Editing X-ray microscope (section)

== Biological applications ==
One early applications of X-ray microscopy in biology was contact imaging, pioneered by [[P Goby|Goby]] in 1913. In this technique, [[Soft X-rays|soft x-rays]] irradiate a specimen and expose the x-ray sensitive emulsions beneath it. Then, magnified tomographic images of the emulsions, which correspond to the x-ray opacity maps of the specimen, are recorded using a light microscope or an electron microscope. A unique advantage that X-ray contact imaging offered over electron microscopy was the ability to image wet biological materials. Thus, it was used to study the micro and nanoscale structures of plants, insects, and human cells. However, several factors, including emulsion distortions, poor illumination conditions, and low resolutions of ways to examine the emulsions, limit the resolution of contacting imaging. Electron damage of the emulsions and diffraction effects can also result in artifacts in the final images.<ref>{{Cite book |title=X-ray Microscopy: Instrumentation and Biological Applications |last=Cheng, Ping-chin. |date=1987 |publisher=Springer Berlin Heidelberg |others=Jan, Gwo-jen. |isbn=9783642728815 |location=Berlin, Heidelberg |oclc=851741568}}</ref>

X-ray microscopy has its unique advantages in terms of nanoscale resolution and high penetration ability, both of which are needed in biological studies. With the recent significant progress in instruments and focusing, the three classic forms of optics—diffractive,<ref>{{Cite journal |last1=Chao |first1=Weilun |last2=Harteneck |first2=Bruce D. |last3=Liddle |first3=J. Alexander |last4=Anderson |first4=Erik H. |last5=Attwood |first5=David T. |date=2005 |title=Soft X-ray microscopy at a spatial resolution better than 15&nbsp;nm |journal=Nature |volume=435 |issue=7046 |pages=1210–1213 |doi=10.1038/nature03719 |pmid=15988520 |issn=0028-0836 |bibcode=2005Natur.435.1210C|s2cid=4314046 }}</ref> reflective,<ref>{{Cite journal |last1=Hignette |first1=O. |last2=Cloetens |first2=P. |last3=Rostaing |first3=G. |last4=Bernard |first4=P. |last5=Morawe |first5=C. |date=June 2005 |title=Efficient sub 100&nbsp;nm focusing of hard x rays |journal=Review of Scientific Instruments |volume=76 |issue=6 |pages=063709–063709–5 |doi=10.1063/1.1928191 |issn=0034-6748 |bibcode=2005RScI...76f3709H}}</ref><ref>{{Cite journal |last1=Mimura |first1=Hidekazu |last2=Handa |first2=Soichiro |last3=Kimura |first3=Takashi |last4=Yumoto |first4=Hirokatsu |last5=Yamakawa |first5=Daisuke |last6=Yokoyama |first6=Hikaru |last7=Matsuyama |first7=Satoshi |last8=Inagaki |first8=Kouji |last9=Yamamura |first9=Kazuya |date=2009-11-22 |title=Breaking the 10&nbsp;nm barrier in hard-X-ray focusing |journal=Nature Physics |volume=6 |issue=2 |pages=122–125 |doi=10.1038/nphys1457 |issn=1745-2473 |doi-access=free}}</ref> refractive<ref>{{Cite journal |last1=Schroer |first1=C. G. |last2=Kurapova |first2=O. |last3=Patommel |first3=J. |last4=Boye |first4=P. |last5=Feldkamp |first5=J. |last6=Lengeler |first6=B. |last7=Burghammer |first7=M. |last8=Riekel |first8=C. |last9=Vincze |first9=L. |date=2005-09-19 |title=Hard x-ray nanoprobe based on refractive x-ray lenses |journal=Applied Physics Letters |volume=87 |issue=12 |pages=124103 |doi=10.1063/1.2053350 |issn=0003-6951 |bibcode=2005ApPhL..87l4103S}}</ref> optics—have all successfully expanded into the X-ray range and have been used to investigate the structures and dynamics at cellular and sub-cellular scales. In 2005, Shapiro et al. reported cellular imaging of yeasts at a 30&nbsp;nm resolution using coherent soft X-ray diffraction microscopy.<ref>{{Cite journal |last1=Shapiro |first1=D. |last2=Thibault |first2=P. |last3=Beetz |first3=T. |last4=Elser |first4=V. |last5=Howells |first5=M. |last6=Jacobsen |first6=C. |last7=Kirz |first7=J. |last8=Lima |first8=E. |last9=Miao |first9=H. |date=2005-10-11 |title=Biological imaging by soft x-ray diffraction microscopy |journal=Proceedings of the National Academy of Sciences |volume=102 |issue=43 |pages=15343–15346 |doi=10.1073/pnas.0503305102 |pmid=16219701 |issn=0027-8424 |pmc=1250270 |bibcode=2005PNAS..10215343S|doi-access=free }}</ref> In 2008, X-ray imaging of an unstained virus was demonstrated.<ref>{{Cite journal |last1=Song |first1=Changyong |last2=Jiang |first2=Huaidong |last3=Mancuso |first3=Adrian |last4=Amirbekian |first4=Bagrat |last5=Peng |first5=Li |last6=Sun |first6=Ren |last7=Shah |first7=Sanket S. |last8=Zhou |first8=Z. Hong |last9=Ishikawa |first9=Tetsuya |date=2008-10-07 |title=Quantitative Imaging of Single, Unstained Viruses with Coherent X Rays |journal=Physical Review Letters |volume=101 |issue=15 |pages=158101 |doi=10.1103/physrevlett.101.158101 |pmid=18999646 |issn=0031-9007 |arxiv=0806.2875 |bibcode=2008PhRvL.101o8101S|s2cid=24164658 }}</ref> A year later, X-ray diffraction was further applied to visualize the three-dimensional structure of an unstained human chromosome.<ref>{{Cite journal |last1=Nishino |first1=Yoshinori |last2=Takahashi |first2=Yukio |last3=Imamoto |first3=Naoko |last4=Ishikawa |first4=Tetsuya |last5=Maeshima |first5=Kazuhiro |date=2009-01-05 |title=Three-Dimensional Visualization of a Human Chromosome Using Coherent X-Ray Diffraction |journal=Physical Review Letters |volume=102 |issue=1 |pages=018101 |doi=10.1103/physrevlett.102.018101 |pmid=19257243 |issn=0031-9007 |bibcode=2009PhRvL.102a8101N}}</ref> X-ray microscopy has thus shown its great ability to circumvent the diffractive limit of classic light microscopes; however, further enhancement of the resolution is limited by detector pixels, optical instruments, and source sizes.

A longstanding major concern of X-ray microscopy is radiation damage, as high energy X-rays produce strong radicals and trigger harmful reactions in wet specimens. As a result, biological samples are usually fixated or freeze-dried before being irradiated with high-power X-rays. Rapid cryo-treatments are also commonly used in order to preserve intact hydrated structures.<ref>{{Cite book |title=Super-resolution microscopy techniques in the neurosciences |editor=Fornasiero, Eugenio F. |editor2=Rizzoli, Silvio O. |publisher=Springer |year=2014 |isbn=9781627039833 |location=New York |oclc=878059219}}</ref>