  Engineered electromagnetic fields in plasmonic nanopores enable enhanced
optical detection and their use in single molecule sequencing. Here, a
plasmonic nanopore prepared in a thick nanoporous film is used to investigate
the interaction between the metal and a long-chain double strand DNA molecule.
We discuss how the matrix of nanoporous metal can interact with the molecule
thanks to: i) transient aspecific interactions between the porous surface and
DNA and ii) optical forces exerted by the localized field in a metallic
nanostructure. A duration of interaction up to tens of milliseconds enables to
collect high signal-to-noise Raman vibrations allowing an easy label-free
reading of information from the DNA molecule. Moreover, in order to further
increase the event of detection rate, we tested a polymeric porous hydrogel
placed beneath the solid-state membrane. This approach enables a slowdown of
the molecule diffusion, thus increasing the number of detected interactions by
a factor of about 20.
