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Hyperbolic metamaterials for applications to biosensing
There is an ongoing need for simple and cost-effective biosensor systems with sufficient sensitivity, specificity, and speed. Plasmonic structures for biomedical sensing have been 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 performed finite-element-method-based simulations of these structures for gold, silver, copper and aluminum using COM SOL Multiphysics. We estimate a detection limit of 10e-9 for refractive index. We will also present a comparison of sensitivities with other optical sensing approaches, such as sensors based on optical fiber, dielectric waveguide, surface plasmon-polariton (SPP), and long-range surface plasmon-polariton (LRSPP). For all structures, we use a diffraction grating as a coupling device. HMM structures offer high-sensitivity and ultra-low detection limit for numerous possible biosensing applications in medical diagnosis, environmental monitoring, biodefense, and food safety.
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