fusion techniques the membrane on the waveguide surface can then be exposed to a solution of avidin and allowed to incubate for 5 minutes following rinsing by pbs the biotinylated antibody can be added and incubated for 5 minutes a sample cell containing the active membrane can then be ready for exposure to a sample in one embodiment the present invention has been demonstrated using a sandwich assay structure in accordance with the present invention using antibodies for the n and a3 domains of cea specifically t84 1 e3 t84 1 and t84 66 a3 1 h11 t84 66 the t84 66 antibodies are described in u s pat no 4 873 313 and have been deposited with the american type culture collection and are identified by the designation hb8747 while the t84 1 antibodies are also shown in u s pat no 4 873 313 and the journal of immunology references described previously the domain structure and epitope map for antibodies to cea are shown in fig2 in the presently shown results monoclonal antibodies mab t84 1 for the n domain have been used as the recognition ligands capture antibodies and monoclonal antibodies mab t84 66 for the a3 domain used for the reporter ligand this may be reversed if desired or other recognition ligands and reporter ligands may be used for differing epitopes of any target for sensor system development and optimization and for the demonstration of the cea assay on waveguides a portable test bed system has been.