  Nanoporous gold can be exploited as plasmonic material for enhanced
spectroscopy both in the visible and in the near infrared spectral regions. In
particular, with respect to bulk metal it presents interesting optical
properties in the infrared where it presents a significantly higher field
confinement with respect to conventional materials. This latter can be
exploited to achieve extremely high sensitivity to the environment conditions,
hence realizing interesting sensors. Here we compare the sensitivity of a
plasmonic resonators made of nanoporous gold with a similar structures made of
bulk metal. The experimental test of the enhanced sensitivity was performed by
depositing the same stoichiometric quantity of dielectric material onto the two
considered structures. The result, also confirmed by the biosensing of a short
peptide, can be ascribed to the better field confinement and enhancement in
porous metal. This suggests an application of nanoporous 3D structures as
sensor platform in the near-infrared with sensitivity over 4.000 nm/RIU.
