From its very birth, the study of nanophotonics has become a vibrant field of research that continues to surprise year after year with disruptive innovation opportunities. Using artificially engineered subwavelength metallic or all-dielectric building blocks (e.g., 3D and flatland metastructures), researchers now control the flow of light far beyond the classical diffraction limits and unveil unique functionalities not accessible in nature. In light of these, this thesis reports: (i) refractive index sensing characteristics of a plasmonic metal dimer on a substrate of the same metal and (ii) third harmonic generation (THG) of deep ultraviolet (DUV) light using toroidal dipole-based plasmonic meta-atoms. Chapter 1 presents the developed monolithic metal dimer-on-film structure in-detail, where the implementation of such all-metal magnetic dipole-resonant metasurface provides high-performance localized surface plasmon resonance (LSPR)- and surface lattice resonance (SLR)-based plasmonic sensors. Chapter 2 demonstrates a reliable candidate to generate high-energy light using toroidal excitations (an intriguing concept in light-matter interactions), as the first example of its kind.