1. Department of Chemistry and Biochemistry, University of California–Los Angeles (UCLA), Los Angeles, CA 90095-1569, USA.
2. Department of Microbiology, Immunology and Molecular Genetics, and the Biomedical Engineering Program, UCLA, Los Angeles, CA 90095, USA.
3. The California NanoSystems Institute (CNSI), UCLA, Los Angeles, CA 90095, USA.
4. Department of Materials Science and Engineering, UCLA, Los Angeles, CA 90095, USA.