1. Corporate R&D Headquarters, Frontier Research Center, Canon Inc., 30-2, Shimomaruko 3-chome, Ohta-ku, Tokyo 146-8501, Japan, and Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, 6-6-07, Aoba-yama, Aoba-ku, Sendai, Miyagi 980-8579, Japan