Probing the protein conformation and adsorption behaviors in nanographene oxide-protein complexes

In this report, the adsorption characteristics and conformation changes of model protein bovine serum albumin (BSA) adsorbed on nanographene oxide (NGO) are described. The adsorption isotherms obtained at pH 4.0, 4.7, 7.4 and 8.8 show that NGO has the highest affinity for BSA in the acid environment of pH 4.0, but the protein adsorption capacity decreases with the pH value increasing. The data imply that the spontaneously binding of BSA to the NGO surfaces is mainly due to the protein conformation and an electrostatic attraction mechanism. The fluorescence and synchronous fluorescence spectroscopic studies show that NGO quenches the fluorescence of BSA both statically and dynamically, and induces obvious perturbations on the conformation of BSA as well as the microenvironments around the Trp and Tyr residues. Moreover, analysis of the secondary structure of the proteins via Fourier transform infrared spectroscopy revealed that evident secondary structural changes may undergo upon adsorption. This study gives an insight into the interaction between NGO and proteins, which is critical in the design of optimal graphene nanosheets-protein conjugates.