Scientists have used X-ray diffraction microscopy to make images of whole yeast cells, achieving the highest resolution -- 11 to 13 nanometers (billionths of a meter) -- ever obtained with this method for biological specimens. Their success indicates that full 3-D tomography of whole cells at equivalent resolution should soon be possible.
"We have demonstrated that lensless imaging techniques can achieve very high resolution while overcoming the limitations of x-ray optics -- limitations that include requiring 20 to 50 times the radiation exposure to get a magnified image of the sample," says Chris Jacobsen, formerly of Stony Brook University, now of Argonne National Laboratory and Northwestern University, who designed the lensless-imaging research program at beamline 9.0.1. "While at present it takes us a long time to image a single specimen -- and full 3-D imaging of hydrated cells will take even more work -- this is a big step in the right direction."
Three-dimensional imaging of whole cells under conditions close to those in nature, namely a hydrated (watery) environment, is already done at the National Center for X-Ray Tomography at ALS beamline 2.1, under the direction of Carolyn Larabell of Berkeley Lab's Physical Biosciences Division, where large numbers of cells can be processed in a short time at resolutions of 40 to 60 nanometers. The ability to increase resolution to the 10-nanometer range would significantly advance research in both biology and materials sciences.
"Ten-nanometer resolution is easy to achieve with an electron microscope," says Janos Kirz of the ALS, co-designer with Jacobsen of the lensless imaging program. "The problem is that electron microscopy is limited to very thin samples, a few hundred nanometers or less -- so you can't use it to look through a whole cell."
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Lensless imaging of whole biological cells with soft X-rays
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