Project Summary/Abstract X-ray microscopy has evolved into an important ultrastructure imaging approach for visualizing and measuring intact cells in three dimensions. Beamlines dedicated to cellular imaging have been constructed at synchrotron facilities around the world, and the co-PI of this proposal developed the first commercial laboratory x-ray microscope for cellular imaging. The approaches thus far have centered around the use of “water window” x-rays, having energies between 285 to 540eV and for which water is transparent but organic content is absorbing. However, there are several major drawbacks to using these low energy x-rays: they severely limit the size of cells that can be imaged (e.g., <10 µm when many mammalian cells are 10-100 µm). This SBIR proposal aims to develop a 3D nano x-ray microscope capable of high throughput (~30 minute) 3D imaging of cryogenically preserved cells of up to 80 µm in diameter at down to 30nm resolution. The system utilizes the phenomenon of Zernike phase contrast at higher (2.7 keV) energy x-rays, which can achieve even higher contrast for biological samples than water window x-rays. Additionally, the system will enable several major advantages over water window x-ray microscopy, including much larger cell imaging (80µm vs. 10µm), larger depth-of- field for higher 3D resolution, and practical benefits (more stable x-ray source and larger working distance to incorporate correlative techniques). The microscope uses the company’s patented high brightness x-ray source and proprietary x-ray optic technology. The project will develop the proposing company’s existing 2.7 keV ambient system to enable cryogenic operation and optimize its performance for cellular imaging. The proposed Phase II 24-month project is to develop a complete cryogenic 2.7 keV system for cellular imaging and to experimentally demonstrate its performance on mammalian cells.