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

Abstract

The amount of covalently immobilized horseradish peroxidase (HRP), ΓHRP, and its electrocatalytic current, ired, are measured with changing the monolayer composition for two kinds of mixed self-assembled monolayers (SAMs) of COOH- and OH-terminated 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 ΓHRP and ired 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 ΓHRP and ired values reach constant values at the mole fraction of MUA, χMUA=0.4.