1. Department of Pharmaceutical Engineering, College of Chemistry and Chemical Engineering, Central South University, Changsha, Hunan 410083, P. R. China
2. Department of Pharmaceutics, Xiangya School of Pharmaceutical Sciences, Central South University, Changsha, Hunan 410013, P. R. China
3. Molecular Imaging Research Center of Central South University, Changsha, Hunan 410008, P. R. China