1. Fitzpatrick Institute for Photonics, Duke University, Durham, North Carolina 27708, United States
2. Department of Biomedical Engineering, Duke University, Durham, North Carolina 27708, United States
3. Guangdong Provincial Key Laboratory of Optical Fiber Sensing and Communications, Institute of Photonics Technology, Jinan University, Guangzhou 510632, China
4. Department of Chemistry, Duke University, Durham, North Carolina 27708, United States
5. Department of Biology, Duke University, Durham, North Carolina 27708, United States