Resolving sub-diffraction limit encounters in nanoparticle tracking using live cell plasmon coupling microscopy.

We use plasmon coupling between individual gold nanoparticle labels to monitor subdiffraction limit distances in live cell nanoparticle tracking experiments. While the resolving power of our optical microscope is limited to approximately 500 nm, we improve this by more than an order of magnitude by detecting plasmon coupling between individual gold nanoparticle labels using a ratiometric detection scheme. We apply this plasmon coupling microscopy to resolve the interparticle separations during individual encounters of gold nanoparticle labeled fibronectin-integrin complexes in living HeLa cells.