1. Nanotechnology Laboratory; School of Engineering; University of Birmingham; Birmingham B15 2TT UK
2. Harvard Medical School and Wellman Center for Photomedicine; Massachusetts General Hospital; 65 Landsdowne Street Cambridge Massachusetts 02139 USA
3. Harvard-MIT Division of Health Sciences and Technology; Massachusetts Institute of Technology; Cambridge Massachusetts 02139 USA
4. Center of Excellence in Nanotechnology; King Fahd University of Petroleum & Minerals; Dhahran Saudi Arabia
5. Department of Physics; COMSATS Institute of Information Technology; Islamabad Pakistan