Metasurfaces are on-chip imaging platforms composed of periodically repeating sub-wavelength geometries. The rational and controlled design of these geometries leads to unique and selective interactions with electromagnetic waves. In the past, these light-matter interactions have been exploited for the detection and differentiation of media with varying levels of chirality. However, existing techniques require the chiral media to be sufficiently close or in contact with the metasurface, rendering the metasurfaces as a single-use device. Chiral media composed of proteins suffer a disadvantage from this close proximity: The relatively larger size of proteins, compared to the nanometre-scale of the near-field electromagnetic interactions, results in significant challenges in determining the protein conformation using metasurfaces. A detection technique wherein the chiral media are not in direct contact with the metasurface holds potential to overcome these barriers.<br/><br/>To accomplish such a task, this project focuses on how proteins affect the polarisation of incident light and how metasurfaces can be used to enhance those effects for the far field detection of protein-composed chiral media. Outlined first are systematic explorations of how increases and decreases in rotational symmetry of metasurface nanostructures affect the corresponding electromagnetic interactions within the visible light range. From this, first-principle design guidelines are set forth as to how rotational symmetry should be violated to maximise polarisation-sensitivity of metasurfaces. Finally, this increase in the polarisation-sensitivity is leveraged to detect chiral media without direct contact with the metasurface. Our results present insights on how symmetry-violations can be quantitatively engineered to control the arising electromagnetic interactions from metasurfaces and provide a new toolbox for the sensing applications of chiral media. This paves the way towards future applications wherein the strategic incorporation of appropriately-engineered metasurfaces can be used for disease detection and drug monitoring.

Leveraging symmetry-violated nano-optical metasurfaces for the far field detection of protein-composed chiral media

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