To identify aptamers against AGR2, recombinant AGR2 was fused with glutathione-S-transferase (GST) to facilitate the attachment of the protein to solid supports (Sepharose GSHbeads). The resulting AGR2-GST-beads were used as the positive target in SELEX while the GST-beads as negative control to remove non-specific surface binding sequences. The process of in vitro sepharose-bead-based SELEX is schematically illustrated in Figure 1 .