1. Department of Physics; Research Institution for Biomimetics and Soft Matter; Fujian Key Provincial Laboratory for Soft Functional Materials Research; Xiamen University; 422 Siming Nan Road Xiamen 361005 P. R. China
2. Department of Biomaterials; College of Materials; Xiamen University; 422 Siming Nan Road Xiamen 361005 P. R. China
3. College of the Environment and Ecology; Xiamen University; 422 Siming Nan Road Xiamen 361005 P. R. China
4. Department of Physics; National University of Singapore; 2 Science Drive 3 Singapore 117542 Singapore