1. ZJU-UIUC Institute, International Campus, Zhejiang University, Haining, Zhejiang 314400, China
2. Nanobio Group, Micro-systems Technology and Solutions, IBM T.J. Watson Research Center, Yorktown Heights, New York 10598, USA
3. Microsystem Group, IBM T. J. Watson Research Center, Yorktown Heights, New York 10598, USA