Researchers Employ High-Energy X-Ray to Image Living Cancer Cells

In the future, the new technique should make it possible to study unaltered living cells at high resolution.

“The new method for the first time enables us to investigate the internal structures of living cells in their natural environment using hard X-rays,” reported the researchers from the working group. “Thanks to the ever-greater resolution of the various investigative techniques, it is increasingly important to know whether the internal structure of the sample changes during sample preparation.” Scientists are working on the new research at the Deutsches Elektronen-Synchrotron DESY (Hamburg, Germany) PETRA III research light source. The new technology reveals distinct differences in the internal cellular structure between the living and dead, chemically fixed cells. “The new method for the first time enables us to investigate the internal structures of living cells in their natural environment using hard X-rays,” emphasized the leader of the working group, Prof. Sarah Köster from the Institute for X-Ray Physics of the University of Göttingen (Germany). The researchers published their findings on February 25, 2014, in the scientific journal Physical Review Letters.

Due to newly developed analytic methods with ever-higher resolution, scientists now can study biologic cells at the level of individual molecules. The cells are frequently chemically fixed before they are studied with the help of optical X-ray or electron microscopes. The process of chemical fixation involves immersing the cells in a type of chemical preservative that fixes all of the cell’s organelles and even the proteins in place. “Minor changes to the internal structure of the cells are unavoidable in this process,” stated Prof. Köster. “In our studies, we were able to show these changes in direct comparison for the first time.”

The scientists used cancer cells from the adrenal cortex for their study. They grew the cells on a silicon nitrite substrate, which is nearly transparent to X-rays. To keep the cells alive in the experimental chamber during the research, they were supplied with nutrients, and their metabolic products were driven away via fine channels only 0.5 mm in diameter. “The biological cells are thus located in a sample environment which very closely resembles their natural environment,” explained Dr. Britta Weinhausen from Prof. Köster’s group, the article’s first author.

The research was performed at the Nanofocus Setup (GINIX) of PETRA III’s experimental station P10. The scientists used the brilliant X-ray beam from PETRA III to scan the cells to gather data about their internal nanostructure. “Each frame was exposed for just 0.05 seconds, in order to avoid damaging the living cells too quickly,” clarified coauthor Dr. Michael Sprung from DESY. “Even nanometer-scale structures can be measured with the GINIX assembly, thanks to the combination of PETRA III’s high brilliance and the GINIX setup which is matched to the source.”

The researchers studied living and chemically fixed cells using this so-called nanodiffraction technique and compared the cells’ internal structures on the basis of the X-ray diffraction images. The results showed that the chemical fixation produces noticeable differences in the cellular structure on a scale of 30–50 nm.

“Thanks to the ever-greater resolution of the various investigative techniques, it is increasingly important to know whether the internal structure of the sample changes during sample preparation,” clarified Prof. Köster.

In the future, this new technology will make it possible to examine unchanged living cells at high resolution. Although other techniques have an even higher resolution than X-ray scattering, they require a chemical fixation or complex and invasive preparation of the cells. Lower-energy, so-called soft X-rays have already been used for studies of living cells. However, the study of structures with sizes as small as 12 nm first becomes possible through the analysis of diffraction images generated using hard X-rays.

Related Links:
Deutsches Elektronen-Synchrotron DESY
Institute for X-Ray Physics of the University of Göttingen