Anisotropic Gold Nanostars: Seedless Growth Mechanism, Post-Synthetic Separation, and Ligand Distribution QuantificationPublic Deposited
etal particles at the nanoscale display unique physical, chemical, and optical properties corresponding to their size, shape, and ligands. These factors can be manipulated to target specific biomedical applications, such as drug delivery and sensing, through functionalized surfaces. The development of specialized synthetic methods for the precise control of nanoparticle size and morphology enables the desired ligand distribution. Nanoparticle curvature has a significant effect on ligand loading; understanding this relationship is critical in determining particle-cell interactions. This work focused on the factors affecting the synthesis mechanism and post-synthetic separation of anisotropic gold nanostars (AuNS) and the quantification of ligand distribution on varying nanoparticle morphologies. The seedless synthesis of AuNS requires two precursors, but the methodology often resulted in poor yield of branched particles. In Chapter 2, we described four critical factors affecting the final nanoparticle morphology: mechanical agitation, concentration ratio, buffer type, and chemical environment. We established a set of design considerations to increase the homogeneity of nanoparticle shape and anisotropic particle yield and expanded the library of precursors used for anisotropic growth to include a morpholine-based buffer. This work led to the creation and classification of a collection of nanoparticles with tunable optical properties. </DISS_para> <DISS_para>While synthesizing AuNS with a morpholine-based buffer was possible, the buffer created unstable and heterogenous particles. In Chapter 3, we showed a robust strategy to obtain highly homogenous AuNS populations through a stabilization and sorting method. By altering the storage conditions, particle stability increased three-fold. The stable AuNS were separated through density gradient centrifugation (DGC) based on branch length and number. We demonstrated that one round of DGC efficiently separated AuNS populations and additional rounds did not improve homogeneity.</DISS_para> <DISS_para>In Chapter 4, we used our optimized separation methodology to obtain DNA-functionalized particles. Specifically, we probed how curvature of individual particles impacted ligand distribution through time-of-flight secondary ion mass spectrometry. AuNS with a medium density of branches had six-fold more ligands per particle than a spherical nanoparticle of comparable size. As branch number increased beyond this point, the negative curvature increased and hindered additional ligand loading. This fundamental tool allowed for the simultaneously probing of an inorganic core and unlabeled-ligands on the single particle level. Finally, in chapter 5, we explored the mechanism of the seedless growth of anisotropic AuNS through evaluating the intermediate species of the reaction. By repurposing electron paramagnetic resonance spectroscopy, we studied the radical concentration in situ during the reaction and determined the effect of buffer concentration and type. We correlated the trend in radical intensity to the ensemble optical properties and individual particle morphology.
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