  Theory predicts a distinct spectral shift between the near- and far-field
optical responses of plasmonic antennas. Here we combine near-field optical
microscopy and far-field spectroscopy of individual infrared-resonant
nanoantennas to verify experimentally this spectral shift. Numerical
calculations corroborate our experimental results. We furthermore discuss the
implications of this effect in surface-enhanced infrared spectroscopy (SEIRS).
