Dynamic Plasmonic Coupling in Gold Nanosphere Oligomers: Mechanically Tuned Red and Blue Shifts for SERS/SEF.

Controlling the surface plasmon resonances of metal nanostructures is crucial for advancing numerous high-sensitivity optical (bio)sensing applications. Furthermore, dynamically adjusting these resonances enables real-time tuning of the spectrum of enhanced electromagnetic fields in the near field, thereby regulating the optical interactions between molecules and the metal surface. In this study, we investigate the plasmonic behavior of linear oligomers composed of gold nanospheres using finite-difference time-domain electromagnetic simulations. The extinction spectra of linear arrangements such as dimers, trimers, and quadrumers are obtained for different sphere sizes, interparticle gaps, and polarization of the incident light. In view of (bio)sensing applications based on plasmon-enhanced optical spectroscopy such as surface-enhanced Raman/fluorescence (SERS/SEF), the sensitivity of various coupled plasmon modes to the variation of the interparticle gap is evaluated. The achievement of both red-shifting and blue-shifting plasmon modes offers ways to mechanically control the optical response of the linear oligomers in real-time and design new optical sensing protocols. Based on these findings, both an approach for trapping molecules into SERS hotspots and an approach for dual-mode SERS/SEF using a single excitation wavelength are proposed, contributing to the future development of (bio)sensing protocols.