The Influence of the Underlying Gold Substrate on Glucose Oxidase Electrodes Fabricated Using Self-Assembled Monolayers

Abstract

The influence of the underlying gold surface topography on the response of enzyme electrodes fabricated by covalent attachment of glucose oxidase to a 3-mercaptopropionic acid self-assembled monolayer was assessed. Six different gold substrates were prepared. The bare substrates were evaluated for roughness and defects using atomic force microscopy (AFM) and scanning tunneling microscopy (STM). Despite large variations in surface roughness, the shapes of the enzyme electrode calibration plots indicate that approximately the same amount of MPA was adsorbed on the surface and from electrochemical stripping experiments the same number of active enzyme molecules were attached. However, compared with the smoother surfaces, enzyme electrodes fabricated on surfaces with high microscopic roughness had a smaller linear range but a similar current sensitivity in the linear portion of the calibration plot. Tapping-mode AFM images of the enzyme modified surfaces showed that the enzyme adsorbed onto the surface as clusters of five or six enzyme molecules. The formation of these clusters did not appear to be influenced by the surface roughness.