Metal affinity-carboxymethyl cellulose functionalized magnetic graphene composite for highly selective isolation of histidine-rich proteins.

A metal affinity-carboxymethyl cellulose functionalized magnetic graphene, namely MGCI-Cu composite, was prepared by successive modifications of graphene oxide nanosheets with magnetic nanoparticles, carboxymethyl cellulose (CMC), iminodiacetic acid (IDA) and then chelated with copper ions. The successful modifications of the graphene surface were demonstrated by various characterizations, and a high density of 6.17 μmol m for metal affinity groups was obtained. The composite exhibited high adsorption selectivity toward histidine-rich proteins. The adsorption was governed by strong metal affinity binding force between hisitidine residues of proteins and immobilized Cu ions of MGCI-Cu composite. In particular, highly selective isolation of hemoglobin (Hb) was achieved in 0.2 mol L phosphate buffer at pH 8. The adsorption capacity of Hb significantly increased to 769 mg g in comparison to that of 435 mg g on metal affinity modified magnetic graphene composite (MGI-Cu) without CMC modification. The adsorbed Hb molecules were recovered with a carbonate buffer (0.2 mol L pH 10) containing 0.5 mol L imidazole. MGCI-Cu composite displayed favorable reusability for at least four times after regeneration of the composite by edetic acid (EDTA) and Cu solution. The practical applications demonstrated that MGCI-Cu composite could highly selectively isolate Hb from human whole blood and polyhistidine-tagged recombinant protein from Escherichia coli (E. coli) lysate.