Efficiency of GFP display on the capsid of the double displaying phage GFP/α-CEA-λ. Lambda phage clones, displaying GFP at the C-terminus of gpD or double displaying GFP at the same position and anti-CEA scFv antibody as a fusion to the truncated gpV, were evaluated for the GFP display efficiency. On the abscissa are indicated the amount of wild type phage measured in pfu. The amounts of the phage used in ELISA have been normalized relative to wild type phage in order to have identical number of physical particles per well. ELISA was performed by using anti-gpV antibody-coated plates and the displayed GFP was revealed by using an anti-GFP AP-conjugated antibody. 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.