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Second Harmonic Generation Spectroscopy Studies of Polymers and Nanomaterials at Model Biological Interfaces

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The projected increase in the use of nanomaterials raises concerns about adverse impacts new technologies utilizing these materials may have on the environment. These concerns can be addressed from a chemical perspective by studying how emerging nanomaterials interact with biological systems. Fundamentally, the key interactions for nanomaterial uptake into a cell occurs at the nano/bio interface. This interface is difficult to access experimentally, mainly because traditional methods used to probe these interactions do not provide molecular information, are not interface-specific, or are not sensitive enough to detect small surface coverages, even at saturation. As a result, the amount of molecular information regarding how nanoparticles interact with aqueous/solid interfaces, including biological membranes, is limited. There exists therefore an urgent need to bridge this knowledge gap by probing the nano/bio interface with new tools. The motivation of this thesis is to address this need by using advanced spectroscopic techniques that will improve our ability to understand, control, and predict how emerging nanomaterials will impact the environment and biological systems. Herein we take a bottom-up approach to better understand, from a fundamental perspective, what factors contribute to nano/bio interactions. The interactions that take place at the nano/bio interface are directly influenced by the chemistry of the biological surface, the properties of the nanomaterial (size, shape, functionalization, surface charge, charge density, etc.), and environmental conditions (ionic strength, pH, temperature, etc.). Given the complexity of both nanomaterials and biological surfaces, we simplify our systems to include biomimetic membranes, model nanomaterials, and polyelectrolytes which are often used to functionalize nanomaterials. We use a combinatorial approach that employs second harmonic generation (SHG) spectroscopy, sum frequency generation spectroscopy (SFG), and quartz crystal microbalance with dissipation monitoring (QCM-D) measurements to explore the influence of surface charge, charge density, chemical functionality, ionic strength, and electrostatics, on nano/bio interactions. Specifically, SHG spectroscopy is used here to estimate equilibrium constants, changes in interfacial potential, and surface charge densities of model biological membranes interacting with nanomaterials and polyelectrolytes. With insights from complementary tools, we discuss the impacts that nanomaterials have on the structure of biomimetic surfaces and provide estimates for the adsorbed mass, number densities, and percent ionizations. In addition to building a better understanding of nano/bio interactions, we aim to use this information to develop better design rules for nano-scale materials, to minimize or attenuate some outcomes, and to exploit more favorable outcomes. The results generated from these studies are reported in collaboration with the Center for Sustainable Nanotechnology.

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  • 04/09/2019
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