Opt. Lett. 36, 2728–2730 (2011)

Three-dimensional high-resolution imaging of intact cells in a near-native state is important for a wide variety of biological studies. Soft-X-ray microscopes are advantageous for such imaging tasks because they do not require the use of chemical fixation, staining or sectioning. Although laboratory soft-X-ray microscopes based on laser-induced plasmas have been demonstrated, the imaging quality of these devices is still far from that of large, high-brightness synchrotron X-ray facilities. This may be about to change, thanks to the research of Michael Bertilson and co-workers at the KTH Royal Institute of Technology in Stockholm, Sweden. The researchers report that their laboratory soft-X-ray microscope has an imaging quality approaching that of a synchrotron. They produced their soft-X-ray source by focusing high-energy laser pulses (130 mJ per pulse, repetition rate of 100 Hz and pulse width of 3 ns) from a frequency-doubled (532 nm) Nd:YAG laser onto a nitrogen jet to create a plasma. The resulting X-ray emission was reflected by a multilayer mirror to provide a 2.48 nm source. The soft-X-ray microscope was used to perform tomographic imaging of a human kidney cell; by tilting the sample holder in 1.5° increments, the researchers took 58 cross-sectional images, each with an exposure time of 120 s. The reconstructed three-dimensional image showed nucleus, nucleoli and vacuoles. The smallest visible detail in these sections was ∼100 nm.