September 24, 2009
The two-day Advanced Electron Microscopy in NanoMedicine Symposium from Friday, Oct. 2—Saturday, Oct. 3 at the California NanoSystems (CNSI) at UCLA brings together researchers from academia and industry to discuss cryo-electron microscopy, or cryoEM, an important new imaging tool with major applications for nanobiology and nanomedicine, particularly for understanding viruses and other macromolecular complexes. Researchers can use cryoEM to visualize a broad range of assemblies and nanometer-scale structures in three dimensions — from molecular to atomic resolution.
Organized by the Electron Imaging Center for Nanomachines (EICN) , a newly established CNSI core lab, the symposium will also serve as a venue for the public unveiling of the top-of-the-line Titan Krios cryoEM and Titan (S)TEM microscopes in the EICN lab.
For more information and to register for the event, visit: http://www.cnsi.ucla.edu/electron-microscopy/
September 23, 2009
Uranium single atoms (circled) and small crystallites on a carbon support imaged simultaneously using a scanning probe to produce forward scattering through the sample (top) and backward scattering emerging from the surface (bottom). Center panel shows superimposition of the two in red (bulk) and green (surface). Atoms not seen in the lower image are on the bottom surface of the support. Source: Brookhaven National Laboratory
Scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory, in collaboration with researchers from Hitachi High Technologies Corp., have demonstrated a new scanning electron microscope capable of selectively imaging single atoms on the top surface of a specimen while a second, simultaneous imaging signal shows atoms throughout the sample’s depth. This new tool, located at Brookhaven Lab’s Center for Functional Nanomaterials (CFN), will greatly expand scientists’ ability to understand and ultimately control chemical reactions, such as those of catalysts in energy-conversion devices.
Like all scanning electron microscopes, the new tool probes a sample with an electron beam focused to a tiny spot and detects so-called secondary electrons emitted by the sample to reveal its surface structure and topography. Though this technique has been a workhorse of surface imaging in industrial and academic laboratories for decades, its resolution has left much to be desired because of imperfect focusing due to lens aberrations.
Using a newly developed spherical aberration corrector, the new tool corrects these distortions to create a smaller probe with significantly increased brightness.
The new device also employs specialized electron optics to channel the emitted secondary electrons to the detector. The result is a fourfold improvement in resolution to below one tenth of a nanometer — and thus, the ability to image single atoms.
Additional detectors, located below the sample, detect electrons transmitted through the sample, revealing details about the entire structure at the exact instant the “shutter” snapped to record each pixel of the surface image. This simultaneous imaging allows the scientists to correlate information in the two images to understand precisely what is happening on the surface and throughout the sample at the same time.
Because of its extreme sensitivity, the new microscope must be kept isolated from a range of environmental effects such as variations in temperature, mechanical vibrations, and electromagnetic fields. Even the slightest waft of air could cause distortions in the images.
Zhu Y., Inada H., Nakamura K., Wall J.: Imaging single atoms using secondary electrons with an aberration-corrected microscope. Nat Mater. 2009 Sep 20. [Epub ahead of print]
September 21, 2009
Coherent X-ray Diffraction patterns of collagen in soft tissues have been measured for the first time by Dr Felisa Berenguer (London Centre for Nanotechnology) with her colleagues. This development opens doors to better understanding of living tissues like skin and bones, as well as the bio-mineralization processes which turn flexible collagen into semi-flexible cartilage and eventually into rigid bones. In a distant future, the understanding of the collagen structure will eventually lead to cures for of bone diseases, notably osteoporosis, or assist ongoing efforts to develop artificial skin.
Dr Berenguer is part of Prof Ian Robinson’s group in the London Centre for Nanotechnology. This group is developing methods of using the coherence properties of these X-rays for imaging materials on the nanoscale. They use new synchrotron X-ray sources with extremely high brightness such as the Diamond Light Source on the Harwell campus near Oxford. While new light lines at the Diamond Light Source are still under construction, the London Centre Nanotechnology operates one of the experimental out-stations of the Advanced Photon Source (APS), an X-ray synchrotron in Chicago, USA. The group is focusing its efforts on X-rays because this type of light has small wavelengths and is strongly penetrating into material. There is thus an opportunity for imaging physical structures in three dimensions with resolution well beyond that of the visible light microscope. The group is also developing phase-contrast methods that are sensitive to nanoscale strains, or the detailed packing arrangement of molecules in biological tissues.
Berenguer de la Cuesta F, Wenger MP, Bean RJ, Bozec L, Horton MA, Robinson IK. : Coherent X-ray diffraction from collagenous soft tissues. Proc Natl Acad Sci U S A. 2009 Aug 24. [Epub ahead of print]
Diffraction pattern of collagen obtain by Dr Berenguer and al during the scope of this research. Source: London Centre for Nanotechnology
September 17, 2009
Scientists in the National Institute of Biomedical Imaging and Bioengineering (NIBIB) Laboratory of Bioengineering and Physical Science have developed a new technique, BF STEM tomography, that allows researchers to visualize fine details of cell structure three-dimensionally in thick sections, thus providing greater insight into how cells are organized and how they function.
Electron tomography is carried out at the nanoscale on individual cells. Conventionally, high-resolution imaging of biological specimens has been accomplished by cutting cells into thin sections (300 nanometers or less) and imaging each section separately. Although reconstructing an entire structure from thin sections is laborious, thin sections are used because images of thicker sections typically are blurred. Serial BF STEM tomography accomplishes the same work using fewer yet thicker specimen sections, leading to faster reconstruction of intact organelles, intracellular pathogens, and even entire mammalian cells.
Drs. Alioscka Sousa, Martin Hohmann-Marriott, Richard Leapman and colleagues in NIBIB, in collaboration with Dr. Joshua Zimmerberg and colleagues in the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), demonstrated feasibility and advantages of BF-STEM tomography in a study of red blood cells infected with Plasmodium falciparum, a parasite that causes malaria. High-resolution 3D reconstructions of entire cells were generated by serially imaging just a few thick sections. The intricate system of red blood cell and parasite membranes, as well as several organelles, can be seen in detail.
Hohmann-Marriott MF, Sousa AA, Azari AA, Glushakova S, Zhang G, Zimmerberg J & Leapman RD.: Nanoscale 3D cellular imaging by axial scanning transmission electron tomography. Nature Methods, Published online: 30 August 2009 | doi:10.1038/nmeth.1367.
September 17, 2009
Atomic force microscopy is well-known even in the public as a versatile tool for the production of images on the nanoscale level. Kelvin probe force microscopy is a special type of this imaging technique named after Lord Kelvin. When brought to the market in 1991, a scientific description of how to interprete the images was delivered. To this, physicist Christine Baumgart, a doctoral student of the nanospintronics group at the research center Forschungszentrum Dresden-Rossendorf (FZD), has now added new features.
Christine Baumgart now discovered what exactly is measured by Kelvin probe force microscopy. It is the electric potential which is needed to move electrons or holes from the inside to the surface of a semiconductor. Her new findings will simplify the microscopic technique itself, and will lead to unambiguous and reproducible results concerning the structure and electronic properties of samples. Also, Kelvin probe force microscopy, which has been used mainly in materials science and semiconductor physics so far, is likely to become more attractive for other areas like biotechnology.
But how exactly does a Kelvin probe force microscope work? The tip is deflected by the electrostatic force between cantilever and sample when moved over the sample. By applying bias to the sample, electrons and holes are moved to the surface of the semiconductor and the electrostatic force decreases. The cantilever moves back to its original position and the applied bias is stored as the signal measured. To be more precise, there is a quantitative relation between the measured Kelvin bias and the difference between the calculated Fermi energy and respective semiconductor band edge independent of the work function of the probing microscope tip. Thus, Christine Baumgart’s novel explanation of how the Kelvin probe force microscope works elucidates why the signal depends on the bias necessary for injecting majority charge carriers towards the interface between insulator and semiconductor.
Baumgart C., Helm M., Schmidt H., (2009): Quantitativ dopant profiling in semiconducters: A Kelvin probe force microscopy model. DOI: 10.1103/PhysRevB.80.085305.
