Avidin Antibody. Conjugation of anti-human Dlk-1 monoclonal antibody or reduced antibody to avidin was performed with EZ-link maleimide activated NeutrAvidin™ protein, in accordance with the manufacturer's instruction (Pierce). The avidin-bound antibody was purified by gel filtration column chromatography using a TSK gel G3000SW column (Tosoh). Collected fractions were diluted and then added to a 96-well plate precoated with goat anti-mouse IgG. After the plate was washed, a solution of FPB was added and incubation was carried out. Bioluminescent measurements were performed with a 96-well plate reader (Berthold Technologies) after adding of 100 μL of 1 μM Cypridina luciferin solution (0.1 M Tris-HCl pH7.4/0.3 M sodium ascorbate/0.02 M sodium sulfite) to each well.