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 This work was supported by NIH grants 1RO1EB013689-01/NIBIB, 1R41EB013520-01 and 1R42EB013520-01. Part of this work was conducted at the University of Washington NanoTech User Facility, a member of the NSF National Nanotechnology Infrastructure Network (NNIN). Research performed at Pacific Northwest National Laboratory (PNNL) was supported by the Chemical Imaging Initiative under Contract DE-AC05-76RL01830 operated for the Department of Energy by Battelle. A portion of this work was performed at EMSL, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at PNNL..