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An Optical Nanofiber Total Internal Reflection Microscopy Platform for Quantitatively Probing Nanoscale Interactions


An Optical Nanofiber Total Internal Reflection Microscopy Platform for Quantitatively Probing Nanoscale Interactions


Joshua T. Villanueva

Doctor of Philosophy in NanoEngineering

University of California, San Diego, 2016

Professor Donald Sirbuly, Chair

Pushing the boundaries of nanoscience and engineering requires the development of sensitive instrumentation for studying small-scale systems and interactions. One of the most fundamental nanoscale phenomena, Brownian motion, remains difficult to characterize experimentally and serves as the primary motivation for developing new tools capable of quantifying the stochastic nature of systems at this scale. The behavior of colloidal nanoparticles are particularly interesting as they are ubiquitous in nature and are foundational to the field of nanomedicine.

This dissertation discusses the development of an optical nanofiber-based total internal reflection microscopy (TIRM) platform for the statistical analysis of colloidal behavior near a surface. In this technique, the evanescent field surrounding a nanofiber waveguide provides a means for probing the physical interactions between a Brownian nanoparticle and the nanofiber. This interaction is quantified optically via the far field detection of an optical signal generated from the light scattered by a nanoparticle in the evanescent field. The accumulation of individual scattering events results in a statistical distribution of distance-dependent intensities that provides information about the underlying state of the system using appropriate physical models. While the technique is simple in principle, characterizing Brownian systems requires a thorough analysis of all parts of the instrumentation process to identify possible sources of error and verify the accuracy of quantitative measurements.

The nanofiber-based TIRM’s overall function is validated by comparison with predicted results from a steady-state theoretical model of the Brownian motion of a particle near a surface, mediated by an electric double layer interaction. This analysis identifies practical limitations on the types of colloidal system that are able to be investigated using this technique. Additionally, further examination of the far-field imaging process reveals that the error in quantifying nanoparticle behavior is directly related to the finite exposure time of the data collection process. With these system limitations in mind, the last part of the dissertation discusses extensions of the platform configuration for advanced characterization modalities.

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