  A number of researchers are attempting to develop a biosensor based on
terahertz sensing. Key to the realization of any biosensor system is the access
of the target molecules to the sensor. In the case of using terahertz
spectroscopy, there are limitations due to high attenuation by water and
sensitivity levels. In order to have a significant response at THz frequencies
generally requires a minimum pathlength of 100 microns. Solid thin films of
this thickness will have limited interaction with target molecules. We propose
to use xerogels as biomolecular probe substrates. We have characterized the THz
transmission of xerogel substrates as a function of hydration and protein
content. These measurements demonstrate that xerogels are excellent candidates
for biomolecular probe substrates to realize THz biosensors.
