1. National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory , Berkeley, California , United States
2. California NanoSystems Institute, University of California , Los Angeles, California , United States
3. Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory , Berkeley, California , United States
4. Department of Chemistry and Biochemistry, University of California , Los Angeles, California , United States