1. Laboratory of Nanoscale Biology, Institute of Bioengineering, Ecole Polytechnique Federale de Lausanne (EPFL), Lausanne, 1015, Switzerland
2. Interuniversity Microelectronics Centre (IMEC), Kapeldreef 75, B-3001 Leuven, Belgium
3. Laboratory of Nanoscale Electronics and Structures, Electrical Engineering Institute and Institute of Materials Science Ecole Polytechnique Federale de Lausanne (EPFL), Lausanne, 1015, Switzerland
4. National Institute of Standards and Technology, Applied Chemicals and Materials Division, 325 Broadway, Boulder, Colorado 80305, United States