“…The crystal structures of GO, Ch–Trp/GO, and Ch–Met/GO were analyzed using Raman spectroscopy (Figure b). As shown in Figure b, the functionalized Ch–Trp/GO ( I D / I G = 1.15) and Ch–Met/GO ( I D / I G = 1.10) produced more structural defects and disorders than GO ( I D / I G = 0.99) because of the reaction between the AA with GO . Moreover, characteristic elements, i.e., N and S, of Ch–Met/GO and Ch–Trp/GO were observed in the XPS energy spectrum (Figure c).…”