1. School of Chemical and Biomedical Engineering and Center for Advanced Bionanosystems, Nanyang Technological University, 70 Nanyang Drive, Singapore 637457, School of Electrical & Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, School of Materials Science and Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798, and Department of Materials Science and Engineering, University of Toronto, Toronto, Ontario, Canada