Theoretical biosensing performance of surface plasmon polariton Bragg gratings

Surface plasmons have raised much interest over the past few decades in part for their potential in biosensing applications. Waveguide Bragg gratings supporting long-range surface plasmon polaritons, constructed by stepping the width of a metal stripe embedded in Cytop, with an etched microfluidic channel to expose the sensing surface, are proposed as biosensors. Several designs are investigated theoretically to evaluate their bulk and surface sensitivities under wavelength interrogation. Detection limits of ∼10−6 RIU and ∼8 pg/mm2 are predicted for bulk and surface sensing, respectively, with corresponding figures of merit of ∼1000 RIU−1 and ∼0.2 nm−1. Third-order gratings are good choices because they have essentially the same sensitivity as first-order gratings but over a narrower bandwidth, and they are easier to fabricate due to their larger pitch.