Leaky Mode Resonance of Polyimide Waveguide Couples Metal Plasmon Resonance for Surface-Enhanced Raman Scattering

In the studies of surface-enhanced Raman scattering (SERS), it is considered to be a key point to couple the surface plasmons of metallic nanomaterials and structures to resonate, which can assist higher SERS signal enhancement. This paper is to explore a strategy for plasmon resonating based on the leaky mode resonance (LMR) of a polyimide (PI) optical waveguide (OWG), for the purpose of achieving the highly sensitive evanescent field-excited SERS. PI was chosen to build the waveguide layer due to its merits of exhibiting small extinction coefficients in the natural light frequency, low cost, high flexibility, easy fabrication, and almost no Raman spectral interference. The OWG configuration guarantees a high harvesting efficiency for the incident light. Ag nanoparticles were assembled on top of the OWG layer as plasmonic antennas to provide a large scattering cross section based on the coupling of the LMR and metal plasmon resonance (MPR), which supports highly efficient SERS radiation and being conducive to the far-field collection. The LMR-MPR coupling can facilitate stronger local electromagnetic field around the side surfaces of the Ag nanoparticles, which is favorable to the adsorption of analytes. The PI OWG-coupled MPR structure can realize the integration of SERS excitation light paths and elements, which is not only a valuable SERS enhancement configuration but also a promising technique for the surface and thin film analysis.