In addition, the relative area of both C O component in C1s region and C O component in O 1s region becomes the biggest at the sample of EDC/NHS-modified protein that is correlated with the presence of carbonyl groups in the molecular structure of amine-reactive NHS ester in the modified protein, then the peak area hasbeing decreased back after the modification with ethylenediaminethat is suggested due to the replacement of NHS ester species by ethylenediamine conjugated to the protein and removal of those carbonyl groups. The spectra of N 1s are shown and discussed in Supplementary information (Fig. S1).