1. Shaanxi Key Laboratory of Macromolecular Science and Technology School of Chemistry and Chemical Engineering Northwestern Polytechnical University Xi'an Shaanxi 710072 P. R. China
2. Division of Chemistry and Biological Chemistry School of Physical and Mathematical Sciences Nanyang Technological University 21 Nanyang Link 637371 Singapore Singapore
3. Analytical & Testing Center of Northwestern Polytechnical University Xi'an Shaanxi 710072 P. R. China
4. The Key Laboratory of Biomedical Information Engineering of Ministry of Education School of Life Science and Technology Xi'an Jiaotong University Xi'an, Shaanxi 710049 P. R. China