Dynamic birefringence and chirality of magnetically controllable assemblies of anisotropic plasmonic nanoparticles in dispersion.

The ability to control the orientation and arrangement of plasmonic nanoparticles with shape anisotropy offers a promising route to achieving highly tunable optical properties. In this study, we introduce a synthetic approach for magnetically controllable plasmonic nanoparticles (MPs) consisting of an anisotropic gold core encapsulated by an iron oxide shell. The superparamagnetic property of the iron oxide shell enables rapid, reversible, and remotely controlled alignment of MPs, allowing for dynamic manipulation of their optical properties. Linearly aligned MPs demonstrate tunable transmission colors via plasmon-mediated birefringence. Helical MP arrays exhibit circular dichroism of up to 12° and g-factors reaching 0.21-the highest reported value for solution-phase assemblies of achiral nanoparticles. The synthetic method is applicable to nanoparticles of various sizes and shapes, highlighting its generality and expandability.