  Plasmonic nanopores are extensively investigated as single molecules
detectors. The main limitations in plasmonic nanopore technology are the too
fast translocation velocity of the molecule through the pore and the consequent
very short analysis times, as well as the possible instabilities due to local
heating. The most interesting approach to control the translocation of
molecules and enable longer acquisition times is represented by the ability to
efficiently trap and tune the motion of nanoparticles that can be used to tag
molecules. Here, we theoretically investigate the performance of a
magneto-plasmonic nanopore prepared with a thin layer of cobalt sandwiched
between two gold layers. A nanopore is then coupled with a translocating
magnetic nanoparticle. By setting the magnetic configuration of the cobalt
layer around the pore by an external magnetic field, it is possible to generate
a nanoscale magnetic tweezer to trap the nanoparticle at a specific point.
Considering a 10 nm magnetite nanoparticle we calculate a trapping force up to
28 pN, an order of magnitude above the force that can be obtained with standard
optical or plasmonic trapping approaches. Moreover, the magnetic force pulls
the nanoparticle in close contact with the plasmonic nanopore's wall, thus
enabling the formation of a nanocavity enclosing a deeply sub-wavelength
confined electromagnetic field with an average field intensity enhancement up
to 230 at near-infrared wavelengths. The presented hybrid magneto-plasmonic
system points towards a strategy to improve nanopore-based biosensors for
single-molecule detection and potentially for analysis of various biomolecules.
