Investigation of Controllable Nanoscale Heat-Denatured Bovine Serum Albumin Films on Graphene.

Two-dimensional graphene devices are widely used for biomolecule detection. Nevertheless, the surface modification of graphene is critical to achieve the high sensitivity and specificity required for biological detection. Herein, native bovine serum albumin (BSA) in inorganic solution is denatured on the graphene surface by heating, leading to the formation of nanoscale BSA protein films adsorbed on the graphene substrate via π-stacking interactions. This technique yields a controllable, scalable, uniform, and high-coverage method for graphene biosensors. Further, the application of such nanoscale heat-denatured BSA films on graphene as a universal graphene biosensor platform is explored. The thickness of heat-denatured BSA films increased with heating time and BSA concentration but decreased with solvent concentration as confirmed by atomic force microscopy. The noncovalent interaction between denatured BSA films and graphene was investigated by Raman spectroscopy. BSA can act as a p-type and n-type dopant by modulating pH-dependent net charges on the layered BSA-graphene surface, as assessed by current-voltage measurements. Chemical groups of denatured BSA films, including amino and carboxyl groups, were verified by X-ray photoelectron microscopy, attenuated total reflectance-Fourier transform infrared spectra, and fluorescent labeling. The tailoring of the BSA-graphene surfaces through chemical modification, controlled thickness, and doping type via noncovalent interactions provides a controllable, multifunctional biosensor platform for molecular diagnosis without the possibility of nonspecific adsorption on graphene.