Transmission IR spectra of modified PSi. (a) Hydrogenated surface after electrochemical fabrication. (b) After thermal grafting of undecylenic acid. (c) After activation treatment of 90 min in an aqueous solution of 5 mM EDC and 5 mM NHS. (d) After amidation in 0.1 mM Gly-His-Gly-His in 1 × PBS buffer.