Infrared Spectroscopy\nof Live Cells Using High-Aspect-Ratio\nMetal-on-Dielectric Metasurfaces

Fourier transform infrared (FTIR) spectroscopy is widely\nused for\nmolecular analysis. However, for the materials situated in an aqueous\nenvironment, a precondition for live biological objects such as cells,\ntransmission-based FTIR is prevented by strong water absorption of\nmid-infrared (MIR) light. Reflection-based cellular assays using internal\nreflection elements (IREs) such as high-index prisms or flat plasmonic\nmetasurfaces mitigate these issues but suffer from a shallow probing\nvolume localized near the plasma membrane. Inspired by the recent\nintroduction of high-aspect-ratio nanostructures as a novel platform\nfor manipulating cellular behavior, we demonstrate that the integration\nof plasmonic metasurfaces with tall dielectric nanostructures dramatically\nenhances the sensing capabilities of FTIR spectroscopy. We also demonstrate\nthe ability of a metal-on-dielectric metasurface to transduce intracellular\nprocesses, such as protein translocation to high-curvature membrane\nregions during cell adhesion, into interpretable spectral signatures\nof the reflected light.