Experimental Observation of Protein Interactions with Atomic-Scale Perturbations on an Open Plasmonic Metasurface.

Atomic-scale perturbations on plasmonic surfaces can give rise to enhanced optical fields on the picoscale due to adatom formation or metallic crystal rearrangements, called picocavity and flare, respectively. To date, these atomic-scale effects have been observed exclusively in closed nanogaps upon interaction with small organic molecules. Here, we generate these atomic-scale effects on an open plasmonic metasurface, which is a monolayer of Au nanoparticles on a Au film. We observe picocavity and flare spectral signatures for proteins spanning 2 orders of magnitude in mass, from lysozyme (14 kDa) to encapsulin (1932 kDa). The atomic-scale interactions reveal 1 order of magnitude picocavity-enhanced Raman intensity, a single-exponential spectral wandering distribution, and a biexponential picocavity lifetime. Our results demonstrate the plasmonic metasurface as a platform to access picoscale-enhanced optical fields that can be harnessed to study light-matter interactions and applications for sensing of large molecules and particles.