Angle-multiplexed all-dielectric metasurfaces for broadband molecular fingerprint retrieval

TLDR

Infrared spectroscopy identifies molecular structure through vibrational fingerprints, and although subwavelength confinement has enabled monolayer studies, current methods still require complex equipment or tunable light sources. The authors present a metasurface‑based approach that detects broadband molecular absorption fingerprints by combining the simplicity of angle‑scanning refractometric sensors with the chemical specificity of infrared spectroscopy. They fabricate germanium high‑Q metasurfaces that provide numerous spectrally selective resonances between 1100 and 1800 cm⁻¹, and by using broadband incoherent illumination and angle‑resolved reflectance, they correlate total reflectance with absorption strength to achieve spectrometer‑less, compact, field‑deployable detection.

Abstract

Infrared spectroscopy resolves the structure of molecules by detecting their characteristic vibrational fingerprints. Subwavelength light confinement and nanophotonic enhancement have extended the scope of this technique for monolayer studies. However, current approaches still require complex spectroscopic equipment or tunable light sources. Here, we introduce a novel metasurface-based method for detecting molecular absorption fingerprints over a broad spectrum, which combines the device-level simplicity of state-of-the-art angle-scanning refractometric sensors with the chemical specificity of infrared spectroscopy. Specifically, we develop germanium-based high-Q metasurfaces capable of delivering a multitude of spectrally selective and surface-sensitive resonances between 1100 and 1800 cm-1. We use this approach to detect distinct absorption signatures of different interacting analytes including proteins, aptamers, and polylysine. In combination with broadband incoherent illumination and detection, our method correlates the total reflectance signal at each incidence angle with the strength of the molecular absorption, enabling spectrometer-less operation in a compact angle-scanning configuration ideally suited for field-deployable applications.