Notes:
This work was partially supported by the U.S. Department of Energy, Office of Basic Energy Sciences, and the Division of Materials Science and Engineering, under award number DE-SC0005247 (hierarchical nanostructure fabrication on high-aspect-ratio structures and 3D electrodes for hydrogel deposition), and the U.S. Air Force Office of Scientific Research Multidisciplinary University Research Initiative under award number FA9550-09-1-0669-DOD35CAP (optical properties). Part of this work was also performed at the Center for Nanoscale Systems (CNS) at Harvard University, a member of the National Nanotechnology Infrastructure Network (NNIN), which is supported by the National Science Foundation under NSF award no. ECS-0335765. We thank Prof. Robert Wood and Prof. George Whitesides for the use of equipment and Mr. Wilmer Adorno for technical assistance, and Dr. Michael Aizenberg for comments on the manuscript.