1. Department of Bioengineering, ‡CalIT2 Nanomedicine Laboratory, §Moores Cancer Center, ∥Department of Chemistry & Biochemistry, ⊥Department of NanoEngineering, #Program in Materials Science and Engineering, and ∇Department of Physics, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0358, United States