Photonic crystal nanostructures for optical biosensing applications

We present the design, fabrication and optical investigation of photonic crystal (PhC) nanocavity drop filters for use as optical biosensors. The resonant cavity mode wavelength and Q-factor are studied as a function of the ambient refractive index and as a function of adsorbed proteins (bovine serum albumin) on the sensor surface. Experiments were performed by evanescent excitation of the cavity mode via a PhC waveguide. This in turn is coupled to a ridge waveguide that allows the introduction of a fluid flow cell on a chip. A response of ∂ λ / ∂ c = (4.54 ± 0.66) × 1 0⁵ nm/M is measured leading to a measured detection limit as good as Δ m = 4.0 ± 0.6 fg or Δ m / Δ A = (4.9 ± 0.7) × 1 0² pg/mm²in the sensitive area.