Use of Mixed Self-Assembled Monolayers in a Study of the Effect of the Microenvironment on Immobilized Glucose Oxidase

Abstract

Mixed self-assembled monolayers (SAMs) composed of a medium length, reactive, n-organothiol (11-mercaptoundecanoic acid) and a short length, unreactive, hydrophobic n-alkylthiol (7-heptanethiol) chemisorbed onto evaporated gold surfaces, were used to study the effect of the microenvironment on the structure and activity of immobilized glucose oxidase (GOX). The mixed SAMs were characterized by X-ray photoelectron spectroscopy, contact angle measurements, and cyclic voltammetry. The derivatization of the SAMs for the covalent attachment and the immobilized enzyme were studied by X-ray photoelectron spectroscopy. Quantitative analysis of the amide I band of the infrared spectra of GOX immobilized onto surfaces at the two attainable extremes of the hydrophilicity range available to us indicated that the percentage of β sheet increased with increasing hydrophilicity of the microenvironment. The specific activity of GOX was higher when the enzyme was immobilized onto the hydrophobic microenvironment.