Surface-Enhanced Infrared Absorption Sensor Incorporating Liquid Galinstan with Three-Dimensional Metagratings

Surface-enhanced infrared absorption (SEIRA) sensors offer a highly sensitive platform with enhanced intensity and low noise for various molecular sensing applications. However, the sensing area in traditional metallic SEIRA sensors is limited, and fabrication of such sensors heavily relies on electron-beam lithography or photolithography, which is time-consuming and requires the procedure of metal lift-off. Here, we present an experimental demonstration of a high-performance SEIRA sensor based on liquid gallium-indium-tin (Galinstan). The SEIRA sensor incorporates the metagratings fabricated using two-photon laser writing, which enables a direct patterning of three-dimensional micro- or nanostructures. Simulation results reveal an enhancement in electric field intensity compared to the bare substrate by 2 orders of magnitude. The integration of three-dimensional structures with liquid metals is capable of achieving ultrahigh field confinement and enhancement and simultaneously expanding the effective interaction areas with analytes. Furthermore, we demonstrate the proof-of-concept sensing of molecular vibrational modes in melamine and substrate temperature, which align well with the measured signal of reflectance. The SEIRA sensor enabled by liquid Galinstan and the two-photon direct laser writing technique provides novel approaches for expanding the area of hot spots and improving capabilities of sensing in a fast, convenient, efficient, and lift-off-free manner.