Modifying Single-Molecule Fluorescence with a Plasmonic Optical Antenna: Theory, Methodology, and Measurement

Abstract

Nanophotonics is the study and technological application of light on the nanometer scale. This dissertation brings together two disparate branches of nanophotonics: plasmonics and single-molecule super-resolution microscopy. Plasmonics studies the collective oscillations of free electrons in a conductor, which enable light to be manipulated on subwavelength length scales. Plasmonics, and in particular plasmonic optical antennas, have generated a huge amount of interest due to their rich new physics and countless applications, ranging from surface-enhanced spectroscopies, to novel cancer therapies, and to quantum information platforms. With single-molecule fluorescence super-resolution microscopy, the optical properties of individual molecules can be studied with nanometer-scale resolution, far better than the micron scale of traditional microscopy. Super-resolution microscopy has revolutionized cellular biomedicine, ushering in a new generation of fundamental discoveries and associated medical therapies. Super-resolution microscopy is also increasingly enabling discoveries and advances across disciplines, allowing direct visualizations of phenomena ranging from chemical imaging of surface reactions to nanoscale fluid dynamics. By bringing together these two fields, this dissertation supports two synergistic directions for applications of this science: enhancing the resolution of single-molecule fluorescence super-resolution imaging and using a novel technique to directly study how a single emitter interacts with an optical antenna.

In this dissertation, I present a new theoretical approach to understand the interaction of a single fluorescent molecule with an optical antenna, a broadly applicable new image analysis algorithm, and experimental measurements of antenna-modified fluorescence. The theoretical framework expands an established theory of antenna-modified fluorescence to incorporate the variability of real experiments. This research has uncovered a mislocalization effect: differences between the actual position of an emitter and the apparent, super-resolved position of the emitter image. I therefore present computational methods to predict the emission mislocalization of single fluorescent molecules coupled to an optical antenna and compare these predictions to experiments. I describe the SMALL-LABS algorithm, a general data analysis approach to accurately locating and measuring the intensity of single molecules, regardless of the shape or brightness of an obscuring background. Finally, I present the results of experiments studying the polarization dependence of coupling a single fluorescent molecule to a gold nanorod plasmonic optical antenna, and I compare these measurements with theoretical predictions. This work advances the fundamental science of nanophotonics and will pave the way for next generation super-resolution imaging and optical antenna technologies.