Detection of CEA protein in ELISA applying AP/α-CEA-λ phage. AP/α-CEA-λ phage, displaying AP as a fusion to the C-terminus of gpD and scFv anti-CEA antibody to C-terminus of the truncated gpV, was tested by ELISA against purified CEA and an irrelevant GST protein, and developed directly by adding an AP chromogenic substrate. λKM4 wild type phage was also tested as a negative control. Results are expressed as A=A405-A620. Data reported are the average values of assays performed in duplicate. Error bars represent the standard deviation of the mean.