Super-resolution Optical Imaging of Single-Molecule SERS Hot Spots

We present the first super-resolution optical images of single-molecule surface-enhanced Raman scattering (SM-SERS). hot spots, using super resolution imaging as a powerful new tool for understanding the interaction between single molecules and nanoparticle hot spots. Using point spread function fitting, we map the centroid position of SM-SERS with +/- 10 nm resolution, revealing a spatial relationship between the SM-SERS centroid position and the highest SERS intensity We are also able to measure the unique position of the SM-SERS centroid relative to the centroid associated with nanoparticle photoluminescence, which allows us to speculate on the presence of multiple hot spots within a single diffraction-limited spot, These measurements allow us to follow dynamic movement of the SM-SERS centroid position over time as it samples different locations in space and explores regions larger than the expected size of a SM-SERS hot spot. We have proposed that the movement of the SERS centroid is due to diffusion of a single molecule on the surface of the nanoparticle. which leads to changes in coupling between-the scattering dipole and the optical near field of the nanoparticle.