Nonperturbative chemical modification of graphene for protein micropatterning

Graphene's extraordinary physical properties and its planar geometry make it an ideal candidate for a wide array of applications, many of which require controlled chemical modification and the spatial organization of molecules on its surface. In particular, the ability to functionalize and micropattern graphene with proteins is relevant to bioscience applications such as biomolecular sensors, single-cell sensors, and tissue engineering. We report a general strategy for the noncovalent chemical modification of epitaxial graphene for protein immobilization and micropatterning. We show that bifunctional molecule pyrenebutanoic acid-succinimidyl ester (PYR-NHS), composed of the hydrophobic pyrene and the reactive succinimide ester group, binds to graphene noncovalently but irreversibly. We investigate whether the chemical treatment perturbs the electronic band structure of graphene using X-ray photoemission (XPS) and Raman spectroscopy. Our results show that the sp(2) hybridization remains intact and that the π band maintains its characteristic Lorentzian shape in the Raman spectra. The modified graphene surfaces, which bind specifically to amines in proteins, are micropatterned with arrays of fluorescently labeled proteins that are relevant to glucose sensors (glucose oxidase) and cell sensor and tissue engineering applications (laminin).