Graphene oxide (GO) nanosheets have been immobilized onto SiO2 particles through electrostatic interactions by surface assembly. The surface-assembled composite material was characterized by means of SEM and FTIR and UV/Vis spectroscopy to reveal an assembling ratio of 2.3 % (w/w, GO/SiO2). The GO/SiO2 composites were subsequently used, for the first time, as adsorbents for the adsorption/isolation of proteins. Selective isolation of proteins of interest, namely, hemoglobin (Hb) in this case, from complex sample matrices, for example, human whole blood, could be obtained by carefully manipulating the adsorption/desorption process. At pH 7, an adsorption of 85 % was achieved for Hb (70 mg L−1) in sample solution (1.0 mL) by the GO/SiO2 composites (3.0 mg). The adsorption behavior was consistent with the Langmuir adsorption model, corresponding to a theoretical adsorption capacity of 50.5 mg g−1 for Hb. The retained Hb could be readily recovered by using a Tris-HCl buffer at pH 8.9 to give a recovery of 80 %. Circular dichroism and specific activity investigations indicated that the GO/SiO2 composites exhibited favorable biocompatibility, characterized by virtually no effect on the conformation and activity of Hb after adsorption/desorption. The composites were used for the selective isolation of Hb from human whole blood and achieved satisfactory results by assaying with sodium dodecyl sulfate polyacrylamide gel electrophoresis.
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