Browsing by Author "Hafner, Jason H"
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Item Anisotropic Noble Metal Nanomaterials for Analytical Surface Enhanced Raman Spectroscopy(2014-09-03) Payne, Courtney Michelle; Hafner, Jason H; Colvin, Vicki L; Pasquali, MatteoNoble metal mesoscale and nanoscale materials exhibit unique optical properties that are of interest to a wide variety of fields including sensing, imaging, biomedicine, and catalysis. The properties of the nanomaterial are strongly dependent on the size, morphology, composition, and local molecular environment of the material, all of which can be controlled by material design and synthesis. A novel nanomaterial referred to as a gold nanobelt was synthesized and characterized. Gold nanobelts synthesized in cetyltrimethylammonium bromide and sodium dodecylsulfate and with sub-100 nm rectangular cross sections were found to exhibit a strong transverse plasmon peak at visible wavelengths. Unlike larger diameter silver nanowires, these nanobelts exhibit sharp, tunable plasmon resonances similar to those of nanoparticles. The gold nanobelt crystal structure contains a mixture of face centered cubic and hexagonally close packed lattice phases that can be isolated and examined individually due to the unique nanobelt size and shape. The nanobelt synthesis is very sensitive to temperature which is likely due to the transition of the surfactant solution from wormlike micelles to spherical micelles. The electromagnetic field enhancing properties of gold nanobelts, silver nanowires, gold microplates, and gold nanorods were used to fabricate platforms for analytical surface enhanced Raman spectroscopy. Gold nanobelts and silver nanowires were deposited on glass substrates and when used alone or in combination with a gold microplate demonstrate surface enhancing capabilities. A thin film of gold nanorods was shown to be easily modifiable and provide surface enhanced Raman spectra of the local chemical environment.Item Investigating Cholesterol Orientation in Lipid Bilayer by Raman Spectroscopy(2020-07-29) Demers, Steven Meyer; Hafner, Jason HBiological membranes are composed of numerous types of molecules ranging from different sterols to phospholipids to membrane partitioning proteins. While the overall compositions of these various elements are understood in part, how the phospholipid bilayer in cells accommodates the different processes for the copious types of proteins is not fully understood. Cholesterol however has been proven to play a key role in animal membrane functions. By using gold nanorods as a substrate, lipid membranes encapsulated the nanorods for the lipid structure to be analyzed by SERS. Optical excitation of gold nanoparticles at their size and shape-dependent plasmon resonant frequency induces strong oscillations of the nanoparticle’s free electron gas, leading to surfaced enhanced Raman scattering (SERS) – an enhancement of Raman scattering signals with a molecular scale distance dependence from the gold surface. The gold nanorods used for this project were tuned to an excitation laser wavelength of 785 nm. From previous lipid membrane studies, dioleoylphosphatidylcholine (DOPC) was demonstrated to have a well ordered, gold supported bilayer. Once a lipid bilayer was exchanged to the gold nanorod surface, a lipid solution interspersed with cholesterol was exchanged to the surface. The presence of cholesterol was confirmed in SERS by additional Raman peaks being observed that were characteristic of only cholesterol. Structural analysis by the surfaced enhanced Raman scattering (SABERS) method combines SERS and unenhanced Raman spectra with theoretical calculations of the optical field and molecular polarizability. Raman measurements of the samples are orientationally averaged while SERS spectra contain information on molecular position and orientation relative to the surface. Together these reveal the molecular orientation and position of cholesterol in phospholipid bilayers. This method offers an approach to analyzing lipid membrane molecular structure under ambient conditions, with microscopic quantities, and without molecular labels.Item Optical and Transport Properties of Nano-objects(2015-09-01) Wang, Lin-yung; Link, Stephan; Nordlander, Peter; Hafner, Jason HThis dissertation presents theoretical and experimental studies on the optical and transport properties of selected nano-objects. The theoretical part of this work is particularly devoted to the study of the optical spectra of quasi-1D gold nanoparticle assemblies, single gold nanorod and its chiral dimer. The theoretical method is based on the analytical and numerical solutions to the classical Maxwell's equations. Specifically, quasi-1D gold nanoparticle assemblies of equal width comprising nanoparticles with different sizes, the onset of the infinite chain limit and its associated energy are governed by the number of repeat units and not the overall length of the polymer. Chiral, twisted, self-assembled gold nanorod dimers were modelled by the finite-difference time-domain