Protein sensing using ultra-high refractive index plasmonic hyperbolic metamaterials

Abstract

Plasmonic structures for biomedical sensing are in use for a long time. However, there is a fundamental limitation of their sensitivity due to low effective refractive index of layered plasmonic structures. We are proposing a hyperbolic metamaterial (HMM) structure which is a combination of surface plasmon Polaritons (SPPs) and long-range surface plasmon Polaritons (LRSPPs) modes. The result of the interaction between these modes leads to plasmonic modes with ultra-high effective refractive index. We calculated and optimized plasmonic HMM structure with effective refractive index equal to 8.1, i.e. twice as much as that of germanium, a natural material with the highest refractive index. We simulated these structures for gold, silver, copper and aluminum. The best way to use these structures for protein sensing is to use diffraction gratings – there is no natural material which can be used as a prism. By optimizing layer parameters and diffraction grating we were able to build a model of the structure with sensitivity as 10-9 for refractive index. We are hoping to achieve sensitivity up to 10-11, so this structure can be used for different protein sensing application including detection of metastatic cells spreading the human body.