[1] Natl Univ Singapore, Dept Pharm, Singapore 117543, Singapore
[2] Natl Univ Singapore, Graphene Res Ctr, Singapore 117542, Singapore
[3] Natl Univ Singapore, Dept Phys, Singapore 117542, Singapore
[4] Nikon Imaging Ctr, Singapore 138677, Singapore
[5] Sungkyunkwan Univ, SKKU Adv Inst Nanotechnol SAINT, Suwon 440746, South Korea
[6] Sungkyunkwan Univ, Ctr Human Interface Nano Technol HINT, Suwon 440746, South Korea
[7] Sungkyunkwan Univ, Sch Adv Mat Sci & Engn, Suwon 440746, South Korea
[8] Sungkyunkwan Univ, Dept Chem, Suwon 440746, South Korea
[9] NUS Grad Sch Integrat Sci & Engn, Ctr Life Sci CeLS, Singapore 117456, Singapore
[10] Natl Univ Singapore, Fac Engn, Singapore 117576, Singapore