Date of Award
12-2018
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
School of Materials Science and Engineering
Committee Member
Stephen H. Foulger, Committee Chair
Committee Member
Igor Luzinov
Committee Member
Marek Urban
Committee Member
Jeffrey Anker
Abstract
Nanoparticles continue to be studied for their properties as carriers for small molecules, such as bio-imaging agents, biologically relevant targeting ligands, and therapeutic drugs as tethering these small molecules to a larger particle provides stability to the molecule and lessens the probability that the system is cleared prematurely from the body. However, the body suffers from intense auto-fluorescence, so one way to improve imaging agents to combat the auto-fluorescence issue is to create a system that is fluorescence activatable; the activation must occur when the system is only in the intended environment. Additionally, intense light scattering occurs at the blue end of the visible spectrum; one approach to overcome this issue in various nano-photonic applications is to generate scintillating (i.e. a material that converts ionizing energy, such as x-rays, to visible light) nanoparticles: 1) nanoparticles can be doped with various blue emitting organic scintillators, which emit even as single molecules, making the system x-ray active and 2) utilize a blue-emitting inorganic polycrystalline ceramic nano-scintillator. X-rays also more effectively penetrate the body when compared to visible light so x-ray excitable materials may have more advantageous imaging and therapeutic properties when compared to traditional light based theranostics. To address these issues three main approaches were taken: (1) Fluorophore functionalized bovine serum coated polymeric nanoparticles with far red activated fluorescence Activated fluorescence was achieved for a poly(propargyl acrylate) (PA) nanoparticle system. In this work, the system consisted of an azide modified bovine serum albumin (azBSA) that had been covalently attached to a newly synthesized alkyne modified silicon phthalocyanine (alSiPc) derivative through a copper catalyzed azide alkyne Huisgen cycloaddition, (“click chemistry”). The azBSA/alSiPc was then covalently attached, via click chemistry, to the PA particle sized at ca. 67 nm (PA/BSA/alSiPc). The native system had no emission. However, when the system was incubated at 37 °C for 30 min with the digestive enzyme, trypsin, it was seen that the system became fluorescent. This phenomenon is due to the trypsin digesting the “weak link” BSA, which releases free alSiPc, a highly fluorescent dye. The PA/BSA/alSiPc system was confirmed to be biocompatible, and, to investigate activated fluorescence in cancer cells, human non-small cell lung cancer cells (A549 cell line) were used. The PA/BSA/alSiPc system was incubated with the cells at varying time points in an effort to observe a fluorescence increase over time as the cells uptake the system. The particle is taken to the lysosomes and endosomes of the cancer cell. This is where the digestive enzymes are located, and the BSA is digested via endocytosis, resulting in the release of free alSiPc in the cell. It was seen, through live cell scanning confocal microscopy, that the fluorescence was activated in the cell. Additionally, the system was evaluated in an in vitro photodynamic therapy set-up and compared to the free fluorophore as well as the particulate system without the BSA linker. (2) Fully organic x-ray active colloidal crystalline arrays exhibiting color control via sequential Förster Resonance Energy Transfer (FRET) and photonic band gap control In an effort to overcome the inherent scattering in optical bio-imaging, x-rays excited optical luminescence and x-ray fluorescence computed tomography (XFCT) are attractive alternates to traditional optical imaging techniques. To avoid potential toxicity issues that come with imaging agents containing heavy metals, especially gadolinium, we propose a fully organic system that can be tuned across the entire visible through judicious choices of donor/acceptor Förster Resonance Energy Transfer (FRET) pairs. In the current system, polystyrene sub-100nm nanoparticles were synthesized with a variety of organic dyes encapsulated inside the particle. Three emitter series were synthesized, with anthracene (Anth), Anth and an azide modified naphthalimide derivative (Napth), and Anth, Napth, and a rhodamine B derivative (RhB) (emitter series no1, no2, and no3, respectively). Anthracene, a widely used organic blue-emitting scintillator, is used as the x-ray “pump” source to then transfer energy to Napth (green emitter) followed by transfer from Napth to RhB (red emitter), where applicable. Additionally, the nanoparticles self-assembled into electrostatically stabilized crystalline colloidal arrays. By tuning the stop band of the crystal through the emission of the Anth, Napth, and RhB for emitter series no1, no2, and no3, respectively, the color could be greatly influenced by the change in the local density of optical states. Additionally, all emitter series could be combined to produce a variety of colors including white. In this way, a fully tunable organic x-ray active colloidal crystal could emit a wide variety of colors all while mitigating the toxic effects observed from x-ray active heavy metal-containing imaging compounds. (3) Organic fluorophore coated polycrystalline ceramic LSO:Ce scintillators for x-ray bio- imaging Lutetium oxyorthosilicate doped with 1-10% cerium (Lu2SiO5:Ce, LSO:Ce) radioluminescent particles are coated with a single dye or multiple dyes to generate an effective energy transfer between the core and dye or between two dyes when excited via x-rays. LSO:Ce particles were surface modified with an alkyne modified naphthalimide (6-piperidin-1-yl-2-prop-2-yn-1-yl-1H - benzo[de]isoquinoline-1,3-(2H )-dione, AlNap) and/or alkyne modified rhodamine B (N -(6-diethylamino)- 9-{2-[(prop-2-yn-1-yloxy)carbonyl]phenyl}-3H -xanthen-3-ylidene)-N -ethylethanaminium, AlRhod) derivatives to tune the x-ray excited optical luminescence from blue to green to red using Förster Resonance Energy Transfer (FRET). As x-rays penetrate tissue much more effectively than UV/visible light, the fluorophore modified phosphors may have applications as bio-imaging agents. To that end, the phosphors were incubated with rat cortical neurons and imaged after 24 hours. The LSO:Ce surface modified with AlNap were able to be successfully imaged in vitro with a low power x-ray tube. To use the LSO:Ce fluorophore modified particles as imaging agents, they must not induce cytotoxicity. Neither LSO:Ce nor LSO:Ce modified with AlNap showed any cytotoxicity toward normal human dermal fibroblast cells or mouse cortical neurons, respectively.
Recommended Citation
Burdette, Mary, "Surface Functionalized Organic/Inorganic Colloids: Imaging and Spectroscopy with X-ray and Optical Excitation" (2018). All Dissertations. 2241.
https://open.clemson.edu/all_dissertations/2241