Enhanced biochemical sensing with high-Q transmission resonances in free-standing membrane metasurfaces

TL;DR

This paper introduces a novel free-standing silicon metasurface platform that achieves high-Q transmission resonances using BIC and EIT modes, enabling sensitive, compact, and scalable biochemical sensing in the mid-infrared spectrum.

Contribution

The work demonstrates a new metasurface design with high-Q transmission resonances in free-standing silicon membranes, suitable for integrated biochemical sensing applications.

Findings

Achieved Q factor of approximately 734 at 8.8 μm in transmission mode.

Demonstrated tunability of resonances through geometric scaling.

Observed strong coupling with protein monolayers, evidenced by Rabi splitting.

Abstract

Optical metasurfaces provide novel solutions to label-free biochemical sensing by localizing light resonantly beyond the diffraction limit, thereby selectively enhancing light-matter interactions for improved analytical performance. However, high-Q resonances in metasurfaces are usually achieved in the reflection mode, which impedes metasurface integration into compact imaging systems. Here, we demonstrate a novel metasurface platform for advanced biochemical sensing based on the physics of the bound states in the continuum (BIC) and electromagnetically induced transparency (EIT) modes, which arise when two interfering resonances from a periodic pattern of tilted elliptic holes overlap both spectrally and spatially, creating a narrow transparency window in the mid-infrared spectrum. We experimentally measure these resonant peaks observed in transmission mode (Q~734 at ~8.8 um) in free-standing silicon membranes and confirm their tunability through geometric scaling. We also demonstrate the strong coupling of the BIC-EIT modes with a thinly coated PMMA film on the metasurface, characterized by a large Rabi splitting (32 cm-1) and biosensing of protein monolayers in transmission mode. Our new photonic platform can facilitate the integration of metasurface biochemical sensors into compact and monolithic optical systems while being compatible with scalable manufacturing, thereby clearing the way for on-site biochemical sensing in everyday applications.