Chemistry & Biochemistry Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2752
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Item Design and Assembly of Block Copolymer-Modified Nanoparticles into Supracolloidal, Molecular Mimics(2023) Webb, Kyle; Fourkas, John T; Nie, Zhihong; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Large strides have been achieved in nanoparticle self-assembly, using various strategies to achieve ordered, supracolloidal structures, ranging from dimers to chains and vesicles to 3-D lattices. However, these methods, while expanding the scope and accessibility of design, face inherent limitations in targeting complex structures with high yields, particularly when using isotropic building blocks (e.g. gold nanoparticles and polystyrene nanoparticles). Additionally, research studying the reversibility of nanoparticle assemblies is mostly limited to small-ligand-modified particles rather than polymer-modified nanoparticles. Polymers are particularly advantageous as they provide a higher degree of functionality to the nanoparticle surface and allow for increased control in directing particle interactions. This control is necessary to continue furthering the advancement of gold nanoparticles in plasmonics, sensors, and catalysts. Here, we introduce two strategies to assemble gold nanoparticles into supracolloidal nanostructures. Gold nanoparticles are modified with complementary, functionalized-block-copolymers that drive the assembly of the nanoparticles. The first strategy uses a diblock copolymer composed of a hydrophilic outer block and an acid or base-functionalized inner block. Upon mixing, particles are assembled due to the acid–base neutralization between the complementary block copolymers. The resultant supracolloids consist of nanoparticles precisely arranged in space, which mimic the geometries of small molecules. The particle interactions are fine tuned by varying the size and feeding ratio of the nanoparticles, along with the length and composition of the block copolymers. Careful tuning of these parameters yields nanostructures with different valences that were produced in high yield. Additionally, the implementation of a long outer, hydrophilic polymer block provided the assembled nanostructures stability when transferred from THF to water. Colloidal stability in an aqueous medium could allow for expanded use of these nanostructures in cellular uptake studies and biomedical applications. The second strategy uses a diblock copolymer composed of a hydrophilic outer block and an inner block containing either complementary host or guest moieties. Particularly, we take advantage of the well-established interactions between β-cyclodextrin and adamantane as the host and guest molecules. Upon the slow addition of water, particles assemble due to the host–guest interactions between the complementary block copolymers, as the hydrophobic adamantane moieties are driven within the β-cyclodextrin macrocycles. Fine tuning of the nanoparticle sizes and feeding ratios and the block copolymer lengths and compositions results in high yields of targeted supracolloids that also mimic the geometries of molecules. Interestingly, the size difference between the host and guest-modified particles led to different types of nanostructures. In addition, due to the reversibility of the host–guest interactions, we demonstrate the ability of our system to reorder in response to competitive host moieties. Upon addition of free β-cyclodextrin, the host–guest interactions are disrupted, resulting in disassembly of the nanostructures, which we could reassemble upon removal of the free cyclodextrin. Finally, due to the strength of the nanoparticle interactions, we also tested the selectivity of the nanoparticle interactions by assembling the host building block with different guest building blocks. We showed that when assembled with competing guest building blocks, the β-cyclodextrin building blocks preferentially interact the adamantane building blocks due to the stronger particle interactions. This reversibility and selectivity make our system a potential candidate for use in biosensors.Item New Nanoparticle Characterization Techniques by Differential Mobility Analysis(2022) Duelge, Kaleb John; Zachariah, Michael R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Nanoparticles are being used increasingly in new fields for new applications. Thoroughcharacterization of particle properties such as size, aggregation, and mass are key to understanding particle behavior. In this dissertation I discuss a variety of new measurement approaches using the aerosol-based technique: differential mobility analysis (DMAS). This technique consists of the combination (hyphenation) of several components, the primary being an ion mobility chamber for the spatial separation of nanoparticles. The specific aerosol source and detector used is flexible and allows for wide applicability of the technique. The applications discussed here relate to a variety of everyday scenarios. Medicinal protein particles are studied to improve the health outcomes associated with this growing class of medicine. Nanoparticle catalysts are studied to improve the activity and repeatability, analogous to how a catalytic converter is used in cars to reduce combustion emissions. Detailed size measurements are made for gold nanoparticles, a class of particles that have been used for cancer treatments and as carrier particles, for example to transport medicine to a particular location within the body. Finally, determination of nanoparticle size is studied by comparing results from different instruments, as determining size in the nanometer scale is more complicated than an analogous measurement of a macroscopic sphere (for example, measuring the length with a ruler and comparing the result to the length derived from the mass of a sphere with a known density). In the second chapter, I demonstrate protein aggregation kinetics measurements by DMAS and asymmetrical flow field flow fractionation. Thermal aggregation was conducted in traditional formulation buffers and good agreement was determined between the two techniques. These are potential alternative instruments to the gold standard, size exclusion chromatography, used by the biopharmaceutical industry. In the third chapter, I demonstrate a calibration technique for mass distribution measurements by DMAS using inductively coupled plasma mass spectrometry for detection. Determination of the total mass of a sprayed ionic standard was sufficient to calibrate measurements of monodisperse gold nanoparticles of various shapes. A disagreement was determined between the ionic standard and a polydisperse distribution of titania coated with small gold nanoparticles. A multiple charge correction was applied that significantly improved the agreement, though the issue remained. In the fourth chapter, comparison measurements are presented for monodisperse gold nanoparticles made in two operational modes of DMAS: step voltage mode and scan voltage mode. The step voltage mode remains at each voltage for a certain dwell time (on the order of 30 s), while the scan voltage mode continuously changes voltages. Good agreement was determined for the two approaches when calibrated using a nanoparticle size standard. Additionally, the scan voltage mode data were analyzed with an alternative calibration method: a direct measurement of the sheath volumetric flow rate. The data from the two scan voltage mode calibrations bracket the measurement made in step voltage mode. This agreement suggests that scan voltage mode measurements for certification of nanoparticle size standards could be used in the future if a few additional uncertainty terms are explored. In the fifth chapter, traceable measurements with quantitative uncertainty analyses are compared for a size standard. The measurement by DMAS is compared to atomic force microscopy, scanning electron microscopy, and electro-gravitational aerosol balance. The measurement by DMAS was bracketed by the other techniques, with microscopy measuring a slightly smaller size and electro-gravitational aerosol balance measuring a slightly larger size. The measurements all agreed within 3%, but some of the differences exceeded the 95% confidence intervals of the measurements. These differences may be significant if these techniques are used to develop future size standards.