1. Paul C. Lauterbur Research Center for Biomedical Imaging; Institute of Biomedical and Health Engineering; Shenzhen Institutes of Advanced Technology; Chinese Academy of Sciences; Shenzhen 518055 P. R. China
2. Department of Chemical and Biomolecular Engineering; National University of Singapore; 4 Engineering Drive 4 Singapore 117585 Singapore
3. Institute of Materials Research and Engineering; 2 Fusionopolis Way, Innovis Singapore 138634 Singapore
4. Research Laboratory for Biomedical Optics and Molecular Imaging; Institute of Biomedical and Health Engineering; Shenzhen Institutes of Advanced Technology; Chinese Academy of Sciences; Shenzhen 518055 P. R. China