Acknowledment
Authors are thankful to the Department of Biotechnology (DBT) of the Government of India for the Raman Tweezers facility under the grant BT/PR6413/MED/14/802/2005 and Ms. Surekha Barkur is thankful to Manipal Academy of Higher Education for Dr. TMA Pai fellowship for Ph.D. program and SPIE (the international society for optics and photonics) for SPIE education scholarship.