1. Department of Electrical and Computer Engineering; Micro and Nanotechnology Laboratory; University of Illinois at Urbana Champaign; Urbana IL 61801 USA
2. Department of Bioengineering; University of Illinois at Urbana Champaign; Urbana IL 61801 USA
3. Department of Mechanical and Industrial Engineering; Louisiana State University; Baton Rouge LA 70803 USA
4. Department of Computer Science; XiamenUniversity; Xiamen 361005 Peoples R China