λ3/1000 Plasmonic Nanocavities for Biosensing Fabricated by Soft UV Nanoimprint Lithography

Arrays of plasmonic nanocavities with very low volumes, down to lambda(3)/1000, have been fabricated by soft UV nanoimprint lithography. Nearly perfect omnidirectional absorption (3-70 degrees) is demonstrated for the fundamental mode of the cavity (lambda similar or equal to 1.15 mu m). The second-order mode exhibits a sharper resonance with strong angular dependence and total optical absorption when the critical coupling condition is fulfilled (45-50 degrees, lambda similar or equal to 750 nm). It leads to high refractive index sensitivity (405 nm/RIU) and figure of merit (similar to 21) and offers new perspectives for efficient biosensing experiments in ultralow volumes.