It is important to point out that the effects on electron transfer through different linkages depend on the electrode surface, molecule to immobilize, type of linkage, distance between the surface to the attached molecule, reaction/electron transfer mechanism, and so on. It is inexpedient to implicitly assume that non-covalent immobilization will result in faster electron transfer rate than covalent immobilization or vice versa. In fact, we will present studies indicating one immobilization method may surpass the other under specific circumstances for both cases.