ATOMIC FORCE MICROSCOPY STUDY OF PROTEIN-INCORPORATING LANGMUIR-BLODGETT-FILMS

The microscopic surface morphology of glucose oxidase protein-incorporating arachidic acid Langmuir-Blodgett (LB) films were investigated using atomic force microscopy (AFM) and replica transmission electron microscopy (TEM). AFM images showing clear morphology of protein molecules were observed over a 100-600 nm area. It is indicated that the glucose oxidase molecules make their aggregates, and glucose oxidase aggregates are randomly and sparsely distributed with an average size estimated to be 20-50 nm in diameter. The size and distribution are in fair agreement with those observed by replica TEM. Furthermore, high-resolution images of arachidic acid molecules on top of the protein molecules were successfully observed for the first time. The images show two-dimensional regular structures and the periods of regularity of the arachidic acid molecules are 0.54 and 0.48 nm, respectively. The area per molecule is estimated to be 0.26 nm2. This value is consistent with that obtained from the isotherm of a monolayer of arachidic acid. Our observations provide rough confirmation of our model of the structure of glucose oxidase-incorporating arachidic acid LB film.