Comparative analysis of isolated cellular organelles by means of soft X-ray contact microscopy with laser-plasma source and transmission electron microscopy

Soft X-ray contact microscopy (SXCM) is, at present, a useful tool for the examination at submicrometre resolution of biological systems maintained in their natural hydrated conditions. Among current X-ray-generating devices, laser-plasma sources are now easily available and, owing to their pulse nature, offer the opportunity to observe living biological samples before radiation damage occurs, even if the resolution achievable is not as high as with synchrotron-produced X-rays. To assess the potential of laser-plasma source SXCM in the study of cellular organelles, we applied it for the analysis of chloroplasts extracted from spinach leaves and mitochondria isolated from bovine heart and liver. X-ray radiation was generated by a nanosecond laser-plasma source, produced by a single shot excimer XeCl laser focused onto an yttrium target. The images obtained with SXCM were then compared with those produced by transmission electron microscopy observation of the same samples prepared with negative staining, a technique requiring no chemical fixation, in order to facilitate their interpretation and test the applicability of SXCM imaging.