Single-Molecule Fluorescence Imaging of the Electrochemical Interface

Abstract

In this dissertation, I firstly aim to use a solvatochromic dye, Nile red, to probe the dynamics of translocating oil emulsions through a nanopore, as well as to probe the hydrophobicity of bubble surface. Chapter 2 presents the work using Nile red as a fluorescent dye to only label oil emulsions, where we observe the collision and coalescence of single emulsion droplets at a nanopore orifice. This work is believed to have a significant impact on future studies of the stability of emulsion droplets, droplet−droplet interactions, and ion-transfer processes, and micro-scale oil/water interface. In Chapter 3, Nile red is used to probe the electrochemically generated surface nanobubbles. Nanobubble detections are observed, indicating that the bubble surface (e.g., gas/liquid interface) is hydrophobic because of the solvatochromism of Nile red. The step-wise increase in fluorescence intensity indicates multi-fluorophore labeling, possibly caused by molecular aggregation. This work also verifies the high stability and long lifetime of surface nanobubbles. To better and further understand how fluorophores behave at the bubble surface, a series of rhodamine dyes are used to study the kinetics of fluorophore adsorption and desorption, presented in Chapter 4. Langmuir isotherm adsorption model is applied to extract the equilibrium constants of fluorophore adsorption at the bubble surface. This is the first application of the Langmuir model at the gas/liquid nano-interface. We believe that the ability to apply the Langmuir model at nano-interface would be beneficial for studies on various interfaces down to the nanoscale in the future. Lastly, in Chapter 5, some of the ongoing and future works are discussed, including combining TIRF imaging and electrochemistry measurement, dual fluorophore labeling, etc.