Surface-enhanced infrared absorption spectroscopy

When molecules are placed at the interface to metals or metal oxides, an increase in their infrared (IR) spectral intensities is observed, a phenomenon termed surface-enhanced infrared absorption (SEIRA). This effect was found initially for polydisperse metal island films with moderate to strong enhancements enabling the detection of IR signals at the monolayer level. Later, the advancement of lithographic techniques gave access to specifically tailored nano-antennas with plasmonic resonances, which provide enhancements by several orders of magnitude, such that a detection in the range of 103 molecules became possible. With the chemical resolution inherent to IR spectroscopy and its non-destructive and label-free nature, the SEIRA effect, therefore, opened the door to a large range of chemical and biophysical applications, which had not been possible earlier without SEIRA's surface sensitivity and enhancing effect. This Primer describes the mechanisms underlying the SEIRA effect, common methods to fabricate SEIRA-active materials, and the advantages and limitations of this powerful approach. Furthermore, the broad applicability of SEIRA is presented with a particular focus on examples from the fields of analytics, electrochemistry and catalysis as well as biophysical functional investigations, finally concluding on future trends in this vibrant field of research.