1. Department of Chemical and Biomolecular EngineeringNational University of Singapore 4 Engineering Drive 4 Singapore 117585 Singapore
2. Paul C. Lauterbur Research Center for Biomedical ImagingInstitute of Biomedical and Health EngineeringShenzhen Institute of Advanced TechnologyChinese Academy of Sciences Shenzhen 518055 P. R. China
3. Research Laboratory for Biomedical Optics and Molecular ImagingInstitute of Biomedical and Health EngineeringShenzhen Institute of Advanced TechnologyChinese Academy of Sciences Shenzhen 518055 P. R. China