Plasmonic Photochemistry as a Tool to Prepare Metallic Nanopores with Controlled Diameter

Abstract

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