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X marks the subcellular spot

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Margaret W. Bushee, [email protected]

Using x-ray techniques to image live cells on the nanoscale has long been problematic. The advantage of x-ray microscopy is that, unlike conventional electron scanning, it penetrates below the surface to yield images with high spatial and temporal resolution. However, x-rays also can be toxic to fragile biological samples.

The limitations of x-ray microscopy have been overcome in large part thanks to biophysicists Dr. Franz Pfeiffer, Dr. Pierre Thibault and Martin Dierolf, all of Technical University Munich in Germany. The Swiss Light Source, a dedicated high-power microscope at Paul Scherrer Institute, has been instrumental in their accomplishments.

Most recently, the researchers published images of the nucleoid structure, or genetic material, of the bacteria and polyextremophile Deinococcus radiodurans, which is characterized by an unusual tolerance to ionizing radiation. Capturing a clear image of this subcellular structure is an important step for scientists in the quest to study disease and survival. The study was published online in the November 2009 issue of the Proceedings of the National Academy of Sciences.

The rendering of these images was made possible by the Pfeiffer team’s further refinement of a technique introduced in the 1970s called ptychography, which involves recording full far-field diffraction patterns while a sample is raster-scanned (line by line) through the focal spot of the beam, one minuscule section at a time. An algorithm designed by the team uses this data to create an image of the sample in its entirety.

A year prior to its recent breakthrough, the team demonstrated the superresolution capability of ptychography in conjunction with x-rays by combining two independent techniques – coherent diffractive imaging and scanning transmission x-ray microscopy – to image a buried gold nanostructure. Hard, or high-energy, x-rays were used during this “lensless microscopy” technique. The results were published in the July 18, 2008, issue of Science.

Now that the investigators have researched the resolution, reproducibility and reliability of their technique, they are working on three-dimensional imaging of biological cells. X-ray imaging’s capacity to visualize what is beneath the surface could bring new insights to biotechnology and evolutionary biology.
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Published: February 2010
Glossary
electron scanning
The deflection of a beam of electrons, at regular intervals, across a cathode-ray tube screen, according to a definite pattern.
ionizing radiation
Generally, any radiation that can form ions, either directly or indirectly, while traveling through a substance.
lensless microscopy
Lensless microscopy, also known as computational or holographic microscopy, is an imaging technique that captures and reconstructs microscopic images without the use of traditional lenses. Instead of relying on conventional lenses to magnify and focus light, lensless microscopy employs computational methods to reconstruct images from the diffraction patterns or holograms generated by the interaction of light with the specimen. Key features and principles of lensless microscopy: Digital...
nanotechnology
The use of atoms, molecules and molecular-scale structures to enhance existing technology and develop new materials and devices. The goal of this technology is to manipulate atomic and molecular particles to create devices that are thousands of times smaller and faster than those of the current microtechnologies.
spatial resolution
Spatial resolution refers to the level of detail or granularity in an image or a spatial dataset. It is a measure of the smallest discernible or resolvable features in the spatial domain, typically expressed as the distance between two adjacent pixels or data points. In various contexts, spatial resolution can have slightly different meanings: Imaging and remote sensing: In the context of satellite imagery, aerial photography, or other imaging technologies, spatial resolution refers to the...
superresolution
Superresolution refers to the enhancement or improvement of the spatial resolution beyond the conventional limits imposed by the diffraction of light. In the context of imaging, it is a set of techniques and algorithms that aim to achieve higher resolution images than what is traditionally possible using standard imaging systems. In conventional optical microscopy, the resolution is limited by the diffraction of light, a phenomenon described by Ernst Abbe's diffraction limit. This limit sets a...
3-D imagingBiophotonicsBioScancoherent diffractive imagingDr. Franz PfeifferDr. Pierre Thibaultelectron scanningfar-field diffractionhard x-raysImagingionizing radiationlensless microscopyMargaret W. BusheeMartin DierolfMicroscopynanotechnologyNewsnucleoid structure Deinococcus radioduransOpticsPaul Scherrer InstitutePNASProceedings of the National Academy of Sciencesptychographyraster scanningscanning transmission x-ray microscopysciencespatial resolutionsuperresolutionSwiss Light SourceSwitzerlandTechnical University MunichTemporal ResolutionVilligenx-ray microscopy

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