* Corresponding authors

^a Institute of Molecular Functional Materials, Department of Chemistry and Institute of Advanced Materials, Hong Kong Baptist University, Waterloo Road, Kowloon Tong, Hong Kong, P. R. China
E-mail: rwywong@hkbu.edu.hk, clamho@hkbu.edu.hk
Fax: +852-3411-7348

^b Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Hong Kong, P. R. China
E-mail: dennis.leung@polyu.edu.hk

^c School of Chemistry, University of Bristol, Bristol, UK
E-mail: Ian.Manners@bristol.ac.uk

^d Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Hong Kong, P. R. China
E-mail: wai-yeung.wong@polyu.edu.hk