Probing the Plasmonic Properties of Heterometallic Nanoprisms with Near-Field Fluorescence Microscopy

In an effort to optimize both the optical properties and chemical stability of plasmonic platforms for surface-enhanced fluorescence spectroscopy, a series of multilayered heterometallic structures were prepared. Gold–silver multilayered array of prisms were designed, where the gold layers acts as protective layers for the silver and extends the spectral range of the resulting localized surface plasmon resonances. Herein, we report an experimental study of the enhanced near-field fluorescence from quantum dots deposited at the surface of these platforms. This was performed using near-field scanning optical microscopy yielding simultaneous measurements of topographical features and near-field fluorescence of the prismatic arrays. Hence, the individual localized fluorescent hot-spots could be imaged and spatially correlated with the geometry of the nanostructures for distinct polarization configuration of the excitation light with respect to the orientation of the structures. Furthermore, the fluorescence enhancement was evaluated spatially and temporally for the series of the nanoprism platforms. In particular, the quenching of the near-field fluorescence due to the metal structures was carefully evaluated for the metal–fluorophore hybrid systems.