method. It is demonsrated through extensive simulations that the lineshape of the scattering circular dichroism spectra of twisted gold nanorod dimers is tuned through two major ways of symmetry breakings: size mismatch and twistness. Finally, using single-molecule fluorescence microscopy, the transport properties of an interesting surface-rolling molecule, \textit{nanocar}, is characterized by means of its 2D diffusion coefficient and fraction of moving, which are in good agreement with a 2D surface diffusion model. The findings presented in this thesis bring deeper and more sophisticated understanding to the underlying mechanisms of nanoscience.Item Structural Analysis by Enhanced Raman Scattering(2017-01-25) Matthews, James R; Hafner, Jason HBiological membrane structure is inherently complex, and understanding the structure of peptide chains inserted in membranes is vitally important for the development of effective diagnosis and treatments of diseases. Surface Enhanced Raman Spectroscopy (SERS) was used as a tool for studying lipid membrane structure in a natural fluid, room temperature environment. Gold nanostructures focus light to a molecular length scale at their surface, creating the possibility to visualize molecular structure. Optical excitation of gold nanoparticles at their size and shape-dependent plasmon resonant frequency induces strong oscillations of the nanoparticle’s free electron gas, leading to SERS – an enhancement of Raman scattering signals in a distance dependent manner at the molecular scale. This project utilizes gold nanorods, tuned to an excitation laser wavelength of 785 nm, as a substrate for lipid membranes so that their structure can be analyzed by SERS. The surfactant cetyltrimethylammonium bromide (CTAB) that stabilizes nanorods was exchanged with the biologically relevant lipid dioleoylphosphatidylcholine (DOPC), and the insertion of the peptide residue tryptophan into the lipid membrane was observed using SERS for confirmation. Full characterization of the lipid membranes was carried out, demonstrating a well ordered, gold supported bilayer. SERS spectra also contain information on molecular position and orientation relative to the surface, but are difficult to interpret quantitatively. An analysis method that combines SERS and unenhanced Raman spectra with theoretical calculations of the optical field and molecular polarizability is introduced. Together these reveal the molecular orientation and position of surfactant layers on gold nanorods and of tryptophan in phospholipid bilayers. This method offers a new approach to analyzing lipid membrane molecular structure under ambient conditions, with microscopic quantities, and without molecular labels.Item Surface Chemistry of Gold Nanoparticles and Applications(2022-06-24) Zhang, Aobo; Hafner, Jason HThe interactions between commonly used surfactants and gold nanoparticles (GNPs) are studied primarily by surface enhanced Raman spectroscopy (SERS). New GNPs stabilization strategies are developed with industrial surfactants. GNPs stabilized by these surfactants can provide more surface chemistry options as starting points for photothermal therapy. The structure of surfactant cetyltrimethylammonium bromide (CTAB) on the surface of gold nano bipyramid is studied by an analytic method. The method takes a ratio of four peak intensities from two vibration modes of CTAB in SERS and unenhanced Raman spectra. The comparison between the ratios from experiments and simulations is only accurate if conformational variations of the chain are taken into account, thus indicating the importantce of structural fluctuations when using SERS to determine molecular structure. The effect of mixing CTAB with another surfactant, sodium dodecyl sulfate (SDS), and their interactions with gold nanorods (GNRs) are studied. The GNRs are synthesized by a silver-assisted seed-mediated method improved for higher yield and smaller reaction volume. It is observed that SDS together with a tiny amount of encapsulated CTAB can stabilize GNRs. SERS are taken to infer a probable structure that CTA$^+$ cations on the surface of GNRs while DS$^-$ anions form outer layers. GNRs stabilized in SDS are tested for stability in serum and toxicity in cancer cells cultures. The result is compared with GNRs stabilized with CTAB. It is found that GNRs in SDS are stable and do not affect serum while GNRs in CTAB aggregate in serum. Cancer cells in culture medium remain a high viability when GNRs in SDS are injected. On the contrary, cancer cells die when GNRs in CTAB are injected because CTAB is cytotoxic and can solubilize cell membranes. Thus, GNRs in SDS can potentially be applied to photothermal therapy to cure cancer. Conditions and environments for gold nanowire (GNW) synthesis in mixture of CTAB and SDS are tuned and explored. It is found that GNWs can be synthesized in high yield with mono-disperse shape in a 0.1 mm thick and 2 mm wide glass vitro tube. The interaction between surfactants and container surface becomes critical in such narrow space. If methods