Chemistry & Biochemistry Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2752
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Item Immobilized Seed-mediated Growth of Two Dimensional Arrays of Shaped Metallic Nanocrystals(2017) Perez Cardenas, Maria Teresa; Nie, Zhihong; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Acknowledging that the optical properties of noble metal nanocrystals (NMNCs) are largely determined by their size, composition, and shape, the demand for NMNCs with controlled shapes is expected to increase. To expand the property discovery and application development of polyhedral NMNCs, it is pivotal to understand the key factors involve in the nucleation and growth processes of NMNCs for better control over the crystal facets. Furthermore, to implement polyhedral NMNCs into functional devices for applications in such as chemical sensors, photovoltaics, and catalysis, it is essential to design cost-effective methods to assemble NMNCs into two-dimensional arrays with controlled orientation and particle distance. This dissertation describes the stability and interaction of molecular species formed during the reduction of gold metal precursor, as well as factors that influence the formation of nanocrystals with different shapes. Our study suggests that during the Au reduction step, an intermediate complex is formed. Over time the complex degrades decreasing the concentration of gold ions and subsequently slowing down or inhibiting the nucleation; thereby, affecting the reproducibility of synthetic methods. My findings will provide guidance for the development of more simple, reliable methods to control the shapes of the nanocrystals. Additionally, I developed an immobilized seed-mediated growth strategy for the fabrication of two-dimensional arrays of mono- and bi-metallic polyhedral nanocrystals with well-defined shapes and orientations on a substrate. This method relies on the controlled solution-phase deposition of gold and palladium metals on a selectively exposed surface of self-assembled seed nanoparticles that are immobilized on a substrate through collapsed polymer brushes. The synthetic approach I developed presents an important addition to current tools for the fabrication of substrate-supported functional nanocrystals as new materials and devices.Item Barcoded Silica Nanotubes for Bioanalysis(2007-09-25) He, Bo; Lee, Sang Bok; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Analysis of the chemical/biological species involved in health care is the most important step for diseases diagnosis and new drug screening. Barcoded nano/microparticles are attracting more and more interest for detection and identification of multiplexed chemical/biological species simultaneously. However, the development of barcoded particles is still in an early stage. To solve problems existing in current barcoded particles, such as spectral overlap and degradation of materials, our group has invented barcoded silica nanotubes (SNTs) and applied them to multiplexed immunoassays and cancer marker detection as coding materials. Barcode SNTs are fabricated by a multistep anodization template synthesis method. Each barcoded SNT has several segments with different reflectance values depending on their diameters and wall thicknesses. Therefore, the barcode of each SNT can be "read-out" with a conventional optical microscope. Barcoded SNTs have shown high stability and dispersibility in aqueous buffer media. Suspension arrays with barcoded SNTs have shown high sensitivity and high selectivity for the detection of multianalytes in the multiplexed immunoassays. Magnetic field separation is one promising technique to replace tedious filtration or centrifugation separation for rapid, gentle, and reliable isolation of target analytes. Barcoded SNTs have been coupled with magnetic bead (MB) separation for protein detection and analysis. The species and number of final collected SNTs represent the types and amount of analyte proteins, respectively. By using barcoded SNTs instead of fluorescence as signals, these suspension arrays overcome the problems existing in current MB suspension arrays, such as fluorescence quenching and interference of MBs' autofluorescence. Barcoded magnetic nanotubes (BMNTs) have also been successfully fabricated as dual-functional microcarriers for multiplexed immunoassays and cancer biomarker detection with magnetic separation. BMNTs combine the shape variety of barcoded SNTs and superparamagnetic properties of magnetic nanotubes. BMNTs overcome the problems in the existing dual-functional particles. The iron oxide nanocrystals are evenly dispersed in the inner void of the tubular structures without interference with the optical barcoded patterns. BMNTs have shown high selectivity when applied in multiplexed assays and cancer biomarker detection. The identification of BMNTs with software shows promising results for rapid data analysis. The dual-functional BMNTs provide a promising way for ultrafast, gentle, efficient, and automated detection of target chemical/biochemical molecules for diagnosis and drug screening.Item Synthesis and Characterization of Binary Clusters to Controllable Binary Nanoparticles "The New Role of Zintl Anions"(2004-10-27) Moses, Melanie Jean; Eichhorn, Bryan W; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Zintl anions are best described as polyatomic main group clusters (i.e. E73-; E = P, As, Sb) with structures characteristic of isoelectronic clusters (i.e. hydrocarbon and borohydride clusters). Combining these main group clusters and transition-metal precursors (Ni(COD)2; COD = cyclooctadiene, and Pd(PCy3)2; PCy3 = tricyclohexyl phosphine) with very labile ligands allows for the isolation of novel binary molecular clusters. The freedom these structures experience due to the absence of organic ligands lends itself to the very unique structure growth the binary clusters exhibit. Direct oxidation of these binary molecular clusters results in the formation of binary phases (i.e. PdAs2, NiAs, NiAs2). More control of the phase-specific binaries obtained can be achieved by controlling the reaction of the precursors, eliminating the need to isolate the clusters. Binary nanoparticles are in the forefront of heterogeneous catalyst development and application, making this an area of intense investigation. Structural characteristics of the binary clusters, [As@Ni12@As20]3-, [(Ni2Sb2)(Sb7)2]4-, [Ni5Sb17]4-, [Pd7As16]4- and [Pd2(E7)2]4- (E = P, As), and evidence for the formation of phase-specific binary nanoparticles (Ni5As2, Ni11As8, NiAs and NiAs2) under very mild conditions will be presented.