1. Centre for Magnetic Resonance, University of Queensland, St. Lucia, Queensland 4072, Australia, Australian Institute for Bioengineering and Nanotechnology, University of Queensland, St. Lucia, Queensland 4072, Australia, School of Physical and Chemical Sciences, Queensland University of Technology, Brisbane, Queensland, 4001, Australia, and Materials Research Laboratory, University of California Santa Barbara, Santa Barbara, California 93106-5121