Real-Time Optical Control of Plasmonic Coupling in Gold Nanosphere Dimers via Optical Trapping

Optical trapping (OT), recognized with the 2018 Nobel Prize, is widely used in biophysics but remains underutilized in plasmonics and nanophotonics. Here, we present a custom-built OT system integrated with dark-field (DF) microscopy that enables real-time control and characterization of plasmonic nanostructures in solution. Gold nanosphere (AuNS) dimers are assembled at multiple length scales, forming tunable junctions that exhibit localized surface plasmon resonance (LSPR) coupling and strong electromagnetic field enhancement. The LSPR of individual dimers is precisely measured at the single-particle level, allowing real-time monitoring of junction size. Localized laser-induced heating enables dynamic tuning of the junction, as detected by spectral shifts in the LSPR. This in situ control over plasmonic coupling establishes a tunable platform for studying light-matter interactions within plasmonic junctions, advancing nanoscale sensing and single-molecule spectroscopy.