Nanotech 2010

Exciting Dark Resonances in Plasmonic Nanocross Cavities for High Sensitivity Biosensing

N. Verellen, C. Huang, K. Lodewijks, G.A.E. Vandenbosch, V. Moshchalkov, T. Stakenborg, L. Lagae, K. Jans, P. Dorpe

Keywords: nanocross, localized surface plasmon resonance


In the present work we propose a planar Au nano-cross geometry as a highly tunable cavity structure with small linewidth multipolar resonances in the visible and near-infrared spectral region. Using finite difference time domain (FDTD) calculations and optical transmission measurements we show that spectral position and spectral separation of the distinct plasmon modes can be tuned and optimized by changing the cross arm angle and length. Coupling to a single armed dipole antenna results in a complex spectral response including narrow Fano and hybridized subradiant resonances. We experimentally demonstrate that these subradiance and Fano interference could be one of the key ingredients for high sensitivity localized surface plasmon resonance biosensors. This was demonstrated by performing refractive index sensing experiments using different glycerol solutions onto the nano-cross based nanocavities using a microfluidic chip. Refractive index sensitivities of the subradiant resonance higher than 1000nm/RIU are observed with Figure of Merit (FOM) numbers exceeding 4 in the near-infrared. These are among the highest experimental numbers reported in literature for individual nanoparticles and can even further be increased by fine tuning the geometry, making these nano-cross systems valuable platforms for enhanced bio-sensing applications.
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