RESUMO
We show, both theoretically and experimentally, that long-range surface plasmons (LRSPs) are supported by asymmetric structure, consisting of a thin silver/gold bilayer metallic film sandwiched between a magnesium fluoride (i.e., MgF2) buffer layer and a sensing medium (water). The geometrical parameters of the structure are optimized to yield efficient excitation of LRSPs by using transfer matrix method based on Fresnel reflection. The excitation of LRSPs was performed by using a custom-made automated optical setup based on angular interrogation with the precision of 0.01°. We demonstrate that the bimetallic asymmetric structure achieves better minimum reflectivity resolution than monometallic (gold) asymmetric structure. Finally, figures of merit are compared for bimetallic, monometallic, and conventional SPR structures, and we found that the bimetallic asymmetric structure provides a higher figure of merit; e.g., more than double for monometallic LRSP configuration and 8 times as compared to the conventional surface plasmon resonance sensor.
Assuntos
Técnicas Biossensoriais/instrumentação , Diagnóstico por Imagem/instrumentação , Metais/química , Ressonância de Plasmônio de Superfície/instrumentação , Técnicas Biossensoriais/métodos , Campos Eletromagnéticos , Elétrons , Fluoretos/química , Ouro/química , Ligantes , Compostos de Magnésio/química , Teste de Materiais , Fenômenos Ópticos , Oscilometria , Refratometria , Prata/química , Ressonância de Plasmônio de Superfície/métodos , Água/químicaRESUMO
We propose a plasmonic structure, based on a silver-gold two-layered metallic film, where two surface plasmons (SPs) with equal propagation constants are excited simultaneously at different wavelengths. We show theoretically that the bimetallic film provides unique opportunities for manipulation of plasmons and optimization of the accuracy and cross-sensitivity. The structure can be used as an effective self-reference SP sensor in wavelength-interrogated design.