ME-FIRST: a metasurface-enhanced fingerprint infrared spectroscopic tool for fluid analytes.

Infrared (IR) spectroscopy has emerged as a pivotal tool in biomedical diagnostics, offering label-free spectral biomarkers for the detection of numerous diseases, particularly in the fingerprint region. However, the lack of rapid and sensitive IR spectroscopic techniques for analyzing complex fluid analytes remains a critical challenge in clinical practice. To address this limitation, we present a metasurface-enhanced fingerprint infrared spectroscopic tool (ME-FIRST) that enhances light-matter interactions in sub-wavelength volumes through plasmonic resonances generated with a designed metasurface across the entire fingerprint range from 1900 cm-1 to 1000 cm-1. Numerical simulations reveal confined and enhanced electric near-field, with an average probing depth of ∼100 nm and an enhancement factor |E/E0| of ∼60-fold at resonant peaks. The ME-FIRST device is further experimentally fabricated and validated, and as a proof of concept, we demonstrate the sensing of molecular vibrational modes with a considerable sensitivity in L-lysine over the full fingerprint IR spectral range. The proposed ME-FIRST presents a promising platform for high-sensitivity IR spectroscopy of fluid analytes, paving the way for clinical applications of infrared spectroscopy in biofluid analysis and pathological scenarios.