Tunable Yagi-Uda-type plasmonic nanoantennas: Implications for nanoscale optical sensing

We introduce broadband and tunable Yagi-Uda-type plasmonic nanoantennas created by arrays of metal nanorods of varying length, and explore their use for nanoscale optical sensing. We suggest placing active nanoparticles, sensitive to chemical substances and biological agents, in close vicinity of individual nanoantenna elements at the points of subwavelength light confinement and enhancement. A change in the optical properties of the nanoparticles on exposure to e.g. inflammable gases influences the response of the nanoantenna at characteristic operating wavelengths given by the nanoantenna architecture. We also explore the possibility to dynamically adjust the operating band by using metalsemiconductor nanorods for nanoantenna elements and pumping them with a tightly focused laser beam. The operating band of more than 300 nm, all-optical tunability range of 200 nm and a high sensitivity due to subwavelength light confinement make the suggested nanoantennas attractive for nanoscale sensing applications, including real-time monitoring of low concentrations of gases and observation of chemical or biological events at the nanoscale.