Mass-Manufactured Gradient Plasmonic Metasurfaces for Enhanced Mid-IR Spectrochemical Analysis of Complex Biofluids

Mid-infrared (Mid-IR) spectroscopy offers powerful label-free molecular analysis capabilities but faces significant challenges when analyzing complex biological samples. Here, a transformative surface-enhanced infrared absorption spectroscopy (SEIRAS) platform is presented that overcomes fundamental limitations through key innovations. First, high-throughput wafer-scale fabrication of mid-IR plasmonic micro-hole-array (MHA) metasurfaces is demonstrated on free-standing silicon nitride (Si₃N₄) membranes, yielding ≈400 sensor chips per 6-inch wafer. Second, the gradient MHA metasurface design supports spectrally cascaded plasmonic modes, generating over 400 sharp resonance peaks across the 1200-2000 cm^-1 fingerprint region. This approach enables comprehensive molecular fingerprinting using simple imaging optics in transmission mode. Third, the SEIRAS platform is validated using a model polymer system and clinical peritoneal fluid samples from ovarian cancer patients, demonstrating its capability to resolve complex molecular signatures in real biological specimens. The platform's dense spectral coverage ensures optimal on-resonance enhancement across the broad fingerprint region, revealing previously obscured vibrational bands that conventional IR spectroscopy cannot distinguish. By combining high-throughput fabrication with simplified optical readout and the capability to analyze complex biological samples, this work establishes a foundation for translating SEIRAS technology into practical biomedical applications, promising a real-world impact.