1. Simpson Querrey Institute for BioNanotechnology, Northwestern University, Chicago, IL 60611, USA.
2. Department of Medicine, Northwestern University, Chicago, IL 60611, USA.
3. Department of Biomedical Engineering, Northwestern University, Evanston, IL 60208, USA.
4. Department of Chemistry, Northwestern University, Evanston, IL 60208, USA.
5. The Ken & Ruth Davee Department of Neurology, Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA.
6. Materials and Manufacturing Directorate, Nanostructured and Biological Materials Branch, Air Force Research Laboratories, Wright-Patterson AFB, OH 45433, USA.
7. DuPont-Northwestern-Dow Collaborative Access Team Synchrotron Research Center, Northwestern University, DND-CAT, Argonne, IL 60439, USA.
8. Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA.