PhD Thesis Defense: Magnetoplasmonic Nanopores

Solid-state nanopores provide an effective platform for the nanoscale interrogation of individual analytes, including biomolecules and functionalized nanoparticles, by confining them within a well-defined sensing volume. However, their largely passive nature limits practical applications, as neither the optical signal strength nor the position and dynamics of analytes within the pore can be deterministically controlled. This thesis addresses these challenges through the development of magnetoplasmonic nanopore architectures that integrate plasmonic field enhancement with magnetic functionality. In this approach, the magnetic functionality is primarily used to control magnetic or magnetoplasmonic particles, which can act either as model analytes or as functional labels for otherwise non-magnetic analytes. This enables controlled trapping, positioning, and release near the nanopore. In these architectures, the nanopore itself acts as a magnetic discontinuity within a ferromagnetic environment, generating localized magnetic stray fields that enable magnetic trapping and manipulation.

First, reconfigurable magnetic nanopore architectures are realized for dynamic control of particle trapping. By engineering the magnetic configuration to switch between high-stray-field and flux-closure states under applied magnetic fields, the trapping potential can be dynamically turned on and off, allowing controlled capture and release of tagged particles. Proof-of-concept experiments demonstrate selective magnetic trapping of fluorescent magnetic nanoparticles. Second, a hybrid magnetoplasmonic nanopore/waveguide platform based on a bullseye geometry is developed to enhance optical readout. The bullseye geometry concentrates surface plasmon polaritons toward the central nanopore, resulting in strong near-field enhancement and improved optical sensitivity. The incorporation of a thin ferromagnetic layer minimally affects the optical performance while introducing magnetic stray fields that enable trapping and positioning of magnetoplasmonic or magnetic nanoparticle-labelled analytes. Electromagnetic and micromagnetic simulations, supported by experiments, reveal that particle--nanopore coupling in the nanogap region leads to substantial additional field enhancement, providing a route toward improved optical detection.

In addition, exploratory electrical-readout experiments using sub-50 nm nanopores demonstrate the potential of extending the platform toward iontronic sensing. These experiments provide a complementary direction for investigating ion-current rectification and the possible coupling between magnetic materials, surface charge, and nanoscale ion transport. Together, these approaches establish a versatile magnetoplasmonic nanopore platform that combines enhanced optical sensitivity with active, reconfigurable control over particle position and dynamics. This work provides a foundation for next-generation nanopore technologies for single-molecule sensing, sequencing, and on-chip manipulation.