Efficient ultra-wideband nano-antennas are becoming key components for novel photonic applications, such as energy harvesting and optical sensing of particles, fluid refractive index, chemical and biological agents, etc. Downscaling the well-known configurations of metallic antennas from radio to the optical and infra-red (IR) frequencies offers unique advantages for many of these applications. Furthermore, metallic nano-antennas can be loaded with carbon nano-devices to provide specific functionality. Two types of ultra-wideband highly efficient nano-antenna arrays developed by our group will be described. Also, a novel technique for antenna and load impedance measurements using scattering data will be presented. Various applications of nano-antennas will be discussed.