Self-Assembled Spherical Supercluster Metamaterials from Nanoscale Building Blocks

We report on a simple, universal, and large-scale self-assembly method for generation of spherical superclusters from nanoscopic building blocks. The fundamentals of this approach rely on the ultrahigh preconcentration of nanoparticles (NP) followed by using either emulsification strategies or alternatively multiphase microfluidic microdroplets. In both cases drying of the NP droplets yields highly spherical self-assembled superclusters with unique optical properties. We demonstrate that the behavior of these spheres can be controlled by surface functionalization before and after the self-assembly process. These structures show unique plasmonic collective response both on the surface and within the supercluster in the visible and infrared regions. Furthermore, we demonstrate that these strong, tunable optical modes can be used toward ultrasensitive, reproducible, surface-enhanced spectroscopies.