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Plasmonic solid-state nanopores with tunable hole diameters can be prepared via a photocatalytic effect resulting from the enhanced electromagnetic (EM) field inside a metallic ring on top of a dielectric nanotube. Under white light illumination, the plasmon-enhanced EM-field induces a site-selective metal nucleation and growth within the ring. This approach is used 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 sizes. As a proof-of-concept, single object detection of double stranded DNA (dsDNA) and Au nanoparticles (AuNPs) with a diameter down to 15 nm is performed. Numerical simulations provide insights into the EM-field distribution and confinement, showing that a field intensity enhancement of up to 104 can be achieved inside the nanopores. This localized EM-field can be used to perform enhanced optical measurements and generate local heating, thereby modifying the properties of the nanopore. Such a flexible approach also represents a valuable tool to investigate plasmon-driven photochemical reactions, and it can represent an important step toward the realization of new plasmonic devices.