SEIRAS operates on the principle that the electromagnetic field near a metallic surface is enhanced when IR light interacts with the metal. This enhancement occurs due to the excitation of surface plasmons—coherent oscillations of free electrons at the metal surface. The amplified electromagnetic field increases the absorption of IR light by molecules present on the surface, thereby boosting the signal intensity. Commonly used metals in SEIRAS include gold, silver, and copper due to their excellent plasmonic properties.
