Advanced Mid‐Infrared Laser Spectroscopy for Ultra‐Low Concentration Protein Detection

Abstract Mid‐infrared absorption spectroscopy stands as a pivotal technique for protein analysis, offering noninvasive, label‐free detection and the capability of real‐time monitoring, and can reflect conformational changes through spectral characteristics. Despite its significance, the prevailing mid‐infrared absorption spectroscopy systems for protein analysis are hampered by instrument complexity, high costs, and limited sensitivity, which impede their widespread application. Here, a high‐sensitivity protein mid‐infrared laser spectroscopy sensor using a quartz hollow waveguide as a microfluidic reaction vessel is proposed. On the ultra‐long reaction path provided by quartz hollow waveguides, gold core–shell nanoparticles are modified to induce surface‐enhanced infrared absorption (SEIRA) effect, and further biotin functionalization to obtain streptavidin capture capability. Notably, the gold core–shell particles are optimized based on the time‐coupled mode theory (TCMT) to better match the hollow waveguide transmission structure. The results demonstrate that the detection limits of streptavidin in the amide I and amide II bands are 35.68 and 38.69 ng mL −1 , respectively. The proposed surface enhanced hollow waveguide realizes the simultaneous detection of the lowest detection limit of the protein amide I and amide II bands by infrared spectroscopy, which provides a powerful platform for protein analysis.