Sensing refractive index gradients along dielectric nanopillar metasurfaces.

Abstract

Metasurfaces exhibit unique optical properties that depend on the ratio of their refractive index and that of their surroundings. As such, they are effective for sensing global changes in refractive index based on the shifts of resonances in their reflectivity spectra. However, when used as a biosensor, the metasurface can be exposed to a spatial distribution of biomolecules that brings about gradients in refractive index along the plane of the metasurface. Such gradients produce complex global reflectivity spectrum but with distinct optical enhancements in localized areas along the metasurface. Here, we propose a unique sensing paradigm that images and maps out the optical enhancements that..