SPR experimental protocol. (A) Schematic representation of fibrinogen and the 2 major regions, E and D. Plasmin treated fibrinogen, and purification of the fragments generates D fragment. (B) Surface plasmon resonance (SPR) experimental set-up with D fragment immobilized to an SPR chip acting as the ligand and the knob A peptides flow across the surface as the analyte. (C) Representative SPR sensorgram for D fragment immobilization where the carboxyl-terminated self-assembled monolayers were activated by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)/N-hydroxysuccinimide (NHS), enabling amine-targeted immobilization of D fragment. Ethanolamine quenched any unreacted carboxyl groups and rid the surface of nonspecifically bound D fragment.