Enhancement of extraordinary optical transmission and sensing performance through coupling between metal nanohole and nanoparticle arrays

The extraordinary optical transmission (EOT) of sub-wavelength nanohole array is significantly enhanced through introducing nanoparticles, including nanospheres and nanocylinders, into the centers of the nanoholes. Maxima of 56% and 48% for nanocylinder and nanosphere matrices are achieved, compared with that of 37% for a none-in-hole nanohole array gold film. The mechanism behind the phenomena is discussed, indicating that surface plasmon mode coupling between nanoholes and nanoparticles rather than Fabry-Perot resonance is the cause for the EOT enhancement. High near-field intensity enhancement also leads to the interaction between analytes and optical field increasing, therefore an improved sensitivity and figure of merit for biosensing. The modified structures are highly promising in practical sensing applications due to the incident angle independence. Similar results are obtained for a hexagonal array of nanohole gold film and nanoparticle modifications thereof.