Figure 3.

Results of characterization by Raman spectroscopy and atomic force microscopy (AFM). (a) Raman spectrum of graphene before (red data) and after (black data) exposure to diazonium salt solution. The strongly enhanced D-band (near 1360 cm^–1) after diazonium treatment indicates the formation of carboxybenzene sites on the graphene surface. (b) AFM image of soluble μ-receptor proteins (white dots) decorating the graphene surface. The density of protein molecules is approximately 10 times greater on the graphene as compared to the SiO₂ substrate. Scale bar is 2 μm. (c) Histogram of the heights of proteins indicating that the 46 kDa μ-receptor monomer is ∼4 nm tall on the surface, with dimers and trimers of 8 and 12 nm, respectively.