1. Bioelectronics Research Group, Department of Electronics and Electrical Engineering, University of Glasgow, Glasgow, G12 8LT, U.K., Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Aramaki07, Aoba, Sendai 980-8579, Japan, and Central Technology Laboratory, Asahi Kasei Corporation, 2-1, Samejima, Fuji, Shizuoka 416-8501, Japan