Dielectric Mie-Resonant Metasurface Integrated ATR Chip for Spectrally Tunable Surface-Enhanced Infrared Spectroscopy in Aqueous Media

Fourier transform infrared (FTIR) spectroscopy provides label-free molecular fingerprints but often lacks sensitivity for trace analysis in aqueous media. Surface-enhanced infrared absorption (SEIRA) spectroscopy amplifies vibrational signals near nanostructured surfaces, yet conventional SEIRA platforms typically require sample drying, preconcentration, or noble metal substrates. Here, we introduce a monolithic all-silicon chip that integrates dielectric Mie-resonant micropillar arrays onto a microattenuated total reflection (µ-ATR) element using a complementary metal–oxide–semiconductor (CMOS)-compatible fabrication process. This µ-ATR SEIRA (µ-SEIRA) chip enables SEIRA directly in bulk aqueous media without sample drying, preconcentration, or noble metals. The µ-SEIRA chip provides spectrally tunable field enhancement, achieving a limit of detection (LOD) of 0.57 mM for aqueous sodium acetate, a 3.6-fold improvement over a flat silicon reference. Resonance tuning via the micropillar array geometry enables selective enhancement of specific vibrational bands, as demonstrated by the preferential enhancement of the Amide II band (∼1550 cm–1) over the Amide I band (∼1650 cm–1) in bovine serum albumin. The µ-SEIRA chip is low-cost, scalable, and disposable, reducing cross-contamination and throughput limitations associated with reusable ATR crystals for aqueous sample measurements.