1. Electrical and Computer Engineering, University of Illinois at Chicago, Chicago, Illinois 60607, USA
2. Department of Physics, University of Illinois at Chicago, Chicago, Illinois 60607, USA
3. Department of Bioengineering, University of Illinois at Chicago, Chicago, Illinois 60607, USA
4. U.S. Army Research Laboratory, 2800 Powder Mill Road, Adelphi, Maryland 20783, USA