are developed to take GNWs out of such thin tube, this synthesis idea can be an efficient and convenient way to produce GNWs.Item The Development of a Low-Resource Appropriate Diagnostic for the Detection of Malaria DNA(2015-03-11) Cordray, Michael Scott; Richards-Kortum, Rebecca Rae; Drezek, Rebekah A; Hafner, Jason H; Storthz, KarenDespite recent progress, malaria remains one of the most serious global health threats, especially since it disproportionately affects low-resource areas. One of the keys to management of the disease is access to effective diagnostics. Nucleic acid tests (NATs) are the most sensitive and specific type of diagnostic for malaria, but require too much infrastructure, training, and cost to be widespread in many malaria affected regions. The aim of this thesis was to develop a NAT for malaria that can detect 50 copies/µL or less of target DNA in blood and then package that assay into an easy to use and self-contained system. An assay was investigated to detect small amounts of target DNA using gold nanoparticle (AuNP) aggregation. A method was developed to quantify the results using spectroscopy and found a limit of detection (LOD) of 150 amoles of target DNA and a linear dynamic range that spans 150 amoles – 15fmoles. The conditions of the assay were optimized and a novel method of measuring the assay results was developed, eliminating the need for heating and reducing the time to result to 10 minutes (from 2 hours). These changes also dropped the LOD to 50 amoles (approximately 107 copies/µL) and increased the linear dynamic range of the assay to 50 amoles - 500 fmoles. Since the LOD of the AuNP assay was not low enough to detect clinically relevant amounts of target on its own, I investigated recombinase polymerase amplification (RPA) and a lateral flow dipstick assay to detect the product. Blood was found to inhibit the RPA reaction and protocols were developed to minimize this inhibition. A LOD of 15 copies/µL of target DNA spiked into blood was found. Finally, a paper and plastic platform was developed to carry out the RPA reaction and lateral flow detection of the amplified products. A novel set of RPA primers were designed which target a sequence found in all of the species of malaria which infect humans. Testing these primers in the paper and plastic device I found an LOD of 5 copies/µL in aqueous solution, and 200 copies/µL in blood.Item The Interpretation of Raman Spectra Using Time-Dependent Functional Theory for Atomic-Resolution Structure of Cell Biomembrane Models(2023-04-19) Simeral, Mathieu Liam; Hafner, Jason HLipid membranes are composed of a diverse set of phospholipids, proteins, and sterols. These molecules organize themselves into heterogeneous structures adapted for numerous biological functions. For example, mammalian cell membranes contain a large fraction of cholesterol which changes the membrane’s mechanical properties. Many techniques, such as fluorescence microscopy, NMR spectroscopy, and x-ray scattering, and molecular dynamics, have probed cell membranes to understand how their structure relates to their functions. Raman spectroscopy is another promising technique used to study membrane models. Raman-scattered light can be studied directly or enhanced by nanometallic structures to obtain surface-enhanced Raman spectra (SERS). Raman spectra relate to the vibrational energy levels of the membrane molecules and contain information about molecular structure. However, interpreting spectra is limited by the difficulty of assigning spectral features to molecular features. This is particularly true for larger molecules of biological relevance such as phospholipids and sterols. Our group has had success in using time-dependent density functional theory (TDDFT) to produce theoretical Raman spectra. These TDDFT spectra have been used in conjunction with Raman and SERS experimental spectra to find the orientation of bilayer-forming surfactants DTAB and CTAB. Similarly, our group obtained the orientation in a phospholipid bilayer of the membrane dyes laurdan, prodan, and di-4-ANNEPS, the amino acid tryptophan, and the sterol cholesterol. In this work, we will show molecular orientation result for the common phospholipid DOPC in a bilayer which we find to agree with other experimental techniques with an average chain tilt of 34°. TDDFT also allows us to calculate experimental spectra for different conformations of the same molecule. The resulting spectra have small but revealing differences. Comparing these TDDFT spectra with experimental Raman spectra, we can select the conformations likely present in the sample under study. We applied this analysis to anthraquinones, a large class of biomolecules. We identified common “fingerprint” modes of dihydroxyanthraquinones, and our conformational analysis agreed with crystal structure studies. We applied a similar analysis to cholesterol comparing the spectra of 10 conformers with powder and DOPC vesicle measurements. We found that cholesterol adopts a more space-filling set of conformations in vesicles than in powder.