Solid-state nanopore devices are potential platforms for single-molecule detection and sequencing. These devices detect entities such as molecules, nanoparticles, or nanoparticles tagged with molecules as they travel across a thin membrane via nanopore. Their enticement originates from the ability to investigate entities using extremely small sample volumes and without the need for extensive preparation. However, conventional nanopore techniques had a significant limitation- molecules often traversed the pore very quickly and in a stochastic fashion, providing only a little time window for study. This rapid translocation made it challenging to obtain robust and consistent signals, particularly for advanced applications like molecular identification, extended optical measurements, and sequencing.

Plasmonic nanopores significantly improved conventional solid state nanopore devices by integrating metallic nanostructures. These metallic structures can confine light, allowing optical detection methods like as fluorescence and Raman spectroscopy. This enabled the combination of electrical and optical readouts, which improved sensitivity significantly. However, plasmonic nanopores presented new obstacles. Strong optical fields can generate local heating, disrupt the liquid environment and prevent steady trapping or measurement. Furthermore, optical or plasmonic forces alone are insufficient to ensure stable, regulated and robust entrapment of tiny particles or tagged biomolecules near the pores.

Our group earlier proposed a theoretical concept, a hybrid magnetoplasmonic nanopore design with a thin cobalt layer sandwiched between two gold layers. The goal was to combine plasmonic optical enhancement and magnetic control in a single nanopore platform. In this notion, an external magnetic field might configure the magnetic layer, resulting in localized magnetic tweezers near the nanopore edge. These magnetic tweezers were expected to catch magnetic core-shell nanoparticles near to the pore wall, extending observation time and aiding particle positioning. This work anticipated magnetic trapping forces of up to 28 pN for a 10 nm magnetite nanoparticle, which was substantially higher than the forces generally obtained using standard optical or plasmonic trapping methods.

This theoretical work explained that magnetism could overcome one of the fundamental limitations of nanopores: a lack of active control over analyte location and movement. It also proposed that placing a magnetoplasmonic nanoparticle close to the nanopore wall could result in a small nanocavity with improved optical fields. However, at that point, the technique remained theoretical. The optical enhancement inside the original nanopore design was still restricted, and the integration of cobalt resulted in higher optical losses when compared to a pure gold nanopore. As a result, the field had a compelling concept, but no empirically validated platform that integrated plasmonic enhancements, magnetic trapping in a single device. The main open challenges were to experimentally realize such hybrid devices, improve the optical signal, reduce limitations associated with local heating or weak trapping, and design architectures capable of plasmonic enhancements and controlling particles at the same nanopore which we explored in this work.