Silver film over nanospheres (AgFoN) as tri-modal plasmonic sensing platform for Surface Plasmon Resonance Spectroscopy, Surface-Enhanced Raman Scattering, and Surface-Enhanced Fluorescence

In this work, it is demonstrated that silver films deposited over regular arrays of polystyrene colloids, known as silver film over nanospheres (AgFoN), can operate as a single, common plasmonic substrate for Surface Plasmon Resonance Spectroscopy (SPRS), Surface-Enhanced Raman Scattering (SERS), and Surface-Enhanced Fluorescence (SEF). First, the optical/plasmonic response of AgFoN is discussed, with input from Finite-Difference Time-Domain (FDTD) modelling. The reflectivity spectra of AgFoN fabricated with different-sized colloids (210, 340, and 450 nm) are shown to be highly sensitive to the adsorption of 11-mercaptoundecanoic acid (MUA) molecular layer. The SERS spectra of the same MUA molecules adsorbed on the AgFoN are then obtained by two excitation wavelengths (532 and 633 nm). Finally, the SEF spectra of Rose Bengal fluorophores deposited over the MUA monolayer are recorded. FDTD simulations are then used in order to explain the experimentally observed size-dependent SERS behaviors. These results constitute a proof-of-concept of the tri-modal, SPRS, SERS, and SEF sensing capabilities of AgFoN, expanding their potential for more reliable analytical applications based on multiple plasmon-enhanced optical readouts.