In recent years, nanoscience has become a major focus: from technologies in solar cell coatings, to developments in biomolecular detection methods. Utilization of unique optical absorption properties of noble metals, such as gold or silver, opens the door for harnessing photons in new and innovative ways. For these reasons, great emphasis has been placed on the synthesis and characterization of nanostructures. The Pozzo Group has recently shown that structured gold clusters can be formed in solution by exploiting the hydrophobic and steric interactions in self-assembling nanoparticles. Hydrophilic polyethylene-glycol (PEG) chains control long-range steric interactions, while hydrophobic alkane-thiol chains induce clustering through short-range attraction. This simple method has the potential to be a cheap and viable option for nanoscale fabrication; starting from the molecular level and building up. This method of nanoclustering yields multi-particle aggregates in solution. Clusters of different geometries and sizes are formed based on the number of consistuent gold particles in each aggregate. It has been shown that the total amount of PEG adhered to the surface of the gold particle impacts the extent of clustering. At lower PEG concentrations, more diverse populations of nanoclusters are observed. In this project, size-exclusion chromatography (SEC) is being utilized for separating cluster populations. A cluster dispersion is pumped through a column that is packed with a porous stationary phase. By size-exclusion, the largest clusters exit the bottom of the column first, while the smaller clusters have a higher retention time as they navigate the pores of the matrix. The viability of SEC for controlled separation of cluster populations is being investigated on different systems, with the goal of isolating populations of similar aggregation types. Population analysis with SEC is simple and can be used to identify the fundamental parameters that lead to polydispersity in cluster size and shape.

Self-assembling silver nanoparticles have been of great interest to the scientific community due to their unique optical properties and potential use in areas such as cancer therapy and semiconductors. This research explores using a simple one-pot technique to produce self-assembling silver nanoparticles with controllable geometries based on steric interactions. The core advantage of this method is that it employs a bottom-up approach using commonly available and relatively inexpensive materials. Successive doping of long hydrophilic polyethylene glycol (PEG) chains followed by a short hydrophobic alkane-thiol renders the nanoparticles amphiphilic. Clusters of different sizes self-assemble depending on the concentration of PEG added to the silver dispersion. As PEG concentration increases, the extent of clustering decreases as the long chained PEG molecules create a corona around the silver particles and inhibit functionalization with alkane-thiol. This synthesis method is analyzed with Dynamic Light Scattering (DLS), Small Angle X-ray Scattering (SAXS), and Transmission Electron Microscopy (TEM). While the samples follow the expected clustering size trends, data indicates that monodisperse silver is critical to the reproducibility of the technique.

A strong understanding of the intricacies of blood coagulation is essential for proper treatment of coagulopathies such as hemophilia, hemorrhage, Von Willebrand’s disease, and numerous thrombosis related conditions. The coagulation behavior of blood is directly related to the structure of the supporting protein networks. Fibrinogen is a protein found in human blood that, upon polymerization into cross-linked fibers, forms the scaffold-like support structure of a blood clot. Based on the observation that emergency room patients with traumatic injuries experience a greater extent of hemorrhage and abnormal hemostasis, our group has investigated the effect of acidic oxidation on the structure and mechanical properties of fibrin gels. Purified fibrinogen was oxidized using hypochlorous acid to simulate the acidification of blood during trauma and shock. Rheological, x-ray scattering, and turbidity studies were performed to characterize the structural and mechanical differences between oxidized and normal fibrin gels. Preliminary results from these studies indicate the oxidation causes a delay in fibrin gelation as well as a decrease in the elastic modulus of the fiber network. Additionally, evidence from turbidity studies suggests that oxidation prevents lateral aggregation between protofibrils leading to an overall reduction in fiber diameter.