Novel microscope offers intact, high-resolution 3D images of cells
German and US scientists have done the seemingly impossible: they have developed a state-of-the-art microscope that delivers an instant three-dimensional (3D) image of intact cells without having to chemically fix, cut or even stain them for study. Presented in the journal Nature Methods, the new device could fill the gap in current technologies and prove useful in the medical sciences as well as structural biology. The scientists from the Institute for Soft Matter and Functional Materials at Helmholtz Zentrum Berlin (HZB) in Germany and the US-based National Cancer Institute studied whole, fast-frozen cells in their natural environment. According to the researchers, high-resolution 3D images of the entire cell are delivered in one step. This new device wins over electron microscopy for instance because it generates 3D images of cells when they are intact. In addition, it is quicker than electron microscopy, in which it can take weeks for a researcher to deliver a 3D image of just one cell. The new microscope also beats out florescence microscopy, which allows researchers to see only labelled structures after they've been dyed. By taking advantage of the natural contrast between organic material and water, the team could form an image of all cell structures, they said. The researchers reconstructed mouse adenocarcinoma cells in three dimensions. They could even see the tiniest details of the cells including the nuclear pores in the nuclear envelope, the double membrane of the cell nucleus, invaginations of the inner mitochondrial membrane, membrane channels in the nucleus and inclusions in cell organelles like lysosomes. The X-ray imaged the ultrastructure of cells down to 30 nanometres (10 nanometres are around 1 ten-thousandth of the width of a human hair). Ultrastructure is the detailed structure of a biological specimen that is not visible with an optical microscope. The team used partially coherent light to illuminate the tiny structures of the frozen-hydrated object and obtain the high 3D resolution. HZB's synchrotron source, called BESSY II, was used to produce the light. The researchers explained that partial coherence is the property of two waves whose relative phase experiences random fluctuations that are not enough to generate a completely incoherent wave. By using this approach together with a high-resolution lens, they successfully visualised the ultrastructures of cells with unprecedented contrast. 'We built a transmission soft X-ray microscope that takes advantage of improved nanofabrication techniques, allowing manufacture of higher-resolution X-ray objectives with smaller outermost zone widths,' the authors wrote in the paper. 'We combined this higher-resolution objective with partially coherent specimen illumination instead of the lower-resolution objective and quasi-incoherent illumination used in previous designs. Whereas partial coherence lowers the maximal possible resolution compared to incoherence, it provides much larger contrast at medium to higher spatial frequencies. Thus, combining partial coherence with a better-resolution objective should yield better contrast for fine-scale features. ' According to the researchers, these latest developments will offer the medical world key insight into inner-cellular processes, namely, how viruses or nanoparticles penetrate into cells or into the nucleus. And from a general standpoint, they will offer a new tool in structural biology for bolstering understanding of the cell structure.
Countries
Germany, United States