a. Screening of clones by polyclonal phage ELISA. Epsilon toxoid was coated to plastic and then detected with an anti-c-Myc antibody. The coating was carried out in duplicate; the mean value is presented, the error bars indicat the standard deviation of the two values. 5% MPBS buffer was coated as a negative control. S1, S2, S3 = selection rounds 1, 2 and 3. b. Screening of clones by monoclonal phage ELISA of Tomlinson I + J and DAb libraries. Individual phage clones from the second and third rounds of selection were tested by monoclonal phage ELISA against purified epsilon toxoid. Phages were applied as follows; S2: 32 clones picked at random after round 2 of selection; S3: 36 clones picked at random after round 3 of selection. OD at 450 nm was measured after 10 minutes.