1. School of Materials Science and Engineering; Nanyang Technological University; 50 Nanyang Avenue 639798 Singapore
2. Centre for Biomimetic Sensor Science; Nanyang Technological University; 50 Nanyang Drive 637553 Singapore
3. Department of Electrical and Computer Engineering; University of Minnesota; 200 Union Street SE Minneapolis MN 55455 USA
4. School of Chemical and Biomedical Engineering; Nanyang Technological University; 62 Nanyang Drive 637459 Singapore