Schematic drawing of a Kelvin probe force microscopy probe above a doped semiconductor with a thin oxide layer (grey blue atomic layer). Occupied surface states at the interface between the oxide layer and the semiconductor are animated in red and the same number of unscreened dopant atoms is animated in dark blue. Left: The resulting asymmetric electric dipole causes the deflection of the probe. Center: By applying a bias mobile majority charge carriers are injected into the semiconductor (animated in orange) and screen the unscreened ionized dopant atoms. Right: As a result the electrostatic force onto the cantilever vanishes. The cantilever moves back to its normal position. The applied bias is measured and depends on the concentration of dopant atoms. Picture: Sander Münster, Kunstkosmos
September 10, 2009
IBM scientists have been able to image the “anatomy”—or chemical structure—inside a molecule with unprecedented resolution, using a complex technique known as noncontact atomic force microscopy (AFM).
The results push the exploration of using molecules and atoms at the smallest scale and could greatly impact the field of nanotechnology, which seeks to understand and control some of the smallest objects know to mankind.
As reported in the August 28 issue of Science magazine, IBM Research – Zurich scientists Leo Gross, Fabian Mohn, Nikolaj Moll and Gerhard Meyer, in collaboration with Peter Liljeroth of Utrecht University, used an AFM operated in an ultrahigh vacuum and at very low temperatures (–268°C or – 451°F) to image the chemical structure of individual pentacene molecules. With their AFM, the IBM scientists, for the first time ever, were able to look through the electron cloud and see the atomic backbone of an individual molecule. While not a direct technological comparison, this is reminiscent of X-rays that pass through soft tissue to enable clear images of bones.
Gross L, Mohn F, Moll N, Liljeroth P, and Meyer G, (2009): The Chemical Structure of a Molecule Resolved by Atomic Force Microscopy, Science, Vol. 325, Issue 5944, pp. 1110 – 1114 (28 August 2009).
The delicate inner structure of a pentacene molecule imaged with an atomic force microscope. For the first time, scientists achieved a resolution that revealed the chemical structure of a molecule. The hexagonal shapes of the five carbon rings in the pentacene molecule are clearly resolved. Even the positions of the hydrogen atoms around the carbon rings can be deduced from the image. (Pixels correspond to actual data points). Source: IBM Research – Zurich
September 9, 2009
Two-photon-microscopy of neuron. Source: FMI
Fifty years after it was originally discovered, scientists at the Friedrich Miescher Institute for Biomedical Research have elucidated the function of a microscopic network of tubules found in neurons. This structure modulates the strength of connections between two neurons, thereby contributing to our ability to learn and to adapt to new situations.
In the current online issue of the Proceedings of the National Academy of Sciences, Oertner’s group describes how the microscopic network of tubules known as the endoplasmic reticulum (ER) modulates the strength of connections between neurons. Neural connections play an important role in our ability to learn new information and constantly adapt to new conditions. In the brain, synaptic connections between neurons are thus continually formed, strengthened or weakened.
In addition, there are connections that remain stable – for example, when we store an important memory for many years. Connections of both types coexist, and their close proximity was one of the first key findings of Thomas Oertner’s study: the two types occur side by side on the same neuron and are individually controlled.
Observations and comparisons of individual dendritic spines and synapses are anything but routine. The findings just published were only possible thanks to a new method known as two photon microscopy. In this imaging technique, a pulsed infrared laser is used to excite fluorescence in a dye molecule in a cell. It is a gentle method of investigating cells, which yields unique, high-resolution images. Thomas Oertner’s research group is one of only a few worldwide that use this technique to optically stimulate and observe individual synapses, and to measure their activity. As equipment of this type cannot simply be purchased off the shelf, these innovative microscopes are custom-built and refined by Thomas Oertner himself.
Holbro N et al. (2009) Differential distribution of endoplasmic reticulum controls metabotropic signaling and plasticity at hippocampal synapses. PNAS, 18 August 2009, doi: 10.1073/pnas.0905110106 -> Online publication