This work was supported by the National Institute of Health, grants 1R21CA133641 and R01GM094816 and Hamill Innovation Award to D.O.L., P01CA098912 to M.C.F.C. Authors thank Professor S. Link (Rice University) for
providing gold nanorods, Professor R.A. Drezek for providing silica - gold shells and the members of the Carson laboratory, especially Drs. Brian Danysh and Pam Constantinou, for many helpful discussions.