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 on top of a dielectric nanotube. Under white light illumination, the plasmon-enhanced electromagnetic field induces a site selective metal nucleation and growth within the ring. We use this approach to prepare Au and bimetallic Au-Ag nano-rings and demonstrate the reduction of the initial inner diameter of the nanopore down to 4 nm. The tunability of the nanopore diameter can be used to enable optimized detection of single entities with different size. As proof-of-concept, we demonstrate the versatility of the platform to perform single object detection of dsDNA, and Au nanoparticles with a diameter down to 15 nm. Numerical simulations provide insights into the electromagnetic field distribution, showing that a field intensity enhancement of up to 104 can be achieved inside the nanopores. The field confinement inside the nanopores can be used to perform enhanced optical measurements, and to generate local heating, thereby modifying the properties of the nanopore. Such a flexible approach represents a valuable tool to investigate plasmon-driven photochemical reactions, and it can represent an important step forward towards the realization of new plasmonic devices.