1. Department of Chemical Engineering, Indian Institute of Technology Madras, Chennai 600 036, India, DST Unit on Nanoscience, Department of Chemistry and Sophisticated Analytical Instrument Facility, Indian Institute of Technology Madras, Chennai 600 036, India, Rajiv Gandhi Centre for Biotechnology, Thiruvananthapuram 695 014, India, and Sri Chitra Tirunal Institute of Medical Sciences and Technology, Thiruvananthapuram 695 011, India