  Capabilities of highly sensitive surface-enhanced infrared absorption (SEIRA)
spectroscopy are demonstrated by exploiting large-area templates ($cm^2$) based
on self-organized (SO) nanorod antennas. We engineered highly dense arrays of
gold nanorod antennas featuring polarization-sensitive localized plasmon
resonances, tunable over a broadband near- and mid-infrared (IR) spectrum, in
overlap with the so-called 'functional group' window. We demonstrate
polarization-sensitive SEIRA activity, homogeneous over macroscopic areas and
stable in time, by exploiting prototype self-assembled monolayers of IR-active
octadecanthiol (ODT) molecules. The strong coupling between the plasmonic
excitation and molecular stretching modes gives rise to characteristic Fano
resonances in SEIRA. The SO engineering of the active hotspots in the arrays
allows us to achieve signal amplitude improved up to 5.7%. This figure is
competitive to the response of lithographic nanoantennas and is stable when the
optical excitation spot varies from the micro- to macroscale, thus enabling
highly sensitive SEIRA spectroscopy with cost-effective nanosensor devices.
