Metal nanostructures offer a large variety of applications in today's technologies, because their optical properties from coherent oscillations of free electrons (so called plasmons) can be tuned over a broad frequency range from the far infrared to the visible. Of special interest is the huge near-field enhancement at resonance, because it enables extraordinarily sensitive infrared detection of vibrational excitations. The vibrational absorption lines of molecules that are located in the near-field range of the nanostructures appear as Fano-type signals on the broad plasmonic spectrum. Compared to molecular absorption spectra, the signal size in this kind of surface enhanced infrared absorption (SEIRA) can be 105 - 106 times stronger due to the contribution of resonant plasmonic light scattering. This kind of SEIRA allows very sensitive detection of biomolecules, chemicals, and ultrafine dust.
