Response curves (SPR signal (RU) vs time for TGTG-X-GTGT on OH– and CH3–SAMs at 25 °C. (A) X = V, (B) X = D, and (C) X = T on the OH–SAM surface and (D) X = V, (E) X = D, and (F) X = T on the CH3–SAM surface. (For clarity, not all of the concentration curves are listed for each peptide/surface pair because some of the low-concentration curves overlap one another and are thus not separately distinguishable).