Compact coupled double layer metal nano-strips arrays as resonators and antennas for biophotonic applications

In this paper, we present a new compact coupled double layer hybrid plasmonic system based on metal nano-strips arrays. We demonstrate the feasibility of this device as a platform for biophotonic applications by means of modal analysis and two-dimensional (2D) finite-difference time-domain (FDTD). With the resonant condition being satisfied, the metal nano-strips behave as optical resonators and antennas through constructive interference of the short range surface plasmon polaritons (SPPs), thus enhancing their scattering cross section and the near-field electromagnetic field concentration. This can be explained by considering the strong electric field coupling in the double layer structure. We have studied the normalized scattering cross sections and near-field electric field distributions of the structures in detail. For biosensing applications, the device exhibits a refractive index sensitivity in the order of 200 nm/RIU and a maximum surface enhanced Raman scattering (SERS) factor of 10⁹-10¹⁰, particularly when metal nano-cylinders have been incorporated. In addition, the characteristic resonant condition may be tuned by having a metallic nanoparticle in the middle of each metal strips. The proposed device platform shows reasonable figure-of-merit and is ready for integration with common optofluidic biosensing system platforms.