Development of polymer-coated nanoparticle imaging agents for diagnostic applications

Cancer is the second most common cause of death in the United States, with over 500,000 deaths expected this year. While significant progress has been made in the treatment and management of cancer, challenges remain because of the complexity and the heterogeneous nature of the disease. The improvement that has been seen in survival rates reflects advancements not only in treatment, but also in early stage detection and diagnostics for certain cancers. In particular, early stage detection and treatment of cancer before it has metastasized to other organs has resulted in a dramatic improvement in patient survival rates. One area of research that has shown considerable promise in further advancing diagnostics and early cancer detection is nanotechnology. Specifically, semiconductor and metal nanoparticles have great potential to provide advanced technology platforms for ultrasensitive and multiplexed detection of disease markers and probe disease on the molecular level. Because they are in the same size regime as biological molecules, these nanoparticles exhibit unique interactions with proteins, nucleic acids and other biomarkers of interest for detecting and diagnosing disease. However, high-quality nanoparticles are often unsuited for use in complex biological environments because of their coatings and surface chemistry.In this dissertation, we describe the design and development of polymer-coated nanoparticle imaging agents for use in blood, cell and tissue diagnostic applications. First, low-molecular weight, amphiphilic polymers, with hydrocarbon chains capable of noncovalent interactions with nanoparticle surface ligands and a hydrophilic backbone to render the nanoparticle water soluble, were synthesized and characterized for use in nanoparticle coating applications. We demonstrate that the hydrophobic and hydrophilic interactions between the nanoparticle surface, the amphiphilic polymer and the aqueous solvent were able to drive the coating and water solubilization of quantum dots. Second, synthesis techniques were developed using amphiphilic polymers in a one-pot method to make high quality nanoparticles and stabilize and encapsulate the particles for transfer into water. Using the polymer functional groups as multidentate ligands, nanoparticles were synthesized with a high degree of size control and increased stability. In addition, by performing the synthesis in a noncoordinating amphiphilic solvent such as polyethylene glycol, nanoparticles were immediately transferred to water with the excess polymer forming a water soluble coating.Next, nanoparticle surface charge and how it relates to the nonspecific binding of nanoparticles in cells, tissues and other complex biological samples was studied. We have found that highly charged (negative and positive) particles exhibit significant nonspecific binding to biomolecules and other cellular components in biological environments. By reducing the surface charge through the incorporation of hydroxyl functional groups, we have nearly eliminated the nonspecific binding of quantum dots in blood, cells and tissues. Moreover, through crosslinking and altering the surface chemistry of the polymer-coated quantum dots, we have increased the stability of the nanoparticles while maintaining a small hydrodynamic size. Finally, we have investigated the use of the low-binding, hydroxyl quantum dots in tissue staining applications, where nonspecific binding presents a considerable challenge to detection sensitivity and specificity. A number of biomolecule conjugation techniques were examined for the coupling of quantum dots to antibody targeting molecules and preliminary staining experiments were performed.In summary, this dissertation makes significant contributions to the fields of nanotechnology and cancer diagnostics, particularly with new polymer coatings for quantum dots and other nanoparticles. Novel synthesis techniques were developed using multidentate amphiphilic polymers to produce water soluble nanoparticle imaging agents in a one-pot method. Nanoparticle surface chemistry was also explored as a means to improve the functionality of these imaging agents in biological environments, leading to a novel, non-stick hydroxyl surface chemistry for nanoparticles with utility in clinical applications, particularly blood, cell and tissue assays. These advancements further elucidate the properties of polymer coatings and nanoparticle surfaces and enhance our understanding of nanoparticle interactions in clinically relevant environments. The technologies developed in this work will have a significant impact on nanoparticle use in ultrasensitive biomarker detection in complex biological samples and provide further advancements in early stage disease diagnostics.