Immobilization of horseradish peroxidase on binary self-assembled monolayers with carboxyl- And hydroxyl-terminal groups: Dependence of the amount of immobilized enzymes and their electrocatalytic activity on the monolayer composition

The amount of covalently immobilized horseradish peroxidase (HRP), FHRP, and its electrocatalytic current, i_red, are measured with changing the monolayer composition for two kinds of mixed self-assembled monolayers (SAMs) of COOH- and OH-termmated alkanethiols with different domain structures. In phase-separated SAMs of mercaptopropionic acid (MPA) and 11-mercaptoundecanol (MUOL), HRP is selectively immobilized on the MPA domains and, therefore, both γ_HRP and i_red values increase in proportion to the surface mole fraction of MPA. In homogeneously mixed SAMs of 11-mercaptoundecanoic acid (MUA) and MUOL, HRP is homogeneously immobilized on the entire surface of the SAM, and γ_HRP and i_red values reach constant values at the mole fraction of MUA, χ_MUA = 0.4. j.