Waveguide-coupled localized surface plasmon resonance for surface-enhanced Raman scattering: Antenna array as emitters

Metal nanostructures with the configurations of narrow gaps or sharp tips attract plenty of researchers due to their superior performances in plasmonic sensing and surface-enhanced spectroscopy. Too many attempts were devoted for manufacturing elaborate structures to achieve controllable and better performance. However, the excitation and emission ways for these nanostructures which can more feasibly tune the plasmonic features of these nanostructures are lack of study. In this work, we demonstrate a strategy to obtain the considerable signal amplification by efficiently exciting a nanohemisphere array with dozens of nanometers' gap and a non-sharp nanocone array with different waveguide modes under two polarizations of light in the evanescent field. For the gap-type structure, the TE light is preferred. The enhancement is attributed from the dipolar resonance of nanohemisphere. The best enhancement is achieved on the tip-type nanocone array due to the lightning rod effect under TM polarized light, which allows for the lowest detectable concentration for the Raman signal of 4-mercapto-benzoic acid reaching to 1.0 x 10(-10) M. The waveguide-coupled antenna array has great potential for label-free sensing and detections of macromolecules and biomolecules.