1. School of Physics and Microelectronics Zhengzhou University Zhengzhou 450001 China
2. Biophysics Group Department of Physics and Astronomy University College London (UCL) London WC1E 6BT UK
3. UCL Healthcare Biomagnetic and Nanomaterials Laboratories London W1S 4BS UK
4. Tianjin Key Laboratory of Molecular Optoelectronic Sciences Department of Chemistry School of Science Tianjin University and Collaborative Innovation Center of Chemical Science and Engineering Tianjin 300072 China