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X-ray microscopes provide higher resolution than visible light microscopes. Wet, biological materials with a water thickness of up to about 10 μm can be imaged with good contrast using soft X-rays with wavelengths between the oxygen and carbon absorption edges (at 24 and 43 Å). The Stony Brook group has developed and operates a scanning transmission X-ray microscope (STXM) at the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory. The microscope is used for imaging with a current resolution of 50 nm, and for elemental and chemical state mapping. Radiation damage imposes a significant limitation upon high resolution X-ray microscopy of room temperature wet specimens. Experience from electron microscopy suggests that cryo techniques allow vitrified specimens to be imaged repeatedly. This is due to the increased radiation stability of biological specimens in the frozen hydrated state. Better radiation stability has been shown recently with a cryo transmission X-ray microscope developed by the University of Gottingen, operating at the BESSY storage ring in Berlin, Germany. At Stony Brook, we are developing a cryo scanning transmission X-ray microscope (CryoSTXM) to carry out imaging and spectra-microscopy experiments on frozen hydrated specimens. This article will give an outlook onto the research projects that we plan to perform using the CryoSTXM.

We have used the method of x-ray diffraction microscopy to image the complex-valued exit wave of an intact and unstained yeast cell. The images of the freeze-dried cell, obtained by using 750-eV x-rays from different angular orientations, portray several of the cell's major internal components to 30-nm resolution. The good agreement among the independently recovered structures demonstrates the accuracy of the imaging technique. To obtain the best possible reconstructions, we have implemented procedures for handling noisy and incomplete diffraction data, and we propose a method for determining the reconstructed resolution. This work represents a previously uncharacterized application of x-ray diffraction microscopy to a specimen of this complexity and provides confidence in the feasibility of the ultimate goal of imaging biological specimens at 10-nm resolution in three dimensions. © 2005 by The National Academy of Sciences of the USA.