Free-standing membrane metasurfaces for enhanced biochemical sensing

Metasurfaces are thin, engineered planar structures that uniquely manipulate electromagnetic waves, providing exceptional control over light properties. High-index dielectric metasurfaces with sharp resonances in the mid-infrared (mid-IR) spectrum are ideal for studying light-matter interactions near cavities. Traditionally, mid-IR metasurfaces are made on transparent solid substrates like CaF2, BaF2, and MgF2, which degrade resonance quality (Q factor) and hinder efficient sample binding to near-field hotspots. These substrates also obstruct scalable manufacturing. Here, we report free-standing silicon membrane metasurfaces with high-Q (Q factor ~734) resonances that trap light in air cavities etched into single-crystal Si membranes. Applications of these photonic metadevices include vibrational strong coupling with the polymethyl methacrylate (PMMA) C=O bond and biosensing by detecting a protein monolayer. This new metasurface platform promises compact, sensitive photonic devices, enabling monolithic integration with chip-based light sources and detectors for polaritonic chemistry and biochemical sensing