The central aim of this thesis is to investigate single molecule phenomena in self-assembled plasmonic nanocavities, focusing on achieving single molecule sensitivity within these highly confined electromagnetic environments. While self-assembled nanocavities offer reproducible nanogaps and strong near-field enhancement, the collective contribution of multiple molecules often obscures single-molecule behavior. This work presents experimental results and electromagnetic simulations that demonstrate how single-molecule sensitivity can be achieved and applied.

The research explores various aspects of light-matter interactions at the nanoscale, including excitation enhancement, the Purcell effect and near-field coupling. Specific phenomena such as picocavity formation in nanoparticle-on-mirror structures and fluorescence reshaping in DNA origami-based nanocavities are studied. Additionally, the thesis examines how spectral overlap and dipole-dipole interactions between molecules can be enhanced in these nanocavities.