Coupling between plasmonic metal nano-components generates strongly red-shifted resonances combined with intense local field amplification on the nanoscale. This allows directly seeing molecules as well as excitations in semiconductors. We have recently explored plasmonic coupling which can be tuned dynamically, through reliable bottom-up self-assembly using the nanoparticle-on-mirror geometry (NPoM) [1-5]. We recently demonstrated how individual molecules can be strongly coupled to these ultralow volume plasmonic cavities as well as how they act as optomechanical constructs with enormously enhanced coupling.

We also demonstrate the possibility to track few molecules using the extreme enhancements. We are able to watch individual electrons hopping onto and off molecules in the gap, and watch redox processes in real time. These have encouraging prospective applications in (bio)molecular sensing as well as fundamental science. The ability to track and watch molecules interact and react opens up the ability to study chemistry molecule-by-molecule and potentially to control single reaction pathways.