A Study of Synthesis and Characterization of Gold Bipyramid Nanoparticle Bioconjugates

Materials at the nanometer scale have unique optical, electrical, and magnetic properties, which have applications in biosensing, molecular imaging, diagnostics, and therapies. Gold nanoparticles have been extensively studied for biomedical application due to their high biocompatibility and the ease with which they can become bioconjugated. The high surface area to volume ratio of gold nanoparticles allows for the loading of various functional agents for biomedical application. However, due to the small size, a challenge at the pre-clinical use stage comes in fully characterizing and optimizing functionalized nanoparticle bioconjugates. The size of gold nanoparticles is below the diffraction limit of light. As optical microscopes are diffraction-limited, the ability to accurately determine the number of biomolecules per nanoparticle and their spatial arrangement is not possible by conventional optical microscopy.

Techniques such as Dynamic Light Scattering (DLS) are commonly used to verify the functionalization of nanoparticle bioconjugates. However, these are ensemble-based measurements, which only provide average properties across a nanoparticle preparation. Single-particle measurements, on the other hand, enable us to determine properties such as the number of biomolecules per nanoparticle, their spatial arrangement, and whether or not the biomolecules retain their function; they enable us to describe the distribution of these properties over a nanoparticle preparation.

This dissertation addresses two goals related to nanoparticle bioconjugates. First, we prepared and characterized nanoparticle bioconjugates in an aqueous solution. Second, we determined the number of antibodies bound to a nanoparticle and the distribution thereof within a sample using optical single-particle methods.

Nanoparticles (gold bipyramids) were prepared using colloidal chemistry and then functionalized with carboxyl-terminated ligands (alkanethiol self-assembled monolayers). Epidermal growth factor receptor (EGFR) is a transmembrane protein, which is often overexpressed in many types of cancer cells. Coupling the ligands with anti-EGFR antibodies not only allowed for the determination of the number of antibodies per nanoparticle but will also ultimately allow for the engineering of nano-bioconjugates for EGFR targeting in cancer therapies.