Carolyn Larabell, Director, National Center for X-ray Tomography
The National Center for X-ray Tomography (NCXT) soft x-ray microscope, Beamline 2.1, is now in its third year of operation. This was the world’s first soft x-ray microscope to be designed specifically for biological and biomedical imaging, and as such has set the pace on developing this modality for imaging biological cells. Under DOE-BER and NIH funding, the NCXT has taken a somewhat esoteric synchrotron-based imaging technique and turned it into an increasingly mainstream biological tool [for example, a recent issue of the Journal of Structural Biology was dedicated in entirety to x-ray microscopy of biological materials (Carrascosa, 2012 #3)]. Consequently, this beamline is following a common trajectory in terms of increases in both requests for access to beamtime, and publications. To a great extent this growth in interest from the biological community can be attributed to the uniqueness of the data and information produced by this type of microscopy. No other technique can image an intact, fully hydrated eukaryotic cell with such high fidelity and spatial resolution.
The NCXT is no by means a one-trick pony. In laboratories near Beamline 2.1 staff have been working on further developing "High Numerical Aperture Cryo-Fluorescence Microscopy."* . Again, this breakthrough microscope was the first in the world, and represents an enormous coup for the ALS in terms of a light source impacting cell biology. This new light microscopy has a number of unique features that make it exciting as a stand-alone instrument for determining the location of labeled molecules inside a cell. However, when it is coupled with soft x-ray tomography – on the same cell – it becomes a veritable powerhouse technique. Soft x-ray tomography produces quantitative, high-resolution, 3D images of the cellular and sub-cellular architecture of fully hydrated, unstained cells, including eukaryotic cells. Currently, this microscope operates with optics that produce images with a spatial resolution of 50 nm, with the prospect of achieving 10nm resolution in the near future with the installation of the latest generation of zone plates developed by the Center for X-Ray Optics. High NA cryogenic fluorescence microscopy generates 3D maps—with isotropic precision—that detail the position of fluorescently labeled molecules inside the cell. Both of these techniques are closely matched in terms of resolution/precision, and therefore optimally suited to the generation of a correlated view of a cell, and answering questions important in fields as diverse as medicine and biofuel production.
*Larabell, C. A. & Nugent, K. A., "Imaging cellular architecture with X-rays,". Curr Opin Struc Biol 20, 623-631, (2010)
McDermott, G., Le Gros, M. A. & Larabell, C. A., "Visualizing cell architecture and molecular location using soft x-ray tomography and correlated cryo-light microscopy," Annual review of physical chemistry 63, 225-239, (2012).
McDermott, G., Le Gros, M. A., Knoechel, C. G., Uchida, M. & Larabell, C. A., "Soft X-ray tomography and cryogenic light microscopy: the cool combination in cellular imaging," Trends Cell Biol 19, 587-595, (2009)