Plasmonic nanoparticles and their assembly have the potential to serve as a platform in practical applications such as photonics, sensing, and nano-medicine. To use plasmonic nanoparticles in these applications, it is important to understand their optical properties and find methods to control their optical response. Using polarization-sensitive dark-field spectroscopy to study self-assembled nanoparticle rings on substrates with different permittivities I show that the interaction between collective plasmon resonances and the substrate can control the spatial scattering image. Using liquid crystals as an active medium that can be controlled with an external electric field I show that the Fano resonance of an asymmetric plasmonic assembly can be actively controlled utilizing the polarization change of scattered light passing through the liquid crystal device. Furthermore, utilizing the strong electromagnetic field enhancement of coupled plasmonic “nanospikes” on the surface of gold nanoshells with a silica core, I show the use of single spiky nanoshells as surface-enhanced Raman spectroscopy substrates. Individual spiky nanoshells give surprisingly reproducible surface-enhanced Raman spectroscopy intensities with a low standard deviation compared to clusters of nanoparticles. In summary, the work presented here provides understanding of the plasmonic response for assembled nanoparticles on different substrates, illustrated a new method to actively control the optical response of plasmonic nanoparticles, and characterizes spiky nanoshells as surface-enhanced Raman scattering platform.