A molecular resolution AFM study of gold-adsorbed glucose oxidase as influenced by enzyme concentration

Atomic force microscopy (AFM) was applied to the investigation of the adsorption of glucose oxidase (GOd) molecules onto the surface of a gold amperometric glucose biosensor. The study was carried out in order to check the dependence of the enzyme density, as revealed by AFM images, on the original concentrations in the adsorption manufacturing solutions. At the highest concentrations (1-5 x 10(-3) mg dm(-3)) the gold surface appeared to be completely covered by a thick and strongly attached molecular layer. At intermediate concentration ranges (0.1-1 x 10(-3) mg dm(-3)), the clusters of GOd molecules appeared sparsely scattered onto the gold surface, showing the underlying microcrystal organisation typical of untreated surfaces. At the lowest concentration used (10(-5) mg dm(-3)) single molecules were visualised in a lying position on gold granules or within surface microslits. The molecule shape fits with the morphometric data already known for GOd. When compared to electrochemical data resulting from tests carried out at the same concentration ranges, a significant correspondence of the molecular adsorption patterns with the enzyme amperometric responses was observed. (C) 1998 Elsevier Science S.A. All rights reserved.