Gold/PNIPAM core-shell nanoparticles (NPs) possess proven photothermal and sensing capabilities. In this contribution we report in situ spectroscopic ellipsometry (SE) measurements to determine the complex, temperaturedependent properties of ordered lattices of such NPs. The approach proposed here is instrumental to the analysis and design of functional hybrid metasurfaces with plasmonic functionalities, including particle-to-film coupled systems.