Figure 1: Schematic drawing of peptide-based ELISA-like assay (pep- ELISA). a) Enzyme-on-peptide (EOP) mode. The target protein (enzyme cathepsin E), trapped by the peptide on the matrix (or a bead), exerts the protease activity, generating fluorescent products. b) Peptide-based Sandwich ELISA-like. The roles of two kinds of antibodies are replaced by two kinds of peptides. The other scheme is quite similar tothe conventional one.