  Surface Plasmon Resonance sensors are a well-established class of sensors
which includes a very large variety of materials and detection schemes.
However, the development of portable devices is still challenging as due to the
intrinsic complexity of the optical excitation/detection schemes. In this work
we show that Nanoporous gold (NPG) films may overcome these limitations by
providing excellent sensitivity without the need of sophisticated fabrication
approaches and/or optical setup. The sensing mechanism is related the
co-localization of optical energy and analytes into the pores that promote an
enhanced light-matter coupling. As result, when molecules are adsorbed into the
pores, the NPG film shows a significant spectral shift of the effective plasma
frequency and then an abrupt change of the reflectivity. By monitoring the
reflectivity in the spectral region close to the plasma frequency (namely the
plasma edge) is then possible to detect the analyte. Through a set of
experiments we demonstrated a sensitivity exceeding 15.000 nm/RIU in the Near
Infrared Range that is comparable with the state of the art of plasmonic
metamaterials.
