[1] Univ Illinois, Dept Elect & Comp Engn, Urbana, IL 61801 USA
[2] Univ Illinois, Beckman Inst Adv Sci & Technol, Urbana, IL 61801 USA
[3] Univ Aalborg, Dept Phys & Nanotechnol, Aalborg, Denmark
[4] Tech Univ Denmark, Res Ctr COM, Lyngby, Denmark
[5] Univ Penn, Dept Bioengn, Philadelphia, PA 19104 USA