Soft X-ray Tomography: From Concept to Awards

Le résumé fourni par la source

Soft X-ray tomograpahy (SXT) is similar in concept to the well-established medical diagnostic technique, computed axial tomography (CAT), except SXT is capable of imaging with a spatial resolution of 50 nm, or better. With SXT we can examine whole, hydrated cells (between 10-15 µm thick), eliminating the need for time-consuming embedding and sectioning procedures. For SXT, cells are imaged using X-ray energies between the K shell absorption edges of carbon (284 eV, λ=4.4 nm) and oxygen (543 eV, λ=2.3 nm). In this energy range, photons readily penetrate the aqueous environment while encountering significant absorption from carbon- and nitrogen-containing organic material. Consequently organic material absorbs approximately an order of magnitude more strongly than water, producing a quantifiable natural contrast image of cellular structures [1]. SXT, like other tomography modalities, requires recording images from multiple different viewing angles. By collecting images from multiple angles through 360 degrees of rotation, SXT reconstructions yield information at isotropic resolution. Images are formed using unique optics called zone plates (ZP). An X-ray ZP optic consists of a number of concentric nanostructured metal rings, or zones, formed on a thin X-ray transmissive silicon nitride membrane. The width of the outermost ring determines the spatial resolution of the ZP lens, whereas the thickness of the rings determines the focusing efficiency. In the microscope we utilize, the condenser ZP lens has an overall diameter of 1 cm, 41,667 zones made with approximately 200 nm thick nickel, and a 5 mm central stop. The high-resolution objective ZP lens has a diameter of 63 µm and an outer zone width of 50 nm to assure the entire cell is in focus. Because SXT is fast (∼ 5 min per tomographic data set), we can examine large numbers of cells. Since organic material absorbs approximately an order of magnitude more strongly than water, the high-contrast image of cellular structures is quantifiable. X-ray absorption follows Beer’s Law, therefore the absorption of photons is linear and a function of the biochemical composition at each point in the cell. As a result, a linear absorption coefficient (LAC) value of each voxel can be calculated. For example, lipid drops with high concentrations of carbon are more highly absorbing (LAC=0.7 μm-1) than fluid-filled vesicles (LAC=0.2 μm-1) [2]. To determine the location of specific molecules with respect to cellular structures, we overlay molecular information obtained with fluorescence microscopy of a cell on the structural information obtained with x-ray tomography of the same cell [3]. This makes it possible to localize molecules tagged with genetically encoded proteins (XFPs, etc.) without having to fix and permeabilize cells to allow metal particle entry into cells. SXT is revolutionizing cell biology, as shown by groundbreaking research that highlights its unparalleled power in biological imaging. This cutting-edge technology has unlocked new frontiers, enabling scientists to: 1. Uncover nucleoid remodeling during environmental adaptation [4]. 2. Precisely quantify insulin granules in pristine, unlabeled pancreatic beta cells [5]. 3. Map and analyze intricate organelle interactions at the mesoscale [6]. 4. Capture vivid images of SARS-CoV-2-infected cells [7]. 5. Investigate elusive misfolded protein inclusions in whole cells [8]. 6. Model the mesmerizing gliding motility of parasites [9]. 7. And, in a groundbreaking discovery, identify an entirely new organelle – the Nitroplast [10]. Over the past 25 years, our relentless pursuit of innovation has transformed SXT into a powerful technology capable of imaging whole, intact cells in a near-native state. These advancements have not only deepened our understanding of cellular architecture but also paved the way for discoveries that redefine what we know about life at the microscopic level [11].

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.