Nisin Peptide Conjugation on SPEEK-GO Substrate

The necessary quantity (0.5 wt.%) of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC, Sigma Aldrich, St. Louis, MO, USA) was first dissolved in DI water and stirred well. In this work, the nisin A peptide [ITSISLCTPGCKTGALMGCNMKTATCHCSIHVSK] was obtained from Sigma Aldrich and used as received. The nisin peptide (1 wt.%) was separately dissolved in DI water and stirred to obtain a homogeneous solution. Both the EDC and nisin solutions were slowly mixed together and continuously stirred for 40 min at ambient temperature. The SPEEK-GO plate was soaked in the nisin/EDC solution and kept in a dark atmosphere for 48 h at room temperature. Through amide linkage, the nisin peptide was conjugated to the GO using the coupling chemistry between the –NH₂ group of the nisin and the –CO₂H group of GO via the cross-linking reagent of EDC [32 (link)]. The SPEEK-GO-nisin was softly taken out of the nisin solution and washed with DI water to remove the residual reagents. The SPEEK-GO-nisin was then dried overnight at 40 °C in a vacuum oven. The sample was stored in a dark atmosphere at room temperature for further experiments. The nisin conjugation on a three-dimensional porous SPEEK-GO sample from a pure PEEK substrate is shown in the schematic illustration (Figure 8).