1. National Core Research Center for Nanomedical Technology, Yonsei University, Seoul 120-749, Korea
2. Department of Physics, Yonsei University, Seoul 120-749, Korea
3. Department of Radiology, College of Medicine, Yonsei University, Seoul 120-752, Korea
4. Department of Chemical and Biomolecular Engineering, Yonsei University, Seoul 120-749, Korea
5. Department of Microbiology, Yonsei University, Seoul 120-749, Korea