Neuron-neuron communication is facilitated by the release of neurotransmitters in a process called exocytosis. The development and use of bipolar electrochemical arrays coupled with optical imaging techniques opens up many exciting opportunities in understanding neurotransmitter release behavior in the brain. The goal of this project is to develop, characterize, and use a novel highly-sensitive, highly-resolving, and ultrafast electrochemical imaging method to image neuronal exocytosis. In this project, I have developed a new method of fabricating bipolar gold nanoelectrode arrays by depositing an array of metal nanoparticles, embedding them in an ultrathin insulating polymer film, and exposing the particles from the top and bottom surfaces of the film. My method starts with depositing a thin film of an organic polymer called poly(methyl methacrylate) (PMMA) onto a layer of gold nanoparticles pre-adsorbed on a silane-modified glass surface. A chemical etching step is then used to lift off the PMMA/gold nanoparticles composite film for further experimentation. I then characterize the films using darkfield microscopy to ensure the adequate deposition and density of gold nanoparticles in the film. My study has yielded free-standing gold nanoparticle arrays with a film thickness in the range of 150-300 nanometers. In my ongoing experiments, I will be using these nanoelectrode arrays to study collision and catalytic activity of individual nanoparticles. My future research will focus on the study of neuronal release and neuron-neuron communication using these arrays. I anticipate that my research will yield a highly sensitive imaging platform for better understanding brain chemistry and neuronal communication which can inform the development of more effective therapies for treating brain disorders.

A mesoporous silica (MPS) membrane is an ultrathin permeable material characterized by numerous and uniform embedded pores whose sizes are on the order of 2-3 nanometers. MPS membranes are widely used in a number of research and industrial applications such as biomedicine for the isolation and characterization of macromolecules including DNAs and proteins. Such membranes can be synthesized in a variety of ways including electrodeposition. In our research, we have been developing an electrochemistry-based method for the preparation of ultrathin MPS membranes ranging from 50 to 150 nm in thickness. These membranes are synthesized on an electrode by a novel pulse deposition process and can be transferred onto other solid supports. A highly sensitive single-molecule analysis platform is being developed based on the use of such MPS membranes. We anticipate that our MPS membranes will find extensive use in future applications ranging from single-molecule analysis to high efficiency purification of macromolecules and other small biomolecules of interest.

New technologies capable of controlling the position-and-spacing of nanostructures have advanced applications such as electronics, sensing, and catalysis. In contrast to conventional top-down approaches such as lithography, biological-macromolecule-templates offer an attractive way to direct the assembly of nanoparticles because their high-information content can be used to direct complex structures over multiple length-scales, just as they encode living structures. Here, we study the use of de novo designed protein-nanofibers to control the assembly of gold nanoparticle chains as a model system. We employ Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, which combines the energy contributions of van-der-Waals-attraction (vdW) and electrostatic-double-layer-repulsion (EDL) to understand the factors governing electrostatic assembly of gold nanoparticles along a protein-nanofiber anchored to a charged substrate, explain observed experimental results, and predict the assembly outcome under varying solution conditions. During the assembly process, as the distance between nanoparticle and protein-functionalized substrate decreases, we expect an increase in the magnitude of vdW and EDL forces. Varying nanoparticle size reveals particle-substrate EDL repulsion limits larger nanoparticles from reaching the protein despite an increase in vdW attraction, while tuning the pH varies EDL particle-protein-attraction and particle-substrate-repulsion, resulting in predictable particle density and binding specificity. We use Python 3.7.2 programming to calculate total system energies at different stages of the assembly process using equations based on the surface-element-integration method. By constructing a virtual representation of the protein-nanofiber as a chain of spheres on a flat plane and a spherical nanoparticle above the fiber at varying distances, we can use DLVO theory to map out the interaction energies for all solution conditions. With the ability to define the energy of a system, we will be able to design new biotemplates, indefinitely predict the solution conditions, and identify potential intervention points that would allow the self-assembly of plasmonic particles for new and/or difficult-to-achieve photonic applications.

Colloidal semiconductor nanostructures are promising materials for myriad applications ranging from display technologies to plastic upcycling. Recent advancements in colloidal chemistry have enabled the synthesis of colloidal semiconductor nanocrystals of distinct morphologies. Boasting size- and surface chemistry-specific optoelectronic properties, two-dimensional nanostructures such as nanoplatelets and self-assembled quantum dot networks are inherently desirable materials for areas including photonics, electronics, and optoelectronic devices. Distinct from colloidal structures of other dimensions, nanometer-scale two-dimensional colloidal crystals exhibit quantum confinement effect only in the vertical dimension, which allows for direct modulation of their precise emission and heterostructure growth through size-controlled synthesis and surface chemistry modification. This research seeks to fabricate mono-dispersed nanoplatelets as well as two-dimensional quantum dot assemblies using combinations of II-VI and III-V semiconductors such as InP and CdSe. Through characterization of the synthesized materials using UV-visible spectroscopy, fluorescence spectroscopy, and transmission electron microscopy, this work will probe the optical properties of the samples as a function of reaction conditions. This effort will give insight into the realization and optimization of desired properties, such as narrow emission linewidth, high quantum yields, and charge transfer efficiency in two-dimensional nanomaterials by testing combinations of reaction conditions. These results will not only advance the study of colloidal semiconductor materials suitable for large-scale applications but also contribute new generalizable synthesis principles for anisotropic nanomaterials and nanomaterial assemblies.

Dissolved oxygen (DO) is a vital component of marine ecosystems, providing the key life source for thousands of species of marine vertebrates and invertebrates. Oxygen’s solubility in seawater is influenced by many variables, which can make DO difficult to predict. Estuarine systems experience DO fluctuations, as DO can limit ecosystem reproduction and health. Levels below 4 mg/L induce hypoxic conditions, creating stress for marine organisms, which makes tracking DO levels over time an essential tool for monitoring marine ecosystem health. My research provides Spatial-temporal depth analysis of DO data from the years 2014 through 2021 in the Snohomish River Estuary in Everett, Washington. Temporally, I predicted DO to exhibit a seasonal trend with highs in the winter and lows in the summer and decrease yearly at all depths due to global ocean temperature increase. Spatially, I expected DO to be higher at sites closer to the Snohomish River, and slightly lower at locations further from the river, in the center of the sound. With regard to depths, I predicted DO to be higher near the surface and lower near the bottom, and the oxycline is expected to get closer to the surface over time. Data were collected using an EXO2 Sonde at five different field sites at varying distances from the Snohomish River. I analyzed data using Excel, RStudio, and ArcGIS. Results found that DO is increasing over most sites with seasonal fluctuations of higher DO in the winter, and lower in the summer. There was one hypoxic event in 2016 at Buoy, along with a yearly increase in DO that suggests hypoxic conditions in Possession Sound may not last. Spatially, DO is higher at sites closer to the mainland, contrary to my hypothesis. Continuation of research will include further analysis of Spatial-temporal data in ArcGIS and Rstudio.