The structure of content: phase contrast in a microprobe

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DESCRIPTION (provided by applicant): Numerous key functions of cells hinge upon the catalytic properties of metals, yet if metals are present in abnormally high concentrations (or incorrectly regulated) many of these same metals can be extremely toxic, or lead to debilitating diseases. Copper and zinc are components of the anti-oxidant protein Cu/Zn superoxide dismutase, which has been implied in cellular aging and in mutant forms has been linked to neurodegenerative diseases such as amytrophic lateral sclerosis (ALS, or Lou Gehrig's disease). Cisplatin is a well-known drug for cancer therapy but its affinity for specific regions in a cell is imperfectly understood. Hard X-ray microprobes excel at detecting and quantifying trace metal concentrations in biological samples, but at present they cannot image ultrastructure to place the metals in their correct cellular context, or determine the specimen mass so as to deliver truly quantitative information on trace metal concentration. We wish to implement quantitative phase contrast imaging in a hard x-ray microprobe to address this problem. We will develop an optimized segmented detector for differential phase contrast imaging that will be incorporated into routine use in a zone plate based microprobe at the Advanced Photon Source at Argonne National Laboratory, the premier hard x-ray synchroton light source in the U.S. We will develop methodology and software for quantitative phase contrast analysis using data obtained with the new detector. While we have demonstrated a few examples of quantitative phase contrast images in soft x-ray microscopy, we now wish to develop software to make this analysis approach routinely available to users of the APS microprobe. Our goal is to allow users expert in their biomedical studies (but not in x-ray optics and analysis methods) to exploit this capability with freely-available software in a user friendly fashion. We then wish to demonstrate the ability of the system to quantify specimen mass and observe sub-100 nm structure in cells simultaneously with mapping trace elemental distributions. X-ray microprobes at third generation storage rings represent a multimillion dollar investment. The ability to truly quantify element concentrations instead of just elemental content, and to correlate this to cellular ultrastructure, is keenly desired as indicated by letters of support from independent investigators who use X-ray microprobes for their NIH-supported studies.