λ³/1000 plasmonic nanocavities for biosensing fabricated by soft UV nanoimprint lithography

Arrays of plasmonic nanocavities with very low volumes, down to λ(3)/1000, have been fabricated by soft UV nanoimprint lithography. Nearly perfect omnidirectional absorption (3-70°) is demonstrated for the fundamental mode of the cavity (λ ≃ 1.15 μm). 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°, λ ≃ 750 nm). It leads to high refractive index sensitivity (405 nm/RIU) and figure of merit (∼21) and offers new perspectives for efficient biosensing experiments in ultralow volumes.