1. Institute
of Photonics, Department of Optics and Optical Engineering, University of Science and Technology of China, Hefei, Anhui 230026, China
2. Center
for Micro- and Nanoscale Research and Fabrication, Hefei National
Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China
3. School
of Science, Southwest University of Science and Technology, Mianyang, Sichuan 621010, China
4. State
Key Laboratory of Modern Optical Instrumentation, Department of Optical
Engineering, Zhejiang University, Hangzhou 310027, China
5. Center
for Fluorescence Spectroscopy, Department of Biochemistry and Molecular
Biology, University of Maryland School of Medicine, Baltimore, Maryland 21201, United States