PH Reversible Conjugates of Graphene Oxide with Peptides and Proteins

Graphene Oxide (GO) is an attractive material for biomedical applications due to its unique properties, such as the abundance of surface polar groups, amphiphilicity, and biocompatibility. Much focus has been given to elastin-like polypeptides because of their stimulus responsive behavior, displaying lower critical solution temperature phase behavior, making them attractive for biomedical and biotechnological applications. Our aim is to engineer similar behavior in GO, combining it with engineered biomolecules such as peptides and proteins for pH, temperature and structural stimulus responses. Understanding the interaction between the GO and proteins at the molecular level is critical. However, this is a formidable challenge due to the complexity of proteins and the heterogeneous nature of the GO surface. In this work we elucidate the interaction between GO and biomolecules ranging from free amino acids to peptides and proteins. We used various biophysical methods like UV-Vis, Dynamic Light Scattering, Zeta Potential, Raman spectroscopy, optical imaging, etc. to characterize and understand the GO and biomolecule interactions in detail. Understanding the molecular interaction helps us to successfully form the pH reversible conjugates of GO in the presence of peptides and proteins. Our results suggest that electrostatic interactions are the driving force for the formation of amino acid and peptide-GO conjugates, but in the case of proteins, electrostatic interactions alone are insufficient; exposed hydrophobic groups or reduction in electrostatic repulsion between the proteins during denaturation in conjunction with electrostatics drive the formation of GO-protein conjugates. This property of GO may be utilized for many biomedical and nanotechnology applications such as drug delivery, biosensor applications and hybrid nano-biomaterials.