Enhancing angular sensitivity of plasmonic nanostructures using mode transition in hexagonal gold nanohole arrays

Abstract We presented a surface plasmon resonance (SPR) sensor with an angular sensitivity up to 440 deg/RIU by using (±1,∓1) mode on a hexagonal gold nanohole array. The large-area gold nanohole arrays were fabricated by thermal-annealing template-stripping method with 180-nm-hole diameter and 600-nm period. A flat dispersion curve deviated from Bragg condition for (±1,∓1) mode occurred when incident angle was larger than 20°. The finite-difference time-domain calculations verified that plasmonic mode changed from surface plasmon mode to cavity mode in nanoholes. Such mode transition resulted in the large change of dispersion curve. The angular sensitivity of the (±1,∓1) mode near the transition band was 6.2 times higher than surface plasmon mode under Bragg condition and 4.5 times higher than prism-based SPR sensors at 850 nm wavelength. Biosensing experiments for antigen-antibody interactions verified the surface binding sensitivity was higher than prism-based SPR machine.