  We show that plasmonic solid-state nanopores with tunable hole diameter can
be prepared via a photocatalytic effect resulting from the enhanced
electromagnetic field inside a metallic ring prepared on top of a dielectric
nanotube. Under white light illumination, the maximum field intensity in these
nanorings induces a site selective metal nucleation and growth. We used this
approach to prepare bare Au and bimetallic Au-Ag nanorings and demonstrate the
reduction of the initial inner diameter of the nanopore down to 4 nanometers.
This process can be applied over large arrays with good reproducibility and
good control on the nanopore diameter. The tunability of the nanopore diameter
can be used to enable optimized detection of single entities with different
size, such as single nanoparticles or biomolecules. As proof-of-concept, we
demonstrate the versatility of the platform to perform single object detection
of dsDNA, and Au nanoparticles with a diameter of 15 nm and 30 nm. We support
our experimental findings with numerical simulations that provide insights into
the electromagnetic field intensity distribution, showing that a field
intensity enhancement of up to 104 can be achieved inside the nanopores. This
strong field confinement inside the final nanopore can be used to perform
enhanced optical measurements, and to generate local heating, thereby modifying
the ionic conductance of the nanopore
