The document describes a method for creating controlled mixed monolayers on glassy carbon surfaces. The method involves electrochemically grafting a mixture of diamine linkers with different ratios and orthogonal protecting groups. It is then possible to selectively remove one protecting group, couple an osmium complex, and cap the remaining amines. Removing the second protecting group allows coupling of anthraquinone. Characterization shows the surface coverage of the osmium complex and anthraquinone can be varied based on the initial ratio of linking amines. The osmium complex can then act as a mediator for glucose dehydrogenase covalently bonded to the surface.