In a diagnostic apparatus system, a one piece porous substrate is located in a container. The substrate serves both to extract an antigen in or on a top layer with the remainder of the substrate serving as a reservoir. The pores in the top surface of the substrate are microscopic for entrapment of microspheres...http://www.google.ca/patents/US5073344?utm_source=gb-gplus-sharePatent US5073344 - Diagnostic system employing a unitary substrate to immobilize microspheres
