1. Biomolecular Measurement Division, Material Measurement Laboratory, National Institute of Standards and Technology (NIST), Gaithersburg, Maryland20899, United States
2. Sensing Labs, Inc., Rockville, Maryland20850, United States
3. Center for Nanoscale Science and Technology, Physical Measurement Laboratory, National Institute of Standards and Technology (NIST), Gaithersburg, Maryland20899, United States