Comparative Characterization of Peanut ss-Amylase Immobilization onto Graphene Oxide and Graphene Oxide Carbon Nanotubes by Solid-State NMR

In this Article, we describe solid-state NMR experiments on a model biocatalyst system consisting of the enzyme ss-amylase covalently immobilized on graphene oxide nanosheets (GO) and graphene oxide carbon nanotube composites (GO-CNT). One-dimensional magic angle spinning (MAS) NMR technique was employed on carbon nuclei (C-13) in natural abundance. The support systems (GO and GO-CNTs) were characterized first, and it was possible to assign carbon species. The difference in the C-13 spectrum between GO and GO-CNT indicated that CNT rods were successfully incorporated within GO sheets, producing sharp peaks. The shifts in the spectrum of enzyme-immobilized support systems indicated immobilization. Many more changes were observed in the C-13 MAS NMR spectra during the immobilization process, which arose from cross-linking of the surface carbon species via glutaraldehyde with the amino group of enzyme. This study showed the potential of natural abundance C-13 MAS NMR for comparative characterization of the two nanobiocatalyst systems and supported the results of our previous finding that GO-CNT composites are better platforms for enzyme immobilization owing to their large surface area. In addition, this study is the first report on C-13 NMR spectra of GO-CNT nanocomposites.