Porous silicon is a suitable host material for biosensing applications due to its high surface area to volume ratio, which
enables substantial infiltration of biomolecules. Resonant waveguides can be fabricated from porous silicon based on a
two layer porous silicon structure. Light is coupled into the waveguide only at a particular angle of incidence.
Biomolecular binding inside the pores induces an increase in the effective porous silicon refractive index and causes a
change in the angle at which light is coupled into the waveguide. A biosensor for DNA detection based on a porous
silicon waveguide has been fabricated. Detection of DNA at concentrations on the level of ~μM is reported. Simulations
suggest significantly lower detection levels are possible.