SPR characterization of the specific interaction between AuNP–Pep1 and HEWL. (A) Binding of AuNPs functionalized with 20 Pep1 and different numbers of Pep1s per AuNP onto the immobilized HEWL. (B) SPR kinetics of the interaction between AuNP–60Pep... SPR characterization of the specific interaction between AuNP–Pep1 and HEWL. (A) Binding of AuNPs functionalized with 20 Pep1 and different numbers of Pep1s per AuNP onto the immobilized HEWL. (B) SPR kinetics of the interaction between AuNP–60Pep1 and immobilized HEWL. Red curves are the fitting lines (see SI Appendix, Fig. S8A for the residue plot). (C) SPR binding of AuNP–60Pep1 (red), AuNP–60Pep1s (green), AuNP–60Pep1m (blue), and free Pep1 (cyan) with the same “peptide concentration” onto the immobilized HEWL, RNase A, and BSA. (D) SPR binding of AuNP–60Pep1 and AuNP–60Pep1s onto the immobilized HEWL in the absence (red) and presence of 0.5 mM (green) or 5 mM (blue) Tri-NAG. Error bars indicate SDs. RU, resonance unit. Gui-Hua Yan et al. PNAS 2018;115:1:E34-E43 ©2018 by National Academy of Sciences