Affinity maturation of phage-displayed, PSMA-binding ligands. (a) Phage-based ELISA with the first generation PSMA-1 and PSMA-2 ligands. Throughout this report, error bars in ELISAs indicate standard error (n=3). (b) The homolog-shotgun scanning library design used the PSMA-2 sequence as a template with the programmed mutations shown in red. The selectants incorporated the mutations highlighted in red. (c) Phage-based ELISA with the affinity-matured, PSMA-binding selectants. (d) Phage-based ELISA comparing PSMA-1,-2, and -3.