Synthesis of amine-rich poly(oxanorbornene) functionalized gold nanoparticles as a model for understanding nanoparticle membrane interactions

Abstract

The incorporation of nanoparticles in technologies for medical and industrial purposes is steadily growing. The unique properties of these materials are derived from their nanoscale size, which gives them useful optical, electronic, and physical properties not present in bulk materials of the same composition. However, there is growing concern regarding the toxicity of nanoparticles released into the environment, of which the mechanisms remain poorly understood. The research presented in this dissertations aims to gain a more detailed understanding of how nanoparticle surface functionalization affects the membranes of organisms to bridge this gap in knowledge.Nanoparticles are often functionalized with surface molecules that stabilize them in solution and serve to modify their function. Cationic polyelectrolytes are a commonly used class of molecules for this purpose. These molecules often derive their cationic properties from amine and ammonium-containing functional groups which provide a stabilizing positive charge to nanoparticle surfaces. Recent studies have shown significant membrane disruptive properties of cationic nanoparticles. However, many of these studies have only investigated the properties of nanoparticles functionalized with commercially available cationic polyelectrolytes. While this research has been important in establishing the role of positive nanoparticle charge on membrane impact, there has been limited research on how the density of charge modifies this impact. Poly(oxanorbornenes) (PONs) are a class of amine-rich cationic polyelectrolytes that can be synthesized with variable amine density. Previous research has shown that varying the amine density in free PONs polyelectrolytes significantly affect their membrane interactions. Conjugation of PONs to nanoparticles can be used to systematically vary their surface amine density and charge to better understand how this impact their membrane interactions. Furthermore, PONs have been shown to possess membrane selective properties that can minimize membrane impact towards eukaryotes while being disruptive to bacterial membranes. This allows PONs-functionalized nanoparticles to be potentially useful as an antibacterial nanomaterial. The first study in this dissertations uses gold nanoparticles (AuNPs) as model for nanoparticle surface functionalization by PONs and uses liposomes as a membrane model. The size, concentration, and stability of PONs functionalized AuNPs (PONs-AuNPs) is measured using UV-Vis absorbance, transmission electron microscopy (TEM), and dynamic light scattering (DLS). The charge of PONs-AuNPs is measured using zeta potential measurements which is used to approximate surface charge. The polyelectrolyte conjugation efficiency of PONs-AuNP as a function of PONs amine density is measured using X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and fluorescamine assays. Fluorescence intensity measurements of dye-encapsulating liposomes are used to determine the relationship between the amine density of PONs-AuNPs and their membrane impact. The second study in this dissertations describes the synthesis of variable amine PONs polyelectrolytes containing 10 and 70 monomers. These were used to synthesized PONs-AuNPs with two different coating thicknesses. This study explores how the length of PONs affects their conjugation efficiency, nanoparticle stability, nanoparticle surface properties, and membrane impact. The third study in this dissertations describes the synthesis of highly colored antifouling microcapillary needles using PEGylated AuNPs (PEG-AuNP). The strong absorbance of AuNPs and antifouling properties of PEG were combined as thin films on microcapillary needles and used to increase needle visibility and reduce needle clogging during zebrafish embryo injections. These were compared to industry standard needles to determine the improvement in their function. This study also serves as proof of concept for creating functional AuNP thin films on glass surfaces that will eventually be used to incorporate PONs, for use as a potential biocompatible antibacterial surface material.