1. Department of Chemistry & Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States
2. California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California 90095, United States
3. Key Laboratory of Molecular Microbiology and Technology, Ministry of Education, Department of Microbiology, College of Life Sciences, Nankai University, Tianjin 300071, P. R. China