Scanning transmission x-ray microscopy of unaltered biological specimens
A scanning transmission x-ray microscope at the National Synchrotron Light Source was used to image fresh, wet biological specimens at 32 Angstroms, with resolution better than 750 Angstroms. A gold Fresnel zone plate (outer zone width 500 Angstroms) was used to focus the undulator radiation, and the sample was scanned through the spot. Absorption data was recorded digitally as a gridded array. The major accomplishment of the experiment was the demonstration of the ability to image biological
... mples in their natural state with high resolution and natural elemental contrast mechanisms. This was achieved through the design of a sample holder that maintains an aqueous environment for the sample, yet is transparent to x-rays at 32 Angstroms. The specimens used were isolated zymogen granules (approximately 1 micron diameter) from the pancreatic acinar cells of rats. The absorption data was corrreiated to protein concentration, and estimates of the protein concentrations within the granules were obtained. The data also yields some information about the spatial organization of the protein in the granules, and our data is compared to models for the internal structure. The success of this experiment points toward future opportunities for dynamical studies on living systems The work described here was made possible by the efforts and talents of many people. I, would like to acknowledge the support, guidance and inspiration given to this project by Dr. David Attwood of the Center for X-Ray Optics at LBL, and Professor Stephen Rothman of the Department of Physiology at UCSF. My sponsor in the Physics Department was Professor Steve Kahn. I wish to thank Harvey Rarback (NSLS) and Janos Kirz (SUNY Stony Brook) for giving us a share of the limited time available to use the microscope. The zone plates were manufactured at IBM by Yuli Vladimirsky of the Center for X-Ray Optics. Helping in the development and construction of the microscope were Harald Ade, Chris Jacobsen, and Ian McNulty of SUNY Stony Brook, Kate of NSLS, and Dealing Shu of the Institute for High Energy Physics, Beijing. The biological specimens were prepared by Ken McQuaid of UCSF. The components of the wet cell were built by Dino Ciarlo of LLNL, and Phil Batson of the Center for X-Ray Optics.