1. Department of Biomedical Engineering, Hong Kong Polytechnic University, Hong Kong, P. R. China
2. Shenzhen Research Institute, Hong Kong Polytechnic University, Shenzhen 518057, P. R. China
3. Britton Chance Center for Biomedical Photonics, Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, Hubei 430074, P. R. China