Plasmonic metamaterials for ultrasensitive refractive index sensing at near infrared

We experimentally report a kind of plasmonic metamaterials for high sensitive refractive index sensing. The metamaterials are an X-shaped metal nanohole array fabricated by holographic lithography followed by electron-beam evaporation and lift-off procedure. Transmission spectrum measurements reveal that the localized surface plasmon resonance (LSPR) wavelength of such nanohole array shows ultrasensitive response to refractive index change in the surrounding medium. A sensitivity of 1398 nm per refractive index unit is achieved at near infrared. The high sensitivity is attributed to the well confined and greatly enhanced electric field created by LSPR as well as the increased spatial overlap between the localized electric field and the surrounding medium. The robust fabrication technique and high sensitivity provide the present plasmonic metamaterials great potentials for the development of chip-based high sensitive nanooptical biomedicine sensors and integrated devices.