The invention is the design of a biological measuring device for the
determination of the concentration of biomolecules (e.g. glucose) in an
environment which is designed for implantation into an individual or for
use in the context of an external apparatus. The device contains a
composite membrane that is essentially entirely permeable to oxygen and
permeable to larger biomolecules only in discrete hydrophilic regions.
The membrane diffusionally limits the access of biomolecules to an
enzyme, present in the hydrophilic region that catalyzes the oxidation of
the biomolecule to produce hydrogen peroxide. A sensor in communication
with the hydrophilic region is used to determine the amount of product
produced or the amount of excess oxygen present allowing for the
concentration of the biomolecule to be determined.