The sensitivity of a photonic crystal optical biosensor is greatly enhanced through the incorporation of low refractive index porous dielectric material into the device structure. In this work, computer models are used to predict the reflectance spectra and sensitivity performance of a one-dimensional photonic crystal biosensor. A manufacturable replication method is demonstrated that can produce a low-index dielectric periodic surface structure with a 550 nm period over large surface areas. The sensitivity of porous glass biosensors is characterized and compared with sensors incorporating non-porous polymer material. Results for detection of proteins, polymer layers, and bulk liquids indicate up to a four fold sensitivity increase.