1. Institute of Bioengineering and Nanotechnology, 31 Biopolis Way, The Nanos, Singapore 138669, Singapore
2. IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, United States
3. POLYMAT, University of the Basque Country UPV/EHU Joxe Mari Korta Center, Avda. Tolosa
72, 20018 Donostia-San
Sebastián, Spain
4. Department
of Chemistry, Stanford University, Stanford, California 94305, United States