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October 7, 2009 Electron microscopes are the most powerful type of microscope, capable of distinguishing even individual atoms. However, these microscopes cannot be used to image living cells because the electrons destroy the samples. Now, MIT assistant professor Mehmet Fatih Yanik and his student, William Putnam, propose a new scheme that can overcome this limitation by using a quantum mechanical measurement technique that allows electrons to sense objects remotely. Damage would be avoided because the electrons would never actually hit the imaged objects. Such a non-invasive electron microscope could shed light on fundamental questions about life and matter, allowing researchers to observe molecules inside a living cell without disturbing them. Yanik and Putnam report their new approach in the October issue of Physical Review A — Rapid Communications. If successful, such microscopes would surmount what Nobel laureate Dennis Gabor concluded in 1956 was the fundamental limitation of electron microscopy: “the destruction of the object by the exploring agent.” Electron flow Electron microscopes use a particle beam of electrons, instead of light, to image specimens. Resolution of electron microscope images ranges from 0.2 to 10 nanometers — 10 to 1,000 times greater than a traditional light microscope. Electron microscopes can also magnify samples up to two million times, while light microscopes are limited to 2,000 times. However, biologists have been unable to unleash the high power of electron microscopes on living specimens, because of the destructive power of the electrons. The radiation dose received by a specimen during electron microscope imaging is comparable to the irradiation from a 10-megaton hydrogen bomb exploded about 30 meters away. When exposed to such energetic electron beams, biological specimens experience rapid breakdown, modification of chemical bonds, or other structural damages. Although there exist special chambers to keep biological samples in a watery environment within the high vacuum required for electron microscopes, chemical preservation or freezing, which kill cells, is still required before biological samples can be viewed with existing electron microscopes. In the proposed quantum mechanical setup, electrons would not directly strike the object being imaged. Instead, an electron would flow around one of two rings, arranged one above the other. The rings would be close enough together that the electron could hop easily between them. However, if an object (such as a cell) were placed between the rings, it would prevent the electron from hopping, and the electron would be trapped in one ring. This setup would scan one “pixel” of the specimen at a time, putting them all together to create the full image. Whenever the electron is trapped, the system would know that there is a dark pixel in that spot. Though technical challenges would need to be overcome (such as preventing the imaging electron from interacting with electrons of the metals in the microscope), Yanik believes that eventually such a microscope could achieve a few nanometers of resolution. That level of resolution would allow scientists to view molecules such as enzymes in action inside living cells, and even single nucleic acids — the building blocks of DNA. Yanik, the Robert J. Shillman Career Development Assistant Professor of Electrical Engineering, says he expects the work will launch experimental efforts that could lead to a prototype within the next five years. Charles Lieber, professor of chemistry at Harvard and an expert in nanoscale technology, describes Yanik’s proposal as a “highly original and exciting concept for ‘noninvasive’ high-resolution imaging” using an electron microscope. “From my perspective, it has the potential to be a breakthrough for those working with sensitive samples, such as biological imaging,” Lieber says. “Also, in general terms I find his work intellectually exciting because it is not incremental but takes a quantum (excuse the pun) jump forward through creative thinking.” Source:
October 7, 2009 It’s often the little things that count in industrial manufacturing processes. Particles less than half the diameter of a hair in size can significantly impair quality in production. For example, there should be no particles larger than five micrometers on the packaging film of food and medicines, as these could contaminate the contents. Tiny particles also cause problems in the printing industry, as they reduce the quality of the print if they remain on the surface of the paper. And fine particles on electrical components can cause operational failures. Manufacturers usually resort to a type of vacuum cleaner to remove the dust – it blows air on the contaminated surface, then sucks this in again, together with the undesired particles. However, this method does not effectively remove particles smaller than 20 micrometers, as the electrostatic force causes the majority of them to remain on the surface. Researchers at the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB in Stuttgart have developed a system which also removes these fine dust particles effectively from the product surfaces. Colleagues from NITO A/S in Denmark, Ziegener + Frick GmbH in Ellhofen and the Danish Innovation Institute were involved in the development process. “The system guarantees the quality of the product and improves the working environment of employees, as it reliably collects the harmful particles, preventing them from going into the air and then into the lungs of employees,“ says Sukhanes Laopeamthong, a researcher at the IGB. The researchers charge the dust particles with positive ions. A negatively charged electrode attracts the positively charged dust particles, the resulting force lifting the dust particles easily from the surface of the product. A controlled air current carries them to the dust collector. Prior to the construction of the test equipment, the researchers have already resolved a few questions using special simulation software. What electrical field strength is required to lift the dust particles? What are the required characteristics of the air current transporting the particles? The test equipment removes on average 85 percent of dust particles smaller than 15 micrometers and more than 95 percent of dust particles bigger than 15 micrometers. The researchers are presenting the exhibit at the Parts2Clean trade fair from 20 to 22 October in Stuttgart (hall 1, stand F 610/G 709). The scientists expect the system to be operational in industry in approximately two years. Source:
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