Noble metal nanoparticles are an important class of catalysts. However they are inherently heterogeneous, which makes studying them at the single-particle level desirable, as it then becomes possible to quantify these differences. A highthroughput fluorescence microscopy technique was developed in which a nonfluorescent reactant gets catalyzed to a fluorescent product on a gold catalyst surface. By recording the fluorescence signals at the single-molecule level from many particles on a camera and fitting the emitted point spread function to a two-dimensional Gaussian function, sub-diffraction spatial resolution of ~25 nm was achieved. By overlaying the optical imaging results onto a scanning electron microscopy (SEM) image of the same nanoparticles, correlation of structure and activity was achieved for individual nanoparticles. Since this technique can monitor the activity of many particles simultaneously, it was used to resolve sub-populations of both size and activity within a heterogeneous sample. This can be used to aid in future catalyst design. Also, bimetallic catalysts made from combinations of Au, Pt, and Pd were produced in order to study the effects of a bimetallic junction on catalytic activity. By making and studying catalysts larger than the spatial resolution of this technique, it becomes possible to resolve intraparticle activity distributions. Bimetallic segmented Au/Pt nanorods were prepared so that the catalytic activity could be mapped onto each of the domains and the interface region between the two metal domains, enabling the quantification of the effect the interface has on activity. Additionally, orthogonal, intersecting Au and Pt microstripe arrays were fabricated using photolithography to study the interface effect as well. Finally, a series of AuPd core-shell particles were synthesized using colloidal growth to study the effect of the shell thickness on catalytic activity, thus enabling the measurement of the effect of the core metal on the shell.