AVS 56th International Symposium & Exhibition
    Biomaterial Interfaces Tuesday Sessions
       Session BI-TuP

Paper BI-TuP8
Self-assembly of Proteins on Well-defined Sapphire Surfaces

Tuesday, November 10, 2009, 6:00 pm, Room Hall 3

Session: Biomaterial Interfaces Poster Session I
Presenter: T. Isono, Yokohama National University, Japan
Authors: T. Isono, Yokohama National University, Japan
K. Yamazaki, Yokohama National University, Japan
T. Ogino, Yokohama National University, Japan
Correspondent: Click to Email
Non-specific adsorption is a very serious issue when biomolecules are immobilized on solid surfaces. Non-specific adsorption should be suppressed especially in application of solid surfaces to biosensors or implant devices. We have tried to control protein adsorption on step-controlled sapphire surfaces. Because sapphire surface is chemically stable in liquid as well as in air, it is a suitable material for bioapplication. To control interactions between the sapphire surfaces and protein molecules, we designed surface atomic structures. In this study, we report on self-assembly of several kinds of protein molecules by using well-defined sapphire surfaces. Single crystalline sapphire (0001) surfaces were used for protein adsorption. By a high temperature annealing, the sapphire surfaces are covered with bunched steps accompanied with crossing steps when the miscut direction slightly tilts from the stable direction of atomic steps. These surfaces were cleaned by a mixture of sulfuric acid and hydrogen peroxide. We call this surface oxidized surface. Two domains, which exhibit different hydrophilicity and charge density from each other, coexist on this surface. Center regions of the terraces (domain A) are relatively hydrophobic and weakly charged, and the others (domain B) hydrophilic and negatively charged. To control the surface chemical properties, the oxidized surfaces were slightly etched by phosphoric acid. We call this surface etched surface. Protein molecules were physically adsorbed on the oxidized and the etched surfaces in a buffer solution. Protein adsorption patterns were observed by atomic force microscopy in the same buffer solution. When the oxidized surfaces were immersed in a solution of ferritin molecules whose surfaces exhibit a negative charge, ferritin molecules were selectively adsorbed on the domain A by the electrical repulsion between the domain B and the molecules. On the other hand, avidin molecules whose surfaces exhibit a positive charge were selectively adsorbed on the domain B by the attractive interaction. These protein molecules were adsorbed on the sapphire surfaces depending on the surface charges. However, small amount of avidin molecules were adsorbed on the hydrophobic domain A. Generally, it is easier for protein molecules to be adsorbed on hydrophobic surfaces than hydrophilic ones. To make the domain A hydrophilic, the oxidized surfaces were etched using phosphoric acid. When the etched surfaces were immersed in a solution of avidin molecules, avidin molecules were selectively adsorbed without non-specific adsorption on the domain A.