a piezoelectric biosensor substrate useful for immobilizing biomolecules in an oriented manner on the surface of a piezoelectric sensor has a ladder polymer of polyacrylonitrile . to make the substrate , a solution of an organic polymer , preferably polyacrylonitrile , is applied to the surface of a piezoelectric sensor . the organic polymer is modifying by heating the polymer in a controlled fashion in air such that a ladder polymer is produced which , in turn , forms the attachment point for the biomolecules comprising the piezoelectric biosensor .