Improved molecular detection sensitivity through photonic crystal unit cell design

We report improved surface sensing capabilities of photonic crystal biosensors through the inclusion of a subwavelength dielectric feature inside the photonic crystal unit cell. Incorporation of a 50 nm silicon bar (i.e., anti-slot) spanning a traditional silicon photonic crystal unit cell increases the local energy density and consequently increases the resonance shift when molecules are captured on the sensor surface. Simulations and corroborating proof-of-concept experimental results based on a layer-by-layer polymer deposition are demonstrated. A perturbation theory approach for more computationally efficient predictions of photonic crystal biosensor performance is also reported, along with a discussion of the biosensor performance as a function of the spatial position of molecule attachment on the different sensor surfaces.