1. Department of Chemical Engineering, Yonsei University, Seoul 120-749, Korea, Graduate Program for Nanomedical Science, Yonsei University, Seoul 120-752, Korea, Department of Chemistry, Korea University, Seoul 136-701, Korea, Department of Radiology, College of Medicine, Yonsei University, Seoul 120-752, Korea, and Department of Biochemistry and Molecular Biology, Yonsei University, Seoul 120-752, Korea