundamental mechanisms responsible for transport on the nanoscale. </p><p> Solid-state membranes offer well-defined structural surrogates to directly address the science underlying pore functionality. Numerous protein pores rely on electronic interactions, size exclusion principles and hydrophobic effects to fulfill their duties, regardless of their amino acid sequence. Substituting an engineered and well-characterized pore, we strive to achieve and, thus, understand the hallmarks of biological pore function: analyte recognition and selective transport. </p><p> While we restrict our study to only two readily available membrane materials &ndash; one a polymer and the other a ceramic &ndash; nanofabrication techniques give us access to a virtually limitless combination of pore shapes and sizes. Exploiting this, we investigate the role of pore geometry in mediating the electrostatic and steric interactions responsible for transport on the nanoscale. Through targeted chemical modifications of our homogenous pores, we easily tailor their surface properties to investigate the role of hydrophobic effects in confined environments. Unbound by the physiological limitations of protein structures (such as sensitivity to electrolyte composition and fragility to external forces), our report concludes with the fusion of fabrication and modification considerations to design robust components for nanofluidic circuitry and nanoscopic biosensors.</p>

<p> We present a versatile biosensing strategy that uses nucleic acids programmed to undergo an isothermal toehold mediated strand displacement in the presence of analyte. This rearrangement results in a double biotinylated duplex formation that induces the rapid aggregation of streptavidin decorated quantum dots (QDs). As biosensor reporters, QDs are advantageous to organic fluorophores and fluorescent proteins due to their enhanced spectral and fluorescence properties. Moreover, the nanoscale regime aids in an enhanced surface area that increase the number of binding of macromolecules, thus making cross-linking possible. The biosensing transduction response, in the current approach, is dictated by the analysis of the natural single particle phenomenon known as fluorescence intermittency, or blinking is the stochastic switching of fluorescence intensity ON (bright) and OFF (dark) states observed in single QD or other fluorophores. In contrast to binary blinking that is typical for single QDs, aggregated QDs exhibit quasi-continuous emission. This change is used as an output for the novel biosensing techniques developed by us. Analysis of blinking traces that can be measured by laser scanning confocal microscopy revealed improved detection of analytes in the picomolar ranges. Additionally, this unique biosensing approach does not require the analyte to cause any fluorescence intensity or color changes. Lastly, this biosensing method can be coupled with therapeutics, such as RNA interference inducers, that can be conditionally released and thus used as a theranostic probes.</p><p>

Thesis (Ph. D.)--Duke University, 2007. / Includes bibliographical references.