This project will utilize radiolabeled organic ligands to explore the ligand exchange on the surface of inorganic particles. The majority of nanoparticles are produced with a “sacrificial” ligand which is then exchanged with one with properties better suited for the given biomedical, catalytic, or energy application. This reaction is critical for the success of these applications as the resulting surface chemistry will be a major factor in the resulting colloidal stability, reactivity, and dielectric properties of the particle/ligand system. Moreover, as these engineered nanomaterials have the risk to be introduced to the natural environment, exchange with naturally occurring ligand is a critical factor to the toxicology and fate of these materials. Previous attempts to quantify the amount of ligand on the surface of nanoparticles include techniques, such as thermogravimetric analysis (TGA)1 and fluorescence spectroscopy.2 However, these techniques only provide information of the bulk organic to inorganic ratio or require specialized ligands for measurement of ligand exchange. Alternatively, we have recently developed methods to synthesize radiolabeled metal and metal oxide nanoparticles with radiolabeled capping ligands and use liquid scintillation counting (LSC) to measure how much radiolabeled original ligand has been displaced on the surface of the nanoparticles during exchange with a hydrophilic ligand. LSC is a technique used to detect the presence of emitted low and high energetic beta particles and some alpha and gamma-ray emitters, and has the potential for low levels of detection not possible with other techniques. Initial results show that ligand exchange reactions that have been traditionally assumed to be robust reactions do not necessarily occur to completion, leading to the formation of mix surface coverage, and undesirable surface chemistry. For this project, students will focus on the interaction of engineered nanoparticle systems with naturally occurring organic matter in the natural environment. By observing how the surface chemistry of the particles is affected by different bio-sourced moieties, we can begin to construct a larger model for the potential prediction of the fate of nanomaterials in the natural environment. In addition to the LSC measurements, the radiolabeled particles will be characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). In addition, unlabeled particles will be synthesized and modified in order to compare LSC to other methods commonly used to characterize modified particles, including TEM, DLS, and TGA.
Students involved in this project will gain first hand experience in the chemical synthesis of nanomaterials, measurement of the colloidal properties of these materials, and unique radiolabeling techniques. Specifically, the student will learn synthetic techniques for the formation of metal oxide nanoparticles through controlled LaMer reaction kinetics. The student will then characterized these materials via TEM, Zeta potential, DLS, and X-ray diffraction (XRD). Meanwhile, the student will utilize end group modification of poly(ethylene glycol) PEG based polymers3 with radiolabeled bio-sourced ligands, such amino acids, nucleic acids, saccharides. Finally, the student will utilize our recently developed techniques to measure the change in surface chemistry of the engineered nanoparticles with the radiolabeled ligands, and make inferences regarding the reactivity of different bio-derived chemical moieties.